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No sign of Part L and F AD’s yet…

by Mel Starrs on April 14, 2010

in Part L

So the election has been called for May 6th. Despite the statutory instrument being laid down before the election was called (to allow work to continue between now and the election and prevent purdah kicking in) things are still looking very quiet over at CLG.

To alleviate the drumming of fingers on tables as we all wait with baited breath, the Consultation Responses have been released. You can read the 264 page pdf here.

I won’t go into the entire detail but pick out some interesting points re: SBEM and DSM which I have pulled out below. These points won’t make it in for 2010, but perhaps 2013 will see the demise of SBEM (we live in hope).

The SBEM calculation engine is based on a monthly energy balance that can only ever be a crude approximation to how the building performs. Yet energy assessors are required to gather large amounts of data and the proposals for Part L 2010 exacerbate this. There is a mistaken belief that adding more data and complexity will improve accuracy. There are two possible alternative options:

i. Simplify SBEM and greatly reduce the amount of data required, thereby recognising it can only ever be a simple comparison tool to allow a building’s performance to be compared with a reference building. There is much data currently required that has little effect on the rating and an aim should be to reduce the information required perhaps by 50%.

ii. Recognise that SBEM was only ever going to be a stopgap measure and encourage the development of software tools that can produce EPCs and BRUKL reports from realistic computer models that can be also be used for design. These tools could be used to realistically assess the effectiveness of improvement measures which should be the main output of the recommendation report. The recommendation report needs to be made more prominent and summary recommendations shown on the EPC.

This is an important point to remember when doing concept and initial calculations – the accuracy of the calculation needs to be appropriate to the scale of the problem. If you are trying to figure out baseline figures on figures to the nearest 5kWh/m², there’s no point in calculating to the nearest 6 decimal points. I was recently reminded of the excellent book Chaos: Making a New Science by James Gleick which makes a similar point:

The choice is always the same.  You can make your model more complex and more faithful to reality, or you can make it simpler and easier to handle.  Only the most naive scientist believes that the perfect model is the one that perfectly represents reality. Such a model would have the same drawbacks as a map as large and detailed as the city it represents, a map depicting every park, every street, every building, every tree, every pothole, every inhabitant, and every map.  Were such a map possible, its specificity would defaet its purpose: to generalise and abstract. Mapmakers highlight such features as their clients choose.  Whatever their purpose, maps and models must simplify as much as they mimic the world.

I really recommend the book – it explains the pitfalls of complexity perfectly.

This is a conversation I think we need to continue to have when it comes to BIM, SBEM and DSM in the near future. The consultation responses give me heart. Here is another point which was made:

There are reservations about the ability of SBEM to model low and zero carbon buildings in a robust manner. Dynamic simulation should be more heavily incentivised and eventually made mandatory. For example, the current SBEM software is not capable of modelling fabric designs that employ passive measures or intelligent or active facades to reduce solar gains. Indicating compliance in the software with a “yes” or “no” does not provide any guidance on how fabric performance can be improved. Experience suggests that daylight savings are much more effective in reducing CO2 emissions than marginal improvements in heat loss, especially when heat recovery is implemented, but this is not reflected in the cSBEM methodology.

Whilst I’m all in favour of using simplified tools where they are appropriate (see my point about scale above), many of the current problems with SBEM* stem from the fact that it is being substituted as a design tool rather than being used purely as a compliance tool (it’s initial purpose). We can either improve the compliance tool so it can be used for design also, or rethink the entire approach. A suite of DSM tools, with differing levels of detail seem the most logical solution to me. One model gets constantly refines throughout the work flow (in an ideal world) rather than one model being forced to do tasks it was never set up for.

Thoughts anyone?

*worth reading the whole post on Pathethic Part L

  • Pingback: On Site Renewable Energy « Building Energy Exposed()

  • Iain

    Good post but I’ll have to correct one part of it. Adrian Hewitt, for it was he, who set up Merton’s 10% rule wasn’t mistaken by the 0.1 LZC factor used in the Part L emissions reduction calculation from the notional building. His reasoning was based that a 10% expectation on developers would stimulate growth of a small scale renewables industry in Merton with investment and jobs being associated with this change in policy.And while I completely agree that some on-site renewables are wrong, that isn’t to say all are. As Edmund Burke once said ‘Nobody made a greater mistake than he who did nothing because he could do only a little’.
    This comment was originally posted on Building Energy Exposed

  • http://greenbldskeptic.wordpress.com/ greenbldskeptic

    Thanks for the comment and much appreciate the information regarding the origin of the Merton rule. While I agree with you that its good to stimulate investment in renewable technologies, it is unlikely that I will ever be convinced that on site renewable technologies are a good thing. I know that when people push the use of renewable energy they have good intentions, its just that I still believe that renewable technologies are better installed off site, rather than on site.One way around this would be to make buildings as energy efficient as possible as I have proposed and replace the requirements of the Merton rule to install on site technologies, with a more effective requirement to fund the installation of off site renewables. My main concern is that many sites, especially sites in urban environments are just not suitable for most renewable technologies. It is much more effective to use the money, which would be largely wasted on installing the renewable technology on site, to fund more efficient off site developments. I am by no means proposing doing nothing, I am suggesting that there are much better ways to spend the money which has been thrown at buildings. As I hope I have demonstrated in my post, it can be counter productive to insist on the installation of on site renewables. I hope that we all have the same aim, that of reducing energy consumption and hence CO2 emissions.
    This comment was originally posted on Building Energy Exposed

  • http://www.elementalsolutions.co.uk Nick Grant

    Hi Mel

    IMHO the most crucial things with modelling are getting the inputs good enough, especially thermal bridges, fenestration and internal gains assumptions and and, as Bob Lowe says, being able to look under the hood. The more I work alongside people using dynamic models for whole buildings the more convinced I am that a spreadsheet or pocket calculator is a more powerful design tool.

    If we are designing genuinely low energy, comfortable buildings, then temperatures and heat inputs and losses do not vary hour by hour to any significant degree and so simpler modelling and assumptions becomes possible.

    This is always a hot topic on the AECB forum with dynamic v degree day approaches splitting pople like politics or religion.

  • http://www.elementalsolutions.co.uk Nick Grant

    Hi Mel

    IMHO the most crucial things with modelling are getting the inputs good enough, especially thermal bridges, fenestration and internal gains assumptions and and, as Bob Lowe says, being able to look under the hood. The more I work alongside people using dynamic models for whole buildings the more convinced I am that a spreadsheet or pocket calculator is a more powerful design tool.

    If we are designing genuinely low energy, comfortable buildings, then temperatures and heat inputs and losses do not vary hour by hour to any significant degree and so simpler modelling and assumptions becomes possible.

    This is always a hot topic on the AECB forum with dynamic v degree day approaches splitting pople like politics or religion.

  • http://www.elementalsolutions.co.uk/ Nick Grant

    Nobody made a greater mistake than he who did only a little and at great expense when he could have done so much more for so much less . . .
    This comment was originally posted on Building Energy Exposed