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What is an HVAC Unit?

By R. Anacan
Updated May 16, 2024
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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.

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Discussion Comments

By anon266804 — On May 07, 2012

Can you have a hvac unit without having a coil in them?

By ValleyFiah — On May 20, 2011

Does anyone know anything about HVAC unit prices? Approximately how much should I pay for a unit for a 2,300 square foot home? I would like something that is higher quality and efficient. Additionally, what types of rebates are available for purchasing new HVAC units? What happens with the old unit, is there a way to get any money for it?

By aplenty — On May 18, 2011

@georgesplane- I am not an HVAC professional, but I know a little about residential HVAC units (I study energy in the built environment). I would tell the technician to check your evaporator or the fluid in refrigerant in your unit. The evaporator is supposed to work below the dew point so that it condenses the humid air that comes into contact with the evaporator coils. The water that is drawn out of the air is then supposed to be drained out of the building through a drain or piping.

It sounds like your evaporator is not condensing the humid air properly, so instead, your HVAC unit is just concentrating and redistributing the humid air until the humidity creeps up. I would get your HOA on this quickly because building humidity should generally stay within 20-40 percent. Anything more can cause damage to furniture, artwork, and electronics. It can also lead to mold and mildew as well as poor indoor air quality.

By Georgesplane — On May 17, 2011

I am having problems with my HVAC unit. The unit was manufactured 21 years ago and has been installed 18 years ago (according to the stickers attached to the unit). The unit is already very inefficient but it is the HOA's responsibility to repair or replace the unit. The HOA sent someone to my house for HVAC repair, but all the repairperson did was replace the thermostat.

The problem with the unit is it increases the humidity in my condominium when it is running. I actually bought a hygrometer to monitor humidity after the neck on one of my guitars cracked (from humidity changes I suspect). The humidity is around 25-35% when I do not run the unit, but when I turn it on, it slowly climbs to 60-65%. The technician tried telling me there was nothing wrong with the unit, but the humidity only increases when I turn on the air conditioning. Does anyone have any advice?

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