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
Director
Australian Institute of Tropical Architecture
James Cook University
Townsville, QLD
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)
GEORGIA USA
Email: ilradra@earthlink.net