PERFORMANCE

Two years on, the house works. Our primary goal was to be energy self-sufficient, i.e. to generate more energy than we consumed and export a modest (or better) surplus to the grid. This we achieved, so Tree House is demonstrably one of the few genuinely zero carbon houses in Britain.

Here are the figures:

Power consumption can be broken down as follows:

The values for the heating and hot water describe the power consumed by the heat pump, not the heat output. The output will depend on the co-efficient of performance of the heat pump which can be estimated at 300%, though may be higher in practice (if it was lower the thermal performance of the building would be better than its design values - unlikely).

The average energy consumption of a UK dwelling is 23,200kWh (heat and electric combined), so it's obvious that the key to the success of our zero carbon strategy was to get our demand as low as possible before working out how to meet it on site with renewable technology.

We have also kept our mains water consumption down to 62 litres per person per day, compared to the UK average for a two person house of 152 litres per person per day.

For a more detailed discussion of the performance of the building, see Green Building Magazine 18(1), Summer 2008 (www.newbuilder.co.uk).

The house has also been published as a case study by NHER.