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10 steps to boiler efficiency

06 January 2011

Through its experience of retrofitting intelligent boiler load optimisers, Sabien Technology has identified some key things to consider in improving boiler efficiency. With increasing pressure to reduce energy costs and carbon emissions its vital that existing boiler plant is fully optimised and maintained to deliver the maximum efficiencies.To that end it’s useful to have a ‘check list’ of what to look out for.

Maintaining the BMS

Building Management Systems or Building Energy Management Systems (BMS/BEMS) need to be regularly maintained, including re-calibration of sensors, or the readout on the BMS PC terminal may be inaccurate. It’s also worth remembering that a BMS manages the building’s requirements and typically doesn’t control individual boilers, so each boiler should be optimised separately.

Sequence the boilers

Most boilers deliver maximum thermal efficiency at 80% of the boiler firing capacity, so it is important to ensure the minimum number of boilers is operating at any one time.Key areas to inspect include the motorised isolating valves (two-port valves) on each boiler to ensure they are working correctly. The most efficient boiler is the one that is not firing!

Prevent Dry Cycling

Boiler dry cycling is an inherent problem in all boilers of any size and age. Early attempts to overcome this created a predetermined firing period (time delays) or lowered the boilers’ set points. These measures impacted on ambient room temperatures and comfort levels and potentially reduced hot water storage temperatures, increasing the risk of Legionella. Both measures will also conflict with existing BMS or weather compensation controls.

In recent years technology has been developed to prevent dry cycling without reducing the boilers’ set points or ambient room temperatures. It optimises the load of individual boilers using real time analysis of each boiler’s temperature profiles, rather than using predicted or historical firing patterns. By analysing real-time flow and return temperature profiles for each boiler, it differentiates between general heating demands and false demands created by standing losses that lead to dry cycling. This technology also integrates seamlessly with existing controls such as BMS, weather compensation and boiler sequencing.

Regularly check boiler operating times

Check that time clocks are correctly set for required operating/occupancy times, with different settings for weekends and holidays and adjustment between GMT and BST. Building optimisation/weather compensation controls must also be correctly commissioned and occupancy times and sensors should be regularly calibrated.

De-scale the boilers and clean the flue-ways

Boilers with scale or sludge waste energy through reduced heat transfer efficiency so it’s important to check for correct chemical dosing and for leaks that may result in untreated water continuously refilling the system. Flue-ways should also be cleaned regularly; dirty boiler flue-ways can decrease boiler efficiency by more than 10%.

Ensure your temperature set-points are correct

Boilers and controls should be set correctly for the required demand, particularly with high-low burners where changing boiler set points to a lower value can result in comfort level issues. Hot water storage temperatures need to be within legal requirements.

Check boilers are correctly designed for the application

Boiler plant should be correctly designed and commissioned for the application with close attention paid to service reports and combustion efficiency. When boiler plant is replaced the existing distribution system may need to be re-commissioned.

Understand the energy consumption

Sub-metering is essential for understanding energy consumption at individual plant level and measuring the benefits of energy improvement initiatives. Any analysis of energy consumption needs to be degree-day-corrected to include the impacts of weather conditions, as well as taking account of other variables.

Check for conflicts between heating and cooling

It’s surprising how often poor space temperature control results in a space being heated and cooled at the same time. HVAC systems should be integrated so they work in harmony and avoid these conflicts.

Assess occupants’ behaviour

Actions by a building’s occupants, such as changing room thermostats, opening windows and altering timers for special events can have a serious impact on boiler/ system efficiency. Regular evaluation of such behaviours will prevent these actions going unnoticed for extended periods.

Visitors to the Energy Event can discuss these matters in more detail by visiting stand 56 and find out more about Sabien’s M2G intelligent boiler load optimiser.

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