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Energy Efficiency: Time to take control of boiler efficiency

With the latest generation of boilers already close to peak performance, future efficiencies in commercial heating systems will largely come from improved controls, says Paul Sands.
The Coalition Government has gone ahead with legislative drivers to bring about change in terms of the UK's energy efficiency performance. Amendments to Part L (Conservation of Fuel and Power) of the Building Regulations came into force in England and Wales on 1 October 1, 2010.

Last year also saw the introduction of the Carbon Reduction Commitment (CRC) Energy Efficiency Scheme. The CRC scheme is mandatory and aims to raise revenues from large energy users of around £1 billion per year by 2014-15 by effectively taxing organisations for the carbon dioxide emissions that are attributable to energy consumption.

Labour's original plan was to hand revenues back to participants to reward investment in energy-saving technology, but this was reversed in George Osborne's recent Comprehensive Spending Review when he decided to hang on to the revenue from the sale of carbon allowances.

According to the Carbon Trust, about a third of the UK's energy consumption is used for heating or producing hot water. A significant proportion of this is provided by commercial boiler plant, so it should be included in any energy reduction strategy.
Typically, energy improvements of 10 per cent or more can be made relatively easily through maintenance and low cost, straightforward improvements.

Many buildings may still be using very old hot water boilers that had an operating efficiency of only about 70 per cent when first installed and which will now be worse due to poor maintenance. New condensing boilers can achieve efficiencies of more than 90 per cent so it can be worth considering replacement.

Today's breed of low water content, modulating condensing boilers with low NOx emissions are arguably pretty much at the peak of their possible performance. Further efficiencies in commercial heating systems will largely come from improved controls and system design, starting with ensuring that your boiler plant is not oversized for the application.

Heating efficiency credits

The Non Domestic Building Compliance Guide details how to meet the requirements of Part L of the Building Regulations. It operates a system of heating efficiency credits in terms of controls applied to boiler systems.

The minimum control strategy should encompass valved zone control, demand control via thermostats and timed control. Further credits can be achieved by applying enhanced strategies to the boiler and heating system controls:

· Sequential control
· Thermostatic radiator valves
· Weather compensation
· Optimised start/stop
· Full zoned time control
· Building management system
· Decentralising the heating system to avoid long pipe runs.

If there are two or more boilers, it is a good idea to consider sequence control if it is not already installed. If all boilers are firing under mild conditions, it is likely that they are operating only at part-load and do not have sequence control.

Good sequence control ensures that only the minimum number of boilers required to meet the heat demand actually fire and that these boilers are used to full capacity rather than part-load. Also, sequence controllers ensure that the order in which the boilers fire can be rotated to minimise maintenance costs. Sequence control could save 5-10 per cent of the overall energy consumption.

An optimiser, meanwhile, is a sophisticated timeswitch linked to the internal and external thermostats that switch the boiler on at exactly the right time to ensure that the building reaches the required internal temperature in time for occupation. Similarly, the boiler is switched off early so that the internal temperature is maintained only when required. Savings of 5-10 per cent of the overall energy consumption of the boiler plant could be achieved.

To achieve more savings, the temperature of the water can be regulated according to outside temperature. In milder weather, the flow temperature is reduced, thus saving energy. This is done through the use of a compensator linked to internal and external thermostats.

This form of control is particularly useful in condensing boilers as lower return water temperatures can be achieved, thus ensuring that maximum condensation occurs within the boiler and increasing efficiency.
27 January 2011


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