BMS | CONTROL PRINCIPLES UNLOCKING THE SECRETS OF THE BLACK BOX Changes in controls can deliver big energy savings, but many shy away from tackling the BMS system, says Vercos Tom Randall, who sets out his thoughts on control-strategy principles to help demystify the black box B uilding management systems (BMSs) and the control strategies they implement are an essential requirement for delivering building performance in operation (see Class control: optimising HVAC controls in schools, CIBSE Journal, December 2019). It is common for improvements in control strategies alone to deliver 15-20% reductions in energy use. However, BMSs can be perceived as complex black boxes by many professionals who have the potential to influence how these systems are designed, set up and operated. If some simple, overarching principles for efficient, effective control could be established, these may help demystify the BMS and prompt more detailed discussions between building services engineers, facilities managers and BMS engineers on the development of control strategies that improve performance. BMS engineers are knowledgeable about implementing efficient control strategies, but are usually not asked to, and avoid the contractual risk of deviating from a specification. In addition, their work on new buildings comes at the very end, when, invariably, their time has been compressed between project delays and pressure to complete as soon as possible. On existing buildings, facilities management contractual incentives to minimise cost, rather than maximise value, can mean expenditure on BMS subcontractors is limited. This article proposes such overarching control-strategy principles for fellow professionals, and seeks feedback from readers on potential improvements and oversights. The proposed principles for control strategies include: 1. Sufcient demand a. Meet the service need. Not too little, but not too much to achieve the required service outcome: heating, cooling, ventilation, lighting, hot water and frost protection. b. Avoid extraneous demands. Most notably, as a result of inadvertent conflicts between systems such as heating and cooling. 2. Efcient supply a. Select the most efficient system available for the service demand. b. Operate the selected system as efficiently as possible. To ensure the control principles are 38 March 2020 www.cibsejournal.com CIBSE Mar20 pp38-40 Controls.indd 38 21/02/2020 14:54