Sabien's M2G reduces unnecessary boiler cycling and wastes less energy

Industry comment

Published: 11 February

Author: Alan O'Brien

Type: Industry comment

Year: 2008

Boiler demand is at its lowest during partial loads resulting in increased energy wastage and carbon emissions. Tony Willis, Technical Manager at Sabien Technology Ltd, explains why and what can be done to prevent it.

What causes boiler cycling?

During warmer months, boiler demand reduces. Typically the only boiler demand is to provide hot water generation or partial heating loads. As a consequence, energy wastage from the boiler is at its highest caused by the boiler plant excessively "cycling", this isn?t the only reason a boiler cycles. It is commonly known that up to 80% of commercial boilers are oversized for their application. This is defined as a boiler plant having operational capacity greater than what is required from the designed building load. Heating systems are generally designed to provide a continual and comfortable working environment internally no matter what the outside conditions are. Therefore boilers are oversized for the designed base load to take into account worst case scenarios and designed redundancy for maintenance and repairs, again causing over capacity and boilers to cycle on and off. So why is boiler plant cycling an issue and how can it be prevented?

As a result of cycling, burner operation increases causing inefficiencies due to the fact that force draught burners have to purge the combustion space each time it fires, causing the boiler to cool down, effectively "cooling something you just heated up". The boiler needs to recover this heat loss through additional firing, therefore wasting further energy and causing unnecessary thermal stress on the boiler plant.

Typically a boiler will lose between 1 and 2% heat through radiated losses, the boiler effectively becoming a large radiator heating the boiler house. This is a continuous process, causing the boiler to re-fire unnecessary without contributing heat or energy into the building load. As a result significant energy is wasted. However technology is available to prevent this occurring. Boiler controls can significantly reduce the energy consumed and carbon emissions. For example, Sabien's M2G is an intelligent boiler optimisation control, a simple, unobtrusive technology to fit. The pay back is typically between 6 months and 2 years and energy and carbon savings are typically between 10% and 35%, depending on the application. Therefore, implementing boiler optimisation controls is a very viable investment for any organisations that either want to reduce, or are reducing, their energy costs and carbon emissions.

Shouldn't a Building Management System (BMS) provide intelligent boiler control?

Many of Sabien's clients initially believe that their existing Building Management Systems (BMS) can control the boilers as effectively as a boiler control, but this isn't the case. Firstly, the BMS controls the building comfort levels by zone control and weather compensation via mixing valves. Secondly, BMS typically do not manage boilers/burner in an intelligent manner compared to direct boiler load optimisation controls. As a consequence the cycling issues are not removed and can in some cases be increased.

Why aren't more organisations installing intelligent boiler controls?

These types of controls are not to be confused with simple time delay devices used historically. For example, the M2G is intelligent. It will measure the flow and return temperatures via digital sensors every 10 seconds providing accurate data capture to build a profile of the boiler demand. Furthermore the unit can monitor the "call for heat" via the Opto isolators from the thermostat wiring connections and intelligently implement the control algorithms.

On first firing, the boiler will reach the normal thermostat set point and the boiler will turn off. On the next stage the M2G will check for the "call for heat" and checks if the boiler differential is within the designed temperature differential (parameter) and whether the boiler needs to be fired based on this information. In this case, the boiler will hold off the boiler firing (save mode) based on delta T and time, which are both adaptive. This control function will also prevent the burner from firing on low fire if the boiler load demand is low, ensuring the best efficiency for the current demand. Additional savings can be achieved with 2 stage burners. The M2G will determine the best firing stage for the boiler demand based on the flow and return differential temperature and true boiler load conditions.

Blue chip clients using M2G include the Royal Bank of Scotland Group, KPMG, Bank of England, Institution of Mechanical Engineers, Investec Bank and NHS Trusts.

With interest in "green issues" being at an all time high for private and public organisations, the need to achieve both financial savings, as well as an improved environmental profile, is becoming increasingly important in the Boardrooms of UK PLC.

Rising energy prices also create a more immediate imperative to reduce energy consumption and cut energy costs. The urgency to seek new solutions is most definitely a growing feature of the market and consequently companies are beginning to implement energy strategies to meet challenging energy reduction targets.

As we enter the warmer months implementing proven boiler load optimisation controls can deliver significant energy and carbon savings, benefiting any organisation?s bottom line and carbon footprint.