DOE-2 Reference Manual Version 2.1 - DOE2.com

Economizer:For SYSTEM-TYPE equals SZRH, MZS, DDS, SZCI, TPIU, FPIU, VAVS, RHFS,HVSYS, CBVAV, PSZ, PMZS, and PVAVS, an economizer ~ill automatically besimulated, unless the user specifies a value for OA-CONTROL = FIXED in theSYSTEM-AIR subcommand. The code-word FIXED will set the outside air damper atthe value expressed for MIN-OUTSIDE-AIR, which essentially means that noeconomizer exists. The economizer will attempt to maintain the mixed (returnand outside) air temperature at the cooling coil (or cold deck) temperaturesspecified using COOL-CONTROL minus the fan heat gain, if any (the onlyexception to this statement is for SYSTEM-TYPE = HVSYS, where the economizerwill attempt to maintain the mixed air temperature at the temperaturesspecified using HEAT-CONTROL, because the keyword COOL-CONTROL is notapplicable to HVSYS).Humidification:In DOE-2 the process of humidification (if applicable to the SYSTEM-TYPEand if specified) is simulated by the injection of steam or hot water into theSYSTEM supply air stream. The relative humidity is calculated for the mixed(return and outside) air stream. The humidification process is described inthe 1977 ASHRAE Handbook of Fundamentals (Ref. 5, p. 5.9, Example 5). Theenergy associated with humidification is the amount of energy required toevaporate the required amount of water. The minimum allowed relative humidity(per cent R. H.) in the SYSTEM return air stream (at the dry-bulb temperaturefor the hour) is specified with the keyword MIN-HUMIDITY in the SYSTEM-CONTROLsubcommand.Dehumidification:The process of dehumidification, if and when required, is calculated asthe energy required to cool the air to its dew point plus reheating, ifnecessary. If the cooling coil is operating at or below the dew point of themixed (return and outSide) air, dehumidification will occur. There will,however, be no control of the dehumidification process unless the userspecifies a value for the keyword MAX-HUMIDITY in the SYSTEM-CONTROLsubcommand. MAX-HUMIDITY is used to specify the maximum allowed relativehumidity (per cent R.H.) in the SYSTEM return air stream. Not allSYSTEM-TYPEs have the capability for dehumidifying air. The SYSTEM-TYPEsSZRH, MZS, DDS, SZCI, FPFC, TPIU, FPIU, VAVS, RHFS, CBVAV, PSZ, PMZS, andPVAVS normally have the required equipment and controls. The user is remindedhere that to have dehumidification and subsequent reheating, both the coolingand heating must be on; that is, the SCHEDULEs referenced by COOLING-SCHEDULEand HEATING-SCHEDULE must possess positive hourly values.The value specified for MAX-HUMIDITY can override the cold decktemperatures, specified V1a COOL-CONTROL, 1n an attempt to maintain the returna1r relat1ve humidity at the value specified for MAX-HUMIDITY. The programwill reset the cooling coil temperature down toward MIN-SUPPLY-T, to increasedehumidification, and then the SYSTEM will either reheat the air (using themain heating coil), lower the volume of air to meet the temperature demands ofthe ZONEs, or overcool the ZONEs.I V .113 (Revised 5/81)