Heating, Ventilation, and Air Conditioning (HVAC) systems provide the means to control the temperature, humidity, and cleanliness of the air we breathe in homes, schools, offices, and factories.
Members of the HVAC trade install, maintain, and repair these systems.
Most heating systems operate on the heat transfer principle. That is, heat is created in one place and carried to another by means of circulating air or water.
In a forced-air system, a hot metal heat exchanger in the furnace is heated by burning a fuel such as natural gas. Air flows over the heat exchangers and heat is transferred to the air, which is circulated through ducts to the locations needing heat.
In a hot water (hydronic) heating system, water (the heat exchange medium) is heated in a boiler then piped to heat exchangers in the heated space. Air from the heated space flows over the heat exchanger, and heat is transferred to the air.
A variety of fuel can be burned to heat the air or water, but natural gas and oil are the most common. Of these, natural gas is the most popular in cold climates.
Electricity is also used as a heat source. The electricity flows though a coil of heavy wire, causing the wire to heat up. The heat is then transferred to air flowing over the coil.
Ventilation is the introduction of fresh air into a closed space in order to control air quality.
In addition to fresh air, methods are needed to remove dust, pollen, molds, vapors, and odors from the indoor air.
In a residential forced air system, a humidifier and an electronic air cleaner can be added to the system to improve air quality.
In an industrial environment, special ventilation and air quality management systems, including fans, ventilating devices, and special filters, may be needed to eliminate toxic and noxious particles from the air.
The U.S. government has strict regulations governing indoor air quality (IAQ) in industrial environments to protect workers and prevent the release of toxic materials to the outside air.
Mechanical refrigeration systems provide cooling by using a principle known as the refrigeration cycle.
The refrigeration cycle relies on the ability of chemical refrigerants to absorb heat as it flows through a warm space.
The space becomes cooler because it has transferred its heat to the refrigerant, which carries it away.
It is important to recognize that air conditioning does not add cool air to an indoor space; it simply uses refrigerant to carry heat to another location such as the outdoors.
The mechanical refrigeration cycle relies on four main components: compressor, evaporator, condenser, and expansion device.
The compressor provides the force that circulates refrigerant and creates a pressure differential in the system.
The evaporator is a heat exchanger where the heat in the warm indoor air is transferred to the cold refrigerant.
The condenser is also a heat exchanger. Heat absorbed by the refrigerant is rejected to the outdoor air by the condenser.
The expansion device provides a pressure drop that lowers the boiling point of the refrigerant so that it can absorb heat in the evaporator.
The mechanical refrigeration cycle relies on the relationship between temperature and pressure.
A rise in pressure causes a rise in temperature and vice versa. This is why the refrigerant temperature can be very low at one point in the system and very high at another.
A heat pump is a special type of air conditioner that can provide both heating and cooling.
HVAC technicians must be familiar with the various codes, specifications, and blueprints that they will encounter on the job.
A complete set of blueprints will often contain several types of drawings. Information about HVAC ductwork and wiring can be found on the architectural, electrical, and mechanical plans of construction drawings.
HVAC drawings show piping for water supplies and returns, air handling equipment, AC systems, HVAC component diagrams and schematics, and more.
HVAC schedules are tables shown on HVAC drawings that provide necessary details.
Shop drawings show how a specific portion of the job is to be done, such as the fabrication and installation of duct runs.
Various types of pipe will be encountered on project drawings. Piping systems used in HVAC use iron, steel, copper, and plastic pipe.
Building codes are used to regulate the health and safety aspects of building construction in a community. Local codes are based on the International Building Code.
The specifications for a building or project are the written descriptions of work and duties required by the owner, architect, and consulting engineer.
Discrepancies may exist between drawings and specifications. The project manager must determine whether the drawings or specifications take precedence.
System commissioning is a process by which a formal and organized approach is taken to obtaining, verifying, and documenting the installation and performance of a particular system.
There are tens of millions of heating and cooling systems in the U.S. and millions are added every year. This creates opportunities for workers to install, service, troubleshoot, and build HVAC systems.
The industry can be viewed as having three segments, each of which has distinct career opportunities.
Community-based firms install and service residential and light commercial systems.
Many community-based firms are subsidiaries of nationwide firms known as consolidators that provide centralized management, purchasing, training, and other benefits that only a large organization can provide.
Commercial/industrial firms install and service equipment in office buildings, factories, and apartment complexes.
The manufacturing sector includes the companies that build HVAC systems and equipment. Manufacturers employ many types of workers, including the people who write instruction manuals and training programs.
Training can be done on the job (OJT) or as a formal apprenticeship-training program.