DOE-2 Reference Manual Version 2.1 - DOE2.com

temperature. It should be noted that deviation of the space air temperaturefrom the reference temperature, or design set-point, causes the actual rate ofheat extraction from the space to be different from the calculated spacecooling load. Thus, the calculation of the actual space air temperature andspace heat extraction rate is very important. A set of room air weightingfactors for the space, along with information about the performance characteristicsof the thermostat temperature-control and HVAC systems, are used forthis calculation. Whereas the previous steps in the weighting factor methodare carried out in the LOADS portion of the DOE-2 program, this final step isdone in SYSTEMS, where the information on the control and HVAC systems isavailable.Decision on DOE-2 Weighting Factor Method:Depending on the type of building and the application, the user mustchoose one of the two weighting factor methods available in DOE-2.1. Precalculated Weighting Factor method:DOE-2 has available sets of ASHRAE precalculated weighting factorsfor typical constructions (Ref. 1). The only parameter that variesis the combined weight of floors, walls, and furniture, that is, theeffective thermal mass of the space. The user can select the weightingfactors that best describe his structure from the precalculatedset. To use this option it is only necessary to use the INPUT LOADScommand and the appropriate value for the FLOOR-WEIGHT keyword (seeSec. B.9 of this chapter).2. Custom Weighting Factor* method:In DOE-2 it is possible for the user to specify weighting factorsthat are customized, or tailored, to the building (or to specificspaces within the building) under investigation. To input thenecessary data to calculate these weighting factors, either (1)specify FLOOR-WEIGHT = 0 in the SPACE or SPACE-CONDITIONS instruction,or (2) refer to the LIBRARY-INPUT LOADS instruction discussedbelow.The user may specify both types of weighting factors in one simulationrun; that is, some spaces may use Precalculated Weighting Factors and otherspaces may use Custom Weighting Factors.To aid the user in deciding which of the above methods to use for HVACcalculations, the following can be stated. The Precalculated weifhting Factormethod (1) requires the least computer time and produces tne leas accurate results. The Custom Weighting Factor method (2) is more accurate than the PrecalculatedWeightlng Factor method, but requires more user-input effort and* The general theoretical basis for the Custom Weighting Factor calculationswas developed by CCB/Cumali Associates (Refs. 6 and 7). The algorithms andtheir supporting analytical basis were developed by the Los Alamos NationalLaboratory (Ref. 8).111.143 (Revised 5/81)