It seems that a long-running dispute between the Passivhaus community and other green homes experts here has been resolved through a detailed piece of technical research which has compared the two main methodologies for assessing the energy performance of new homes. It would appear that the two sides are not as far apart as they once thought.
Three leading UK organisations in this space – the AECB, Passivhaus Trust and (our new client) Elmhurst Energy – are now going to work together for the first time to rationalise the methodologies into a single solution for use by architects, housebuilders, energy consultants and other green building professionals. This should finally allow for a direct and fair comparison between all homes.
This statement was provided directly to EiD
SAP and PHPP – two approaches, one goal
The Association for Environment Conscious Building (AECB), the Passivhaus Trust and Elmhurst Energy have reviewed in detail the calculations and outputs of the Passive House Planning Package (PHPP) and the Standard Assessment Procedure (SAP) for domestic homes.
We have concluded, contrary to some rhetoric, that the core of the models is very similar. While PHPP allows a user to enter more data in some areas and considers some element such as thermal junctions differently from SAP, the physics behind the methodologies that calculate the energy efficiency of the building fabric is very similar.
However, as the two modelling systems were designed for different tasks, the way in which they are employed and the scope of their outputs differ. For example, PHPP uses local climate data and includes unregulated energy to give an overall assessment of actual energy use. In contrast, SAP uses average UK climate data and excludes unregulated energy to ensure a consistent output which can be used for EPCs and compared across different dwellings in different locations.
The key point is that most of these differences relate to how the model is employed rather than the accuracy of the model itself.
The three leading organisations intend to work together to present government and industry with a proposal that will allow direct and fair comparison between all homes whatever their type or level of energy performance.
Our objectives are to:
- Learn from the strengths and weaknesses of both approaches, thus improving both.
- Make it easier to demonstrate compliance for both building regulation purposes and for those that want to build homes that are above and beyond the minimum regulatory standards.
- Work together to produce a solution that presents key performance data for a property in a clear manner, and giving equal prominence to carbon emissions, energy demand, running costs and fabric efficiency.
- Provide clarity regarding the scope of the of the energy use covered, such as space heating only, regulated energy or all energy use.
- Standardise the units of measurement of a home’s performance to allow for direct and fair comparison.
- Develop a common energy reporting process capable of being driven by either PHPP or SAP as the starting point.
Ultimately all three organisations, and their members, understand that their aims are the same – ie. to facilitate the building of energy efficient homes – and that what are currently considered to be high performing homes will, very soon, become the norm. By working together that goal will be easier to achieve.
Martyn Reed, managing director of Elmhurst Energy, said:
“It is clear the underlying physics of the two different methodologies model fabric energy efficiency results similarly. We must build upon this common ground and show consumers and industry a common set of easy to understand results that allow fair comparison. We all want homes to be more energy efficient and we are delighted to work alongside Passivhaus Trust and AECB to advocate for a solution that will meet our energy efficiency targets moving forwards, not only encouraging people to build to the compliance standards but to show a clear route to the low energy use buildings that we need.”
John Palmer, policy director at the Passivhaus Trust, said:
“The Passivhaus Trust is fully supportive of this initiative. Both SAP and PHPP are effective tools at what they do. Bringing them together in some way and aligning with national regulations will make life easier for energy assessors and house builders whilst also presenting consumers with a clear and unambiguous statement of a home’s overall performance.”
Andrew Simmonds, chief executive of the AECB, said:
“The AECB works with its members to inspire, develop and share environmentally responsible building practices – and to deploy them. This collaboration will further enable transformational action in making building practice more sustainable. It will improve key industry tools, support better outcomes and enhance our collective intelligence.”