The Association for Environment Conscious Building (AECB), Passivhaus Trust and Elmhurst Energy have reviewed in detail, the calculations and outputs of Passive House Planning Package (PHPP) and Standard Assessment Procedure (SAP) for domestic homes and 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 are 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 five objectives are:
1. To learn from the strengths and weaknesses of both approaches, thus improving both.
2. Making 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.
3. To 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 Cost
• Fabric efficiency
Also providing clarity regarding the scope of the of the energy use covered:
• Space heating only
• Regulated energy
• All energy use
4. To standardise the units of measurement of a home’s performance to allow for direct and fair comparison.
5. To 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, 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 MD Elmhurst “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, Passivhaus Trust “The Trust are 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, CEO of the AECB,“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.”