We set out with some pretty lofty goals for our Canada’s Greenest Home project. The idea was to use only the healthiest, most ecologically friendly building materials and use them to create a home with outstanding energy performance. And we wanted to do it in a way that would be cost-comparative and easily achievable for other contractors. We finally have the data to show our results on the energy performance side.
From modelling to the real world
Much is made during the design process of “green” homes of energy modelling figures and estimates of consumption and/or savings based on the design. However, in few cases do we ever get to see an accurate portrayal of the actual consumption figures as compared to the models.
Obtaining real-world performance data was one of the key reasons we wanted to spend at least a year living in Canada’s Greenest Home. And now that we have been living here for a year, the results are in!
Energy produced compared to energy used at Canada’s Greenest Home
Canada’s Greenest Home components
To recap, the home has a 5kw PV array, that is grid-tied using Ontario’s MicroFIT program. This means that there are two electricity meters on the house, one recording power going out to the grid via MicroFIT, and one recording power coming into the home. These figures allow us to see a clear picture of our consumption versus our production. There is no other fuel source in the home, as our heating system is powered electrically, via a Mitsubishi Zuba air source heat pump.
Our total annual consumption (including heat, refrigeration, cooking and all other plug loads) was 8,867 kilowatt hours, and our total production was 6,075 kilowatt hours. So we were 2,792 kw/h short of being net zero energy. Some of this can be attributed to the fact that the winter of 2013/2014 was quite a bit colder than average, and ice covered our panels for much of January and February (the output numbers are typically higher than December, but are quite a bit lower). In a different year, we would be quite a bit closer to net zero.
Financially, the picture is quite rosy. At our MicroFIT rate of 54.9 cents per kilowatt hour, our earnings from the PV system were $2,028.07 higher than our utility costs. Not many homes earn money for the owners, rather than costing them! That surplus goes a long way to putting a dent in the mortgage costs.
Comparing to other homes in Ontario
Comparing our energy usage to averages for Ontario (using the most recent StatsCan figures) is also illuminating. The average home of this size (2,000-2,500 square feet) built since 1996 uses 107 gigajoules of total energy (GJ is used to be able to compare measurements between different fuel sources like natural gas, oil, and electricity). Converting our kilowatt hours to gigajoules shows that we used 31.92 GJ, or just under 30% of the comparable average home! By square meters, we used 0.15 GJ per meter squared of floor area.
On Dec 21, the south windows are getting full sun exposure. This solar gain helps to offset heating needs appreciably.
On June 21, the sun is being fully excluded on the south. This helps the home get through a summer with no air conditioning.
Passive House modelling slightly off
Interestingly, the energy modelling done in the Passive House software (PHPP) showed that our heating demand should have been 11,529 kw/h for the year, but our total usage including all non-heating loads was 8,867 kw/h, a substantial difference. As a guess, I would say that it is low R-value figures given for straw bale walls that accounts for this difference. Tested R-values and real world performance are always different beasts, but seem to be even more so for straw bale wall systems.
Doing better isn’t hard
We are very proud of these results. Considering that the costs for the shell of the home were very comparable to “conventional” construction (the majority of our additional costs were for mechanical systems like rainwater harvesting, composting toilets and solar hot water, as well as the PV), it bodes well to show that with small, achievable, and affordable changes in construction, vast improvements in performance can be achieved.
In our case, these improvements were made using locally-sourced, low-impact and mostly renewable resources, showing that eco-friendliness has many facets, and that being good for the planet when choosing materials can also mean being good for the planet in long-term impacts.
Anybody can build a home like this, with very low environmental impacts and great performance. The question is, why don’t more people do it?