Control system for hvac system

Abstract

A heating, ventilation, and/or air conditioning (HVAC) system includes a controller configured to receive data communications from a communicating thermostat and also configured to receive a demand signal from a non-communicating thermostat. When the controller is receiving the data communications from the communicating thermostat, the controller is configured to generate a compressor speed control signal based on the data communications from the communicating thermostat. The data communications are based on a difference between a thermostat temperature set point and a temperature measurement for a conditioned space. When the controller is receiving the demand signal from the non-communicating thermostat, the controller is configured to generate the compressor speed control signal based on a predefined coil temperature set point and a measured coil temperature. The demand signal is based on a non-communicating thermostat temperature set point not corresponding to the temperature measurement.

1 . A heating, ventilation, and/or air conditioning (HVAC) system, comprising:
 a thermostat configured to generate a thermostat signal to control a vapor compression system based on a difference between a temperature setpoint and a measured temperature; and   control circuitry configured to:
 receive the thermostat signal; 
 determine a target evaporator temperature based on the thermostat signal; and 
 adjust a compressor speed of a compressor based on a difference between the target evaporator temperature and a measured evaporator temperature. 
   
     
     
         2 . The HVAC system of  claim 1 , wherein the control circuitry is configured to implement a first feedback control loop to adjust the compressor speed using the target evaporator temperature as a reference input. 
     
     
         3 . The HVAC system of  claim 2 , wherein the first feedback control loop comprises a PID controller configured to generate a control signal to adjust the compressor speed. 
     
     
         4 . The HVAC system of  claim 2 , wherein the first feedback control loop is configured to adjust the compressor speed in response to operation of the vapor compression system exceeding one or more limit conditions including a maximum pressure, a minimum pressure, a discharge temperature, a current, or a combination thereof associated with operation of the compressor. 
     
     
         5 . The HVAC system of  claim 1 , wherein:
 the control circuitry is configured to operate in a first mode in response to determining that the thermostat is a communicating thermostat; and   the control circuitry is configured to operate in a second mode in response to determining that the thermostat is a non-communicating thermostat.   
     
     
         6 . The HVAC system of  claim 5 , wherein in the first mode, the control circuitry is configured to implement a second feedback control loop to determine the target evaporator temperature using the measured evaporator temperature as a feedback signal. 
     
     
         7 . The HVAC system of  claim 6 , wherein the temperature feedback control loop comprises an additional PID controller. 
     
     
         8 . The HVAC system of  claim 7 , wherein in the second mode, the control circuitry is configured to select the target evaporator temperature from one or more preset evaporator temperatures based on the thermostat signal. 
     
     
         9 . The HVAC system of  claim 1 , wherein the control circuitry is configured to adjust a position of an electronic expansion valve (EEV) based on the compressor speed. 
     
     
         10 . The HVAC system of  claim 1 , wherein the control circuitry is configured to adjust a position of an injection EEV based on the compressor speed. 
     
     
         11 . The HVAC system of  claim 1 , wherein the control circuitry is configured to adjust a fan speed of an outdoor unit based on the compressor speed. 
     
     
         12 . A method of controlling a heating, ventilation, and/or air conditioning (HVAC) system, comprising:
 receiving, via control circuitry, a thermostat signal from a thermostat indicative of an instruction to operate a vapor compression system;   determining, via the control circuitry, a target evaporator temperature based on the thermostat signal; and   generating, via the control circuitry, a control signal to control a compressor speed of a compressor based on a difference between the target evaporator temperature and a measured evaporator temperature.   
     
     
         13 . The method of  claim 12 , wherein generating the control signal comprises implementing, via the control circuitry, a first feedback control loop to adjust the compressor speed using the target evaporator temperature as a reference input, wherein the feedback control loop comprises a controller having a proportional component and an integral component. 
     
     
         14 . The method of  claim 12 , comprising adjusting, via the control circuitry, the control signal in response to operation of the vapor compression system exceeding one or more limit conditions including a maximum pressure, a minimum pressure, a discharge temperature, a current, or a combination thereof associated with operation of the compressor. 
     
     
         15 . The method of  claim 12 , comprising determining, via the control circuitry, that the thermostat is a communicating thermostat, wherein determining the target evaporator temperature comprises implementing, via the control circuitry, a second feedback control loop to determine the target evaporator temperature using the measured evaporator temperature as a feedback signal in response to determining that the thermostat is a communicating thermostat. 
     
     
         16 . The method of  claim 12 , comprising determining, via the control circuitry, that the thermostat is a non-communicating thermostat, wherein determining the target evaporator temperature comprises selecting the target evaporator temperature from one or more preset evaporator temperatures based on the thermostat signal in response to determining that the thermostat is a non-communicating thermostat. 
     
     
         17 . A heating, ventilation, and/or air conditioning (HVAC) system, comprising:
 control circuitry configured to operate in a first mode when connected to a communicating thermostat and configured to operate in a second mode when connected to a non-communicating thermostat, wherein:   in the first mode, the control circuitry is configured to:
 receive digital communication from the communicating thermostat; 
 determine a target evaporator temperature based on the digital communication; and 
 adjust a compressor speed of a compressor based on the target evaporator temperature; and 
   in the second mode, the control circuitry is configured to:
 receive an activation signal from the non-communicating thermostat; 
 set the target evaporator temperature to a predetermined value associated with the activation signal; and 
 adjust the compressor speed of the compressor based on the target evaporator temperature. 
   
     
     
         18 . The HVAC system of  claim 17 , wherein in the first mode and in the second mode, the control circuitry is configured to implement a first feedback control loop to adjust the compressor speed based on the target evaporator temperature and a measured evaporator temperature. 
     
     
         19 . The HVAC system of  claim 17 , wherein in the first mode, the control circuitry is configured to implement a second feedback control loop to determine the target evaporator temperature based on a temperature setpoint and a measured temperature. 
     
     
         20 . The HVAC system of  claim 17 , wherein in the second mode, the activation signal corresponds to a call for a first cooling stage, and the control circuitry is configured to:
 receive an additional activation signal from the non-communicating thermostat corresponding to a second cooling stage; and   set the target evaporator temperature to an additional predetermined value associated with the additional activation signal.