DOE-2 Reference Manual Version 2.1 - DOE2.com

Much of the discussion that follows is related to the consequences of requiringthis equation to hold true and to be internally consistent. The basic equation,(A), appears in the following forms:CFM =(-) heat addition rate (B)1.08 x [(DESIGN-HEAT-T) - (MAX-SUPPLY-T)]CFM =heat extraction rate (C)1.08 x [(DESIGN-COOL-T) - (MIN-SUPPLY-T)]CFM =heating capacity (D)1.08. x [(mixed air temp.) - (air temp. off heating coil)]CFM = sensible cooling capacity (E)1.08 x [(mixed air temp.) - (air temp. off cooling coil)]where the mixed (return and outside ventilation) air temperatures and the airtemperatures off the coils are calculated at the peak heating/ventilating andpeak cooling/ventilating conditions.a. Zone and System Supply Air Flow RateIf the user specifies no keywords that size the system, such as cfm's,capacities, or addition/extraction rates, the program will look for the peakheating and cooling loads and will use equations (B) or (C) to determine theCFM in each zone. If the user specifies only the outside air quantity and/orthe exhaust cfm for a zone, the CFM determined for the zone will be themaximum of the values calculated from (B), (C), the outside air, and theexhaust air. In either case, the maximum heating and cooling capacities arethen determined from (D) and (E).The only way for the user to absolutely specify the zone air quantity isto use the ASSIGNED-CFM keyword. Any other choice may be overridden by thedesign routine in its insistence on obeying the First Law of Thermodynamics,as it applies to equations (A) through (E). Even the value of ASSIGNED-CFMwill be changed at least to account for the difference between the altitude ofthe building and sea level. It will also be multiplied by the SIZING-RATIOwhose default is 1.0. If other user-specified data cause equations (D) or (E)to be over specified, i.e., each of the variables is supplied by the user in amanner that does not satisfy (D) or (E), the air temperatures off the coilsare adjusted to bring the equations back into balance. To illustrate this ina slightly over-simplified way, suppose the user has entered values forDESIGN-HEAT-T, MAX-SUPPLY-T, ASSIGNED-CFM, and HEATING-CAPACITY for a zonalsystem. The design routine will calculate a mixed air temperature for thezone by using (a) the outside dry-bulb temperature at the time of the peakheating load for the building, (b) the minimum outside ventilation air thatwas specified elsewhere in the input, and (c) the DESIGN-HEAT-T. Similarly,the design routine will calculate the air temperature off the coil by using(a) the temperature drop in the ducts and (b) the temperature increase causedby the fans. If these two calculated values (mixed air temperature and airtemperature off the coil) are entered into (D), along with ASSIGNED-CFM andHEATING-CAPACITY, it is probable that the left hand side and the right handside of the equation will not be consistent. If and when this happens, theIV.300 (Revised 5/81)