FXSTD – Alternative Energy Center

By: Paul Giesberg
The inclusion of locally generated energy from renewable sources in new real estate development proposals is strongly stimulated. Both the BREEAM and the Code for Sustainable Homes schemes award credits when a certain amount of carbon is displaced by installing energy generating systems on site. The Code for Sustainable Homes awards 1 credit when at least 10% of the carbon emissions is reduced by the use of LZC technology and 2 credits when at least 15% is displaced. Local planning authorities also often require the generation of on site renewable energy to displace a certain amount of the carbon from the energy demand of the operational building.

There are methods to estimate the carbon footprint of operational buildings (for instance SAP and SBEM) and there are methods to calculate the carbon reduction that can be achieved by employing various renewable energy generating technologies. It appears therefore a relatively straightforwardexercise to determine what would be the most appropriate system or mix of systems to include in any particular development. There are however a number of issues that need to be considered that make the process less straightforward. Although BREEAM and Code for Sustainable Homes deal with this issue in a largely similar manner, there are slight changes in the detail. The remainder of this article considers the Code for Sustainable Homes.



The energy use category

The Code for Sustainable Homes awards credits for the installation of low and zero carbon technologies. The award of these credits is related to the relative reduction of carbon emissions through LZC. For this purpose the baseline energy demand for each unit is the energy use that is regulated by part L of the building regulations and excludes the energy use of television sets, computers and washing machines and neither does it include energy use for cooking. This differs from theintuitive situation of considering all energy demand. It also often differs from the requirements made by the local planning authority, who routinely base the reduction requirement on a baseline that includes all energy use.

There is a set of calculations that have to be used to predict the regulated energy demand of a building. For dwellings in the UK this is done using the SAP methodology. There is no standardised method of determining the total energy demand of a new home, although there are a number of benchmark data sets available that can be used. The Code for Sustainable Homes also requires the developer to consider renewable energy technologies at two moments in the development process.

At an early stage in the process the developer is required to undertake a feasibility study. This is usually carried out before sufficient detail is available to carry out a set of SAP calculations. A thorough feasibility study needs to be based on the energy demand of the development. Inevitably benchmark data will need to be considered to get an indication of the energy demand. This is often the same set of benchmark figures as is used for predicting the total energy demand. To determine an estimate of the regulated energy demand a correction can be made by excluding the energy use for cooking and adjusting the figure for Light and Appliances. A reasonable estimation of the latter figure is a reduction by 40%. This is the average contribution of appliances to the total amount of electricity use in a household.

The second point in the design process that the developer is required to take account of renewable energy is pre-construction. Usually there is sufficient information available at this time to carry out SAP calculations for the dwellings and have anaccurate forecast of the regulated energy demand.

The pollution category

Issue Pol 2 of the Code for sustainable Homes describes how credits can be awarded by using a heating system with reduced the NOx emissions. A number of the LZC technologies will reduce the likelihood of meeting the requirements in this category. Because electricity from the grid is produced with very high NOx emissions, the selection of ground source heat pumps or air source heat pumps would effectively prevent the project achieving any of the credits in this category.

The use of wood pellet burners also lead to of high NOx emissions and installation of this technology will also prevent the project achieving credits in this category.