" After that, the mechanical systems are amplifying something the walls have already done."
THE MECHANICAL LAYER
With the envelope doing most of the work, the services at House Willett are lean. An air source heat pump handles all heating and domestic hot water, drawing renewable energy from the air outside, even on a cold morning. A mechanical ventilation and heat recovery unit( MVHR) captures up to 90 per cent of the warmth from stale outgoing air and transfers it to the fresh supply, so the house breathes clean, filtered air continuously without losing the energy it took to heat the interior. For a family with young children, the filtration alone, removing pollen, particulates, and the residual pollution that drifts this far from the A3, was worth the specification.
The storage layer is where House Willett becomes genuinely unusual for an English home. The southfacing roof carries a photovoltaic array sized to cover the household ' s typical annual demand. Surplus generation— which in a well-insulated home can be considerable even in sunshine— flows into a pair of Tesla Powerwalls installed in the plant room beside the heat pump. The Powerwalls store up to 27 kilowatt-hours between them, enough to run the house through a cloudy night, power the underfloor heating through a cold morning, and and charge the Microlino in the garage without drawing a single watt from the National Grid.
The Microlino, is a 90-kilometre-range, twoseat electric microcar that occupies roughly the footprint of a large sofa. For a Surrey household whose second-car journeys are school runs, station trips, and the weekly shop, it is a rational object. Its 10.5-kilowatt-hour battery charges from empty in under four hours on a standard home wallbox. At House Willett, that wallbox is fed by the Powerwalls. The car costs, in practice, nothing to run.
INTELLIGENCE ON TOP
The final layer of House Willett is its brain. Baufritz integrates KNX-based smart home technology throughout— an open, manufacturer-neutral protocol that coordinates heating, shading, lighting, and ventilation in a single system. The occupants can warm a room before they arrive home, drop the blinds on the west elevation at the moment the afternoon sun would otherwise overheat the living space, and schedule the Powerwalls to charge from the grid overnight on the rare weeks when the solar yield is genuinely poor. Ole Heins estimates that intelligent automation of this kind typically delivers a further 10 to 30 per cent reduction in energy use on top of what the envelope and services already achieve— the system uses energy only when and where it is needed.
The result is a home that, across a full year, produces at least as much energy as it consumes. In the months between April and September, it produces considerably more, selling surplus back to the grid. The annual energy bill— accounting for the modest grid imports of deep winter— is projected to be close to zero, and in a good year, negative.
What House Willett demonstrates, more than anything, is that zero-energy living is not a lifestyle proposition or an act of ecological self-denial. It is an engineering outcome, the natural consequence, as Baufritz puts it, of doing the building correctly in the first place. The house is warm, quiet, and unusually clean-aired. The car is cheerful and costs nothing to charge. The electricity meter, on a July afternoon, runs backwards.
That is, by any reasonable measure, a pleasant way to live.
www. baufritz. com
CASE STUDY
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