Passively Recovering Waste Heat Energy With Every Shower

WWHRS in SAP & Part L

What is SAP?

The Standard Assessment Procedure (SAP) is the methodology used by the Government to assess and compare the energy and environmental performance of dwellings. It was developed by the Building Research Establishment in 1992 and its purpose is to provide accurate and reliable assessments of dwelling energy performances.

Part L of the building regulations uses SAP (Since 1994) to assess a buildings energy performance and a reduced data SAP (rdSAP) was introduced in 2005 as a lower cost method to assess the performance of existing dwellings.

How SAP works

SAP assess how much energy a dwelling will use while delivering a defined level of comfort and service provision. The assessment is based on standardised assumptions for occupancy and behaviour and enables a like-for-like comparison of dwelling performance, with factors such as fuel costs and emissions of carbon dioxide (CO2) determined from the assessment. SAP quantifies a dwelling’s performance in terms of: energy use per unit floor area, a fuel-cost-based energy efficiency rating (the SAP Rating) and emissions of CO2 (the Environmental Impact Rating).

SAP 2012

SAP 2012 is the latest revision of the SAP document and was published to underpin the 2013 Amendment to Part L of the Building Regulations for England and Wales, which is expected to deliver a 6% improvement in new dwelling performance

Waste Water Heat Recovery (WWHRS) in Standard Assessment Procedure (SAP) - SAP & Part L


WWHRS is a listed technology on the Products Characteristics Database (PCDB), and this database holds product information for a range of technologies used within different National Calculation Methodologies (NCM’s) of which SAP and rdSAP are two.

WWHRS is a technology that targets specifically energy use in the home associated with hot water use, of which showering is the large proportion. Due to the amount of energy required to heat hot water, WWHRS has one of the highest cost vs SAP impact ratios within the software.

Savings are applied to a room with a shower that has WWHRS associated with it through the SAP modelling software. The level of impact in SAP will be determined by a few key factors: –

  • The number of occupants SAP has calculated for the dwelling
  • The total number of rooms for showering/bathing
  • The number of rooms with WWHRS attached
  • If the room has only a shower or a bath and shower.
  • The System (A/B/C) installation method used during installation

Recoup Energy Solutions can offer support to specifiers / SAP assessors to help ensure that the impact of WWHRS is optimised for a specific dwelling. Contact us for more information.

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