SBEM Is Not A Design Tool

By Terry McDonald on 6th March, 2015

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T&D welcome a new guest blog from Chris Maloney (Senior Building Services Engineer - MLM). Chris, 28 years in the construction industry, is a Senior Mechanical & Public Health building services engineer responsible for the design and specification of building services systems in the domestic and commercial construction industry.

In a previous blog Chris evaluated the benefits of specifying heat tracing systems to provide hot water supply to building services.  Today, Chris will discuss whether the Simplified Building Energy Model is a design tool.

SBEM is a software tool developed by BRE that provides an analysis of a building's energy consumption. 

SBEM is used for non domestic buildings in support of the National Calculation Methodology (NCM), the Energy Performance of Buildings Directive (EPBD) and the Green Deal.

The tool is currently used to determine CO2 emission rates for new buildings in compliance with Part L of the Building Regulations (England and Wales) and equivalent Regulations in Scotland, Northern Ireland, the Republic of Ireland and Jersey. 

Without further ado, let's hand over to Chris now for today's blog topic, “SBEM Is Not A Design Tool.”

SBEM - The Simplified Building Energy Model

Enough to strike a chill into many a design and build contractor. The end product of the SBEM calculation is the EPC (Energy Performance Certificate), the BRUKL document detailing all the building energy use characteristics, building fabric parameters (U values) and overheating characteristics (if they occur).

All these are of critical importance at the end of the project, as without the golden egg of the EPC or SBEM showing a “PASS”, Building Control will not accept the building has been completed to meet the ever more stringent targets of building regulations.

Sorry for the boring explanation, but there is a reason to it. The regulatory powers insist that “SBEM is not a design tool”. It states it in the software and in the documentation, as if they are trying to escape any sort of responsibility for the hoops we have to go through to build our buildings.

The problem is, we at the sharp end, have to make a project profitable, otherwise what is the point in doing it. Quickest way to go broke – don’t make money! So on one hand we have to comply with building regulations, on the other we have to make a profit. This is where it gets difficult.

Nobody ever said going green was easy, or cheap. We all love our high tech buildings, our fancy IT, incredible lighting and our comfortable air conditioned environments. All this takes energy, lots of it, and most of it electricity. We have worked so hard now to minimise heat loss from our buildings that heating them is the easy part. Low U value windows with double and triple glazing, extremely low heat transfer building materials, all mean we can stay warm in winter relatively cheaply in energy terms.

This is a good thing with the ever decreasing energy and CO2 targets, but electricity usage keeps climbing, and we have to do something about it as designers. Why? Because of the SBEM.

Every kilowatt hour of energy we use attracts a carbon “penalty” and the SBEM takes into account every kilowatt of energy used and calculates your CO2 emissions per m2 for the year, and rolls it all up into two figures. The Target Emission Rate (TER) for your building, and the Building Emission Rate (BER) the actual emission rate for your real building.

The issue is this. Mr Smith Contracting wants to build his office block as cheaply as possible, but it must comply with building regs. To do this he must design very carefully to ensure the energy targets are met. But to meet the targets needs an incredibly efficient building these days, so a detailed design needs to be carried out so early in the project that it attracts a significant cost.

Possibly even before Mr Smith Contracting has won the job. So he decides not to spend the money, and goes on past experience, after all he’s done this type of building before. Right?.....Wrong.

Current building regulations and future targets have reduced emission targets so much any “bog standard” building will almost certainly fail drastically. If the SBEM is not carried out till the end of the project, when the Building Control officer asks for it, panic so often set in when the “As Built” SBEM is produced and the building fails by a mile.

The usual reasons for this are lighting where cheaper less efficient lights have been used, and hot water demand. This leads to the inevitable question asked by Mr Smith “What do I need to do to get a pass?” often asked in a panicked voice with a month or so to practical completion.

As SBEM engineers, the usual answer is “reduce your electricity usage” as grid generated electricity is carbon “dirty”, and there is an easy option in providing additional solar photovoltaic panels. This can be a fairly quick and simple answer, but is also a planning issue and expensive.

Also if you building fails by a significant margin, you may need a lot of panels which can be very expensive. You could change all the lights to LED, reducing the lighting load by up to 75%, but not cheap or quick. All this leads to major costs, programme delays and stress for Mr Smith.

The solution is to carry out your SBEM calculation earlier. Know what you, as the builder, need to do to get that golden “PASS”, and therefore the SBEM has to be integral in the design process. Absolutely. No argument. If you work with your SBEM engineer from the start in your design you can see where the energy is going, and where your carbon emissions are coming from.

This will avoid those nasty expensive surprises at the end of the project, and hopefully we all make a penny or two, gain valuable experience and move on to the next project.

“SBEM is not a design tool”? Sorry. SBEM is THE design tool.

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