The way you build a home goes half way to making it sustainable. The other half is its M&E and water harvesting. Alex Smith looks at how the homes in the BRE innovation park used new technology to tackle both
Automatic biomass boiler
Kingspan’s Lighthouse prototype home in the BRE Innovation Park, hits the highest rating of the Code for Sustainable Homes. It is so well insulated and airtight that for most of the year it supplies its own space heating, hot water and electricity. During the winter, only a tiny 2kW biomass boiler is needed.
This was easier to specify than it was to supply. The design team wanted a boiler with an automatic pellet feed and ignition system. The smallest available was the Windhager BioWIN, a 10kW model. It is fired by wood pellets, which it stores in its hopper. When the boiler’s sensors tell it to ignite, it drops the pellets into the burner. The main problem with the product is that takes up most of the utility room and could supply five homes of this type. On the other hand, it only needs topping up three times a year and Sheppard Robson says it should cost £31 a year to run, compared with the £500 required to heat a home of this size and shape built to 2006 Part L of the Building Regulations.
Phase change dry lining
It requires great precision to make a building envelope airtight, and this is easier to achieve in a factory than a building site. The disadvantage is that offsite manufacture tends to be lightweight, but the energy performance of buildings improves as their thermal mass increases.
One answer to this problem is the use of “phase change” materials, which can be incorporated within a home’s dry lining. These use the extra energy needed to change a solid to a liquid, or vice versa, to increase a structure’s effective thermal mass. Chemical company BASF has exploited this effect with Micronal, a paraffin-based substance. This can be incorporated between sheets of Knauf’s SmartBoard plasterboard where BASF says it mimics the thermal capacity of 90mm of concrete.
The second product is Dupont’s Energain. Here, the phase change material is sandwiched between aluminium foil fixed behind the plasterboard.
German heating products specialist Viessmann has launched the Vitotres 343, a whole-house ventilation system with heat recovery. It is designed for use in homes with water and space heating requirements of less than 15kWh/m2 a year. It looks similar to a large fridge–freezer, and is about same size: 600mm wide, 670mm deep and 2,095mm tall.
It uses an air-source heat pump to extract heat from air that is being expelled from the house. This has an output of 1.5kW, and can be used to warm incoming air or to heat a 250 litre hot water cylinder, which can also be connected to thermal solar panels. A built-in electric element provides back up heating for cold days.
In the summer the heat pump can be operated in reverse to cool incoming air. The Vitotres 343 has been fitted to the EcoTech Organics home built in BRE’s Innovation Park where it provides all the home’s heating and hot water needs in combination with a thermal solar panel on the roof.
Green ventilation units
Homes must be airtight to achieve high code ratings, which means ventilation must be carefully controlled. In practice this means installing a whole-house ventilation system with heat recovery. This is a unit that combines ventilation fans with a heat exchanger that is installed in an attic or utility room. It sucks stale air from kitchens or bathrooms and passes it through a heat exchanger before expelling it. The energy extracted from the outgoing air is used to warm the incoming air, which is supplied to living areas and bedrooms. In this way, little heat is lost – indeed, many manufacturers claim up to 90% efficiency. There are several companies that make these units, these include Nuaire, Vent-Axia, Xpelair and Greenwood Airvac
Reducing water consumption is an important element of the code. The targets are particularly demanding at levels five and six: 80 litres of water per person per day. Given that the UK average is 150 litres, some serious cuts in water use are necessary. This includes reduced-flow taps, smaller baths and reduced-flush WCs.
But the only way to hit the higher level ratings is to install a rainwater harvesting system. This consists of a large tank buried in the garden or driveway outside the home. Rainwater is collected from the roof and diverted to the tank via a filter that traps leaves and other debris. A diverter allows excess water to flow into the drains as normal. A pump inside the tank delivers water in two ways. With direct systems water is supplied straight to WCs and the outside tap by way of another filter. Gravity systems use a secondary tank in the roofspace and water is distributed to appliances from there. There are several manufacturers who specialise in all the components needed for a system. These include Rainharvesting systems, Envireau, Hydro International and Freerain
This article was originally headline Cracker in the 3 million green homes by 2020 supplement on 23 November 2007
Housing Supplement Nov 2007
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