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1. Scuola Universitaria Professionale Dipartimento Istituto della Svizzera Italiana Ambiente Sostenibilit Costruzioni e Applicata Q Design Ambiente gt Costrutivo P PILESIM2 Simulation Tool for Heating Cooling Systems with Energy Piles or multiple Borehole Heat Exchangers User Manual Dr Daniel PAHUD ISAAC DACD SUPSI Switzerland Lugano March 2007 SUPSI DACD ISAAC page 2 Table of content 1 PC and System Requirement ollare 4 2 Installation ProcedUre ssc talia aria iaia ila ia 4 3 Howto Start PIEESIM2 ses ac cette eet ee deh palati noli dille ee 5 4 Limitation of the Technical Support iiiiiiinn 5 5 Introduction to Energy Pile SyStems sseccceeseeneeeeeeeeeeeeeeeneeeeeeeeeeeeesseeeeeeesseneeeeeeseneeneeeseees 6 6 The PILESIM2 Simulatlon To l afle libia dla 8 6 1 What Does PILESIM gt SmulateC clel lee alal cadena a rrn ent 8 6 2 Which Types of Parameters Does PILESIM2 Require 9 6 3 How May PILESIM2 Be Us d ici lla ei peieiagiea 10 6 4 What Does PILESIM2 Calculate pci 10 6 5 How Does PILESIM2 Calculate 2 celle iii 10 6 6 Main Assumptions of the PILESIM2 Simulation TOOl 13 7 Simulation Models Used in PILESIM2 1 rr 14 7 1 The Heat Pump Cooling Machine Model i 14 7 2 The Energy Pile Model Lera lai
2. KW maximum hourly cold demand of the system during the month or the year KW maximum hourly heat power injected through the piles bores during the month or the year degree C minimum inlet fluid temperature in the piles bores during the month or the year degree C maximum inlet fluid temperature in the piles bores during the month or the year kWh total energy demand for heating kWh heating energy covered by the heat pump Auxiliary heating energy QHeatAux QHeat QHeatCov kWh total energy demand for cooling kWh cooling energy covered by the pile bore system geocooling and cooling machine Auxiliary cooling energy QColdAux QCold QColdCov kWh total electric energy used by the pile bore system heat pump cooling ma chine but without circulation pumps Electric energy used by the heat pump QelIPAC QHeatCov COP Electric energy used by the cooling machine QelCoolM QElecTot QelPAC PILESIM2 user manual SUPSI DACD ISAAC page 43 QHeatPil QFreeCool COP COPglobal EffCoolM QHextCold QHextGrnd QHinjGrnd GrndRatio FracHeat Qext mPil FracCold Qinj mPil Tminbuild TmCellar TmSurfFlo kWh heating energy covered by the heat pump coupled to the piles boreholes The rest QHeatCov QHeatPil is covered by the heat pump coupled to the cold energy demand kWh cooling energy that is provided by geocooling with the piles borehole
3. HGi HG1 HG2 and HG3 Darcy velocity of ground water in layer i DAi 1 2 and 3 this parameter sets the Darcy ve locity of the ground water in the ground layer i This parameter determines the forced convec tion in the ground layer i due to a horizontal regional ground water flow A zero value means no forced convection The Darcy velocity in m s can be obtained by the product of the ground layer permeability in m s times the horizontal hydraulic gradient of the regional ground water flow in m m More information on ground permeability can be found for example in Fromentin et al 1997 The Darcy velocity of ground water in layer iis labelled DAi DA1 DA2 and DA3 NB only a direct thermal interaction with the piles bores is computed In other terms if the ground layer i lies below the bottom of the piles bores the effect of a regional ground water flow will not be computed If only the upper part of ground layer i is crossed by the energy piles boreholes the effect will be computed in the upper part only The thermal influence will be then propagated upwards and downwards by pure heat conduction NB the full influence of a ground water flow is only calculated if the following two parameters switches are ON Simulate forced convection on global process this parameter determines if the global effect of the forced convection is taken into account see below YES global effect of forced convection taken into account
4. NO global effect of forced convection not taken into account This parameter is labelled FGLOB PILESIM2 user manual SUPSI DACD ISAAC page 40 Simulate forced convection on local process this parameter determines if the local effect of the forced convection is taken into account see below YES local effect of forced convection taken into account NO local effect of forced convection not taken into account This parameter is labelled FLOCAL The effect of forced convection is treated as the superposition of two effects the global process a heat balance of the heat transfer by forced convection is performed on the boundary of the ground volume that is ascribed to the energy piles boreholes The heat quantity transferred by forced convection to or from the ground volume is treated as a global temperature change of the ground temperature in the volume The global process takes into account long term effects which in particular determine the magnitude of a natural thermal recharge of the ground by a regional ground water flow the local process for the case of pure heat conduction a temperature gradient takes place around the energy piles boreholes when they are used to transfer heat with the ground As a result the heat trans fer is limited by the presence of a local temperature difference between the piles bores and the mean ground temperature If ground water flows across the piles bores the temperature field will
5. Pilesim2 get output xls set the time interval for output results to monthly results Print hourly values for last year this parameter determines if the hourly values of some selected quantities are written or not for the last operational year see chapter 5 for more details Rec ommendation for the use of the Excel file Pilesim2 get output xls answer yes to the question print hourly values for last year PILESIM2 user manual SUPSI DACD ISAAC page 24 8 3 Weather Data and Loading Conditions The weather data and the loading conditions are read in a file The data files are grouped in the PILEDATA directory The input file to be chosen has the extension PIL This is a listing file con taining the key word FILES on the first line followed by the path name of the data file with the ex tension TXT repeated 25 times on the next lines For example data contained in the USERDATA TXT file require the creation of a USERDATA PIL file in the PILEDATA directory The USERDATA PIL file is a text file that contains FILES piledata userdata txt piledata userdata txt piledata userdata txt The data file with the extension TXT contains the hourly values of the outdoor air temperature and the loading conditions determined by the heat and cold demand and their associated tem perature level The first line must correspond to the first hour of the year Each line must contain in the order given below the fol
6. is prescribed at the outer boundary due to geometrical considerations Under steady flux condi tions and for pure heat conduction the heat flux exchanged by an energy pile can be expressed in terms of the ground temperatures at the inner and outer boundaries see Hellstr6m 1991 2 2 Tcen al shy a 7 11 2m An E r 2 ZE With ro radius of the energy pile ro D 2 m ri outer radius of the ground cylinder ascribed to the energy pile m Tw ground temperature at the energy pile T r ro C To ground temperature at the outer radius T r r1 C A effective thermal conductivity of the porous medium W mK cond Neat transfer rate per unit length transferred by the energy pile W m In order to be able to compare the heat fluxes transferred by forced convection and pure conduc tion the ground temperature at the outer boundary at the radius r from a energy pile is assimi lated to the far field temperature T the accuracy of this assertion is still to be checked With this assumption it is now possible to compare the heat fluxes by noting that q q z D 7 12 Combining 7 7 7 8 7 11 and 7 12 gives at 2 2 q__Nu a In di a ni 7 13 cond 2 I z TL r 2 2 I PILESIM2 user manual SUPSI DACD ISAAC page 20 q 1 q cond heat conduction only This ratio is used as a correction factor for the calculations of the heat trans fer rate exchanged by the energy piles but onl
7. m effective pile oorehole diameter for heat capacitive effects cf equation 8 17 PILESIM2 user manual SUPSI DACD ISAAC page 42 AveRbPile EffRbPile FlowRate AveEfGrndL AveGrndCap K W m average pile borehole thermal resistance cf equation 8 14 K W m effective pile borehole thermal resistance for heat capacitive effects cf equation 8 18 kg h total flow rate through the pile bore circuit when heating i e when the heat pump is on See the description of parameter design inlet outlet temperature dif ference in evaporator in section 8 6 W mK effective mean thermal conductivity in the ground volume GrndVolume the effective value includes the effect of forced convection on the local problem see comment for equation 8 14 kJ m K mean volumetric heat capacity in the ground volume GrndVolume see comment for equation 8 17 9 4 The Output File PILESIM OUT This file contains integrated or average quantities during long period of time month or year as well as the maximum or minimum values of some selected quantities The labels of each calcula ted quantity are explained below MaxHeatDem MaxExtPile MaxColdDem MaxiInjPile TinPileMin TinPileMax QHeat QHeatCov QCold QColdCov QElecTot KW maximum hourly heat demand of the system during the month or the year KW maximum hourly heat power extracted from the piles bores during the month or the year
8. the pipe installation in the pile bore is formed by a coaxial pipe Pipe number in a cross section of a pile borehole average number of pipes in a pile bore cross section This number is used to estimate the total volume of fluid that is contained in the energy piles boreholes This parameter is only used to take into account the heat capacitive effects of the heat carrier fluid in the piles bores The total volume of heat carrier fluid contained in the piles is calculated with relation 8 16 Fluid_volume NTUB x TT x Inner_pipe_radius x PileNumber x AvePLength 8 16 NTUB is the pipe number in a pile bore cross section Inner_pipe_radius is defined with the next input parameter pipe number in a cross section of a pile PileNumber and AvePLength are re spectively the total number and the average active length of the energy piles boreholes If Fluid_volume the volume of heat carrier fluid in the piles bores is known then relation 8 16 can be used to calculate the average number of pipes in a pile bore cross section The pipe number in a cross section of a pile bore is labelled NTUB Inner diameter of one pipe this parameter represents the average inner diameter of the pipes in the energy piles bores It is only used to estimate the total volume of fluid that is contained in the energy piles boreholes with relation 8 16 The total volume of fluid is only used to take into account the heat capacitive effects of the heat carrier fluid in t
9. Heat Exchanger Piles User Manual December 1996 Ver sion Internal Report LASEN DGC EPFL Switzerland Pahud D Fromentin A and Hadorn J C 1996c The Superposition Borehole Model for TRNSYS TRNSBM User Manual for the November 1996 Version Internal Report LASEN DGC EPFL Switzerland Seiwald H and Hahne E 1994 Sensitivity Analysis of a Central Solar Heating System with High Temperature Duct Seasonal Storage In Proceedins of Calorstock 94 22 25 August Espoo Finland Kangas M T and Lund P D Eds Vol 2 pp 705 712 Cosmoprint Oy Helsinki 11 SEL TESS AND TRANSSOLAR TRNSYS DISTRIBUTORS Solar Energy Laboratory SEL University of Wisconsin Madison 1500 Engineering Drive Madison WI 53706 USA http sel me wisc edu trnsys Phone 1 608 263 1589 Fax 1 608 262 8464 Thermal Energy System Specialists TESS 2916 Marketplace Drive Suite 104 Madison WI 53719 USA http www tess inc com Phone 1 608 274 2577 Fax 1 608278 1475 Transsolar Energietechnik GmbH Curiestrasse 2 D 70563 Stutgart http www transsolar com Phone 49 0 711 67 97 60 Fax 49 0 711 67 97 611 PILESIM2 user manual
10. Pahud and Hellstr m 1996 has been extensively used for the simulation of thermal processes that involve heat storage and or cold storage in the ground see for example Pahud 1996 or Seiwald 1994 This model DST was chosen in 1981 by the participants of the International Energy Agency Solar R amp D Task VII Central Solar Heating Plant with Seasonal Storage for the simulation of a duct ground heat storage A simpler but faster ver sion was implemented by Hellstr m 1983 in the MINSUN programme Mazzarella 1991 a simu lation tool for the optimisation of a central solar heating plant with a seasonal storage CSHPSS A TRNSYS version based on this faster version called TRNVDST has been implemented by Mazza rella 1993 A more recent version of TRNVDST Hellstr m et al 1996 has combined the easy utilisation of the simple version with the additional features of the more detailed original DST pro gramme Hellstr m 1989 This version also offers the possibility of a detailed computation of the local heat transfer along the flow path within the storage region see Pahud and Hellstr m 1996 The latest version Pahud et al 1996a offers the possibility of having several ground layers that cross the storage region each having their own thermal properties The TRNVDST model assumes a relatively large number of uniformly placed ground heat ex changers or energy piles that are arranged in a ground volume which has the shape of a verti
11. a heat exchanger equ 7 3 7 4 Qc UAc Tc Tcf 7 3 Qe UAe Tef Te 7 4 where Qc heat rate delivered at the condenser kW UAc overall heat transfer coefficient of the condenser heat exchanger kW K Tc temperature level of the working fluid in the condenser C Tcf mean temperature of the heat carrier fluid determined as the average of the inlet and outlet fluid temperature in the condenser C Qe heat rate extracted at the evaporator kW UAe overall heat transfer coefficient of the evaporator heat exchanger kW k Te temperature level of the working fluid in the evaporator C Tef mean temperature of the heat carrier fluid determined as the average of the inlet and outlet fluid temperature in the evaporator C As previously mentioned see section 7 5 the size of the heat pump and the cooling machine are fixed by their respective design electric power The design conditions determine their respective heating and cooling power under fixed temperature levels of the heat carrier fluid in the condenser and evaporator For other conditions the model described above is used to calculate the corre sponding heating and cooling power 7 2 The Energy Pile Model When a pile foundation is used the upper layers of soil are usually water saturated and ground water movement is quite common The piles are reasonably thick from 30 to 150 cm in diameter and have a relatively short length common val
12. al 1996a has been adapted for energy piles Pahud et al 1996b In the framework of the research project relative to the simulation of an energy pile system at ZU rich airport Hubbuch 1998 the experience gained in the simulation of such systems was used to create PILESIM2 The development of simulation tools that were validated with measurements from existing systems Fromentin et al 1997 forms the basis of PILESIM2 The system s thermal performances the utilisation potential of energy piles and a variety of system designs can be as sessed with PILESIM2 PILESIM2 offers easy use and relatively fast calculations This programme may also be used for the simulation of ground coupled systems with a relatively large number of borehole heat exchangers A borehole heat exchanger is a borehole equipped with a pipe system for example with U shape pipes to exchange heat between the heat carrier fluid and the ground In chapter 6 The PILESIM2 Simulation Tool an overview of the programme is presented In chapter 7 Simulation Models Used in PILESIM2 the resolution methods of the main simulation models are described in order to show the main assumptions used by the simulation tool Chapter PILESIM2 user manual SUPSI DACD ISAAC page 7 8 Input Data to PILESIM2 contains explanations on the input parameters and how they are used In chapter 9 Output Results from PILESIM2 the quantities calculated by PIL
13. atea 15 8 Input Data to PILESIM2 ile boia iena delia re bill pit atid 23 g omulalon ParameleiSLcacle tiara ila 23 8 2 Quipur Resul cu Eee ila E RE 23 8 3 Weather Data and Loading Conditions i 24 BA Sy StS TYPE eta e iui Rn alata 25 8 5 Annual Energies and Temperature Levels i 26 8 6 Temperature LIMMAMOMSeris ccscccdedess Geass Gio treni rara nai 28 8 7 Heat Pump and Cooling Machine sccsccas rato lele rara tene 28 8 8 Counterflow Heat ExchangersS Enss nEnnnn EnEn nnsn nennen 31 8 9 Interface Greund BuilldiNgi scsati ea han eeaanatanetti 31 8 10 Energy Piles or Borehole Heat Exchangers cccccccessecccceeeeeeeeesseeeeeeeeeeeeeseeeseeeeneneeeeeeeees 34 8 11 GrOUnoGharacigHistio Sante alain 38 9 Output Results from PILESIM2 c Lelio 41 9 1 TheListing File PILESIM LS T rrene leale ai EE 41 SANEA EEDE DYA A AE EE AEE n o eil iii lic ie 41 PILESIM2 user manual SUPSI DACD ISAAC page 3 9 3 The Parameter File PIFESIM OP A clelia 41 9 4 The Output File PILESIM OUT sis cveseaestdae nsatinnd taeae liti 42 9 5 The RlotEie PIFESIM PER career 45 9 6 Heat Balance of the SYSIeMeiaan heal alicell 45 9 7 Heat Balance of the Energy PIleS 47 10 REFERENCES licei aaa aa 49 11 SEL TESS AND TRANSSOLAR TRNSYS DISTRIBUTORS rssrsrerrriinnnee 50 PILESIM2 user manual SUPSI DACD IS
14. be shifted For a sufficiently large flow the local temperature difference will be decreased and the heat transfer between the piles bores and the ground improved The local process takes into account the improvement of this heat transfer PILESIM2 user manual SUPSI DACD ISAAC page 41 9 Output Results from PILESIM2 The output data from PILESIM2 are written in five different files Two files contain the input infor mation given to PILESIM2 and possible error messages and three files contains the calculated quantities by PILESIM2 Assuming that the file containing the input data is called PILESIM TRD the following files are written PILESIM LST listing file contains run time error message if any DST DAT input data related to TRNVDSTP PILESIM OPA output data calculated parameters used by the programme PILESIM OUT output data integrated quantities PILESIM PLT output data evolution of selected variables After a simulation the file PILESIM LST can be viewed in the Windows menu of the TRNSED pro gramme and the files PILESIM OPA and PILESIM OUT in the Windows Output menu A plot can be made with the file PILESIM PLT and viewed in the Plot menu The file DST DAT can be viewed in the File Open menu The file name DST DAT has to be entered in the File name field of the dialogue box which popped on the screen An error message will then appear as DST DAT is supposed to be a TRNSED file However it is still poss
15. borehole under a given heat transfer rate For example a thermal resistance value of 0 1 K W m will induce a temperature difference of 5 K between the fluid temperature and the ground temperature at the pile bore border when a heat transfer rate of 50 W m takes place in steady flux conditions in the pile bore For more information on pile thermal resistances see Fromentin et al 1997 For borehole thermal resistances the use of the programme EED Earth Energy Designer is recommended Hellstr6m and Sanner 1994 In EED a tool for the calcula tion of borehole thermal resistances with single double triple U pipe or coaxial pipes is inte grated Other pipe configurations in a borehole or a pile can be treated with the programme MPC Bennet et al 1987 Some thermal resistance values are given below Energy pile thermal resistances 0 15 K W m hollow prefabricated pile with a double U pipe pile diameter 30 to 50 cm 0 10 0 11 K W m pre cast or cast in place pile double U pipe fixed on the metallic rein forcement Pile diameter 30 to 150 cm 0 07 0 08 K W m pre cast or cast in place pile triple U pipe fixed on the metallic rein forcement Pile diameter 30 to 150 cm 0 06 K W m pre cast or cast in place pile quadruple U pipe fixed on the metallic reinforcement Pile diameter 30 to 150 cm PILESIM2 user manual SUPSI DACD ISAAC page 36 Borehole thermal resistances A typical value of 0 1 K W m is r
16. con stant temperature during the year Heat Capacitive Effects of the Piles The heat capacity of the piles is composed of the fluid contained in the pipes and the material forming the piles concrete etc The heat capacitive effects of the fluid are simulated by coupling a pipe component in series to TRNVDSTP The fluid volume of the pipe component corresponds to the fluid volume contained in the piles When the piles are at rest the fluid contained in the pipe component is circulated in the piles so that the fluid temperature follows the pile temperature A zero heat transfer coefficient is ascribed to the pipe component as only the heat capacitive effects are to be simulated A plug flow model is used in this standard pipe component of the TRNSYS li brary The heat capacitive effects of the pile material have thermal behaviour which differs from that of the heat carrier fluid Due to the heat transfer by conduction around the pipes only a fraction of the pile material is actually playing a role in the heat capacitive effects It is to be remembered that these effects are not taken into account in TRNVDSTP In this model steady state conditions are assumed in the pile and the heat transfer from the fluid to the ground is calculated with the help of thermal resistances In PILESIM2 it is possible to specify a fraction of the pile material which will take part in the heat capacitive effects This effective heat capacity is simulated by reduc
17. drop between the inlet and outlet fluid that crosses the heat pump condenser This temperature drop is also used for the cooling machine condenser if any Together with the heat power injected by the cooling machine under design conditions it determines the flow rate through the condenser This flow rate is called cooling flow rate it is also the total flow rate in the flow circuit of the energy piles when the cooling machine is operating This parameter is labelled dTcond 8 8 Counterflow Heat Exchangers Design temperature loss in cooling heat exchanger LossTCool design temperature loss in the cooling heat exchanger The cooling heat exchanger if present separates the cooling ma chine condenser flow circuit from the pile bore flow circuit A zero value has to be entered if no heat exchanger is present This parameter is labelled LossTCool Design temperature loss in geocooling heat exchanger LossTGeo design temperature loss in the geocooling heat exchanger The geocooling heat exchanger if present separates the cooling distribution flow circuit from the pile bore flow circuit A zero value has to be entered if no heat exchanger is present This parameter is labelled LossTGeo 8 9 Interface Ground Building Room air temperature in the building TairH the room air temperature is prescribed in the building and assumed to be constant during the year A non heated cellar separates the heated rooms from the ground below the buildin
18. is the volumetric heat capacity of the pile concrete Cconcr is set to 2 592 kJ m K AveGrndCap is the average volumetric heat capacity of the ground in the zone crossed by the average active pile length EffRbPil AveRbPil 1 I en 8 18 27 Aavegr EffPilDiam AveRbPil is the average pile thermal resistance and Aavegr is the average ground thermal con ductivity see equation 8 14 AvePilDiam and EffPilDiam are respectively the average pile di ameter and the effective average pile diameter see equations 8 11 and 8 17 The fraction of pile concrete thermal capacity is labelled FrCapa 8 11 Ground Characteristics Up to 3 different horizontal ground layers can be specified A ground layer is defined by its thick ness the thermal conductivity and volumetric heat capacity of the ground and the Darcy velocity of the water contained in the ground layer Initial ground temperature TGRDIN this parameter specifies the initial temperature of the ground before the construction of the building This temperature should be set to the annual av erage value of the ground near the surface A rough estimation is to use the mean annual air temperature at the surface The initial ground temperature is labelled TGRDIN Mean temperature gradient in the undisturbed ground ATGRND geothermal temperature gradient present at the project location Assumed to be constant it defines the temperature in crease in the ground with depth PILESI
19. of relation 8 10 is the thermal resistance from the outer pipe wall to the average temperature of the ground in the plane of the pipes The thermal conductivity of the ground in the pipe plane is de noted Ag is fixed to 1 3 W mK The outer diameter of the pipe is do_pipe and fixed to 32mm The length of the horizontal pipes on ground is labelled LCOEPF 8 10 Energy Piles or Borehole Heat Exchangers Up to 6 different pile oore types can be specified A pile bore type is defined by its diameter ther mal resistance and average active pile bore length Average values are calculated from these quantities as only one pile bore type is simulated Diameter of pile borehole type i i 1 dp1 2 3 4 5 or 6 This parameter determines the di ameter of pile bore type i The average pile bore diameter is calculated so that the total volume of piles bores is preserved see relation 8 11 It is written in the output parameter file with the extension OPA parameter label AvePilDiam T 2 6 gt dpi 2 Hi Ni i l AvePilDiam 2 7 gt Hi Ni i l 8 11 dpi is the pile bore diameter of type i Hi the pile bore active length and Ni the pile bore number see below PILESIM2 user manual SUPSI DACD ISAAC page 35 The diameter of pile bore type is labelled dpi dp1 dp2 dp3 dp4 dp5 or dp6 Number of piles boreholes for type i i 1 N1 2 3 4 5 or 6 This parameter determines the number of piles bores of
20. see the next parameters Teln the design inlet fluid temperature in evaporator and TcOut the design outlet fluid temperature from condenser The design performance coefficient is expressed by relation 8 1 COPo Qco Pel 8 1 Qco design heating power delivered by the heat pump Pel design electric power of the heat pump This parameter is labelled COPo Constant COP and efficiency during simulation this parameter determines if the performance coefficient COP of the heat pump and the efficiency of the cooling machine are kept constant at their design value or free to vary according to the fluid temperatures in the condenser and evaporator The two possible answer are No the COP and efficiency are free to vary according to the operating conditions Yes the COP and efficiency are kept constant and set to their respective design values COPo and EffCOM If a penalty is chosen by the user the COP and efficiency are decreased by the penalty value see below the parameter COPpen the penalty on the COP PAC and cooling machine PILESIM2 user manual SUPSI DACD ISAAC page 29 This parameter is labelled ICTCOP Design inlet fluid temperature in evaporator design inlet fluid temperature in the evaporator that leads to the design performance coefficient COPo of the heat pump This parameter is labelled Teln Design outlet fluid temperature from condenser design outlet fluid temperature from the con denser that
21. system can be performed which may include the temperature dependent heat pump performance coefficient and cooling machine efficiency 6 4 What Does PILESIM2 Calculate The energies transferred between the different components of the systems are calculated on a monthly or a yearly basis A global heat balance of the system can be made month by month or year by year Temperature levels the heat pump performance coefficient and cooling machine effi ciency etc are also calculated see chapter 9 Output Results from PILESIM2 for a detailed de scription of the calculated quantities In particular the net auxiliary energy for heating and cooling the electricity used by the heat pump and the cooling machine are calculated The influence of long term effects on the results can be assessed for up to 25 years The temporal evolution of some energy rates and temperatures are printed in a file for the last simulated year see chapter 9 They can then be plotted thanks to a functionality of TRNSED 6 5 How Does PILESIM2 Calculate Once the loading conditions are chosen and all the system parameters fixed a simulation can be started The undisturbed ground temperature is chosen for the initial conditions of the ground The thermal simulation is performed with a time step set to one hour At each time step the operational PILESIM2 user manual SUPSI DACD ISAAC page 11 mode of the system is determined depending on the system type chos
22. the piles bores are summed kWh energy extracted from the ground by the horizontal connection pipes The hourly heat transfer values are summed only when heat is extracted from these pipes kWh thermal energy injected in the ground through the piles bores alone with out the horizontal connection pipes A negative value means extracted energy kWh thermal energy injected in the ground through the horizontal connection pipes A negative value means extracted energy kWh total heat losses from the ground volume ascribed to the energy piles bores A negative value is a heat gain kWh variation of the internal energy of the ground in the volume ascribed to the piles bores A positive value means stored energy i e a global increase of the ground temperatures A negative value means a cooling of the ground tempera tures error on the heat balance performed on the ground volume ascribed to the piles bores for calculation control error on the energy extracted from the ground for calculation control error on the energy injected into the ground for calculation control kWh heat losses through the top side of the ground volume ascribed to the en ergy piles bores A negative value is a heat gain kWh heat losses through the vertical sides of the ground volume ascribed to the energy piles bores A negative value is a heat gain kWh heat losses through the bottom side of the ground volume ascrib
23. type i The total number of energy piles or boreholes is the sum of each pile bore type number see 8 12 and is written in the output parameter file with the exten sion OPA parameter label PileNumber 6 PileNumber Y Ni 8 12 i l The number of piles bores for type iis labelled Ni N1 N2 N3 N4 N5 or N6 Average active length of piles boreholes type i i 1 H1 2 3 4 5 or 6 This parameter de termines the average active pile length of pile type i The active length of a pile is defined by the pile length for which a radial heat transfer with the ground may occur In other terms it is the length of the pile that is equipped with pipes The pile active length is smaller than the total pile length An average active pile length is calculated for ALL the heat exchanger piles see formula 8 13 It defines the vertical extension of the ground volume that contains the simulated piles It is written in the output parameter file with the extension OPA parameter label AvePLength 6 gt Ni Hi AvePLength _ 8 13 6 gt Ni i l The average active length of piles type is labelled Hi H1 H2 H3 H4 H5 or H6 Thermal resistance Rb of pile borehole type i 1 Rb1 2 3 4 5 or 6 This parameter de termines the thermal resistance of pile bore type i The thermal resistance of a pile borehole de termines the temperature difference between the fluid and the ground in the immediate vicinity of the pile
24. 2 has been installed Search the executable file TRNSED EXE Select the file TRNSED EXE with the mouse and right click on it A context sensi tive menu appears Choose Send to and select Desktop to send the shortcut on the desktop You can then rename the shortcut to PILESIM2 When PILESIM2 is started i e when the programme TRNSED EXE from the PILESIM2 directory is executed a dialogue box pops onto the screen to ask you which TRNSED file to open the file has the extension TRD Choose the file PILESIM TRD click on the name and then open it click on the Open button To check that PILESIM2 is working properly run the TRNSED file PILESIM TRD with the default parameter values To start the calculation choose TRNSYS Calculate in the menu The calcu lated results are stored in several files PILESIM OUT PILESIM OPA PILESIM PLT and DST DAT They should be the same as the output results stored in the directory PILERESU An original copy of PILESIM TRD is also stored in this directory 4 Limitation of the Technical Support A hotline is provided through e mail only use the e mail address daniel pahud supsi ch The hotline covers a reduced help service problems related to the PILESIM2 installation bad con figuration or incompatibility of the personal computer system are not covered by the hotline Prob lems related to the use of the programme TRNSED are also not covered For each purchased
25. AAC page 4 Il PC and System Requirement PILESIM2 was tested on a laptop Pentium 1 7 GHz and 512 MBytes of RAM with Windows XP Professional PILESIM2 requires about 10 to 20 MBytes of hard disk space PILESIM2 is based on PILESIM the former version of June 1999 which had successfully been tested on a machine with Windows 98 and Windows NT PILESIM2 is a 32 bits programme and is not working with Windows 3 x PILESIM2 is a TRANSED application of the TRNSYS package simulation tool made with the TRNSYS version 15 3 2 Installation Procedure All the necessary files are compressed in a single zipped file To install PILESIM2 you may start the programme Windows Explorer and select the drive and directory where the compressed file is e g select the drive C MySavedFiles provided you have saved the PILESIM2 zipped file in this directory You may also click on the My Computer icon in order to find the drive and directory where the file is stored To install PILESIM2 you have to create a directory on your local hard drive It is recommended to created a new directory for example CAPILESIM2 and copy in this di rectory the PILESIM2 ZIP file Unzip the file and be sure that the subdirectory structure is main tained If you already have TRNSYS on your computer it is not advised to install PILESIM2 in the same directory Several of your original TRNSYS files would be overwritten and lost To remove PILESIM2 from your computer simply d
26. ESIM2 are described Explanations to make a Sankey diagrams are also given The Swiss Federal Office of Energy OFEN is greatly acknowledged for his financial support The TRNSYS distributors Solar Energy Laboratory SEL Thermal Energy System Specialist TESS and TRANSSOLAR are also acknowledged for their permission to use the TRNSED feature of TRNSYS for the build up of PILESIM2 Neither the authors nor any employees of the above mentioned institutions makes any warranty expressed or implied or assumes any liability or responsibility for the accuracy completeness or usefulness of any information apparatus product or process disclosed or represents that its use would not infringe privately owned rights The data files and programmes sent per e mail may not be distributed to other users PILESIM2 user manual SUPSI DACD ISAAC page 8 6 The PILESIM2 Simulation Tool PILESIM2 is version 2 of the PILESIM programme PILESIM has been developed with TRNSYS Klein et al 1998 and then adapted to the TRNSED format Thanks to the TRNSED application a stand alone programme can be created In addition the TRNSYS simulation tool is embedded in a user friendly interface which provides online help and allows a non specialist TRNSYS user to use the programme Relatively to PILESIM PILESIM2 allows the user to calculate a geocooling potential with a better precision taking into account the forward or return fluid temperature leve
27. Hellstr m G 1989 Duct Ground Heat Storage Model Manual for Computer Code Department of Mathematical Physics University of Lund Sweden Hellstr m G 1991 Ground Heat Storage Thermal Analyses of Duct Storage Systems Theory Thesis Department of Mathematical Physics University of Lund Sweden Hellstr m G and Sanner B 1994 Earth Energy Designer Software for Dimensioning of Deep Boreholes for Heat Extraction Dept of Mathematical Physics Lund University P O Box 118 S 22100 Lund Sweden Inst f r Angew Geowissenschaften der Justus Liebig Universit t Diezstrasse 15 D 35390 Giessen Germany Hellstr m G Mazzarella L and Pahud D 1996 Duct Ground Heat Storage Model Lund DST TRNSYS 13 1 Version January 1996 Department of Mathematical Physics University of Lund Sweden Hubbuch M 1998 Energiepf hle Beispiel Dock Midfield Energieforschung im Hochbau 10 Schweizerisches Status Seminar 1998 EMPA KWH 10 septembre ETH Z rich pp 275 282 Klein S A et al 1998 TRNSYS A Transient System Simulation Program Version 14 2 Solar Energy Laboratory University of Wisconsin Madison USA Koschenz M and Dorer V 1996 Design of Air Systems with Concrete Slab Cooling Room vent 96 5 International Conference on Air Distribution in Rooms Yokohama Japan Mazzarella L 1991 MINSUN 6 0 NEWMIN 2 0 A Revised IEA Computer Program for Perform ance Simulation of Energy Systems with Seasonal Thermal E
28. M2 user manual SUPSI DACD ISAAC page 39 The geothermal temperature gradient is labelled dTGRND Thermal conductivity of ground layer i LGi i 1 2 and 3 this parameter sets the thermal conductivity of ground layer For water saturated soils that requires the use of foundation piles a typical value of 2 W mK can be assumed More information on ground thermal conductivity can be found for example in Fromentin et al 1997 or Hellstr m and Sanner 1994 The thermal conductivity of ground layer iis labelled LGi LG1 LG2 and LG3 Volumetric thermal capacity of layer i CGi i 1 2 and 3 this parameter sets the volumetric thermal capacity of ground layer For water saturated soils that requires the use of foundation piles typical values lie between 2 and 3 MJ m K More information on ground volumetric ther mal capacity can be found for example in Fromentin et al 1997 or Hellstr m and Sanner 1994 The volumetric heat capacity of ground layer iis labelled CGI CG1 CG2 and CG3 Thickness of ground layer i i 1 2 and 3 this parameter sets the thickness of ground layer i The first ground layer must be larger than 0 3m which is the layer 0 in which lie the horizontal pipes that connect the heat exchanger pile to the heat pump The thickness ground layer 3 which is the lowest ground layer is supposed to extend downward as far as necessary by the thermal calculations The thickness of ground layer iis labelled
29. TRNVDST are given in chapter 7 The main assumptions that can be mentioned in this section are the number of energy piles is relatively large the spatial arrangement of the energy piles is more or less regular the ground area occupied by the energy piles has a shape which is more or less the shape of a circle or a square the energy piles have about the same active length The active length of an energy pile is the length along which a radial heat transfer takes place i e heat is transferred from the pile to the ground These assumptions imply that most of the energy piles are surrounded by other energy piles In other terms PILESIM2 is not suited to the simulation of a single energy pile or several energy piles arranged in a line When the shape of the ground area occupied by the energy piles is far from be ing a circle or a square or the pile arrangement is highly irregular the average pile spacing which is an input parameter to PILESIM2 can be calibrated with another programme For example TRNSBM Eskilson 1986 Eskilson 1987 Pahud et al 1996c can be used PILESIM2 user manual SUPSI DACD ISAAC page 14 TA Simulation Models Used in PILESIM2 In this chapter the heat pump model and the energy pile model are briefly presented 7 1 The Heat Pump Cooling Machine Model The heat pump cooling machine model is based on the model used in MINSUN 1985 A heat balance of the machine gives heat loss
30. achine Fig 9 1 Energy fluxes diagram of the system QColdCo The quantities used for the Sankey diagram of Fig 9 1 are read or deducted from the PILE SIM OUT file They are PILESIM2 user manual SUPSI DACD ISAAC page 46 QHeat QHeatAux QHeatCov COP QelPAC QHextGrnd QHinjGrnd EffCoolM QHextCold QFreeCool QCoolMach QelCoolM QColdAux QColdCov QCold kWh total energy demand for heating in PILESIM OUT kWh heating energy covered by auxiliary energy QHeatAux QHeat QHeatCov kWh heating energy covered by the heat pump in PILESIM OUT average performance coefficient of the heat pump in PILESIM OUT kWh electric energy used by the heat pump QelPAC QHeatCov COP kWh energy extracted from the ground by the heat pump in PILESIM OUT kWh energy injected into the ground by geocooling and the cooling machine in PILESIM OUT average efficiency of the cooling machine in PILESIM OUT kWh energy extracted from the cold demand by the heat pump for heating pur poses in PILESIM OUT kWh cooling energy that is provided by geocooling with the piles bores in PILE SIM OUT kWh energy extracted from the cooling demand by the cooling machine QCoolMach QColdCov QfreeCool QHextCold kWh electric energy used by the cooling machine QelCoolM QElecTot QHeatCov COP kWh cooling energy covered by auxiliary energy QC
31. al pipes on ground LCOEPF the length of the horizontal pipes on ground is the effective pipe length that connects the heat exchanger piles to the pipe collectors This parameter is used for the determination of the heat transfer that occurs between the fluid in these pipes and the ground in the plane of the pipes The pipes are supposed to lie below the concrete plate and the insulation layer if any The calculation assumes a uniform density of horizontal pipes in the interface ground cellar In reality this is not the case and a rough ap proximation is to set this parameter to half of the total horizontal pipe length This heat transfer coefficient is calculated with an approximation developed by Koschenz and Dorer 1996 See formulas 8 9 and 8 10 ECARCO m Cellar_floor_area m LCOEPF m 8 9 ECARCO is the average distance between the horizontal pipes on ground and the Cel lar_floor_area is defined by formula 8 5 LCOEPF is the label for the length of the horizontal pipes on ground The heat transfer coefficient from the fluid in the pipes to the ground in the plane of the pipes UPipeCo is given by two thermal resistances in series see relation 8 10 1 UPipeCo W m K 8 10 ECARCO Rfluid_pipe l ln PERSO 2a Ag m go_pipe Rfluid_pipe K W m is the thermal resistance between the fluid and the outer side of the pipe wall This resistance is arbitrarily fixed to 0 272 K W m The second term in the parenthesis
32. at their design value constant during a simulation This parameter is labelled TcutCo Design inlet outlet temperature difference in evaporator PAC and cooling machine design temperature drop between the inlet and outlet fluid that crosses the heat pump evaporator To gether with the heat power extracted under design conditions this temperature drop determines PILESIM2 user manual SUPSI DACD ISAAC page 31 the flow rate through the evaporator This flow rate is also the total flow rate in the flow circuit of the energy piles The temperature drop is also used for the cooling machine evaporator if any The flow rate used for the simulation is written in the output parameter file with the extension OPA parameter label FlowRate This flow rate is used when the PAC is operating It is called the heating flow rate If a cooling machine is included in the system a cooling flow rate is determined on the basis of dTcond the design inlet outlet temperature difference in the condenser see the 2nd following parameter When the operating mode is geocooling the flow rate through the pile flow circuit is variable and depends on the forward return temperature difference in the cooling distribution dTGeocool and the instant cooling power demand The design inlet outlet temperature difference in evaporator is labelled dTevap Design inlet outlet temperature difference in condenser PAC and cooling machine design temperature
33. ature of the heat carrier fluid in the piles boreholes TfMin mini mum tolerated fluid temperature in the bores piles hydraulic circuit This value may limit the heat rate that is extracted from the ground as the simulated inlet fluid temperature in the piles will never be lower than this value This constraint limits the size of the heat pump It is recommended not to set this value below 0 C when energy piles are used This parameter is labelled TfMin Maximum allowed temperature of the heat carrier fluid in the piles boreholes TfMax maxi mum tolerated fluid temperature in the bores piles hydraulic circuit This value may limit the heat rate that is injected into the ground as the simulated fluid temperature in the piles will never be greater than this value This constraint limits the size of the cooling machine This parameter is labelled TfMax 8 7 Heat Pump and Cooling Machine Design electric power of the heat pump Pel the design or nominal electric power is the elec tric power consumed by the heat pump PAC at full load It is assumed that the temperature levels in the condenser and evaporator do not influence the design electric power This parameter is labelled Pel Design performance coefficient COPo the design performance coefficient is the performance coefficient of the heat pump when the inlet fluid temperature in the evaporator and the outlet fluid temperature from the condenser are at their design values
34. boreholes BPILE this parameter specifies the effective average spacing of ALL the piles boreholes in the TWO spatial directions of the ground area that contains the piles boreholes This parameter determines the ground volume GrndVolume that is ascribed to the piles boreholes with relation 8 15 GrndVolume BPILE x PileNumber x AvePLength 8 15 See equations 8 12 and 8 13 for the total number of energy piles boreholes PileNumber and the average active pile bore length AvePLength The average spacing between the piles bores is called BPILE The ground volume used for the simulation is written in the output parameter file with the extension OPA parameter label GrndVolume The best pile bore arrangement for increased thermal performances is obtained with a regular spacing between the piles boreholes If the shape of the area occupied by the piles bores is close to a square then the average spacing is easy to calculate A method to establish this parameter is to draw a line around the ground area that is occupied by the piles boreholes A half average spacing is maintained between the line and the PILESIM2 user manual SUPSI DACD ISAAC page 37 piles bores in the periphery The area drawn by this line is then divided by the total number of energy piles boreholes and the average spacing is obtained by taking the square root of this number If the energy piles boreholes are not uniformly placed within this area it w
35. cal cylinder There is convective heat transfer in the pipes and conductive heat transfer in the ground The thermal process in the ground is treated as a superposition of a global problem and a local problem The global problem handles the large scale heat flows in the store and the surrounding ground whereas the local problem takes into account the heat transfer between the heat carrier fluid and the store The local problem uses local solutions around the boreholes or energy piles and a steady flux part by which the number of local solutions and thereby computation time can be reduced without significant loss of accuracy The global and the local problems are solved with the use of the explicit finite difference method FDM whereas the steady flux part is given by an analytical solution The total temperature at one point is obtained by a superposition of these three parts The short time effects of the injection extraction through the pipes are simulated with the local so lutions which depend only on a radial coordinate and cover a cylindrical volume exclusively as cribed to each borehole or energy pile As the model assumes a relatively large number of bore holes most of them are surrounded by other boreholes In consequence a zero heat flux at the outer boundary is prescribed due to the symmetrical positions of the neighbouring boreholes A transient period of time is calculated which would correspond if no heat flux was transferred b
36. d constant The steady state heat transfer rate between the surface of the cylinder at temperature T and the saturated porous medium at far field temperature T can be expressed in terms of an average Nusselt number Nield and Bejan 1992 a DE 7 7 T T A W co m With Nup average value of the Nusselt number over the cylinder surface based on the a diameter of the cylinder D q average heat transfer rate per unit area on the cylinder surface W m Tw surface temperature of the cylinder C Tes temperature of the undisturbed porous medium C D diameter of the cylinder m Aa effective thermal conductivity of the porous medium W mK PILESIM2 user manual SUPSI DACD ISAAC page 19 When the boundary layer is distinct thin i e when the boundary layer thickness is smaller than the cylinder radius the average value of the Nusselt number can be calculated Nield and Bejan 1992 by taking the Darcy flow model as valid Nup 1 015 Pe 7 8 D Pe 7 9 With Pep P clet number based on the cylinder diameter D a thermal diffusivity of the porous medium m s defined by the ratio A Cwi The requirement for the validity of 7 8 can be written as Pel gt gt 1 or Nup gt gt 1 7 10 As previously mentioned the local solutions depend only on a radial coordinate and cover a cylin drical ground volume of radius r which is exclusively ascribed to each energy pile A zero heat flux
37. dimensional temperature field in the ground is reconstructed by a superposition technique TRNSBM does not have all the capabili ties of TRNVDSTP and is too time consuming to run with many energy piles Nevertheless it can be used to calibrate TRNVDSTP for a particular spatial arrangement of the piles Providing that the parameters of both models are equivalent and in particular that the number and total length of energy piles are the same in both programmes the volume or the average spacing of the en ergy piles is varied in TRNVDSTP so that the calculated thermal response is as close as possible to that obtained with TRNSBM PILESIM2 user manual SUPSI DACD ISAAC page 23 8 Input Data to PILESIM2 The input data to PILESIM2 concern all the information that can be varied by the user In particu lar the input data define the type of system to be simulated the size and characteristics of the dif ferent parts of the system and the driving conditions which will condition the operation of the sys tem In this chapter each parameter required to PILESIM2 is described and explained Once the data are defined as desired it is recommended to save the data before a simulation is started The input data are saved in the file PILESIM TRD It is done in the File Save menu of the TRNSED programme A simulation is started in the menu TRNSYS Calculate A series of simula tions can also be defined and then simulated The user
38. e system is not used Heating Yes demand Resting mode Heating mode Cooling demand Geocooling Yes possible Geocooling mode Greater part of cooling demand covered with cooling machine Yes Cooling mode gt lt Fig 6 3 Schematic presentation of the procedure followed to determine the operational mode The heat pump performance coefficient and the cooling machine efficiency may depend on the temperature levels of the heat carrier fluid in the condenser and evaporator The performance co efficient determines the heating power with the help of the design electric power of the heat pump set to a constant value The design electric power determines the size of the heat pump and is fi xed by the user If the heating requirement is smaller the heating power is decreased to match the heating requirement As a result the electric power consumed by the heat pump and the heat rate extracted at the evaporator are recalculated with the help of the performance coefficient The heat ing power of the heat pump may also be reduced by the temperature constraint associated with the PILESIM2 user manual SUPSI DACD ISAAC page 13 heat carrier fluid which circulates in the piles This constraint requires that the fluid temperature in the piles never drops below a user given value normally fixed at 0 C If this
39. ease with increasing air temperature down to 20 C for an air temperature of 20 C COOLING Cooling is calculated for space cooling requirements only Cooling is needed only when the outside air temperature is greater than 20 C The cooling requirement is proportional to the difference be tween the outside air temperature and a reference temperature The reference temperature is fixed at 16 C The forward fluid temperature for cooling is constant and set to 16 C 8 4 System Type Four types of system can be selected Heating combined with a possible forced recharge of the ground the heat demand is partly or completely covered by one or more heat pumps coupled to the energy piles boreholes No cooling demand is satisfied by the pile bore system A thermal recharge of the ground can be realised every year during 1000 consecutive hours The recharge period starts July 1 The an nual energy of the thermal recharge is an input parameter see below the parameter description for Annual energy demand for cooling Heating combined with geocooling the heat demand is partly or completely covered by one or more heat pumps coupled to the energy piles boreholes If there is a cooling demand only geocooling on the piles bores is performed No cooling machine connected to the piles bores is used PILESIM2 user manual SUPSI DACD ISAAC page 26 Heating combined with geocooling or a cooling machine the heat demand is partly or com ple
40. ecting pipes and the average ground temperature in the plane of the pipes W m k Lpipe total length of the pipes m Sintertace Surface of the plane containing the horizontal pipes m pipe diameter m Roipe thermal resistance between the fluid and the outer border of the pipe K W m x thermal conductivity of the ground containing the pipes W mK Equation 7 14 is accurate if the thickness d of the ground layer which contains the pipes see DMESH below is greater than the average pipe spacing Sintertace Lpipe A uniform placement of the pipes in the surface Sintertace is assumed In practice this is not the case and the effective heat transfer coefficient Hpipe represents a maximum value The total pipe length should be decreased but the reduction depends on the pipe arrangement and cannot easily be estimated By default half the total pipe length is assumed to be reasonable The TRNVDSTP module has two additional inputs to collect the heat transfer rates exchanged by the connecting pipes Two additional outputs return the average ground temperature on top of the store and the total heat rate exchanged by the connecting pipes PILESIM2 user manual SUPSI DACD ISAAC page 21 The average ground temperature on top of the store is determined with the mesh temperatures of the uppermost mesh layer of the store The vertical extension of this mesh layer DMESH is de termined by the extension of the small
41. ed to the energy piles bores A negative value is a heat gain PILESIM2 user manual SUPSI DACD ISAAC page 45 9 5 The Plot File PILESIM PLT This file contains the time evolution of some temperatures and heat rates for the last year of the simulation period Hourly values of these quantities are written in this file only if the input parame ter Print hourly values for last year is set to Yes Their labels are explained below TempinPile degree C inlet fluid temperature in the pile bore flow circuit TempOutPil degree C outlet fluid temperature from the pile bore flow circuit HeatDemand kW heat demand of the building HeatSatisf KW heat demand covered by the heat pump ColdDemand kW cold demand of the building ColdSatisf kW cold demand covered by the pile bore system geocooling or cooling ma chine 9 6 Heat Balance of the System The quantities contained in the file PILESIM OUT allows the user to establish an overall heat ba lance of the system A diagram of the energy fluxes is shown in Fig 9 1 Auxiliary heating GLOBAL SYSTEM HEAT BALANCE energy Total heat QHeatAux demand Heating with PAC QHeat QHeatCov Electricity PAC QelPAC Energy piles Auxiliary cooling energy boreholes Cooling by heating Total cold GHinjGrnd QHextCold QColdAux _ demand Geocooling Cooling with pilesS QCold QFreeCool Coolin machine QCoolMach EffCoolM Electricity cooling m
42. elete the directory in which PILESIM2 was installed Two additional utilities are distributed in two separate zipped files These utilities are 2 Excel files and require the EXCEL programme to be used They are MakeLoadFile zip Zipped excel file MakeLoadFile zip This file is devised to generate hourly profiles for the loading conditions on the basis of the hourly evolutions of the outdoor air temperature and the global solar radiation for a typical year Unzip this file in the PILEDATA subdirectory Pilesim2 get output zip Zipped excel file Pilesim2 get output xls This file is devised to visualise the results of a simula tion contained in the various output files produced with PILESIM2 Unzip this file in the PILESIM2 directory PILESIM2 user manual SUPSI DACD ISAAC page 5 3 How to Start PILESIM2 With Windows there are different ways of starting PILESIM2 PILESIM2 is started by running the executable file TRNSED EXE It is important to run the TRNSED EXE file from the directory where PILESIM2 is installed If TRNSYS or another TRANSED application is installed on the computer another TRNSED EXE files are present in their respective directory and these executable files must not be run instead of the one in the PILESIM2 directory The best way to avoid this is to cre ate on the desktop a shortcut to the correct TRNSED EXE file To do this search with Windows Explorer the directory in which PILESIM
43. en the current loading con ditions and the system component s thermal performances heat pump cooling machine energy piles etc Three basic operational modes are possible cf Fig 6 2 Operational mode HEATING Heat Cold distribution Heat pump distribution Electricity 3 Operational mode GEOCOOLING Heat Cold distribution distribution Electricity Energy piles Energy piles Operational mode COOLING Heat Cold distribution oolng machine distribution Energy piles A Fig 6 2 The three drawings illustrate the three basic operational modes of the pile system The arrows indicate the direction of the positive energy fluxes Heating and cooling can be simultaneously satisfied with each of these three operational modes If there is no cooling requirement when heating is needed or vice versa the three basic operational modes are reduced to three simple situations heating with the heat pump connected to the piles geocooling with the piles connected to the cold distribution cooling with the cooling machine connected to the piles PILESIM2 user manual SUPSI DACD ISAAC page 12 The mode that satisfies the greatest part of the heating and cooling demands is chosen A sche matic procedure to determine the operational mode is shown in Fig 6 3 Note that the resting mode corresponds to the periods when th
44. energy extracted from the ground per energy pile bore meter fraction of the total cold demand covered by the pile bores system pile bores and cooling machine FracCold QColdCov QCold kWh m energy injected into the ground per energy pile bore meter degree C air temperature in the heated or cooled rooms degree C air temperature in the cellar degree C surface temperature of the cellar floor PILESIM2 user manual SUPSI DACD ISAAC page 44 TmGrndTop TmGround QBuiToCel QCelToOut QCelToGrd QTotExtGd QHoPipExt QDSTtoGrd QPIPtoGrd QlossOut QEDSTin ERRDS ErrorExt Errorlnj QlossTout QlossSout QlossBout degree C mean temperature of the 30 cm thick ground layer that contains the horizontal connection pipes degree C mean temperature of the ground volume that is ascribed to the energy piles bores kWh thermal energy transferred from the heated or cooled rooms to the cellar A negative value means thermal energy transferred from the cellar to the ground kWh thermal energy transferred from the cellar to outside A negative value means thermal energy transferred from outside to the cellar kWh thermal energy transferred from the cellar to the ground A negative value means thermal energy transferred from the ground to the cellar kWh total energy extracted from the ground by the pile bore system Only the hourly values of the extracted energy from
45. epresentative for a double U pipe in a borehole of diameter 10 to 15 cm An average pile bore thermal resistance is calculated for ALL the energy piles boreholes with the help of formula 8 14 The average pile bore thermal resistance is calculated relatively to the average pile diameter AvePilDiam It is written in the output parameter file with the extension OPA parameter label AveRbPile 6 6 Hi N Hi Ni 2 a veRbPile a 8 14 Rbi n 27 Aavegr i l AvePilDiam dpi Xavegr is the average ground thermal conductivity This value takes into account the thermal conductivity of each ground layer which is crossed by the average active pile bore length Ave PLength It also takes into account the influence of a regional ground water flow by using the correction factor applied on the thermal conductivity see section 7 2 The thermal resistance of pile bore type iis labelled Rbi Rb1 Rb2 Rb3 Rb4 Rb5 or Rb6 Internal thermal resistance Ra of pile borehole type i i 1 Ra1 2 3 4 5 or 6 This parame ter determines the internal thermal resistance of the piles boreholes The internal thermal resis tance of a pile bore determines the internal heat transfers within the pile bore A typical value is comprised between 0 1 0 4 K W m for a double U pipe in a borehole heat exchanger The internal resistance of pile bore type iis labelled Ra Rai Ra2 Ra3 Ra4 Rad or Ra6 Average spacing between the piles
46. er of the cooling machine PelCOM the design electric power is the elec tric power consumed by the cooling machine at full load It is assumed that the temperature lev els in the condenser and evaporator do not influence the design electric power This parameter is ignored if no cooling machine is used in the system If a cooling machine is used there are two possibilities the heat pump is used in reverse mode as a cooling machine In this case the design electric power of the cooling machine should be set as equal to that of the heat pump It can automati cally be done by setting this parameter to a negative value PILESIM2 user manual SUPSI DACD ISAAC page 30 a separate cooling machine is used This parameter is simply the design electric power con sumed by the cooling machine NB in a real system a heat exchanger is likely to be present between the cooling machine condenser and the pile bore flow circuit It induces an additional temperature loss between the two flow circuits and penalises the efficiency of the cooling mode This temperature loss is taken into account with the parameter LossTCool in the following Counterflow Heat Exchangers sec tion This parameter is labelled PelCOM Design efficiency of cooling machine EffCOM this parameter defines the design efficiency of the cooling machine A negative value means that the design parameters used for the heat pump are also used for the cooling machi
47. es are supposed to be small Pel Qe Qc 7 1 where Pel electric power used by the machine kW Qe heat rate extracted at the evaporator kW Qc heat rate delivered at the condenser kW The performance coefficient COP defined by the ratio Qc Pel is calculated with the help of the Carnot efficiency equ 7 2 Tc COP _ 7 2 I tech TE z Te where Tc and Te represent the temperature levels of the working fluid in respectively the con denser and the evaporator of the machine The technical efficiency nNiech takes into account irre versible processes and losses in the Carnot cycle The technical efficiency is determined as for the MINSUN programme MINSUN 1985 by the diagram shown in Fig 7 1 Technical efficiency MN tech dTCOP dTstag se Temperature difference Tc Te ll 6 Fig 7 1 Technical efficiency shape of the heat pump cooling machine The minimum COP value is limited by 1 A maximum value is also given so that the calculated COP may not have an unrealistic large value PILESIM2 user manual SUPSI DACD ISAAC page 15 In the evaporator the mean temperature of the heat carrier fluid used to extract heat from the cold source piles boreholes or else is higher than the working fluid temperature In the condenser it is the other way round and this leads to a temperature loss in both cases These temperature los ses are calculated by using a simple relation that models
48. ess of the insulation layer that lies between the cel lar and the ground A thermal conductivity of 0 05 W mK is assumed for the insulation material The horizontal pipes that connect the heat exchanger piles to the pipe collectors are supposed to lie below the insulation layer A different thermal conductivity for the insulation material for example New_lambda_insulation W mK can be taken into account by using formula 8 7 Hinsul Hinsul_actual x 0 05 W mK New_lambda_insulation W mk 8 7 Where Hinsul_ actual is the actual thickness of the insulation layer The insulation thickness between ground and cellar is labelled Hinsul Concrete thickness between ground and cellar Hmagco the concrete thickness between the ground and the cellar determines the thickness of the concrete plate that lies between the cellar and the ground A thermal conductivity of 1 3 W mK is assumed for this concrete The horizontal pipes that connect the heat exchanger piles to the pipe collectors are supposed to lie below the concrete plate A different thermal conductivity for the concrete for example New_lambda_concrete W mK can be taken into account by using formula 8 8 Hmagco Hmagco_actual x 1 3 W mK New_lambda_concrete W mk 8 8 Where Hmagco_ actual is the actual thickness of the concrete plate The concrete thickness between ground and cellar is labelled Hmagco PILESIM2 user manual SUPSI DACD ISAAC page 34 Length of the horizont
49. est mesh DMIN used for the computation of the global process It may be influenced by the vertical extension of the first ground layer in the store DLAY 1 if the user specifies a value smaller than twice the smallest mesh If DLAY1 gt 2 DMIN then DMESH DMIN 7 15a If DMIN lt DLAY1 lt 2 DMIN then DMESH DLAY1 2 7 15b If DLAY1 lt DMIN then DMESH DLAY1 7 15c The value of DMESH is written in DST DAT an output file that gives a summary of the input pa rameters and automatic settings performed by the TRNVDSTP In PILESIM2 DLAY 1 is set to 0 3 m and is in most cases smaller than DMIN In other terms the vertical extension of the uppermost mesh layer of the store where the horizontal connecting pipes lie is normally equal to 0 3 m DMESH Thermal Influence of the Building As previously mentioned a time varying temperature is given to TRNVDSTP on the ground sur face in two different zones The first zone is located on the top side of the ground volume which contains the energy piles The second zone is everywhere else and the corresponding input tem perature is the outdoor air temperature The temperature of the first zone corresponds to the build ing ground floor or ground space which is assumed to be un heated This temperature is calcu lated on the basis of a heat balance which takes into account the heat gains or heat losses from the ground the outdoor air and the heated cooled part of the building supposed to have a
50. f 2 makes the hourly values of the heat demand two times larger The scaling factor is used for both normalised and no normalised data This parameter is labelled ScaleH Annual energy demand for cooling annual cold demand of the system given with a positive va lue This value is only used with normalised input loading conditions or when a forced thermal recharge of the ground is realised It is otherwise ignored The cooling demand or the forced re charge of the ground are scaled with the next parameter Scaling factor for cooling demand This parameter is labelled QcYEAR NB Normalised loading conditions are written with negative values in the input data file The cold demand values are written in the fourth column of the input data file Data files whose names start with NORM were prepared with normalised loading conditions Scaling factor for cooling demand ScaleC the cooling demand is scaled with this factor A de fault value of 1 must be set if no scaling is desired A scaling factor of 2 makes the hourly values of the cold demand two times larger This scaling factor is used for both normalised and non normalised data It is also used when a forced thermal recharge of the ground is realised This parameter is labelled ScaleC PILESIM2 user manual SUPSI DACD ISAAC page 27 Outdoor air temperature for heating design this temperature parameter is the minimum outdoor air temperature for which the heating system i
51. for the calculation of the global temperature field in the ground calculated to about 1 day for a typical case s Econ heat quantity transferred by forced convection in the storage layer during the time step At J Econv max Maximum possible heat quantity transferred by forced convection in the storage layer during the time step At J The heat quantity transferred Econ is then equally distributed as a temperature correction on each cell of the ground layer within the storage volume If Econ is greater than Econ max then the tem peratures are set to T the undisturbed ground water temperature The Darcy velocity in each ground layer is an additional parameter required for the model The Darcy velocity is set to zero if there is no regional ground water flow A ground water flow specified outside the storage volume is not taken into account in the calculations The second approximation concerns the local problem or the short term influence of a regional ground water flow influence on the heat transfer around the energy piles The influence of a re gional ground water flow on the heat transferred by the energy piles can be estimated with the help of the Nusselt number associated with a cylinder imbedded in a porous medium and submitted to a regional ground water flow The cylinder is perpendicular to the flow This latter is assumed to be uniform when far enough from the cylinder The surface temperature of the cylinder is prescribed an
52. forward fluid temperature in the cooling distribution This temperature difference is supposed to be constant As a consequence for the geocooling mode it results a smaller fluid flow rate in the pile bore flow circuit when the cooling demand is smaller This parameter is labelled dTGeocool Relevant temperature level for geocooling operation the relevant temperature level for geo cooling operation can be determined by the forward fluid temperature to the cooling distribution or the return one These two possible choice are selected with Forward fluid temperature to cooling distribution geocooling energy is produced to the re quired temperature level and this even if the cooling demand is not completely met In that case an auxiliary cooling production has to be used The geocooling and auxiliary cooling pro ductions are performed in parallel or at the same temperature level Return fluid temperature from cooling distribution geocooling is performed with the highest possible temperature level If the cooling demand is not completely covered by geocooling geocooling is achieving a pre cooling An auxiliary cooling production has to be used to lower the temperature level of the cooling energy to the required one The geocooling and auxiliary cooling productions are performed in series and at two different temperature levels PILESIM2 user manual SUPSI DACD ISAAC page 28 8 6 Temperature Limitations Minimum allowed temper
53. g This parameter is labelled TairH PILESIM2 user manual SUPSI DACD ISAAC page 32 Height of the cellar between rooms and ground Hfloor height of the cellar that lies between the ground and the heated rooms This parameter is used to estimated the air volume of the cel lar for air change losses This parameter is labelled Hfloor Air change rate in the cellar AchRat this air change rate determine the heat losses or gains with the outdoor air For the sake of simplicity the losses from the cellar to the exterior outdoor air are only computed by ventilation losses Thus the specific heat losses from the cellar to the exterior Uce are established with formula 8 3 Uce kJ hK Cellar_floor_area m x Cellar_height m x 1 2 kJ m8K x Cellar_air_change rate 1 h 8 3 Uce W K Uce kJ hK x 1000 J kJ 3600 s h 8 4 The Cellar_air_change_rate is AchRat label of this parameter the Cellar_height is Hfloor la bel of the previous parameter and the Cellar_floor_area supposed to be delimited by the area occupied by the energy piles or boreholes is calculated with relation 8 5 Cellar_floor_area BPILE x BPILE x PileNumber 8 5 BPILE is the average spacing between the piles see below Average spacing between the piles PileNumber is the total number of energy piles or boreholes If the top of the bore pile field is in contact with the outside air temperature set the two pa rameters AchRat a
54. he piles bores PILESIM2 user manual SUPSI DACD ISAAC page 38 The inner diameter of one pipe is labelled DIAMI Fraction of pile borehole concrete filling thermal capacity this parameter defines the fraction of the pile concrete bore filling material in the active zone of a pile bore which contributes to heat capacitive effects The active zone of a pile bore is the part that is equipped with plastic pipes for the heat transfer with the ground i e the heat exchanger A typical value of 50 was found to satisfactorily match measured data of a pile system pile diameter of 30 to 40 cm A large value may produce an error which aborts the programme when run An error message is written in the listing file PILESIM LST Do not forget to read a possible error message near the end of this file if you can not run your case If borehole heat exchangers are simulated the heat capacitive effects are small and a fraction of 0 can be set The heat capacitive effects of the pile concrete are calculated with an effective pile diameter and an effective pile thermal resistance see equation 8 17 and 8 18 They are written in the output parameter file with the extension OPA the parameter labels are respectively Eff PilDiam and EffRbPil 1 EffPilDiam AvePilDiam 1 FrCapa Cconcr AveGrndCap 2 8 17 AvePilDiam is the average pile diameter see equation 8 11 FrCapa is the fraction of pile thermal capacity taken into account Cconcr
55. ible to view the file The PILESIM2 output files can be easily processed and analysed with the Pilesim2 get output xls excel file 9 1 The Listing File PILESIM LST This is the listing file written by TRNSYS All the information contained in PILESIM TRD is written in the listing file together with some information related to the simulation itself simulation duration total number of call for each component warning message if any etc It should be noted that if an error makes a simulation to abort the corresponding error message is written at the end of the li sting file It is recommended to read this file every time a simulation is terminated with an error 9 2 The File DST DAT This file is written by the TRNVDSTP component which simulates the energy piles or the borehole heat exchangers It contains all the parameter used by this component together with information on the fields used for the simulation of the heat transport in the ground 9 3 The Parameter File PILESIM OPA This file contains some of the mean parameter values which are calculated and used for the simu lation They are PileNumber total number of energy piles boreholes cf equation 8 12 AvePLength m average active pile length of the energy piles boreholes cf equation 8 13 GrndVolume m ground volume ascribed to the energy piles boreholes cf equation 8 15 AvePilDiam m average pile borehole diameter cf equation 8 11 EffPilDiam
56. ill result in a smaller average spacing However the effective average spacing remains greater than the smallest spacing between two energy piles boreholes If the shape of the area that contains the piles bores is close to a rectangle which is character ised by a large difference between its width and its length then the average spacing will tend to be greater As an example about 200 heat exchanger piles uniformly placed in a rectangular shape of 500m x 30m were simulated The calibration described below resulted in an increase of the average spacing from 9 3 to 10 1 m thus less than 10 A more accurate method is to calibrate the model used in PILESIM2 with a model that takes into account the exact position of the piles bores It can be done with TRNSBM the Superposition Borehole Model Contact the PILESIM2 author for more information The average spacing between the piles is labelled BPILE Number of piles boreholes coupled in series NSERIE This parameter determines the number of piles bores that are connected in series As the simulation model simulates a cylinder a ra dial interconnection of the piles bores is taken into account This parameter is labelled NSERIE Pipe configuration in pile borehole The two possible pipe configuration in the pile bore are U pipe configuration the pipe installation in the pile bore is formed by one or more U pipes placed close to the circumference of the pile borehole Coaxial pipe installation
57. ing the pi le diameter so that the additional heat capacity obtained with a greater simulated ground volume equals the effective heat capacity of the pile material The thermal resistance of the additional PILESIM2 user manual SUPSI DACD ISAAC page 22 ground annulus simulated is deducted from the pile thermal resistance This latter characterises the heat transfer between the fluid and the ground at the pile wall In that way the heat transferred under steady state conditions is the same with or without a reduction of the pile diameter How ever the effective heat capacity of a pile remains to be assessed Calibrations with measured ther mal performances have shown that half of the pile heat capacity provides a reasonable value for pile diameter of 30 50cm Influence of an Irregular Arrangement of the Piles The influence of an irregular arrangement of the piles can not be taken into account with PILE SIM2 As previously mentioned a uniform arrangement of the piles in a cylindrical volume is as sumed Such an influence can be assessed with the Superposition Borehole Model Eskilson 1986 This model is devised for the simulation of multiple heat extraction boreholes or energy piles A TRNSYS version TRNSBM has been adapted by Pahud et al 1996c The position the active length and the tilting of each pile is specified in the programme The heat transfer in the ground is assumed to occur by pure heat conduction The three
58. iod of time This temperature con straint influences the size of the heat pump which in turn affects the heating potential provided by the energy piles When geocooling is performed i e when the pile flow circuit is connected to the cold distribution without a cooling machine in between the cooling potential also depends directly on the temperature level of the fluid in the cooling system The annual extracted and injected ther mal energy through the piles determines the evolution of the ground temperature year after year which in turn may affect the thermal performances of the system An accurate assessment of the heating and cooling potential offered by an energy pile system requests a dynamic simulation of the system which takes into account both short term and long term thermal performances It re quires good knowledge of the system s thermal characteristics the local ground conditions and the use of an accurate system simulation tool Simulation tools of energy pile systems have been developed in the Laboratory of Energy Systems LASEN at the Swiss Federal Institute of Technology in Lausanne EPFL see Fromentin et al 1997 Their development has been carried out with the help of measurements from existing sys tems for comparison and validation purposes The well known transient system simulation pro gramme TRNSYS was used A non standard simulation model devised for heat storage in the ground with borehole heat exchangers Pahud et
59. is advised to read the help provided with the TRNSED programme It is found in the menu Help TRNSED Help and then look for the topic Parametrics Menu An Excel file called Pilesim2 get output xls has been devised to help visualise the results of a PILESIM2 simulation It conditions the values of the three parameters Length of simulation Time interval for output results and Print hourly values for last year see below 8 1 Simulation Parameters The two entries related to these parameters define the month of the year when the simulation starts and the duration of the simulation period Month for simulation start the simulation starts the first day of the chosen month Length of simulation duration of the simulation period The maximum duration is limited to 25 years if the simulation starts in January If the simulation starts another month the maximum duration is shorter as the maximum of 25 years is counted from January of the first operational year Recommendation for the use of the Excel file Pilesim2 get output xls set the length of a simulation to 20 years 8 2 Output Results These two parameters condition the writing of the output results Time interval for output results quantities can be calculated on a monthly basis or a yearly ba sis They are integrated heat rates or average values See chapter 5 for a complete description of the output results Recommendation for the use of the Excel file
60. is not the case the heat rate extracted by the heat pump is decreased until the fluid temperature satisfies the criterion As a result the heating power delivered by the heat pump is reduced In consequence an over sized heat pump will not yield much more heating energy per year than a correctly sized one A temperature constraint is also given for the highest allowed fluid temperature in the pile flow circuit The same kind of considerations apply for the cooling machine PILESIM2 assumes an optimal system control the best operational mode is selected the heating and cooling powers are adjusted to the heating and cooling demands if necessary while the tem perature constraints on the heat carrier fluid in the piles are satisfied The influence of frequent starts and stops of the heat pump and cooling machine is not taken into account although a con stant penalty value can be specified by the user on the performance coefficient and efficiency The simulation models used for the heat pump or the cooling machine and the energy piles are briefly described in chapter 7 6 6 Main Assumptions of the PILESIM2 Simulation Tool As previously mentioned the system control in PILESIM2 is optimal Frequent starts and stops of the heat pump and the cooling machine are not taken into account Other assumptions are related to the specificity of the simulation model used for the energy piles which is TRNVDSTP Pahud et al 1996b Some characteristics of
61. l in the cooling distribu tion Temperature losses in additional heat exchangers is also now taken into account heat ex changer between the cooling machine condenser and the pile bore circuit or between the cooling distribution and the pile bore circuit Additional parameters have also been added to better simu late a field of borehole heat exchangers by taking into account a geothermal temperature gradient in the ground and the internal heat transfer in a borehole heat exchanger 6 1 What Does PILESIM2 Simulate In Fig 6 1 a schematic view of the type of systems simulated by PILESIM2 is shown Great flexi bility has been given to PILESIM2 in order to provide a large variety of systems that can be simu lated see Fig 6 1 Heated cooled building Heat distribution Cold distribution System border Ground layer 1 Ground layer 2 Ground 3 Ground layer Fig 6 1 Schematic view of a energy pile system The part of the system which is simulated by the PILESIM2 programme is delimited by the pile system border shown with the dashed line PILESIM2 user manual SUPSI DACD ISAAC page 9 The system border shown in Fig 6 1 indicates the limits of the thermal simulations The heat trans fers are calculated from the ground to the thermal energy distributed in the building heating and cooling In particular the heat transferred by the piles by the horizontal connecting pipes
62. leads to the design performance coefficient COPo of the heat pump This parameter is labelled TcOut Temperature difference for COP reduction parameter ATCOP for the heat pump and cooling machine model see Fig 7 1 of chapter 7 the heat pump model This parameter is ignored if the COP and efficiency are not allowed to vary parameter ICTCOP set to YES This parameter is labelled dTCOP Temperature difference for COP stagnation parameter dTstag for the heat pump and cooling machine model see Fig 7 1 of chapter 7 the heat pump model This parameter is ignored if the COP and efficiency are not allowed to vary parameter ICTCOP set to YES This parameter is labelled dTstag Maximum possible COP PAC and cooling machine maximum value that the performance co efficient of the heat pump COP may have This maximum value is also used with the cooling machine if present In that case the maximum efficiency is limited to COPmax 1 This parameter is labelled COPmax Penalty on the COP PAC and cooling machine penalty on the performance coefficient This value is subtracted from the calculated or constant value so that transient effects bad control of the heat pump or something else can be artificially taken into account The same penalty value is used on the cooling machine efficiency if a cooling machine is present Typical values are comprised between 0 and 0 5 This parameter is labelled COPpen Design electric pow
63. loading conditions are given in hourly values They are determined by the heat and cold de mands and their corresponding temperature level The hourly values are read from a text file Pre defined values are stored in files for several locations and can readily be used for a simulation These predefined loading conditions were established on the basis of simple models which deter mine the space heating and space cooling requirements see chapter 8 Input Data to PILESIM2 for more details The user also has the possibility to use his own loading conditions with PILE SIM2 in order to make them correspond to his particular problem A temporal evolution of the hourly loading conditions is required for a whole year see chapter 8 Input Data to PILESIM2 for the creation of an input data file 6 3 How May PILESIM2 Be Used PILESIM2 can be used in different ways depending on the degree of knowledge of a project At an early stage a pre simulation can be performed by using a predefined file for the loading conditions a constant performance coefficient for the heat pump and a constant efficiency for the cooling ma chine Later in the project more will obviously be known about the building The pile system s pa rameters will also be known in greater detail and more accurate loading conditions can be estab lished with the help of other programmes They can be used to create an input data file for PILE SIM2 and a more precise simulation of the pile
64. lowing quantities separated by a space or a tab character the outdoor air temperature C the total heat demand kW the temperature level of the distributed heat or the forward fluid temperature for heating C the total cold demand kW the temperature level of the distributed cooling energy or the forward fluid temperature for cool ing C There are actually two possible ways of writing the heat rates called user hourly data and nor malised hourly data User hourly data With this option the hourly values of the heat and cold demands are written in kW with positive va lues This provides more flexibility for the user who has the possibility to build his own input data and use for example detailed loading conditions obtained with another programme He would only need to arrange the data with a spreadsheet programme according to the above description a list ing file PIL is also needed Normalised hourly data The normalised heat rates are written with a negative sign The hourly values of the heat demand are divided by the annual energy demand for heating and expressed in 1 h or KW kWh These numbers are then multiplied by 10 000 The same procedure is used for the cold demand In this way the user gives annual values for the heat and cold demand and the normalised hourly values transform the annual energies into hourly thermal powers according to the models that were used to prepare the n
65. nd UCelBu to AchRat 10 1 h UCelBu 0 W m K next parameter If the heated zone with a room air temperature fixed to TairH is in direct contact with the bore pile field no cellar set the two parameters AchRat and UCelBu to AchRat 0 1 h UCelBu 10 W m K next parameter The air change rate in the cellar is labelled AchRat PILESIM2 user manual SUPSI DACD ISAAC page 33 Global room cellar heat transfer coefficient UCelBu the global room cellar heat transfer coef ficient determines the total heat transfer coefficient transmission and ventilation between the heated rooms and the cellar The corresponding specific losses Ucm are obtained with formula 8 6 Ucm W K Cellar_floor_area m x UCelBu W m K 8 6 See formula 8 5 for the calculation of Cellar_floor_area If the top of the bore pile field is in contact with the outside air temperature set the two pa rameters AchRat and UCelBu to AchRat 10 1 h previous parameter UCelBu 0 W m k If the heated zone with a room air temperature fixed to TairH is in direct contact with the bore pile field no cellar set the two parameters AchRat and UCelBu to AchRat 0 1 h previous parameter UCelBu 10 W m K The global room cellar heat transfer coefficient is labelled UCelBu Insulation thickness between ground and cellar Hinsul the insulation thickness between the ground and the cellar determines the thickn
66. ne The design efficiency is the efficiency of the cooling machine when the inlet fluid temperature in the evaporator and the outlet fluid temperature from the condenser are at their design values see the next parameters TeinCo the design inlet fluid temperature in evaporator and TcutCo the design outlet fluid temperature from condenser The design efficiency is expressed by rela tion 8 2 EffCOM Qevo PelCOM 8 2 Qevo design cooling power provided by the cooling machine PelCOM design electric power of the cooling machine This parameter is ignored if no cooling machine is used in the system This parameter is labelled EffCOM Design inlet fluid temperature in evaporator design inlet fluid temperature in the evaporator that leads to the design efficiency EffCOM of the cooling machine This parameter is ignored if no cooling machine is used in the system It is also ignored if Eff COM see previous parameter is set to a negative value or the COP and efficiency are fixed at their design value constant during a simulation This parameter is labelled TeinCo Design outlet fluid temperature from condenser design outlet fluid temperature from the con denser that leads to the design efficiency EffCOM of the cooling machine This parameter is ignored if no cooling machine is used in the system It is also ignored if Eff COM see the second previous parameter is set to a negative value or the COP and efficiency are fixed
67. nergy Storage Proceedings Thermastock 91 pp 3 5 1 3 5 7 Scheveningen The Netherlands Mazzarella L 1993 Duct Thermal Storage Model Lund DST TRNSYS 13 1 Version 1993 ITW Universit t Stuttgart Germany Dipartimento di Energetica Politechnico di Milano Italy MINSUN 1985 Central Solar Heating Plants with Seasonal Storage The MINSUN Simulation and Optimization Program Application and User s Guide International Energy Agency Solar Heat ing and Cooling Programme Task VII September 1985 Nield D A and Bejan A 1992 Convection in Porous Media Springer Verlag New York PILESIM2 user manual SUPSI DACD ISAAC page 50 Pahud D 1996 Simulation of Central Solar Heating Plants Using a Duct Store an Application for Switzerland Swiss Grant Nr 8220 0422846 Department of Mathematical Physics University of Lund Sweden ENET 9006008 1 Pahud D Hellstr m G 1996 The New Duct Ground Heat Model for TRNSYS Eurotherm Semi nar N 49 Eindhoven The Netherlands pp 127 136 Pahud D Fromentin A Hadorn J C 1996a The Duct Ground Heat Storage Model DST for TRNSYS Used for the Simulation of Energy Piles User manual for the December 1996 ver sion Internal report Laboratory of Energy Systems LASEN Swiss Federal Institute of Tech nology EPFL Lausanne Switzerland Pahud D Fromentin A and Hadorn J C 1996b The Duct Ground Heat Storage Model DST for TRNSYS Used for the Simulation of
68. nput temperature can be the air temperature of a building s ground floor The second zone is everywhere else and the corresponding input temperature is normally the outdoor air temperature The last TRNVDST version is chosen for the simulation of systems that use energy piles In order to have a more appropriate simulation model the features given below were implemented in TRNVDST The resulting model is called TRNVDSTP Pahud et al 1996b A ground water flow can be specified for each ground layer The heat transfer caused by forced convection in the storage region is estimated for each ground layer The heat transferred by the pipe connections on ground surface can be estimated Influence of a Regional Ground Water Flow An accurate simulation of the influence of the ground water flow can not be realised with a calcula tion procedure that assumes a cylindrical geometry around the boreholes and the store as a re gional ground water flow will shift the temperature field in the direction of its displacement A priori DST is not suitable for such calculations as the cylindrical geometry is extensively used Unfortu nately a 3 dimensional DST model could not be developed in the framework of this study Approximations are implemented in the two dimensional version of DST A more accurate model developed for a typical situation should be used to highlight the limitations of such approximations However they have not yet been checked to a
69. of the heat fluxes through the cellar allows the calculation of its temperature see equation 9 1 ToutsideAir x Uce TmInbuild x Ucm TmGrndTop x Ucg TmCellar diga Uce Ucm Ucg 9 1 ToutsideAir is the temperature of the air outside the building TmInbuild is the indoor air tempera ture of the heated and cooled part of the building above the cellar and TmGrndTop is the mean temperature of the 30 cm thick ground layer that contains the horizontal connection pipes Uce is the specific heat losses between the cellar and the exterior see equation 8 4 Ucm is the specific heat losses between the heated cooled part of the building and the cellar see equation 8 6 Ucg is the specific heat losses between the cellar and the top part of the ground It is calculated with 4 thermal resistances in series see equation 9 2 PILESIM2 user manual SUPSI DACD ISAAC page 48 1 DLAY1 2 F Hinsul Hmagco 1 AtopGrnd Ainsul Amagco AcgSur Ucg Cellar_floor_area x The 4 thermal resistances at the denominator are from left to right e thermal resistance of half of the ground layer that contains the horizontal connection pipes DLAY1 is set to 0 3 m and AtopGrnd to 1 3 W mK e thermal resistance of the insulation layer between the ground and the cellar Hinsul is the insu lation layer thickness input parameter and Ainsul the insulation thermal conductivity set to 0 05 W mk e thermal resistance of the concrete pla
70. oldAux QCold QColdCov kWh cooling energy covered by the pile bore system geocooling and cooling machine in PILESIM OUT kWh total energy demand for cooling in PILESIM OUT PILESIM2 user manual SUPSI DACD ISAAC page 47 9 7 Heat Balance of the Energy Piles The quantities contained in the file PILESIM OUT allows the user to establish a heat balance of the energy piles borehole heat exchangers An energy fluxes diagram relative to the energy pi les borehole heat exchangers is shown in Fig 9 2 ENERGY PILES BOREHOLES Heated cooled part HEAT BALANCE of the building TmCellar QBuiToCel Building cellar buffer space between the building s rooms and the ground QCelToGrd Outside air QCelToOut Extracted heat from the ground with the piles bores Ground volume ascribed Heat losses through to the energy piles bores the vertical sides Injected heat into the ground with the piles bores QEDSTin Heat losses through the bottom Fig 9 2 Energy fluxes diagram of the energy piles borehole heat exchangers The definitions of the labels shown in Fig 9 2 are given in section 9 4 and the corresponding en ergy quantities are found in the PILESIM OUT file The cellar is considered as a non heated zone Its temperature TmCellar calculated and written in the PILESIM OUT file depends on the heat gain or losses from the building the ground and the outside air A steady flux heat balance
71. ormalised data PILESIM2 user manual SUPSI DACD ISAAC page 25 The following files were prepared with normalised data and available to PILESIM2 NormBase pil input data file for the area of Basel Switzerland NormBern pil input data file for the area of Bern Switzerland NormChur pil input data file for the area of Chur Switzerland NormGene pil input data file for the area of Gen ve Switzerland NormLaus pil input data file for the area of Lausanne Switzerland NormLuga pil input data file for the area of Lugano Switzerland NormNeuc pil input data file for the area of Neuchatel Switzerland NormSion pil input data file for the area of Sion Switzerland NormVadu pil input data file for the area of Vaduz Liechtenstein NormZuri pil input data file for the area of Zurich Switzerland In these files the heating and cooling requirements are calculated as follows HEATING Heating is calculated for space heating requirements only Heating is needed only when the aver age outside air temperature during the previous 24 hours is lower than 12 C The heating require ment is proportional to the difference between a reference temperature and the outside air tem perature The reference temperature is fixed to 16 C The forward fluid temperature for heating is set to 50 C when the outside air temperature is 10 C or less For higher air temperatures the for ward fluid temperature follows a linear decr
72. pro gramme the duration of the work spent for the hotline will not exceed 1 hour If the ISAAC thinks that the help demanded is actually consulting work or does not correspond to the help described above the client will be informed and an offer will be proposed the hourly price is fixed at 150 CHF hour or 100 EU hour PILESIM2 user manual SUPSI DACD ISAAC page 6 5 Introduction to Energy Pile Systems A pile foundation is used when the upper layers of soil are too soft and compressible to support the loads of a superstructure normally a building An energy pile is a pile foundation equipped with a channel system in which a heat carrier fluid can be circulated so as to exchange heat with the sur rounding ground The two main functions of an energy pile are thus to support the loads of a su perstructure and to serve as a heat exchanger with the ground A energy pile system comprises a set of energy piles which are connected together hydraulically and normally are coupled to a heat pump Such a system is usually used for heating and or cooling purposes The principal constraint on the system is that the thermal solicitations withstood by the piles must not deteriorate their mechanical properties i e their ability to support the loads of the building In particular freezing of the piles must be avoided In a safely sized energy pile system the fluid temperature in the piles never drops below 0 C for a long per
73. s The rest QColdCov QFreeCool is provided by the heat pump extracted energy at the evaporator when there is a simultaneous demand for heating and cooling i e see below QHextCold and the cooling machine if any The energy extracted from the cold demand by the cooling machine is QCoolMach QColdCov QFreeCool QHextCold average performance coefficient of the heat pump It is defined as the ratio of the delivered heating energy by the electric energy used by the heat pump COP GHeatCov QelPAC mean performance coefficient including the cooling machine COPglobal QHeatCov QHCoolMach QElecTot Where QHCoolMach is the waste heat energy dissipated in the ground by the cooling machine QHCoolMach QHinjGrnd QFreeCool average efficiency of the cooling machine EffCoolM QCoolMach QelCoolM QCoolMach QColdCov QFreeCool QHextCold QelCoolM QElecTot QHeatCov COP kWh energy extracted from the cold demand by the heat pump for heating pur poses kWh energy extracted from the ground by the heat pump kWh energy injected into the ground geocooling and cooling machine The en ergy injected into the ground by the cooling machine is QHCoolMach QHinjGrnd QFreeCool ratio energy injected in the ground over energy extracted from the ground GrndRation QHinjGrnd QHextGrnd fraction of the total heat demand covered by the heat pump FracHeat QHeatCov QHeat kWh m
74. s designed for If the next parameter design forward fluid temperature for heating is lower than 20 C the for ward fluid temperature for heating is read from the input data file and this parameter is ignored This parameter is labelled TexMin Design forward fluid temperature for heating TfoHea maximum fluid temperature for heating The forward fluid temperature for heating is set to this value if the outdoor air temperature is be low the outdoor air temperature for heating design previous parameter For higher air tempera tures the forward fluid temperature follows a linear decrease with increasing air temperature down to 20 C for an air temperature of 20 C With normalised loading conditions the heating is stopped if the air temperature exceeds 12 C If this parameter is set to a value lower than 20 C the forward fluid temperature for heating is read from the input data file and this parameter is ignored This parameter is labelled TfoHea Design forward fluid temperature for cooling TfoCol design forward fluid temperature for cooling This value is assumed to be constant all through the year If this parameter is set to a value lower than 0 C the forward fluid temperature for cooling is read from the input data file and this parameter is ignored This parameter is labelled TfoCol Design forward return temperature difference in cooling distribution dTGeocool design temperature difference between return and
75. ssess their validity The first approximation concerns the global problem or the long term influence of a regional ground water flow Two methods are implemented in TRNVDSTP With the method used in PILE SIM2 the convective loss or gain is calculated with the temperature difference between Timean the average temperature of the ground layer within the storage region and Ta the undisturbed ground water temperature in the ground layer see equation 7 5 The convective heat loss during a simu lation time step At is limited to the maximum possible value defined by relation 7 6 In that case the global temperature field within the storage region is replaced by T the undisturbed ground water temperature Econv U S Cw Ta Tmean At 7 5 E conv max V Coround To T mean 7 6 PILESIM2 user manual SUPSI DACD ISAAC page 18 With u Darcy velocity in the ground layer m m s d storage diameter cylindrical shape m H vertical extension of the ground layer inside the storage volume m S cross area of the storage submitted to the Darcy flow S H x d m V volume of the ground layer inside the storage volume V x d 4 x H m Cw volumetric heat capacity of ground water J m k Cogrouna volumetric heat capacity of the ground layer inside the store J m8K Tg undisturbed ground water temperature in the ground layer C Tmean Mean storage temperature in the ground layer C At time step
76. te between the ground and the cellar Hmagco is the con crete plate thickness input parameter and Amagco the concrete thermal conductivity set to 1 3 W mk e thermal resistance between the surface of the floor and the air of the cellar AcgSur is fixed to 6 W m K The Cellar_Floor_Area is the top side area of the ground volume ascribed to the energy pi les borehole heat exchangers see equation 8 5 PILESIM2 user manual SUPSI DACD ISAAC page 49 10 REFERENCES Bennet J Claesson J Hellstr m G 1987 Multipole Method to Compute the Conductive Heat Flows to and between Pipes in a Composite Cylinder Notes on Heat Transfer 3 1987 Depts Of Building Physics and Mathematical Physics Lund Institute of Technology Lund Sweden Eskilson P 1986 Superposition Borehole Model Manual for Computer Code Department of Mathematical Physics Lund Institute of Technology Lund Sweden Eskilson P 1987 Thermal Analysis of Heat Extraction Boreholes Department of Mathematical Physics Lund Institute of Technology Lund Sweden Fromentin A Pahud D Jaquier C et Morath M 1997 Recommandations pour la r alisation d installations avec pieux changeurs Empfehlungen f r Energiepfahlsysteme Rapport final d cembre 1997 Office f d ral de l nergie Bern Switzerland Hellstr m G 1983 Heat Storage Subroutines in Minsun Duct Storage Systems Department of Mathematical Physics University of Lund Sweden
77. tely covered by one or more heat pumps coupled to the energy piles boreholes If there is a cooling demand geocooling with the piles bores is tried in priority If a greater part of the cooling demand can be met with the cooling machine the cooling machine takes over geocooling The thermal loads of the cooling machine are injected in the ground through the piles bores Heating combined with a cooling machine the heat demand is partly or completely covered by one or more heat pumps coupled to the energy piles boreholes If there is a cooling demand it will be partly or completely covered by one or more cooling machine s coupled to the en ergy piles boreholes 8 5 Annual Energies and Temperature Levels Annual energy demand for heating annual heat demand of the system given with a positive va lue This value is only used with normalised input loading conditions It is otherwise ignored The heating demand can be scaled with the next parameter Scaling factor for heating de mano This parameter is labelled QhYEAR NB Normalised loading conditions are written with negative values in the input data file The heat demand values are written in the second column of the input data file Data files whose names start with NORM were prepared with normalised loading conditions Scaling factor for heating demand ScaleH the heat demand is scaled with this factor A de fault value of 1 must be set if no scaling is desired A scaling factor o
78. the piles A fraction or the totality of the cooling requirement is also realised by a cooling machine con nected to the piles Geocooling is not performed 6 2 Which Types of Parameters Does PILESIM2 Require A energy pile system is defined by 5 main categories of parameters see chapter 8 Input Data to PILESIM2 for a complete description of the parameters These categories are 1 the ground characteristics they define the thermal properties of the ground layers up to 3 a possible regional ground wa ter flow in each layer and the initial undisturbed ground temperature 2 the energy piles up to 6 different types of energy piles can be defined 3 the ground building interface these parameters are related to the cellar and the horizontal connecting pipes 3 Geocooling is realised by connecting the pile flow circuit to the cold distribution without a cooling machine in between It is also called direct cooling The design power of the cooling machine is fixed before simulation by the user PILESIM2 user manual SUPSI DACD ISAAC page 10 4 the heat pump and cooling machine these parameters define the thermal performances of the heat pump and the cooling machine 5 the loading conditions for heating and cooling the loading conditions are read from a file However these parameters allow the user to quickly change the annual energy requirements and the temperature levels of the distributed thermal energy The
79. ues are between 10 to 30 m The spacing between the piles varies between 3 to 10 m for most of the cases and is not necessarily regular When a energy pile system is installed the length of the horizontal pipes that connect the piles to the main pipe collector is often large in relation to the pile length Computer programmes devised for the simulation of a duct ground heat storage or multiple heat extraction boreholes can be used to simulate a set of energy piles if the following effects are taken into account the influence of a regional ground water flow in a ground layer the heat transfer of the connecting pipes between the piles on the ground surface the thermal influence of the building on the ground volume containing the piles the heat capacitive effects of the piles the influence of an irregular arrangement of the piles PILESIM2 user manual SUPSI DACD ISAAC page 16 Simulation of a Duct Ground Heat Storage A duct ground heat storage system is defined as a system where heat or cold is stored directly in the ground A ground heat exchanger formed by a duct or pipe system inserted in either bore holes foundation piles or directly into the ground is used for heat exchange between a heat carrier fluid which is circulated through the pipes and the storage region The heat transfer from the pipe system to the surrounding ground takes place by ordinary heat conduction The duct storage model Hellstr m 1989
80. under the concrete plate of the cellar through the floor and ceiling of the cellar are assessed The cellar assumed to be unheated has a temperature which depends on the indoor building temperature the outside air temperature and the ground temperature below the building The cellar may be given the temperature of the outside air by an appropriate setting of the heat transfer coefficients Four different types of system can be simulated 1 heating only a fraction or the totality of the heat demand is covered by a heat pump coupled to the piles A thermal recharge of the ground can be realised during the summer 2 heating and geocooling a fraction or the totality of the heat demand is covered by a heat pump coupled to the piles A cooling requirement can be partly or totally covered by geocooling with the piles No cooling machine connected to the piles is used 3 heating and cooling with geocooling or a cooling machine a fraction or the totality of the heat demand is covered by a heat pump coupled to the piles The cooling requirement is satisfied in priority by geocooling with the piles If a greater part of the cooling demand can be realised with the cooling machine the cooling machine is used and takes over geocooling The thermal loads of the cooling machine are injected in the ground through the piles 4 heating and cooling with a cooling machine a fraction or the totality of the heat demand is covered by a heat pump coupled to
81. y the boreholes during this period of time to an equilibrium of the local temperature field The energy transferred by the local problem prior to this period of time is simply transferred to the global prob lem by means of a constant temperature correction in the local and global temperature fields In that way the local problem keeps only in memory the short term thermal perturbations induced by the boreholes PILESIM2 user manual SUPSI DACD ISAAC page 17 The heat transfer from the fluid to the ground in the immediate vicinity of the borehole is calculated with a heat transfer resistance A steady state heat balance for the heat carrier fluid gives the tem perature variation along the flow path The local solutions may take into account a radial stratifica tion of the store temperatures due to a coupling in series of the boreholes as well as increased resolution in the vertical direction The local heat transfer resistance from the fluid to the ground or borehole thermal resistance may take into account the unfavourable internal heat transfer be tween the downward and upward flow channels in a borehole The three dimensional heat flow in the ground is simulated using a two dimensional mesh with a radial and vertical coordinate A time varying temperature is given on the ground surface in two dif ferent zones The first zone is located at the top side of the ground volume which contains the boreholes The corresponding i
82. y if it is greater than 1 The same correction factor is assumed for the calculations of the transient heat transfers around the energy piles The ratio indicates by how much the actual heat transfer rate differs from that resulting from Heat Transfer of the Connecting Pipes on the Ground Surface The heat transferred by the connecting pipes can be simulated by using two pipe modules in TRNSYS one for the fluid flowing to the energy piles and one for the returning fluid During a simu lation time step the pipe modules lose or gain heat relative to a given temperature set to the av erage ground temperature on top of the store The resulting transferred heat is then injected on top of the storage as a temperature correction to the temperatures of the meshes in the uppermost mesh layer of the store The new ground temperature on top of the store will be the next tempera ture input to the pipe modules for the calculation of the pipe heat loss or gain and so on Other modules can be used as long as an input temperature is used to calculate the heat transfer rate exchanged by the pipes which is then returned as an output variable An estimation of the pipe loss factor is calculated with the method given by Koschenz and Dorrer 1996 Lpipe Sinterface Rpipe 1 In S interface 274 Lpipe 7 Hpipe W m k 7 14 With Hpipe effective heat transfer coefficient between the fluid temperature of the horizontal conn

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