In order to keep our energy consumption to a minimum the home is designed to use the principles of passive solar and pasive ventilation.
It means there will ben no active heating or cooling system like a heat pump and it will be heated by the sun only. To achieve this the following strategies have been applied:
- The shape of the house is compact to reduce the exterior surface area versus volume ratio.
- This shape and the open floor plan helps to distribute the heath evenly
- High levels of insulation for the floor, walls and roof
- A building method with SIP’s to create an airtight design wihtout any gaps for infiltration of air
- The living areas are situated on the sunny warmer Northern side, the bedrooms on the cooler South side
- A large window area on the Northern side to gain solar energy
- Minimal windows on the South side to reduce energy loses through windows
- Overhangs over the walls that will shade the windows in summer but will let the lower angled winter sun in.
- The angle of the louvers in the roof over the exterior deck are designed to let winter sun in and give shade in summer
- Ideally we would have a 10 cm concrete floor to act as thermal mass to store the heat and balance the daily temperature fluctuation but this is too expensive to achieve on a pole foundation. To create a little bit of thermal mass capacity we will most likely get a dark tiled floor.
To avoid overheating the amount of windows on the West should be limited. This is however where our view is over the Kaipara harbour so no windows on the Western side was no option for us. To prevent over heating due to our big Western windows we will need some external vertical shades. Because of all the windows and mainly the Western windows the house is expected to get fairly hot so we need proper ventilation. Luckily most of the time there is a fairly big difference between day and night temperatures so this will give the opportunity to cool the house down overnight.
To achieve passive ventilation without mechanical ventilation to following principles are used:
- All 4 exterior walls have opposite openable windows for cross ventilation independent of the wind direction
- The stack effect is used where on the high wall clerestory windows can be opened to let the hot risen air out of the home. On the other side of the wall windows can be openend to aid the chimney effect
- An open plan and ventilation openings in the internal walls all around the house for easy movement of the air.
This picture below is not the lay-out of our home but I thought it explains passive ventilation well.
Phase change materials
If the home turns out to be too hot due to the Western windows and lack of sufficient thermal mass there is an expensive plan B; Phase Change Materials (PCM’s). There are several products on the market which can absorb heat at a certain temperature. They use the principles of physics where at a certain temperature a material, mostly parrafine based, melts from solid state to liquid state and in the process absorbs heat and keeps the temperature at a constant level untill all the PCM has melted (remember in school when you learned that when water melts it stays at 0 degrees until the iceblock is melted or boiling water stays at 100 degrees celsius untill all water has evaporated). At night when the temperature drops they return to solid state and release the heat. These products from eg Microtek or Phase Change Energy Solutions are available as additive to plasters, as board or seperate blankets or cylinders to add to the ceiling or attic space. I can’t remember the prices but they didn’t come cheap.
I searched if there were materials used as PCM’s that were not oil derived products like paraffin. They exist and are called bio-PCM’s but in the process I also found out coconut oil has a melting point between 24-26 degrees celsius. Perfect I would say and I should at some point do a little science project to see what the effect is on the temperature fluctuation when I add a couple boxes of coconut oil cans to the house :).