Primary Energy and Emission Factors: Updates and energy shortfall penalties
The Home Energy Model: Future Homes Standard (HEM FHS) assessment consultation has provided updated emission and primary energy factors compared to the current SAP 10.2 methodology. These factors set how much primary energy is used or emissions generated to provide a final kWh of mains and renewable electricity, natural gas or other source of energy.
To calculate the emission rate and primary energy rate of a dwelling for purposes of compliance, the FHS assessment wrapper applies these factors to the energy consumption results from the core engine.
What are the updated factors?
Below we have put the emissions factors for mains electricity, renewable on-site electricity generation, mains gas and all types of LPG. The full list of factors can be found on page 57, Annex A of the HEM FHS assessment consultation.
Heat networks and community heating schemes are not currently being assigned generic emissions or primary energy factors.
There are several reason why these factors have changed, as listed in 5.2 Fuel assumptions (emissions and primary energy) of the HEM FHS assessment consultation.
One significant change in this is the use of the government’s Dynamic Dispatch Model (DDM) to determine the emission and primary energy factors to be used for mains electricity in the FHS assessment wrapper. This aims to better project the future generation mix for electricity between 2025 and 2029, which is forecast to change considerably as the grid decarbonises.
What is the energy shortfall penalty?
Unlike SAP 10.2, the Home Energy Model can represent the under-supply of energy, resulting in a home not reaching its setpoint temperature. This energy shortfall is reported by the Home Energy Model.
To prevent undersized heating systems being rewarded with a better compliance score than correctly sized systems, HEM plans to introduce an emissions factor and primary energy factor for “energy shortfall” to penalise this. For this consultation these factors have taken placeholder values which are equal to twice the electricity factors for each metric.
What consultation question does this relate to?
This subject relates to questions 24, 25 and 26 within the Home Energy Model: Future Homes Standard assessment consultation:
24.What are your views on the methodological approach to define the emission factors and primary energy factors used within the Home Energy Model: FHS assessment? Please provide your reasoning and any supporting evidence.
25. What are your views on the proposed emission and primary energy factors for electricity? Please explain your reasoning and provide any supporting evidence.
26. What are your views on the penalisation of energy shortfall and the energy shortfall factors? Please provide your reasoning and any supporting evidence.
The Home Energy Model: Future Homes Standards assessment details are still in consultation.
If you have comments on these questions, please send your position to your group lead or Amy Collins using our member feedback form.
To read more on the Future Homes and Building Standards and the Home Energy Model, visit our central resource page.