The importance of being invasive
April 1st 2007

Darren Jones, has recently joined HVAC energy saving company Efficient Air as operations manager. An experienced energy manager, most recently in the NHS, he has some firm views about how real savings can be identified and implemented,and stresses the need to go beyond the BEMS approach to the heart of the building services

aving spent many years managing energy for a large number of sites in the South East as well as chairing the South Thames Energy and Environmental Forum (a group of approximately 30 energy managers) I have heard many arguments for and against the use of Building Energy Management Systems (BEMS) – regarded as the energy saving equivalent of the Building Management System - and whether they really advance the cause of energy saving.

Energy managers have mixed views.While some swear by state-ofthe- art BEMS systems, others find them of no value whatsoever. Like all established technology, they have a useful role to play, but should not be regarded as a panacea.The BEMS is only as good as its control strategy (software) and the controls (hardware) that are in place.

The inherent danger of a BEMS system is that we can rely too much on them.That can give rise to a situation where many engineering and facility managers take the view that the BEMS looks after and controls the operation of plant.

Under this comfortable though dangerous scenario, systems are as a consequence forgotten about.

BEMS systems can be very effective, when a good control strategy is in place and system controls are well maintained and functioning correctly.

BEMS head end computers (BEMS Supervisors) have the advantage of allowing engineering and energy management staff to remotely interrogate the status of plant and conveniently adjust set points that can lead to improved plant efficiency - all without the need to leave the office.

But over time various events will occur that will have a detrimental effect on building and plant efficiency, and I must stress the need to visually inspect plant on a regular basis, as what is seen to be happening from the BEMS Supervisor is very often not what is actually happening in reality. Some examples: set points have been adjusted to compensate for occupants' individual heating needs; offsets have been placed on failing pressure, humidity and temperature sensors; dead bands have accidentally been removed by untrained maintenance staff and bypass valves have been manually opened to overcome faulty control valve actuators.

Very often control strategies are extremely complex and more often than not, they are not understood by the maintenance personnel that have to attend to them.This leads to frustrations, and in many cases it is the inappropriate use or complete avoidance of the BEMS, which often leads to the bypass of control valves in order to overcome problems.

BEMS engineers (during service visits) on the other hand tend to get bogged down with software issues, and in my experience sit at their computers for the majority of their visit and tend not to inspect the physical controls and how the plant is actually running in reality.

P+I control loops, local area networks, display and directory modules all sound very impressive, but – to use just one example - what good is all this technical input if the control actuator motor has burnt out? There is often a lack of communication between BEMS Engineers and Maintenance Staff, who are both inclined to do their own thing without any coordination.

A number of BEMS operators offer clever software that scans the BEMS system to identify parameters within the system such as historic valve positions, temperature, humidity and pressure set points, deadband ranges and PID settings.This information forms the basis of an audit report on which recommendations for improvement are made, but is it enough? I believe not, which is why we at Efficient Air take a more invasive approach, which requires visually inspecting HVAC plant both internally and externally and in doing so picking up and identifying a whole host of issues relating to the efficiency of the plant. In addition to the plant inspections, we take power, temperature and pressure readings between each AHU component during the audit and compare these with what the BMS is reporting.We also look at BEMS set points, dead bands, time schedules and controls strategies to identify quick win opportunities.

Other areas which are not covered within the BEMS scenario but form an integral part of our survey are: the over or under supply of air; optimum use of outside air; excessive system resistances; zoning control and time schedules; fan motor and drive efficiency; heating and cooling efficiency; heat recovery and maintenances issues.

A fairly exhaustive and important list I think you will agree.

There are countless examples of how this approach works in practice. During a recent survey I found a bird's nest wrapped into the pre heat coil of an AHU system.

I wonder what a BEMS system might have made of that? I've selected two other recent cases.

While undertaking a survey for a large pharmaceutical company in the south of England I found that the linkage between a control valve and its actuator was missing (see photograph). On interrogation of the BEMS it appeared that this valve was modulating normally and therefore this would not have been picked up had the visual checks not been undertaken.This resulted in the cooling coil being stuck open resulting in a 10° drop which the heating coil has to provide a 10° lift to compensate costing the client £8631 per year.

In an office, a number of heating bypass valves had been manually opened by maintenance staff during winter months to overcome complaints of cold by occupants.

On undertaking the audit during warmer months it was evident from measurements taken and our visual inspections that these bypass valves had been left in the open position and the chilled battery was having to work at full capacity to offset the heat gains from the heating coil thus costing in the region of an additional £6,000 on the chilled water and heating load.

The conclusion that I hope readers will draw from my observations is that plant inspections and measurement of temperatures,pressures, humidity is absolutely essential to enable a accurate and useful report to be provided to the end client.The 'invasive'approach will always reveal weaknesses that the BEMS one will not, and will more than pay for itself.

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