HVAC stands for Heating Ventilation, and Air Conditioning; it represents the technology used in climate control of indoor environments, whether it be in a residential/office building, automobile, warehouse, etc. Based upon the principles of thermodynamics, fluid mechanics, and heat transfer HVAC falls under the sub-discipline of mechanical engineering.
The meaning behind HVAC isn’t as difficult as it may sound. The definition is in the acronyms: It’s a system designed to heat, ventilate and condition the air in an enclosed environment. Contrary to popular belief “air conditioning” does not refer to cooling, but rather more general as in changing / alternating the temperature either up or down. It is as if you are conditioning the air to fit your requirements (whether it be up or down is irrelevant). It’s a more modern idea that air conditioning (A/C) entails chilling the air.
The photo above actually describes the a/c unit in a car, but for educational purposes it’s a little less clustered and explains the general idea.
Any air conditioning unit circulates air using pressure and a few rules of thermodynamics within an enclosed system. The cool air felt from an a/c doesn’t actually come from the freon itself, but rather from the effects of heat transfer. When heat moves it causes a low pressure behind it which feels cool. Ever noticed how one can sometimes feel a gust of cold air blow on you when opening a refrigerator It’s not cold air from refrigerator but rather a combination of warm air in the room and a persons own body heat rushing into the fridge. An environment will always want to be in equilibrium, which is why you feel that gust of air even though what you are actually feeling is heating moving away from you.
The following four steps explain the general idea:
- The compressor increases the pressure of freon turning it from a gas into a liquid and pushes it towards the evaporator.
- Moving towards the evaporator excess heat is ventilated by passing through a condenser and fan.
- Once the liquid reaches the evaporator pressure is quickly lowered causing the freon to turn into gas. Thermodynamics demands that heat in an environment to always be in equilibrium. When a liquid turns into gas it undergoes a process called phase conversion. During this process the liquid/gas absorbs heat from it’s surrounding environment making the surrounding air cooler. A fan by the evaporator blows this cold air into the room.
- From the evaporator coil the freon is pushed towards the compressor where it once again turned into a liquid and the process starts over.
Some Fun History Stuff:
The process of cooling the air has been around since the early civilizations. The most notable empires to have used some type of temperature regulation are the Roman and the Persian civilizations.
Rome: Only available to the extremely wealthy, the Romans circulated water from their system of aqueducts through pipes in the wall. The circulated water cooled the buildings walls and by that manner cooled the entire home.
The Persians used wind ventilation design called a windcatcher or Malqaf in Arabic. A building would be designed with 1 to 8 openings to catch air flow from one or more directions and releasing it causing a draft. This system does not rely on any type of cooling device, but rather relies more on ventilation and air flow to cool the building. (Javaheri)
“Wikipedia.” HVAC. N.p., 10 2012. Web. 16 Oct 2012. <http://en.wikipedia.org/wiki/HVAC>.
Glass, Nick. “CNN.” Ancient ‘air-conditiong’ cools building sustainably. CNN, 08 2012. Web. 16 Oct 2012. <http://www.cnn.com/2012/02/28/world/asia/ancient-air-conditioning-architecture/index.html>.
Howard, Sawyer. “Coolers Used by Ancient Romans.”eHow – Discover the expert in you.. eHow, n. d. Web. Web. 16 Oct. 2012. <http://www.ehow.com/info_8370402_coolers-used-ancient-romans.html>.
Javaheri, Elyana. “How Ancient Persian Architecture Captured Wind Energy Underground to Green Buildings.” thisbigcity. thisbigcity.net, 20 2012. Web. 16 Oct 2012. <http://thisbigcity.net/how-ancient-persian-architecture-captured-wind-energy-underground-to-green-buildings/>.
Image 1: A-C. N.d. Mt. Healthy Auto RepairWeb. 16 Oct 2012. <http://www.mthealthyautorepair.com/A-C.html>.
Image 2: Fellanamedlime, . Malqaf.jpg. 2010. WikipediaWeb. 16 Oct 2012. <http://en.wikipedia.org/wiki/File:Malqaf.jpg>.