HVAC for Beginners
What does HVAC stand for? The acronym HVAC means Heating, Ventilation, and Air Conditioning. The basic acronym can be pronounced one of two ways: either speaking all the letters individually, which would sound like “H-V-A-C” or in a shorter alternate “H-vac”. Since it is so closely related, an “R” for refrigeration is sometimes added to the end.
HVAC used by itself is a broad technical term—a quick way to describe people, companies, processes, and equipment that measure and control the quantity, flow, and quality of indoor air in various situations. The phrase “indoor climate control” can also be used to describe this topic. The subject of HVAC encompasses two main parts: (a) basic heating, cooling, conditioning and ventilation of air in indoor spaces, and (b) more advanced indoor air quality issues of air filtration for the removal of particulates such as pollen, dust, and smoke; advanced humidity control for comfort and to minimize the growth of molds and mildew; and source elimination or removal of gaseous contaminates given off by materials and appliances inside homes and commercial spaces.
HVAC contractors generally fall into one of two general categories: commercial or residential. Due to differences in the design and size of the equipment involved, often HVAC contractors will either offer a combination of residential and light commercial or heavy commercial work. As described in other sections of this site, hiring the right HVAC contractor is one of the most important steps to having a good heating and air conditioning experience when you buy a new HVAC system. Why? Your HVAC contractor controls the four most important steps:
- Performing the load calculations or heat loss for your indoor space
- Advising you on comfort, energy efficiency, and more regarding HVAC equipment in your specific situation
- Designing the air distribution system including the air handlers and ductwork
- The quality of the HVAC equipment installation
HVAC equipment maintenance, repair service, or replacement
HVAC work can be generally divided into three areas: equipment maintenance, repair service, or replacement. Within those areas, the companies often divide their work into commercial and residential HVAC, with some overlap between residential and light commercial work.
This topic can be sub-divided into light commercial and heavy commercial or industrial heating, ventilation, and air conditioning. Light commercial HVAC applications would be small businesses or offices that use split systems, small package units, heat pumps, or other equipment similar to that found in residences. As the size of the building or the HVAC conditions intensify, contractors use large package units or evaporative systems of varying size and design on rooftops or beside commercial buildings. Unlike residential HVAC which can usually be carried in pieces by hand, the size, weight, and location of the equipment for commercial work often requires special lift trucks or cranes, especially during new installations.
Residential HVAC contractors perform HVAC repairs, maintenance, and installation of new heating and air conditioning systems in dwellings such as homes, duplexes, condos and apartments. The type of HVAC equipment they work with most often depends on the part of the country they cover. For example, in many parts of the country, the furnaces for central heating run on natural gas. In other parts of the country such as the northeast, heating oil is the primary fuel for residential heating. Examples of residential HVAC equipment would be central air conditioning and heating split systems, heat pumps, or ductless heating and air conditioning units used for one-room situations.
Common HVAC Equipment
Thermostats and controls
All HVAC equipment uses controls to monitor and adjust the temperature settings for the space being heated or cooled. HVAC control equipment includes: thermostats, which set the temperature, sensors which read the temperature or humidity, either at the control or at a remote location, and related equipment. Improvements in programming features allow fine tuning, such as setting the sensitivity of the system to optimize for comfort or energy savings.
Heating, cooling, humidity control, and ventilation
Directly or indirectly through the use of electricity, HVAC involves either the combustion of fuel for heating, cooling, and conditioning the air or some combination of capturing, converting and moving naturally occurring heat, cool, or energy from where it exists outdoors (including underground) to where it is needed indoors. One type of HVAC system, the heat pump, uses a combination of both these methods.
Use of compressed refrigerants or working fluids
Another common element across the HVAC industry and refrigeration is the use of compressed refrigerants of various kinds. As the refrigerant in a closed system is compressed or expanded, it changes to a gas (in evaporator coils) and to a liquid (in condenser coils) and back. During this process refrigerants help to cool, or condition the air by removing moisture. In applications such as a refrigerator, freezer, or a window air conditioner, the system containing the refrigerant moves the heat moves in one direction. However, heat pumps contain a reversing valve that allows the system to work in both directions.
In addition to the physical properties needed to expand and condense to move heat and condition air, refrigerants must be non-toxic and non-combustible enough to use around humans, not corrode the equipment that contains it, and not harm the environment. Through the years, refrigerants have not all met enough of these criteria, and they are still evolving. Some of the earlier refrigerants were sulfur dioxide (no longer used) and ammonia. There have been some recent international and national regulatory changes and environmental enhancements regarding refrigerants.
Fans and blowers and ducts to move the warm or cool air around
Once the air has been heated, cooled, or conditioned, it has to be moved to the places where it is needed indoors in the correct proportions. This involves either a forced air system involving duct work with fans or blowers, the piping of liquids or gases such as steam, or the natural flow of air, heat or cool in a passive design.
Load calculation plays a key role before the installation of new HVAC equipment. Why? Too little capacity makes your air conditioning system work to hard to cool the space. The system runs too long, wearing out parts of the system prematurely and wasting energy. You would also not likely feel cool enough in all indoor areas. Too much air conditioning capacity causes the Air conditioner to cycle on and off too quickly. This does not give the A/C system time to adjust the humidity of the air and causes an uncomfortable type of clammy or damp cold feeling.
On the heating side, a furnace with too much heating capacity also causes, at a minimum, you to pay too much for the equipment. Depending on the sensitivity settings, it could also cycle on and off quickly, wasting start-up energy in the fan and the furnace. Too little heating capacity for the features and condition of your home or building could cause cold spots or your heating system to run longer than optimum.
Within the HVAC industry, the Air Conditioning Contractors of America publish, which is known as the “Bible” of the residential contracting industry. This manual is the accepted industry standard, and is approved by ANSI (American National Standards Institute) for the proper sizing and selection of HVAC equipment in residential homes.
Maintaining indoor environments requires the correct air pressure between rooms or floors in a building. Proper zoning, vent layout and air distribution prevent cold and hot spots due to improper distribution of the warmed or cooled air.
The “whole house” approach to HVAC
The goal of HVAC is to provide indoor comfort and good health. Heating, ventilation, and air conditioning exist in the context of a house or building. The part of the structure that affects contact between the inside and outside air is called the “envelope”.
Weaknesses in the envelope, such as poor attic insulation or air leaks around windows and doors increase the load on the air conditioning through unnecessary heat gain and on the heating system through unnecessary heat loss.
When planning for changes or improvements in your HVAC system, be sure to include a well thought out overall plan that coordinates the HVAC equipment and the envelope. Taking a “whole house” approach helps you avoid “weak links” and bring you more comfort and lower bills most efficiently.
The role of HVAC in energy conservation
According to U.S. Department of Energy HVAC in the United States uses almost one third of our annual energy consumption for the heating, ventilation and air conditioning of our homes and businesses.