CN109028496B

CN109028496B - System and method for controlling variable capacity compressor

Info

Publication number: CN109028496B
Application number: CN201810558547.1A
Authority: CN
Inventors: 亨格·M·范; 沙恩·J·安格尔; 爱德华·J·特鲁多; 凯坦·索娃尼
Original assignee: Emerson Climate Technologies Inc
Current assignee: Copeland LP
Priority date: 2014-04-01
Filing date: 2015-04-01
Publication date: 2020-12-08
Anticipated expiration: 2035-04-01
Also published as: CN106133318A; IN2014MU01491A; KR101922958B1; KR20180078336A; EP3126676A1; EP3126676A4; CN106133318B; EP3126676B1; EP3800354B1; KR20160138571A; EP3800354A1; CN109028496A

Abstract

Systems and methods for controlling a variable-capacity compressor are disclosed. A climate control system comprising: a variable-capacity compressor unit operable in a first capacity mode and a second capacity mode higher than the first capacity mode; and a control module configured to control the variable-capacity compressor unit, wherein the control module is configured to switch the compressor unit from an off state to a first capacity mode in response to receiving the demand signal, wherein the control module is configured to selectively switch the compressor unit from the first capacity mode to a second capacity mode based on a comparison of: a comparison of the outdoor air temperature to the predetermined temperature value, and a comparison of the predetermined second capacity runtime threshold to a previous second capacity runtime, wherein the previous second capacity runtime is a previous amount of time for the compressor unit to operate in the second capacity mode from a previous start-up of the second capacity mode until a previous demand is met.

Description

System and method for controlling variable capacity compressor

The present application is a divisional application of patent application with international application numbers PCT/US2015/023889, international application numbers 2015-4-1, international application numbers 201580018201.7, entitled "system and method for controlling variable capacity compressor" filed by the applicant to the chinese patent office at 30/9/2016.

Cross Reference to Related Applications

This application claims priority to U.S. patent application No. 14/674,980 filed on 31/3/2015 and also claims benefit to U.S. provisional application No. 61/973, 528 filed on 1/4/2014. This application also claims the benefits and priority of Indian patent application No. 1491/MUM/2014, filed on 29/4/2014. The entire contents of the above application are incorporated herein by reference.

Technical Field

The present disclosure relates to a climate control system having a variable capacity compressor.

Background

This section provides background information related to the present disclosure and is not necessarily prior art.

A climate control system, such as a heat pump system, a refrigeration system, or an air conditioning system, may include a fluid circuit having an outdoor heat exchanger, an indoor heat exchanger, an expansion device (expansion device) disposed between the indoor and outdoor heat exchangers, and a compressor circulating a working fluid (e.g., refrigerant or carbon dioxide) between the indoor and outdoor heat exchangers. Varying the capacity of the compressor can affect the energy efficiency of the system and the speed at which the system can heat or cool a room or space.

Disclosure of Invention

This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

In one form, the present disclosure provides a climate control system including a variable capacity compressor unit and a control module that controls the compressor unit. The compressor unit is operable in a first capacity mode and a second capacity mode higher than the first capacity mode. The control module may be configured to switch the compressor unit between the off state, the first capacity mode, and the second capacity mode based on the demand signal and the outdoor air temperature data. The control module may include outdoor air temperature sensing and demand signal sensing circuitry.

In some embodiments, the control module receives the demand signal from a single stage thermostat disposed within a space to be cooled by the climate control system.

In some embodiments, a climate control system may include: an indoor heat exchanger receiving a working fluid from the compressor unit; and a blower that forces air into a heat-to-fluid relationship with the working fluid in the indoor heat exchanger. The blower may include, for example, a fixed speed motor or a variable speed motor capable of operating at a selectable fixed speed tap.

In some embodiments, the control module switches the compressor unit between the first capacity mode and the second capacity mode based on a compressor run time.

In some embodiments, the compressor run time is a run time of the compressor unit in the second capacity mode.

In some embodiments, the run time of the compressor unit in the second capacity mode is equal to a previous run time in the second capacity mode during a previous demand period. That is, the operation time of the compressor unit in the second capacity mode may be adaptively compared with the previous operation time in the second capacity mode on a cycle-by-cycle basis.

In some embodiments, the control module switches the compressor unit from the first capacity mode to the second capacity mode based on whether a previous run time was greater than five minutes.

In some embodiments, the control module switches the compressor unit from the first capacity mode to the second capacity mode based on whether the compressor unit has been operating in the first capacity mode for greater than a predetermined period of time.

In some embodiments, a climate control system includes a comfort control interface configured to be placed at one of a plurality of comfort settings. A first comfort setting in the comfort setting may correspond to an energy efficient mode of operation and a second comfort setting in the comfort setting may correspond to a high performance mode of operation.

In some embodiments, the control module is configured to compare the compressor run time to a low capacity run time threshold and a high capacity run time threshold.

In some embodiments, the control module is configured to: the compressor is switched between the low-capacity mode and the high-capacity mode based on a comparison of the compressor operating time with the first capacity operating time and based on a comparison of the compressor operating time with the second capacity operating time.

In some implementations, the low-capacity runtime threshold and the high-capacity runtime threshold are determined based on a selected one of the comfort settings.

In some embodiments, the control module operates the compressor unit in one of the first capacity mode and the second capacity mode based only on the demand signal, the outdoor air temperature data, and the at least one compressor run time.

In some embodiments, the at least one compressor run time is a run time of the compressor unit in the second capacity mode.

In some embodiments, the compressor unit includes only one compressor (e.g., a variable capacity compressor). In other embodiments, the compressor unit may include a plurality of variable capacity and/or fixed capacity compressors.

In another form, the present disclosure provides a method of controlling a compressor that is operable in a first capacity mode and a second capacity mode that is higher than the first capacity mode. The method can comprise the following steps: receiving a demand signal from a thermostat; setting a low-volume runtime threshold based on a user-selected comfort level; operating the compressor in a low-capacity mode in response to receiving the demand signal; comparing the run time of the compressor to a low capacity run time threshold; and switching the compressor from the low-capacity mode to the high-capacity mode based on a comparison of the operating time and the low-capacity operating time threshold.

In some embodiments, the method includes setting a high-volume run-time threshold based on a user-selected comfort level.

In some embodiments, the method comprises: the compressor is switched from the high-capacity mode to the low-capacity mode based on a comparison of the operating time and the high-capacity operating time threshold.

In another form, the present disclosure provides a method of controlling a compressor. The compressor is operable in a first capacity mode and a second capacity mode higher than the first capacity mode. The method can comprise the following steps: receiving a demand signal from a thermostat; comparing the outdoor air temperature to a predetermined temperature value; comparing the operation time of the compressor with a predetermined operation time value; in response to receiving the demand signal, the compressor is operated in one of the first capacity mode and the second capacity mode based on a comparison of the outdoor air temperature to a predetermined temperature value and a comparison of the run time to a predetermined run time value.

In some embodiments, the method comprises: if the outdoor air temperature is less than the predetermined temperature value and if the total operating time of the compressor from the receipt of the demand signal is less than the predetermined operating time value, the compressor is operated only in the first capacity mode until the demand is satisfied.

In some embodiments, the method comprises: the compressor is switched from the first capacity mode to the second capacity mode based on a comparison of the operating time to a predetermined operating time value.

In some embodiments, the method comprises: operating the compressor in a first capacity mode until the run time exceeds a predetermined run time value; and switching the compressor out of the first capacity mode after the run time exceeds a predetermined run time value.

In some embodiments, the predetermined run time value is a previous amount of time that the compressor was previously operating in the second capacity mode from the initiation of the second capacity mode until the satisfaction of the previous demand signal.

In some embodiments, the compressor is operated in one of the first capacity mode and the second capacity mode based only on the demand signal, the outdoor air temperature, and the at least one compressor run time.

In another form, the present disclosure provides a working fluid circuit that may include: an indoor heat exchanger, an outdoor heat exchanger, an expansion device, a variable-capacity compressor, and a control module. The outdoor heat exchanger may be in fluid communication with the indoor heat exchanger. The expansion device may be disposed between the indoor heat exchanger and the outdoor heat exchanger. The variable capacity compressor may circulate a working fluid between the indoor heat exchanger and the outdoor heat exchanger. The control module may control the compressor and operate the compressor in one of a low-capacity mode and a high-capacity mode based on the demand signal, the outdoor air temperature data, and the compressor run time.

In some embodiments, the working fluid circuit includes a single stage thermostat in communication with the control module and configured to generate the demand signal. The demand signal is common to operation in the first capacity mode and the second capacity mode.

In some embodiments, the working fluid circuit includes an indoor blower configured to force air into a convective heat exchange relationship with the indoor heat exchanger. The indoor blower has a constant speed motor.

In some embodiments, the control module switches the compressor between the first capacity mode and the second capacity mode based on another compressor run time.

In some embodiments, the working fluid circuit includes a comfort control interface configured to be placed at one of a plurality of comfort settings. A first comfort setting in the comfort setting may correspond to an energy efficient mode of operation and a second comfort setting in the comfort setting may correspond to a high performance mode of operation.

In some embodiments, the control module is configured to compare the compressor run time to a first capacity run time threshold and a second capacity run time threshold.

In some embodiments, the control module is configured to switch the compressor between the first capacity mode and the second capacity mode based on a comparison of the compressor run time to the first capacity run time and based on a comparison of the compressor run time to the second capacity run time.

In some implementations, the first and second capacity run time thresholds are determined based on a selected one of the comfort settings.

In another form, the present disclosure provides a climate control system comprising: a variable-capacity compressor unit operable in a first capacity mode and a second capacity mode higher than the first capacity mode; and a control module configured to control the variable-capacity compressor unit, wherein the control module is configured to switch the variable-capacity compressor unit from an off state to the first capacity mode in response to receiving a demand signal, and wherein the control module is configured to selectively switch the compressor unit from the first capacity mode to the second capacity mode based on a comparison of: a comparison of the outdoor air temperature to a predetermined temperature value, and a comparison of a predetermined second capacity runtime threshold to a previous second capacity runtime, wherein the previous second capacity runtime is a previous amount of time for the compressor unit to operate in the second capacity mode from a previous start-up of the second capacity mode until a previous demand is met.

In another form, the present disclosure provides a method of controlling a compressor unit operable in a low-capacity mode and a high-capacity mode, the method comprising: receiving a demand signal from a thermostat; setting a low-volume runtime threshold based on the selected comfort level; operating the compressor unit in the low-capacity mode in response to receiving the demand signal; comparing the run time of the compressor unit to the low capacity run time threshold; and switching the compressor unit from the low-capacity mode to the high-capacity mode based on a comparison of the run time to the low-capacity run time threshold.

In another form, the present disclosure provides a climate control system comprising: a compressor unit operable in a low-capacity mode and a high-capacity mode; and a control module configured to control the compressor unit, wherein the control module is configured to switch the compressor unit from an off state to the low-capacity mode in response to receiving a demand signal, and wherein the control module is configured to: setting a low-volume runtime threshold based on a user-selected comfort level; comparing the run time of the compressor unit to the low capacity run time threshold; and switching the compressor unit from the low-capacity mode to the high-capacity mode based on a comparison of the run time to the low-capacity run time threshold.

Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

Drawings

The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

FIG. 1 is a schematic diagram of a heat pump system having a variable capacity compressor according to the principles of the present disclosure;

FIG. 2 is a state diagram illustrating a method and algorithm for controlling the variable-capacity compressor of FIG. 1;

FIG. 3 is a graph illustrating a relationship between low and high capacity levels for a compressor, a thermal load of a house, and an outdoor air temperature for an example climate control system sized for an example house;

FIG. 4 is a graph illustrating the percentage of run time for the low-capacity mode versus the high-capacity mode for a range of outdoor air temperatures;

FIG. 5 is a state diagram showing another method and algorithm for controlling the variable-capacity compressor of FIG. 1;

FIG. 6 is a look-up table including low capacity run time thresholds for a given comfort and a given outdoor ambient air temperature;

FIG. 7 is a look-up table including high capacity run time thresholds for a given comfort and a given outdoor ambient air temperature;

FIG. 8 is a graph depicting low and high capacity run times during operation at a first comfort level;

FIG. 9 is a graph depicting low and high capacity run times during operation at a second comfort level;

FIG. 10 is a graph depicting low and high capacity run times during operation at a third comfort level; and

FIG. 11 is a schematic diagram of a comfort control interface and control module.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

Detailed Description

Example embodiments are now described more fully with reference to the accompanying drawings.

Example embodiments are provided so that this disclosure will be thorough and will fully convey the scope to those skilled in the art. Numerous specific details are set forth, such as examples of specific components, devices, and methods, in order to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, and that example embodiments may be embodied in many different forms and should not be construed as limiting the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms "a", "an" and "the" may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises," "comprising," "including," and "having" are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not necessarily to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.

When an element or layer is referred to as being "on," "engaged to," "connected to," or "coupled to" another element or layer, it can be directly on, engaged, connected or coupled to the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on," "directly engaged to," "directly connected to" or "directly coupled to" another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements (e.g., "between …" and "directly between …", "adjacent" and "directly adjacent", etc.) should be understood in a similar manner. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as "first," "second," and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

Spatially relative terms, such as "inner," "outer," "below … …," "below … …," "below," "over … …," "over," and the like, may be used herein to describe one element or feature's relationship to another element or feature as illustrated in the figures for ease of description. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the example term "below … …" can encompass both an orientation above … … and below … …. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

Referring to fig. 1, a system 10 is provided that may include a variable capacity compressor (or variable capacity compressor bank) 12, an outdoor heat exchanger 14, an outdoor blower 15, a first expansion device 16, a second expansion device 17, an indoor heat exchanger 18, and an indoor blower 19. In the particular configuration shown in fig. 1, the system 10 is a heat pump system having a reversing valve 20, the reversing valve 20 being operable to control the direction of working fluid flow through the system 10 to switch the system 10 between heating and cooling modes. In some configurations, the system 10 may be an air conditioning system or a refrigeration system, for example, and may operate only in a cooling mode. As described in more detail below, the control module 22 may control operation of the compressor 12 and may switch the compressor 12 between the low-capacity mode and the high-capacity mode based on data received from the outdoor-air-temperature sensor 24, a signal received from the thermostat 26, a comparison between the operating time T of the compressor 12 and a predetermined low-capacity operating time threshold T1, and a comparison of a previous high-capacity operating time threshold T2 and a predetermined value. The control module 22 may minimize or reduce the adoption of high-volume mode operation to minimize or reduce energy usage while maintaining acceptable comfort within the space to be heated or cooled.

Compressor 12 may be, or may include, for example, a scroll compressor, a reciprocating compressor, or a vane-type compressor, and/or any other type of compressor. The compressor 12 may be any type of variable capacity compressor capable of operating in at least a low capacity mode and a high capacity mode. For example, the compressor 12 may be, or may include, a multi-stage compressor, a set of independently operable compressors, a multi-speed or variable-speed compressor (with a variable-speed or multi-speed motor), a compressor with modulated suction (e.g., impeded suction), a compressor with fluid injection (e.g., an economizer circuit), a pulse width modulated scroll compressor (e.g., a digital scroll compressor) configured for scroll separation, a compressor with a variable volume ratio valve configured to leak intermediate pressure working fluid, or a compressor with two or more of the above capacity modulation devices. It will be appreciated that the compressor 12 may include any other additional or alternative structure for varying its capacity and/or the operating capacity of the system 10. It will be appreciated that the low-capacity mode and/or the high-capacity mode may be a continuous, steady-state operating mode, or the compressor 12 may be modulated (e.g., pulse-width modulated) during operation in the low-capacity mode and/or during operation in the high-capacity mode. Exemplary variable capacity compressors are disclosed in commonly owned U.S. patent No. 8,616,014, U.S. patent No. 6,679,072, U.S. patent No. 8,585,382, U.S. patent No. 6,213,731, U.S. patent No. 8,485,789, U.S. patent No. 8,459,053, and U.S. patent No. 5,385,453, the disclosures of which are incorporated herein by reference.

The compressor 12, the outdoor heat exchanger 14, the outdoor blower fan 15, the first expansion device 16, and the reversing valve 20 may be disposed in the outdoor unit 28. The second expansion device 17, the indoor heat exchanger 18, and the indoor blower 19 may be disposed in an indoor unit 30 (e.g., an air handler or a furnace), the indoor unit 30 being disposed within a home or other building 32. The first check valve 34 may be disposed between the outdoor heat exchanger 14 and the first expansion device 16, and may restrict or prevent fluid flow through the first expansion device 16 in the cooling mode and may allow fluid flow through the first expansion device 16 in the heating mode. The second check valve 36 may be disposed between the second expansion device 17 and the indoor heat exchanger 18, and may restrict or prevent fluid flow through the second expansion device 17 in the heating mode, and may allow fluid flow through the second expansion device 17 in the cooling mode.

The outdoor air temperature sensor 24 is disposed outside the building 32 and within or outside the outdoor unit 28, and is configured to measure the outdoor ambient air temperature and communicate the outdoor ambient air temperature value to the control module 22 intermittently, continuously, or on demand. In some configurations, the outdoor air temperature sensor 24 may be a thermometer or other sensor associated with a weather monitoring and/or weather reporting system or entity. In such a configuration, the control module 22 may, for example, be via the Internet, Wi-Fi,

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Power Line Carrier Communication (PLCC), or cellular connection or any other wired or wireless communication protocol, obtains the outdoor air temperature (measured by the sensor 24) from a weather monitoring and/or weather reporting system or entity. For example, the control module 22 may communicate with a weather monitoring and/or weather reporting system or entity over the Internet via a Wi-Fi connection with a Wi-Fi router located in the building 32 or associated with the building 32. The thermostat 26 is disposed within the building 32 and outside of the indoor unit 30, and is configured to measure the air temperature within a room or space to be cooled or heated by the system 10. The thermostat 26 may be a single stage thermostat that generates only one type of demand signal, for example, in response to the temperature within a room or space rising above a set point temperature (in a cooling mode) or falling below the set point temperature (in a heating mode). The control module 22 may be disposed in any suitable location, such as within or adjacent to the outdoor unit 28, or within or adjacent to the indoor unit 30.

In the cooling mode, the outdoor heat exchanger 14 may operate as a condenser or as a gas cooler, and may cool the discharge pressure working fluid received from the compressor 12, for example, by transferring heat from the working fluid to air forced to the outdoor heat exchanger 14 by the outdoor blower 15. The outdoor blower 15 may include a fixed speed fan, a multi-speed fan, or a variable speed fan. In the cooling mode, the indoor heat exchanger 18 may operate as an evaporator, wherein the working fluid absorbs heat from air forced to the indoor heat exchanger 18 by the indoor blower 19 to cool a space within the home or building 32. The indoor blower 19 may include a fixed speed fan, a multi-speed fan, or a variable speed fan. In the heating mode, the outdoor heat exchanger 14 may operate as an evaporator and the indoor heat exchanger 18 may operate as a condenser or a gas cooler and may transfer heat from the working fluid discharged by the compressor 12 to the space to be heated.

Referring to fig. 1 and 2, a method and control algorithm 100 of the control module 22 will be described. The algorithm 100 may control the operation of the compressor 12 and switch the compressor 12 between the low-capacity mode and the high-capacity mode. In the initial state 110, the compressor 12 may be off. The thermostat 26 may send a demand signal Y to the control module 22 in response to the temperature in the space to be heated or cooled by the system 10 falling below a selected set point temperature (in a heating mode) or rising above the selected set point temperature (in a cooling mode). In response to receiving the demand signal Y, the control module 22 may initiate operation of the compressor 12 in the low-capacity mode (state 120). Starting operation of compressor 12 in the low-capacity mode (state 120) may reduce or minimize surging and mechanical stress of energy during startup of compressor 12.

Control module 22 may receive the outdoor ambient air temperature measured by sensor 24 (input 130) and determine whether the outdoor ambient air temperature is greater than a first predetermined temperature value (e.g., such as 90 degrees fahrenheit) while system 10 is in the cooling mode. If the outdoor ambient air temperature is less than the first predetermined temperature value, the control module 22 may continue to operate the compressor in the low-capacity mode (state 120) until the cooling demand is met (i.e., the temperature in the space to be cooled falls below the selected set-point temperature as indicated by the thermostat 26, and the thermostat switches the demand signal Y "off"), until the total run time T of the compressor 12 exceeds a predetermined low-capacity run time T1 from the time the demand signal Y is received, or until the compressor 12 or system 10 is manually shut down or the diagnostic or protection algorithm overrides the algorithm 100. For example, the predetermined low capacity runtime T1 may be approximately forty minutes. If the demand is met before the total operating time T reaches the predetermined low-capacity operating time T1, the control module 22 may shut down the compressor 12 (state 140). The first predetermined temperature value may be selected to minimize run time in the high-capacity mode in many or most of the houses or buildings under many or most of the weather conditions for one or more geographic locations. The predetermined low capacity operation T1 may be selected to avoid operating the low capacity mode longer than desired for comfort and/or to prevent premature switching to the high capacity mode (which would use more energy than desired). In some embodiments and in certain circumstances, it may be desirable that the compressor 12 may be operated in the low-capacity mode for most of the time (e.g., more than 80% of the time) of the cooling season (e.g., summer) for many or most of the houses or buildings in many or most climates or geographic areas.

If the compressor 12 has been operating longer than the predetermined low-capacity runtime T1 and the demand has not been met, the control module 22 may switch the compressor 12 from the low-capacity mode to the high-capacity mode (state 150). The compressor 12 may continue to operate in the high-capacity mode until the cooling demand is met (or until the compressor 12 or system 10 is manually shut down or a diagnostic or protection algorithm overrides the algorithm 100). When the demand is met, the control module 22 may turn off the compressor 12 (state 140), rather than switching back to the low-capacity mode. When the compressor 12 is turned off after the demand has been met by operating in the high-capacity mode, the control module 22 may record a run time T2 of the compressor 12 in the high-capacity mode and store the run time T2 in a memory module (not shown) associated with the control module 22.

After initially starting the compressor 12 in the low-capacity mode in response to the initial receipt of the demand signal Y, if the control module 22 determines that the outdoor ambient air temperature is at or above the first predetermined temperature value, the control module 22 may wait (state 160) and allow the compressor 12 to continue operating in the low-capacity mode for a predetermined wait period (e.g., approximately five seconds). The predetermined wait period may be selected to ensure a stable start of the compressor 12 without significantly affecting the capacity of the overall system and/or the ability of the system to control comfort. After the predetermined wait period has expired, the control module 22 may determine whether the last time the compressor 12 was operated in the high-capacity mode T2 is greater than a predetermined period of time (e.g., approximately five minutes) (state 170). The predetermined period of time may be selected to determine whether the thermal load of the house or building 32 is high enough that switching to the high-capacity mode is necessary or desirable to achieve the desired comfort level, or low enough to continue operating in the low-capacity mode and still obtain the desired comfort control. If the last high-capacity run time T2 is greater than or equal to the predetermined period of time, the control module 22 may switch the compressor 12 from the low-capacity mode (state 120) to the high-capacity mode (state 150). Thereafter, the compressor 12 may continue to operate in the high-capacity mode until the cooling demand is met (or until the compressor 12 or system 10 is manually shut down or the diagnostic or protection algorithm overrides the algorithm 100). When the cooling demand is met, the control module 22 may shut down the compressor 12 (state 140).

If the last high-capacity run time T2 is less than the predetermined period of time at state 170, the control module 22 may continue to operate in the low-capacity mode (state 120) until the cooling demand is met, until the total run time T of the compressor 12 exceeds the predetermined low-capacity run time T1 since the demand signal Y was received, or until the algorithm 100 is overridden.

When the system 10 is in heating mode, the algorithm 100 may operate similarly or equivalently as described above, except that the conditions to be met before the algorithm enters the state 160 would be: whether the outdoor ambient air temperature is less than a second predetermined temperature value. The second predetermined temperature value when system 10 is in the heating mode may be different than the first predetermined temperature value in the cooling mode. For example, the second predetermined temperature value in the heating mode may be approximately forty degrees Fahrenheit, for example. Thus, in the heating mode, if the control module 22 determines that the outdoor ambient air temperature is greater than the second predetermined temperature value, the control module 22 may continue to operate the compressor 12 in the low-capacity mode (state 120) until the heating demand is met, until the run time T exceeds the predetermined low-capacity run time T1, or until the algorithm 100 is overridden. If, in the heating mode, the control module 22 determines that the outdoor ambient air temperature is less than the second predetermined temperature value, the algorithm 100 may proceed to state 160. From state 160, the algorithm 100 may operate similarly or equivalently as described above with respect to the cooling mode. It is contemplated for many houses or buildings that when the outdoor air temperature is at or above forty degrees fahrenheit, operating in the low-capacity mode in the heating mode may be sufficient to meet the heating demand, while high-capacity mode operation may not be necessary or desirable until the outdoor air temperature is below forty degrees fahrenheit.

Below a third predetermined outdoor air temperature (e.g., twenty degrees fahrenheit), many heat pump systems do not have sufficient capacity to meet the heating demand even if they continue to operate in the high-capacity mode. Accordingly, alternative or supplemental heating systems may be employed instead of or in addition to such heat pump systems. Below this third predetermined temperature, the control module 22 may operate the compressor 12 in the high-capacity mode for a third predetermined run time (e.g., thirty minutes) before turning on the alternative or supplemental heating system.

As described above, the variable-capacity compressor 12, the control module 22, and the algorithm 100 are operable with a single-stage indoor thermostat 26 and an indoor unit 30 having a constant-speed blower 19. Thus, the control module 22 and algorithm 100 of the present disclosure allow a preexisting climate control system having a fixed capacity to be retrofitted to include the variable-capacity compressor 12 and the control module 22 without the need to retrofit the system to also include a multi-stage thermostat and/or an indoor unit having a multi-speed blower. Retrofitting a fixed capacity climate control system to include the variable capacity compressor 12 and the control module 22 without replacing the single stage thermostat 26 and the fixed speed blower 19 improves the performance and efficiency of the climate control system without the added significant expense and complexity associated with retrofitting a climate control system to include a multi-stage thermostat and/or an indoor unit having a multi-speed blower. Alternatively, a multi-stage thermostat may be employed in the following cases: wherein the multi-stage thermostats are connected only to send a single demand signal (e.g., only one demand line is connected to the compressor 12 and/or the control module 22, rather than having both a low capacity demand line and a high capacity demand line connected to the compressor 12 and/or the control module 22).

It will be appreciated that the first predetermined temperature value, the second predetermined temperature value, the predetermined low-capacity run time T1, the predetermined wait period, and/or the predetermined time period may be selected based on the climate, geographic location, tonnage size of the compressor 12 relative to the thermal load of the house or building 32, and/or whether the system is operating in a cooling mode or a heating mode.

In some embodiments, the outdoor air temperature used in the algorithm 100 is not necessarily an instantaneous or real-time temperature value. Instead, the control module 22 may obtain or determine an average outdoor air temperature over a previous operating cycle or over a specified period of time to account for the effects of solar radiation and/or thermal mass of the building 32 or space to be heated or cooled.

In some embodiments where the control module 22 receives outdoor temperature from a remote weather report and/or weather forecast database or source, the control module 22 may be configured to record a high-volume mode operating history versus (vers) outdoor air temperature history and time of day. In such embodiments, the control module 22 may be configured to: an expected future date and time of switching to the high-capacity mode is predicted based on the forecasted outdoor air temperature and the recorded history of operation versus outdoor air temperature history and time of day.

FIG. 3 is a graph illustrating the capacity of an exemplary variable-capacity compressor in a low-capacity mode and a high-capacity mode under various outdoor air temperatures and thermal loads of an exemplary house under various outdoor air temperatures. Fig. 4 is a graph illustrating the percentage operating time of the compressor in the low capacity mode and the high capacity mode. When the outdoor air temperature is within the following range: in this range, the heat load of the house is less than the compressor capacity in the low capacity mode, and the control module 22 may operate the compressor in the low capacity mode only. When the outdoor air temperature is within the following range: in this range, the house has a heat load greater than the compressor capacity in the low capacity mode and less than the compressor capacity in the high capacity mode, and the control module 22 may switch the compressor between the low capacity mode and the high capacity mode to meet the demand. When the outdoor air temperature is within the following range: in this range, the house's heat load is greater than the compressor capacity in the high-capacity mode, and the control module 22 may operate the compressor in the high-capacity mode entirely or nearly entirely.

The percent run time shown in fig. 4 can be derived as the ratio of the thermal load of the house to the unit capacity of each capacity level at a given outdoor ambient temperature shown in fig. 3. Based on experimentation, the predetermined runtime T1 (e.g., forty minutes) may be selected to represent a maximum runtime in the low-capacity mode that is required or acceptable before a switch to the high-capacity mode is required. The predetermined operating time T1 may vary depending on the relative capacities of the compressor in the low capacity mode and the high capacity mode with respect to the thermal load of the house. FIG. 3 is based on a sizing rule (sizing rule) for a high capacity mode approximately ten percent higher than the thermal load of a house at an ambient temperature of ninety-five degrees. The predetermined ambient temperature at which the high capacity stage will begin operation may be in the range of eighty-five to ninety degrees Fahrenheit.

Referring to fig. 1 and 5-11, another method and control algorithm 200 of the control module 22 will be described. The algorithm 200 may control the operation of the compressor 12 and switch the compressor 12 between the low-capacity mode and the high-capacity mode. In the initial state 210, the compressor 12 may be off. The thermostat 26 may send a demand signal Y to the control module 22 in response to the temperature of air in the space to be heated or cooled by the system 10 falling below a selected set point temperature (in a heating mode) or rising above the selected set point temperature (in a cooling mode). In response to receiving the demand signal Y, the control module 22 may initiate operation of the compressor 12 in the low-capacity mode (state 220). As described above, starting the operation of compressor 12 in the low-capacity mode may reduce or minimize energy surges and mechanical stresses during starting compressor 12.

Upon receiving the demand signal Y, the control module 22 may determine and set (before, concurrently with, or after the initial startup of the compressor 12 at state 220) the low-capacity run time threshold T1 'and the high-capacity run time threshold T2'. At state 230, the control module 22 may determine the run time thresholds T1 ', T2' based on the outdoor ambient air temperature (input 232) and the comfort selection (input 234). As described above, the outdoor ambient air temperature may be received from the outdoor air temperature sensor 24. The comfort level selection may be received from a comfort control interface (fig. 11) in communication with the control module 22.

In some configurations, the comfort control interface 225 may include a dial 227, for example, the dial 227 may be movable between a plurality of positions. In the particular configuration shown in fig. 11, the dial 227 is movable between five different positions, each position corresponding to a different one of the comforters 1 to 5 (indicated by reference 229 in fig. 11). The comfort control interface 225 may communicate with the control module 22 via a wired connection or a wireless connection. For example, the comfort control interface 225 may be connected via an Internet connection (wired or wireless), a cellular connection, a wired connection, a wireless connection, a,

Connections, radio frequency signals, infrared signals, and/or any other suitable means to communicate with control module 22. In some configurations, user control interface 225 may also include one or more buttons, switches, and/or a touch screen interface instead of or in addition to dial 227. In some configurations, the comfort control interface 225 may include or be part of, for example, a thermostat 26, a computer, a smart phone, or a tablet computer or any other computing, control, and/or communication device.

The comfort interface 225 allows the user to adjust the low capacity runtime threshold T1 'and the high capacity runtime threshold T2' to adjust the energy efficiency and performance of the system 10. In the configuration shown in the figure, comfort 1 is a setting that reduces the amount of time that the compressor 12 can operate in the high-capacity mode, and increases the amount of time that the compressor 12 can operate in the low-capacity mode, thereby increasing the energy efficiency of the system 10. Comfort 5 is a setting that increases the amount of time that compressor 12 can operate in a high capacity mode and decreases the amount of time that compressor 12 can operate in a low capacity mode, thereby increasing the performance of system 10 (i.e., increasing the ability of system 10 to cool or heat a space more quickly).

Fig. 6 and 7 depict a first lookup table 231 and a second lookup table 233, the first and second lookup tables 231, 233 providing, for each of the five comfort levels, a low-capacity run-time threshold T1 'and a high-capacity run-time threshold T2' for a given outdoor ambient air temperature (or temperature range). The values of the lookup tables 231, 233 may be stored in a memory unit associated with the control module 22, and/or on a memory unit associated with any one of: a computer, a tablet, a smart phone, any handheld device, a cloud (i.e., networked server), and/or any suitable computing and/or memory device that may be configured to communicate with control module 22. As shown in fig. 6 and 7, for each given outdoor ambient air temperature, the low-capacity run-time threshold T1 'decreases as comfort increases from comfort 1 to comfort 5, and the high-capacity run-time threshold T2' increases as comfort increases from comfort 1 to comfort 5. The exemplary lookup tables 231, 233 shown in fig. 6 and 7 are used when the system 10 is operating in the cooling mode. Additional tables (not shown) may be stored in a memory unit of the control module 22 for use in the heating mode. Such additional tables may include values different from those provided in tables 231, 233.

At state 230, the control module 22 may determine a low capacity run time threshold T1 'and a high capacity run time threshold T2' selected for the outdoor ambient air temperature received at input 234 and the comfort level received at input 232 based on tables 231, 233. Then, at the

states

236, 238, the control module 22 may set the threshold T1 'and the threshold T2' to the values determined at the state 230, respectively. It will be appreciated that the control module 22 may apply a formula or series of calculations to determine the run-time thresholds T1 ', T2' rather than referencing the look-up tables 231, 233.

The compressor 12 may continue to operate in the low capacity mode (state 220) as long as the demand signal Y is on and as long as the total operating time T of the compressor 12 from the initial receipt of the demand signal Y is less than the low capacity operating time threshold T1' set at state 236. If the demand signal Y is off, the control module 22 may turn off the compressor 12 at state 240. If and when the total operating time T exceeds the low-capacity operating time threshold T1', the control module 22 may reset the total operating time T to zero (state 250) and switch the compressor 12 to the high-capacity mode (state 260). As long as the demand signal Y is on and as long as the total operating time T is less than the high-capacity operating time threshold T2' set at state 238, the compressor 12 may continue to operate in the high-capacity mode (state 260). If and when the total run time T exceeds the high capacity run time threshold T2 ', the control module 22 may reset the total run time T to zero (state 270) and the algorithm 200 may return to state 230 to determine and set the low capacity run time threshold T1 ' and the high capacity run time threshold T2 ' before returning the compressor 12 to the low capacity mode at state 220. Thereafter, the algorithm 200 may repeat some or all of the above steps until the demand signal Y is turned off, or until operation of the compressor 12 is overridden (e.g., manually overridden or overridden by a compressor protection routine, for example).

Fig. 8-10 depict the operating times of the compressor 12 in the low-capacity mode and the high-capacity mode for various comfort levels. Fig. 8 depicts a low-volume runtime and a high-volume runtime for a low comfort level (e.g., comfort level 1). Fig. 9 depicts low-volume runtime and high-volume runtime for medium comfort (e.g., comfort 3). Fig. 10 depicts low-volume runtime and high-volume runtime for high comfort (e.g., comfort 5). As shown in fig. 8-10, the higher comfort setting enables the compressor 12 to operate longer in the high-capacity mode, which improves the performance of the system 10. The lower comfort setting allows the compressor 12 to operate longer in the low-capacity mode, which improves the energy efficiency of the system 10 by reducing power consumption. As shown in fig. 8 to 10, the operation time in the low-capacity mode decreases as the comfort increases.

It will be appreciated that the comfort level may be changed at any point during the algorithm 200, and the low-volume run time threshold T1 'and the high-volume run time threshold T2' may be updated immediately in response to changes in comfort level.

In some configurations, the control module 22 may adjust the runtime thresholds T1 ', T2' based on, for example, weather forecasts and/or current weather conditions (e.g., humidity, cloud cover, and/or rainfall). In some configurations, if the current weather conditions include low humidity, significant cloud cover, and/or rain, the control module 22 may increase the low-volume run-time threshold T1 'and/or decrease the high-volume run-time threshold T2' for a given comfort level. In some configurations, the control module 22 may adjust the values of the tables 231, 232 (or use different tables in the algorithm 200) based on the climate of the particular geographic region in which the system 10 is to be installed. For example, comfort control interface 225 or thermostat 26 may be configured to allow a user or installation contractor to enter the geographic area or climate type in which system 10 is installed. In some configurations, the control module 22 may adjust the values of the tables 231, 233 based on historical data (such as previous run times, previous outdoor ambient air temperatures, and/or other previous weather conditions). In some configurations, the values of tables 231, 233 may be adjusted based on current or predicted future energy costs. In some configurations, a set of reference values for tables 231, 233 may be stored in a memory unit for future use.

In some configurations, comfort may be a parameter set by an installation contractor or by a service contractor when installing the system 10 or the services of the system 10. In some of such configurations, the homeowner and/or the occupant of the home or building may not easily adjust the comfort selection. In some configurations, for example, an electric utility company or entity may have the ability to set and adjust comfort choices and/or the ability to override comfort choices made by a homeowner and/or an occupant of a residence/building. In such a configuration, the utility company may choose to use a lower charge comfort during periods of high demand for power in the area or community in which the residence or building 32 is located.

In this application, including the definitions below, the term "module" may be replaced with the term "circuit". The term "module" may refer to or include a portion of: an Application Specific Integrated Circuit (ASIC); digital, analog, or hybrid analog/digital discrete circuits; digital, analog, or hybrid analog/digital integrated circuits; a combinational logic circuit; a Field Programmable Gate Array (FPGA); a processor (shared, dedicated, or group) that executes code; a memory (shared, dedicated, or group) that stores code executed by the processor; other suitable hardware components that provide the described functionality; or a combination of some or all of the above, such as a system on a chip.

The foregoing description is merely illustrative in nature and is not intended to limit the present disclosure, application, or uses in any way. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. As used herein, at least one of the phrases A, B and C should be construed to mean logic (a or B or C), using the non-exclusive logical "or". It should be understood that one or more steps of the method may be performed in a different order (or simultaneously) without altering the principles of the present disclosure.

The foregoing description of embodiments has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The individual elements or features of a particular embodiment may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

Further, the present invention may also be configured as follows.

(1) A climate control system comprising a variable capacity compressor unit and a control module controlling the compressor unit, the compressor unit operable in a first capacity mode and a second capacity mode higher than the first capacity mode, the control module configured to switch the compressor unit between an off state, the first capacity mode, and the second capacity mode based on a demand signal and outdoor air temperature data.

(2) The climate-control system of (1), wherein the control module receives the demand signal from a single-stage thermostat disposed within a space cooled by the climate-control system.

(3) The climate-control system of (2), further comprising an indoor heat exchanger receiving working fluid from the compressor unit and a blower forcing air into a heat-convection relationship with the working fluid in the indoor heat exchanger, the blower including a fixed speed motor or a variable speed motor capable of operating at a selectable fixed speed tap.

(4) The climate-control system of (1), wherein the control module switches the compressor unit between the first capacity mode and the second capacity mode based on a compressor run time.

(5) The climate-control system of (4), wherein the compressor runtime is a runtime of the compressor unit in the second capacity mode.

(6) The climate-control system of (5), wherein a runtime of the compressor unit in the second capacity mode is equal to a previous runtime in the second capacity mode during a previous demand period.

(7) The climate-control system of (6), wherein the control module switches the compressor unit from the first capacity mode to the second capacity mode based on whether the previous run time is greater than five minutes.

(8) The climate-control system of (6), wherein the control module switches the compressor unit from the first capacity mode to the second capacity mode based on whether the compressor unit has been operating in the first capacity mode for greater than a predetermined period of time.

(9) The climate-control system of (4), further comprising a comfort control interface configured to be placed at one of a plurality of comfort settings, wherein a first one of the comfort settings corresponds to an energy-efficient mode of operation and a second one of the comfort settings corresponds to a high-performance mode of operation.

(10) The climate-control system of (9), wherein the control module is configured to compare the compressor run time to a low-capacity run time threshold and a high-capacity run time threshold.

(11) The climate-control system of (10), wherein the control module is configured to: switching the compressor between a low-capacity mode and a high-capacity mode based on a comparison of the compressor run time and the first capacity run time, and based on a comparison of the compressor run time and the second capacity run time.

(12) The climate-control system of (1), wherein the low-capacity run-time threshold and the high-capacity run-time threshold are determined based on a selected one of the comfort settings.

(13) The climate-control system of (1), wherein the control module operates the compressor unit in one of the first capacity mode and the second capacity mode based only on the demand signal, the outdoor-air-temperature data, and at least one compressor run time.

(14) The climate-control system of (13), wherein the at least one compressor runtime is a runtime of the compressor unit in the second capacity mode.

(15) A method of controlling a compressor operable in a first capacity mode and a second capacity mode higher than the first capacity mode, the method comprising:

receiving a demand signal from a thermostat;

comparing the outdoor air temperature to a predetermined temperature value;

comparing the operating time of the compressor to a predetermined operating time value; and

in response to receiving the demand signal, operating the compressor in one of the first capacity mode and the second capacity mode based on a comparison of the outdoor air temperature to the predetermined temperature value and a comparison of the run time to the predetermined run time value.

(16) The method according to (15), further comprising: if the outdoor air temperature is less than the predetermined temperature value and if the total run time of the compressor from receipt of the demand signal is less than the predetermined run time value, operating the compressor in only the first capacity mode until demand is met.

(17) The method according to (15), further comprising: switching the compressor from the first capacity mode to the second capacity mode based on a comparison of the run time to the predetermined run time value.

(18) The method according to (15), further comprising: operating the compressor in the first capacity mode until the run time exceeds the predetermined run time value; and switching the compressor out of the first capacity mode after the run time exceeds the predetermined run time value.

(19) The method of (15), wherein the predetermined run time value is a previous amount of time that the compressor was previously operating in the second capacity mode, the previous amount of time from initiation of the second capacity mode until satisfaction of a previous demand signal.

(20) The method of (15), wherein the compressor is operated in one of the first capacity mode and the second capacity mode based only on the demand signal, the outdoor air temperature, and at least one compressor run time.

Claims

1. A climate control system, comprising:

a variable-capacity compressor unit operable in a first capacity mode and a second capacity mode higher than the first capacity mode; and

a control module configured to control the variable-capacity compressor unit,

wherein the control module is configured to switch the variable-capacity compressor unit from an off state to the first capacity mode in response to receiving a demand signal generated by a thermostat, an

Wherein the control module is configured to selectively switch the variable-capacity compressor unit from the first capacity mode to the second capacity mode based on a comparison of:

comparison of the outdoor air temperature with a predetermined temperature value, an

A comparison of a predetermined second capacity runtime threshold with a previous second capacity runtime, wherein the previous second capacity runtime is a previous amount of time that the variable-capacity compressor unit was operating in the second capacity mode from a previous start of the second capacity mode until a previous demand was met.

2. The climate-control system of claim 1, wherein the control module switches the variable-capacity compressor unit from the first capacity mode to the second capacity mode upon receiving the same demand signal.

3. The climate-control system of claim 1, further comprising a comfort control interface configured to be placed at one of a plurality of comfort settings, wherein the plurality of comfort settings includes at least a first comfort setting and a second comfort setting, wherein the first comfort setting corresponds to an energy-efficient mode of operation and the second comfort setting corresponds to a high-performance mode of operation.

4. The climate-control system of claim 3, wherein the control module is configured to compare a compressor run time to a first capacity run time threshold.

5. The climate-control system of claim 1, further comprising a single-stage thermostat configured to generate the demand signal.

6. A method of controlling a compressor unit operable in a low-capacity mode and a high-capacity mode, the method comprising:

receiving a demand signal from a thermostat;

setting a low-volume runtime threshold based on a selected comfort level, wherein the selected comfort level is set using a comfort control interface configured to be set at one of a plurality of comfort level settings, wherein the plurality of comfort level settings includes at least a first comfort level setting and a second comfort level setting, wherein the first comfort level setting corresponds to an energy-efficient mode of operation and the second comfort level setting corresponds to a high-performance mode of operation;

operating the compressor unit in the low-capacity mode in response to receiving the demand signal;

comparing a total run time of the compressor unit to the low-capacity run time threshold, wherein the total run time of the compressor unit is an amount of time the compressor unit has been running since the demand signal was received; and

switching the compressor unit from the low-capacity mode to the high-capacity mode based on a comparison of the total run time to the low-capacity run time threshold.

7. The method of claim 6, further comprising: setting a high-volume runtime threshold based on the selected comfort level.

8. The method of claim 7, further comprising: switching the compressor unit from the high-capacity mode to the low-capacity mode based on a comparison of the total run time to the high-capacity run time threshold.

9. The method of claim 6, further comprising: a set point temperature is set at which the demand signal will be sent.

10. The method of claim 6, wherein the comfort level is set based on one of a geographic area in which the compressor unit is installed and a climate type in which the compressor unit is installed.

11. The method of claim 6, wherein the comfort control interface comprises at least another one of the comfort settings between the first and second comfort settings.

12. The method of claim 6, wherein the comfort control interface is configured to be manually placed at one of the plurality of comfort settings.

13. The method of claim 6, wherein the low-capacity runtime threshold is greater when the comfort control interface is set at the first comfort setting than when the comfort control interface is set at the second comfort setting.

14. The method of claim 6, wherein the compressor unit is switched from an off state to the low capacity mode in response to receiving the demand signal, and wherein the compressor unit is switched from the low capacity mode to the high capacity mode upon receiving the same demand signal.

15. The method of claim 6, wherein the thermostat is a single stage thermostat.

16. A climate control system, comprising:

a compressor unit operable in a low-capacity mode and a high-capacity mode; and

a control module configured to control the compressor unit,

wherein the control module is configured to switch the compressor unit from an off state to the low-capacity mode in response to receiving a demand signal generated by a thermostat, an

Wherein the control module is configured to:

17. The climate-control system of claim 16, wherein the control module sets a high-capacity run-time threshold based on the selected comfort level.

18. The climate-control system of claim 17, wherein the control module switches the compressor unit from the high-capacity mode to the low-capacity mode based on a comparison of the total run time to the high-capacity run time threshold.

19. The climate-control system of claim 16, wherein the comfort level is set based on one of a geographic area in which the compressor unit is installed and a climate type in which the compressor unit is installed.

20. The climate-control system of claim 16, wherein the comfort control interface comprises at least another one of the comfort settings between the first and second comfort settings.

21. The climate-control system of claim 16, wherein the comfort control interface is configured to be manually placed at one of the plurality of comfort settings.

22. The climate-control system of claim 16, wherein the low-volume run-time threshold is greater when the comfort control interface is set to a first one of the comfort settings than when the comfort control interface is set to a second one of the comfort settings.

23. The climate-control system of claim 16, wherein the compressor unit is switched from an off state to the low-capacity mode in response to receiving the demand signal, and wherein the compressor unit is switched from the low-capacity mode to the high-capacity mode upon receiving the same demand signal.

24. The climate-control system of claim 23, further comprising a single-stage thermostat configured to generate the demand signal.