And Air Conditioning (Part I)

The power used in running a building's Heating, Ventilation and Air Conditioning (HVAC) is quite substantial, so any measures to improve its efficiency will save energy and cash. An upgrade of the HVAC system can be carried out by replacing the old worn components with modern, more efficient units.

Components of a Typical HVAC System: Ducting, Air Handling Unit (AHU),Filters, Attenuators, Humidifiers and De-humidifiers, Volume Control and Fire/Smoke Dampers, Air Distribution Diffusers, Air Return Grills, Air Handling Unit. Depending on the requirement of hot air or air conditioning, hot water or chilled water can be supplied to the coils. Alternatively, a heat pump can be used with an evaporator / condenser supplying the hot or cold medium. Excessive noise due to the air being circulated through the ducting is both annoying and distracting to the workforce. To mitigate the noise, attenuators (baffles or silencers) are fitted to the ducting.The fans or blowers draw the air through heating/cooling coils, circulating it through the supply and return ducting.

Suction and Discharge Filters. Suction filters are on the return ducting into the AHU; these remove any dust, smoke or other undesirable particles or fumes before the air enters the heating/cooling coils and fan chambers. Discharge filters remove any remaining particles before the air is recirculated again.

Diffusers and Grilles. Diffusers, being designed to slow the discharge velocity of the air, are normally located in the room’s ceilings. This is to ensure the air is distributed evenly and in the required direction into the rooms and offices of the buildings. These are set into the ceiling; the louvers are automatically adjustable or fixed, directing the air into the return ducting. The return ducting is run back to the discharge plenum, through the return filter, then back into the air handling unit, completing the system circuit. Volume control dampers are incorporated into the ducting to control the quantity and velocity of the air flow. Fire and smoke dampers and can also be installed that shut automatically in the event of a fire. These dampers need to be reset manually. The heating and cooling coils can be supplied by hot or chilled water; or a heat pump can also be used.

Electric Motors. Air circulating fan electric drive motors are a classic example of overrating, so the first thing to check is the rating plate against the design requirement in the original specification. This will tell you if you can downgrade the motor output. If the system has been operating for a long time, 10-15 years for example, fitting variable speed motors is a worthwhile investment. This will allow the speed of the fan to be altered to suit changing conditions in the system. This has been reported to achieve savings in energy of up to 50% and, if the existing switchboard and wiring are retained, even more savings can be made, ensuring a short pay-back period.