Peak demand response operation with improved sensible capacity
An HVAC system includes a variable-speed compressor which compresses refrigerant flowing through the HVAC system, a blower which provides a flow of air through the HVAC system at a controllable flow rate, and a controller communicatively coupled to the variable-speed compressor and the blower. The controller receives a demand request, which includes a command to operate the HVAC system at a predefined setpoint temperature. In response to receiving the demand request, a setpoint temperature associated with the HVAC system is adjusted to the predefined setpoint temperature. The variable-speed compressor is adjusted to a low-speed setting, thereby operating the HVAC system at a first tonnage of cooling. The rate of the flow of air provided by the blower is adjusted to a first flow rate, such that a ratio of the first flow rate to the first tonnage of cooling is increased to a first predefined value.
1. A heating, ventilation, and air conditioning (HVAC) system comprising:
a variable-speed compressor configured to compress refrigerant flowing through the HVAC system;
a blower configured to provide a flow of air through the HVAC system at a controllable flow rate; and
a controller communicatively coupled to the variable-speed compressor and the blower, the controller configured to:
receive a demand request, the demand request comprising a command to operate the HVAC system at a predefined setpoint temperature;
in response to receiving the demand request:
adjust a setpoint temperature associated with the HVAC system to the predefined setpoint temperature;
decrease a speed of the variable-speed compressor to a low-speed setting, thereby operating the HVAC system at a first tonnage of cooling, the first tonnage of cooling corresponding to a decreased tonnage of cooling associated with the decreased speed of the variable-speed compressor, wherein the low-speed setting corresponds to operation of the variable-speed compressor at a low speed of about 75% or less of a recommended operating speed of the variable-speed compressor; and
adjust the controllable flow rate of the flow of air provided by the blower to a first flow rate, based on a predefined ratio of blower flow rate to tonnage of cooling (CFM/ton ratio);
wherein, following decreasing the speed of the variable-speed compressor and adjusting the controllable flow rate of the flow of air provided by the blower, a CFM/ton ratio of the HVAC system is greater than or equal to a first predefined value.
2. The HVAC system of claim 1 , wherein the first predefined value is 500 cubic feet per minute per tonnage of cooling.
3. The HVAC system of claim 1 , wherein:
the demand request comprises a start time associated with the command to operate the HVAC system at the predefined setpoint temperature; and
the controller is further configured to, prior to adjusting the setpoint temperature to the predefined setpoint temperature, cause a space conditioned by the HVAC system to be dehumidified before the start time is reached.
4. The HVAC system of claim 1 , the controller further configured to:
determine whether a temperature of a space conditioned by the HVAC system is within a predefined temperature range encompassing the setpoint temperature;
in response to determining the temperature of the space is not within the predefined temperature range, increase the speed of the variable-speed compressor to a medium-speed setting, thereby operating the HVAC system at a second tonnage, the second tonnage of cooling corresponding to an increased tonnage of cooling associated with the increased speed of the variable-speed compressor, wherein a medium speed associated with the medium-speed setting is greater than the low speed of the low-speed setting; and
adjust the controllable flow rate of the flow of air provided by the blower to a second flow rate, such that a ratio of the second flow rate to the second tonnage of cooling is maintained at the first predefined value.
5. The HVAC system of claim 4 , the controller further configured to:
determine whether the temperature of a space conditioned by the HVAC system is greater than a threshold temperature;
in response to determining the temperature of the space is greater than a threshold temperature, further increase the speed of the variable-speed compressor to a high-speed setting, thereby operating the HVAC system at a third tonnage of cooling, the third tonnage of cooling corresponding to a further increased tonnage of cooling associated with the further increased speed of the variable-speed compressor, wherein a high speed associated with the high-speed setting is greater than the medium speed associated with the medium-speed setting; and
adjust the controllable flow rate of the flow of air provided by the blower to a third flow rate, such that a ratio of the third flow rate to the third tonnage of cooling is decreased to a second predefined value, wherein the second predefined value is less than the first predefined value.
6. The HVAC system of claim 5 , wherein the second predefined value is in a range from about 400 to about 450 cubic feet per minute per tonnage of cooling.
7. The HVAC system of claim 1 , the controller further configured to:
determine if a relative humidity of a space conditioned by the HVAC system is greater than a predefined maximum relative humidity value;
in response to determining the relative humidity of the space is greater than the predefined maximum relative humidity value:
adjust the speed of the variable-speed compressor, thereby operating the HVAC system at a second tonnage of cooling, the second tonnage of cooling corresponding to an adjusted tonnage of cooling associated with the adjusted speed of the variable-speed compressor; and
adjust the controllable flow rate of the flow of air provided by the blower to a second flow rate, such that a ratio of the second flow rate to the second tonnage of cooling is decreased to a second predefined value, wherein the second predefined value is less than the first predefined value.
8. The HVAC system of claim 1 , wherein the demand request is received from a third party.
9. A method of operating a heating, ventilation, and air conditioning (HVAC) system, the method comprising:
receiving a demand request, the demand request comprising a command to operate the HVAC system at a predefined setpoint temperature;
in response to receiving of the demand request:
adjusting a setpoint temperature associated with the HVAC system to the predefined setpoint temperature;
decreasing a speed of a variable-speed compressor of the HVAC system to a low-speed setting, thereby operating the HVAC system at a first tonnage of cooling, the first tonnage of cooling corresponding to a decreased tonnage of cooling associated with the decreased speed of the variable-speed compressor, wherein the low-speed setting corresponds to operation of the variable-speed compressor at a low speed of about 75% or less of a recommended operating speed of the variable-speed compressor; and
adjusting a controllable flow rate of a flow of air provided by a blower of the HVAC system to a first flow rate, based on a predefined ratio of blower flow rate to tonnage of cooling (CFM/ton ratio);
wherein, following decreasing the speed of the variable-speed compressor and adjusting the controllable flow rate of the flow of air provided by the blower, a CFM/ton ratio of the HVAC system is greater than or equal to a first predefined value.
10. The method of claim 9 , wherein the first predefined value is 500 cubic feet per minute per tonnage of cooling.
11. The method of claim 9 , wherein:
the demand request comprises a start time associated with the command to operate the HVAC system at the predefined setpoint temperature; and
the method further comprises, prior to adjusting the setpoint temperature to the predefined setpoint temperature, dehumidifying a space conditioned by the HVAC system before the start time is reached.
12. The method of claim 9 , the method further comprising:
determining whether a temperature of a space conditioned by the HVAC system is within a predefined temperature range encompassing the setpoint temperature;
in response to determining the temperature of the space is not within the predefined temperature range, increasing the speed of the variable-speed compressor to a medium-speed setting, thereby operating the HVAC system at a second tonnage of cooling, the second tonnage of cooling corresponding to an increased tonnage of cooling associated with the increased speed of the variable-speed compressor, wherein a medium speed associated with the medium-speed setting is greater than the low speed of the low-speed setting; and
adjusting the controllable flow rate of the flow of air provided by the blower to a second flow rate, such that a ratio of the second flow rate to the second tonnage of cooling is maintained at the first predefined value.
13. The method of claim 12 , the method further comprising:
determining whether the temperature of a space conditioned by the HVAC system is greater than a threshold temperature;
in response to determining the temperature of the space is greater than a threshold temperature, further increasing the speed of the variable-speed compressor to a high-speed setting, thereby operating the HVAC system at a third tonnage of cooling corresponding to a further increased tonnage of cooling associated with the further increased speed of the variable-speed compressor, wherein a high speed associated with the high-speed setting is greater than the medium speed associated with the medium-speed setting; and
adjusting the controllable flow rate of the flow of air provided by the blower to a third flow rate, such that a ratio of the third flow rate to the third tonnage of cooling is decreased to a second predefined value, wherein the second predefined value is less than the first predefined value.
14. The method of claim 13 , wherein the second predefined value is in a range from about 400 to about 450 cubic feet per minute per tonnage of cooling.
15. The method of claim 9 , the method further comprising:
determining if a relative humidity of a space conditioned by the HVAC system is greater than a predefined maximum relative humidity value;
in response to determining the relative humidity of the space is greater than the predefined maximum relative humidity value:
adjusting the speed of the variable-speed compressor, thereby operating the HVAC system at a second tonnage of cooling, the second tonnage of cooling corresponding to an adjusted tonnage of cooling associated with the adjusted speed of the variable-speed compressor; and
adjusting the controllable flow rate of the flow of air provided by the blower to a second flow rate, such that a ratio of the second flow rate to the second tonnage of cooling is decreased to a second predefined value, wherein the second predefined value is less than the first predefined value.