(typical of damp clay soil),
If, as above, we assume a population density corresponding to 160 m2 per
person, then the maximum power per person deliverable by ground-source
heat pumps, if everyone in a neighbourhood has them, is 480 W, which is
12 kWh/d per person.
So again we come to the conclusion that in a typical suburban area
composed of poorly insulated houses like mine, not everyone can use ground-
source heat pumps, unless they are careful to actively dump heat back into
the ground during the summer. And in cities with higher population density,
ground-source heat pumps are unlikely to be viable.
I therefore suggest air-source heat pumps are the best heating choice
for most people.
Does increasing the thermal mass of a building help reduce its heating and
cooling bills? It depends. The outdoor temperature can vary during the
day by about 10 °C. A building with large thermal mass – thick stone walls,
for example – will naturally ride out those variations in temperature, and,
without heating or cooling, will have a temperature close to the average
outdoor temperature. Such buildings, in the UK, need neither heating nor
cooling for many months of the year. In contrast, a poorly-insulated building
with low thermal mass might be judged too hot during the day and
too cool at night, leading to greater expenditure on cooling and heating.
However, large thermal mass is not always a boon. If a room is occupied
in winter for just a couple of hours a day (think of a lecture room
for example), the energy cost of warming the room up to a comfortable
temperature will be greater, the greater the room’s thermal mass. This extra
invested heat will linger for longer in a thermally massive room, but if
nobody is there to enjoy it, it’s wasted heat. So in the case of infrequently-used
rooms it makes sense to aim for a structure with low thermal mass,
and to warm that small mass rapidly when required.
304Table E.18. Sources: Bonan (2002),