DOE-2 Reference Manual Version 2.1 - DOE2.com

Cooling Coil Load is the rate at which energy is removed at the coolingcoil, WhlCh serves one or more conditioned spaces in any central HVAC system.This load is equal to the instantaneous sum of the space cooling loads (orspace heat extraction rates if the space temperature is assumed to "swing")for all spaces served by the system, plus any additional load imposed on thesystem external to the conditioned spaces. Such additional load componentsinclude heat gain into the HVAC distribution system in the ducting and pipingbetween the individual spaces and the HVAC equipment, and outdoor hot andmoist air introduced into the HVAC distribution system through the HVACequipment. The following figure shows the heat transfer modes that take placeamong the space instantaneous heat gain, space cooling load, and space heatextraction rate.-InstantaneousSpaceConvection Space Space HeatCooling r-:- Extraction t-Heat Gain Load I Rate1Radiation 1Conl/ection 11Furnishinos, (with limo dolay) 1I., Structure, 1r- 1H.at Storo08 11, 1I 1IL Air Temperatur. Swing JI-----------------Fig. 111.24.Heat transfer modes in a building.The calculation of space instantaneous heat gains, space cooling loads,and space heat extraction rates can be accomplished by a number of methods.The most accurate technique involves a simultaneous solution of a set ofenergy balance equations for all the space surfaces and the space air(Ref. 1). It is called the "thermal balance method." The three space energyflows noted above, as well as the space air temperature, are calculated in onestep at each time of interest (usually hourly). However, because of thesimultaneous solution of the energy balance equations, this method requiresconsiderable computer time.In the "weighting factor method" the space energy flows and space airtemperature are determined by a multistep calculation that eliminates the needfor the simultaneous solution of a set of equations (Ref. 1). In the firststep, the space instantaneous heat gains are calculated, for the same point intime, assuming that the space air temperature is held fixed at some referencevalue. These instantaneous heat gains must then be combined to yield a spacecooling load. As noted previously, this combining procedure is not a simpleaddition because space instantaneous heat gains from different sources undergodifferent time delays before appearing as space cooling loads. These timedelays are taken into account with the room weighting factors for the space,one set for each type of heat gain considered in the calculation. The coolingload for the space weighting factors are transfer functions relating the spacecooling loads to the instantaneous space heat gains. The final step in thismethod is the calculation of the space heat extraction rate and the space airII 1.142 (Revised 5/81)