Location as the key to exploiting renewable energy
Location is a key factor in the exploitation of renewable energy — Ant Wilson.
Many refurbishment projects provide scope for including low or zero carbon technologies. Ant Wilson of Faber Maunsell explores some of the options and their viabilities for different geographical locations.Most refurbishment projects will require some ‘consequential improvements’ under Part L of the Building Regulations, opening the door to wider use of low- or zero-carbon (LZC) technologies in more buildings. However, when considering the options there are number of factors to take into account. Not least of them is the geographical location of the project. The UK may be a relatively small land mass, but it still has a number of micro-climates with quite different conditions. For example, height and exposure will influence the viability of including wind turbines in a project. Biomass boilers may be an ideal replacement for fossil-fuel boilers — but only if there is sufficient space for fuel storage, access for large delivery vehicles and a local and reliable source of fuel. So there are unlikely to be many installations of biomass boilers in town centres. Similarly, the south west of the country receives more annual solar energy than the north east, so the calculations for including solar energy will be influenced by this. Having said that, there is a great deal of potential for making better use of solar energy throughout most of the UK — as photovoltaic (PV) or solar thermal panels are relatively easy to retrofit. In the case of highly priced PVs, the simple payback calculations are also changing rapidly as PV costs come down and their efficiencies increase — while energy prices continue to soar. More important than the location is the need to consider energy efficiency itself as a ‘renewable’, insofar as improving the efficiency of the building fabric can make a huge difference to its heating and cooling loads. Better thermal insulation minimises the capacity of heating plant and may facilitate use of LZC technologies such as solar thermal and air-source or ground-source heat pumps to supplement conventional heating plant. Similarly, lowering solar heat gains will reduce cooling demands. In commercial premises where occupation densities of people and computers are increasing rapidly, such measures become more important in mitigating total internal heat gains. Of course, because of the consequential-improvement element of Part L, such performance enhancements are something that should be happening to existing building stock on an ongoing basis. When considering the use of solar technologies, in all cases the surface area available for collecting solar energy needs to be balanced against the demands for electrical power or hot water. Thus, a single-storey building may have more potential for using solar energy than a 10-storey building. However, there are also innovative ways to increase the surface area available for solar collection.
Biomass boilers may be an ideal replacement for fossil-fuel boilers, but only if there is sufficient space for fuel storage and access for large delivery vehicles — as at Stradbroke Business & Enterprise College in Suffolk, where a single Broag 450 kW wood-chip boiler replaced three elderly oil boilers.
One option is the use of PV laminates on the glazing, as these will provide solar shading and generate electricity at the same time. So such technology is well worth considering when the project includes a need to reduce solar heat gains — in a highly glazed building for instance. It is also becoming increasingly common to introduce brise soleil in refurbishments (and new-build projects) to reduce solar heat gains. Given that brise soleil should be at the optimum angle to provide shading, its is then also optimally positioned to collect solar energy via PVs or evacuated tubes for hot water. Nor do these principles need to be confined to major refurbishments. For example, many retail stores have reduced energy wastage by the simple expedient of constructing a porch outside their doors. So why not roof the porch with solar thermal panels and give the hot-water systems a renewables boost at the same time? Where variable heat sources are being used for DHW, one of the biggest challenges is to cope with the variable heat input while maximising the renewable energy available. In some cases, refurbishment may allow the opportunity for extensive, super-insulated underground hot-water storage, which could iron out much of the inter-seasonal fluctuation. There is also scope for combining PVs with grass roofs. It is well established that grassing a roof with sedum will help to absorb heat before it warms the building fabric, as well as providing some evaporative cooling to the building. It is also established that PVs are more efficient at lower temperatures. So if PV panels are mounted around the perimeter of a grassed roof, the cooler micro-climate will increase the energy collected by the PVs while retaining the other benefits of a sedum roof. While most solar thermal installations are designed to supply or pre-heat domestic hot water (DHW), there is the potential to use the hot water to drive absorption chillers. On the plus side, this provides a balanced demand scenario, as most hot water would be generated when cooling demands are highest. On the negative side, absorption chillers have a low COP, are expensive and have demanding maintenance requirements. Rather than considering every single option, which it certainly has not done, the purpose of this article has been to provoke and encourage a structured and reasoned approach to determining the most suitable options. Considering fabric improvements first and thinking about the characteristics of the location second are certainly good starting points.
Ant Wilson is a director with Faber Maunsell.
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