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SAP Calculations for UK Dwellings

How cove.tool works in conjunction with the Standard Assessment Procedure (SAP)

Patrick Chopson avatar
Written by Patrick Chopson
Updated over a week ago

The Standard Assessment Procedure (SAP) is adopted by the UK Government as the methodology for calculating the energy performance of dwellings specifically. The calculation is based on the building's energy balance that accounts for a range of factors that contribute to energy efficiency, such as:

  • construction materials

  • envelope insulation

  • infiltration and mechanical ventilation equipment

  • efficiency and control of the heating system(s)

  • solar gains through openings of the dwelling

  • the fuel used to provide space and water heating, ventilation, and lighting

  • energy for space cooling, if applicable

  • renewable energy technologies

The procedure used for the calculation is based on the Building Research Establishment Domestic Energy Model (BREDEM), which provides a framework for the calculation of energy use in dwellings. The procedure is consistent with the standard BS EN ISO 13790, which is the same standard that cove.tool's simulation engine is based off.

Calculation Procedure

The method of calculating the energy performance is set out in the form of a worksheet, accompanied by a series of tables. The worksheet is intended to describe the calculation, to be used for implementing the calculation into computer software, rather than for manual calculations. The numbered entries (n) in each section are either calculated, carried forward from earlier entries, or obtained using linear interpolation by referencing the included tables or from user-supplied data. To access the worksheet and detailed notes on conventions for the procedure, please refer to the SAP 2012 document provided by BRE.

The platform may be used in conjunction with the worksheet for each of the sections, as described below. Though, full compatibility with the SAP calculation spreadsheet is not available.

  1. Dwelling Dimensions
    The Geometry tab and drawing.tool allows users to accurately model the geometry, which is then used to assess the overall dwelling volume.

  2. Ventilation Rate
    Our platform accepts estimated values for infiltration rate, exhaust heat recovery, ventilation type, and effective air change rate, all located within the Baseline Energy > Building System tab.

  3. Heat Transmission
    Thermal properties of the fabric of a dwelling may be customized within the Baseline > Envelope tab. Here, users may input the parameters that influence the total fabric heat loss.

    In the case that the dwelling has party walls (named interior wall on the platform) with differing thermal properties, go to drawing.tool to manually update them.

  4. Domestic Hot Water Energy

    Estimates for water heating energy can be inserted under the Baseline Energy > Building System tab. Heating losses due to DHW distribution between the point of generation and use can be approximated using the Hot Water Distribution System parameter.

    Furthermore, for a more in-depth investigation into the total water budget of the dwelling, both indoor and outdoor, our platform's Water Use tab is a great tool for modeling and visualizing the buildings water consumption.

  5. Internal Gains
    The total internal gains from various sources such as occupants, lighting, appliances, and cooking can be inputted in the Baseline > Usage and Schedules tab.

  6. Solar Gains and Utilization Factor
    Although the platform does not display the total solar gains in watts per month, loadmodeling.tool produces a report that breaks down all gains per room, that includes solar gains, which can be accessed in loadmodeling.tool > Results > Room Load Results > Detailed Cooling Load Results.

  7. Climatic Data
    The weather file used for the simulation is automatically selected once the location has been set within the Project tab. For a detailed analysis of the site's relative temperature & humidity, radiation, comfort, and wind conditions, refer to the Climate Analysis page.

  8. Space Heating and Cooling Requirement
    Peak heating and cooling load details can be accessed within loadmodeling.tool > Results > Room Load Results.

  9. Fuel Costs
    The type of fuel used and their associated costs are calculated in the Baseline > General tab. The electricity and gas utility rate defaults are localized to each project location, including the currency. For a breakdown of each of these inputs, visit our Engineering Inputs: General Tab help article.

  10. Carbon Dioxide Emission and Primary Energy
    The dwelling carbon dioxide emission rate is automatically calculated on the Baseline Energy main display.

  11. Building Regulations and Dwelling Emissions Rate (DER)
    Building regulations may refer to CO2 emissions as calculated by the SAP as a method of demonstrating compliance with regulations for the conservation of fuel and power and/or limitation of energy use. The current requirements of regulations can be checked against documents available at:

    Building regulations in all four jurisdictions mentioned above place limitations on the permissible annual CO2 emissions from new dwellings, expressed in kilograms per square meter of floor area (kg/m²). This quantity, when calculated taking account of specific requirements in the applicable regulatory document and expressed in kilograms per unit floor area, is known as the Dwelling Emissions Rate, or DER.

  12. Site-wide Electricity Generation Technologies
    To offset a dwelling's carbon emissions, our platform allows for the basic modeling of solar PV and solar DHW collectors on site. The inputs for this can be found in the Baseline > Energy Generation tab.

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