QNET Experiment #05: HVAC System Identification Heating
Contents
1. Lab 5 System Identification START STOP CONTROL Sampling Rate Acquisition Time R1 Ea Pause Re Start Display ij E _ osn i 22 02 22 015 o7 o7 J22 dege 195 dege t lt Figure 4 Front Panel Used for the QNET HVACT System Identification Laboratory 5 3 Estimate The Heater Steady State Gain And Time Constant Step 3 First select COOLING in the Input Signal Properties box by flipping as required the vertical toggle switch Ensure that the Vb Numeric Control is set to more than 16 Volts and that the initially green START push button has been pressed The fan Document Number 576 Revision 01 Page 11 System Identification Laboratory Manual should now blow in order to initialize the system by bringing the chamber to ambient temperature Step 4 Click on the red STOP button to stop the blowing once a steady state temperature has been reached Let the chamber air settle for about 20 seconds and reach ambient temperature Step 5 Then select HEATING in the Input Signal Properties box by flipping the toggle switch Set the Vh Numeric Control to 1 5 Volts Clear the chart by right clicking on it and selecting the Clear Chart context menu item You can now start the step input test by pressing the green START push button which will apply the desired voltages to the system The halogen lamp should now be heating proportionally to V and the chamber temperature should b2. And Blower Deadband Voltages ccceccceesceeeeeeeneeeteeeeeeees 18 Document Number 576 Revision 01 Page i System Identification Laboratory Manual 1 Laboratory Objectives The objective of this experiment is to run open loop tests on a Heating Ventilation and Air Conditioning HVAC plant in order to gain insights in the effects of heat radiation The system dynamics are studied by collecting measurements that are used to perform system identification The obtained model is required to design closed loop controllers in subsequent experiments 2 References 1 NI ELVIS User Manual 2 QNET HVACT User Manual 3 HVAC Plant Presentation 3 1 Component Nomenclature As a quick nomenclature Table 1 below provides a list of the principal elements composing the Heating Ventilation and Air Conditioning HVAC Trainer system Every element is located and identified through a unique identification ID number on the HVAC plant represented in Figure 1 below ID Description ID Description 1 Heater Halogen Lamp 2 Blower Fan 3 Temperature Sensor 4 Chamber Duct Table 1 HVAC Component Nomenclature Document Number 576 Revision 01 Page 1 System Identification Laboratory Manual Figure 1 HVAC System 3 2 HVAC Plant Description The QNET HVAC Trainer system consists of a pexiglass duct or chamber equipped with a heater on one end and a blower on the other A thermistor is place
3. s Th3 s Th s Kss a C V 1 2 Average Values Table 4 Heating Step Actual Response Characteristics And Parameter Estimation Step 8 Obtain a second step response Step 2 for the heating process by repeating Steps 2 to 6 as described above but with the Vh Numeric Control set to 3 0 Volts instead of 6 in Step 1 Step 9 From your experimental results from Step 1 and Step 2 in Table 4 above take the average of the two estimates found for the heater steady state gain Kss n and time constant t What are your final estimated i e average values for Kss n and th Step 10 Once your results are obtained you can stop the VI by pressing the red EXIT button System Identification Laboratory Manual 5 4 Estimate The Blower Steady State Gain And Time Constant Step 11 Select HEATING in the Input Signal Properties box by flipping as required the vertical toggle switch Set the Vh Numeric Control to 4 0 Volts Start the LabVIEW VI Ctrl R if it has been stopped and ensure that the initially green START push button has been pressed The halogen lamp should now be on and heat up the inside of the chamber This raises the chamber temperature and initializes the system before the cooling step Step 12 Monitor the heating the chamber on the front panel Be prepared to toggle the switch to COOLING once the chamber temperature is above 60 degrees Celsius This will stop heating and start blowing cooling step te
4. the average of three different experimental estimates 11 T2 and ts which will be expressed as a functions of to and tin tz and tz respectively Document Number 576 Revision 01 Page 8 _ Document Number 576 Rev ision 01 Page 9 System Identification Laboratory Manual 2 Finally derive an expression for Kss as a function of Kv Te o and Te ss 5 In Lab Session 5 1 System Hardware Configuration This in lab session is performed using the NI ELVIS system equipped with a QNET HVACT board and the Quanser Virtual Instrument VI controller file QNET_HVAC_Lab_05_Sys_ID vi Please refer to Reference 2 for the setup and wiring information required to carry out the present control laboratory Reference 2 also provides the specifications and a description of the main components composing your system Before beginning the lab session ensure the system is configured as follows QNET HVACT module is connected to the ELVIS ELVIS Communication Switch is set to BYPASS DC power supply is connected to the QNET HVAC Trainer module The 4 LEDs B 15V 15V 5V on the QNET module should be ON 5 2 Software User Interface Please follow the steps described below Step 1 Read through Section 5 1 and go through the setup guide in Reference 2 Step 2 Open the VI controller QNET_HVAC_Lab_05_Sys_ID vi shown in Figure 4 The default sampling rate for the implemented digital controller is 35
5. 0 Hz However you can adjust it to your system s computing power Please refer to Reference 1 for a complete system s description The chamber temperature directly sensed by the thermistor is plotted on a chart as well as displayed in a Numeric Indicator and a Thermometer located in the Temperature degC front panel box The values are in degrees Celsius Run the LabVIEW VI Ctrl R to initialize the open loop controller At this point both heater and blower voltages i e Va and V are set to zero and the Document Number 576 Revision 01 Page 10 System Identification Laboratory Manual chamber temperature is read The vertical toggle switch in the Input Signal Properties box allows you to choose between the heating or cooling process of the system In heating mode the blower voltage V is zero and the heater voltage Vn can be set by the user through the Vh Numeric Control Likewise in cooling mode the heater voltage is set to zero while the blower voltage is user defined through the Vb Numeric Control However the green START push button should be pressed in order for both commanded voltages to be applied to the HVAC plant With the open loop control action active the initially green START push button should now show as a red STOP button that you can trigger to pause the controller execution I QNET_HVAC_Lab_05_Sys_ID vi File Edit Operate Tools Browse Window Help Quanser NI ELVIS Trainer QNET HVAC TRAINER HVACT
6. Quanser NI ELVIS Trainer QNET Series Q QNET Experiment 05 X HVAC System GUANSER Identification Heating Ventilation and Air Conditioning Trainer HVACT Student Manual System Identification Laboratory Manual Table of Contents Le Labotat ry OD IC VES acts seia is ea rstnen oti nile ait cadinnd a aa d i O Oa aA A EE 1 DORR CLORGNCCS ceia ennn a dik tala t a a A tvnclia idan dt o aA 1 SOV AC Plant Pre semi Al tO esx onerar des stund ves e na a E a i ai aa 1 3 1 Component Nomenclature nisasie i a Ride shaes taken std suepattbes 1 3 2 HVAC Plant De s riptiois ese enan aa reese E teed sey sake ecte uit ay eka rie 2 4 Pre aD ASsignments nars n ea See Ns oie E Ea E E 3 4 1 Pre Lab Assignment 1 Open Loop Modelling ccccccecesseceseeceeseceeseeeenteeeseeeeees 3 4 2 Pre Lab Assignment 2 Estimating The Heater Gain And Time Constant 4 4 3 Pre Lab Assignment 3 Estimating The Blower Gain And Time Constant 7 Sn ab Session 56s Ase iiacstssveaen ws oaoaigai sai tase eae E a Gaeta Ae 10 5 1 System Hardware Configurations scsccssssiets ce eccccde ccs cleaseecstceciss daasels atten sateeetaintianlags 10 5 2 Software User lnter lace sacs tsszveidssseceiad riea i cus aa a aAa omy aS aii aa 10 5 3 Estimate The Heater Steady State Gain And Time Constant eccceeeeceeeteees 11 5 4 Estimate The Blower Steady State Gain And Time Constant 0 ccceceeeeeeeeteees 15 5 5 Estimate The Heater
7. Starting Time Teo Starting Chamber Temperature Tess Steady State Chamber Temperature Table 3 First Order Step Response Parameters The time parameters presented in Figure 2 above are characterized below such that t is defined by Letti 4 to by t 1 24 5 and tz by t t 3t 6 1 Applying the theory associated with first order systems determine the chamber temperatures Te 1 Te 2 and Te 3 obtained at the times ti tz and ts respectively This is illustrated in Figure 2 above The expressions obtained for Te 1 Te 2 and Te 3 should be functions of T o and T ss Document Number 576 Revision 01 Page 5 System Identification Laboratory Manual 2 As illustrated in Figure 2 above the measurement times ti tz and tz can be estimated by locating Tei Tez and T 3 respectively on the experimentally obtained step response plot and by measuring their corresponding time values As induced by Equations 4 5 and 6 each measurement time results in an estimate of the heater open loop time constant tn Express the resulting time constant estimates namely Tn Th and Tm as functions of to and the measurement times tz tz and tz respectively 3 A valid estimation of the heater time constant ta is assumed to be the average of the three Document Number 576 Revision 01 Page 6 System Identification Laboratory Manual previously obtained estimates Th Tm and Tm D
8. d in between at the loca tion in the chamber where the temperature is to be controlled The heater is made of a 12 Volt halogen lamp The blower is a 24 Volt variable speed fan Document Number 576 Revision 01 Page 2 System Identification Laboratory Manual 4 Pre Lab Assignments This section must be read understood and performed before you go to the laboratory session 4 1 Pre Lab Assignment 1 Open Loop Modelling The HVAC plant consists of two inputs namely the heater and blower voltages for one output the chamber temperature The system thermal resistance and capacitance are not known Additionally the heater and blower heatflow rate constants are also unknown Therefore system identification is required to model the dynamics of the plant The thermodynamics theory shows that the behaviour of space heating can be approximated by the following first order transfer function G s from heater voltage to chamber temperature difference AT s K ss_h TONI VCs 7 91 1 where the difference with a constant ambient temperature is defined as ATST oT 2 Likewise it can also be shown that the chamber cooling dynamics due to air blowing can be approximated by the following simple lag Laplace transfer function G s from blower voltage to chamber temperature difference AT s Kg G s b Vs t s 1 3 The HVAC model parameters and variables are defined in Table 2 below Symbol De
9. e 5 the first line presents the data from Step 1 which corresponds to a blower input voltage of 14 Volts i e Kv The second line of Table 5 is for an input step of 18 Volts which is called Step 2 Determine the corresponding estimates for the blower steady state gain Kss and time constant Tv Document Number 576 Revision 01 Page 16 Step K V Teo C Tess C Ter C Step Tez C Te 32 C bir s bor s tr s 2 Step Ta S Ta S Tes S Ts s Kss a a CAG 1 2 Average Values Table 5 Blowing Step Actual Response Characteristics And Parameter Estimation Step 16 Obtain a second step response Step 2 for the blowing process by repeating Steps 10 to 14 as described above but with the Vb Numeric Control set to 18 Volts instead of 6 in Step 1 Step 17 From your experimental results from Step 1 and Step 2 in Table 5 above take the average of the two estimates found for the blower steady state gain Kss 4 and time constant tT What are your final estimated i e average values for Kss and Te Step 18 Once your results are obtained you can stop the VI by pressing the red EXIT button System Identification Laboratory Manual 5 5 Estimate The Heater And Blower Deadband Voltages Step 19 Let us define V om and V om the heater and blower positive i e upper limit deadband vo
10. e rising The settling time should be less than 600 seconds so that the complete step response fits within the chart time scale At this point also stop the heater by pressing the red STOP button DO NOT press EXIT and do not stop the VI Step 6 Make a screen capture of the obtained step response plot once the response has reached steady state and join a printout to your report Your actual response should look similar to the theoretical temperature heating plot presented in Figure 2 Document Number 576 Revision 01 Page 12 System Identification Laboratory Manual Step 7 Determine the characteristics of the obtained step response plot by using the Graph Palette located on top of the Chart top left corner Fill up the following table i e Table 4 by measuring the required data points from the actual plot and by carrying out the estimation procedure detailed in Pre Lab Assignment 2 In Table 4 the first line presents the data from Step 1 which corresponds to a heater input voltage of 1 5 Volts i e Kv n The second line of Table 4 is for an input step of 3 0 Volts which is called Step 2 Determine the corresponding estimates for the heater steady state gain Kss n and time constant Tn Document Number 576 Revision 01 Page 13 Step K n V Teo C Tess C Ter C Step Tez C Te 32 C bir s bor s tr s 2 Step Thi s Th2
11. etermine the expression for Th as a function of Thi Tr and Tps 4 Finally determine the expression for Kss n as a function of Ky n Teo and Te ss 4 3 Pre Lab Assignment 3 Estimating The Blower Gain And Time Constant As defined in Equation 3 the HVAC system steady state gain and time constant during blowing i e Kss and Te can also be determined experimentally by analyzing the system open loop response to a step input A typical first order temperature response to a blower voltage step input is illustrated in Figure 3 below The heater voltage is held constant at zero Document Number 576 Revision 01 Page 7 System Identification Laboratory Manual Chamber Temperature C t 2T ae Time s Figure 3 Model Parameter Estimation From A First Order Step Response During Blowing During the laboratory session you will obtain the system responses to different amplitudes Ks of step input voltage to the blower For each experimental step response the same parameters as those shown in Table 3 and illustrated in Figure 3 should be measured However in this case the time parameters presented in Figure 3 above are characterized below such that ti is defined by t t t 7 to by Lait 2 1 8 and tz by ee T 9 1 Following a reasoning similar to the one previously detailed in Pre Lab Assignment 2 derive a way to estimate the blower open loop time constant t Hint To should result as
12. ltages respectively Deadband or deadzone is chiefly due to nonlinearity in the system such as static friction or electrical offset and the like Step 20 To determine Vn of experimentally select HEATING in the Input Signal Properties box by flipping as required the vertical toggle switch and set the Vh Numeric Control to 0 Volts to start Start the LabVIEW VI Ctrl R if it has been stopped and ensure that the initially green START push button has been pressed Both halogen lamp and fan should be off as their respective input voltages Va and V are set to zero Now slowly increase Vn by steps of 0 1 Volts until the halogen lamp filament becomes on and turns orange You can do so by using the increment decrement button on the left side of the Vh Numeric Control Wait for a few seconds between two increment steps to let the heater settle at the new input voltage Stop incrementing as soon as the bulb starts switching on Step 21 What is your measured heater deadband voltage Step 22 To determine V of experimentally set the Vb Numeric Control in the Input Signal Properties box to 0 Volts and flip the toggle switch to COOLING Start the LabVIEW VI Ctrl R if it has been stopped and ensure that the initially green START push button has been pressed Both halogen lamp and fan should be off as their respective input voltages Vn and Vi are set to zero Now slowly increase V by steps of 0 1 Volts until the fan starts to turn Y
13. ou can do so by using the increment decrement button on the left side of the Vb Numeric Control Wait for a few seconds between two increment steps to let the fan settle at the new input voltage Stop incrementing as soon as the fan has started Document Number 576 Revision 01 Page 18 System Identification Laboratory Manual Step 23 What is your measured blower deadband voltage Step 24 Both V off and V o could be used in a control system scheme for deadband compensation Step 25 Shut off the PROTOTYPING POWER BOARD switch and the SYSTEM POWER switch at the back of the ELVIS unit Unplug the module AC cord Finally stop the VI by pressing the red EXIT button Step 26 Before leaving the laboratory session ensure that you have all the experimental results required for your lab report Document Number 576 Revision 01 Page 19
14. scription Ta Ambient Temperature Outside the Chamber C Te Chamber Air Temperature C AT Chamber Temperature Difference C Va Heater Input Voltage V Document Number 576 Revision 01 Page 3 System Identification Laboratory Manual Symbol Description Blower Input Voltage Heater Open Loop Steady State Gain Heater Open Loop Time Constant Blower Open Loop Steady State Gain Blower Open Loop Time Constant Laplace Operator Continuous Time Table 2 HVAC Model Nomenclature 4 2 Pre Lab Assignment 2 Estimating The Heater Gain And Time Constant As defined in Equation 1 the HVAC system steady state gain and time constant during heating i e Kss n and Th can be determined experimentally by analyzing the system open loop response to a step input A typical first order temperature response to a heater voltage step input is illustrated in Figure 2 below The blower voltage is held constant at zero Vee Chamber Temperature C 1r 2T tyt Time s Figure 2 Model Parameter Estimation From A First Order Step Response During Heating Document Number 576 Revision 01 Page 4 System Identification Laboratory Manual During the laboratory session you will obtain the system responses to different amplitudes Kv 1 of step input voltage to the heater For each experimental step response the following parameters as shown in Table 3 and illustrated in Figure 2 should be measured Symbol Description to Step
15. st However beforehand ensure that the Vb Numeric Control is first set to 14 Volts Step 13 Once the temperature is above 60 C first clear the chart by right clicking on it and selecting the Clear Chart context menu item Then select COOLING in the Input Signal Properties box by flipping the toggle switch The open loop step input test is now started by applying the desired voltages Vi and V to the system The fan should now be blowing proportionally to V and the chamber temperature should be dropping The settling time should be less than 600 seconds so that the complete step response fits within the chart time scale At this point also stop the blower by pressing the red STOP button DO NOT press EXIT and do not stop the VI Step 14 Make a screen capture of the obtained step response plot once the response has reached steady state which should be around ambient temperature and join a printout to your report Your actual response should look similar to the theoretical temperature cooling plot presented in Figure 3 Document Number 576 Revision 01 Page 15 System Identification Laboratory Manual Step 15 Determine the characteristics of the obtained step response plot by using the Graph Palette located on top of the Chart top left corner Fill up the following table i e Table 5 by measuring the required data points from the actual plot and by carrying out the estimation procedure detailed in Pre Lab Assignment 3 In Tabl
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