A model answer to a difficult problem

The Department for Education and Skills wants all schools to be “models of energy efficiency and renewable energy” by 2020. In May, The Edge argued that the schools about to be built under the Building Schools for the Future programme should be as near to zero carbon as possible. Edge members have recently met to establish ways of achieving this goal.

The DfES’ energy data for 2004 shows that the median UK school used 155 kWh of fossil fuel per year per m2 of gross floor area and 39 kWh/m² of electricity. Together, these account for about 50 kg/m² of carbon dioxide a year. The DfES’ Building Bulletin 87 has the much lower target of 18 kg/m2 for new work. Although heating fuel consumption in recent low-energy schools can be 40-80 kWh/m², electricity consumption is often rising, so emissions levels of less than 30 kg/m2 per year are rare.

The latest building regulations and BREEAM requirements should improve these figures, but this is still a long way from the 12 kg/m2 reportedly achieved at Waldshut, the first school built to the German Passivhaus standard and completed in 2003.

In economic terms there is little point in contemplating generating on-site energy until one has reduced energy requirements to Passivhaus levels. How can one bring down energy demands this far? Reducing heating energy requirements by a factor of seven to 10 (that is, to 15-20 kWh/m²) is a necessary first step. Reducing fabric heat loss is not too difficult, with high insulation and a well-sealed envelope. The problem is getting a good supply of fresh air with minimum heating and electricity requirements, for example, by pre-heating (and in summer pre-cooling) the incoming air.

There is little point generating on-site energy until energy requirements have been reduced to Passivhaus levels

Such requirements make school premises more complex to design, install, commission, control and manage. There is also an urgent need to stop electricity requirements growing. Lighting still tends to be the single biggest consumer, but IT is catching up, as is other equipment including mechanical ventilation, cooling, and security equipment.

Good design needs to bring down energy use by lighting by a factor of three. Good use of daylight is more than possible in classrooms, but it needs to be glare-free and controllable to allow for computer projection and interactive whiteboards, which have recently undermined many a daylighting strategy. Good daylight and control can add costs, which frequently disappear during value engineering – a false economy that should be fiercely resisted. Controls for electric lighting are relatively cheap and reliable; they should be used to ensure that lights are on only when absolutely necessary.

IT is putting school environments under increasing strain, producing unwanted heat and sometimes requiring air-conditioning. Both new and replacement equipment must be rigorously specified as low energy; and such market pressure will in turn lead to more efficient products. Like lighting load, the hours of use of equipment must also be brought down to prevent much of it remaining on when it is not in use. The electrical demand from equipment needs to come down by a factor of two, even as the amount of kit supplied is rapidly rising.

Finally low-carbon energy generation can be considered. Any remaining heating load can be met relatively cost-effectively by biomass boilers and to some extent by solar water heating. For electricity, wind turbines could provide the most cost-effective means of on-site generation; and schools with large sites might even consider renting out space to generating companies. Photovoltaics come a poor fourth in their effectiveness and the length of their payback period.