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Why go beyond the BMS?

21 February 2012

When a building management system (BMS) is in place, is there a need for additional controls? Sabien Technology explains how further savings can be achieved with discrete controls.

It is well established that the majority of commercial boilers waste energy through the inherent problem of boiler dry cycling. Furthermore, most people naturally expect that their BMS will prevent this from happening. However, this is not typically the case as the BMS has not been designed or programmed to identify or prevent boiler dry cycling.

This is because boiler dry cycling occurs at individual boiler level, whereas a BMS strategy is typically designed to optimise a building rather than the individual boiler plant.

So it is not uncommon for the boilers to be dry cycling during their daily operation. The BMS won’t know because it will be seeing the overall picture and ensuring that systems are satisfied, irrespective of what each individual boiler is doing.

This is why additional efficiency can be achieved by taking control of boiler dry cycling at each boiler and why BT is just one of many organisations that is rolling out boiler load optimisation across its estate. You can see which other organisations are doing the same at – and achieving energy savings of 10-25% with typical paybacks from 6 months to 2 years.

Why does it happen?

All boilers, even modern well-insulated ones, lose some heat to their surroundings (the boiler house), even when they are not firing, this is known as ‘standing losses’. As the temperature of the boiler falls, the boiler’s internal controls cause it to fire to recover the lost temperature – even if the building is not requesting heat. So this firing is unnecessary and wasteful – and is known in the industry as boiler dry cycling.

Sabien’s M2G boiler load optimiser can differentiate between boiler dry cycling and a genuine call for heat from the building and prevent energy being wasted. It does this in real time and, crucially, works in harmony with the BMS, without altering the designed set points and thus ensuring that comfort conditions in the building are not compromised (most other technologies change set points or delay firing with no real time analysis or control).

FMs should take the tour

There is a very simple way to assess whether your boilers may be dry cycling -simply visit the boiler house!

It will soon become apparent if boiler dry cycling is occurring in your boiler house. For example, during the milder periods of the heating season when there is less demand on the boiler plant, dry cycling will be occurring and the boilers will be constantly coming on and off. Also if only one boiler is firing and the other boilers are warm, then increased standing losses could be occurring and the boilers will fire unnecessarily to replace this lost heat.

While it may be surprising to think boiler dry cycling is occurring in your boiler house even though you have a fully optimised BMS, the deployment of discrete retrofit controls can deliver untapped energy savings.

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