Perth Homes – either too hot or too cold

Article originally written for the AMA Magazine “Medicus”.
“Comfort & the Modern Home” by Andrew Abercromby

Civil/Environmental Engineer, Registered Builder, Building Designer
(Director of Consortium Builders)

A recent article in The Lancet attributed almost 6% of premature deaths in Australia to mildly colder-than-optimum temperatures, more than in Sweden or Canada.

Ref: Lancet 2015; 386: 369-75


Perth Homes and Energy Inefficiency

perth homes - ideal house temperaturesIn Western Australia more than 93% of Perth homes are air-conditioned. This is mainly to address summer cooling. The energy required for winter heating in Perth is more than five times the summer cooling demand. The design of Australian homes is changing rapidly in response to smaller block sizes, energy concerns and an increasing focus on comfort. A tighter, more European form of construction is replacing our draughty homestead and verandah style.

Blower tests of typical Australian homes reveal leakage rates from 15 to 25 Air Changes/Hour when pressurized to +/- 50 Pa. Efficient internal comfort management requires better insulated and less draughty buildings. In place of high-energy air-conditioning units that recirculate internal air and largely rely on a “leaky” building, tighter construction and balanced ventilation systems with heat recovery can provide significant advantages; better thermal comfort, higher air quality and moisture control.
Source: National Asthma Council Australia; Indoor Humidity Levels, April 8, 2015 & DIN 1964-2

Low Energy Housing & Passivhaus Australia

perth homes - temperature humidity and climateIn January 2015 Dr Tim Isaacs moved into his new family home dubbed “Passivhaus Cottesloe” – the first of its kind to be built in Western Australia. Passivhaus is the world’s most exacting standard for high comfort, low energy design and construction. Perth homes need to rigorously adhere to higher energy standards (read more about Passivehaus Standards here) or watch the video.

Dr Isaacs’ home includes insulation of all in-ground elements and the use of SIPS (Structural Insulated Panel System) for all above-ground walls and the roof structure. Doors and windows are German uPVC sections with tilt-and-turn action and double-glazing. At lock-up the building was pressurized to +/- 50Pa with air leakage rates recorded at only 0.25 ACH – an Australian & NZ record.

At the heart of the home is a state-of-the-art heat recovery ventilation system (HRV). Filtered, fresh air is constantly ducted into all the living areas and extracted from the kitchen and bathrooms. Up to 90 per cent of the energy of the outgoing air is recaptured by the HRV’s heat exchanger and used to heat or cool the fresh, incoming air. Driven by only two 30W fans running 24/7, the HRV costs less than 40 cents a day to run. Windows and doors can be opened anytime, while the ventilation system maintains comfort all year round. A small reverse cycle split system is installed separately to provide additional heating and cooling. To further lower the energy needs of his home Dr Isaacs integrated geothermal air heating, mains pressure solar water heating with heat pump boosters and an in-line cooler with his HRV unit.

Affordable Heating and Cooling Costs

passivehaus perth humidity scoreThe cost of heating or cooling required to maintain ideal indoor temperature all year round should be as little as 10 per cent of a normal home.

The German DIN standard defines indoor thermal comfort in terms of both temperature and relative humidity. Recent data from Passivhaus Cottesloe are shown here – together with the DIN comfort bounds.

Note: In May 2017 Dr Isaacs had 10.8kW of Photovoltaic panels to the roof of his home and the property is now effectively Grid-Plus – ie. a net exporter of energy back to the grid!