SYSTEM AND METHOD FOR COMPRESSOR CAPACITY MODULATION IN A HEAT PUMP

1 . A method for modulating capacity in a compressor for a heat pump operating in a heating mode, the method comprising:

providing a controller configured to provide a plurality of discrete output frequencies to a motor for the compressor of the heat pump;

measuring an outdoor ambient temperature;

selecting a discrete output frequency of the plurality of discrete output frequencies in response to the measured outdoor ambient temperature;

operating the motor at the selected discrete output frequency and a corresponding voltage to produce a corresponding output capacity for the compressor; and

wherein the selected discrete output frequency of the plurality of discrete output frequencies is inversely related to the measured outdoor ambient temperature.

2 . The method of claim 1 further comprising repeating the steps of measuring an outdoor ambient temperature, selecting a discrete output frequency, and operating the motor at the selected discrete output frequency until a demand for heating is satisfied.

3 . The method of claim 1 further comprising the step of executing a start-up process for the compressor, the step of executing a start-up process for the compressor includes:

receiving a first stage heating signal indicating a demand for heating; and

operating the motor at a predetermined startup frequency and a corresponding voltage to produce a corresponding output capacity for the compressor.

4 . The method of claim 1 further comprising:

determining whether a demand for additional heating is present; and

executing the steps of selecting a discrete output frequency and operating the motor at the selected discrete output frequency in response to no demand for additional heating being present.

5 . The method of claim 4 further comprising the step of:

determining whether an operating frequency for the motor is less than a predetermined frequency in response to a demand for additional heating being present;

executing the steps of selecting a discrete output frequency and operating the motor at the selected discrete output frequency in response to the operating frequency for the motor being greater than the predetermined frequency; and

operating the motor at the predetermined frequency in response to the operating frequency for the motor being less than a predetermined frequency.

6 . The method of claim 4 further comprising the step of:

determining whether the demand for additional heating has been present more than one time in response to a demand for additional heating being present;

executing the steps of selecting a discrete output frequency and operating the motor at the selected discrete output frequency in response to the demand for additional heating being present more than one time; and

selecting a discrete output frequency of the plurality of discrete output frequencies greater than an operating frequency of the motor in response to the demand for additional heating being present one time.

7 . The method of claim 6 wherein the step of selecting a discrete output frequency of the plurality of discrete output frequencies greater than an operating frequency of the motor includes selecting a next greater discrete output frequency of the plurality of discrete output frequencies.

8 . The method of claim 1 wherein each discrete output frequency of the plurality of output frequencies has a corresponding predetermined temperature setpoint.

9 . The method of claim 8 further comprising the step of programming, by a user, at least one of the plurality of discrete output frequencies or the corresponding predetermined temperature setpoints for the plurality of discrete output frequencies.

10 . The method of claim 8 wherein:

the plurality of discrete output frequencies includes at least two discrete output frequencies selected from the group consisting of about 35 Hz, about 45 Hz, about 60 Hz, about 80 Hz, about 100 Hz and about 120 Hz; and

the corresponding predetermined temperature setpoints for the plurality of discrete output frequencies includes at least two predetermined temperature setpoints selected from the group consisting of about 50° F., about 40° F., about 30° F., about 20° F., about 10° F. and about 0° F.

11 . The method of claim 8 wherein the corresponding predetermined temperature setpoints progressively decrease in response to the discrete output frequencies progressively increasing.

12 . The method of claim 1 wherein the plurality of discrete output frequencies are separated by at least 5 Hz.

13 . An HVAC&R system comprising:

a compressor, a condenser arrangement and an evaporator arrangement connected in a closed refrigerant loop;

a motor connected to the compressor to power the compressor, the motor being configured to operate at a plurality of output speeds to generate a plurality of output capacities from the compressor;

a control system, the control system being configured to provide the motor with a plurality of discrete output frequencies to generate the plurality of output speeds in the motor;

a sensor arrangement to measure a parameter corresponding to an outdoor ambient temperature and to provide a signal to the control system with the measured parameter; and

wherein, in response to the HVAC&R system operating in a heating mode, the control system being configured to provide a discrete output frequency of the plurality of discrete output frequencies to the motor in response to the measured parameter, the provided discrete output frequency being increased in response to a decrease in the outdoor ambient temperature to generate an increase in the output capacity of the compressor.

14 . The HVAC&R system of claim 13 wherein the sensor arrangement is a temperature sensor and the temperature sensor is configured to measure the outdoor ambient temperature.

15 . The HVAC&R system of claim 13 further comprising a thermostat, the thermostat being configured to provide one of a first stage heating signal or a second stage heating signal to the control system, and wherein a second stage heating signal indicates a greater demand for heating than a first stage heating signal.

16 . The HVAC&R system of claim 15 wherein the control system is configured to provide a discrete output frequency of the plurality of discrete output frequencies to the motor greater than an operating frequency of the motor to generate an increase in the output capacity of the compressor in response to receiving a second stage heating signal for a first time.

17 . The HVAC&R system of claim 13 wherein each discrete output frequency of the plurality of output frequencies has a corresponding predetermined temperature setpoint.

18 . The HVAC&R system of claim 17 wherein at least one parameter selected from the group consisting of the plurality of discrete output frequencies and the corresponding predetermined temperature setpoints for the plurality of discrete output frequencies is programmable by a user.

19 . The HVAC&R system of claim 17 wherein:

the plurality of discrete output frequencies includes at least two discrete output frequencies selected from the group consisting of about 35 Hz, about 45 Hz, about 60 Hz, about 80 Hz, about 100 Hz and about 120 Hz; and

the corresponding predetermined temperature setpoints for the plurality of discrete output frequencies includes at least two predetermined temperature setpoints selected from the group consisting of about 50° F., about 40° F., about 30° F., about 20° F., about 10° F. and about 0° F.

20 . The HVAC&R system of claim 13 wherein the plurality of discrete output frequencies are separated by at least 5 Hz.

21 . The HVAC&R system of claim 13 wherein the control system comprises:

a motor drive connected to the motor; and

a controller, the controller being configured to receive the signal with the measured parameter, determine the provided discrete output frequency and provide control signals to the motor drive to operate the motor at the provided discrete output frequency.

22 . The HVAC&R system of claim 13 wherein the compressor is a reciprocating compressor and the motor is a switched reluctance motor.

23 . A method for controlling capacity in a compressor of an HVAC&R system, the method comprising:

providing a controller configured to provide a plurality of discrete output frequencies to a motor for the compressor;

measuring an outdoor ambient temperature;

determining whether the HVAC&R system is operating in a heating mode or a cooling mode;

in response to the HVAC&R system operating in a heating mode, executing a heating mode operation process comprising:

selecting a discrete heating mode output frequency of a plurality of discrete heating mode output frequencies in response to the measured outdoor ambient temperature;

operating the motor at the selected discrete heating mode output frequency and a corresponding voltage to produce a corresponding output capacity for the compressor; and

wherein the selected discrete heating mode output frequency of the plurality of discrete heating mode output frequencies progressively increases in response to the measured outdoor ambient temperature decreasing to provide an increase in the output capacity of the compressor; and

in response to the HVAC&R system operating in a cooling mode, executing a cooling mode operation process comprising:

comparing the measured outdoor ambient temperature to at least one predetermined temperature setpoint;

selecting a discrete cooling mode output frequency of a plurality of discrete cooling mode output frequencies based on the comparison of the measured outdoor ambient temperature and the at least one predetermined temperature setpoint;

operating the motor at the selected cooling mode discrete output frequency and a corresponding voltage to produce a corresponding output capacity for the compressor; and

wherein the selected discrete cooling mode output frequency of the plurality of discrete cooling mode output frequencies progressively increases in response to the measured outdoor ambient temperature increasing to provide an increase in the output capacity of the compressor.

24 . The method of claim 23 wherein the plurality of discrete output frequencies includes the plurality of discrete heating mode output frequencies and the plurality of discrete cooling mode output frequencies.

25 . The method of claim 24 wherein the plurality of discrete output frequencies are separated by at least 5 Hz.

26 . The method of claim 24 wherein the plurality of discrete heating mode output frequencies are different from each discrete cooling mode output frequency of the plurality of discrete cooling mode output frequencies.

27 . The method of claim 24 wherein the plurality of discrete heating mode output frequencies includes at least one discrete cooling mode output frequency of the plurality of discrete cooling mode output frequencies.

28 . The method of claim 23 wherein:

the step of comparing the measured outdoor ambient temperature to at least one predetermined temperature setpoint includes:

comparing the measured outdoor ambient temperature to a first predetermined temperature setpoint; and

comparing the measured outdoor ambient temperature to a second predetermined temperature setpoint; and

the step of selecting a discrete cooling mode output frequency of the plurality of discrete cooling mode output frequencies includes:

selecting a first cooling mode output frequency and corresponding voltage in response to the measured outdoor ambient temperature being greater than the first predetermined temperature setpoint; and

selecting a second cooling mode output frequency and corresponding voltage in response to the measured outdoor ambient temperature being less than or equal to the second predetermined temperature setpoint.