It is friggin cold outside, and I can’t shake the urge to keep talking about heating related matters, so here we go again:
One goal of our deep energy retrofit was to save energy, and along with it, some Benjamin Franklins. The money we invested in tightening and insulating the building was meant to save us dollars on our heating bill, for instance.
But how would we measure how much we save? Our problem was that we had no starting point. We bought our building as a foreclosure in 2009 and thus had no data – no access to utility bills – that would tell us what it took to keep the building heated and comfortable.
That said, there are plenty of buildings in our neighborhood that could serve as a comparable (comp). Not only are they the same construction type, but also in the same energy deficient shape as our building was before we started with our deep energy retrofit.
I found a building that was a good match, and the owner that was happy to share their utility data with us.
To compare apples to apples – or in this case, therms to therms – I calculated the amount of therms used per square foot per month for both buildings. Our building’s natural gas consumption is reflected in the blue bars, while the comp, or pre-retrofit state, is reflected in the red bars.
Why is there natural gas used during the summer months (off heating season)? Because in both cases natural gas is used to produce domestic hot water, i.e. washing the dishes, running the washing machine on warm or hot cycle, taking a shower, etc.
You may have seen me bragging about turning our heat on as late as mid November. If you look at the consumption for November 2016, you see that we mostly used domestic hot water while our neighbor in the comp building had the boiler already buzzing away.
Looking at the big picture, our building consumed 0.200 therms/square foot over the course of one year, while the comp usage was at 0.976. Our deep energy retrofit improvements appear to have reduced our natural gas consumption by 0.776 therms/square foot/year. That equals a reduction in our heating needs from November 2015 through December 2016 by a whopping 80%!
For our metric friends (i.e. the world with the exception of the U.S.): Our natural gas consumption equated 63.04 kWh (or 226.95 MJ) per square meter, while the comp came in at 307.89 kWh (or 1108.39 MJ) per square meter.
I typically don’t like to measure the improvements in cost savings, as supply cost and taxes may vary between jurisdictions or energy companies. In addition, the fixed costs on the gas bill, although often small, prevent accurate scaling to a square foot basis.
Yet getting an approximation of the monetary savings would give us a sense of the potential return on investment. We paid $0.27 for natural gas per square foot over the course of a year. The cost of the comp were $0.98. The estimated total cost savings for the 2,900 square foot of conditioned space in our building from November 2015 through December 2016 would be in the range of $2,000.
Yes – I am beaming right now! Yet, this somehow seems too good to be true. I think the flaw with my analysis is that I have based it on one comp only. I plan to find another couple of buildings that I could include in the analysis. That should give me a number that would be easier to defend.
Stay tuned, because I will keep you posted!