DOE-2 Reference Manual Version 2.1 - DOE2.com

air, the program will use the smaller quantity. If the outsideair temperature is above the temperature set point ofthe mixed air, no energy is exchanged. If the differencebetween exhaust and outside air temperatures is less than 10degrees, no recovery is simulated.A simpler, but less precise way of expressing the above is:RECOVERY-EFF = the fraction of recoverab le energy actuallyrecovered.(If the heat recovery occurs through a single heat exchanger,i.e., heat pipe or thermal wheel, then RECOVERY-EFF is identicalto the heat exchanger effectiveness. See Kays andLondon, "Compact Heat Exchangers", 2nd edition, McGraw-Hill,1964) .The exhaust air flow used for the calculation of heatrecovery is always the central exhaust, and is assumed to beequal, at any given time, to the fresh air supplied at thattime, minus specified direct exhaust from zones. Anyimbalance between fresh air and exhaust air flow rates,resulting from direct zone exhaust, should be considered whenselecting the value for RECOVERY-EFF (i .e., a higherpercentage of the heat avail- able in the exhaust air can berecovered when this heat is to be rejected to a larger massof fresh air). At the present time, only sensible heatrecovery is simulated.TABLE IV.34Code-WordFIXEDTEMPENTHALPYOA-CONTROLNo moveable dampers. Outside air quantity is afixed amount specified, calculated, or scheduled.Temperature-controlled economizer. In response tothe mixed air temperature going above the controllerset point (equal to the supply air set point for thehour), the outside air damper is opened. (Thisassumes a cooling mode and that the outside air iscooler than the return air.) The outside airquantity returns to its minimum (outside air dampersclose but minimum outside air dampers remain open)when the outside air temperature is at or above theECONO-LIMIT -T.En th a 1 py-con tro 11 ed economi zer. Same as TEMP aboveexcept that if the return air enthalpy is less thanthe outside air enthalpy, the dampers are forced tominimum outside air position.I V • 216 (Revised 5/81)