DOE-2 Reference Manual Version 2.1 - DOE2.com

viii. Example Control Strategies for SYSTEM-TYPE Equals TPIU or FPIUIf the user has not done so, he should read the General subsection (Sec.B.5.a of this chapter)·before continuing here. That subsection containsinformation that is appropriate to these SYSTEM-TYPEs. There is only onemajor control strategy (for each of these SYSTEM-TYPEs) that is defined by theselective specification of values for the keywords INDUCTION-RATIO,COOL-CONTROL, COOL-TEMP-SCH, HEAT-TEMP-SCH, and INDUC-MODE-SCH (TPIU only).SYSTEM-TYPE Equals TPIUThe Two Pipe Induction Unit (TPIU) SYSTEM-TYPE is a "zonal" type system,although a portion of the cooling and heating is supplied by a primary system.TPIU has one central air cooling source and one central air heating source,which either cool or heat the primary supply air. The tempered primary supplyair is then distributed, at con·stant volume flow rate, through a single ductdistribution system, to the induction units, which are located in the individualZONEs. In each induction unit, the primary air is mixed with "temperedroom air" before the mixture is introduced into the room. To temper the roomair in the induction unit, the room air passes over the zone coil. To supplya working fluid to the zone coil, the TPIU system has one central liquidcooling source, one central liquid heating source, and a single pipe loop,which distributes the working liquid to and from all the ZONEs. The loopprovides either cooling fluid or heating fluid to all the induction units, butnot both at anyone time. --Only sensible cooling is simulated in the induction units and all dehumidificationis simulated at the SYSTEM level. Each TPIU induction unit has oneheat exchanger coil and a modulating control valve, which is operated by a twoset point thermostat in the ZONE. The desired set points are specified,respectively, with the keywords COOL-TEMP-SCH and HEAT-TEMP-SCH plus theirassociated SCHEDULEs.The basic concept of the TPIU SYSTEM-TYPE is one of providing a method bywhich some ZONEs in a SYSTEM can be cooled, while other ZONEs are being heated.Although this feature is available on a year-round basis, in the summer it isnormal to provide cooling at the zone level and heating of the zones, ifnecessary, by resetting the central supply air temperature. The opposite istrue for winter; cooling is provided at the system level and heating isprovided at the zone level. The changeover (date and hour) from winteroperation to summer operation, and vice versa, is specified, in thesimulation, by the user via the keyword INDUC-MODE-SCH. The changeover is notautomatic, based upon outdoor dry-bulb temperature, due to the difficulty ofheating and cooling of the potentially large mass of fluid in the zone coilpipe loop during the changeover. In a real system, the changeover isaccomplished manually, on a seasonal basis, by the operator of the system.The selection of a changeover date and hour can drastically affect theconsumption of energy and building comfort.When the hourly values specified in the SCHEDULE that is referenced byINDUC-MODE-SCH are positive (see right side of Fig. IV.6), the zone coils arein the cooling mode and the central coil may be either heating or cooling,depending upon how the user specifies COOL-CONTROL and HEAT-SET-T. The mostIV.155 (Revised 5/81)