Martin Cooke, Technical Director at EOGB Energy Products Ltd, discusses the points to consider when choosing a replacement commercial heating system to improve energy efficiency

The commercial heating industry has changed a great deal in recent years. Emerging trends are to replace cast iron sectional boilers with gas-fired cascade multi boiler systems or to add a biomass installation with a smaller gas boiler back up.

Of course, at a glance, these new options look good. However, some question marks still hang over these new trends, such as increased maintenance schedules, extra space requirements for biomass storage, efficiency claims for renewable installations, and the overall comparable life of the new plant compared to traditional cast iron sectional or shell/tube boiler installations.

A well designed and correctly sized plant with multiple sectional boilers and correctly matched burners can provide excellent reliability and energy efficiency and shouldn’t be overlooked over new trends and possible government ‘green’ incentives. Unfortunately, during the economic downturn, many installation projects were price driven and, in order to win tenders, the emphasis was on cheaper equipment over equipment that would benefit the user and save energy in the long term.

Meeting energy efficiency standards

As per BS EN 15232:2012 Energy performance of buildings automation, controls and building management there is a minimum recommended efficiency standard of band C.

For example, on natural gas, this equates to:

• A single boiler system less than 2 MW having a gross seasonal efficiency of 91%
• Each individual boiler in a multiple boiler system having an efficiency of 82%
• An overall multi-boiler system efficiency of 86%

When a boiler is specified, many choices of heat generator (i.e. burners) are available and with careful consideration at this stage, a huge impact on plant running costs and overall environmental impact can be achieved.

When selecting a burner, it is critical to consider:

• Whether fully modulating or two stage operation is best
• Whether it should be pre-mix or blown gas
• Its turndown ratio (the amount a burner can increase and decrease its power across its range)
• The use of inverter driven fan motors
• If it has a low NOx combustion head (class 3 as per EN 676)
• If it has advanced combustion control, such as O₂ and CO trim

All the above should be specified at the point of order. However, certain features such as combustion controls can often be retrofitted if required, providing the controls are compatible.

ErPD

This month, the Energy Related Products Directive (ErPD) comes into force. This is part of the EU’s plan to reduce energy emissions by 20% by 2020 and applies to all heating and hot water products with outputs from 70kW to 400kW.

It aims to improve the energy efficiency of domestic and commercial heating systems, reduce emissions and lower building running costs.

To comply with the ErPD, manufacturers will need to meet minimum energy performance standards, nitrogen oxide and noise emissions on all products covered by the regulations in order to bear a CE mark and be available for sale.

Add-on controls

Energy saving can be significant when combustion control is added. For example, the EOGB/Baltur TBG ME range of burners uses the Lamtec BT320 burner management system which is extremely versatile and allows extra control systems to be incorporated to suit the plant requirements.

Adding CO trim to the Lamtec BT320 allows combustion systems to get closer to stoichiometric conditions whilst remaining safe. CO sensors use a modified version of zirconia O₂ sensors that enable them to detect the products of incomplete combustion. The Lamtec CO trim is a self-learning algorithm that last for eight hours and then learns all over again to adapt to any changes in conditions. By monitoring CO it ensures that the plant is running as efficiently as possible as it will keep excess air in combustion to the minimum and reduces excess heat being drawn up the flue and wasted.

It is predicted that through using a Lamtec system, fuel bills are reduced by approximately 1.8%. This may not sound like much, but when applied to very large plants with fuel bills of hundreds of thousands of pounds a year, it is a significant saving.

Environmental Considerations

Along with attempting to ensure the plant is as efficient as possible, there is also the environmental impact of burning fuels that now is a major concern for air quality. Nitrogen Oxide (NOx) levels are another extremely important factor to consider when selecting the correct heating equipment.

As per EN 676, gas burners are classified into three classes, with Class 3 being the lowest NOx levels of up to 80 mg/KWh. All EOGB/Baltur gas burner heads are now class 3 as standard.

Burner to boiler matching

When a burner is matched to a boiler it is extremely important to ensure that the burner’s working field (i.e. the range in which the burner’s fan can overcome the back pressure of the appliance it’s fitted to) is looked at very closely.

The information that is needed to make a perfect boiler/burner match is:

• The ‘over pressure’ of the boiler or appliance – the internal resistance of the combustion chamber that the burners fan must overcome.

• The boiler’s maximum heat input – the amount of heat required usually in KW to produce the required output. Losses will always happen during the combustion process therefore it is always required to put more heat in than you will get out.

• Internal heat exchanger dimensions – this is important to ensure that adequate flame space is available for the combustion chamber. Ideally the flame from the burner will burn without directly impinging on the surface of the boilers heat exchanger.

• The burner’s ‘working field’ – the parameters in which the burner can operate within. This field is created when a burner is tested to see what resistance it can overcome within a heat exchanger and, at the same time, the output it is able to fire.

Ideally a burner will be selected to allow the maximum turndown ratio. In order to obtain this, the burner that operates towards its maximum output against the appliance resistance pressure for the output of the appliance is the best suited. This is particularly important when selecting a modulating burner to ensure a broad operating range.

There are many options available to installers and specifiers when selecting burners for a heating system in terms of NOx emissions and energy savings and, with the correct selections, energy savings of over 50% can be achieved.