Building Management System or caretaker: which route to energy savings?
If you listen to manufacturers, Building Management Systems (BMS) are technology's solution to the energy manager's need to reduce wastage in building services. They are often rated as saving up to 30% of energy consumption in heating and cooling for investment purposes and by the company providing the finance. However, they save absolutely nothing unless expert hands manipulate them.
They take control of the building’s energy using systems (like heating, air conditioning, ventilation, lighting) and even have the capability to control things like window shades and rotate photovoltaics as well as read meters – in fact, if there is no limit to capital available, they can control almost anything.
The history of building heating is interesting and informative; the first building heating was by open fires and the control was simple – as long as they were lit, heat was available, possibly not enough and probably not where wanted but available. If you got too warm, you fed the fire less often, damped it down or open doors or windows. If you were too cold, you added more fuel to the fire or added another fire. All not very effective or efficient.
The Romans, as usual, increased sophistication by the hypocaust and control was similar and effected by slave power. It was a long time later that boilers appeared using hot water (and steam, later) to more effectively distribute heat from a central source around a building. They were initially fired by coal (or wood – biomass isn’t a recent innovation) and control was as much by increasing or decreasing the rate of stoking as anything else. Distribution of heat around the building was mostly via “gravity” – actually, convective currents in the pipework- which had to be large to accommodate.
The advent of pumps (initially mechanical and driven by muscle power) allowed greater control and effectiveness. As sophistication improved, thermostats and electric pumps meant that control was improved but it still required manual intervention. Even if boilers could feed their own fuel and flow rates.
Even within living memory, buildings like schools often had basically manually controlled boiler systems requiring the active control of a caretaker who would manually light the boiler each morning – that required him (very few ladies!) to start work in time for the building to heat up in time for occupancy – rather onerous in winter.
The advent of the timeclock and automatic ignition improved things, but left a dilemma: if you set the start time early enough to achieve comfort levels on the worst winter day, you waste energy (and money) for most of the year. If you set the start more frugally, you risk being too cold on wintry days.
In practice, caretakers took on one of the roles of a BMS, that of an optimiser. That adjusts the start time of the heating system to just achieve the desired temperature at building occupancy by measuring internal and external temperatures and using an algorithm to estimate the heating time. (in fact, modern systems can also measure wind chill, solar gain, equipment usage and other levels and learn from the previous thermal behaviour of the building fabric).
The caretaker would listen to the weather forecast and take a judgement on how early the heating needed to start on the basis of the predicted temperature and the previous days’ occupancy. This was obviously less exact than monitoring the temperature in real-time and apparently often resulted in the caretaker arriving before dawn to change the setting following a sudden cold snap (if it got warmer, he almost certainly wouldn’t bother and wasted energy).
He might also perform other functions now included within a BMS like acting as a compensator by adjusting the flow temperature to react to different internal and external conditions; he might even be more efficient than the BMS which will have been programmed at commissioning with a set of parameters which it might not be able to adjust and which might be inappropriate for the actual building in use.
Another function a BMS demonstrates that the caretaker might also provide relates to zoning. A good BMS with the right control valves and sensors can individually control a number of zones, each potentially heated for a different period and to a different temperature. A caretaker might also be able to do the same by use of room thermostats and manually operated valves. If he would do this is a different question as you could expect the valves to be difficult to access behind panels or above false ceilings (hidden away to prevent unauthorised tampering) and, even if he fully understood the way the water flows worked, he might find frequent adjustment onerous and a distraction from other “more important” tasks. A BMS doesn’t care how often it has to make an adjustment.
Another comparison relates to programming. To ‘program’ the caretaker, you simply go and talk to him and explain what is needed in whatever language he speaks – if you get the desired result could be a different matter.
A BMS usually uses some sort of Graphical User Interface (GUI) – in my presentation on 23 May at edie Live I will talk about a couple of examples that didn’t – accessible to the user or his contractor and this (usually) enables a suitably knowledgeable person to make reasonable adjustments. It also allows him to make mistakes. A similar interface?
So, which do you choose: active manual control or a sophisticated BMS? The former will use and waste more energy take significant maintenance. The latter as high capital cost, requires sophisticated adjustment and maintenance but has the potential to save you more than it costs in energy
You choose. I have no axe to grind (just one to cut wood…)
Andy Clarke at edie Live 2017
Andy Clarke is among the industry experts appearing on stage at the edie Live 2017 exhibition at the NEC Birmingham on 23-24 May. Andy will be chairing a session within the Energy Management Theatre on the first day of the show, discussing the challenges and opportunities in driving down energy usage.
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