BRE has pulled out all the stops to develop software that tests compliance with the new energy regulations - but how well does it work in practice.

Now that the Christmas and the New Year festivities are nothing but a fond memory, you've probably had a chance to sit down and try your hand at the Simplified Building Energy Model, or SBEM.

For any of you still too busy fine-tuning your Christmas-gifted gadgets to pay attention to work-related technology, SBEM is the ODPM's long-anticipated computer program. It provides the only official means currently available to demonstrate compliance with the new energy regulations that come into force on 6 April for buildings other than dwellings, although more complex simulation tools should soon be accredited for the purpose, too.

The team at BRE has taken just 12 months to deliver SBEM and its user interface, iSBEM. Following two Beta test versions in 2005, BRE launched the official version (V1.0) in late December and followed it up with a revised (debugged) version of the programme (V1.0.b) in January - this can now be downloaded free of charge from its website (www.ncm.bre.co.uk).

SBEM provides an analysis of a building's energy consumption by calculating monthly energy use and CO2 emissions based on a description of its geometry, construction, use and HVAC and lighting equipment.

With the latest version up and running, BSJ decided it would be a useful exercise to get a group of consultants to try their hand at it and find out what they thought.

What are SBEM and iSBEM?

Demonstrating compliance with the latest Part L2 requirements of the Building Regulations requires calculation of annual CO2 emissions, so the ODPM commissioned BRE to develop a computer tool to assess the majority of ordinary buildings - for more complex buildings, designers will be able to use sophisticated certified energy simulation models.

The SBEM tool is part of the National Calculation Methodology (NCM). This is the process that demonstrates a building's compliance with the minimum energy performance standards - and because the new Part L has been written to ensure compliance with the EU's EPBD, the NCM is also the process that will eventually be used to work out a building's energy performance certificates.

The NCM takes into account many factors, such as the building's fabric, HVAC systems, position, orientation, occupancy and usage. It uses a notional building with the same geometry and activity data as the actual building but built with fabric and services systems in accordance with the 2002 Part L2 standards. The methodology then requires that two calculations are performed: one on the real building with the actual fabric and services, and one on the equivalent notional building. For part L compliance, the actual building has to perform better than the notional building by a specified percentage improvement. This approach has to be used whether using simulation or BRE's SBEM software to do the calculation.

In order to carry out the calculation, BRE has developed a basic user interface called iSBEM that captures all the required information in terms of its geometry and construction, the activities within it and the service systems.

So, what did our industry guinea pigs think?

Where they have rated the use of the system from 1 - 5

1 = easy, 5 = difficult; while for their confidence in its results, 1 = confident, 5 = not very confident

Chris Britton, executive engineer, Hoare Lea

How easy was it to use?
4 - It’s relatively straightforward, although the download could be simplified by making the download icon more obvious.

Does data entry take long?
4 - Data entry is quicker than one might anticipate at first use. It’s important to prepare data first. For example, in the Geometry section, you define the zone and then add the envelopes to it; when you’re in the HVAC section, you can define the system, but then have to go to the zones and add it to them, so you have to go backwards.

How flexible and easy is it to adapt to different schemes?
4 - It seems comprehensive in building types and activities – and data entry.

Are the results easy to interpret?
5 - Very straightforward.

Are you confident in its results?
2 - Confidence will come with application.

Will you use a different interface to the BRE-developed iSBEM?
We intend to use IES so we’ll also be able to check for solar control and overheating as required by ADL2A criterion 3.

What’s good about SBEM?
The interface is logical, easy to use once familiar and robust.

What are its limitations?
Non-graphical interfaces are prone to data entry errors because they limit visual feedback.

What could be improved?
Inclusion of overheating checks. Publication of the draft standards and any other documents upon which the SBEM calculation is based.

Could all buildings end up looking the same?
No, but I think it could sway a lot of people to a single solution.

Stephen Tien, sustainable design engineer, Foreman Roberts

How easy was it to use?
4 - The download was quite straightforward and once you understand the flow of inputting data, that becomes quite straightforward.

Does data entry take long?
3 - I had difficulty understanding the interface and flow of data entry at first, but the process is quicker than many simulation software packages.

How flexible and easy is it to adapt to different schemes?
2 - It does not cover many different building geometries or services.

Are the results easy to interpret?
5 - Very easy.

Are you confident in its results?
3 - Breakdown of results gives confidence of data and calculation method, but results due to PV and other renewables are questionable.

Will you use a different interface to the BRE-developed iSBEM?
No, other than the dynamic simulation software currently used.

What’s good about SBEM?
Breakdown of the end-use graph helps identify and improve the building’s energy performance rating; the five-criteria check point is useful for Part L compliance, and it’s relatively quick to get a result.

What are its limitations?
The geometry input is limited. Mixed mode HVAC systems cannot currently be handled in SBEM; and the window shading does not seem detailed enough.

What could be improved?
The data entry process is not straightforward – assigning windows/systems to surfaces then to zones and switching between the tabs can be confusing for large buildings. The daylighting calculation could also be improved.

David Kingstone, associate, CoSA Solutions, Buro Happold

How easy was it to use?
4 - Much better than the beta versions previously released, although the download was slightly confusing. The biggest improvement over the beta test version is the introduction of the “quick envelopes,” which allow you to speedily assign envelopes to particular building zones and help with the input of the geometry data.

Does data entry take long?
3 - Much better following the introduction of the “Quick envelope” tool – this needs extending to the include data entry for internal partitions.

How flexible and easy is it to adapt to different schemes?
2 - Not that easy.

Are the results easy to interpret?
2

Are you confident in its results?
2 - I need more output to be able to compare results.

What’s good about SBEM? It’s simple to use. When used in conjunction with simulation software, the benefits of simple or complex calculations can be identified – and it is a good effort in the time available.

What are its limitations? No links to adjacent rooms and there’s not enough information given on the assumptions made in the calculation method. It would be useful if it could automatically run a check on things such as the building area, wall areas and floor areas and flag up any inconsistency that might indicate data entry errors. [These checks have been addressed in V1.0.b]

What could be improved? More data output would enable checks on the effect of changing particular inputs – eg the savings made by introducing local thermal water heaters.

Terry Dix, director, MEP Europe business leader, Arup

How easy was it to use?
3 - When downloading the software, the icon could be clearer – there’s the temptation to click the icon at the bottom of the page, and that just downloads the databases.

Does data entry take long?
4 - It’s relatively easy to get to grips with.

How flexible and easy is it to adapt to different schemes?
3

Are the results easy to interpret?
5 - Very clear.

Are you confident in its results?
3 - Though there are some initial findings that I’d query.

Will you use a different interface to the BRE-developed iSBEM?
Yes – IES.

What’s good about SBEM?
It’s readily available and easy to use by other building professionals who may want to change glazing areas, fabric etc. It has a good results page/output and represents an excellent achievement by BRE in a short timescale.

What are its limitations?
Results can be counter-intuitive – ie the more glazing, the less energy is used. (See story below)

What could be improved?
It’s difficult to spot input errors as there is no graphical output of the building’s appearance based on data entry.

Matthew Collin, building physicist, Arup

How easy was it to use?
2 - It’s fairly easy to use but not Windows (or Mac) standard.

Does data entry take long?
5 - for simple buildings; 3 - for more complex ones. It’s quicker than a full simulation tool.

How flexible and easy is it to adapt to different schemes?
5 - As long as it’s one of the options available in the database library.

Are the results easy to interpret?
5 - Baseline result is very clear, and it is also possible to dig deeper if necessary.

Are you confident in its results? The main calculation appears to be sound; I would question some assumptions made in the models. So 5 - taken at face value, and 1 once I’ve checked the results, the same with any modelling software.

Will you use a different interface to the BRE developed iSBEM?
Yes: IES when it’s released.

What’s good about it?
It’s free, the only tool needed for simpler schemes and seems to cover all bases in terms of systems/energy sources.

What are its limitations?
 In terms of its brief there are very few. Incomplete documentation, though this seems to be developing rapidly.

What could be improved?
Slicker installation and starting – and taking the Documentation to an almost narrative level.

Richard Wheal, senior building services engineer, White Young Green

How easy was it to use?
3

Does data entry take long?
The actual data entry is fine 4 but it does take a quite a while - 2.

How flexible and easy is it to adapt to different schemes?
3

Are the results easy to interpret?
5 - Yes, very straightforward.

Are you confident in its results?
It’s difficult to say at present.

What’s good about SBEM?
It’s a fantastic achievement, given the timeframe, and once you’re trained it should be easy to use.

What are its limitations?
Complex buildings take a very long time to model; it would probably be easier with a graphical user interface. It’s not clear how you deal with curved surfaces, and it’s misleading for asset ratings.

What could be improved?
The bugs in the software; and clearer user guides are required.

Could BRE’s programme precipitate a return to highly glazed buildings?

When Arup carried out some early trials reviewing air-conditioned buildings with SBEM V1.0, it revealed some counter-intuitive results. It seems that SBEM rates buildings as using less energy as you put more glass into the facade – to the point where, in general terms, a fully glazed facade is seen as comparatively energy efficient.

It appears this arises as a result of reduced lighting demand as glazing levels increase. This makes sense, but SBEM does not take into account that with many fully glazed facades, blinds come down and lights go on when it is bright and then remain on all day. In most fully glazed buildings, this is essential to control problems of glare or discomfort arising from direct solar radiation.

Part L Criterion 3 (limits on solar gain) does not apply any solar gain limitations to comfort cooled buildings, which would act as a backstop in this situation. As it is, it’s difficult to see a way that SBEM could effectively take these issues on board, as they arise from meeting comfort criteria rather than satisfying an energy balance. There may also be an issue with the way SBEM treats glazed facades during winter conditions. It may see the heat loss from glazing as being a benefit in a space with typical internal heat gains. Again, a simple energy balance might conclude that this is a reasonable assumption. However, many fully glazed buildings have perimeter heating to counter problems with cold downdraughts and to provide fabric protection when the ventilation system is off. This “fortuitous cooling effect” is therefore often reduced – and in fact, the reverse is true as the building is supplying energy to counter the heat lost from the glazing while cooling the internal areas.

It is important to understand that SBEM is probably giving reasonable results – similar, in fact, to those you might expect from other simulation software. But no software is particularly good at modelling real life – this requires interpretation and modification by experienced engineers. The problem is that SBEM is not simulation software, but will be used as an absolute device for calculating compliance with regulations.

But, while there’s no denying that SBEM can’t tick all the boxes, all of this seems good news in terms of design flexibility and for clients and architects who feared that Part L would restrict the use of glass.

Source

Building Sustainable Design

Postscript

What is your experience of SBEM? Email: bsjeditorial@cmpinformation.co.uk with your comments.