http://www.ck12.org Chapter 3. Making A Difference
9 ◦C× 7. 7 kW h/d/◦C' 70 kW h/d.Finally, to calculate the power required, we divide this heat loss by the efficiency of the heating system. In my house,
the condensing gas boiler has an efficiency of 90%, so we find:
power used=
9 ◦C× 7. 7 kW h/d/◦C
0. 9= 77 kW h/d.That’s bigger than the space-heating requirement we estimated in Chapter Heating and cooling. It’s bigger for two
reasons: first, this formula assumes that all the heat is supplied by the boiler, whereas in fact some heat is supplied
by incidental heat gains from occupants, gadgets, and the sun; second, in Chapter Heating and cooling we assumed
that a person kept just two rooms at 20◦Call the time; keeping an entire house at this temperature all the time would
require more.
OK, how can we reduce the power used by heating? Well, obviously, there are three lines of attack.
a. Reduce the average temperature difference. This can be achieved by turning thermostats down (or, if you have
friends in high places, by changing the weather).
b. Reduce the leakiness of the building. This can be done by improving the building’s insulation – think triple
glazing, draught-proofing, and fluffy blankets in the loft – or, more radically, by demolishing the building
and replacing it with a better insulated building; or perhaps by living in a building of smaller size per person.
(Leakiness tends to be bigger, the larger a building’s floor area, because the areas of external wall, window,
and roof tend to be bigger too.)
c. Increase the efficiency of the heating system. You might think that 90% sounds hard to beat, but actually we
can do much better.Cool technology: the thermostat
The thermostat (accompanied by woolly jumpers) is hard to beat, when it comes to value-for-money technology. You
turn it down, and your building uses less energy. Magic! In Britain, for every degree that you turn the thermostat
down, the heat loss decreases by about 10%. Turning the thermostat down from 20◦Cto 15◦Cwould nearly halve
the heat loss. Thanks to incidental heat gains by the building, the savings in heating power will be even bigger than
these reductions in heat loss.