Southwest Environmental Limited

TER and DER Explained

(TER) Target Emission Rate

The Target Emission Rate is a number derived from modeling of an "as designed" building using the The Government’s approved methodology for assessing the energy performance of new dwellings. The procedure accounts for energy used in:

• Space heating and cooling
• Hot water provision
• Fixed lighting

and Energy Lost through:

• Air Leakage
• Fabric Energy Losses

The indicators of energy performance are energy consumption per unit floor area, energy cost rating (SAP rating), environmental impact rating based on CO2 emissions (EI rating) and dwelling CO2 emission rate (DER). They are used in the production of energy performance certificates (EPCs) and to demonstrate compliance with AD L1A and the Code for Sustainable Homes.

To contribute to reducing CO2 emissions as calculated by SAP, heat and power must be generated either on or in the home, on the development or through other local community arrangements (including district heat and power).

For a mid terrace flat we might see a generated TER of 25 KgCO2/m2/year, depending on the code level required you will then have to tinker with the building envelope until you have the required reduction.

A detached house will have a different TER to a terrace house. One would expect a terrace house to be more efficient (because it is surround by other heated spaces) and as such a terrace house will have a lower TER when compared to detached dwellings.

Another variable is primary fuel type, a home run on gas will have a lower TER than a house run on electricity. As gas has a lower footprint than electricity when considering CO2e/KWh of UK grid average electricity. This balance will likely change over time as the UK electricity is generated from renewables rather then fossil energy. Although this transition is likely slowed owing to fossil fuel lobbying. 

(DER) Dwelling Emission Rate

The DER is the estimated CO2emissions per m2 per year (KgCO2/m2/year) for the dwelling as designed. It accounts for energy used in heating, fixed cooling, hot water and lighting. The table below shows the necessary reduction depending on the require code rating.

In order for a SAP assessment to be passed the DER must be lower than the TER. In short the house you are going to build should meet the target set by SAP for the type of house you modeled. 

Summary

TER - A target cooked up from SAP.

DER - Modeled Emissions for your particular development, based on SAP methodology.