DOE-2 Reference Manual Version 2.1 - DOE2.com

8. SPECIFYING EXTERIOR WALLS, EXTERIOR FLOORS, AND ROOFSNote: The following general discussion applies only to exterior walls,exterior floors, and roofs. fCor discussion of other surfaces, refer to thesection in this chapter entitled "SPECIFYING INTERIOR WALLS, INTERIOR FLOORS,CEILINGS, UNDERGROUND WALLS, UNDERGROUND FLOORS, AND NON-GLASS DOORS."Before specifying data for exterior walls, exterior floors, and roofs, itwould be prudent to consider the following:Entering a CONSTRUCTION instruction without a U-VALUE (but with a valuefor LAYERS) is done to specify a dynamic, or "delayed", type-of construction.In this case, the calculation of heat transfer (by conduction and radiation)considers time and thermal mass. As such, computational time and cost can begreater than when specifying a CONSTRUCTION instruction with a U-VALUE. Thelatter approach is taken to specify a steady-state, or "quick", wall that hasno heat capacitance and where heat flow is not delayed.Specifying a wall by the dynamic, or "delayed", method (without a U-VALUE)tends to produce more accurate results, especially for massive exterior wallconstruction, but this is at the expense of additional computer time and cost.Note: In the following discuSSion, the reader should pay particularattention to the use of the words "keyword" and "instruction".The OOE-2 program treats exterior walls, exterior floors, and roofs in anidentical manner. The only difference is the physical orientation of thesurface. In the following discussion, all three surfaces will be referred togenerically as "exterior wall".Although there is only one DOE-2 instruction for specifying an exteriorwall or roof (see EXTERIOR-WALL instruction), there are many possible methodsof specifying the physical makeup of an exterior wall (see Fig. IlLI6). Thisphysical makeup is specified through the CONSTRUCTION keyword in theEXTERIOR-WALL instruction. When the user tries to specify an EXTERIOR-WALLinstruction, it will refer the user back to the CONSTRUCTION instruction,which in turn may refer the user back to either the LAYERS instruction or totables of prespecified LAYERS in the DOE-2 Library. In short, this means thatthe user cannot define an exterior wall solely in the EXTERIOR-WALLinstruction; certain other data items must also be specified first.In order of increas ing compl exity, the common ways to speci fy anEXTERIOR-WALL are:1. Specify a numerical value for the U-VALUE keyword in the CONSTRUCTIONinstruction (specify nothing for the LAYERS keyword). Then refer tothe CONSTRUCTION instruction, by its U-name, in the CONSTRUCTIONkeyword of an EXTERIOR-WALL instruction. This will yield a steadystate,or "quick", exterior wall (see Fig. IlLI7).II 1.57 (Revised 5/81)