Good Understanding Of Sbem Important For Construction Construction Essay

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The Simplified Building Energy Model (SBEM) calculates the energy used by buildings. It was produced by BRE in 2006 for the Communities and Local Government Department (CLG) in England and Wales as part of the department's process for implementing the European Energy Performance of Buildings Directive. It has subsequently been adopted (with some changes) by the rest of the UK and by several other European Union member states. ref

A building's energy requirements which include heating, cooling, lighting and electrical appliance usage account for about half of both the energy consumed and the carbon emitted in the UK. Clearly, if energy consumption levels are to be reduced then energy use by buildings needs to play a very important role in achieving this. This obvious conclusion led the EU to produce the Energy Performance of Buildings Directive (EPBD) in 2002, which defines a number of measures which are to be introduced into every member state by specified deadlines.

In practice, the effect of the regulations on design and construction will become clearer as 2010-compliant assessment software becomes available and is used to assess design. The only 2010-compliant software currently available for calculating target emissions rates (TER) and building emissions rates (BER) is the simplified building energy model (SBEM). Sophisticated software that can deal with more complex buildings will not be available until September, meaning that for owners of buildings with more complex features such as atriums or moveable solar shading, assessment is more challenging than it should be.

The change to an aggregate approach has resulted in a change in calculation methodology. From now on, the TER will be calculated with reference to a 2010-compliant reference building, rather than the notional 2002 building currently in use. This will result in a learning curve for all involved. The design criteria used to determine the performance of the notional building have been tightened significantly - by 26% in the case of thermal transmittance through walls. However, the limiting fabric parameters for the actual building are the area-weighted average U-values used in Part L 2006, so designers have some degree of freedom in meeting the TER. Other standards have also increased, such as minimum efficiency standards for services plant; most of these requirements can readily be met by current equipment specifications.

Exploiting this freedom will require a more holistic approach to design than has been the case. Much of the focus will be on trade-offs between different systems and design disciplines, and some of the options are illustrated in the cost models.

Another effect of Part L 2010 is that EPCs issued after 1 October will be recalibrated to use the revised carbon emissions rates, which in the case of grid-supplied electricity is increased 23%. This will mean that when buildings are reassessed, they are likely to get a lower EPC rating. This could help to accelerate measures to improve the energy efficiency of existing buildings - or could accelerate the obsolescence of unimproved buildings.

Limits of solar gain at the perimeter Part L 2010 has much stricter limits on solar gain, expressed by "reference cases" for side-lit and top-lit buildings. This is probably the greatest source of concern for designers, although it should not be assumed that the requirement means the end of highly glazed buildings.

Part L 2010 proposes a system of accredited details and/or approved calculation methods that demonstrate that expected targets for linear thermal transmittance will be met. Where compliance cannot be demonstrated at the design stage assessment then penalty increases in the value of linear thermal transmittance of up to 50% are applied, potentially making overall compliance more difficult than with accredited details.

Whether this change has a significant effect on design and procurement will depend on the importance of linear thermal transmittance as a component of overall carbon emissions. This will not be a problem for a warehouse, but for a complex design with lots of framing in the facade, opening lights and junctions between systems, it could be a material consideration.

It is unlikely that specialist facade contractors will publish their proprietary design details as part of any accredited detail scheme, which will result in penalty values being applied to transmittance calculations, and possibly increased building control fees. The irony is, of course, that these details are likely to perform well. Penalties will be higher for organisations that cannot demonstrate competence in an approved calculation process, which could create opportunities for specialist engineers in support of smaller specialist contractors.

Other measures to assure building performance include an increased standard for air pressure testing for infiltration (5m3/m2/sec), as well as enhanced requirements for building services testing and commissioning. The infiltration standard is not a problem for system-based facades, but will require good quality detailing of insitu construction and interfaces between systems, potentially encouraging a more holistic approach to procuring building envelopes.

Design-stage and actual building assessment Building control submissions based on the NCM need to be made before construction starts and upon completion. The assessment of the completed building has to take into account design variations introduced during the construction stage. One interesting feature of the new regulations is an explicit focus on key features, that is, building components that make a greater contribution to the BER than might have been expected. The requirement for the design-stage submission introduces some interesting procurement considerations. Under previous iterations, designers would always take informal steps to ensure that designs were compliant. However, under the 2010 rules, in order to avoid penalties, it will be necessary to ensure that specialist contractors can comply with technical requirements to support assumptions made in the design-stage assessment. This is not necessarily difficult, but it does require that competence is accounted for in the selection process.

Taken in the round, the two main challenges for the project team are the absolute scale of carbon reduction, which will necessitate a holistic approach to design, and the learning curve associated with the revised NCM. In their favour, designers will continue to benefit from innovation by manufacturers, who, in common with sectors such as automotive, have responded effectively to the low carbon challenge. Air-conditioning manufacturers have led the charge since 2006, and lighting firms appear to be picking up the baton with LED-based luminaires. The performance of facades continues to improve, and building-integrated renewables such as PVs may provide opportunities to offset carbon emissions elsewhere in a scheme.

03 / Design challenges

The devil is very much in the detail of the supporting documentation of the 2010 regulations. How project teams collaborate to deliver buildings that meet reduced TERs without a disproportionate loss of performance or value will be an important measure of success and a pointer towards how even lower carbon design solutions will be developed.

The main issues that need to be considered include:

A tougher baseline 

Aspects of the baseline calculation that make the carbon emissions cut much harder to achieve include:

No gain from design fundamentals. The location, orientation and massing of the design can have a critical effect on actual energy use and a building's EPC rating, but as the notional building and actual building are the same shape and size, benefits are not accounted for in the calculation

The increased carbon intensity of energy sources. As part of the change in the NCM, the baseline values of energy have increased by more than 20%; electricity for example has increased from 0.422kgC/kW to 0.517

Changes in the fuel types are assumed in the notional model. Low carbon fuel sources such as biomass have been included as a notional fuel in the 2010 NCM, and therefore cannot be used to contribute to a reduction in the TER. This is intended to stop poorly performing buildings being able to comply through the use of low carbon technologies. But low carbon technologies support better EPC ratings, so there are still benefits from these technologies

Substantial improvements in design criteria such as U-values will require efficient envelopes, additional reductions to services emissions or the adoption of a holistic approach to intelligent design

Limiting factors on aspects of building services design, including ventilation and lighting will have an effect on other aspects of design - such as increased duct sizes.

Implications of the baseline 

Some of the baseline standards are difficult to deliver without affecting other aspects of the design. Project teams must be careful when assuming that assumed performance is deliverable, or relying on offsets from other aspects of the design.

The notional building assumes a solid wall with 40% glazing. A comparable area-weighted U-value for such a construction is difficult to deliver using a framed curtain wall. This is likely to result in a greater take-up of solid, insulated substrates, the adoption of thermally efficient composite framing sections, or the use of intelligent facade solutions on higher value buildings.

Implications for efficiency 

Aspects of the limiting factors in the regulations could have a significant impact on the development efficiency and operational effectiveness of future buildings, and this will require an even greater consideration of set-off within a holistic design solution. Examples include:

Specific fan power calculations. One of the limiting factors in the calculation is a reduction in specific fan power from 2.2W/l/s to 1.8W/l/s. This cut is typically achieved by increasing the cross-sectional area of air handling units and ducts. Bigger air handling units and ducts are more expensive in themselves and also need larger plant rooms and ducts, which reduce building efficiency. Given occupier expectations for increased occupation densities, requiring even greater air volumes, the affordability challenges that result from low carbon design are plain to see. The cost models in this article illustrate the cost implications of meeting a lower rating of 1.4W/l/s, which is necessary to compensate for other aspects of design

Limits on solar gain. The measures on limiting the effects of solar gain are aimed at future-proofing buildings against climate change. There are a number of means of meeting the criteria that could have an impact on the quality of internal spaces, or energy consumption related to artificial lighting. In the cost models, variant one complies with 34% glazing, whereas iteration three, with 60% glazing, has a much darker tinted glass. Both will result in quite dark interiors.

Where budgets allow for the active control of solar gain through moving shading or automated blinds, then a better holistic solution, involving less reliance on artificial lighting, may be achievable, which should in turn result in buildings that are able to respond more effectively to year round conditions. However, these buildings have operational and maintenance issues associated with the upkeep of complex systems.

04 / Procurement implications

Part L 2010 will have a greater focus on ensuring that the design is delivered on the ground, and that the effect of variations is recorded and accounted for as part of the as-built assessment. In practice, the effect of these requirements will be determined by the ability of Building Control to enforce. Although these changes will not have a fundamental effect on procurement, there are some areas where consideration of current practice may yield some benefit.

Building services design. Requirements for a more holistic approach to design will need earlier input from building services engineers to determine the optimum balance between fabric and system performance. This in turn will require the early fixing of building plans and layouts to facilitate thermal modelling.

Performance specifications for building envelopes. As well as setting out physical performance requirements, procurement will need to ensure that contractors have the calculation competences and accredited details needed to secure the linear thermal transmittance credits assumed in design calculations.

Specification risk. Designs that rely on a disproportionate contribution from one or two elements could be subject to greater scrutiny from building control and could in turn represent a greater risk to the contractor team charged with delivery - low-risk solutions are likely to be more attractive to bidders in the long run, as competitive conditions resume.

Early involvement of specialist contractors. Advanced solutions necessary to meet the revised requirement such as an active facade will require the early engagement of specialist contractors to provide specialist expertise and to ensure co-ordination with aspects of the building services and fit out such as lighting control, BMS control and blinds.

Change management. The requirement to assess all material variations for their impact on the as-built BER should in itself discourage variations, but will also increase the importance of impact assessment ahead of issue.

One of the benefits of Part L 2010 is that more owners will need to specify plant and equipment that qualifies for Enhanced Capital Allowances (ECAs) and could benefit from increased tax relief. ECAs are available for high-efficiency plant and equipment such as boilers, chillers, motors and lighting, so long as they are on the ECA approved technology list. The 100% tax allowance can be recovered in the year of expenditure and in our cost model contributes to an increase in the net present value of tax allowances of 12% a year to about £1.23m, when calculated using a 6% discount rate. Other features such as the motorised solar shading qualify for capital allowances as "integral features" but the rate of recovery is slower, 10% a year on a reducing balance basis and as a result the value of the benefit is lower. The net present value of the allowances for option four, for example, is only 2% higher than option one, although the capital cost is 7.5% higher.

The costs in the model are at third quarter 2010 prices. The base building costs include category A fit-out, preliminaries and contingencies. Costs of demolitions, external works, tenant fit-out, professional fees and VAT are excluded.

Yorkshire Evening Post, Thursday November 5 2009


FIRMS in Leeds are being offered £100m in interest-free loans to update equipment and reduce carbon output.

Government Environment Secretary and Leeds MP Hilary Benn launched the Leeds arm of the Carbon Trust's "Big Business Refit" which is giving out £100m interest-free to help small and modern companies modernise and slash energy costs.

He said Leeds businesses lose £50m in energy bills every year due to old energy-guzzling equipment.


Businesses can get between £3,000 and £400,000 interest-free from the Carbon Trust to replace almost any old equipment from chip fryers to production lines.  One Leeds firm already making savings after scrapping its old equipment is Flexible Packaging Printers, Roberts Mart and Co Ltd.

Sales director Ben Roberts said: "We've taken advantage of two Carbon Trust loans, totalling over £300,000, to replace printing press drying systems, a boiler and lighting.  As a result we're saving around £130,000 a year on our energy bills."