Building Energy Modelling part 1 - The Whole House Book

In the blog post what kind of information can we extract from power measurements I concluded that I needed a simple model of my electricity use in addition to the monitored data in order to ultimately get to a list of actions that I need to do to optimise my electricity use.

The other conclusion was that to significantly reduce electricity consumption further I would need to change the heating system and to take a whole house view: improve the building fabric performance by increasing insulation levels, reducing draughts and improving solar gain in order to reduce heating demand in the first place.

For a while now I have had a growing interest in looking at heating energy consumption and how to reduce heating energy demand through building fabric improvements in addition to electricity consumption.

In the energy study of local households that we did in 2011-2012 heating energy came out as the largest energy user, we recorded details about house construction, levels of insulation, perceived comfort, temperature, draught levels, amount of glazing etc but didn't have the tools or knowledge to be able to give any sort of tailored advice, relate general statements that we're all familiar with like insulation can reduce energy demand by x% to a particular households situation, it wasn't in the remit of the project but we could see that that was what was needed next.

At home it was also clear that heating was the largest user of energy and the area with the most potential to achieve significant energy savings and carbon reduction especially as electricity use is already optimised as far as possible.

I started to read up on low energy building design to get a better understanding of the subject. I had an Aha moment when I read chapter 7 of The Whole House Book by Pat Borer & Cindy Harris which outlines a really simple building energy model:

The model starts by calculating how many Watts are lost through the building fabric per degree Kelvin (same for Celsius) temperature difference between the inside and outside temperature. This is calculated by multiplying the area of the various building elements such as walls, windows, roof and floor by their U-values. The model also takes into account the amount of heat lost via draughts (infiltration). The model then uses the concept of degree-days to calculate the annual heating demand.

Before reading this I had thought that to get any sort of useful estimated output on effect of adding insulation to a building a full dynamic simulation would be needed. But this simple model showed that you can get some surprisingly informative estimates from some quite straightforward calculations.

For the rest of the book Pat Borer & Cindy Harris use a more detailed calculation that also takes into account solar gains, internal (casual) gains and water heating requirements. If your looking for a good book on low energy building design, self-build and energy calculations Id really recommend this book.
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