No sign of Part L and F AD’s yet…

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

Tagged as: CLG, Part L