Heat Pump Electric Backup Heating
Typically, air-source heat pumps are more common in southern climate regions where the temperatures in the winter are mild. When the temperature outdoors drops below 38 degrees Fahrenheit, the outside heat pump units start lagging behind. That is a lag on demand to heat the structure. Therefore, a backup source of heat is needed to provide heating when the temperature outside drops below this temperature. If you have an air source heat pump, you likely use electric backup heating.
Heat Pump Electric Backup Heating - Staging Electric Heat Strips for Heat Pump Back-up Heat
As the temperature outside falls the ability of the outside heat pump condensing unit to provide declines. A heat pump condenser absorbs heat from the outside air and moves this heat indoors. Even though the temperature outside is 40 or 45 degrees Fahrenheit, there is still heat present in the air. However, as the temperature drops, the mechanical process used to move this heat to the indoors declines. For this reason, it becomes necessary to provide backup heat for the structure. That is sometimes done in stages to minimize energy usage.
When a heat pump system with back up heat strips is properly controlled, only the amount of energy necessary to provide heat for the demand is utilized. This is down with a heat pump thermostat. As the temperature outside drops and the outside unit loses its ability to provide heat, the thermostat ambient temperature reading drops. But, the unit cannot keep up with demand, and the temperature in the structure drops. Depending on the thermostat, staging set points or the settings of the stage set points (in some heat pump thermostats the temperature set point for staging is manually set on installation. These are usually top of the line digital heat pump thermostats.).
A heat pump system with two stages of heat will have temperature set point differentials of 2 to 4 degrees Fahrenheit. These degree differentials initiate staging of the heat strips. If the temperature drops below 2 to 4 degrees Fahrenheit of the manual setpoint stage, one will turn on. Stage one will provide backup heat for the system. A temperature drop of 2 to 4 degrees Fahrenheit further below the manual setpoint adjustment, then the second stage of electric heat strips will engage. That provides additional heat above the first stage for the structure.
Electric Heat Strips and Heat Pump Condenser Defrost
Every air to air heat pump system needs a defrost cycle to defrost the coils of frost and ice. The heat pump condenser almost always operates below the dew point when in the heating mode. When the heat pump condenser is operating below the dew point, moisture in the air will cause frost or ice to build up. The frost or ice build-up happens on the outside heat pump condenser unit. Therefore, it is necessary to defrost the heat pump condenser coils on a periodic basis to prevent blockage of the heat pump condenser coils from ice and frost build-up. A defrost timer control board controls that (printed circuit board).
Lastly, the outside heat pump condenser unit will change from the heating cycle to the cooling cycle. In the cooling cycle, the heat pump condenser unit will begin to heat up so that the ice and frost will defrost. When this happens, cold air can be introduced into the structure and needs to be countered. The defrost timer control board, when it calls for the heat pump condenser unit to go into the defrost mode, will also engage the electric heat strips to counter the cold air produced by the heat pump condenser when it goes into defrost mode.
The video below is about a hybrid heat pump system. A hybrid heat pump system uses a gas furnace backup heat rather than electric heat strips. Don’t forget to share our page on social media with the handy buttons located below the video. Thanks!!
Heat Pump Electric Backup Heating
Technical Resource: Refrigeration and Air Conditioning Technology