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The above cases apply to perhaps the majority of Irish homes as most are constructed either with a fireplace or some other form of focal point heater. In the rare situation where none of the above conditions apply, no secondary system has to be specified and the efficiency of the main heating system is all that matters.
CARBON DIOXIDE EMISSIONS RATING (CDER) & MAXIMUM PERMITTED CARBON DIOXIDE EMISSIONS RATING (MPCDER)
Designers should understand the concept of CDER and MPCDER as used in DEAP.
Firstly these elements are issues to do with Part L compliance and do not form part of the BER calculation. For all new properties the CDER value must be less than the MPCDER if Part L is to be satisfied.
The MPCDER is calculated for a reference dwelling of the same shape and size as the actual dwelling being considered, but with minimum criteria for acceptable design being assumed. For example, the reference dwelling has limited wall openings of 25% of the total floor area. The CDER for the actual dwelling is now calculated and if it is greater than the MPCDER then the designer must find ways to save energy in other areas (generally by a small amount) to reduce the figure to below the maximum permitted. This might be done, for instance, by adding a draught lobby to the front door or reducing the area of glazing.
In Table 37, Appendix C of Part L, it is stated that the heating system of the reference dwelling is to be the same as the actual dwelling being considered. What this means is that the type of heating system chosen for a project is factored out of Part L compliance. The reason, we understand, for this was that if electric heating systems were going to be allowed for the heating of homes then this would have made it ridiculously easy for gas and other more sustainable heating systems to achieve the same (net) fossil fuel efficiency targets. To avoid getting involved in the specification of heating systems, Part L takes the proposed design and calculates a MPCDER for that type of heating system. This means that the MPCDER is not a fixed value for a given house but varies, most significantly, with the type of heating system being proposed. This can be somewhat disconcerting initially.
The main point for designers though is that, for the above reasons, compliance with the MPCDER does not necessarily indicate a good Primary or Secondary BER or even low running costs although low values do indicate low carbon emissions and therefore a good secondary label.
CASE STUDY SPECIFICATION
In our case study we have selected a large 2 storey detached house, with extensive glazing. The following, is the key data entered into the DEAP software:
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