The Standard Assessment Procedure (SAP) methodology may undervalue technologies that reduce hot water demand at source, despite growing pressure to improve household efficiency and cut energy use, a new report from Triton Showers has warned.
The report Recognising Domestic Hot Water Demand-Reduction in SAP 10.3 explores how the SAP 10.3 methodology treats domestic hot water (DHW), which is expected to represent a significantly larger proportion of regulated household energy use as space heating demand falls in highly efficient, low-heat-loss homes constructed under the Future Homes Standard.
It claims the current SAP 10.3 approach appears to place greater emphasis on central heating system efficiency, fabric performance and photovoltaic (PV) provision than on reducing DHW demand at source. It suggests this risks encouraging homes that are compliant on paper but not fully optimised for hot water demand, water consumption and long-term system efficiency. Showering remains one of the most significant uses of DHW, making it an important area for improving efficiency and reducing consumption.
The report explores the benefits of the latest shower demand-reduction technologies, including high-efficiency instantaneous electric showers and waste water heat recovery systems (WWHRS). It assesses four shower-system configurations:
• A conventional mixer shower supplied by a heat pump and cylinder
• An instantaneous electric shower
• A mixer shower paired with WWHRS, supplied by a heat pump and cylinder
• An instantaneous electric shower designed to be paired with WWHRS. Based on standard SAP assumptions and two daily showers, the report estimates choosing an instantaneous electric shower paired with a WWHRS could reduce annual shower-related energy use by 35.1%, potable water consumption by 41.6%, and carbon emissions by 36.7%. Annual combined energy and water costs, meanwhile, would drop by £137 compared with a conventional mixer shower supplied by a heat pump and hot water cylinder.