Has my improved attic insulation actually reduced my carbon footprint?
You may be thinking about upgrading the energy efficiency of your building – your home or office, for example – to be more comfortable, to save money, to save energy and/or to reduce your carbon footprint. With some upgrades – such as switching out lighting – the impact is typically immediate and obvious in your energy bills as you will probably use your lights the same way after the upgrade as you did before. However, when it comes to insulation improvements, identifying the impact is made more difficult by the fact that how much heating is required depends on both your insulation levels and the outdoor air temperature (simply put, the colder it is, the more heating you’ll need).
I got to thinking about this recently as I upgraded my own home insulation. I moved home two winters ago, to a older, bungalow-style home which has a large roof area relative to its size. I’d been assured that the attic insulation was around R30 by my home inspection – which isn’t too bad and certainly better than a home this age would normally have – but in the first winter it seemed to get cold, fast, particularly in some rooms. So, this past winter, I decided to increase my attic insulation.
On crawling into the roof-space, the installers discovered that the insulation was patchy and above one room it was almost non-existent (which certainly would help explain why that room always felt cold!) Overall, they assessed the insulation as being around R30 and subsequently they topped this up to R62. So, my home feels warmer.
But how do I know if this insulation improvement has worked? How do I identify how much energy, money and emissions this project has saved?
For this, I need to introduce the concept of Heating Degree Days (HDDs), which, according to the folks over at www.degreedays.net can be defined as:
“a measure of how much (in degrees), and for how long (in days), outside air temperature was lower than a specific "base temperature" (or "balance point")”
In other words, it’s a way of measuring the temperature that allows you to fairly compare one time period with another. If a winter has more HDDs than the previous winter, that means it actually was objectively colder.
Now, to the technical part, which I will keep short. To use these HDDs I had to build a simple model which would show the relationship between how much natural gas – my current heating fuel – my home needs to stay warm and the HDDs. I did this via a linear regression based on my gas bills and HDD data from the year before my attic insulation was improved. Now, by inputting HDD for the time after my roof insulation was improved, this simple model tells me how much energy my home would have needed if I hadn’t upgraded it. I can then compare this to my actual, post-upgrade gas bills to see if there is a difference. And if there is, I know it is not due to changes in the weather!
And lo and behold…check out the graph. The blue columns show my actual natural gas consumption. The orange columns show the natural gas use my model predicted. And the gray line shows the cumulative difference between the two. As can be seen, that gray line dips below zero after the baseline period (in other words, as soon as the attic insulation was improved) and has stayed that way.
In other words, accounting for any differences in the weather, I can be sure that my insulation project has reduced my energy consumption and reduced my impact on the environment. So far, I calculate my upgrade has saved me around 3.1 GJ, or around 4.5% off my natural gas consumption. This in turn is around 160 kg of CO2e not emitted into the atmosphere. Of course, if I’d been starting from a poorer baseline – R10 or R15, for example, my savings would have been even greater.
So, if you're looking at improving your own insulation and want to be able to track the difference it makes, you're going to want to ensure you start tracking your current heating energy consumption and get smart on using HDDs (or find someone who is).
I’ll be tracking this all year and will interested to see the difference this insulation improvement makes next winter, when it has a chance to perform over an entire heating season. I’ll post an update then!