Passive solar data

In 2010 we undertook a fairly substantial renovation to the house. One of the major goals of the renovation was to lower our energy expenditure through the inclusion of some passive solar design. I have already covered details of the construction in my posts on insulation and windows, but the summary would be that we drastically improved the insulation and air leakage of the house as well as converting the south wall from mostly opaque to having large windows along most of its length.

Since we still heat with baseboard electric, the improvement to our hydro bills was obvious the first year after the renovation. Recently, however, I have taken advantage of some easily accessible data to do some proper number crunching. The first set of data I had access to is that provided by my hydro company. As part of their electronic billing system, I can download .csv files of our electricity usage over the years. During the time we have had an account, the hydro company switched from meter readings to smart meters and then later to time-of-use pricing. This resulted in some irregular metering periods and made a straight month-to-month comparison infeasible. Instead, I consolidated the data into a spreadsheet of metering dates and the number of kWh used in the corresponding intervals, from which I calculated a figure of kWh/day for each metering interval. Knowing that the baseboards are turned off entirely for the summer, I used the periods metered between June and September of each year to calculate an average kWh/day for the non-heating period and set this as a baseline for the year. The difference between the kWh/day being used for any metering period and the baseline for that year could then be calculated, with metering periods below average being floored at zero. This resulted in a figure of “kWh/day above baseline” for each metering period, which should provide some indication of the electricity being used for heating. Although some additional electricity will also be used for lighting or entertainment during the shorter days and heating household water from its colder initial temperatures, these values should have remained somewhat constant through the years.

As can be seen in the graph, the renovations have made a substantial difference. Years prior to the renovation have been coloured in various shades of blue; the renovation year in salmon; the post-renovation years in various shades of green.

Performance data for passive solar renovations

The second set of data to which I have access is historical weather data provided by Environment Canada. Using data for the nearest weather station, I compiled total Heating Degree Days (°C) for each metering period. When combined with the electricity data, this allowed for the calculation of (kWh/day over baseline)/Heating Degree Day(°C). The average could then be taken of periods between November and February.

This provides only a rough overview of the trends but it is clear that the renovations did make a substantial difference to our electricity consumption. The installation of the slate floor is slated (heh) for this spring and I also intend to tackle an unanticipated source of heat loss in our current envelope once the weather is more favourable. It will be interesting to see what further benefits we garner from these two changes.

Data