IMPACT OF SIMULTANEOUS SIMULATION OFBUILDINGS AND MECHANICAL SYSTEMS IN HEAT BALANCE BASED ENERGY ANALYSIS PROGRAMS ONSYSTEM RESPONSE AND CONTROL

摘要

The current generation of building simulation software isrnbased upon separate building, mechanical system, and equipmentrnsimulations. This scheme evolved primarily because of memoryrnlimitations of the computers which were used to develop thernprograms. Hardware advancements have eliminated some of thesernlimitations so the separate building and system scheme needs to bernreevaluated. In addition to discussing methods of introducingrnsimultaneous building and system simulations into the BLASTrnprogram, this paper will also address new system specificationrnand control strategy options which are made possible by thernsimultaneous simulation method.rnBLAST currently uses a linear univariate control profile torndescribe the heating and cooling provided by the fan system as arnfunction of room temperature during the loads calculation. Controlrnprofiles for each thermal zone are used to model the systemrnresponse during the loads simulation. Alternatively, a combinedrnsimulation of the zone and the system determines the systemrnoutput by allowing each system component to respond to changesrnwithin the zone and the outside environment. The combinedrnsimulation technique also allows modelling of systems which arernimpossible to represent using BLAST control profiles: forrnexample, cooling to the zone provided by outside air ventilation.rnThe combined simulation is accomplished by using time stepsrnshort compared with conventional hourly energy -balance basedrnprograms, but long compared with finite difference methods. Inrnaddition, the system response is allowed to lag the zonernconditions by one time step. This completely eliminates iterationrnfrom the solution procedure: however, instabilities may bernintroduced due to the feedback between zone and system.rnMethods have been developed to simulate physical controllersrnwhich modify the response of system components to variablernzone conditioning demands. The use of short time steps alsornaffects the calculation of conduction transfer functions (CTF's)rnused to compute surface temperatures and heat fluxes. For a givenrnconstruction the accuracy of CTF calculations decreases as thernnumber of terms in the CTF series increases, due to round-off andrntruncation errors. This problem has been avoided by calculatingrnthe CTF series at large enough time steps to ensure accuracy andrnmaintaining a "master" set of surface temperature and fluxrnhistories from which intermediate "temporary" histories can berninterpolated to give temperatures and fluxes at the desired times.This paper specifically discusses the results of performing arncomplete system simulation within the loads calculation portion of thernBLAST program by using a shortened time step combined withrnlagging the system simulation. In addition, new ideas for specifyingrnsystems to take advantage of this scheme are presented along withrnconcepts for system control.