The 25% dwelling emission rate (DER) improvement over Part L1A 2010 CO2 standards required for Code for Sustainable Homes Level 4 compliance is being achievable via multiple routes. These have focussed on the use of decentralised energy, heat pump technology, or high efficiency gas boilers, with further CO2 reductions through the use of renewable technologies.
In this note we examine how, in theory, Code Level 4 could be achieved with electric panel heaters and electric immersion hot water systems. The key principle in both our strategies developed is minimising heat loss through building fabric, combined with the specification of high performance ventilation.
Routes to compliance
The table below outlines two specifications capable of delivering the necessary 25% DER improvement for Code Level 4 compliance in flats. In addition, they achieve a block average Fabric Energy Efficiency Standard of >38, providing more than 7 ENE 2 credits.
This scenario focusses on exceptionally high performance building fabric, with performance standards often associated with structurally insulated panels. Critically, triple glazing has been adopted, as well as very low thermal bridging (heat lost through breaks in insulation, such as window lintels, balconies and floor details).
This scenario provides more flexibility in the building fabric specification, with very high performance standards achievable with masonry construction. The use of triple glazing is still integral to the overall strategy, and low air permeability with heat recovery ventilation is required. To substitute the more exacting fabric standards used in Scenario 1, waste water heat recovery has been specified to reduce hot water loads.
- The additional costs of achieving higher fabric performance and MVHR should be compared to savings associated with avoiding renewable technologies or district heating.
- Our experience has confirmed that thermal bridging y-values of 0.08W/m2K and 0.04W/m2K will be very challenging to achieve on apartments.
- To achieve an air permeability of 3m3/m2/hr for all dwellings on a site, it is likely that a 100% testing regime will be necessary. Any untested dwellings will automatically incur a 2m3/m2/hr penalty under Part L1A 2010.
- Although these specifications achieve mandatory ENE 1 standards, as well as additional ENE 2 credits, no credits for renewable energy will be awarded. Electric heating is also associated with high NOx emissions and therefore fails to achieve POL 2 credits.