CPD PROGRAMME | HEATING AND VENTILATION Heating circuit Heat pump Automatic purger supply variable temperature primary heating water to an internal unit (as in the example of Figure 1). The internal unit controller sets the external unit to supply water at the correct temperature to either service a hydronic space heating sub-system or to heat the domestic hot water store. This particular R290 system, available with 6kW and 8kW output, can operate in outdoor temperatures down to -20C and produce hot water in the 170-litre integral store up to 60C with a seasonal coefficient of performance (SCOP) for the heating up to 4.85 at 35C and up to 3.93 at 55C. (The wider modelling exercise also included a similarly sized split ASHP system and integral store employing R32 refrigerant that provided comparable results to the monobloc system.) A dedicated hot water heat pump (HWHP) is designed to meet the hot water needs of the dwelling (with the space heating being supplied by other means, such as electric radiators). The example shown in Figure 2 is a R290 monobloc heat pump with COP up to 3.36 (at ambient 7C, water 53C), integrated with hot water stores up to 270 litres, supplied with heat from the outdoor air via circular ducting and which rejects cooled air from the evaporator through a separate duct (smaller units employ concentric, single conduit, ducts). Since this is a completely independent unit, it can be employed in a mixed-mode installation with other fuel types. To illustrate the opportunity of employing electrical-powered environmental systems, a selection of example homes with a variety SAP STANDARD ASSESSMENT PROCEDURE FOR ENERGY RATING OF DWELLINGS SAP1 is a UK methodology to determine the energy compliance of dwellings. It sets out the requirements for the energy efficiency of new and existing buildings, including the amount of primary energy use and carbon emissions. The methodology takes into account factors such as the buildings fabric, heating and cooling systems, ventilation mode, lighting, and energy sources. SAP is occasionally updated to reflect changes in building regulations and advances in technology, and its use is a requirement for compliance with England and Wales Building Regulations. The most recent update is SAP 10.2, introduced in 2022. (For existing dwellings, a simplified version of SAP Reduced Data SAP (RdSAP) is used to assess energy performance.) For SAP calculations, dwellings have a standard occupancy and usage pattern, which applies typical values that in practice vary substantially between dwellings of similar size and type. SAP calculations are not suitable for design purposes. 62 April 2023 www.cibsejournal.com 8-litre expansion vessel Heating circulator Heat pump circulator Three-way valve 3kW programmable electric back-up Cast-iron module System contents 170-litre integrated water tank Figure 1: Internal controller, heating circulator and integrated domestic hot water store that is supplied with primary hot water from an external monobloc heat pump (Source: Dimplex) Ambient loop + heat pump Ambient water loop (potentially linked with district heat network) with individual dwelling R290 water sourced monobloc, internal, heat pumps integrated with 172-litre hot water storage in each dwelling Air source heat pump (ASHP) + store Air sourced, external, R290 monobloc heat pump servicing 170-litre hot water store and separate low-temperature heating system Hot water heat pump (HWHP) R290 air sourced hot water monobloc, internal, heat pump complete with integrated 200-litre hot water storage cMEV Continuous mechanical extract ventilation Electric radiator Wall-mounted, electric radiator Gas boiler Natural gas boiler as provider of heating (not hot water) Natural vent Natural ventilation MVHR Mechanical ventilation and heat recovery system Table 1: Example component system types as applied in the modelling reported in this article Figure 2: Hot water heat pump installed in the top section atop an unvented, stainless steel, 200-litre domestic hot water cylinder (this particular model also available with 170- and 270-litre cylinders) (Source: Dimplex) of environmental systems were modelled (on behalf of the supporter of this CPD article) with the method provided by SAP 10.2 (see SAP boxout). The resulting data illustrated in this article are the individually modelled dwelling primary energy rates (DPER). Primary energy is useful for performance comparisons between various building systems, and is described by the Building Research Establishment (BRE) as being energy from renewable and non-renewable sources which has not undergone any conversion of transformation process. The target primary energy rate (TPER) is the regulatory annual maximum primary energy use, expressed as kWhPE per m2 per year. This is determined for a notional building (as part of a SAP10.2 assessment), and the resulting TPER is compared with the DPER calculated for the actual dwelling, using the method in the SAP guidance. Other metrics are provided as output from SAP assessments including carbon emissions and fabric energy efficiency, which similarly have set maxima for compliance.