Monday, December 15, 2008
Quite simpy, halogen downlights are a disaster when it comes to energy efficiency, for the following reasons:
1. they are energy guzzlers
2. they create gaps in your insulation, reducing thermal efficiency dramatically
3. they get hot and so make their own little convection current which sucks the warm air, that rises to the ceiling, up into the roof space... making the pressure difference (or stack effect) in the room greater and drawing more cold air in from the cracks and gaps near your floor. Goodbye heated air, goodbye comfort and ooroo money!
When we run an air leakage assessment, standing beneath a downlight is like standing beneath a small ceiling fan, as air rushes in from the roof space. The thermal image above is of a downlight (not switched on) while we are depressurising the house - the rays of yellow are caused by the warm air from the roof space being drawn in around the edges of the unsealed and uninsulated, hot, energy guzzling downlight! Imagine the opposite happening in winter as you spend your precious pennies trying to keep your house warm... because that is exactly what happens :-(
A couple of other good reasons to avoid downlights:
a. they make gaps in the ceiling through which insulation fibres, dust, dirt and pollutants can drift into the house
b. they are a fire hazard
Read a more thorough analysis by Four Corners' reporter Jonathan Holmes and check out the options for making the best of a bad bunch if you're stuck in a house with lots of standard halogen downlights. There are several places online where you can check out more energy efficient downlight options and downlight covers that reduce the gaps in your insulation and the risk of fire.
Friday, December 5, 2008
Yesterday, we put one of Strine's homes to the test with our blower door and thermal camera... and the results were impressive.
Our testing of Canberra homes (new and old) has so far shown the average number of air changes per hour (ACH) at 50 Pascals to be around 20. Modern European homes, built using advanced sealing techniques, aim for 1.5 - 3.0 ACH at 50 Pa (ie. they are very air tight, energy efficient and comfortable) and require mechanical ventilation systems to maintain healthy indoor air quality.
The three bedroom Strine 'Milennium' home, completed in 2006, had just 6.2 ACH at 50 Pa. At normal pressures of ~ 1 - 4 Pa the house was having roughly 1 - 1.5 ACH. For healthy indoor air quality 0.5 - 1.0 ACH are recommended. So the house is very air tight by Australian standards and if efforts were made to tighten it even further the homeowners would need to consider installing a heat exchange, mechanical ventilation system (to ensure good air quality when all the windows, doors and solar chimneys were closed).
The temperature of the precast concrete walls was remarkably even. Comparison of the external and internal temperatures of a section of eastern wall at 11.30 am on a sunny, 25 degree day showed a 20 degree difference (40.8 & 20.6 degrees, respectively).