Why go beyond the BMS?
When a building management system or building energy management system (BMS/BEMS) is in place, is there a need for additional controls? Sabien Technology’s *Tony Willis explains how specifiers can guide their clients to further savings with discrete retrofit controls.
It is well established that the majority of commercial boilers can waste energy through the inherent problem of boiler dry cycling. Furthermore, most people naturally expect their existing BMS/BEMS will prevent this from happening. However, this is not typically the case as the majority of BMSs and BEMSs are not always designed or commissioned to control individual items of plant down to the finest detail - particularly boiler plant. The primary role of a BMS/BEMS is to optimise a building’s overall energy performance and ensure that services such as space heating and cooling are delivered at the required temperature levels and times.
As a consequence it is not uncommon for the boilers to be ‘dry cycling’ during their daily operation, without the BMS/BEMS being aware of it. So it makes perfect sense to introduce additional controls to prevent boiler dry cycling. In our experience, with over 5,000 of our M2G boiler load optimisers installed, energy savings from controlling boiler dry cycling range from 10-25% with typical paybacks from under 6 months to 2 years. And these savings can be over and above those achieved by a BMS/BEMS or other controls such as weather compensation and boiler sequencing.
The choice of any such additional control is critical. For example, early attempts to address boiler dry cycling were an abject failure (sadly, some have reappeared recently in an attempt to exploit the ‘green pound’). These ‘failures’ either delayed the boilers’ firing, or artificially reduced the boiler set points, both of which allowed temperatures to fall in the spaces being heated. In addition, they can cause direct conflicts with the BMS strategy by artificially changing the boilers’ set point temperatures.
In contrast, Sabien’s patented M2G technology is the latest generation which carries out real-time analysis of each boiler’s flow and return temperatures every 10 seconds and measures the decay of the flow and return every second. This provides a true load profile for each boiler and can therefore differentiate between a genuine call for heat and one that is simply firing due to standing losses.
The advantage of this new approach is that it recalculates the values every time the boiler reaches its required set point temperature, so it adapts to variable set-points and takes its direction from the BMS, ensuring it does not conflict with the BMS/BEMS operation or any other existing controls. It also helps to mitigate the energy wastage caused by short-circuiting and short-cycling.
In this way, retrofitted boiler load optimisation is an example of how the right additional controls (fine tuning) can work in harmony with other controls and increase the energy savings that can be achieved.
For example, Sabien’s M2G boiler optimisation controls have been independently evaluated by organisations such as Serco, Jones Lang LaSalle, BT, Aviva, Royal Mail, central government departments such as Defra, and CLG, along with many local authorities and universities. In fact, over 5,000 M2G units are installed across the private and public sectors.
So if you are considering retrofitting additional controls, the key is to understand how they work, talk to others that have used them and be absolutely certain they won’t compromise comfort or the existing BMS control strategy.
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*Tony Willis is Technical Sales Director with Sabien Technology