[BLDG-SIM] DOE2.1E PTAC cooling coil module

Doug Maddox DougM at TWGI.com
Sun Dec 7 17:46:15 PST 2003

It appears as though the PTAC cooling coil routine in DOE2.1E is overestimating latent load on the coil.  
As shown by the lines of DOE2.1E code listed below, the sensible load is calculated via an averaged supply air temperature (TS), which is derived from the zone load and temperature.  Since the PTAC cooling coil runs either fully on or fully off, the value of TS in a part-load condition becomes a time weighted average between the temperature of the air off the cooling coil in the ON mode and the mixed air temperature. I believe this is all correct.
      IF(PO .GT. 0.0)                                                           PTAC   150
     1TS     = TAVE - <QNOW>/(CONS(1)*<CFMAX>*LSR(1))                           PTAC   151
C              CALC UNIT COOLING LOAD.                                          PTAC   209
    7 CONTINUE                                                                  PTAC   210
      ZQC    = AMAX1(0., (TM-TS)*CONS(1)*FC)                                    PTAC   211
C              THEN ANY MOISTURE REMOVAL INCREASES THE LOAD                     PTAC   212
      ZQC    = ZQC + AMAX1(0.,WM-WCOIL)*CONS(2)*FC                              PTAC   213

The latent load, however, is calculated from the ON mode leaving coil moisture value with no adjustment for the off-time in a given hour. I would expect that an adjustement such as the following line would be needed to only allow latent load for the time that the coil is on.
      IF (DTMC.GT.0) ONTIME = (TM-TS)/(TM-TC)

Am I missing something here?  I think I can fix the problem with a function, but I want to make sure I'm not mistaken that it is a problem.
Doug Maddox
The Weidt Group
dougm at twgi.com

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