This image is meant as a reminder that the key to making passive solar design work is to remember that all ten of the steps outlined above have to work together. If nine are done perfectly and just one is done wrong it can lead to a building that is energy consumptive, unhealthy, uncomfortable, and/or unsafe. The most common problem with bad passive solar design is too much glass. This will cause the building to overheat during a winter’s day and then lose too much heat at night. Remember that windows have much worse insulation than walls so they lose more heat when the sun isn’t shining. Other common problems are: not enough eave overhang on the north side (causes the building to overheat in summer); facing too many windows towards a nice view particularly to the west or south (causes too much heat gain on summer afternoons and/or too much heat loss in the winter); planting evergreen trees in the wrong place (too much shade in winter); and poor air sealing (wind blows through the house and takes or brings heat with it). Remember that the goal is for the building to stay warm in winter AND cool in summer.
It is also important the the occupants “drive” the building the right way. If the windows are left open on a winter’s night or the blinds are left closed during the day the building will be too cold. And vice versa, if the windows and blinds are left open on a hot summer day the interior could become uncomfortably warm. In our climate we have to do the following. In winter we keep the windows and blinds closed during the night to keep the heat in and open the blinds during the day to let the sun in (with the windows closed all the time we have to make sure we run the exhaust fans enough to control humidity and condensation). In summer we have to keep the windows and blinds closed during the day to keep heat out and open them both at night to allow the interior to cool down. In the spring and autumn the operation of the house varies according to the weather. In short, a passive house requires an active owner in order to maximise the energy efficiency.
Once the building envelope is made as energy conserving as possible it is important to use energy efficient appliances. Things like reverse cycle air conditioners, LED lights, and inverter fridges use much less energy to do the same job as their traditional counterparts and thankfully their price is coming down rapidly. In the Greeny Flat we have no heating or cooling system and no dryer. Instead we have good passive solar design (plus a little radiator to add a bit of heat if it’s really needed in winter) and two clothes lines (one in the sun and one under cover for when it is raining). All our lights are LED’s, we use solar hot water, and our fridge and washing machine are the most efficient small units that we could find at a reasonable price.
Once everything has been done to reduce energy consumption the remaining energy required can be produced with renewable energy systems like solar photovoltaics (PV).
On the Greeny Flat we way overshot the size of the PV system. We installed a 3kW system and are making more than twice the amount of energy we are using. Currently we export the excess to the grid but soon energy storage systems and improvements to electric vehicles will make it possible for us to use all of our power and be close to energy independent.
These principles can be applied to any existing building to make it more energy efficient. Obviously, if the building doesn’t get any sun (like the one in the photo above) then solar heat gain is going to be a bit difficult. In this case the most important things are the insulation and air sealing, limiting the heat loss through windows, and using very efficient equipment.
Passive solar design principles can be applied to buildings of any size and shape. In the Nishi Building in Canberra this has led to VERY different treatments on different sides of the building depending on the direction they face.
In conclusion, Passive Solar Design is a simple, highly effective (and cost-effective) method of making buildings more energy efficient by using natural systems to help keep them warm in the winter and cool in the summer. When all of the principles are applied correctly in a holistic way it leads to buildings that are full of light and sunshine in the winter, cool and shady in the summer and cost very little to operate throughout their lifespan.