The APR Control is a capacity-control device that modulates a system’s air conditioning or refrigeration capacity to match variations occurring in the BTU quantity of the existing load. The device accomplishes this capacity modulation by "reading" the heat content of the system return air, which changes the pressure of the suction gas. Using its hot gas bypass valve, the APR Control then bypasses a portion of the hot gas discharge from the compressor through the device’s desuperheating chamber and into the suction inlet of the compressor.
The hot gas enters the desuperheating chamber at an angle creating a circular hot gas path, wiping the walls of the chamber and giving up excess system heat. The gas then travels up the “mixed gas lift tube,” losing energy as it returns to the system’s compressor suction inlet. The increase in suction pressure resulting from the hot gas and suction mix reduces the compression differential in the compressor, causing a decrease in required compressor horsepower.
Through the evaporator coil, the APR Control senses the enthalpy of the return air. A reduction in the enthalpy of the return air causes a drop in coil temperature that causes a drop in the suction pressure. This triggers instant response in the APR Control hot gas bypass valve and causes it to bypass some of the compressor discharge through the APR Control desuperheating chamber to the compressor suction return. This results in a decrease in hot gas to the condenser coil and ultimately less liquid refrigerant to the evaporator coil.
At the evaporator (in an R-410a system), the APR Control attempts to hold the DX coil at 105 p.s.i. by changing the rate of flow of liquid refrigerant into the DX coil and adjusting the dehumidification window of the evaporator coil. Simultaneously, the difference in system BTU capacity and the current BTU load is continually being bypassed in the form of hot gas through the APR Control’s desuperheating chamber and into the suction line at the compressor.
The overall effect is a reduction in cooling capacity of the DX coil corresponding to the reduction in the load. Most importantly, the APR Control will not decrease the maximum or designed capacity of the system when it is needed!