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A hope in L

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understanding part L - If your design simply complies with the current regulations, here are some clues about adapting it to suit the new regs

If you are in the process of designing a building that will not have started on site or will not have full unconditional building regulation approval by 1 April, then you will need to design the building to the new Part L (AJ 17.1.02).

Those working on highly efficient building designs that have features such as part-height glazing, doubleskin facades and chilled ceilings, can breathe a sigh of relief - compliance will be relatively simple.

It is not such a rosy story if your design has full-height, clear double glazing and an energy-intensive airconditioning system. Design changes will more than likely need to be made and these changes will, of course, have aesthetic and cost implications.

With the help of a case study - a building incorporating full-height double glazing and a standard fancoil system - we can see how a holistic approach to certain design changes can achieve building compliance.

Testing compliance The process of testing compliance involves assessing the case study building using the elemental method.

If this fails, re-evaluate using the whole-building method. If that fails too, then modelling the efficiency of the building using the carbon-emission method is necessary. If compliance is still not achieved, the design should be reconsidered. The revised building should then be retested using the carbon-emissions method.

For a transitional building (a building that complies with current regulations but which needs to be reappraised to meet the revised regulations), it is sensible to go straight to the whole-building method. As a rule of thumb, if the current scheme is within five per cent of the allowable Carbon Performance Rating (CPR), it indicates that compliance with the new regulations should be relatively easy if the calculation procedure is changed to the carbon-emissions method. If the CPR is far greater than that allowed by the whole-building method, then some design changes will be needed and changing your method of calculation will not save you.

The following describes the result of this process for our case study building:

The elemental method requires the calculation of the average building Uvalue, satisfying the solar heating calculation and a carbon performance rating (CPR) calculation of the air conditioning and mechanical ventilation (ACMV) system.

A full-height, clear, double-glazed building will clearly not pass the U-value or solar overheating requirement. With compliance using the elemental method ruled out, it is necessary to try the two other methods.

The whole-building method does not require the calculation of the average U-value, nor solar over-heating. It does, however, require the calculation of the carbon performance rating of the air conditioning, heating and artificial lighting. The building services design will need to be sufficiently well developed because the size of the chillers and boilers will need to be known to use this calculation.

The case study building scored a CPR that was 11 per cent higher than allowable for new offices, resulting in non-compliance. Because the building failed both the elemental and the whole-building method, we moved on to the carbon emissions method.

This offers further flexibility, but it is not a simple calculation exercise.

The building and its services have to be modelled using complex energy analysis software. The result of a modelling of the case study building was that the current design produced approximately 2.5 kgC/m 2/a more than the 'notional' building, requiring a total carbon emission reduction of 15 per cent.

If it is to reach compliance, the building's design is beyond applying a simple remedy. A reassessment of the fundamental design of the building is required so we can see where carbon emission savings could be made.

Redesign factors In this section individual design changes that affect the energy consumption of the building are considered. In reality, these changes would not be assessed individually but rather as part of a combined design review.

With a new-build development there will usually be more opportunities of working with the site and surroundings to reduce the energy consumption of the development.

With a transitional building (a building already late on in its design development), the building in its site context is fixed. Achieving compliance for the transitional building thus rests on the building form, envelope and its services. Especially where the built form has been approved for planning, the chances of changing the built form are relatively slim, as mentioned earlier.

One potential for the built form that does not affect planning is to expose the concrete slab and gain the benefit of the thermal mass, typically reducing energy consumption by three per cent. Although only a small saving, this could be the difference between a pass and a fail.Changing the envelope of the building has a big impact on the reduction of carbon emissions, but any changes to this aspect could have a large impact on planning.

One solution would be to reduce the amount of glazing in the elevation.

Introducing a 900mm sill in lieu of full-height glazing - thereby reducing the window area by 30 per cent - reduced our carbon emissions by eight per cent, a considerable reduction. In reality, however, the planning implications may not be acceptable.

The second envelope option analysed was a 10 per cent improvement in U-value and a 40 per cent improvement in shading co-efficient.

This led to an overall carbon emissions reduction of four per cent.

The final element of the envelope design was to consider external shading as an option. Although external shading does present significant cost and design implications, this option led to an overall reduction of seven per cent without a change in the glazing specification.

At this stage of the Part L design review, it is apparent that, without a fundamental change to the building envelope, the building may not pass.

But all is not lost, because the efficiency of the air-conditioning system can also be taken into account.

The two main areas from which we can reap positive benefits for relatively minor design changes are: the use of heat recovery for incoming fresh air, and selecting a more efficient chiller and controls.

For example, increasing the efficiency of the chiller by 40 per cent leads to an overall carbon emission reduction of seven per cent.

Using a plate heat exchanger to reclaim the heat from the exhaust air to pre-heat the fresh air reduced our emissions by six per cent. And lighting control systems that adjust the artificial lighting when there is sufficient daylight can reduce the overall energy consumption by 7 per cent.

Compound savings These design options have shown that individual design changes can reduce the carbon emissions of the proposed building. But no single change by itself has proved to be successful in achieving compliance.

Through combining the individual envelope and services design changes, compliance can be achieved. The following combinations were assessed for the case study building:

-full-height double glazing plus highefficiency chillers and heat exchangers - Fail;

-900mm sill, double glazing plus high-efficiency chillers and heat exchangers - Pass;

-full-height HP double glazing plus high-efficiency chillers and heat exchangers - Pass; and lfull-height double glazing plus external shading plus high-efficiency chillers and heat exchangers - Pass.

In the selection of a facade and M&E systems solution, the comfort of the occupants should not be forgotten. In the case of full-height double glazing, thermal discomfort is often experienced in both summer and winter. The analysis of the interaction of facade and M&E should always be undertaken in conjunction with Part L compliance.

If design changes are adopted individually, then compliance will be difficult to achieve for a '95 Part Lcompliant building that will not obtain full approval or start on site by 1 April 2002.

However, if the changes are considered holistically, a currently compliant building can be redesigned to comply with the new Part L2 without significant cost and appearance implications.

Simon Wild of Genesys Environmental can be contacted on 020 7776 5000

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