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Delivering efficiency through tight control

Whether appraising current assets, planning the renovation of existing systems or procuring a new building, a considered heating control strategy is essential to delivering efficient and effective operation. Paul Hardy examines the opportunities
The provision of heat to our commercial buildings is subject to increasing scrutiny. On one hand we have an ever developing Government policy mix intended to deliver a significant reduction in carbon emissions and reduce demand on national energy networks, whilst at the same time the cost of energy is continuing to rise. From both a corporate social responsibility standpoint and acknowledging the more immediately tangible concern of running costs, facilities operators are rightly concentrating on efficient operation of building services installations.

Some 80 per cent of today's UK building stock is connected to the gas network, employing natural gas-fired appliances to deliver space heating and hot water requirements. This trend is expected to continue for many years to come, albeit with an increasing share of locally deployed low to zero carbon technology providing pre-heat or base load functions.

With this in mind, ensuring that boilers are operating as efficiently as practicable makes sound financial sense to the individual business, as well as aligning with broader UK Government policy objectives of emissions reduction and reducing reliance on fossil fuels.

When considering a new or replacement boiler system it is essential to consider that most buildings are inherently different; be it due to thermal mass, occupancy patterns or simply floor layout and zoning arrangements. With this in mind the operation of building services plant in an applied system must be closely managed to deliver optimum performance. This is where an appropriately considered control strategy becomes utterly essential to delivering in use efficiency.

Indeed, it is claimed that inadequate or incorrect boiler control can increase fuel consumption by up to 30 per cent; when appraising whole life cost of an installation this energy waste can total many times the initial capital outlay for the appliance in question.

Aim will not be achieved

Given forthcoming legislation, such as the Energy Related Products directive, we are approaching a time when, in certain output ranges, only condensing boilers will be available on the market. The intended consequence of this directive is a reduction in energy use across all EU member states. However, in the case of heating systems, this aim will not be achieved without appropriate control.

In replacement situations many existing heating systems will have been designed around cast iron boilers with system flow and return temperatures of 82 and 71 deg C respectively. It is often the case that boiler control in such instances comprises simple 'on/off' operation with perhaps a time clock.

If a condensing boiler is installed onto such a system the boiler will rarely operate in condensing mode, which requires a return temperature below 55 deg C, the manufacturer's declared efficiency value will not be achieved. Where existing emitters and distribution pipework are to be retained, the system will still require relatively high flow and return temperatures to achieve comfort conditions at the coldest times of year. However, this only represents a small proportion of the entire heating season.

Modern condensing boilers offer direct weather compensation so that the boiler flow temperature is lowered as external temperature rises, thereby improving efficiency and allowing the boiler to operate in the condensing range for a large proportion of the year. Further simple control functions, such as optimum start and the ability to serve multiple timed zones, are included as standard in many modern boilers thereby offering enhanced efficiency for minimal outlay.

Perhaps most importantly, condensing boilers are most efficient when operating at part load so it makes sense when considering even a single boiler replacement to employ a number of smaller condensing boilers with cascade control. This approach will ensure that system heat load is shared between the maximum possible number of boilers thereby ensuring they work at part load condition for most of the year, optimising the efficiency of the system.

For this reason, modular and pre-fabricated boiler systems are becoming an increasingly popular option. These products not only offer advanced control functionality as part of the design, but also offer a range of benefits such as reduced installation time owing to off-site manufacturing, standardised design of components and reduced project costs.

A well-implemented building management system (BMS) can offer all of the above control functions. However, in smaller buildings, or in the case of refurbishment projects, the budget may not be available to accommodate a full BMS or bespoke control panel. In such cases, it is important to remember that manufacturers of modern condensing boilers can offer products with advanced on board control functionality, together with application guidance to help ensure excellent in-use efficiency.

// The author is managing director of Baxi Commercial Division //
7 March 2013

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