Heat pump compressor crankcase low differential temperature
Contents
1. response at 131 then the compressor operation will be inhibited and the fault indicator 63 will be actuated Knowledgeable personnel noting that the fault indicator 63 is actuated may take corrective steps one of which is to permit the passage of enough time to permit the crankcase heater to func tion In due course the crankcase temperature should increase to the point where the output from 130 will be a yes response 132 to flow through 120 to block 121 et seq so as to successively enable compressor operation and to turn off the fault indicator 63 On the other hand a persistent fault indication at fault indicator 63 would necessitate further investigation by appropriate servic ing personnel to determ ne and correct the cause of the fault As indicated above an Intel Model 8049 micro processor may be used to practice the subject invention as an assistance reference may be made to INTEL MCS 487M Family of Single Chip Microcomputer s User s Manual a 1978 copyrighted manual of the Intel Corporation Santa Clara California 95051 As a further assistance Appendix A hereto and forming a part hereof comprises a table of machine readable in struction for controlling the aforesaid Intel Model 8049 microprocessor for use in the present invention While we have described a preferred embodiment of our invention it will be understood that the invention is limited only by the scope of the following claims I claim 1 A2. a Carrier Corporation heat pump comprising outdoor unit model No 38CQ033300 and indoor unit model No 40AQ036300JR may be used for the basic heat pump unit depicted in FIG 1 1 components 10 12 14 15 16 and 19 As indicated above multiplexer 40 has applied thereto at 32 and 35 analog signals representative of TODA and TCC respectively The function of the multiplexer 40 is to supply one or the other of the two input signals in analog form to the output 53 thereof depending upon the nature of the control signal being applied to the multiplexer 40 via a lead 52 from the microprocessor 50 1 the microprocessor provides control for the multiplexer 40 to select which of the two input signals is applied to output 53 Output 53 is applied as the input to a standard analog to digital converter 54 herein sometimes referred to as A D having output 55 connected as a second input to the micro processor 50 and also having an input 56 for receiving controlling instructions from the microprocessor 50 The output from analog to digital converter 54 at out put 55 is a signal in digital form indicative of the analog signal applied to input 53 The microprocessor 50 has an output 62 connected to fault indicator 63 The apparatus further includes the above mentioned fault reset means 65 having an output 66 which constitutes a third input to the microprocessor 50 A suitable microprocessor that may be used in the present in
3. in the line may during times that the system is at rest settle in the crankcase of the compres sor This is because in the system OFF condition the refrigerant in the reverse cycle heat pump will tend to condense at the location which has the lowest tempera ture in the system The coldest location typically is in the outdoor unit where the compressor is usually lo cated when a system is in the heating mode because the outdoors is generally much cooler than the indoors for this case Thus the refrigerant may settle i e con dense in the crankcase of the compressor the refriger ant will continue condensing at such coldest location until a point of equilibrium is reached i e an equilib rium of liquid and gaseous refrigerant at the vapor pres sure corresponding to the temperature at such coldest location It has been recognized heretofore that it is important not to start up the compressor when the re frigerant has settled in the compressor crankcase as it is known that the refrigerant in the crankcase will tend to mix with the compressor lubricating oil therein It is likely that this mixture is present at equilibrium because the mixture causes a reduction in the total volume of liquid as compared with a system containing separate pools of oil and refrigerant thus enabling more refriger ant to condense at the same equilibrium vapor pressure Thereafter when the compressor is started if there is refrigerant in the
4. T MICRO PROCESSOR U S Patent Dec 2 1980 Sheet 1 of 2 4 236 379 FIG 1 20 21 Z 2 210 OUTDOOR MEANS INDOOR HEAT HEAT EXCHANGE EXCHANGE COIL COIL pue T law pee TEMPERATURE SENSOR EM CONTROL E 1872 42 44 OUTDOOR AIR ntm mn COMPRESSOR Lemon THERMOSTAT STAT E LT TODAS CRANKCASE T TEMPERATURE INDICATOR RESET 17 SENSOR TCCS A ANALOG TO DIGITAL CONVERTER MULTIPLEXER U S Patent Dec 2 1980 Sheet 2 of 2 4 236 379 FIG 2 LEGEND C ENTRY POINT OPERATION OR INSTRUCTION BLOCK LOGIC lt gt INSTRUCTION BLOCK DIRECTION P oF FLOW C JUNCTION CONNECT TCCS TO A D r INHIBIT COMPRESSO OPERATION 33 R 15 COMPRESSOR RUNNING 4 236 379 1 HEAT PUMP COMPRESSOR CRANKCASE LOW DIFFERENTIAL TEMPERATURE DETECTION AND CONTROL SYSTEM BACKGROUND OF THE INVENTION Heat pumps have been used for many years in the heating and cooling of buildings their popularity has substantially increased in recent times because of the soaring costs of energy used for heating and cooling Heat pumps become more and more attractive for the function of heating and cooling of buildings because of their operating efficiency i e their cost effectiveness However heat pumps do have some problems one of these is connected with the fact that in many systems the refrigerant
5. United States Patent Mueller 54 75 73 21 22 51 52 58 HEAT PUMP COMPRESSOR CRANKCASE LOW DIFFERENTIAL TEMPERATURE DETECTION AND CONTROL SYSTEM Inventor Dale A Mueller St Paul Minn Assignee Honeywell Inc Minneapolis Minn Appl No 868 Filed Jan 4 1979 Int CH3 o eS F04B 49 10 F25B 49 00 US Ck irirna 62 126 62 193 62 472 417 32 Field of Search 62 193 211 127 126 62 472 228 R 229 417 32 OUTDOOR HEAT EXCHANGE COIL REVERSING OUTDOOR AIR TEMPERATURE SENSOR TODAS TCCS MULTIPLEXER DIGITAL gt _ EXPANSION EXPANSK CRANKCASE TEMPERATURE SENSOR ANALOG TO CONVERTER 11 4 236 379 45 Dec 2 1980 56 References Cited U S PATENT DOCUMENTS 4 004 431 1 1977 Hildreth 62 472 4 136 822 1 1979 236 49 Primary Examiner William E Wayner Attorney Agent or Firm Roger W Jensen 57 ABSTRACT A compressor crankcase low differential temperature detection and control system for a reverse cycle refrig eration system for detecting an abnormally low temper ature crankcase and for controlling the system in re sponse to such fault detection by inhibiting the opera tion of the compressor and for providing a fault indica tion 8 Claims 2 Drawing Figures 0 INDOOR HEAT EXCHANGE ROOM THERMOSTAT STAT FAULT INDICATOR RESE
6. as TODAS having output 32 on which is an output signal indicative of the outdoor air temperature hereinafter sometimes ferred to as TODA TODA on output 32 comprises one of two separate inputs to a multiplexer 40 to be described in more detail below The detection and con trol system further comprises a crankcase temperature sensing means 34 hereinafter sometimes referred to as TCCS having an output 35 on which is available an output signal indicative of the crankcase temperature of the compressor this temperature hereinafter sometimes being referred to as TCC such TCC signal on 35 comprising the second input to multiplexer 40 The detection and control system further includes a room thermostat 42 hereinafter sometimes referred to as STAT which responds to the temperature of a room or space in a building or the like the temperature of which is to be controlled by the reverse cycle refrigera tion system Room thermostat 42 is depicted as having a first output 43 connected to the control 18 for the reversing valve 16 A second output 44 of STAT 42 is connected to a microprocessor 50 and also through a set of contacts 46 and a connection means 45 to the controller 15 of compressor 14 Contacts 46 are con tained within a subsection 47 of the microprocessor 50 and both 47 and 50 will be described in more detail below A Honeywell Inc Model T872 heating cooling ther mostat may be used for the room t
7. block 106 measure TCC Thus instructions 103 104 105 and 106 collectively are associated with the measurement of the TODA and TCC temperatures utilizing the aforedescribed multi 4 236 379 5 plexer 40 analog to digital converter 54 and micro processor 50 The flow from block 106 is to a logic instruction 107 gt Trer having a yes response 108 and a no response 109 Trer is a reference temperature or set point with respect to which TODA is compared and is selected to be a temperature high enough so that refrig erant would not normally condense in the crankcase or in the outdoor coil i e the refrigerant would stay in gaseous form in the crankcase and in the outdoor coil and instead the refrigerant would condense in the cooler indoor coil A representative Trer would be 80 F If TODA is greater than Trer then there is not likely to be a problem with refrigerant mixing with the oil of the compressor crankcase hence the yes response 108 flows via a junction 120 to an instruction block 121 enable compressor operation the flow from which is to instruction block 122 turn off fault indicator the flow from which is to instruction block 123 pause the flow from which is via a junction 124 to a logic instruc tion block 125 is compressor running having a yes response 126 and a no response 127 Thus a yes re sponse at 108 from logic block 107 is representative of an absence of any possible pr
8. compressor crankcase low differential tempera ture detection and control system hereinafter control system for a reverse cycle refrigeration system here inafter system for heating and cooling an enclosure wherein said system comprises refrigerant compression means including crankcase heating means refrigerant compression control means an indoor coil an outdoor coil and refrigerant conduit means connecting said compression means and said coils said control system comprising outdoor air temperature sensing means hereinafter TODAS having an output indicative of outdoor air temperature hereinafter TODA compressor crankcase temperature sensing means hereinafter TCCS having an output indicative of the temperature hereinafter TCC of the crankcase of said refrigerant compression means enclosure temperature sensing means hereinafter STAT having an output indicative of a demand for heating or cooling of the enclosure and controller means having operative connections to said TODAS TCCS and STAT so as to receive the outputs thereof said controller means includ ing circuit connect disconnect means selectively interconnecting said STAT output to said refriger ant compression control means whereby when said STAT output is connected thereto said com pression means is enabled to operate in response to a demand from said STAT for heating or cooling and when said STAT output is disconnected th
9. crankcase oil then such refrigerant will tend to boil due to the low pressure on the suction side of the compressor where the crankcase is located and when this happens the refrigerant will agitate the oil causing the oil to foam this foam then is apt to be carried into the intake of the compressor and thereafter be pumped out by the compressor into the refrigerant lines When this happens the oil may be pumped out of the crankcase thus causing the compressor to run with out lubricant unti the oil migrates back having trav elled throughout the complete refrigeration system i e back through the refrigerant tubes and into the crank case Such running without lubrication may cause se vere wear and overheating of the compressor thus shortening the life of the compressor and causing ex pense inconvenience and discomfort Another related problem is that the oil refrigerant foam mixture is not as compressible as refrigerant vapor this can cause slug ging and eventual damage to the valves of the com pressor All of the foregoing has heretofore been recognized and various prior art techniques have been proposed for dealing with the problem Thus at this time many heat pump compressors have some means for heating the crankcase of the compressor so that the crankcase will not be the lowest temperature point in the heat pump system thus preventing the refrigerant from condens 25 40 45 60 65 2 ing in the crankcas
10. e and thus preventing the above described damages to the compressor Thus a frequent practice has been in connection with the installation of new heat pump system to refrain from starting up the compressor for a period of time allowing the crankcase heating means to vaporize any accumulated refrigerant in the crankcase However frequently in practice ei ther through carelessness or ignorance the heat pump installer will energize or turn on the compressor imme diately i e without waiting for the warming up inter val and hence cause damage to the compressor Also a crankcase heater failure will cause every compressor start with potential to dying Also an extended heater power loss could cause foaming It is an object of our invention to provide a new and effective system for detecting compressor crankcase low differential temperatures and for inhibiting the operation of the heat pump compressor until such time as the crankcase temperature increases above the out door air temperature to a safe level SUMMARY OF THE INVENTION The present invention is a compressor crankcase low differential temperature detection and control system for a reverse cycle refrigeration system comprising the usual refrigerant compression means including crank case heating means indoor and outdoor coils refriger ant conduit means connecting the compression means and the coils and refrigerant compression control means In particular the co
11. er control sys tem for a reverse cycle refrigeration system hereinaf ter system for heating and cooling an enclosure 15 20 25 30 35 45 50 55 60 65 8 wherein said system comprises refrigerant compression means including crankcase heating means refrigerant compression control means an indoor coil an outdoor coil and refrigerant conduit means connecting said compression means and said coils said control system comprising outdoor air temperature sensing means hereinafter TODAS having an output indicative of outdoor air temperature hereinafter TODA compressor crankcase temperature sensing means hereinafter having an output indicative of the temperature hereinafter of the crankcase of said refrigerant compression means enclosure temperature sensing means hereinafter STAT having an output indicative of a demand for heating or cooling of the enclosure and controller means having operative connections to said TODAS TCCS and STAT so as to receive the outputs thereof said controller means includ ing circuit connect disconnect means selectively interconnecting said STAT output to said refriger ant compression control means whereby when said STAT output is connected thereto said com pression means is enabled to operate and when said STAT output is disconnected therefrom said com pression means is inhibited from operating said controller
12. ere from said compression means is inhibited from 4 236 379 7 operating said controller means being effective to inhibit said compression means from operating whenever value of TCC minus TODA is less than a preselected amount and said controller means being further characterized by permitting operation of said compression means whenever TODA is greater than a predetermined value 2 Apparatus of claim 1 further characterized by said preselected amount being 10 Fahrenheit when TODA is less than 55 F and 6 F when TODA is greater than 55 F 3 Apparatus of claim 1 further characterized by i said control system including fault indicator means and ii said fault indicator means being actuated upon as aforesaid said controller means inhibiting said compres sion means from operating 4 Apparatus as described in claim 3 further charac terized by said controller means permitting operation of said compression means whenever TODA is greater than a predetermined value 5 Apparatus of claim 1 further characterized by said preselected amount being in the range of 6 to 15 degress Fahrenheit 6 Apparatus of claim 4 further characterized by said preselected amount being in the range of 6 to 15 degrees Fahrenheit 7 Apparatus of claim 6 further characterized by said predetermined value being in the range of 80 F 10 F 8 Compressor crankcase low differential temperature detection and control system hereinaft
13. hange coil 12 a refrigerant compres sion means or compressor 14 and a compressor control ler 15 receiving energization from an appropriate source 17 of electrical energy Also associated with the compressor 14 is a crankcase heater 19 receiving energi zation from source 17 Refrigerant conduit means are 4 236 379 3 provided for interconnecting the coils and the compres sor the conduit means including the usual reversing valve 16 having a controller 18 an expansion means 20 and appropriate interconnecting piping 21 26 The sys tem above described is representative of prior art sys tems such as that shown in U S Pat No 3 170 304 As is well known such systems function whenever the build ing thermostat is calling for heating or cooling to cause compressor 14 to operate If heating is being demanded then the compressed hot refrigerant from the compres sor 14 will be routed through the reversing valve 16 toward the indoor heat exchange coil 10 where its heat is given up to heat the indoor air Conversely if cooling of the building is being demanded then the hot refriger ant from the compressor is routed through the reversing valve to the outdoor heat exchange coil 12 where the refrigerant is cooled for subsequent use indoors to cool the building The compressor crankcase low temperature detec tion and control system as depicted in FIG 1 comprises an outdoor air temperature sensing means 31 hereinaf ter sometimes referred to
14. hermostat 42 depicted in FIG 1 the Model T872 being of the bimetal operated mercury switch type including switch means for pro viding the heating cooling control signals and also for controlling a plurality of auxiliary heating means As will be understood whenever STAT 42 calls for either heating or cooling of the controlled space then a con trol signal is effectively supplied on outputs 43 and 44 thereof the control signal at 43 functioning to position via control 18 the reversing valve 16 to the proper orientation for either heating or cooling of the building and at 44 to advise microprocessor 50 that heating or cooling has been called for by STAT 42 The control signal at 44 is transmitted through the normally closed contacts 46 and connection 45 to control the compres sor 14 from a rest or off condition to an operating or on condition and is also applied to microprocessor 50 to indicate a demand for compressor 14 operation The Honeywell Model T872 STAT further includes a fault 10 20 25 40 45 60 65 4 indicator 63 and a fault reset means 65 i e a switch both of which will be described in further detail below For convenience elements 42 63 and 65 as above de scribed are shown adjacent to one another in FIG 1 all having the common designator T872 Further Honeywell Inc platinum film resistance type temperature sensors models C800A and C800D may be used for TODAS 31 and TCCS 34 respectively Also
15. means being effective to inhibit said compression means from operating unless one of the following conditions is satisfied 1 TODA is above a predetermined value or 2 the value of TCC minus TODA is greater than a preselected amount
16. ntrol system comprises out door air temperature sensing means having an output indicative of outdoor air temperature crankcase tem perature sensing means having an output indicative of the crankcase temperature enclosure e g building temperature sensing means having an output indicative of a demand for either heating or cooling of the enclo sure fault indicator means and controller means The controller means has operative connections to the three recited temperature sensing means so as to receive the outputs thereof The controller means further has a circuit connect disconnect means which selectively interconnects the enclosure temperature sensing means to the refrigerant compression control means The con troller functions so that it is effective to inhibit the com pression means from operating if both the outdoor air temperature is below a predetermined value and if the value of the crankcase temperature minus the outdoor air temperature is greater than a preselected amount BRIEF DESCRIPTION OF THE DRAWINGS FIG 1 is a block diagram of a compressor crankcase low temperature detection and control system for a reverse cycle refrigeration system embodying the pres ent invention and FIG 2 is a flow chart for the control of the apparatus depicted in FIG 1 DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG 1 the reverse cycle refrigeration system comprises an indoor heat exchange coil 10 an outdoor heat exc
17. oblem and hence is com patible with normal operation vis block 121 designates the enabling of compressor operation and 122 is repre sentative of the fault indicator 63 being turned off The block 123 pause is indicative of the periodic recyl cling of the system i e the periodic functioning of the system to determine whether or not there is a problem with the temperature of the crankcase of the compres sor a frequency of 120 cycles per hour having been found satisfactory Flow from 123 via 124 into logic block 125 is compressor running results in either a yes or a no response a yes response 126 flows back to junction 124 and thence to 125 in a closed loop fashion however a no response 127 indicating that the com pressor is not running causes flow back to junction 102 so that the test at logic instruction block 107 may be repeated When TODA is not greater than TREF then the no response 109 from logic instruction 107 causes flow to a logic instruction block 130 TCC minus TODA is greater than having no response 131 and a yes response 132 Logic instruction block 130 thus pro vides a comparison between i AT i e the difference in magnitude between the compressor crankcase tem perature TCC and the outdoor air temperature TODA and ii AT mzn where AT yrvis a predetermined value If AT is greater than AT yrw then this is indicative of a safe operating condition i e the crankcase temperature being
18. sufficiently greater than the outdoor air tempera ture so as to confirm that the crankcase heating means has been operated a sufficient length of time so as to boil away any refrigerant that otherwise might be comin gled with the oil in the crankcase Such safe operating condition causes a yes response 132 to flow via junction 120 to 121 et seq A value of AT iw of 10 has been found satisfactory for TODA less than 55 F and 6 F for TODA greater than 55 F However if the crank case temperature is not high enough then the no re sponse 131 from 130 will cause flow to an instruction bloc 133 inhibit compressor operation the flow from which is back to junction 10 described above via a con nection 135 Thus if the crankcase temperature is too low in comparison to the outdoor air temperature this is indicative of a potential severe problem as described aforesaid thus the no response at 131 causes two event 20 25 35 45 50 55 60 65 6 s operations The first is the inhibiting of the compres sor operation block 133 is indicative of microprocessor 50 operating to open contacts 46 to prevent STAT 42 commanding operation of compressor 14 The second operation resulting from a no response 131 is the actua tion of fault indicator 63 by block 134 The closing of the loop by 135 back to 132 permits the test to be re peated as long as the response from logic instruction 130 continues 10 a no
19. vention as a component of the system de picted in FIG 1 is the Intel Corporation Model 8049 a suitable representative analog to digital converter for use to provide the function of block 54 in FIG 1 is the Texas Instrument Inc Model TL505C see TI Bulletin DLS 12580 and an appropriate multiplexer is the Mo torola Inc Model 14051 It will be understood by those skilled in the art that the functional interconnections depicted in FIG 1 are representative of one or more electrical wires or pipes as the case may be as dictated by the specific equipment used The detailed operation of the detection and control system of FIG 1 may be more specifically understood by reference to the flowchart depicted in FIG 2 where reference numeral 101 designates an entry point sys tem power applied reflecting the status of the heat pump being powered up i e power 17 being applied to compressor controller 15 and crankcase heater 19 and appropriate energization being applied to any other of the depicted apparatus requiring same The system then flows via junction 102 to instruction block 103 connect TODAS to A D this being indicative of the TODA signal on output 32 being applied via multiplexer 40 to the analog to digital A D converter 54 The flow from 103 is to operation or instruction block 104 mea sure TODA the flow from which is to instruction block 105 connect TCCS to A D the flow from which is to instruction
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