Heat pump regulation

A heat pump is a refrigeration device that moves refrigerant between indoor and outdoor coils.This is done by energizing a reversing valve (also known as a "four-way" or "diversion" valve).In cooling, the indoor coil is an evaporator that removes heat from the indoor air and transfers it to the outdoor coil, where it exhausts the outdoor air. When heating, the outdoor coil becomes an evaporator, which takes away the heat from the outdoor air and transfers it to the indoor air through the indoor coil.The reversing valve, controlled by the thermostat, causes the change-over from heat to cool. Residential heat pump thermostats generally have an "O" terminal to energize the reversing valve in cooling.Some residential and many commercial heat pump thermostats use a "B" terminal to energize the reversing valve in heating.The heating capacity of a heat pump decreases as outdoor temperatures fall.At some outdoor temperature (called the balance point) the ability of the refrigeration system to transfer heat into the building falls below the heating needs of the building.A typical heat pump is fitted with electric heating elements to supplement the refrigeration heat when the outdoor temperature is below this balance point.

Operation of the supplemental heat is controlled by a second stage heating contact in the heat pump thermostat.During heating, the outdoor coil is operating at a temperature below the outdoor temperature and condensation on the coil may take place.This condensation may then freeze onto the coil, reducing its heat transfer capacity.Heat pumps therefore have a provision for occasional defrost of the outdoor coil.This is done by reversing the cycle to the cooling mode, shutting off the outdoor fan, and energizing the electric heating elements.The electric heat in defrost mode is needed to keep the system from blowing cold air inside the building.The elements are then used in the "reheat" function.Although the thermostat may indicate the system is in defrost and electric heat is activated, the defrost function is not controlled by the thermostat.Since the heat pump has electric heat elements for supplemental and reheats, the heat pump thermostat provides for use of the electric heat elements should the refrigeration system fail.This function is normally activated by an "E" terminal on the thermostat. When in emergency heat, the thermostat makes no attempt to operate the compressor or outdoor fan.

Thermostat location

The thermostat should not be located on an outside wall or where it could be exposed to direct sunlight at any time during the day.It should be located away from the room's cooling or heating vents or device, yet exposed to general airflow from the room(s) to be regulated.An open hallway may be most appropriate for a single zone system, where living rooms and bedrooms are operated as a single zone.If the hallway may be closed by doors from the regulated spaces then these should be left open when the system is in use.If the thermostat is too close to the source controlled then the system will tend to "short a cycle", and numerous starts and stops can be annoying and in some cases shorten equipment life.A multiple zoned system can save considerable energy by regulating individual spaces, allowing unused rooms to vary in temperature by turning off the heating and cooling.

Setback temperature

HVAC systems take a long time, usually one to several hours, to cool down or  warm up the space from near outdoor conditions in summer or winter.Thus, it is a common practice to set setback temperatures when the space is not occupied (night and/or holidays). On the one hand, compared with maintaining at the original setpoint, substantial energy consumption can be saved. On the other hand, compared with turning off the system completely, it avoids room temperature drifting too much from the comfort zone, thus reducing the time of possible discomfort when the space is again occupied New thermostats are mostly programmable and include an internal clock that allows this setback feature to be easily incorporated.

Dummy thermostats

According to reports, many thermostats in office buildings are non-functioning virtual devices installed to give tenant employees an illusion of control.These virtual thermostats are actually a kind of placebo button. However, these thermostats are often used to detect the temperature in the area, even if their controls are disabled.This feature is often referred to as "locking.