age power per unit area, that’s 6.6 W/m2.E
Figure E.12 compares the power consumption per unit area of this
Heatkeeper house with my house (before and after my efficiency push)
and with the European average. My house’s post-efficiency-push con-
sumption is close to that of the Heatkeeper, thanks to the adoption of
lower thermostat settings.
The German Passivhaus standard aims for power consumption for heating
and cooling of 15 kWh/m2/y, which is 1.7 W/m2; and total power con-
sumption of 120 kWh/m2/y, which is 13.7 W/m2.
The average energy consumption of the UK service sector, per unit floor
area, is 30 W/m2.
The National Energy Foundation built themselves a low-cost low-energy
building. It has solar panels for hot water, solar photovoltaic (PV) panels
generating up to 6.5 kW of electricity, and is heated by a 14-kW ground-
source heat pump and occasionally by a wood stove. The floor area is
400m2 and the number of occupants is about 30. It is a single-storey build-
ing. The walls contain 300mm of rockwool insulation. The heat pump’s
coefficient of performance in winter was 2.5. The energy used is 65 kWh
per year per square metre of floor area (7.4 W/m2). The PV system delivers
almost 20% of this energy.
New office buildings are often hyped up as being amazingly environment-
friendly. Let’s look at some numbers.
The William Gates building at Cambridge University holds computer
science researchers, administrators, and a small café. Its area is 11 110 m2,
and its energy consumption is 2392 MWh/y. That’s a power per unit area
of 215 kWh/m2/y, or 25 W/m2. This building won a RIBA award in 2001
for its predicted energy consumption. “The architects have incorporated
many environmentally friendly features into the building.” [ ]
But are these buildings impressive? Next door, the Rutherford building,
built in the 1970s without any fancy eco-claims – indeed without even
double glazing – has a floor area of 4998 m2 and consumes 1557 MWh per
year; that’s 0.85 kWh/d/m2, or 36 W/m2. So the award-winning building
is just 30% better, in terms of power per unit area, than its simple 1970s
cousin. Figure E.12 compares these buildings and another new building,
the Law Faculty, with the Old Schools, which are ancient offices built pre-