The SAP calculation used is based on a framework for the calculation of energy use in dwellings - The BRE Domestic Energy Model (BREDEM) and is consistent with the European standards BS EN 832 and BS EN ISO 13790.
The SAP calculation is based on the energy balance in a dwelling taking into account a range of factors that contribute to energy efficiency.
These factors include:
- The materials used for construction.
- The thermal insulation of the building fabric.
- The ventilation characteristics (of the dwelling) and ventilation equipment.
- The efficiency and control of the heating system(s).
- The gains from solar radiation through openings of the dwelling.
- The fuel used to provide space and water heating, ventilation and lighting.
- The renewable energy technologies.
- The household size and composition.
- The ownership and efficiency of particular domestic electrical appliances.
- The individual heating patterns and temperatures.
- The geographical location, so that a given dwelling has the same rating in all parts of the UK.
SAP Energy Performance Indicators
The indicators of this energy performance are:
1. An energy consumption per unit floor area
The consumption is adjusted for floor area (m^2) so that it is essentially independent of dwelling size for a given built form - for example a flat or a house (detached or terraced).
2. An energy cost rating (the SAP rating)
The SAP rating is expressed on a scale of 1 to 100, the higher the number the lower the running costs.
3. An Environmental Impact rating based on CO2 emissions (the EI rating)
This rating is based on the annual CO2 emissions associated with space heating, water heating, ventilation and lighting, less the emissions saved by energy generation technologies.
4. A dwelling CO2 Emission Rate (DER) in kg/m²/year.
It is equal to the annual CO2 emissions per unit floor area for space heating, water heating, ventilation and lighting, less the emissions saved by energy generation technologies. The DER is a similar indicator to the EI rating.
SAP within CarbonKit
The Standard Assessment Procedure in CarbonKit is provided as an API. This provides the functionality given in the SAP worksheet and tables.
The current version is the "SAP 2005 specification with 9.83 update" (October 2009). A new version is currently in development.