What regulates the operation of auxiliary electric heat based on outdoor temperatures?

The outdoor ambient thermostat is a critical component in the regulation of auxiliary electric heat, especially in heat pump systems. Its primary function is to monitor the temperature outside the building. When outdoor temperatures drop to a predetermined level, the outdoor ambient thermostat signals the system to activate the auxiliary electric heat. This is particularly important because heat pumps may become less efficient or may not be able to provide sufficient heating at very low outdoor temperatures. The auxiliary heating serves as a backup, ensuring that indoor temperatures remain comfortable even when the heat pump alone cannot meet the heating demand due to low ambient temperatures.

The other options, while they play roles in the functioning of heating systems, do not specifically regulate auxiliary electric heat based on outdoor temperatures. The thermal expansion valve manages refrigerant flow within the system; the room thermostat controls indoor temperatures but does not directly account for outdoor conditions; and the heat load calculator is used for determining the heating needs of a space rather than for real-time operational control based on temperature.