Book - School of Science and Technology

Building management systems 657Continuation of network as figure 22.34Outstation P.C., orcentral processorUnitarycontrollersBoilerFigure 22.35 Unitary controllersChillerAir handlingplantLong-distance communicationIt is not uncommon for communication over long distances to be achieved satisfactorilyusing telephone system networks. Normally the facilities required by clients are faultreporting and data gathering. However, certain types of client who have large numbers ofrelatively small properties (e.g. local authorities) may operate facilities on a day to daybasis, from a central remote location.Benefits in useOne of the major difficulties experienced on many projects, particularly the larger andmore complex, is the achievement of satisfactory completion including correct commissioningand performance testing. At best, it is likely that the systems will be commissionedto satisfy the bases of design: controls set points, for example, would be based upontheoretical steady state calculations, modified perhaps by the judgement of the commissioningengineer, to reflect the dynamic response of the plant under the particularoperating conditions obtaining at the time of the commissioning.Using a BEMS, it is possible for the systems and controls to be finely tuned with theusage patterns of the building and to the actual thermal response of the building elements.This may be undertaken on site or at a remote location, utilising telephone links, whichmay provide an opportunity for the designer to monitor performance. This work may beassisted by the use of computer simulation techniques,* to check the performance againstdesign parameters and to test alternative controls strategies. The system performance overa range of different control philosophies may be simulated through the weather conditionsand operating periods for minimum energy use. It is only after such work iscomplete that the client will gain maximum benefit from the significant investment in abuilding management system.* BRE, IEA (21C), Empirical Validation, Ref. IEA 21RN327/93, January 1993.