Why BEMS provide the best means of cutting boiler energy consumption

Boiler dry-cycling has been the cause of significant energy waste in non-domestic buildings. Yet many building managers and FM providers are unaware of this costly phenomenon, though the recent introduction of products aimed at countering it has drawn attention to the problem. While such products undoubtedly do make savings, this certainly does not mean that they represent the best solution.

Dry cycling is caused by a boiler’s standing losses. It is the repeated firing of the plant - to maintain its internal water temperature - when there is actually no true heating demand from the building it serves. The problem is exacerbated if water continues to be pumped around the heating circuits; the boilers then fire to compensate for thermal losses from the pipework system in order to maintain the desired fixed flow temperature.

In many buildings the running of the heating plant is largely time-based, using time clocks or optimizers. This means it may operate for most of the day, regardless of space conditions, with heat flowing to all parts of the building even when their temperature setpoints are satisfied.

The problem can be mitigated to some extent by simply increasing the normal time delay between firing cycles. A more effective solution is provided by a recently developed type of control device that monitors a boiler’s flow and return temperatures and calculates the latter’s rate of decay. This gives it some measure of actual heating demand, thus enabling it to hold the boiler off for relatively long periods in certain conditions.

Though control units of this type have been used to good effect, their use makes less sense if there is a building energy management system (BEMS) installed – which is likely to be the case in a majority of non-residential premises. It should be relatively straightforward to reprogram most BEMS to perform precisely the same function, thereby avoiding the need for and disruption entailed in fitting additional control units (one for each boiler) plus their temperature sensors. Once made aware of this possibility, many facilities managers and building owners will see this as the preferred option.

Importantly, BEMS are actually capable of making even greater economies than the control devices described. By implementing an entirely demand-led control strategy, they are able to ensure that the heating plant only ever operates when necessary. Such a strategy would look at space temperature conditions in the heating zones and factors like room occupation as measured, say, by presence detectors.

Ever increasing energy prices and the mounting pressure on organisations to reduce their carbon emissions has meant that demand-led control is increasingly being specified when a BEMS is first installed. Upgrading an existing system to apply it is not of course something that can be done overnight. It will involve a level of investment that is higher than simply re-configuring the system to perform the control routines described earlier. However, it will often be an investment that can be justified by the additional savings that accrue.

These savings can be particularly large in today’s well-insulated commercial buildings whose lighting, electrical/IT systems and occupants represent a major source of heat and where there may be separate plant for generating the domestic hot water. In such premises, the requirement for the boilers to run can be very low, even during spring and autumn, so the potential for cutting energy waste is even greater.

Before leaping to install ‘black box’ boiler control devices, building owners and operators would be well-advised to first look at what is achievable using their BEMS. Their BEMS supplier will be able to recommend the best and most cost-effective way of modifying their system to reduce boiler running hours and thus their heating costs.