Building primary energy rate
Approved document L, Conservation of Fuel and Power, Volume 2: Buildings other than dwellings, 2021 edition incorporating 2023 amendments, defines building primary energy rate (BPER) as: ‘Expressed as kWhPE/(m^2.year) and determined using the approved methodology.’
It is a metric used in the UK to assess the energy performance of a building as part of compliance with Building Regulations, particularly under Part L, which deals with the conservation of fuel and power. It was introduced as part of the 2021 changes to Part L, aligning with the UK's adoption of the EU Energy Performance of Buildings Directive (EPBD) and its focus on primary energy as a key performance indicator.
The BPER:
- Encourages the use of energy-efficient building designs.
- Incentivises low-carbon and renewable energy sources.
- Supports the UK's commitment to reducing carbon emissions and achieving net-zero goals.
The BPER quantifies the primary energy consumption of a building in kilowatt-hours per square meter per year over its expected use. It includes energy used for heating, cooling, hot water, lighting, and ventilation, as well as losses in energy generation, transmission, and distribution.
Primary energy refers to the total energy required to deliver usable energy to the building, including:
- Energy consumed on-site.
- Energy losses during generation (e.g., at a power plant).
- Energy losses during transmission and distribution.
To calculate BPER, the energy demand of the building is modelled using a standard methodology, typically the Standard Assessment Procedure (SAP) for dwellings or the Simplified Building Energy Model (SBEM) for non-dwellings. The energy is multiplied by primary energy factors (PEFs), which reflect the upstream energy losses. These factors depend on the type of energy source (e.g., electricity, natural gas, oil).
Approved Document L specifies that a new building’s BPER must not exceed a defined target primary energy rate (TPER). The TPER is a benchmark based on a notional building of the same type, designed to ensure new buildings achieve a minimum standard of energy efficiency.
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