We now have proven communications standards, a wide range of reputable BMS manufacturers, systems integrators, etc. what could possibly go wrong?
Control systems/BMS Controls and their integration have been identified as principal cause of buildings performing poorly in numerous papers by Bill Bordass and others, BSRIA webinars on Soft
Landings and the Australian NABERS programme. In 1994, BRECSU General Information Report 40 Heating systems and their control identified that 90% of systems were not properly controlled
costing £500million in additional energy costs; this is still reported as a fact in current Carbon Trust Publications.
There are many reasons for poor control, the following are a few typical examples:
- Changes to Buildings and Services – Movement of Partitions without considering the effect on services and controls is common. Plant details can change from initial specification to
installation, either by substitution of another product, or by manufacturing changes. This can cause numerous performance issues.
- Controllability – Controllability is poorly understood and can be the Achilles Heel of building performance. If a system is not controllable it will not function properly no matter how good the
control system is, or how many attempts are made to change settings or strategies. System hydraulic arrangements are frequently the cause of controllability issues and changes at design stage can
often be zero or very low cost. Changes after construction can still in many cases be relatively low cost. Controllability should be reviewed at design stage, however, reviews after
construction can also be very beneficial identifying issues that may not be found by other means.
- Inadequate Commissioning – Overrunning installation often squeezes commissioning periods. Modern plant, particularly bivalent systems, will normally require more time to commission properly than
more traditional systems. Coordination of commissioning of plant, balancing and controls/BMS is becoming increasingly important, yet it is often inadequate as those managing the process have
insufficient understanding of the relevant disciplines and their interactions.
- Inadequate Support – Most mainstream BMS companies and their approved Systems Integrators offer good levels of ongoing support, often with legacy product compatibility. Unfortunately this is not
the case with all suppliers and in particular care should be taken with packaged control systems. The author has been known to refuse to work on a project if certain manufacturers are used – they
really can be that bad.
- Interference with settings – Interference can cause many problems, sometimes it is done with the best of intentions, for instance a caretaker used to turn boiler temperatures down manually to
save energy in a school, he continued to do this (despite instructions not to) when the boilers were renewed with a biomass boiler as the lead heat source. Turning down the boilers affected the
overall control and the effective capacity of the thermal store, consequently the system never worked effectively and eventually the biomass boiler was turned off.
- Packaged Controls – Packaged plant controls and their interfaces with the BMS and overall system operation need to be carefully considered, this is becoming increasingly important with modern
plant and bivalent systems, typical examples include:
- Boilers with the option for burner modulation via a BMS, but do not retain maximum limit temperature override when this feature is used.
- Boiler packaged sequence controls which compromise the modulation of the burners and reduce energy efficiency compared with other methods.
- AHU packaged controls that only offer a limited range of control functions, these may be adequate, but cases where they have to be replaced to provide the correct functionality are becoming
- Poor Specification – Many BMS and HVAC specifications are totally inadequate. Control principles are poorly defined, just stating that one item of plant shall always lead is insufficient. It is
often left to the systems integrator to guess the best way to achieve control. This may lead to a successful outcome, but often doesn’t. BMS manufacturers and systems integrators normally have
limited knowledge of thermodynamics, hydraulics, plant characteristics, etc. The system designer should define principles of control based upon system design and plant selection.
- Poor User Interfaces – User interfaces need to be appropriate to the building operation. Occupants like to feel they have control and limited local setpoint adjustment can be very effective in
maintaining occupant satisfaction, yet allowing efficient operation. Mixed mode ventilation systems requiring occupant interaction to achieve effective ventilation are often problematical with some
having debatable principles of operation.
- Split responsibilities – The split of responsibilities between packaged controls and BMS can frequently be a cause of problems. This may be overcome during commissioning by good management.
However, future maintenance may require additional visits from different suppliers that requires coordination, which rarely happens in practice. Service engineers also expect their particular item of
plant to operate in a standard way so often reset things to default modes, which may compromise system operation. Whilst it is often difficult to eliminate split responsibilities, particularly with
modern bivalent systems, systems can be designed to minimise potential issues if the designer has sufficient experience.
- Value Engineering – Value engineering can be recipe for disaster if inadequately managed and implemented. Lower cost alternative products will often compromise correct overall system operation.
Value engineering can be successfully implemented provided all aspects of the changes are fully investigated, scheduled (including any performance changes) and agreed by all parties.