predict the heat savings from turning the thermostat down, double-glazing
the windows, and so forth.

Warming the outdoors, and other luxuries

There’s a growing trend of warming the outdoors with patio heaters. Typ-
ical patio heaters have a power of 15 kW. So if you use one of these for a
couple of hours every evening, you are using an extra 30 kWh per day.

A more modest luxury is an electric blanket. An electric blanket for a
double bed uses 140 W; switching it on for one hour uses 0.14 kWh.


Fridge and freezer

We control the temperatures not only of the hot water and hot air with
which we surround ourselves, but also of the cold cupboards we squeeze
into our hothouses. My fridge-freezer, pictured in figure 7.3, consumes
18 W on average – that’s roughly 0.5 kWh/d.


In countries where the temperature gets above 30 °C, air-conditioning is
viewed as a necessity, and the energy cost of delivering that temperature
control can be large. However, this part of the book is about British energy
consumption, and Britain’s temperatures provide little need for air-
conditioning (figure 7.8).

An economical way to get air-conditioning is an air-source heat pump.
A window-mounted electric air-conditioning unit for a single room uses
0.6 kW of electricity and (by heat-exchanger) delivers 2.6 kW of cooling. To
estimate how much energy someone might use in the UK, I assumed they
might switch such an air-conditioning unit on for about 12 hours per day
on 30 days of the year. On the days when it’s on, the air-conditioner uses
7.2 kWh. The average consumption over the whole year is 0.6 kWh/d.

This chapter’s estimate of the energy cost of cooling – 1 kWh/d per
person – includes this air-conditioning and a domestic refrigerator. Society

Figure 7.7. Hot air total – including domestic and workplace heating – about 24 kWh per day per person.
Figure 7.8. Cambridge temperature in degrees Celsius, daily (red line), and half-hourly (blue line) during 2006.
Figure 7.9. Cooling total – including a refrigerator (fridge/freezer) and a little summer air-conditioning – 1 kWh/d.