HVAC is the collective term for heating, ventilating and air conditioning systems that maintain comfortable temperatures and indoor air quality in a building. The design of any HVAC system has a significant impact on the energy consumption and carbon emissions of the associated building.

There are many configurations of HVAC systems, ranging from separate arrangements for heating, ventilation and air conditioning, to integrated systems that handle all three. Not all buildings have the three systems.

Heating and cooling systems use hot / chilled water or warm / cooled air to maintain comfortable temperatures in a building. In ‘wet’ systems, water is distributed to terminal units throughout the building. Commonly used heating terminal units include radiators, radiant heating panels, fan coils, fan convectors and trench heaters. The amount of heating is controlled by the temperature and / or volume of the circulating hot water. Chilled beams are used for cooling only.

In air based systems, air is warmed or cooled in an air handling unit and supplied through ductwork to supply grilles. The extent of heating or cooling is controlled by the temperature and volume of supply air. In most cases, warm air supplied to a space is a mixture of external fresh air, and air which has been recirculated. The proportion of fresh air should always be sufficient to ensure adequate ventilation. At the same time, optimum use should be made of the heat contained in the recirculated air, so that ventilation levels are balanced with energy efficiency.

Some ventilation systems have no associated heating or cooling, so that their primary objective is to supply sufficient air to maintain acceptable indoor air quality. In some buildings it is possible to maintain indoor air quality solely by opening windows or using grilles. However, in most commercial buildings, mechanical ventilation is necessary.

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