Commercial heating
Coping with the modern shift to condensing boilers
With heating and hot water plant refurbishment projects we are seeing a shift from traditional atmospheric boilers to modern condensing models. Stuart Turner suggests that when embarking on this type of project it is vital to assess the current system along with the proposed new scheme in order to gain the maximum benefit from these products and make the best possible use of the existing system including pipework and flue runs.
approach will ensure an ease of transition from old to new plant with minimal downtime – a crucial factor in commercial buildings that cannot afford to be without heating or hot water for a long period of time.
Scoping Taking an holistic approach from the outset of a project gives you the ability to obtain an objective view, whether it be for space heat- ing, hot water supply or heating and hot water services. It is impor- tant to understand the clients’ phi- losophy and justification for their approach to identify early on any aspirations for building excellence such as BREEAM ratings or partic- ular performance criteria. In existing buildings it is benefi- cial to undertake a thorough plant room survey which will identify factors that, if ignored, will be to the detriment of the project out- come. This can ultimately save substantial time and cost later in the project. However this must not be explored in isolation, but extended to review the building and entire system. Has the build- ing had a change of use, or occu- pancy that may affect the demand or is it an old dirty system that will require specific water treatment prior to any equipment being installed? Are there measures that have been, or could be, put in place for increased efficiency and reduced wastage, such as splitting the system into zones, installing external temperature sensors for weather compensation and ther- mostatic valves on some of the radiators?
There are many factors to con- sider and these will vary on each project, so there is not one solu- tion that will suit all applications.
Coping with condensate It’s crucial to recognise early on the type and condition of the existing flue system and its route, as many boiler refurbishment proj-
22 | March 2014 | HVR
ects today will require a flue sys- tem upgrade or full replacement – particularly if you are no longer replacing like for like.
Updates to the Building Regulations Part L in April 2014 and European Directives such as the Energy Related Products Directive are driving the change from atmos- pheric or pressure jet boilers to condensing or high efficiency mod- els, in order to comply with the outlined efficiencies. However, the existing flues on this type of system are not able to deal with a modern pressurised and wet system where condensate will form. Flues for atmospheric appliances will be larger to create a low resistance system allowing the natural draught to pull flue gases through the system. Modern boilers use a fan to push flue gases through the appliance creating a positive pres- sure at the flue outlet allowing smaller flue diameters, but also typ- ically run at lower flue gas temper- atures with the likelihood of con- densate forming within the flue. The flue system must be water tight and pressure tight, and designed to drain the condensate from the flue and prevent flow back into the boiler. Where possi- ble you may be able to make use of the existing chimney with a liner thus enabling it to cope with condensing operation, as well as keeping installation costs down. A provision must also be made to remove condensate safely from the boiler itself. A 100kW boiler will generate around 13 litres of condensate per hour. The conden- sate is typically 3.5pH, so slightly acidic but can be disposed of nor- mally through the drainage sys- tem. If the boiler is not located next to a suitable outlet, the con- densate trap/drain must be con- nected to a drainage system using corrosion resistant material. It may be beneficial to install a conden- sate pump to assist with effective removal, particularly important in basement plant rooms.
A heating and hot water plant refurbishment should be viewed in a wider context
Hydraulics Modern boilers with low water content are less tolerant to fluctu- ating flow conditions in the heat- ing circuit so a low loss header is recommended to safeguard the condensing boilers from low flow conditions on the secondary cir- cuit, which may be caused by a pump being shut off or a motorised mixing valve changing position. The provision of a low loss header ensures that a steady flow of water is maintained through the boilers protecting them from potential damage as a result of firing when there is insuf- ficient or no water flow.
Controls
Only part of the benefit of a boil- er upgrade can be realised unless a review and improvement to the control system is implemented. It is vital to identify the existing control regime, control features and functionality, plus find out if
and where temperature sensors are fitted. For multiple boiler installa- tions a good boiler sequencer, such as Hamworthy’s Merley sequence controller, will help max- imise the benefits of the new boil- er plant, and since older atmos- pheric boilers only operated on/off or high/low, compared to the fully modulating operation of condens- ing boilers, it is unlikely the previ- ous controls will be sophisticated enough to implement effective sequencing strategies.
Ultimately a heating and hot water plant refurbishment project should always be viewed in the wider context; not just the boilers in isolation. This approach will ensure that a best practice solution is achieved and the customer gets value for money, high efficiency compliant products with full sys- tem integration.
// The author is the southern regional sales manager for Hamworthy Heating //
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