Hot water heat pump solutions and SAP10.2 modelling

Hot water heat pump solutions and SAP10.2 modelling

SAP 10.2 modelling is used to prove that a new dwelling will comply with the energy and carbon emission targets of Approved Document Part L of the building regulations, referred to simply as Part L. Is the modelling of hot water heat pumps in SAP10.2 a straightforward task though?

The building fabric and building services parameters of the proposed dwelling design are entered into the SAP program. The details required include the provision of services such as hot water, therefore the choice of system used, such as a gas boiler or hot water heat pump, will impact whether the compliance of the dwelling is achieved.

SAP sees amends to account for various significant changes such as Part L updates. The latest version of SAP assesses if dwellings comply with Part L 2021. This leads to developers carrying out SAP modelling on proposed dwelling designs to determine the optimum combination of building fabric and service specifications. In the current Part L, the carbon reduction required over the last version, Part L 2013, is 31% and primary energy target is introduced as a new metric. To help achieve these targets, there is a move to encourage lower energy demand and move away from carbon intensive fossil fuels and toward low-carbon electric alternatives.

How do the changes seen when modelling in SAP10.2 encourage the use of hot water heat pumps?

The new Part L encourages the move away from fossil fuels towards fully electric solutions by providing a second notional building, focussing on maximum flow temperatures, making changes to carbon emission factors and introducing a new primary energy metric. The reduction of the CO2 emissions of electricity, and the adjustment of primary factors of various energy sources in the new SAP10.2, further supports the selection of fully electric solutions for new developments. 

Second notional building

Historically, only one notional building, featuring a gas boiler as the main energy source was available for modelling. The notional building shows a compliant specification – in other words, if a new dwelling was designed using a matching specification it would pass SAP and comply with Part L. In reality, final specifications will deviate from this recipe, but it nonetheless provides a useful starting point for designers. 

SAP10.2 has introduced a second notional building with a heat pump at its heart rather than a gas boiler. This encourages designers to see what a compliant fabric and services specification might look like when a hot water heat pump is chosen.

Maximum flow temperatures

As well as including a second notional building to encourage the adoption of heat pumps, a maximum design flow temperature of 55°C has been introduced in Part L. This is in recognition of the fact that heat pumps generally run at their most efficient at lower water flow temperatures than boilers. This is evidenced by the notional building for heat pumps, where the maximum flow temperature is 45°C. When undergoing SAP modelling, this move towards lower maximum flow temperatures will get designers used to working with these new parameters. They will then become more familiar and comfortable with specifying systems such as hot water heat pumps. 

Changes to carbon emission factors and introduction of primary energy

The drive to move away from fossil fuels is implemented in SAP10.2 modelling by changes made to the carbon emissions factors and the introduction of a new metric called ‘primary energy’. 

The carbon emissions factor for each fuel type shows its carbon intensity. Changes in SAP10.2 have resulted in electricity now having a lower carbon emissions factor of 0.136 KgCO2/kWh when compared to gas at 0.210 KgCO2/kWh. Previously in SAP, electricity was much higher at 0.519 KgCO2/kWh. This makes it easier to achieve the CO2 reduction targets when using electrically powered HVAC equipment such as hot water heat pumps.

The newly introduced primary energy metric looks at the raw energy needed to produce one unit of final energy used by the dwelling. Whilst the primary energy for fuels is not new to SAP, this the first time it has been directly linked to a new metric. Fossil fuels, due to the need to extract and process them, have higher primary energy than that associated with renewable energy generation. As the national grid decarbonises by taking an ever-larger mix of power from renewable sources and less from fossil fuel sources, its primary energy will decrease. This makes the use of electrical sources, such as the highly efficient hot water heat pumps, more attractive.

When the grid becomes fully decarbonised the primary energy will reduce even further and there will be no carbon associated with using electricity. This makes switching to all-electric HVAC solutions using hot water heat pumps a great way to future proof a specification to meet the requirements of future policy changes seeking a built environment that supports the UK target of becoming net zero carbon by 2050.

Will modelling hot water heat pumps in SAP 10.2 help prepare for future updates to regulations?

Part L 2021 and SAP 10.2 are seen as the stepping stones to the proposed Future Homes Standard (FHS) where further carbon emission reductions, in the order of 75% to 80% when compared to Part L 2013, are expected. Compliance with the FHS may only be possible using low-carbon electric HVAC solutions, therefore carrying out SAP modelling using SAP 10.2 with hot water heat pumps will be very good preparation for the updates expected in the FHS and beyond.

Dimplex have a range of low-carbon HVAC solutions and an in-depth understanding of how hot water heat pumps can be modelling within SAP 10.2. If you would like to explore how our highly efficient HVAC solutions can be modelled to meet your compliance requirements, please contact our design team today.