This report provides an opinionated view of best practices to achieve a comfortable, energy efficient home based on the authors’ experience in renovating their own home in Melbourne, Australia.
The key principles to which we adhere are as follows:
- Fabric first: ensure the construction is highly insulated and super-airtight
- Electrify everything: no gas, go electric for cooking and space heating
- Hug-a-heat-pump: reverse-cycle air conditioners extract energy from the air, so they have “efficiencies” well over 400%
- Less speculation, more science: the physics of heat transfer and moisture movement are well understood, so use this knowledge to do it right.
The endpoint of this approach is a building which is very comfortable and has minimal operating costs. Having lived in the home for 18 months the following data illustrates the benefits that have been achieved:
- Energy positive: across the year we generate around 20% more electricity than we consume, this includes space heating and cooling and the driving our plug-in hybrid car just under 10,000 km (this does not mean we can disconnect from the grid though, and nor would it be sensible to do so).
- Low cost: over the first 12 months we paid $628 for electricity (two-thirds of which was the daily connection fee) - the “avoided” petrol cost was about $950.
- Low energy: the energy required to maintain a comfortable indoor temperature is around 95% lower than the pre-existing building and is around 80% lower than a reasonably well renovated weatherboard home with double glazing and wall and ceiling insulation.
- Temperature variation: with minimal heating and cooling the home has maintained an average temperature of around 20°C, and very rarely dropped below 18°C or exceeded 27°C. Moreover, on cold winter nights when the outdoor temperature drops to just above freezing the internal building temperature never drops by more than 3°C with no overnight heating. The typical diurnal temperature range (that is, the difference between the highest and lowest temperatures) is less than 1.5°C.
- Healthy: there are no signs of condensation forming within the building, which can lead to mould and structural damage. Instead, on cold winter mornings we observe condensation forming on the outside of the windows - this is a remarkable outcome, and reflects the exceptionally low heat transfer across the glass.