What is an HVAC System?

Figure 1: Refrigeration compressor.

There are many systems and components in a home or building that we take for granted, such as roofs, plumbing, and electricity. HVAC is the main system that probably will be most underrated: a massive heating and cooling system driven by a miniature thermostat.

1. What is HVAC?

HVAC is an acronym for Heating, Ventilation and Air Conditioning and refers to the system in a home or building that produces safe, clean, comfortable air in a space.

• Heating: The "H" in HVAC stands for heating, and as you might guess, the system can heat the air in rooms. Generally, this may involve heating the space with forced hot air from a furnace or radiant heat from a boiler in your home. In commercial buildings, heat may come from boilers, heat exchangers, and coils within the air handler.

• Ventilation: The "V" in HVAC stands for ventilation, which is the process of replacing stale air and carbon monoxide with fresh air to improve indoor air quality. Manual ventilation includes opening doors and windows. Mechanical ventilation usually involves heating or air conditioning units that can draw fresh air into the system. The system purifies the air through filters, regulates its temperature and humidity, and brings fresh air into the room.

• Air Conditioning: As important as the other two components of HVAC, air conditioning is about air comfort and humidity control. The air conditioning component of an HVAC cools the warm, moist air from a space, and also removes moisture from the air to control humidity.

Figure 2: Flow diagram of heat exchange.

2. What are the Main Functions and Equipment of HVAC System?

HVAC engineering is one of the most common projects in our daily life, and it is closely related to our life, so do you know what are the main functions and equipment of HVAC?

2.1 Main Functions

First, it avoids discomfort of indoor personnel caused by low or high indoor temperature and humidity in winter and summer, and transfers the heat and moisture in the air as needed to create a comfortable indoor environment for the human body.

Second, in order to enable the machines, equipment and components working inside the building to operate normally, it maintains indoor temperature and humidity that are suitable for the normal operation of mechanical equipment.

Third, in most buildings with basements or interior spaces constructed without external ventilation, HVAC engineering utilizes mechanical ventilation to force the exchange of indoor and outdoor air.

2.2 Major Equipment

Equipment can be said to be the lifeblood of HVAC projects, and its functions include providing cold and heat sources, power transmission, and thermal energy conversion.

Specifically, the equipment that provides cold and heat sources includes air conditioners, refrigeration units, heating boilers, heat pumps, etc., which create or produce the cooling capacity or heating capacity we need by inputting energy.
The equipment that provides the transmission power mainly refers to water pumps and fans, which provide the transmission power to make the fluid flow according to our needs.
Thermal energy conversion is to convert the heat energy in the fluid through heat exchange devices according to our needs. Common water-water heat exchangers, steam-water heat exchangers and air-air heat exchangers belong to this category.

Figure 3: Ground source heat pump.

It is worth mentioning that the fan coils, air handling units and other equipment we often use combine fans and heat exchanger coils, which provide both air transmission power and heat energy exchange, and are generally called air-conditioning terminal equipment.

In the air-conditioning project, in order to ensure the air quality, there is also air purification equipment, such as various filters, adsorption devices, disinfection and sterilization facilities, etc. In the water system, there are various water filtration devices, water treatment devices and dosing devices.
Various electric air valves, electric water valves, temperature control devices, etc. set up for automatic control are also often included in the category of HVAC equipment, but they mainly play an auxiliary role in the system and improve the system quality. Generally they are called auxiliary equipment or facilities.

3. How does an HVAC System Work?

All HVAC components work together as a system, with different components performing certain functions.

For example, in a home HVAC system, there is usually a central heating unit called a furnace. As the system draws room air through the backflow, the air passes through the furnace and over the heated coils, and then is sent into the room by the blower.

The HVAC system also contains the air conditioner, usually placed outside the home in the form of an outdoor unit. This air conditioning unit contains compressor, condenser, evaporator, check valve, capillary tube assembly, etc. The compressor achieves the purpose of cooling the air in the room by compressing the refrigerant gas and making it circulate in the pipeline.

In terms of ventilation, these systems work in several ways. Some rooms have a simple set of shutters that the homeowner can open and close to allow ventilation or not. Other systems may have advanced components called HRV (Heat Recovery Ventilation) systems. These systems draw in fresh air while allowing the outgoing air to heat or cool the fresh air. In any case, ventilation is to improve indoor air quality.

Figure 4: Ventilation system diagram.

4. What is the Difference between HVAC and Air Conditioning?

Although the two are closely related, there are subtle differences between HVAC and air conditioning. Air conditioning is just about cooling a space and controlling humidity, while HVAC means much more.

All HVAC systems contain air conditioning components, but not all air conditioning systems can be considered HVAC. If an air conditioning system does not have heating and ventilating, then it's just air conditioning. However, if there is a furnace and a ventilation method, it becomes an HVAC system. Think of it this way: Air conditioning is just one part of HVAC.

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