The cost of air distribution

Published:  11 November, 2007

ductwork
The fast-track capabilities and durable thermal performance of the Kingspan KoolDuct pre-insulated ducting system made it the ideal choice for the new £4.5 million purpose-built hospital sterilisation and decontamination unit for Hull & East Yorkshire Hospitals NHS Trust.

John Garbutt describes the results of an independent analysis of the long-term-costs of ductwork.

Saving energy is vital to preserving our planet; saving money is a great business incentive. So when a simple action such as improving the efficiency of our building services by giving some thought to which ductwork system to use can both help the environment and cut costs, it would be foolish to ignore the double benefit. The question is how do we identify the best products to achieve this?

Specification process

One useful tool is to look at whole-life costing as part of the specification process, rather than simply considering the initial capital cost. Indeed, this is the route often taken by the Private Finance Initiative (PFI) market, which is playing an increasingly important role in the construction industry. Worth an estimated £4 billion a year, it is largely used as a means of funding new buildings and services for the public education and health sectors, and then maintaining them over extended leases.

Because these arrangements are business led, private backers need to see a return on their investment and seek assurances that the buildings will perform over long periods without requiring heavy maintenance or upgrading. Consequently, whole-life costing of the products used in construction will often be used to determine what provides best value and performance overall.

For example, there are considerable potential savings to be made, both in the short term and in the long term, simply by giving some real consideration to that often neglected area — HVAC ductwork systems.

EXTRA PICTURE

The Private Finance Initiative (PFI) market is playing an increasingly important role in the construction industry for many public buildings such as hospitals, schools and colleges. Kingspan KoolDuct can reduce energy consumption, keep running costs down and maintenance bills to a minimum, over the lifetime of the building.

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 a number of issues arising from this method in terms of weight, space and time implications — all of which affect the initial capital cost. However, to assess the real costs or savings involved in specifying a traditional system or modern pre-insulated ductwork, a much wider basket of factors needs to be taken into account, such as durability, operational running costs and maintenance.

Independent analysis

Recognising that these are important considerations, Kingspan Insulation commissioned independent consultant Cyril Sweett to look at the implications of ductwork specification on the whole-life costs of a HVAC ductwork system, comparing the traditional method cited above with a modern pre-insulated ducting system.

Cyril Sweett based the comparison of initial capital outlay on a system comprising 308 m of ductwork of a wide variety of dimensions. The initial capital investment costs were as follows.

• Insulated galvanised sheet metal, £47 154.
• Rigid phenolic pre-insulated ductwork, £37 000
These figures demonstrate an initial capital saving of 21.5% on the part of the pre-insulated ductwork.

Once the initial costings had been assessed, Cyril Sweett calculated the whole-life cost over a 30-year period, taking into account the energy saving, maintenance, cleaning costs and general wear and tear over that period.

The estimated costs for the two different systems over the 30-year period are as follows.

• Insulated galvanised sheet metal, £85 058
• Rigid phenolic pre-insulated ductwork, £67 672

Again, the pre-insulated ductwork represents the most cost effective solution, with a 20.4% saving over the thirty years.

One major factor in this differential is that creating access into the duct after installation to carry out maintenance or repair was easier and less time consuming with pre-insulated ductwork, as it was simply a question of cutting into the panel in question and then replacing the damaged area instead of having to replace an entire section of sheet metal ducting and then insulating it.

EXTRA PICTURE

Independent research commissioned by Kingspan Insulation demonstrated that significant savings on the annual costs of running an HVAC system could be made due to the exceptional airtightness that is achievable with pre-insulated ducting. This is the Institute of Cell & Molecular Science of Queen Mary University of London.

Adding the initial cost and the whole life costs involved produces a total saving of £27 540, or 20.8%, if pre-insulated ductwork is used rather than the sheet metal system.

Earlier independent research commissioned by Kingspan Insulation had demonstrated that significant savings could be made due to the exceptional airtightness that is achievable with pre-insulated ducting, which 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 formed part of the data upon which Cyril Sweett based the whole-life costing.

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. This ensures ease of compliance with current Building Regulations, and caters for the long-term performance required by the Energy Performance of Buildings Directive (EPBD). It is not easily compressed and maintains its performance over the whole 30-year ‘life’ period. It is lightweight and takes up less space, making it ideal for refurbishment projects where there may be structural constraints within an existing building.

Ductwork that is pre-insulated ductwork is easy to handle, requiring no specialist equipment or restrictions, and research has shown that it can be installed up to three times faster than sheet metal ducting — not including the further time taken to lag the latter. This also has an impact on the whole-life costing by speeding up programme and moving 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.

Solutions

By looking at the bigger picture through whole-life costing, it is possible to find solutions that will reduce energy consumption, keep running costs down and maintenance bills to a minimum over the lifetime of the building.

John Garbutt is marketing director with Kingspan Insulation Ltd.

MORE INFORMATION
Kingspan Insulation has produced a series of white papers examining the differences between sheet metal and pre-insulated ductwork. Full copies of these and the independent reports commissioned are available on request from the Kingspan Insulation marketing department on 0870 733 8333.

Independent research commissioned by Kingspan Insulation demonstrated that significant savings on the annual costs of running an HVAC system could be made due to the exceptional airtightness that is achievable with pre-insulated ducting. This is the Institute of Cell & Molecular Science of Queen Mary University of London.



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