Most Australians live in houses along the coast where climate extremes are moderated by proximity to the ocean. In the milder climatic regions where there is negligible need for house heating reflective air spaces in roofs offer an ideal means of controlling the dominant summer heat gain through roofs. Ask any house insulation supplier in Brisbane and they will tell you they only sell insulation to householders during the hotter months.
Why Reflective Insulation Should be Used in Warm Coastal Regions
Horizontal reflective air spaces are the only type of insulation which offers:
· A high resistance to heat flow downward through the roof from solar heat gain
· A low resistance to heat flow upward through the roof allowing rapid heat loss in the evening
· No other insulation material has these properties.
In effect horizontal reflective air spaces in roofs act as one-way valves for summer heat flow restricting daytime heat gain while facilitating night time heat loss. This is important because indoor discomfort in the evening which inhibits sleep can be very debilitating.
Use of reflective air spaces in roofs combined with natural ventilation and ceiling fans in houses along much of the Australian coast can provide from 8 to 10 star energy efficiency ratings on the NatHERS scales. These would be amongst the most energy efficient houses in the developed world.
Richard Aynsley, B.Arch(Hons I), MS(Arch Eng), PhD.
Member : AIRAH & ASHRAE
Former UNESCO Professor of Tropical Architecture, James Cook University, QLD
Dean, College of Technology, Southern Polytechnic State University, Marietta GA, USA
24 August 2000
Prof. Richard Aynsley
Australian Institute of Tropical Architecture
James Cook University
1. NatHERS claims to be able to rate any type of house anywhere in Australia - not so. This would require NatHERS star ratings be provided for naturally ventilated houses in warm climates. At present they only give a bar chart indication of degreehours overheating without any numerical values. What is needed for these houses is the energy used by fans to maintain indoor thermal comfort for a year. There has to be a common energy efficiency currency e.g. Mj/m2.annum with associated star bands for there to be any possibility of introducing mandatory declaration of energy efficiency of houses.
2. Much of the software currently used to estimate heat/cooling or comfort in Australian houses (NatHERS, BERS, ARCHIPAK etc) only allow a single R value to be entered for insulation materials. This seriously negates the beneficial attributes of horizontal reflective air spaces in warm climates as demonstrated for Queensland by Coldicutt (1981 NHRC Report) using TEMPAL software. The current version of this software (ENCON) developed by Professor Terry Williamson of the University of Adelaide accepts the different R values for heat flow up and heat flow down associated with horizontal reflective air spaces. It can also estimate the energy needed for fans to maintain indoor thermal comfort in warm humid climate conditions.
3. If energy efficiency regulation as a matter of convenience ignore the beneficial effects of horizontal reflective air spaces in roofs of houses in warm climates, then the situation could be actionable under trade practices legislation. Ignoring these effects would be detrimental to a wide range of aluminium foil insulation products and favour bulk insulation products in spite of the demonstrable consumer benefits of reflective foil insulation in Australia's warm climates.
**As of 18 Sep. 2000 -
Prof Richard Aynsley
Dean of College
Southern Polytechnic State University
Marietta (near Atlanta)