Tuesday, November 13, 2012

What Is HVAC?

What is HVAC?

HVAC (pronounced as an acronym or as “aitch-vac,” depending on individual preference) stands for heating, ventilation, and air conditioning.   The main purpose of an HVAC system is to regulate the climate within a residential or commercial environment so as to keep its occupants comfortable.  While technically many appliances have HVAC properties, the term usually refers to a large system of vents, ducts and equipment used to cool and/or heat a home, workplace, school or church.

The Origins & History of HVAC

The Romans were the first civilization to use any type of warm-air heating system. This was generally reserved for upper-class villas and public bathhouses; the air would be heated in a special furnace and then piped through each room of the house or structure to warm the surrounding air via heat diffusion.

In some cases hot air would be piped through underground channels and allowed to rise through cracks in stone floors after being heated by a furnace in a separate room. These systems, referred to as hypocausts, were remarkably effective for the time.

By the 1700s, hydronic or steam-based heating systems had become popular with Russian and European engineers.

Angier March Perkins installed some of the very first in-home systems in England during the 1830s; his first client was the Governor of the Bank of England, John Horley Palmer, who wished to grow grapes during the cold English winter!

Modern Systems Component Basics
Today, a variety of technologies and methods exist to power home and commercial HVAC systems. The spirit of innovation exhibited by early engineers is still present in the industry today, and the advent of digital technology has sparked exciting new possibilities.  The bare-bones modern HVAC system typically consists of a furnace, an air conditioning unit, a ventilation system, and pipes or PVC ducts to transport air throughout a building.

These ducts will usually have small circular diffusers to release the hot or cool air, while pipes may lead to vents in the walls of individual rooms. Often the air conditioning section of the system is located outside, as this is a more efficient location for heat dispersal. The individual systems rarely interact with each other; only the pipes or ducts connect them to one another.


The heating component of these systems may be one of several different technologies. The most common heating arrangement involves the combustion of a fossil fuel such as oil or propane gas within a furnace, boiler, or other containment device. The heat produced via combustion is then distributed to the other parts of the building via pipes or ducts. Forced air is the most commonly used method of heat distribution in the United States, but engineers in Europe and the UK often design systems that use hot water to produce a similar effect.

Alternative Heat Sources.  In the UK, water is often used to transport heat instead of forced air; water pipes are arranged within a building in such a way that the hot water disperses heat throughout each room on its way to faucets and other outlets. Geothermal heat has also become popular in recent years. These systems can reduce energy bills by 30-40% simply by accessing the steady temperature of the earth. Heat pump technology works similarly, but pulls heat from the outside air instead of from underground. Heat is present in all climates as long as the temperature remains higher than -200 degrees Fahrenheit.


Ventilation is commonly defined as the creation of airflow both in and out of a building. Proper ventilation is one of the main things that ensures air quality within large buildings such as skyscrapers and hotels; without the ability to manage airflow, mildew, mold spores, unpleasant odors, and airborne diseases would be very difficult to control.

A unit called an AHU, which usually connects to the ductwork within a building, controls mechanical ventilation in most circumstances. However, natural ventilation such as windows and simple open vents may be useful for certain specific situations.

Air Conditioning

Most air conditioning components in HVAC systems work via a mechanical refrigeration cycle. Water, ice, and air can all be used as refrigerants, but most modern air conditioners use a chemical refrigerant.

This refrigerant begins the 4-step cooling process in a light, gaseous state. A compressor causes this gas to build up to a high pressure and temperature, whereupon it is released into a condensing coil, allowing heat to dissipate into the outside air and causing the gas to become a liquid.

This liquid is fed into an evaporator, returning to its original gaseous state, and the process of evaporation draws heat from the surrounding air.


In the past, HVAC systems have mainly been reserved for buildings servicing large numbers of people and the homes of the wealthy due to the high cost of installation and, in some cases, maintenance. This is becoming less true as technologies evolve, and many middle-class homes are now designed with central air systems. Units utilizing geothermal heat exchange, for example, may save homeowners a significant amount of money due to their essentially passive technological design.

Environmental Concerns

Certain aspects of HVAC systems are environmentally toxic or detrimental, and this has become increasingly problematic over time. The chemical refrigerant used in air conditioning units contains CFCs, or chlorofluorocarbons, which deplete the ozone layer and contribute to global warming. In addition, the fossil fuels burned to power all aspects of a unit, from the natural gas in the furnace component to the electricity sourced from a coal power plant, are detrimental to a variety of ecological systems.

America’s HVAC Industry

The general American standards for HVAC systems are outlined in the Uniform Mechanical Code, which is published by an organization known as IAPMO (International Association of Plumbing and Mechanical Officials). This code is updated every four years, but does not cover the specifics of system design. The American Society of Heating, Refrigerating, and Air-Conditioning Engineers thus unites American HVAC engineers. ASHRAE puts out a handbook of standards for HVAC design, also updated every four years, which is generally consulted by engineers in addition to the UMC.

Industry Standards.  Most HVAC contractors and companies are members of NADCA, the National Air Duct Cleaners Association. Formed in 1989 as a non-profit, NADCA has established industry standards for cleanliness when it comes to forced air systems. Contractors and companies are most affected by the standards set for by NADCA and IAPMO, as they install and repair systems rather than designing them; that said, ASHRAE standards are often referenced in local building codes, and any contractor worth his or her salt should be familiar with them.

The Future of HVAC Systems

As the global community becomes more and more aware of the finite nature of our energy resources, new technologies have by necessity begun to look toward renewable power. HVAC systems of the future will have a daunting task, as they must regulate temperatures increasingly affected by global warming while relying less on non-renewable fossil fuels such as propane and natural gas. Forward-thinking engineers have risen to meet this challenge, designing new systems that incorporate solar energy and other green technologies.

Going Green.  A variety of strategies will likely be implemented as the HVAC industry goes green. Some designs may choose to integrate electricity requirements with solar panel technology to come up with a self-powering system or to offset traditionally sourced energy needs. Others may eliminate CFC-containing refrigerants or seek ways to access geothermal heat for the furnace portion of modern systems. One company has already invented a self-contained system referred to as the Geosource, which combines air source heat pump and ground heat-exchange technologies.

Alternative Energy.  The components of an HVAC system are as capable of utilizing renewable energy as any other source. One of the major issues with solar generated electricity has been the lack of consistent, powerful generation capacity. However, as the technology improves, it may be a more viable option for HVAC systems. Wind-generated electricity is another renewable option already being used to supplement traditional power plants in many areas. Ultimately, the energy these systems use is likely to be directly connected to the method of generation used by major electricity companies.

A Closing Word

The industry has grown significantly over time as technologies and the needs of consumers have changed. It would be reasonable to expect that this flexibility and fluctuation will continue to extend into the future. In many ways, this makes the present moment an exciting time for those working in the HVAC field. From steam power to geothermal technology, heating, ventilation, and air conditioning systems have come a long way! Possibilities for the future depend primarily on the insight and creativity of the engineers and technicians who make up the current HVAC workforce.

Ultimately, heating, ventilation, and air conditioning systems have a single goal: to create comfortable indoor environments for people. As an industry based on meeting human needs, HVAC technology must evolve along with the human beings it serves in order to provide us all with a clean, well-ventilated future.

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