An HVAC unit is a term used for a centralized heating, ventilation and air conditioning system. An HVAC unit allows for the convenient regulation of the interior temperature and climate of a building. Before the advent of the modern HVAC system, effective interior cooling and heating were often limited to a specific room or portion of a building with localized heating or cooling.
An HVAC unit provides interior cooling by drawing warm interior air into the system through a series of air return ducts. The air is then moved over a series of refrigerated coils. As the air moves over the coils, the heat in the air is transferred to the refrigerant in the coils. A fan or blower sends the cooled air back to the interior of the building through a series of ducts.
As the cold air is being directed into the building, the heated refrigerant is directed to a unit outside of the building. Here the heated refrigerant flows through a series of coils over a cooling fan. The cooling fan helps to dissipate the heat from the refrigerant, which is then directed back to the interior of the HVAC unit to begin the cooling process all over again.
The heating function in an HVAC unit works in much the same manner as the cooling function. Air is drawn into the system through a series of ducts. As the air flows through the system it is heated by the furnace through heat exchangers. A fan or blower sends the heated air back to the interior of a building through a series of ducts.
In addition to heating and cooling the interior of a building, an HVAC unit can actually improve the quality of the interior air through ventilation and filtration. As mentioned previously, HVAC systems draw interior air into the system through a series of ducts. The movement of air prevents stagnation of and circulates interior air and removes odors and excessive moisture. As air moves through the system, some of the existing interior air may also be replaced from air drawn from outside of the building itself. The constant introduction of fresh air also helps to maintain the air quality in the building.
As air is drawn into the HVAC unit, it is also directed through a series of filters. The interior air of a building is a mixture of a variety of things such as human skin particles, insect droppings, pet dander, and pollen. The filtration system protects the unit from these and other airborne pollutants that could cause damage if allowed to enter the inner workings of the unit.
Filters not only protect the HVAC system, but some types of filters are designed to improve the air quality of a building. A HEPA (High Efficiency Particulate Arrestance) filter captures a minimum of 99.7% of all airborne particles and removes almost all allergens from the air. As pollutants are trapped in the filter, they are prevented from re-entering the building when the air is directed back into it.