HVAC (Heating, Ventilating & Air Conditioning)

HVAC is an initialism or acronym that stands for "Heating, Ventilating, and Air Conditioning".

Heating

There are different types of standard heating systems. Central heating is often used in cold climates to heat private houses and public buildings. Such a system contains a boiler, furnace, or heat pump to heat water, steam, or air, all in a central location such as a furnace room in a home or a mechanical room in a large building. The system also contains either ductwork, for forced air systems, or piping to distribute a heated fluid and radiators to transfer this heat to the air. The term radiator in this context is misleading since most heat transfer from the heat exchanger is by convection, not radiation. The radiators may be mounted on walls or buried in the floor to give under-floor heat.

In boiler fed or radiant heating systems, all but the simplest systems have a pump to circulate the water and ensure an equal supply of heat to all the radiators. The heated water can also be fed through another (secondary) heat exchanger inside a storage cylinder to provide hot running water.

Forced air systems send heated air through ductwork. During warm weather the same ductwork can be used for air conditioning. The forced air can also be filtered or put through air cleaners.

Heating can also be provided from electric, or resistance heating using a filament that becomes hot when electricity is caused to pass through it. This type of heat can be found in electric baseboard heaters, portable electric heaters, and as backup or supplemental heating for heat pump (or reverse heating) system.

Ventilating

Ventilating is the process of "changing" or replacing air in any space to control temperature or remove moisture, odors, smoke, heat, dust and airborne bacteria. Ventilation includes both the exchange of air to the outside as well as circulation of air within the building. It is one of the most important factors for maintaining acceptable indoor air quality in buildings. Methods for ventilating a building may be divided into mechanical/forced and natural types. Ventilation is used to remove unpleasant smells and excessive moisture, introduce outside air, and to keep interior building air circulating, to prevent stagnation of the interior air.

Air-conditioning

Air conditioning and refrigeration are provided through the removal of heat. In order to remove heat from something, you simply need to provide a medium that is colder—this is how all air conditioning and refrigeration systems work.

An air conditioning system, or a standalone air conditioner, provides cooling, ventilation, and humidity control for all or part of a house or building. The refrigerant provides cooling through a process called the refrigeration cycle. The refrigeration cycle consists of four essential elements to create a cooling effect. A compressor provides compression for the system. This compression causes the cooling vapor to heat up. The compressed vapor is then cooled by heat exchange with the outside air, so that the vapor condenses to a fluid, in the condenser. The fluid is then pumped to the inside of the building, where it enters an evaporator. In this evaporator, small spray nozzles spray the cooling fluid into a chamber, where the pressure drops and the fluid evaporates. Since the evaporation absorbs heat from the surroundings, the surroundings cool off, and thus the evaporator absorbs or adds heat to the system. The vapor is then returned to the compressor. A metering device acts as a restriction in the system at the evaporator to ensure that the heat being absorbed by the system is absorbed at the proper rate.

Central Air Conditioning Systems are often installed in modern residences, offices, and public buildings, but are difficult to retrofit (install in a building that was not designed to receive it) because of the bulky air ducts required. A duct system must be carefully maintained to prevent the growth of pathogenic bacteria in the ducts. An alternative to large ducts to carry the needed air to heat or cool an area is the use of remote fan coils or split systems. These systems, although most often seen in residential applications, are gaining popularity in small commercial buildings. The coil is connected to a remote condenser unit using piping instead of ducts.