Air condition in Holly helps to remove the heat from indoors by cooling the air for thermal comfort. The comfort applications aim to provide a building indoor environment that remains relatively constant in a range preferred by humans, despite changes in external weather conditions or in internal heat loads.
In milder winter climates, where temperature is quite low, heat pumps are used. Heat pump in Holly is a term for a type of air conditioner in which the refrigeration cycle is able to be reversed, producing heat instead of cold in the indoor environment, commonly referred to, and marketed as, a reverse cycle air conditioner. Some home-owners in Holly elect to have a heat pump system installed, which is actually simply a central air conditioner with heat pump functionality, that is the refrigeration cycle is reversed in the winter. When the heat pump is enabled, the indoor evaporator coil switches roles and becomes the condenser coil, producing heat. The outdoor condenser unit also switches roles to serve as the evaporator, and produces cold air that is colder than the ambient outdoor air.
This is due to the problem of the outdoor unit's coil forming ice, which blocks air flow over the coil. To compensate for this, the heat pump system must temporarily switch back into the regular air conditioning mode to switch the outdoor evaporator coil back to being the condenser coil so that it can heat up and de-ice. A heat pump system has a form of electric resistance heating in the indoor air path that is activated only in this mode in order to compensate for the temporary air conditioning, which would otherwise generate undesirable cold air in the winter.