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Water Heating: Condensing the issues with high efficiency systems

Graham Williamson, business director of commercial heating at Ideal Boilers, talks to HVR to discuss the implications of system design and the issues surrounding the installation of condensing boilers in existing systems
Water Heating: Condensing the issues with high efficiency systems
DEMAND for high efficiency products in the non-domestic sector is on the increase. In the last year alone, the UK market for commercial condensing boilers grew nearly 20% in an otherwise flat market. Not only has this been fuelled by the changes to the Building Regulations but also by innovation in boiler size, ease-of-installation, siting and flue flexibility. It is important now that both specifiers and heating contractors are aware of the product options available to them, along with the requirements of this new legislation.

To date, the increase in demand of condensing boilers in the commercial sector has largely been because of the product attributes rather than related to higher operating efficiency of the equipment. Schemes such as the Carbon Trust's Enhanced Capital Allowance (ECA) have helped to raise awareness of the benefits of condensing boilers in the commercial sector - although much education is still required.

Clearly the move towards high efficiency products is gathering pace and will continue to do so. However, each application must be considered on its own merits and there will probably not be one solution that fits all. For real fuel savings and actual carbon reductions to be realised the correct selection of a product is vitally important.

To gain maximum benefit from a condensing boiler, both the system design and controls need to be integrated to provide lower return temperatures. Without this, a condensing boiler may operate only as efficiently as a standard efficiency boiler type. In truth very few condensing boilers installed in the UK operate in a fully condensing mode. In fact, even new build installations using condensing boilers are still being designed to operate on traditional design parameters - 82 flow, 71 return principles!

Ideal's Imax boiler

It should be recognised that a boiler can only condense when the system allows it to do so. Crucially, this is when the return temperature is maintained below 500C. Once the return temperature exceeds this level then the boiler will stop operating in a condensing mode. These are the key issues that need to be considered if the full benefits of condensing boilers are to be realised, especially in replacement applications, which equates to more than 70% of all boilers installed.

There are further issues when considering a condensing boiler in a replacement application if budgets are limited. In older systems, there is likely to be a significant build up of sludge and debris developed over time. Modern condensing heat exchanger technology, through its compact design, is less likely to be tolerant to these conditions and the system will have to be cleaned before fitting the new boiler plant.

The majority of condensing boilers require a greater flow rate through the boiler to not only maximise performance but also prevent damage to the heat exchanger. Typically, an existing system in the UK is designed on an 11k difference between the flow and return, whereas most condensing boilers require a 20k difference to maximise performance and efficiency. It is often overlooked when considering a condensing boiler that the rated output of the appliance will reduce significantly if it is not operating in a system with a 20k temperature drop. In fact the reduction in output can be as much as 8% which if over looked will have a significant impact on boiler selection and system performance.

Therefore it is essential that to benefit from the performance of a condensing boiler the existing pump duty will need to be verified and if necessary new pumps may need to be fitted. It should also be understood that this increased differential and lower flow temperature can have an adverse effect on radiator performance resulting in lower surface temperatures and a reduction in heat output.

An existing installation will already have a flue system that may well have been installed for a number of years and therefore may not be suitable for the newer condensing boiler. It is critical that the flue system be inspected to ensure that it is in a sound condition and that its construction is suitable for a condensing boiler. Because of the high level of condensate that will be formed within the flue system the material used must be impervious to the acidic nature of the flue gases to prevent a serious failure.

Government commitment to tackling carbon emissions and the impending changes to the Building Regulations will undoubtedly drive further growth in the condensing boiler market. It is therefore ever more critical that specifiers and installers of heating products take a more active role in considering the impact of installing condensing boilers. It is obvious condensing boilers can offer significant benefits but all the implications of fitting them must be considered before carrying out the installation; they should not be seen as a solution for all applications.

Ideal Boilers Commercial 01482 498 690
1 April 2006


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