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SAP Calculations

sap2012The SAP rating is based on the energy costs associated with space heating, water heating, ventilation and lighting, less cost saving from energy generation technologies. It is adjusted for floor area so that it is essentially independent of dwelling size for a given build form. The SAP rating is expressed on a scale of 1 to 100, the higher the number the lower the running costs.

The Environmental Impact rating is based on the annual CO2 emissions associated with space heating, water heating, ventilation and lighting, less cost saving from energy generation technologies. It is adjusted for floor area so that it is essentially independent of dwelling size for a given build form.

Dwelling CO2 Emission rate (DER) is a similar indicator to the Environmental Impact rating, which is used for the purpose of compliance with building regulations. It is equal to the annual CO2 emissions per unit floor area for space heating, water heating, ventilation and lighting, less cost saving from energy generation technologies, expressed in kg/m2/year.

The method of calculating the energy performance and the ratings is set out in the form of a worksheet, accompanied by a series of tables according to the requirements of the Energy Performance of Buildings Directive. The calculation should be carried out using a computer program that implements the worksheet and is approved for SAP calculations.

For further reference, you can download a copy of the Government approved 2005 SAP Manual from this website. It contains details of the SAP calculation worksheet.

Electric underfloor heating systems are one of only two systems recognised by the Government’s Standard Assessment Procedure (SAP) as having the necessary parameters to qualify for inclusion into the SAP calculation – the other being storage heater systems with radiant panels built in and which are controlled as a single unit.

The screed thickness for a direct acting heating system must be no more than 50mm (ref TEHVA document DOM 8) which provides a reasonable heat up period. When underfloor heating is laid within a wooden floor construction to operate as direct heating, it has been allocated as a system with maximum responsiveness in the Government’s Standard Assessment Procedure (SAP).

The relevant data for standard tariff electric underfloor heating systems is:

In thin screed (45 – 60mm) Efficiency – 100%; Heating Type – 2; Responsiveness R – 0.75

In timber floor (inc Vysa-Pron) Efficiency – 100%; Heating Type – 1; Responsiveness R – 1