Parts of an HVAC System

Parts of an HVAC System

Parts of An HVAC System


The HVAC system installed in a commercial or office space differs greatly from the heating and cooling system that can be found in a residential structure. In a home, the heating system is set to deliver warm air during the winter and cool air in the summer. It does this using a furnace, an air conditioner, and a common set of ductwork. When the thermostat detects that a home is too cold, it sends signals to the furnace, which then delivers warm air simultaneously to all parts of the house.

Likewise, in the summer, a thermostat will detect when a home has become uncomfortably warm. It then signals the central air conditioning system to deliver cool air simultaneously to all parts of the house. As with the hot air from the furnace, the cool air is distributed through the ductwork. Note that it is typical to have only one thermostat, and a residential HVAC system does not account for temperature variation in other rooms. Usually, small HVAC systems measure the temperature in only one room.

The conditions in an office or commercial space are quite different. Higher concentrations of people and equipment will generate more heat, making air conditioning or recirculation of air more important than providing heat. Although the air handling equipment is centralized, different rooms and regions in the building will have different needs for heating and cooling. These needs are called “loads” because they place a load or demand on the HVAC system. These loads can come from equipment, people, weather, and many other factors.

In the simplest case, loads are addressed by providing a constant supply of cool air, which is then managed by the HVAC distribution system. The chiller or air conditioner utilizes heat exchangers and circulated fluid or gas to cool the air that is passed through it. The air handler is a fan or blower that moves air throughout the building's ductwork. Axial or centrifugal fan types are found in the air handler. Depending on the configuration and design of the fan, different speeds and strengths can be derived.

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Air Filters

Depending on the requirements of the occupants and the activities in the building, various grades of air filters are used in an HVAC system. General-purpose air filters are included in the air handler itself while more sophisticated filters such as High-Efficiency Particulate Air (HEPA) filters may be used in the downstream ductwork. These filters can purify the air from dust, contaminants, and other particulate matter described in the specifications of the requirements for the HVAC system.

Ductwork and Dampers

Round, square, or rectangular ductwork provides a passage for the conditioned air from the air handling unit to the environment. A damper consists of one or more blades that can be used to control the amount of airflow through a duct. Manual dampers are used to ensure that different parts of the building receive proportional ventilation based on area and demand. Automated dampers may be installed at firewalls because they automatically close in case of a fire.

A terminal unit is a device that uses an automated damper to control the amount of air that is delivered to a room or region. A damper is typically controlled by an electric, pneumatic, or digital actuator, which in turn is regulated by a thermostat.

Heating and Cooling Zones

A set of adjacent rooms or regions in a building that have identical heating and air conditioning needs is called a zone. It is typical to assign at least one terminal unit and a corresponding thermostat to each zone. Manufacturers build many different varieties of terminal units to suit all types of building needs.

Heating coils may be installed after a terminal unit to provide heat on a zone by zone basis. As previously mentioned, buildings with a high number of occupants may not require extensive heating even during the coldest months of the year. Heating coils offer an efficient way of providing heat for those few areas that require it and are controlled by the same thermostat system as the terminal unit.

Various types of ducts have linings that are used to dampen the noise within them. A short length-line ductwork called an attenuator is often installed following the terminal unit to dampen discharge noise.

Delivery and Direction

Ultimately, the test of an HVAC system lies in its ability to deliver conditioned air to the occupant. Air from the ductwork enters the occupied space through grills, registers, or diffusers, often called GRDs.

The term grill is commonly applied to any air outlet or intake that consists of a square or rectangular face and neck, and whose facial appearance is made up of louvers that may be used to deflect the air. A register is a grill that has one or more adjustable blade or dampers that control the amount of the air flowing through it. A diffuser is an air outlet which incorporates structures such as veins, louvers, perforations, and other features for distributing and directing air. The diffuser's job is to direct the airflow throughout the occupied space in the most efficient manner possible.


Once air enters a space, it circulates through the return inlets and returns to the air handling unit. Unlike an air outlet, a return requires no sophisticated veins. However, the relative location of the air inlets and outlets can be critical to the entire efficiency of the system. Upon returning to the air handler, a certain portion of the return air is exhausted and replaced with fresh exterior air. In an average office building or commercial space, approximately 10 to 20 percent is replaced.

While these components and processes generally make up an HVAC system, there are thousands of underlying parts such as condensers, sensors, electronics, and other elements that are integrated into the system. All these pieces work together to create a comfortable atmosphere in the workplace.

Providers of HVAC in Bloomington

Let U.S. Mechanical Services help you with HVAC and other services, including the following:

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US Mechanical Services has certified technicians who can help you design your HVAC system in Bloomington. We have top of the line air conditioning units in Bloomington that are guaranteed to bring comfort to your office. Get in touch with us today.


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About the Company: U.S. Mechanical Services was formed in 1982 and is a service company that provides HVAC/R solutions (Heating, Ventilation, Air Conditioning and Refrigeration), servicing residential, commercial, and industrial clients.


We're known for our 24-hour service when it comes to heating, air conditioning, and refrigeration needs in Bloomington, Normal and all of Central Illinois, offering new products such as digital control of thermodynamic systems, energy efficient HVAC/R equipment, and others. Read more about our capabilities here.


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