What many of us “take for granted” in our daily lives, namely the heating, ventilation, air conditioning, and refrigeration systems, have a long and storied history that relies upon aspects of physics, engineering, and environmental considerations. That history is extensive, and beyond the scope of coverage here given the considerations of electromechanical discoveries and thermodynamics which have led to the compression cycle and other components of HVAC.  Given the variety of considerations in functions, however, each topic of H, V, A, and C will be considered separately:


Heating can be either “central” – via a furnace, pump, or boiler, whereby this heat centrally generated can be disseminated via convection, conduction, or radiation. Heat generation can be done via a variety of types – either using fuels of solid, liquid, or gas, or electricity (used to heat coils); subsequently, distribution is done via water (hydronics, which can also be used to heat water for bathing or other function) or steam via radiators. Air can similarly be used to either heat or cool, typically filtered via air cleaners to remove particles. Risks associated include possibility of by-product of incomplete combustion, e.g. carbon monoxide.


Defined as a means of “changing or replacing air in space to control temperature, moisture, odor, or remove microorganisms or other particulate matter, ventilation occurs both internal and external to a building; it can be divided into mechanical/forced or natural ventilation.

Controllable parameters include flow rate via direct drive fans (which incidentally can be used in cold weather from ceiling to floor, as heat rises and warmer air accumulates higher towards ceiling). Natural ventilation, relying upon windows used sometimes strategically (e.g. in warm weather with desired cooling, allowing outflow via high windows of warmer air and inflow via lower windows of cooler air to replace this escaped warm air, known as “stack effect”), Also, an important concept of air changes per hour is introduced – with normal being 4X/hour (or one air change per 15 minutes), with warehouses having perhaps only two; as an example of the other extreme, crowded nightclubs may have 30-50 air changes per hour, or one every 1-2 minutes. Positive pressure ventilation occurs when more air is supplied than exhausted, to keep out particulate matter; negative pressure does the opposite, keeping unintended internal matter from disseminating outdoors.

Air Conditioning

Air conditioning (AC) provides both cooling and humidity control – with fresh air intake about 10% (normally with an AC unit placed in a sealed open window). Refrigeration or AC rely upon removal of heat, achieved via radiation, convection, and/or conduction – with use of a refrigerant such as water, glycol mix, or a chemical, sent through a cycle which is pumped by a compressor at a high pressure and temperature, sent via heat exchanger which loses energy and heat to outside, returning to a liquid to an evaporating coil absorbing heat from indoors and returning to the compressor. Hence, by controlling its gaseous and pressurized state vs. allowing it to expand and in the process cool (and absorb heat), this cools a room depending upon the proper components being exposed to inside vs. outside; this may be reversed when heating vs. cooling is desired. More efficient systems may use a free cooling mode when outer air is cooler than needed inner cooling, so not requiring mechanical energy. Geothermal heat sources can be used in some cases for any of the functions, e.g. via water within the earth at a high temperature. Refrigerators work on a very similar idea, with added insulation to keep interior materials cool.


Use of present HVAC units will likely be amended to make the units more efficient – e.g. by changing fan blade angles, by considering how much wasted or inefficient function is involved and improving it, and by promoting certain regulation and standardization.

ISO building environmental standards have been developed (e.g. ISO 16813:2006) which provides HVAC considerations for noise, appearance, energy efficiency, sustainability, and evaluation of design.   Most HVAC engineers, members of the ASHRAE, are EPA-certified.

In Europe, the group named CIBSE provides guides for HVAC on a variety of topics, ranging from environmental design to sustainability, weather/solar/illuminance data, electricity in buildings, and maintenance.

As regulatory issues around “traditional” HVAC emerge, a new category for the future is also emerging – one which allows control of HVAC via the internet, remotely. Smartphone technology allows control via different apps (an upcoming topic under www.RavishonApps.com), which has recently been not only the subject of convenience, but concerns over security (as others could take control and cause problems ranging from high monthly bills to potential damage). The topic of HVAC itself is very broad, and so will its future be – essentially “climate control” relies upon HVAC, whether in our homes, offices, hotels, stores, cars, or even airplanes (or the Space Station, for that matter)… it is, in a word, often essential to life itself.


(Information above has been acquired from numerous sources, including www.kudzu.com, www.howstuffworks.com, www.wikipedia.org, and www.constructionknowledge.net, among others)