Building management systems and controls do not always control buildings as effectively and effi ciently as they should. Graham P Smith looks at the underlying causes of this problem


CONTROL TAKING


O


ne of the most common causes of poorly performing buildings is inadequate or defi cient control systems. About 90%


of controls for heating, ventilating and air conditioning (HVAC) systems are inadequate in some way, costing industry and commerce more than £500m a year in additional energy costs, according to the Carbon Trust (see Building Controls Technology Overview – CVT032, 2007). Controllability – or the lack of it – is a key issue when it comes to saving energy and cutting carbon emissions from buildings. There are a number of defi nitions of


controllability. For the purposes of this article, the term is used to mean the ability for the system to be controlled within acceptable limits for both occupancy comfort and energy effi ciency/carbon emissions. Despite advances in control technology, poor control outcomes are still common. Controls can be inadequate or defi cient for a number of reasons, but the


most common are: ● Inadequately specifi ed control systems/ building management systems (BMS);


● Defi cient commissioning and maintenance of control systems/BMS;


● Poorly understood, or ineffectual use of, control systems/BMS; and


● Poor controllability and uncontrollable HVAC services. All these factors are important, but the most misunderstood and diffi cult-to-resolve


22 CIBSE Journal December 2011 www.cibsejournal.com


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