What is SAP?
The DER and TER are calculated according to the Standard Assessment Procedure (SAP) 2009 for domestic buildings and the Simplified Building Energy Model (SBEM) calculation for commercial projects.
SAP is the Government’s standard methodology for assessing the energy consumption in new domestic dwellings.
SAP Assessors are available nationwide.
The latest version of SAP is SAP 2009. The SAP scale runs from 1 (poor) to 100 (excellent) and is based on estimated annual energy use for space heating, domestic hot water, ventilation and internal fixed lighting. A SAP of 100 now represents zero energy cost for these items. It can be above 100 for dwellings that are net exporters of energy.
For SBEM the DER is actually termed the Buildings Emission Rate or BER.
What is SBEM?
SBEM uses a computer program developed by the Building Research Establishment (BRE) that provides an analysis of a commercial building's energy consumption. It is a recognised method to assist in demonstrating compliance with the Building Regulations Part L2A or L2B, (England and Wales).
An SBEM Energy rating is not a design of the heating, ventilation or lighting system, which may be required for more complex building types. SBEM can be provided by some SAP assessors, or a Building Services Engineering Company.
Efficiency & emissions
Ground source heat pumps can help dwellings achieve compliance with Building Regulations by reducing the DER/BER of buildings.
Although a ground source heat pump uses electricity (which has the largest emission rate) to run the compressor and circulation pumps, its ability to be 400% efficient by operating with a COP of 4, i.e. for every one kW of electrical energy used it produces 4 kW of thermal heat, means the actual CO2 emission rate for providing heat to a building is 0.113kg CO2/kWh. This shows a CO2 reduction of typically 37% over gas and 55% over oil.
As a result, the current SAP assessment software packages reflect this energy efficiency in their hard-coded settings (320% if the heat pump is linked to underfloor heating, 320% x 0.7 if radiators are used, with a further 0.7 factor applied if the heat pump is also providing the domestic hot water).
As a consequence, the DER is significantly reduced. Such is the reduction, there might be an opportunity to downgrade the insulation specification and still achieve an acceptable DER. However, this tactic is not recommended because any increase in the property’s heat load will result in a higher flow temperature, a less efficient heat pump and higher running costs.
Later editions of the SAP software are likely to demonstrate even higher efficiencies as BRE, the auditors of the scheme, recognise improved performance data supplied by various manufacturers. By utilising the energy in the ground, a ground source heat pump can produce over twice the amount of energy for the same amount of initial energy input as a gas fired boiler. This means that the CO2 emissions will be lower for a ground source heat pump than other non-renewable fuels.