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The truth about indoor AC

By Barney Richardson

This month I deviate again from refrigeration requirements to compliance requirements for meeting skills training and registration with SAQCC Gas.

To follow on from last month’s discussion I recently read an article regarding a complaint that air conditioning causes illness through colds and hay fever. One point made was that an air conditioner either through the wall or window type, or a split unit does not bring fresh outside air into the space. The popular choice of air conditioner these days is a midwall split air conditioning unit for many applications.

Many people falsely believe that air conditioners bring fresh outside air into the office space or house. For some people with allergies this is of concern when there is high incidence of pollen through spring and summer. There are a lot of pollutants in the air from outside and also inside from furnishings such as carpets, pets and paint. The fact is that air conditioning units do not bring fresh air in from outside.

In hot humid weather the air conditioner is switched on and then the windows of the office or home are tightly shut to keep the cool air in and not to waste cooling energy. The penalty of that is so that no fresh air can come into the space.

If you inspect your air conditioner, you will see that there is an inside unit, the evaporator and an outside condensing unit. These are connected by copper refrigeration pipes with a refrigerant flowing between the two units, either as a liquid going to the indoor unit or suction gas going back to the outdoor unit. The air flowing through the outside unit is just outside air, the air blowing from the indoor unit is recirculated air inside the room. The indoor unit has a return air intake grille which includes a filter to collect dust. No fresh outside air is introduced through a split air conditioner unit.

The outdoor unit has a fan to push air across the condenser coil, taking heat out of the refrigerant and cooling it down to be recirculated to the indoor unit in liquid form. If indoor air quality is a major concern, additional fresh air ventilation steps must be taken to ensure volatiles and pollutants are not re-recirculated. A dedicated ventilation system for a space may be required. A purpose-designed fresh air ventilation system to supply fresh filtered air to the office space and to displace stale air will ensure the quality of indoor air. Filtered ventilation is used to remove the pollutants and odours, dust, bacteria and carbon dioxide. To avoid indoor air stagnation requires the continuous circulation of fresh air through a correctly sized ventilation system. It may not always be possible to have a dedicated ventilation system for a home but leaving one or two windows slightly open will create circulation and dilute stale indoor air.

To repeat last month’s advice for ventilation be aware of minimum fresh air requirements. A good rule of thumb is 6ℓ/s to 12ℓ/s per person dependent on the activities in the space or alternatively 1.2ℓ/s /m².

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