Australian Passive Solar Home

While our passive solar house is conventional in materials and construction, it does have a few tweaks. One of those tweaks is the ventilation system.

The rectangular house uses a 30 degree gable roof. Under this is a large loft used for storage. The loft, and in fact all the roof volume, is permanently ventilated by a 600mm wind and motor powered ventilator. Effectively, the roof space is treated as part of the outside environment. I measure the flow through this ventilator with my data logging system.

Connecting the house volume to the roof volume are four openable vents (one is pictured). These use large air conditioning ‘return’ grilles that are closed by rear-mounted, hinged insulated panels that shut on rubber seals. The panels are opened by 12V linear motors operated from wall switches. The grilles include black dust/insect mesh so it’s not clear from inside inspection when the panel or open or shut. Bright 10mm LED pilot lights are therefore used on the switches.

When ventilation flow through the house is needed, for example to cool the thermal mass at night in summer, one or more vents are opened, along with one or more windows. The convectional flow through the house provides the ventilation. The warmer the house compared to the outside air, the greater the flow. The higher the wind speed, the greater the flow. If there is no wind and more airflow is desired than provided by convection, the ventilator can be powered-up. When powered, the ventilator’s speed can be controlled by wall mounted knob. The motor is not audible in the house.

Two of the vents are located in the ceilings of northerly rooms, and two of the vents are located in the two end rooms that have tall, raked ceilings. On the latter rooms these vents are located high on the walls that connect to the roof space.

Opening a hatch and a window in a room gives excellent airflow speeds through that room, and the effect on temperature in that room is quite pronounced. When the ventilator is not powered, flow can be adjusted by altering window opening (the ceiling vents are either fully open or shut).

Even with the hatches closed, the flow through the roof space itself seldom drops below 10 cubic metres/minute – this air is provided by leaks around the eaves and the downlights in an uninsulated deck veranda under the main roof.

Using a thermal camera shows very little heat leakage through the ceiling and wall hatches – just a tiny bit through the foam rubber seal.

It’s an approach that works very well.

(Acknowledgement to the late Derek Wrigley for the ventilation system idea.)