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Efficient location of ceiling outlets in residential Air Conditioning

Efficient Air Distribution System

Air Motion Characteristics of Outlets mounted in the ceiling near the wall and discharging Cold air horizontally (ASHRAE Fundamentals)
Air Motion Characteristics of Outlets mounted in the ceiling near the wall and discharging Cold air horizontally (ASHRAE Fundamentals)

Inefficient Air Distribution System

Air Motion Characteristics of Outlets mounted in the ceiling near the wall and discharging Cold air horizontally (ASHRAE Fundamentals)
Air Motion Characteristics of Outlets mounted in the ceiling near the wall and discharging Cold air horizontally (ASHRAE Fundamentals)

Preferred outlet locations to minimise heat loss and gain through windows

All glazing products are very sensitive to air movement. The performance of glazing can be greatly diminished through air movement across glass. The position of outlets is critical andshould be located to reduce air movement over the glass and, at the very least, have deflectors fitted. Single glazed products derive over 90% of their thermal resistance from the air film onthe inside of the glass and where these products have a low e coating, the amount of lost perfomance due to air movement will be even greater. While the positioning of outlets and use of deflectors does not effect the rating of the house it can have a significant effect on the actual performance of the house. FirstRate users should take care with these construction details,otherwise the performance of the house may not match its rating.

Residential energy use assumptions

The FirstRate software assumes that the building will be used in the following way:

    • Winter central heating (to 21 C throughout the house from the hours of 7am to Midnight).
    • Summer air conditioning (from 26 C to 28 C depending on the climate zone selected) throughout the house from the hours of 7am to midnight. The cooler the climate the lower the thermostat setting.
    • People will adjust their blinds and curtains to minimise heat gain and heat loss.
    • Windows and doors will be shut during heating and cooling.

Outdoor design conditions

LocationSummer Winter
       
  DB °C WB °C DB °C
Adelaide Airport 36.0   20.8 4.5
Adelaide (Kent Town)    37.0 21.4 4.9
Belair    34.7 20.3 5.4
Coober Peedy 41.6 21.8  5.0
Kapunda 37.0 21.2 2.4
Mt Barker (P.O) 35.2 21.3 1.2
Murray Bridge 37.9 21.6 1.7
Stirling    33.6 19.0 2.4
Victor Harbor    33.6 21.0 5.5

Summer outdoor design conditions are the 3:00pm dry-bulb and wet-bulb temperatures which are individually exceeded on 10 days per year (inclusive of one standard deviation).

Winter outdoor design conditions are the 8:00am dry-bulb and wet-bulb temperatures which are individually exceeded on 10 days per year (inclusive of one standard deviation).

Acknowledgements and sources of information: FirstRate Sustainable Energy Authority Victoria, Australian Institute of Refrigeration H & C

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