As heating demand reduces during warmer periods, boilers become oversized and begin cycling, which leads to an increase in energy use and carbon emission. Tony.Wills (right) from Sabien Technology explains
DEMAND on boilers drops during warmer months. Typically, they are only used to heat water or provide partial, intermittent heating.

This causes excessive cycling - heating up and down - and as a consequence, energy wastage from the boiler is at its highest. But this is not the only reason a boiler cycles.

It is widely believed that up to 80% of commercial boilers are oversized for their application. This is defined as when a boiler plant has an operational capacity greater than that required from the designed building load.

Heating systems are generally designed to provide a continuous comfortable environment no matter what the weather is like. Therefore, boilers are designed to be oversized for the base-load in order to take into account worst case scenarios and designed redundancy for maintenance and repairs. This again causes over-capacity and boilers to cycle on and off.

So, why is boiler plant cycling an issue and how can it be prevented?

Up and down

As a result of cycling, burner operation increases. This causes inefficiencies because force draught burners must purge the combustion space each time they fire. The boiler cools just after you have heated it up.

The boiler needs to recover this heat loss through additional firing. This wastes further energy and causes unnecessary thermal stress on the boiler plant.

Typically, a boiler will lose between 1% and 2% of its heat through radiated losses, the boiler effectively becoming a large radiator heating the boiler house.

This is a continuous process, causing the boiler to refire unnecessarily without contributing heat or energy into the building load. As a result, significant energy is wasted.

But technology is available to prevent this. Intelligent boiler controls (IBC) can significantly reduce the energy consumed and, as a consequence, carbon emissions.

For example, Sabien describes its M2G as an 'intelligent boiler optimisation control' that is unobtrusive and simple to fit. The company says the pay-back period is typically between six months and two years and energy and carbon savings are typically between 10% and 35%, depending on application.

BMS versus IBC

Sabien says that many of its clients initially believe that their existing building management systems (BMS) can control the boilers as effectively as an IBC. But this is not the case.

First, the BMS controls the building comfort levels by zone control and weather compensation via mixing valves.

Secondly, management systems typically do not manage boilers and burner in the same way as direct boiler load optimisation controls. As a consequence, cycling issues still occur and can in some cases be made worse.

Neither should these types of controls be confused with simple time delay devices used in the past. For example, the M2G measures the flow and return temperatures via digital sensors every 10 seconds. This provides accurate data capture to build a profile of boiler demand.

Furthermore, the unit can monitor the demand for heat. It does this via the Opto isolators from the thermostat wiring connections, and then implements the control algorithms.

On first firing, the boiler reaches the normal thermostat set point and the boiler will turn off. On the next, the M2G will check the demand for heat, and that the boiler differential is within the designed parameters.

It will then decide if the boiler needs to be fired based on this information.

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 demand.

Additional savings can be achieved with two-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 business interest in green issues at an all-time high, 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 are also adding to the imperative to reduce energy consumption. The urgency to seek new solutions is most definitely a growing feature of the market.

Consequently, companies are beginning to implement strategies to meet challenging energy reduction targets.

As warmer months approach, implementing boiler load optimisation controls could deliver significant energy and carbon savings. This would benefit any organisation's bottom line - and carbon footprint.

www.sabien-tech.co.uk