There are many projects where refurbishing the air handling plant is a cost-effective and commercially viable alternative to replacing with new. Ron Flewett, ahu refurbishment manager of Envirotec, explains why the refurbishment option often provides the end client with the best value.
There is increasing pressure on building services engineers to ensure the projects they design and/or install incorporate a sustainability approach that minimises environmental impact. And while energy efficiency generally dominates the headlines there are other factors that are equally worthy of consideration.

In existing buildings, for example, there are often opportunities to refurbish major items of plant such as air handling units (ahus), even those which are 20 or 30 years old, instead of replacing them. Not only does this reduce the material consumption and embodied carbon of the project, it also creates an opportunity to upgrade the performance of the plant while reducing costs and disruption for the end client.

To put this into perspective, consider a 2m x 2m x 6m ahu with an airflow of 7m³/s. It incorporates a volume control damper, bare tube frost coil (LPHW), panel filters to F4 efficiency, bag filters to G6, CHW cooling coil, LPHW reheat coil, fan and motors - and would cost £12,500 to supply and install, based on good access. To refurbish a similar unit, replacing all internal components and damaged external panels, treating corrosion, re-commissioning and providing a 12-month warranty would cost £9,125, saving 27 per cent.

Savings up to 50%

In fact, depending on circumstances and the level of experience and expertise applied to the project, the savings achieved by refurbishing rather than replacing will typically range from 20 per cent to 50 per cent.

Furthermore, the end client will benefit from additional lifecycle cost savings through reduced maintenance costs and improved energy efficiency, all providing a fast return on investment. A recommissioned system and updated operation and maintenance manuals will also contribute to reduced cost of ownership.

There are many reasons why a consultant or contractor may advise the building operator to opt for refurbishment, ranging from deterioration of components and casework through to a desire for higher performance and/or improved efficiency. The latter consideration has been fuelled by initiatives like the Carbon Reduction Commitment Energy Efficiency Scheme, Energy Performance Certificates and Display Energy Certificates, all of which have focused attention on the performance of building services plant.

Age deterioration

Clearly, all ahu components will suffer age deterioration, some more than others. On cooling coils, for example, a corrosive oxidation effect will be caused when condensate mixes with airborne pollutants, and this is exacerbated in areas of high air pollution. There will also be wear and tear on moving parts in fans and motors, while static components may have years of life left in them.

For these reasons, an initial inspection of the plant to identify opportunities for refurbishment is the first stage in any project. This is followed by a method statement and a risk assessment, along with detailed costings to facilitate the decision making process.

Very often, it will make sense when refurbishing an ahu to take the opportunity to improve performance. This may even be a necessity if conditions in the building have changed; a common example being an increased cooling demand since the system was originally designed.

In such cases, existing components can be replaced with parts which comply with modern specifications, and offer improved efficiency. For example, it may be possible to replace original standard fans driven by AC motors with backward-curved fans and DC motors to achieve higher efficiencies. Similarly, heat transfer across heating and cooling coils has improved in recent years, as has the efficiency of filters and the thermal and acoustic insulation of replacement ahu panels. The same principles are true of any direct expansion refrigeration kit installed in the ahu.

Where a major upgrade to performance is required, or where major deterioration has occurred, it is also possible to replace whole sections or, indeed, introduce new sections. In such cases, if access is restricted, these may be taken to site and assembled in situ.

Major benefit

In fact, this highlights another major benefit of refurbishment, as there are many buildings where access to the ahu plant is very difficult, so that refurbishment becomes a much more sensible option. When planned properly, refurbishment is less disruptive compared with a new installation as the work can be carried out in phases outside normal working areas. Also, units serving critical areas can be isolated so the work is carried out in line with the business imperatives of the end client.

Clearly, then, there are many good reasons to consider ahu refurbishment. The key to guiding the end client to the best solution is to harness the expertise of specialist companies that have extensive practical experience of AHU refurbishment and can deliver a turnkey solution.