BowZED was developed by Yorklake and designed by “The ZedFactory” specialist architect firm in Surrey. It was built from scratch on a compact urban plot.
ZED stands for Zero Energy Development. It means that the building can generate as much energy from renewable sources as it consumes.
There are two ways it achieves this...
By needing very little energy in the first place: South-facing windows draw enough of the sun's energy to provide up to 40% of space heating. Thermally massive walls and ceilings absorb the warmth and can store it for up to 5 days even when there’s no sunshine whatsoever. The walls are also incredibly well-insulated.
This means you simply do not need a traditional space heating system. In addition to the solar thermal gain, enough heat energy is also contributed by just the occupants and their activites. Unbelievable? The architects have figures to prove it: 109W for a man, 92W for a woman, even 16W for a cat! And of course, electrical goods and cooking also release background warmth into the living space.
This system works all year round, and there is a backup electrical heater for if flat is unoccupied. Finally, ventilation is also superbly efficient, using a heat-exchange system: air going out warms air coming in. The system itself is wind-powered, hence the rotating cowl on the roof.
By using practical, sustainable technology to generate the rest: Photovoltaic panels provide 50% of the electrical energy required, and a small roof-mounted wind turbine is designed to take care of the rest. The four dwellings take all their hot water from a single 15kW wood-pellet boiler. Wood-pellet is zero fossil carbon: it does produce CO2 emissions, but because the fuel is a living and renewable source it only releases as much carbon as the trees absorbed while growing.
Photos courtesy Yorklake Ltd.Inside the flats: For developer Yorklake Ltd, BowZED represents its first low carbon building venture. Yorklake usually focuses on high-spec homes and prime locations, so it's no surprise to find that the first impressions of BowZED's interior are of a no-compromise quality living environment.
The 300mm thick insulated walls that help towards this home's minuscule energy needs do have one drawback: a slight loss of living space. The architects have mitigated this with an open-plan layout that still feels spacious, and the effect of good temperature regulation and ventilation make it comfortable space to occupy. With excellent natural light and a recreational patio / sky garden area, you get the feeling that these homes will suit luxury lifestyles without much compromise.
BowZED's micro-generating technology has also worked fairly successfully to date. Solar PV panels are reasonably well established, but wood-pellet boilers and small wind turbines are still at the pioneering stage. The turbine is due to be upgraded soon, with hopes that a new model will cope better and generate more continuous power from the city's fluctuating winds. Meanwhile the wood pellet boiler, sourced overseas, is going strong although the number of available fuel suppliers is not growing as quickly as expected.
A Sustainable Success Story?: The four apartments are all in private ownership. They were sold promptly and fetched prices higher than expected. Is this because the zero-energy aspect demands a market premium, or is it due more to a buoyant housing market at the time of sale?
James Kafton of developers Yorklake, is aware that a conventional development (i.e. to existing Building Regulations standards) on the same plot would have been more profitable. The construction cost for this type of eco home is higher because of both the quality and quantity of material required. Although the BowZED flats did well commercially, he expressed doubt that an "eco premium" would itself add significantly to the market value.
"We believed in zero-energy building, and we still do. It is the way forward in terms of building. We are keen to do more low carbon developments, but the government ought to be providing more incentives for builders", said Mr. Kafton.
The government is currently proposing a 2016 deadline for all new buildings to meet one of the six levels of carbon reduction set out in the Code For Sustainable Homes. BowZED is built to Level 6, the highest recognised standard of low-carbon building in the Code. Would developing more homes to a middle-ground standard be more commercially rewarding? Perhaps; nobody seems to know for sure. Low-energy construction techniques are still some way from the mainstream, and the simple fact remains that for good energy efficiency you need to use more and better building materials for the walls and insulation. As Mr. Kafton points out: "If it is going to be more expensive to build, who will bear the cost?"
Over to you, the homebuyer. Weighing up the attraction of low energy bills and the chance to live a more sustainable lifestyle, how much more would you be willing to pay for an eco home?