EP0281317A1 - Kälteanlagen - Google Patents

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Publication number
EP0281317A1
EP0281317A1 EP88301610A EP88301610A EP0281317A1 EP 0281317 A1 EP0281317 A1 EP 0281317A1 EP 88301610 A EP88301610 A EP 88301610A EP 88301610 A EP88301610 A EP 88301610A EP 0281317 A1 EP0281317 A1 EP 0281317A1
Authority
EP
European Patent Office
Prior art keywords
compressor
period
load
compressor system
higher capacity
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP88301610A
Other languages
English (en)
French (fr)
Inventor
John Michael Walmsley Lawrence
Stuart Lawson
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
PRESTCOLD Ltd
Original Assignee
PRESTCOLD Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GB878704432A external-priority patent/GB8704432D0/en
Application filed by PRESTCOLD Ltd filed Critical PRESTCOLD Ltd
Publication of EP0281317A1 publication Critical patent/EP0281317A1/de
Withdrawn legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B49/00—Arrangement or mounting of control or safety devices
    • F25B49/02—Arrangement or mounting of control or safety devices for compression type machines, plants or systems
    • F25B49/022—Compressor control arrangements
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B5/00—Compression machines, plants or systems, with several evaporator circuits, e.g. for varying refrigerating capacity
    • F25B5/02—Compression machines, plants or systems, with several evaporator circuits, e.g. for varying refrigerating capacity arranged in parallel
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
    • F25B2400/22—Refrigeration systems for supermarkets
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2600/00—Control issues
    • F25B2600/02—Compressor control
    • F25B2600/025—Compressor control by controlling speed
    • F25B2600/0251—Compressor control by controlling speed with on-off operation

Definitions

  • This invention relates to controlling compressor driven vapour compression heat movement systems as used for example in refrigeration and air conditioning for cooling and in heat pump arrangements for heating. Reference will be made primarily to refrigeration systems for explaining the invention in detail.
  • Figure 1 shows a typical refrigeration system in which there are three refrigerated food cabinets.
  • Two graphs in Figure 2 illustrate two alternative known modes of controlling such a system.
  • the mode illustrated in the left-hand graph permits the compressor inlet pressure to fall to extremely low values on occasions, and on these occasions the system is operating very inefficiently (consuming excessive power) and removing moisture excessively from food stored in the cabinets.
  • the mode shown in the right-hand graph avoids these problems but on occasions may result in the com­pressor being switched on and off unacceptably often.
  • the invention aims to provide an improved method of controlling a compressor driven heat movement system which enables the system to be run particularly efficiently, while rarely if ever exceeding the starts per hour rating of the compressor.
  • the invention provides a method of controlling a compressor driven vapour compression heat movement system in which a common compressor system heats or cools a plurality of load units (e.g. refrigerated cabinets, air-conditioning units or heat pump output units) and is operated in cycles each of which include a com­pressor system higher capacity period and a compressor system lower capacity period, characterised in that the lower capacity period is made sufficiently long that when the compressor system is switched to the higher capacity a majority of the load units are demanding heating or cooling and that the higher capacity period is made sufficiently long that when the compressor system is switched to lower capacity one or more of the load units have had their heat­ing or cooling demand satisfied.
  • load units e.g. refrigerated cabinets, air-conditioning units or heat pump output units
  • the compressor system involved can be a single com­pressor as in the embodiment which will be described in detail below. In that event its higher capacity mode will be when the compressor is running and its lower capacity mode will be when it is not running during which period of course its capacity is actually zero.
  • the invention can also be applied where the compressor system includes a plurality of compressors. Then, in the higher capacity mode some of the compressors are running and in the lower capacity mode a lesser fixed number, which may be zero, are running. For example, it may be desirable to have one compressor, which may be relatively small, which always runs so as to prevent liquid refrigerant accumu­lating in the inlet route to a main compressor, which is switched on and off.
  • the low capacity period may be controlled so as to be sufficiently long that when the compressor system is switched to higher capacity a majority of the load units are demanding heating or cooling or, where the operating conditions are sufficiently predictable, the low capacity period may be fixed at a sufficiently long value to ensure that the same condition is met.
  • the control may be exercised in response to various different sensed characteristics and these will be referred to in more detail below.
  • the length of the lower capacity period is controlled in dependence upon the length of the preceding higher capacity period.
  • this will comprise sensing a variable which represents the load on the compressor system and terminating the higher capacity period when the sensed variable indicates that the load on the compressor system is falling.
  • the method of the invention involves turning the compressor system off when one or more of the load units have had their cooling demand satisified i.e. not very long after the pressure has started to fall from the plateau following one or more of the load units ceasing to take refrigerant flow because it is no longer demanding cooling.
  • the higher capacity period may be terminated when the sensed variable reaches a set point value.
  • the invention further comprises sensing the occurrence of a substantially constant level (or "plateau") of load on the compressor system during its higher capacity period and automatically adjusting the set point value to a value which would re­present a load level below said substantially constant level.
  • a substantially constant level or "plateau"
  • the set point value may be automatically adjusted during each cycle to lie at 80% of the plateau level measured in terms of absolute value of the compressor inlet pressure, though values between 60% and 90% may be employed depending on the circumstances.
  • a "substantially constant level" may be defined for the above purpose as the pressure varying by less than 10% over a significant period (e.g. between 30 and 60 seconds) of time.
  • a variable other than pressure is sensed, its set point value may need to be set at a different percentage of the plateau value in order to achieved the desired percentage for the pressure level itself.
  • This preferred feature prevents the occurrence of problems which may otherwise arise as a consequence of the fact that the level of the plateau will not necessarily be the same during each higher capacity period, but may vary from cycle to cycle or drift over a substantial period of time due to various types of change in operating conditions.
  • the plateau will occur at a lower value when a number of cabinets are taken out of service, as sometimes happens in practice. If the set point were fixed, this could result in the compressor being switched off before the plateau level is reached in which case adequate cooling of the remaining cabinets would not be achieved. Inaccurate manual setting of the set point pressure could have the same effect.
  • Drift may also occur in the characteristics of pressure transducers and this could result in undesirable shift of the effective set point in a system where the set point is ostensibly fixed.
  • the refrigeration system of Figure 1 is typical of systems that might be found in, for example, supermarkets, where a numbr of refrigeration cabinets need to be kept cold and have their temperatures controlled. There may be any number of cabinets, six or more being typical, but for simplicity the Figure 1 system is shown with three.
  • a compressor 2 feeds compressed gaseous refrigerant to condenser 4 where it is condensed to liquid which flows to a receiver or reservoir 6. From the receiver it flows on three parallel paths through three evaporators (one per cabinet) indicated at 8 and from the evaporators back to the compressor 2 in gaseous form, the liquid refrigerant having evaporated within the evaporators to produce the cooling effect.
  • expansion valves 10 precede the evaporators 8 and are automatically controlled in known manner so as to maintain correct conditions within the evaporators.
  • Each cabinet is provided with a temperature sensor 12 which exercises thermostatic control over an on/off value 14 for that particular cabinet.
  • each evaporator only takes liquid refrigerant from the receiver when the temperature of its associated cabinet has risen to such a level that it requires further cooling.
  • the left-hand graph in Figure 2 illustrates the use of a control method in which the compressor inlet pressure (which is related to the evaporator temperature when re­frigerant is boiling in the evaporator) is measured and compared with a set point value P off which is set so low that the pressure will fall below it only when all three evaporators have been turned off by their own thermostatic temperature conrol systems. Consequently, so long as any one of the evaporators is working, the compressor will be running, but with its inlet pressure varying according to how many evaporators are on.
  • the compressor inlet pressure would be approximately at either level 3, 2 or 1 illu­ strated in Figure 2 according to whether three, two or one evaporators are operating, and would fall to the level 0 only when all the evaporators were turned off, so that it is only in this condition that the compressor itself would be turned off. Pressure then rises until P on is reached, when the compressor is re-started. With such a system, at times when the demand for refrigeration is low, then the compressor inlet pressure is permitted to become very low, and the evaporator temperatures will be correspondingly low, and in these conditions the efficiency of the system is very poor in terms of heat removal per unit of energy input.
  • a further and substantial disadvantage of this method of control is that the very low evaporator temperature causes excessive icing with the attendant in­convenience and cost of having to defrost the cabinets more often whilst, undesirably, the product in them warms up. Another is that certain food products will have moisture removed from them excessively.
  • Figure 3 shows a downward continuation of part 24 of the pressure curve to illustrate in more detail how a system operating in accordance with the left-hand side of Figure 2 performs.
  • P off is set at a relatively low value and the pressure continues to fall to that value along the broken-line part 28 of the curve.
  • P off is set so low that it will not be reached until the thermostatic valves of all the cabinets have closed i.e. the demand for cooling has become zero.
  • the compressor system is then switched off and the pressure rises along part 30 of the curve until a pre-set value P on is reached at which time the pressure starts to fall again as the compressor system comes into operation, this being along the broken line 32.
  • P on is set at a relatively low value and the pressure continues to fall to that value along the broken-line part 28 of the curve.
  • P off is set so low that it will not be reached until the thermostatic valves of all the cabinets have closed i.e. the demand for cooling has become zero.
  • the compressor system is then switched off and the pressure rises along part 30
  • the invention achieves greater efficiency because of the high level of plateau 22.
  • the compressor inlet pressure initially rises very rapidly because the expansion valves are open, some of the thermostatic valves are open, and so liquid is entering the evaporators and boiling in them. This is shown at part 34 of the curve and during this phase open thermostatic valves may or may not close.
  • the pressure reaches a certain value, to which the expansion valve controls have been set, the expansion valves close and the remaining refigerant in the evaporators boils off during part 36 of the curve.
  • the pressure at the compressor inlet rises only slowly and at a decreasing rate as the gas at that point becomes gradually warmer, this happening along part 38 of the curve.
  • the off period is controlled as will be described so as to be sufficiently long that at the end of it a majority of the cabinets will once again be demanding cooling.
  • Figure 4 shows the variation of the on and off periods of a compressor controlled by the method of the invention over several cycles.
  • the pressure rises and falls are shown as straight lines (though in reality they would be Figure 3-type curves), and the pressures at which the compressor is shown being switched on and off in Figure 4 actually represent the points 40 and 26 in Figure 3, in accordance with the explanation just given.
  • the compressor is run for a period T on which is terminated when the compressor inlet pressure reaches the set point P set .
  • the compressor is then turned off for a calculated period of time T off which may be equal for example to four minutes.
  • T off a calculated period of time
  • the compressor is turned on again until the inlet pressure has again fallen to P set .
  • the off period of the compressor is derived (as explained below with reference to Figure 6) with reference to the time that it takes for compressor inlet pressure to fall to P set after the compressor has been turned on, this time being taken as a characteristic in­dicative of the load on the compressor system.
  • the subsequent period T off is extended so as to increase the length of the subsequent period T on and hence the length of the next cycle. As well as achieving high efficiency, this also tends to ensure that the total cycle time will be long enough for the number of starts per hour of the compressor rarely if ever to exceed its rated value.
  • Figure 5 shows hardware required to operate the control method of Figures 3 and 4, including a compressor inlet pressure sensor 42, an inlet pressure set point device 44, and a source of time pulses 46 all of which feed their outputs to a controller 48.
  • the controller may be a digital controller which operates in accordance with the flow chart shown in Figure 6 and provides an output signal on line 50 which opens and closes a contactor 52 to switch the compressor 2 off and on.
  • the time factor used in con­trolling the compressor cycles is derived with reference to the time pulses produced by the source 46.
  • FIG. 6 is a flow chart showing the operation of the controller 48 in order to perform the control method of Figures 3 and 4. Initially T off/set is set to four minutes, the compressor is then started, compressor inlet pressure is compared with P set until they are equal at which point the compressor is stopped, T on is recorded and the compressor off period T off/set starts to run.
  • T off/set is increased in inverse proportion to the read value of T on , but subject to a maximum of twelve minutes, and during the next operating cycle the compressor is held off for the new increased period of T off/set . If T on shoud become greater than fifteen minutes, then T off/set is reduced in inverse proportion to T on , but subject to a minimum of four minutes, for the next cycle.
  • the pro­gramming of the controller 22 ( Figure 5) will be arranged, empirically if necessary, such that in the particular system the relationship betwen the current demand for cooling as indicated by the length of the on period T on in each cyle, and the length of the off period T off/set as cal­culated by the algorithm, will result in the majority of the cabinets demanding cooling at the end of the off period.
  • the lower limit value, in this instance four minutes, for T off/set sets a lower limit on the frequency with which the compressor can be started and hence protects it against being started at rates beyond its starts per hour rating.
  • the upper limit of twelve minutes on T off/set avoids the temperatures in the cabinets becoming too high.
  • the off period may be terminated in response to a sensed characteristics of the load units.
  • the sensed characteristics may be the condition of the thermostat systems and, for example, the off period may then be terminated when a majority of the load units are demanding cooling as indicated by the conditions of their thermostat systems.
  • Figure 5 shows in chain-dotted lines 56 connections from the three thermostat switches 12 of Figure 1 by means of which the controller is informed of the conditions of the thermostatic switches and hence can be programmed to detect the closure of a majority of them and in response switch on the compressor system via line 24.
  • the off period actually to be fixed at length which can be relied on to allow the majority of the load units to be demanding cooling when the compressor system is switched on, though provision may be made for manual adjustment of the length of the off period in the event that monitoring of the system indicates that the desired pattern of operation is not in practice being achieved.
  • sensing unit 58 may be associated with the power supply to the compressor motor to sense current con­sumption, power consumption, or power factor. Suitable sensing units are readily available and therefore need not be further described.
  • the output from sensing unit 58 is sent by line 60 to the controller 48, where it will be com­pared with the output of the set point device 44 to detect when the load, falling from its plateau level, reaches the set point value.
  • the set point device 44 will be arranged to deliver a set point signal indicative not of a set point pressure, but of a set point current con­sumption, power consumption or power factor value.
  • the lengths of the on period and the off period may be determined independently of each other by separate systems so long as those systems are com­patible with each other.
  • the controller 48 may be pro­grammed so as to monitor a variable indicative of load, for example compressor inlet pressure from pressure sensor 42, the number of thermostatic valves open as indicated on lines 56, or one of the electrical parameters of the power supply as indicated by unit 58, to recognise when that measrued variable does not change by more than 10%, or pre­ferably 5%, during a predetermined period of time, and to treat the detetion of that occurrence as an indication that the plateau level 22 is then occurring. It can further be programmed to then provide on line 62 a signal effective to adjust the set point device 18 so that it will give a set point output value to the controller equal to, for example, 80% of the measured value in absolute units of the plateau level.
  • a variable indicative of load for example compressor inlet pressure from pressure sensor 42, the number of thermostatic valves open as indicated on lines 56, or one of the electrical parameters of the power supply as indicated by unit 58, to recognise when that measrued variable does not change by more than 10%, or pre­
  • the controller 48 may be programmed to operate a modified control method in which, instead of turning the compressor off as soon as the 80% (of plateau) level is reached, the compressor is held on until either a lower, e.g. 50%, level is reached or until a further predetermined time (e.g. one minute) has elapsed, whichever occurs sooner.
  • a lower e.g. 50%
  • a further predetermined time e.g. one minute
  • T on is the time to reach set point rather than the complete period up until actual switch-off. The requirement that a majority of the cabinets demand cooling at the start of the next on period is not disturbed.
  • a method according to the invention can be applied to a multiple-capacity com­pressor system which runs at more than one different level of capacity during a compressor on period, but not at all during the off period. In that event, steps may occur in the plateau level when an additional capacity stage is switched in but nevertheless it is possible to detect the fall in load from the end of the plateau by any of the techniques referred to above.
  • the method of the invetnion may be applied to a compressor system which includes one, preferably relatively low capacity, com­pressor which runs all the time, and a main compressor which is operated in cycles, the purpose of the small com­pressor being to ensure that liquid refrigerant does not accumulate on the outlet sides of the evaporators which will be capable of damaging the main compressor when it is switched on.
  • the continuous running of the small compressor would depress the level of the maximum pressure reached at the inlet of the main compressor as indicated by the broken line curve parts 18 ⁇ and 38 ⁇ shown in Figure 3. The pressure reduction may be even greater than is illustrated.
  • a control method in accordance with the invention can be applied to air conditioning, where the principles involved are the same as those in refrigeration. Further additionallymore, it can be applied to heat pumps. Heat pump systems are equivalent to refrigeration systems except that the purpose is to deliver heat in the condenser rather than remove it in the evaporator. Consequently, in applying the invention to heat pumps, it would be the compressor outlet pressure that is measured rather than its inlet pressure, this being an indication of the variable which it is intended to control, namely the temperature at which re­frigerant is condensing in the condenser.
  • Figure 7 shows how this outlet pressure varies throughout a cycle in a manner opposite to that of the inlet pressure.
  • the outlet pressure rises whilst the com­pressor is on and, provided that a majority of the heat pump output units are demanding heating at the time when the compressor is switched on, there is a plateau as shown at 22 ⁇ at a relatively low pressure level, which represents efficient operation of the heat pump system.
  • the compressor outlet pressure starts rising again as the heating demand from the output units falls, and the on period is then terminated in a similar manner to that used in the refrigeration system described in more detail.
  • the level of the plateau may be sensed, and a set point value may be set in response to that sensing at a level which is a desired percentage higher than the plateau level so as to ensure that the compressor is switched off relatively soon after the demand from the output units starts to fall.
  • the compressor is then held off, for example in the ways already described in relation to a re­frigeration system, for a sufficient period that when it comes on again at least a majority of the output units are again demanding heating.
  • Other arrangements for seeking to match capacity to demand include mechanical arrangements for shutting off a number of the cylinders of a compressor to reduce its capacity, over re-expansion compressors in which the com­ pression ratio can be changed to alter the capacity, and multiple compressors which can be switched on in varying numbers.
  • a control method of the present invention applied to a simple single compressor may achieved similar results to these more complex systems.
  • the invention can also be applied to the control of such systems to improve their efficiency.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Air Conditioning Control Device (AREA)
  • Control Of Positive-Displacement Pumps (AREA)
EP88301610A 1987-02-25 1988-02-25 Kälteanlagen Withdrawn EP0281317A1 (de)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GB8704432 1987-02-25
GB878704432A GB8704432D0 (en) 1987-02-25 1987-02-25 Refrigeration systems
GB8717923 1987-07-29
GB08717923A GB2202966A (en) 1987-02-25 1987-07-29 Control of heating or cooling

Publications (1)

Publication Number Publication Date
EP0281317A1 true EP0281317A1 (de) 1988-09-07

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP88301610A Withdrawn EP0281317A1 (de) 1987-02-25 1988-02-25 Kälteanlagen

Country Status (4)

Country Link
EP (1) EP0281317A1 (de)
JP (1) JPH01502357A (de)
IL (1) IL85537A0 (de)
WO (1) WO1988006703A1 (de)

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DE3540327A1 (de) * 1984-11-22 1986-05-22 Joh. Vaillant Gmbh U. Co, 5630 Remscheid Verfahren zum betreiben mehrerer waermequellen
EP1025403A1 (de) * 1997-09-29 2000-08-09 Copeland Corporation Selbstanpassende steuerung für eine einen spiralverdichtermit pulsbreitenmoduliertem betrieb verwendende kälteanlage
US8157538B2 (en) 2007-07-23 2012-04-17 Emerson Climate Technologies, Inc. Capacity modulation system for compressor and method
US8308455B2 (en) 2009-01-27 2012-11-13 Emerson Climate Technologies, Inc. Unloader system and method for a compressor
USRE44636E1 (en) 1997-09-29 2013-12-10 Emerson Climate Technologies, Inc. Compressor capacity modulation
US10041713B1 (en) 1999-08-20 2018-08-07 Hudson Technologies, Inc. Method and apparatus for measuring and improving efficiency in refrigeration systems
US11280536B2 (en) * 2015-09-30 2022-03-22 Electrolux Home Products, Inc. Temperature control of refrigeration cavities in low ambient temperature conditions

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US7412842B2 (en) 2004-04-27 2008-08-19 Emerson Climate Technologies, Inc. Compressor diagnostic and protection system
US7275377B2 (en) 2004-08-11 2007-10-02 Lawrence Kates Method and apparatus for monitoring refrigerant-cycle systems
US8590325B2 (en) 2006-07-19 2013-11-26 Emerson Climate Technologies, Inc. Protection and diagnostic module for a refrigeration system
US20080216494A1 (en) 2006-09-07 2008-09-11 Pham Hung M Compressor data module
US20090037142A1 (en) 2007-07-30 2009-02-05 Lawrence Kates Portable method and apparatus for monitoring refrigerant-cycle systems
US8393169B2 (en) 2007-09-19 2013-03-12 Emerson Climate Technologies, Inc. Refrigeration monitoring system and method
US8160827B2 (en) 2007-11-02 2012-04-17 Emerson Climate Technologies, Inc. Compressor sensor module
US9140728B2 (en) 2007-11-02 2015-09-22 Emerson Climate Technologies, Inc. Compressor sensor module
US9285802B2 (en) 2011-02-28 2016-03-15 Emerson Electric Co. Residential solutions HVAC monitoring and diagnosis
US8964338B2 (en) 2012-01-11 2015-02-24 Emerson Climate Technologies, Inc. System and method for compressor motor protection
US9480177B2 (en) 2012-07-27 2016-10-25 Emerson Climate Technologies, Inc. Compressor protection module
US9310439B2 (en) 2012-09-25 2016-04-12 Emerson Climate Technologies, Inc. Compressor having a control and diagnostic module
US9551504B2 (en) 2013-03-15 2017-01-24 Emerson Electric Co. HVAC system remote monitoring and diagnosis
US9803902B2 (en) 2013-03-15 2017-10-31 Emerson Climate Technologies, Inc. System for refrigerant charge verification using two condenser coil temperatures
US9638436B2 (en) 2013-03-15 2017-05-02 Emerson Electric Co. HVAC system remote monitoring and diagnosis
CA2908362C (en) 2013-04-05 2018-01-16 Fadi M. Alsaleem Heat-pump system with refrigerant charge diagnostics

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EP1025403A1 (de) * 1997-09-29 2000-08-09 Copeland Corporation Selbstanpassende steuerung für eine einen spiralverdichtermit pulsbreitenmoduliertem betrieb verwendende kälteanlage
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JPH01502357A (ja) 1989-08-17
IL85537A0 (en) 1988-08-31

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