One of the two main targets that needs to be met when assessing a new domestic building against Part L 2013, together with the Target Fabric Energy Efficiency (TFEE), is the Target Emission Rate (TER) for heating. A legal requirement within Part L1A, the TER sets a minimum allowable standard for a building’s energy performance using the annual CO2 emissions of a notional building similar to the proposed building.
One of the questions we are most commonly asked regarding the TER by designers and developers is “will this dwelling pass with electric or oil heating?” Most buildings are heated using gas, and unfortunately under current Building Regulations it is very difficult to get a new dwelling to pass and exceed the TER using electricity or oil due to the notional building method by which it is calculated.
The calculation methodology has two stages: first a notional building is created to the same size and shape of the actual dwelling which is to be constructed, but using reference values from appendix R of the SAP 2012 document. These values outline the building specification which needs to be met or exceeded to improve upon the TER, and include a notional heating system which is an 89.5 per cent efficient mains gas condensing boiler.
The second stage is to apply a fuel factor to the calculations to give the final TER, and the factors for the most commonplace fuels we use in SAP calculations are 1.00 for mains gas 1.17 for oil and 1.55 for grid electricity.
This shows that different fuel types will have different effects on the TER the proposed dwelling is trying to achieve. In addition, each of the fuel types have different emissions associated with them as well as primary energy factors – which represents the amount of energy needed to delivery one unit of energy.
As the table below shows, oil and electricity have a higher CO2 per kWh of fuel when burnt than mains gas. Therefore when a notional building’s TER is based upon mains gas, and for example the proposed dwelling is using electric heaters, it is clear that associated emissions to provide the electric heating will be over twice that of mains gas.
|Fuel Type||Emissions kg Co2/kWH||Primary Energy Factor|
In conclusion, the difficulty in getting dwellings which use oil or electricity as the main heating fuel to meet the target emission rate lies with the fact that mains gas is used in the notional calculation. There are higher CO2 emissions from oil and electricity when consumed and the energy losses from transporting electricity are significantly higher than mains gas.
This does not mean that it is not possible to meet the TER using oil or electricity as the heating fuel, however significant improvements to the building fabric or the incorporation of renewable technologies will be needed to offset the higher associated emissions.
Written by: Michael Brogden, Sustainable Buildings Assessor, Darren Evans Assessments.