The Filter House in Broome

Unusual in design and energy efficient in operation, a recent assessment of Broome's Filter House has revealed some impressive results.

The Filter House is no ordinary home on a number of levels. It came into being as a result of the 2003 Sustainable House Design Competition held by the Western Australian Department of Housing and Works. The competition's aim was to show that a comfortable living environment can be created using solar passive design principles and that environmentally-friendly designs can achieve significant reductions in energy use.

The competition's winning entry, by Melbourne company Sustainable Built Environments (SBE), outshone 37 other designs from around the country and SBE's design ideas are now showcased in the aptly named Filter House located at Bin Sallek Avenue, Broome.

Key Design Features

This home's climatically-appropriate design can easily be seen in the distinctive slatted timber used on its north and west facades. The slatted exterior provides a layer of screening and protection whilst filtering direct sunlight and reducing heating of external walls. With the home's lightweight construction and timber-slatted exterior, it has no thermal mass as it was designed according to the principle that a light weight house sheds heat quickly thus allowing it to cool down rapidly at night.

The floor level has been raised 1.5 metres off the ground in order to catch and control sea breezes. This also promotes sub-floor ventilation and creates an innovative place in which to locate rainwater tanks.

Passive solar design was a constant consideration throughout the design process. There are carefully calculated solar eaves to shade windows and walls and the living areas and main bedroom have been positioned for optimum solar access. The design also features high set windows to allow hot air to be vented from the towering skillion roof line and the intake of air can be varied using windows placed lower in the building. Louvre windows are also incorporated, which can be fully opened to provide highly effective cross ventilation.

The Filter House is also energy efficient in how it functions on a day-to-day basis. Typically, heating and air-conditioning represent around 26% of average household energy consumption, so reducing the need for and raising the effectiveness of artificial heating and cooling was paramount in the minds of the home's designers. The result is the creation of two 'cool cells' in the living and bedroom pavilions and only these spaces are fitted with split system airconditioners. These areas are well sealed and heavily insulated (including the sub floor) to an R 3.0 rating.

How the house has performed

During the past two years, the energy efficiency and thermal comfort of the Filter House have been monitored to track how it has performed.

Over the same period, another more typical Broome house was also monitored as a 'control building' against which to compare energy use. As with most Broome houses the 'control' house was fitted with extensive air conditioning while the Filter House was designed with air conditioning installed only in the 'cool cells' (living room and bedrooms).

The 'cool cell' approach has resulted with Filter House consuming only 27% of the cooling energy used by the control house when temperatures were less than 30ºC and only 48% of the energy used by the control house when it was over 30ºC.

Part of the explanation for the energy saving lies in the fact that the Filter House was more responsive to diurnal changes, being hotter during the day and cooler during the night than the control house. During the day, the air conditioner appeared to cool the Filter House quickly and was able to maintain the desired temperature with less energy than was required by the control house, which continued to consume power to maintain temperature under the same conditions.

The mass floor in the control house acted as a heat sink that created more stable temperatures, but the Filter House cooled down at night more than the control house once again because of the lack of mass content that would otherwise serve to stabilise the night-time temperatures.

So while the Filter House was enjoying cooler night-time ambient conditions, it appeared that the control house was still using energy to combat the continued stabilising influence of the mass in the floor, which was now emitting heat that had been soaked up during the day.

Another important aspect of the success of the Filter House was the use of natural ventilation. Natural ventilation is considered an essential aspect of living in WA's north-west climate as it provides relief in the dry season when people could otherwise live outdoors. The climate-sensitive design of the Filter House, meant that its outdoor living areas were well shaded. On the other hand, the outdoor living space of the control house was not designed to catch cooling breezes and the occupants rarely used it.

The results of the monitoring process provide important data for anyone designing a home in a tropical location. The data collected so far reveals that, if houses built in Broome are constructed of lightweight materials, elevated off the ground, with good insulation in the ceiling, walls and under the floor, and are well ventilated and shaded, then the likely outcome is a substantial improvement in energy efficiency.

For more information on passive solar design and other energy efficient design elements visit House Design.