Sustainable Energy Without the Hot Air: Keeping toasty with insulation

You could have the best means of heating up a building in the world, but it hardly matters if all that heat leaks out and the heating system has to work overtime reheating the building (note the recent protests in the UK by Insulate Britain). Insulation is both an essential and overlooked element of sustainable energy and confronting climate change. It’s a major feature in David MacKay’s Sustainable Energy Without the Hot Air. The following is an edited extract from the chapter, Smarter Heating.

The war on leakiness

What can be done with leaky old houses, apart from calling in the bulldozers? Figure 1 shows estimates of the space heating required in old detached, semi-detached, and terraced houses as progressively more effort is put into patching them up. Adding loft insulation and cavity-wall insulation reduces heat loss in a typical old house by about 25%. Thanks to incidental heat gains, this 25% reduction in heat loss translates into roughly a 40% reduction in heating consumption.

Let’s put these ideas to the test.

Detached,
no insulation
53kW/d
Semi-Detached
no insulation
43kW/d
Terraced
no insulation
30kW/d
+loft insulation
43kW/d
+loft insulation
29kW/d
+loft insulation
23kW/d
+cavity insulation
27kW/d
+cavity insulation
20.5kW/d
+cavity insulation
18.5kW/d
+double glazing
27kW/d
+double glazing
19kW/d
+double glazing
17kW/d
Figure 1. Estimates of the space heating required in a range of UK houses. From Eden and Bending (1985).

A case study

In 2004 I had a condensing boiler installed, replacing [my] old gas boiler. (Condensing boilers use a heat-exchanger to transfer heat from the exhaust gases to incoming air.) At the same time I removed the house’s hot-water tank (so hot water is now made only on demand), and I put thermostats on all the bedroom radiators. Along with the new condensing boiler came a new heating controller that allows me to set different target temperatures for different times of day. With these changes, my consumption decreased from an average of 50 kWh/d to about 32 kWh/d.

This reduction from 50 to 32 kWh/d is quite satisfying, but it’s not enough, if the aim is to reduce one’s fossil fuel footprint below one ton of CO2 per year. 32 kWh/d of gas corresponds to over 2 tons CO2 per year. In 2007, I started paying more careful attention to my energy meters. I had cavity-wall insulation installed (figure 2) and improved my loft insulation. I replaced the single-glazed back door by a double-glazed door, and added an extra double-glazed door to the front porch (figure 3). Most important of all, I paid more attention to my thermostat settings. This attentiveness has led to a further halving in gas consumption. The latest year’s consumption was 13 kWh/d!

Figure 2. Cavity wall insulation going in
Figure 3. A new front door.

Because this case study is such a hodgepodge of building modifications and behaviour changes, it’s hard to be sure which changes were the most important. According to my calculations, the improvements in insulation reduced the leakiness by 25%, from 7.7 kWh/d/◦C to 5.8 kWh/d/◦C. This is still much leakier than any modern house. It’s frustratingly difficult to reduce the leakiness of an already-built house!

Better Buildings

If you get the chance to build a new building then there are lots of ways to ensure its heating consumption is much smaller than that of an old building. We know that modern houses are built to much better insulation standards than those of the 1940s. But building standards could be still better. The three key ideas for the best results are: (1) have really thick insulation in floors, walls, and roofs; (2) ensure the building is completely sealed and use active ventilation to introduce fresh air and remove stale and humid air, with heat exchangers passively recovering much of the heat from the removed air; (3) design the building to exploit sunshine as much as possible.

Read more about how to reduce your energy consumption and play your role in saving the planet in ‘Sustainable Energy Without the Hot Air’ available for purchase as a paperback where all good books are sold, or you could download the PDF for £/$ 0.00 (yes, really nothing to pay.)

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