SAP/PHPP comparison

[Nick Grant]

Just spotted the AECB SAP/PHPP comparison report on the home page:

https://aecb.net/Comparison_of_PHPP_with_SAP.php

[Tom Foster]

Very clarifying. Do we agree with this analysis? Anything to add?

Even if it seems obvious, would anyone care to spell out the difference between these two approaches, and full thermal modeling by Tas, EIS etc?

[Anonymous]

I think this is an unfair comparison. SAP is not, and was not set out to be a design tool, it is merely the statutory approach to confirming compliance with building regulations part L for dwellings. You do not size your radiators, boiler etc etc based on the SAP calculation. In this PHPP is probably a much greater tool (although I have a copy I have not had the time to go into it).
Personally I use IES modelling software to carry out designs and the differences between SAP and IES in terms of the energy consumption are considerable. We are currently involved in some low energy housing for a housing association where we have modelled the buildings using IES, but also needed to carry out the SAP calculations for the Code for Sustainable Homes paperwork. The main differences are in the heating and hot water energy consumptions – the hot water depends very much on the profile of use which SAP overestimates.
When SAP was first introduced, the idea was to provide a standard rating system for a dwelling which could be calculated manually by anyone. Although the process has moved on since then with accreditation processes now required, the standardisation principle still applies. SAP was not provided to provide real life figures, merely a way of comparing buildings, ie one is better than the other, not that one consumes 10% less energy than the other.
I think what is needed is that other software, such as PHPP should be accepted as an option by building control to confirm compliance with part L, along with acceptance in C4SH etc.

[Nick Grant]

Hi Nathan

Agree with your plea for BC to accept other approved models. Such a pain to design with PHPP then shift headspace to do SAP/CSH. Either the latter is just done because we have to or if the client believes in it, it becomes a complex game of trying to score points without losing the efficiencies gained through rational design.

[Tom Foster]

That's very interesting Alan, especially in view of Bentley's (Microstation + Generative Components) interest in Tas – see http://communities.bentley.com/forums/thread/14108.aspx , which must have as its intention exactly that kind of design-tool usefulness.

[Tom Foster]

There's a deep trend in computing to cut the intelligent designer out of the loop.

We would like computers to feed back instant results of design changes – as Alan says 'tweaking the design and seeing the result change instantly'

However the trend is to rely on a 'black box' coupled to an iteration machine. The internal inter-relationships, becoming ever more sophisticated, are not shown to the designer. The 'designer's' role becomes one of defining a starting scenario, and the target to optimise towards, then setting the machine 'to doing “runs”' – not just one at a time, but endless combinations of variants, and iterative sequences of same, so eventually the perfect optimised design pops out automatically! – which may be nothing like the 'designer' ever imagined!

This may not please us designers, but design/simulation, like everything else, will become commoditised and automated for the mass market – but there will still be the high-value niche providers of design done the traditional way.

See Jan edition of Develop 3D, article on p27 http://www.develop3d.com/downloads/

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