A development of 10 homes

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Description of fictional building

10 new build homes in a sub-urban location. Solar Photovoltaic (PV) arrays are proposed to meet the RSS ENV5.B3 policy requirements.

Baseline energy use and CO2 emissions

Baseline energy use = 147,790 kWh/yr

CO2 emissions = 42,901 kgCO2/yr

Energy use and CO2 emissions figures calculated using Part L 2006 SAP methodology via NHER software.

Things to check:

• Is baseline energy use calculated using approved software?
• Does baseline energy use include cooking and appliances?
• Are Part L fuel emission factors used?

Requirements of Part L 2006

Part L 2006 sets out minimum levels of insulation and heating/lighting efficiencies for new homes but also requires the expected regulated CO2 emissions (the DER or Dwelling Emission Rate) to be calculated and for it to be lower than a Target Emissions Rate (TER) set by Part L.

The new homes are to be insulated beyond minimum standards, uses a high efficiency gas boiler, low energy lighting and solar PV arrays to exceed Part L 2006 by 25%.

DERs are provided and are less than TERs for all house types. Figures are calculated using Part L 2006 SAP methodology via NHER software.

Things to check:

• DER is lower than TER? This can be with or without DRLCTs for Part L requirements but only covers regulated emissions.

Requirements of the Code for Sustainable Homes (CfSH)

Each CfSH level has mandatory CO2 emissions credit (Ene1) requirements and additional credits can be obtained for carbon emission reductions from low carbon technologies (Ene7).

Ene1: Dwellings achieve a 25% improvement (DER vs TER) with the solar PV arrays, this is sufficient for CfSH level 3* mandatory requirements and 5 credits.

Ene7: The solar PV arrays reduces CO2 emissions by 6,435 kgCO2/yr. This is a 15.0% saving on total emissions (including unregulated cooking and appliances). This is therefore sufficient for 2 Ene 7 credits.

Things to check:

• Calculations (SAP calculations showing DERs) are provided both with DRLCTs (for Part L and CfSH Ene 1 credits) and without DRLCTs (for evidence for CfSH Ene7 credits).
• For CfSH Ene 7 credits all savings are in terms of total carbon emissions (kgCO2/yr) including appliances and cooking.

Requirements of RSS policy ENV5.B3

RSS ENV5 policy B3 requires new developments of more than 10 dwellings or 1000m_ of non-residential floorspace to secure at least 10% of their energy from decentralised and renewable or low-carbon sources, unless this is not feasible or viable

 Evidence (SAP calculations showing the energy use with and without solar PV arrays) shows that the solar PV arrays provide 11,329 kWh/yr or 10.2% of regulated emissions but only 7.7% of total energy (including unregulated energy uses) falling short of the RSS policy requirements if other technologies are not viable.

 This example highlights that Code for Sustainable Homes level 3* homes exceeding Part L by 25% and achieving both Ene7 CfSH credits can is some cases fail to meet the RSS ENV5.B3 policy.

Things to check:

• Calculations (SAP calculations showing energy use) are provided both with and without DRLCTs (to enable compliance with RSS policy to be shown).
• Savings are in terms of total energy requirement (kWh/yr) including appliances and cooking.

Other passive design and energy efficiency solutions

It should be noted that other passive design and energy efficiency measures such as increased insulation or higher efficiency boilers may be more cost effective ways of saving energy and carbon. This will help with Part L compliance and CfSH Ene1 credits but are separate to the requirements of RSS ENV5.B3 which requires a more decentralised approach to renewable energy and is not only about reducing carbon emissions.

Other decentralised and Renewable or Low Carbon Technology (DRLCTs) solutions

There are a number of decentralised and renewable and low carbon technologies which could meet the RSS ENV5.B3 requirements for a 10 home development. This example used solar PV arrays but other solutions are available and may be more suitable for specific sites.

Things to check:

• Energy supplies are from decentralised and renewable or low carbon technologies and not from passive design and energy efficiency measures.