What is HVAC?

Put simply, HVAC stands for: 'Heating, Ventilation & Air Conditioning'.

HVAC systems fall into one of two categories; local or ducted/split system. Local heating is a type of ductless heating system, providing heat to a single, localized area. Local cooling/heating sources include fire places, electric radiators, fans, space heaters and single room air conditioners like wall and floor mounted air conditioning units, window units and ceiling cassettes etc.

Ducted/split systems distribute hot or cold air, depending on your needs, throughout your building. This is accomplished through a network of ducts or pipes depending upon system type. A typical air conditioning unit will contain a chiller, boiler, furnace or heat pump; to heat, or cool, moisture and air at a centralized location before distribution throughout a building by way of piping or ductwork. The difference between a ducted and split system air conditioner is visibility. Ducted systems are not possible in all homes as the piping for the air to travel through needs to be installed through your ceiling or floor; all you see are the vents for the cool or warm air to be pumped into your rooms. A split system / multi split system air conditioner has an outdoor unit and one or more indoor units to regulate the temperature of one or more rooms in your home. To achieve this, air is drawn through two coils, one inside each indoor unit (the evaporator fan-coil unit) and one outside (condensing unit).

In cooling mode the compressor, located in the outdoor unit, compresses the low pressure refrigerant gas making it heat up. This high pressure hot gas is then circulated through the outdoor condensing coils where a fan dissipates the heat which cools down the refrigerant changing it from gas to a liquid under high pressure. This high pressure cool liquid travels to the indoor fan-coil where it passes through an expansion valve. As the pressure drops the refrigerant begins to evaporate into a gas. Heat is needed for this process, so warm indoor air is drawn through the coil where it is cooled, and then the cooled air is circulated through the home.

There are various sources of heat that generate from within a building. Human body temperature, windows, walls, roofs, electrical appliances, all add to the ambient heat of a room. Many variables need to be considered when choosing the right HVAC system for you. Your HVAC designer should have thorough knowledge of the principles of thermodynamics, the properties of air, fluid mechanics, heat transfer, comfort conditions, various types of air conditioning systems and their workings.

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