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In 1981 we decided to set up a small field trial near San Francisco on the above residence. The following site description will show that we failed to take account initially of the very heavy wall and ceiling insulation.The home is situated in a lightly wooded area at about 1,800 feet above sea level in hilly terrain. The building faces North East with the ridge of the house running NWISE with the Retroflect treated portion on the SW slope. The heat pump is located on the same side with the intake facing SW. The prevailing wind on the west coast is generally westerly.
Insulation consists of R30 in the ceiling and R1 9 in the walls, with double pane windows and doors. An exhaust fan is mounted in the NW gable and set for 100 deg F. Air vents are located under the eaves. Interior air temperatures are maintained at 78 deg F summer and 65 deg F in winter.
Originally we were looking for reduced roof void temperature to reduce heat radiation through the ceiling. This was not possible due to the nine inches of fibreglass laid over the ceiling, in conjunction with the air vents under the eaves and the exhaust fan in the NW gable. We therefore only completed the SW slope with the air conditioning unit as you can see in the enclosed photographs.
We decided to persevere to see if the cooler surface temperature of the roof would affect the energy consumed in 'cooling months'. The enclosed chart shows 1980/81 before application and 1982/83 after application for the cooling months of May, June, July, August and September.
It was found that application of the solar reflective coating reduced the temperature of the surface of the roof to just below ambient, approximately 80 deg F, whereas prior to treatment the air being drawn in was pre-heated to approximately 135 deg F, thus a dramatic reduction in energy consumption was achieved..
The conclusion was that by lowering the roofs surface temperature, the temperature of the air rising from the roof surface, and passing into the air conditioning intake was dramatically reduced which lowered the loading on the unit, thus reducing air conditioning costs.
An additional benefit reported some five years later was that the untreated shingles on the N. E. slope had shrunk and curled requiring maintenance, whilst on the coated elevation the shingles remained unaffected by ageing.
There is no reason why the same principal cannot be applied in Australia, particularly to local shops and hotels etc., who nearly always have air conditioning units drawing in pre-heated air off the roof surfaces.
In the case of pitched roofs, metal etc., we understand there is little or no insulation, this is where the Singapore report applies. By reflecting the heat and reducing heat build up in the roof void, a great difference will be noticed inside single storey structures from radiated heat through the ceilings. It is here that passive air conditioning can be claimed.
Further information and graphs can be obtained by emailing enquiries@whscreeton.com