The energy challenge

As climate change continues to hit the headlines, the challenge to conserve energy has become an increasingly hot topic. The issue is now widely debated and treated with varying degrees of seriousness, but political pressure and legislation both at home and from Europe is slowly bringing about some necessary changes, particularly for the construction industry.
When Approved Document L2A (ADL2A) arrived on the scene in April 2006, it altered the whole approach to constructing energy efficient buildings. The elemental method used previously, which simply set maximum U-values for the building envelope, was replaced by a requirement to calculate the whole building carbon dioxide emissions and meet or beat a target level. This calculation involves inputting a vast array of data including factors such as occupancy and use, airtightness and efficiency of building services.

Because the calculation is so complex, a national software tool was developed to calculate compliance – the Simplified Building Energy Model (SBEM). This calculates a Target Emission Rate (TER) based on a set of notional values and yields a predicted Building Emission Rate (BER) based on the proposed design. In order to comply with the Regulations, the BER must not exceed the TER.

Included in the data that is required by SBEM is the HVAC system, an area that has all too often been neglected when the energy efficiency of a building is considered by designers. Factors such as the airtightness of ductwork and the resulting fan size needed to drive the system must now be inputted as part of calculating the BER, so it makes sense to look at how to optimise the energy efficiency of the system as a whole by using ductwork that can achieve high levels of airtightness as well as the required levels of insulation.

There are other considerations too; meeting the requirements of ADL2A using SBEM will provide the specifications for an energy efficient building at the point of construction. However, it is just as important to look at the performance of that building in the long term if we are to make a serious contribution to conserving energy, and this long term view is particularly cogent in light of the Energy Performance of Buildings Directive (EPBD).

The introduction of the EPBD was a major driver behind the changes to the Regulations in setting minimum standards for new buildings and in starting to improve existing buildings (covered by Approved Document ADL2B). The next phase of the EPBD looks at thermal efficiency over a building’s lifetime by requiring the production of an Energy Performance Certificate (EPC) giving a performance rating, which is then reviewed at regular intervals. Any deterioration in the performance of the HVAC system over time will therefore be reflected by a poorer EPC rating.

Although the introduction of EPC’s for domestic buildings this year has been delayed, they are still currently due to come into force for all buildings in the UK by October 2008, and will play an important role in raising awareness of the actual performance of our buildings. This is particularly the case for large public buildings as there is a requirement for the EPC to be on public display.

The demands of the EPBD and ADL2B provide a formal recognition that making our existing building stock more energy efficient plays a vital role in meeting government targets to reduce CO2 emissions. The standards expected for replacement HVAC systems are in line with those for newbuild projects, but there is an emphasis on the cost effectiveness of the measures taken.

So, whether a project is new or refurbishment, there are a number of key issues that specifiers need to consider: not only how well the products will perform at the outset, but also whether they can maintain that level of performance in the long term, within the constraints of budget, structure and programme.

For example, the traditional method of providing insulated ductwork is to use a galvanised sheet steel construction, which is then lagged as a secondary operation. There are several potential problems arising from this method in terms of weight, space and time implications, and these now also need to be taken in the context of long term performance.

An alternative method is to use pre-insulated ductwork, which combines the benefits of being lightweight, space saving, easy and quick to install, as the integral rigid phenolic insulation can be much thinner than traditional mineral fibre and eliminates the secondary lagging process. It also provides reliable, high levels of thermal performance.

In order to confirm the benefits of taking this new approach to ductwork, a number of independent research projects have been commissioned by Kingspan Insulation to compare the attributes and performance of rigid phenolic pre-insulated ductwork with those of traditional lagged sheet metal systems.

The results of a study carried out by construction and property consultants Bucknall Austin demonstrated that significant energy and monetary savings could be made due to the exceptional airtightness that is achievable with pre-insulated ducting. This can reduce the size of the fan and energy output needed to power the HVAC system, with potential savings of over 30% on the annual costs of running a fan. This is a significant factor in achieving compliance with ADL2A.

An earlier study showed that pre-insulated ductwork can be installed up to three times faster than sheet metal ducting – not including the further time taken to lag the latter. This also speeds up the programme and moves the installation of services off the critical path, enabling earlier completion of projects.

Last minute changes to the design and unforeseen problems can be more easily dealt with as the sections of ductwork can be cut and assembled on site. This attribute also makes future maintenance and repairs simple to carry out.

In terms of durability, the excellent thermal performance of closed cell rigid phenolic insulation is not prone to long term degradation and is unaffected by air movement or water ingress. It is not easily compressed, and maintains its performance over the life of the building. It is lightweight and takes up less space, making it ideal for refurbishment projects where there may be structural constraints within an existing building.

As a means of meeting the energy challenge, therefore, pre-insulated ductwork can easily satisfy the demands of ADL2A and 2B, as well as the EPBD, without costing the earth – in every respect.

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