CONTROLLING A VARIABLE-SPEED HEATING, VENTILATION AND AIRCONDITIONING SYSTEM USING A NON-COMMUNICATING TWO-STAGE THERMOSTAT

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional patent application Ser. No. 63/725,647, filed Nov. 27, 2024, the entire contents of which are incorporated herein by reference.

BACKGROUND

The present disclosure relates to heating, ventilation and air conditioning (HVAC) systems and, more particularly, to controlling a variable-speed HVAC system using a non-communicating two-stage thermostat.

An increasing number of HVAC units are using variable-speed compressor technology to improve efficiency, comfort, and reliability. Variable-speed systems typically work by connecting a motor control drive to the compressor and then connecting the line input power from the utility to the drive. The drive uses frequency modulation to adjust power output and RPM of the compressor motor, enabling it to speed up or slow down according to the heating or cooling load in the home. This ability to modulate compressor capacity enables many of the advantages of variable-speed technology including improved efficiency and comfort. Other methods to control the power output and RPM of the compressor may also be employed.

It has been found that use of variable-speed compressor technology requires a system control capable of communicating additional information beyond a mere on/off signal to the compressor or motor control drive. Typically, the communicating capability is a part of a proprietary protocol; thus, increasing the number of components of the system and increasing costs. There is therefore a need for a system and method to control a variable-speed system at minimal cost.

BRIEF DESCRIPTION

According to an aspect of the disclosure, a variable-speed heat, ventilation and air conditioning (HVAC) system is provided and includes a thermostat configured to issue first, second and off signals in various combinations and sequences and an HVAC unit receptive of the first, second and off signals and configured to become non-operative and to operate in one of more than three stages responsive to the HVAC unit receiving the first, second and off signals in the various combinations and sequences with increasingly higher stages being associated with the HVAC unit delivering increasingly higher capacity.

In accordance with one or more additional and/or alternative embodiments, the HVAC unit is configured to become non-operative following off signal reception, operate at a maximum stage when the first and second signals are received following off signal reception, operate at a next higher stage when the first and second signals are received following reception of just the first signal, operate at another next higher stage when reception of the first and second signals persists, operate at a next lower stage when just the first signal is received following reception of the first and second signals and operate at another next lower stage when just the first signal is received following reception of the off signal following reception of just the first signal.

In accordance with one or more additional and/or alternative embodiments, the thermostat issues the first, second and off signals in the various combinations and sequences based on a difference between a sensed temperature and a set-point temperature.

In accordance with one or more additional and/or alternative embodiments, the HVAC system further includes first dedicated wiring electrically interposed between the thermostat and the HVAC unit to carry the first signal and second dedicated wiring electrically interposed between the thermostat and the HVAC unit to carry the second signal, wherein at least one of the first signal and the second signal includes a continuous 24 volt signal.

In accordance with one or more additional and/or alternative embodiments, the off signal is represented by an absence of the first and second signals.

In accordance with one or more additional and/or alternative embodiments, the maximum stage is a fifth stage.

In accordance with one or more additional and/or alternative embodiments, the HVAC unit is configured to operate at the next higher stage when the reception of the first signal and the second signal persists for a predefined time.

In accordance with one or more additional and/or alternative embodiments, the HVAC unit is further configured to anticipate load changes due to outdoor air temperature (OAT) changes and change stages accordingly.

In accordance with one or more additional and/or alternative embodiments, the thermostat is configured to issue at least one or more additional signals and the HVAC unit is receptive of the at least one or more additional signals and configured to change stages accordingly.

According to an aspect of the disclosure, a variable-speed heat, ventilation and air conditioning (HVAC) system is provided and includes a non-communicating, two-stage thermostat configured to issue first, second and off signals in various combinations and sequences and an HVAC unit receptive of the first, second and off signals and configured to become non-operative and to operate in one of more than three stages responsive to the HVAC unit receiving the first, second and off signals in the various combinations and sequences with increasingly higher stages being associated with the HVAC unit delivering increasingly higher capacity.

In accordance with one or more additional and/or alternative embodiments, the HVAC unit is configured to become non-operative following off signal reception, operate at a maximum stage when the first and second signals are received following off signal reception, operate at a next higher stage when the first and second signals are received following reception of just the first signal, operate at another next higher stage when reception of the first and second signals persists, operate at a next lower stage when just the first signal is received following reception of the first and second signals and operate at another next lower stage when just the first signal is received following reception of the off signal following reception of just the first signal.

In accordance with one or more additional and/or alternative embodiments, the non-communicating, two-stage thermostat issues the first, second and off signals in the various combinations and sequences based on a difference between a sensed temperature and a set-point temperature.

In accordance with one or more additional and/or alternative embodiments, the HVAC system further includes first dedicated wiring electrically interposed between the non-communicating, two-stage thermostat and the HVAC unit to carry the first signal and second dedicated wiring electrically interposed between the non-communicating, two-stage thermostat and the HVAC unit to carry the second signal, wherein at least one of the first signal and the second signal comprises a continuous 24 volt signal.

In accordance with one or more additional and/or alternative embodiments, the off signal is represented by an absence of the first and second signals.

In accordance with one or more additional and/or alternative embodiments, the maximum stage is a fifth stage.

In accordance with one or more additional and/or alternative embodiments, the HVAC unit is configured to operate at the next higher stage when the reception of the first signal and the second signal persists for a predefined time.

In accordance with one or more additional and/or alternative embodiments, the HVAC unit is further configured to anticipate load changes due to outdoor air temperature (OAT) changes and change stages accordingly.

In accordance with one or more additional and/or alternative embodiments, the non-communicating, two-stage thermostat is configured to issue at least one or more additional signals and the HVAC unit is receptive of the at least one or more additional signals and configured to change stages accordingly.

According to an aspect of the disclosure, a method of operating a variable-speed heat, ventilation and air conditioning (HVAC) system is provided and includes determining a difference between a sensed temperature and a set-point temperature, issuing first, second and off signals in various combinations and sequences based on the difference and placing the HVAC unit in a non-operative state and operating the HVAC unit in one of more than three stages responsive to the HVAC unit receiving the first, second and off signals in the various combinations and sequences with increasingly higher stages being associated with the HVAC unit delivering increasingly higher capacity.

In accordance with one or more additional and/or alternative embodiments, the placing of the HVAC unit in the non-operative state is executed following off signal reception, the operating of the HVAC unit in the one of more than three stages includes operating the HVAC unit at a maximum stage when the first and second signals are received following the off signal reception, operating the HVAC unit at a next higher stage when the first and second signals are received following reception of just the first signal, operating the HVAC at another next higher stage up to the maximum stage when reception of the first and second signals persists, operating at a next lower stage when just the first signal is received following reception of the first and second signals and operating at another next lower stage when just the first signal is received following reception of the off signal following reception of just the first signal and the method further includes anticipating load changes due to outdoor air temperature (OAT) changes and changing stages of the HVAC unit accordingly.

Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed technical concept. For a better understanding of the disclosure with the advantages and the features, refer to the description and to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts:

FIG. 1 is a schematic diagram of a system provided for controlling a variable-speed HVAC system that is configured to condition air within an interior space in accordance with embodiments;

FIG. 2 is a flow diagram illustrating a method for controlling a variable-speed HVAC system, such as the system of FIG. 1, in accordance with embodiments;

FIG. 3 is a flow diagram illustrating a process of the method of FIG. 2 in accordance with embodiments;

FIGS. 4A-4D are graphical depictions of an operation of the system of FIG. 1 executing the method of FIG. 2 in accordance with embodiments;

FIGS. 5A and 5B are graphical depictions of DOE predictions of exemplary building load changes for one system size in accordance with embodiments;

FIG. 6 is a schematic diagram of a system provided for controlling a variable-speed HVAC system by issuance and reception of various signals by a thermostat and an HVAC unit in accordance with embodiments;

FIG. 7 is a graphical illustration of an operation of the variable-speed HVAC system of FIG. 6 in accordance with embodiments; and

FIG. 8 is a flow diagram illustrating a method of operating a variable-speed HVAC system in accordance with embodiments.

DETAILED DESCRIPTION

Variable-speed systems are typically operated using a communicating wall control, such as a thermostat, that can command the system to increase or decrease capacity based on how close an actual temperature is to a commanded set point. Communicating wall controls are, however, much more expensive than non-communicating two-stage thermostats. Systems that are typically used with non-communicating two-stage thermostats often have two (or three) discrete stages—high and low—and are not fully variable.

Thus, as will be described below, a system is provided in which a capacity being delivered by a variable-speed system in an on-going basis is calculated and integrated and that the capacity is used when the system receives a low-stage signal. The system aggregates the capacity that is delivered to, for example, a home, over the course of a predetermined period of time (i.e., an hour) to determine a cooling load or a heating load on the home and then operates to match that capacity when receiving a stage one signal (indicating that house temperature is close to its set point). When the system received a stage two signal, the system would then operate at full capacity because the system cannot determine how far off the actual temperature is from the commanded set point. When stage two operation occurs, it pulls the integrated capacity calculation higher and, when the system is off, it will pull the integrated capacity calculation lower. The next stage one signal will then use the updated capacity calculation to again attempt to match the house load. Using this method will allow for fully variable, adaptive operation.

Also, as will be described below, a system is provided in which a call for a first signal, a call for first and second signals and an off call of a two-stage thermostat is used along with timing and outside air temperature (OAT) to control a variable speed system.

With reference to FIG. 1, a system 10 is provided for controlling a variable-speed HVAC system that is configured to condition air within an interior space, such as the inside of a residential home for example. The system 10 includes a two-stage system controller 12, such as a thermostat, that is disposed in communication with an HVAC unit 14. The HVAC unit 14 is illustrated as an outdoor unit, though it is to be understood that the HVAC unit 14 could be an indoor unit as well. For purposes of clarity and brevity, the following description will generally refer to the controller 12 as “thermostat 12” and will relate to the embodiments in which the HVAC unit 14 is an outdoor unit.

The thermostat 12 includes a processor 16 in communication with a memory 18 that can be, for example, a read only memory (ROM) and/or an electrically erasable programmable read only memory (EEPROM). The processor 16 is disposed in communication with a controller temperature sensor 20 and a display 21 that can be, for example, a liquid crystal display (LCD). The processor 16 and the memory 18 are configured to operate the HVAC unit 14 as described below. The controller temperature sensor 20 is configured to measure the actual air temperature within interior space 22, such as of a building or a residential home. The thermostat 12 is configured to transmit air conditioning signals based in part on system demands to heat or cool the interior space 22. The thermostat 12 can be disposed in wireless electrical communication with the HVAC unit 14 and/or in wired electrical communication with the HVAC unit 14.

The HVAC unit 14 includes a controller 24 in electrical communication with a variable speed compressor 26 and a unit temperature sensor 28. The controller 24 is configured to receive data from the unit temperature sensor 28, to receive the air conditioning signals from the thermostat 12 and transmit a speed signal to the variable speed compressor 26 based in part on the received air conditioning signals and the data. The variable speed compressor 26 is configured to operate at a plurality of speeds in a heating or cooling mode to deliver a compressed refrigerant. The unit temperature sensor 28 is configured to measure an ambient air temperature around the HVAC unit 14. It will be appreciated that the HVAC unit 14 may be provided as one or more of a split system, a variable refrigerant flow ductless unit, a heat pump, a packaged unit, a geothermal heat pump, etc. The unit temperature sensor 28 may be internal or external to the HVAC unit 14.

With reference to FIG. 2, a method 200 is provided for controlling a variable-speed HVAC system, such as the system 10 of FIG. 1, where the variable-speed HVAC system includes a thermostat and a controller, such as the thermostat 12 and the controller 24 of FIG. 1. As shown in FIG. 2, the method 200 includes determining, by the thermostat, whether to issue a first signal indicating low capacity HVAC system operation, a second signal indicating high capacity HVAC system operation and an off signal indicating HVAC system shut-off (block 201) and issuing, based on results of the determining of block 201, one or more of the first signal, the second signal and the off signal to the controller by the thermostat (block 202). The method 200 also includes determining a system capacity and causing the variable-speed HVAC system to provide the system capacity to a space, such as a building or a residential home, by the controller when the controller receives the first signal (block 203), causing the variable-speed HVAC system to provide a system maximum capacity to the space by the controller when the controller receives the first and second signals (block 206) and shutting off the variable-speed HVAC system by the controller when the controller receives the off signal (block 207). The causing of the variable-speed HVAC system to provide the system capacity by the controller of block 203 can include at least one of adding an OAT adjustment based on outdoor air temperature readings of an outdoor unit sensor, such as the unit temperature sensor 28 of FIG. 1, by the controller (block 204) and adding a solar gain adjustment based on a time of day by the controller (block 205).

In accordance with embodiments, the OAT adjustment can be equal to a predicted change to building loads that is caused by an OAT change and the solar gain adjustment can be equal to a predicted change to building loads that is caused by changes in solar gains (i.e., a prediction based on time of day or other factors).

The determining of whether to issue the first signal, the second signal and the off signal of block 201 can be based on a difference between an actual temperature of the space and a set point (it is to be understood that how “close” or “far” from the set point triggers each signal depends on, among other factors, the thermostat manufacturer). The determining of the system capacity of block 203 can include calculating a delivered capacity as a function of an instantaneous capacity delivered to the space over a predetermined time, such as an hour, for example, by the controller (block 2031) and the delivered capacity can be a function of the instantaneous capacity delivered to the space over a past predetermined amount of time, such as a previous hour, for example.

In accordance with embodiments, the delivered capacity can be equal to a sum of a previously delivered capacity (i.e., at t−1) multiplied by n/m and the instantaneous capacity multiplied by (m−n)/m, where n can be 59 and m can be 60, for example. In accordance with further embodiments, the instantaneous capacity can be equal to a refrigerant massflow multiplied by a change in enthalpy, the refrigerant massflow can be equal to refrigerant density as a function of suction pressure multiplied by compressor displacement multiplied by compressor RPMs and the change in enthalpy can be equal to a difference between a vapor enthalpy as a function of discharge pressure and discharge temperature and a liquid enthalpy as a function of a liquid service valve temperature.

With continued reference to FIGS. 1 and 2 and with additional reference to FIG. 3, FIGS. 4A-4D and FIGS. 5A and 5B, an exemplary process of the system 10 of FIG. 1 and the method 200 of FIG. 2 will be described further.

As shown in FIG. 3, at block 301, it is determined whether only a “Y1” signal (i.e., the above-described first signal) is received and, if so, the HVAC system initially determines a delivered capacity at block 302. This delivered capacity can be calculated as being equal to a filtered instantaneous capacity delivered to a space, such as a home, over a past predetermined period of time, such as a previous hour, where for example:

delivered ⁢ capacity = 
 delivered ⁢ capacity ( t - 1 ) * ( 59 / 60 ) + instantaneous ⁢ capacity * ( 1 / 60 ) , instantaneous ⁢ capacity = refrigerant ⁢ massflow * change ⁢ in ⁢ enthalpy , refrigerant ⁢ massflow = 
 refrigerant ⁢ density × compressor ⁢ displacement × compressor ⁢ R ⁢ P ⁢ M , refrigerant ⁢ density = a ⁢ function ⁢ of ⁢ suction ⁢ pressure , change ⁢ in ⁢ enthalpy = vapor ⁢ enthalpy - liquid ⁢ enthalpy , vapor ⁢ enthalpy = 
 a ⁢ function ⁢ of ⁢ discharge ⁢ pressure ⁢ and ⁢ discharge ⁢ temperature , and liquid ⁢ enthalpy = a ⁢ function ⁢ of ⁢ liquid ⁢ service ⁢ valve ⁢ temperature .

Once the delivered capacity is determined at block 302, OAT and solar gain adjustments are executed at blocks 303 and 304, respectively, where the OAT adjustment can be equal to a predicted change to building loads that is caused by an OAT change and the solar gain adjustment can be equal to a predicted change to building loads that is caused by changes in solar gains (i.e., a prediction based on time of day or other factors). Next, at block 305, the HVAC system provides a predicted capacity, which can be equal to the delivered capacity and the OAT and solar gain adjustments.

At block 306, if the “Y1” signal is not the only signal that is received, it is determined whether the “Y1” signal (i.e., the above-described first signal) and a “Y2” signal (i.e., the above-described second signal) are received and, if so, the HVAC system provides a maximum system capacity at block 307. At block 308, it is determined whether an “Off” signal is received and, if so, the HVAC system is shut off at block 309.

As shown in FIG. 4A, during a first hour of operation of an HVAC system of a house, such as the system 10 of FIG. 1, stage 1 operation is 50% of a maximum HVAC system capacity and stage 2 operation is 100% of the maximum HVAC system capacity where the stage 1 operation occurs when only the “Y1” signal is issued and received by the thermostat 12 and the controller 24, respectively, and the stage 2 operation occurs when the “Y1” and the “Y2” signals are both issued and received by the thermostat 12 and the controller 24, respectively. During this hour, the controller 24 calculates a total cooling or heating supplied to the house and results of that calculation becomes an initial value for an integrated capacity. As shown in FIG. 4B, after the first hour, the controller 24 continually integrates capacity over a previous hour and the integrated capacity becomes stage 1 operation where stage 2 operation remains the maximum HVAC system capacity. As shown in FIG. 4C, the stage 1 operation will remain at a same capacity until stage 2 operation or shut-off time is commanded and thus changes the integrated capacity. In such cases, the stage 2 operation pulls the integrated capacity higher and the shut-off time pulls the integrated capacity lower. As shown in FIG. 4D, the stage 1 operation will eventually match a house load until conditions change, such as where OAT and solar gain adjustments are warranted.

As shown in FIG. 5A, Department of Energy (DOE) calculations predict a change of (400×Nominal Tonnage) Btu/hr per degree F. on exemplary building loads in heating and the integrated capacity can be increased or decreased by this amount as OAT changes for one system size. As shown in FIG. 5B, DOE calculations predict a change of (−260×Nominal Tonnage A2) Btu/hr per degree F. on exemplary building loads in heating and the integrated capacity can be increased or decreased by this amount as OAT changes for one system size.

With reference to FIG. 6, a variable-speed HVAC system 601 is provided and configured to condition air within an interior space, such as the inside of a residential home for example. The variable-speed HVAC system 601 includes a non-communicating, two-stage system controller 610, such as a thermostat, which is disposed in communication with an HVAC unit 620. The HVAC unit 620 is illustrated as an outdoor unit, though it is to be understood that the HVAC unit 620 could be an indoor unit as well. For purposes of clarity and brevity, the following description will generally refer to the controller 610 as “thermostat 610” and will relate to the embodiments in which the HVAC unit 620 is an outdoor unit.

The thermostat 610 includes a processor 611 in communication with a memory 612 that can be, for example, a read only memory (ROM) and/or an electrically erasable programmable read only memory (EEPROM). The processor 611 is disposed in communication with a controller temperature sensor 613 and a display 614 that can be, for example, a liquid crystal display (LCD). The processor 611 and the memory 612 are configured to operate and to effectively control certain operations of the HVAC unit 620 as described below. The controller temperature sensor 613 is configured to measure the actual air temperature within interior space 602, such as of a building or a residential home. The thermostat 610 is configured to transmit air conditioning signals based in part on system demands to heat or cool the interior space 602. The thermostat 610 can be disposed in wireless electrical communication with the HVAC unit 620 and/or in wired electrical communication with the HVAC unit 620.

The HVAC unit 620 includes a controller 621 in electrical communication with a variable speed compressor 622 and a unit temperature sensor 623. The controller 621 is configured to receive data from the unit temperature sensor 623, to receive the air conditioning signals from the thermostat 610 and transmit a speed signal to the variable speed compressor 622 based in part on the received air conditioning signals and the data. The variable speed compressor 622 is configured to operate at a plurality of speeds in a heating or cooling mode to deliver a compressed refrigerant. The unit temperature sensor 623 is configured to measure an ambient air temperature around the HVAC unit 620. It will be appreciated that the HVAC unit 620 may be provided as one or more of a split system, a variable refrigerant flow ductless unit, a heat pump, a packaged unit, a geothermal heat pump, etc. The unit temperature sensor 623 may be internal or external to the HVAC unit 620.

In accordance with embodiments and, as shown in FIG. 6, the variable-speed HVAC system 601 can further include first dedicated wiring 631 and second dedicated wiring 632. The first dedicated wiring 631 can be electrically interposed between the thermostat 610 and the HVAC unit 620 and the second dedicated wiring 632 can be electrically interposed between the thermostat 610 and the HVAC unit 620. In these or other cases, the thermostat 610 is configured to determine a difference between a sensed temperature and a set point temperature as noted above and to issue a first signal S1 via the first dedicated wiring 631 (i.e., as a continuous 24 volt signal or as another suitable signal type), a second signal S2 via the second dedicated wiring 632 (i.e., as a continuous 24 volt signal or as another suitable signal type) and an off signal in various combinations and sequences based on that determined difference. The off signal can be represented as a signal of its own or as an absence of the first signal S1 and the second signal S2. The following description will relate to the case of the off signal being represented as the absence of the first signal S1 and the second signal S2.

The HVAC unit 620 is receptive of the first signal S1, the second signal S2 and the off signal. The HVAC unit 620 is thus configured to become non-operative and to operate in one of more than three stages (i.e., a number of stages that exceeds a number of the first signal S1, the second signal S2 and the off signal) responsive to the HVAC unit 620 receiving the first signal S1, the second signal S2 and the off signal in the various combinations and sequences with increasingly higher stages being associated with the HVAC unit 620 delivering increasingly higher capacity. In particular, the HVAC unit 620 is configured to become non-operative following off signal reception, to operate at a maximum stage when the first signal S1 and the second signal S2 are received following the off signal reception, to operate at a next higher stage when the first signal S1 and the second signal S2 are received following reception of just the first signal S1, to operate at another next higher stage when reception of the first signal S1 and the second signal S2 persists for a predefined period of time, such as about 15 minutes, to operate at a next lower stage when just the first signal S1 is received following reception of the first signal S1 and the second signal S2 and to operate at another next lower stage when just the first signal S1 is received following reception of the off signal following reception of just the first signal S1.

In accordance with embodiments, the maximum stage of operation for the HVAC unit 620 can be a fifth stage although it is to be understood that there may be fewer or greater numbers of stages available. When the maximum stage of operation for the HVAC unit 620 is the fifth stage, the HVAC unit 620 is configured to operate at the fifth stage when the first signal S1 and the second signal S2 are received following the off signal reception. Similarly, when the HVAC unit 620 is operating at the fourth stage and the first signal S1 and the second signal S2 persist for the predefined period of time, the HVAC unit 620 will advance to operate at the fifth stage. On the other hand, when the maximum stage is the fifth stage and when the HVAC unit 620 is operating at the fifth stage and the first signal S1 and the second signal S2 persist for the predefined period of time, the HVAC unit 620 cannot advance its stage and will continue at the fifth stage until the signal reception changes.

In accordance with further embodiments, when the HVAC unit 620 is operating at the fifth stage with the first signal S1 and the second signal S2 being received, the HVAC unit 620 will stage down to the fourth stage upon reception of just the first signal S1. Subsequently, the HVAC unit 620 can stage down again to stage three following reception of the off signal and subsequent reception of just the first signal S1.

It is to be understood that the various stages of operation of the HVAC unit 620 generally refer to the speed at which the variable speed compressor 622 runs and in turn to the capacity provided by the HVAC unit 620 as a whole. That is, at the first stage of operation, the variable speed compressor 622 runs at a relatively low speed and the HVAC unit 620 provides relatively low capacity for cooling in a cooling mode or heating in a heating mode. At the second, third and fourth stages of operation, the variable speed compressor 622 runs at sequentially higher speeds and the HVAC unit 620 provides sequentially higher capacity for cooling in a cooling mode or heating in a heating mode. At the fifth or maximum stage of operation, the variable speed compressor 622 runs at its maximum speed and the HVAC unit 620 provides the highest possible capacity for cooling in a cooling mode or heating in a heating mode.

With reference to FIG. 7, a partial operation of the HVAC system 601 of FIG. 6 is illustrated. As shown in FIG. 7, in a cooling mode for example, when an HVAC unit 620 is non-operative and a sensed temperature is determined to be greater than a set point temperature by about 0.5 degrees by the thermostat 610, the thermostat 610 will issue the first signal S1 via the first dedicated wiring 631. Upon receiving just this first signal S1, the HVAC unit 620 will operate in the first stage to thereby bring the temperature back down to and below the set point temperature. In an event the sensed temperature continues to rise and is determined to be greater than the set point temperature by about 1.5 degrees by the thermostat 610, the thermostat 610 will issue the first signal S1 and the second signal S2 via the first dedicated wiring 631 and the second dedicated wiring 632, respectively. Upon receiving the combination of the first signal S1 and the second signal S2, the HVAC unit 620 will advance operation to the second stage to thereby increase the capacity of the HVAC unit 620 for bringing the temperature back down to and below the set point temperature. Similar processes would be in place for the heating mode.

With continued reference to FIG. 7, it is to be understood that advancing from stage to stage does not require a linear relationship with the difference between the sensed temperature and the set point temperature. That is, where there may be a 1.0 degree difference between the conditions for setting first stage operation versus second stage operation (i.e., 0.5 degrees above set point versus 1.5 degrees above set point), there may only be a 0.5 degree difference between the conditions for setting second stage operation versus third stage operation (i.e., 1.5 degrees above set point versus 2.0 degrees above set point) and only a 0.25 degree difference between the conditions for setting third stage operation versus fourth stage operation (i.e., 2.0 degrees above set point versus 2.25 degrees above set point) and so on.

In accordance with further embodiments, the HVAC unit 620 can be further configured to anticipate load changes due to OAT changes and change stages accordingly on its own regardless of a shift in signaling by the thermostat 610. That is, in an event of a sudden drop in OAT due to an incoming storm for example, the HVAC unit 620 may anticipate that high-stage capacity for cooling on an otherwise hot day will not be needed over the next few hours. In these or other cases, when enough capacity change is aggregated to equate to one stage, the HVAC unit 620 may automatically and autonomously lower its stage of operation (i.e., from stage five to stage four, from stage four to stage three, etc.).

With continued reference to FIGS. 6 and 7, it is to be understood that the first and second signals S1 and S2 can be issued via wireless communications. In any case, it is also to be understood that the thermostat 610 can issue and the HVAC unit 620 can receive at least one or more additional signals S_{n, n+1, . . . , n+m} wirelessly or via additional dedicated wiring. Where the HVAC unit 620 is receptive of the at least one or more additional signals S_{n, n+1, . . . , n+m}, the HVAC unit 620 can be configured to change states accordingly. As an example, reception of a third signal by the HVAC unit 620 can lead to the HVAC unit 620 advancing two stages of operation or, alternatively, can lead to the HVAC unit 620 decreasing the operation stage by one or more stages (i.e., from the third stage to the second stage, from the second stage to the first stage, etc.).

With reference to FIG. 8, a method 800 of operating a variable-speed HVAC system, such as the variable-speed HVAC system 601 of FIG. 6, is provided. As shown in FIG. 8, the method 800 includes determining a difference between a sensed temperature and a set-point temperature (block 801) and issuing first, second and off signals based on the difference (block 802). The method 800 further includes placing an HVAC unit in a non-operative state following off signal reception (block 803), operating the HVAC unit at a maximum stage when the first signal and the second signal are received following the off signal reception (block 804), operating the HVAC unit at a next higher stage when the first signal and the second signal are received following reception of just the first signal (block 805), operating the HVAC unit at another next higher stage up to the maximum stage when reception of the first signal and the second signal persists (block 806), operating the HVAC unit at a next lower stage when just the first signal is received following reception of the first and second signals (block 807) and operating the HVAC unit at another next lower stage when just the first signal is received following reception of the off signal following reception of just the first signal (block 808). In a parallel flow, the method 800 can also include anticipating load changes due to OAT changes (block 809) and changing stages of the HVAC unit accordingly (block 810).

Technical effects and benefits of the present disclosure are the provision of a method for controlling a variable-speed HVAC system using a non-communicating two-stage thermostat. Whereas typical systems operating with a non-communicating thermostat will operate in two (or sometimes three) discrete stages, the present disclosure allows for fully variable operation without the need for a more costly communicating wall control.

Additional technical effects and benefits of the present disclosure are the provision of a low-cost variable speed system that is controlled through the use of a call of a non-communicating two-stage thermostat for a first signal, a combination of first and second signals and/or an off signal along with timing and OAT information.

The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the technical concepts in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. The embodiments were chosen and described in order to best explain the principles of the disclosure and the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.

While the preferred embodiments to the disclosure have been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the disclosure first described.