Heat Pump Setback Temperature Control With Cold Weather Override

Heat pump setback temperature control with cold weather override

by

Isabella X

Multistage thermostats have been used for a long time to control stages of heating wherein a refrigeration heat pump is used for one stage and auxiliary electrical strip heat is used for other stages. Also there has been a continual need forprotection for refrigeration apparatus when exposed to cold temperatures such as electrical heaters for the outdoor compressor unit for maintaining the unit warm during the inoperative period. When heat pump apparatus is used for heating as the firststage in a multistage control system, during normal temperature control at a high heating load with low outdoor temperatures, the compressor is almost continually operated.

When a multistage thermostat control system is used with a night setback thermostat, the controlled temperature desired in the space is setback to some lower level during a selected period of time. During a portion of the setback time, there maybe no call for heat and thus the refrigeration heat pump can remain idle for an extended period of time before a call for heat brings it into operation. During low outdoor temperatures, the starting of the heat pump after an extended inoperative periodcan result in damage. Additionally, if the space temperature is allowed to drop for a night setback during a heavy heating load with a low outdoor temperature, the pickup load to bring the temperature back to normal is extremely great. The controlsystem may by necessity need to bring on the more expensive electrical strip heat for a pickup operation.

The present invention provides for a means responsive to outdoor temperature to maintain the refrigeration heat pump in operation when the outdoor temperature drops below some predetermined value during the setback time period. During lightloads even though there is a low outdoor temperature, the continuously energized heat pump may result in an increased space temperature; therefore, the invention contemplates the use of a temperature responsive element mounted in the space to overridethe continuous energization of the heat pump should the space temperature exceed some predetermined value during the setback period.

A multistage timer control setback thermostat control system maintaining a normal temperature in a space and during selected time periods a reduced temperature wherein a first stage is a refrigeration heat pump, the operation of which is affected by outdoor temperature, and a second stage is an auxiliary electrical heating source. An outdoor temperature responsive means is connected in the control system to maintain the heat pump energized during the space temperature setback period if the outdoor temperature is below some predetermined value. Additionally, the indoor thermostat has a high limit temperature responsive means for terminating the operation of the heat pump should the space temperature exceed some predetermined value during the space temperature setback period.

As the outdoor temperature drops below the 35 F. temperature, thermostat closes to maintain the heat pump continuously energized during the setback period of time. If there is sufficient heat output from the heat pump and theinternal heat in the building which might come about by lights or cooking and people to exceed the normal day setpoint of the temperature, limiting thermostat opens to turn off the heat pump. With such an operation of the heat pump continuouslyduring the cold weather below 35 F., upon morning pickup the amount of heat requirement from the auxiliary heat is minimized to increase the efficiency of the heating system.

Many compressor manufacturers also have been concerned with extended off periods of the compressor during cold weather which can lead to premature failure of the heat pump. The continuous energization of the heat pump by thermostat at lowoutdoor temperatures with the exception when the high limit thermostat might open not only increases the efficiency of the system but extends the life of the heat pump.

The refrigeration heat pump has a compressor and an indoor and outdoor heat exchanger wherein the efficiency decreases with the lowering of the outdoor temperature and its operating life is extended when the compressor is not allowed to stop whenthe outdoor temperature is below said first predetermined value, and the auxiliary heating heat source is electrical heating apparatus, which when used during pickup periods of operation after a setback time period, when the space temperature is at the setback temperature, to restore the space temperature to thenormal temperature, is more expensive to operate than a refrigeration heat pump.

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