CalcEffectiveSHR Function

private function CalcEffectiveSHR(DXCoilNum, SHRss, CyclingScheme, RTF, QLatRated, QLatActual, EnteringDB, EnteringWB) result(SHReff)

Arguments

Type	Intent		Name
integer,	intent(in)	::	DXCoilNum
real(kind=r64),	intent(in)	::	SHRss
integer,	intent(in)	::	CyclingScheme
real(kind=r64),	intent(in)	::	RTF
real(kind=r64),	intent(in)	::	QLatRated
real(kind=r64),	intent(in)	::	QLatActual
real(kind=r64),	intent(in)	::	EnteringDB
real(kind=r64),	intent(in)	::	EnteringWB
Return Value real(kind=r64)

Called By

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Source Code

CalcEffectiveSHR
Source Code

FUNCTION CalcEffectiveSHR(DXCoilNum,SHRss, CyclingScheme, RTF, QLatRated, QLatActual, EnteringDB, EnteringWB) RESULT(SHReff)

        ! FUNCTION INFORMATION:
        !    AUTHOR         Bo Shen, based on WatertoAirHeatPumpSimple:CalcEffectiveSHR
        !    DATE WRITTEN   March 2012
        !    MODIFIED       na
        !    RE-ENGINEERED  na

        ! PURPOSE OF THIS FUNCTION:
        !    Adjust sensible heat ratio to account for degradation of DX coil latent
        !    capacity at part-load (cycling) conditions.

        ! METHODOLOGY EMPLOYED:
        !    With model parameters entered by the user, the part-load latent performance
        !    of a DX cooling coil is determined for a constant air flow system with
        !    a cooling coil that cycles on/off. The model calculates the time
        !    required for condensate to begin falling from the cooling coil.
        !    Runtimes greater than this are integrated to a "part-load" latent
        !    capacity which is used to determine the "part-load" sensible heat ratio.
        !    See reference below for additional details (linear decay model, Eq. 8b).

        !    For cycling fan operation, a modified version of Henderson and Rengarajan (1996)
        !    model is used by ultilizing the fan delay time as the time-off (or time duration
        !    for the re-evaporation of moisture from time coil). Refer to Tang, C.C. (2005)

        ! REFERENCES:
        ! na


  IMPLICIT NONE    ! Enforce explicit typing of all variables in this routine

          ! FUNCTION ARGUMENT DEFINITIONS:
  INTEGER, INTENT (IN) :: DXCoilNum         ! Index number for cooling coil
  INTEGER, INTENT (IN) :: CyclingScheme ! Fan/compressor cycling scheme indicator
  REAL(r64), INTENT (IN) :: SHRss         ! Steady-state sensible heat ratio
  REAL(r64), INTENT (IN) :: RTF           ! Compressor run-time fraction
  REAL(r64), INTENT (IN) :: QLatRated     ! Rated latent capacity
  REAL(r64), INTENT (IN) :: QLatActual    ! Actual latent capacity
  REAL(r64), INTENT (IN) :: EnteringDB    ! Entering air dry-bulb temperature
  REAL(r64), INTENT (IN) :: EnteringWB    ! Entering air wet-bulb temperature
  REAL(r64)            :: SHReff        ! Effective sensible heat ratio, includes degradation due to cycling effects

          ! FUNCTION PARAMETER DEFINITIONS:
          ! na

          ! INTERFACE BLOCK SPECIFICATIONS
          ! na

          ! DERIVED TYPE DEFINITIONS
          ! na

          ! FUNCTION LOCAL VARIABLE DECLARATIONS:
  REAL(r64) :: Twet                 ! Nominal time for condensate to begin leaving the coil's condensate drain line
                                    ! at the current operating conditions (sec)
  REAL(r64) :: Gamma                ! Initial moisture evaporation rate divided by steady-state AC latent capacity
                                    ! at the current operating conditions
  REAL(r64) :: Twet_rated           ! Twet at rated conditions (coil air flow rate and air temperatures), sec
  REAL(r64) :: Gamma_rated          ! Gamma at rated conditions (coil air flow rate and air temperatures)
  REAL(r64) :: Twet_max             ! Maximum allowed value for Twet
  REAL(r64) :: MaxONOFFCyclesperHour  ! Maximum cycling rate of heat pump [cycles/hr]
  REAL(r64) :: HPTimeConstant       ! Heat pump time constant [s]
  REAL(r64) :: FanDelayTime         ! Fan delay time, time delay for the HP's fan to
                                    ! shut off after compressor cycle off  [s]
  REAL(r64) :: Ton                  ! Coil on time (sec)
  REAL(r64) :: Toff                 ! Coil off time (sec)
  REAL(r64) :: Toffa                ! Actual coil off time (sec). Equations valid for Toff <= (2.0 * Twet/Gamma)
  REAL(r64) :: aa                   ! Intermediate variable
  REAL(r64) :: To1                  ! Intermediate variable (first guess at To). To = time to the start of moisture removal
  REAL(r64) :: To2                  ! Intermediate variable (second guess at To). To = time to the start of moisture removal
  REAL(r64) :: Error                ! Error for iteration (DO) loop
  REAL(r64) :: LHRmult              ! Latent Heat Ratio (LHR) multiplier. The effective latent heat ratio LHR = (1-SHRss)*LHRmult

   Twet_rated               = VarSpeedCoil(DXCoilNum)%Twet_Rated
   Gamma_rated              = VarSpeedCoil(DXCoilNum)%Gamma_Rated
   MaxONOFFCyclesperHour    = VarSpeedCoil(DXCoilNum)%MaxONOFFCyclesperHour
   HPTimeConstant           = VarSpeedCoil(DXCoilNum)%HPTimeConstant
   FanDelayTime             = VarSpeedCoil(DXCoilNum)%FanDelayTime

!  No moisture evaporation (latent degradation) occurs for runtime fraction of 1.0
!  All latent degradation model parameters cause divide by 0.0 if not greater than 0.0
!  Latent degradation model parameters initialize to 0.0 meaning no evaporation model used.
   IF((RTF.GE.1.0d0) .OR. (QLatRated.EQ.0.0d0) .OR. (QLatActual.EQ.0.0d0) .OR. (Twet_rated.LE.0.0d0) .OR. &
      (Gamma_rated.LE.0.0d0) .OR. (MaxONOFFCyclesperHour.LE.0.0d0) .OR. (HPTimeConstant.LE.0.0d0) .OR. (RTF.LE. 0.0d0)) THEN
     SHReff = SHRss
     RETURN
   ENDIF

   Twet_max   = 9999.0d0 ! high limit for Twet

!  Calculate the model parameters at the actual operating conditions
   Twet    = MIN(Twet_rated*QLatRated /(QLatActual+1.d-10),Twet_max)
   Gamma   = Gamma_rated*QLatRated*(EnteringDB-EnteringWB)/((26.7d0-19.4d0)*QLatActual+1.d-10)

!  Calculate the compressor on and off times using a converntional thermostat curve
   Ton  = 3600.d0/(4.d0*MaxONOFFCyclesperHour*(1.d0-RTF))   ! duration of cooling coil on-cycle (sec)

   IF ((CyclingScheme .EQ. CycFanCycCoil).AND.(FanDelayTime.NE.0.0d0)) THEN
    ! For CycFanCycCoil, moisture is evaporated from the cooling coil back to the air stream
    ! until the fan cycle off. Assume no evaporation from the coil after the fan shuts off.
        Toff = FanDelayTime
   ELSE
    ! For ContFanCycCoil, moisture is evaporated from the cooling coil back to the air stream
    ! for the entire heat pump off-cycle.
        Toff = 3600.d0/(4.d0*MaxONOFFCyclesperHour*RTF)        ! duration of cooling coil off-cycle (sec)
   END IF

!  Cap Toff to meet the equation restriction
   IF(Gamma .GT. 0.0d0)THEN
     Toffa = MIN(Toff, 2.d0*Twet/Gamma)
   ELSE
     Toffa = Toff
   END IF

!  Use sucessive substitution to solve for To
   aa = (Gamma*Toffa) - (0.25d0/Twet)*(Gamma**2)*(Toffa**2)

   To1 = aa+HPTimeConstant
   Error = 1.0d0
   DO WHILE (Error .gt. 0.001d0)
       To2 = aa-HPTimeConstant*(EXP(-To1/HPTimeConstant)-1.0d0)
       Error = ABS((To2-To1)/To1)
       To1 = To2
   END DO

!  Adjust Sensible Heat Ratio (SHR) using Latent Heat Ratio (LHR) multiplier
!  Floating underflow errors occur when -Ton/HPTimeConstant is a large negative number.
!  Cap lower limit at -700 to avoid the underflow errors.
   aa = EXP(MAX(-700.0d0,-Ton/HPTimeConstant))
!  Calculate latent heat ratio multiplier
   LHRmult = MAX(((Ton-To2)/(Ton+HPTimeConstant*(aa-1.0d0))),0.0d0)

!  Calculate part-load or "effective" sensible heat ratio
   SHReff = 1.0-(1.0-SHRss)*LHRmult

   IF (SHReff .LT. SHRss) SHReff = SHRss ! Effective SHR can be less than the steady-state SHR
   IF (SHReff .GT. 1.0d0) SHReff=1.0d0 ! Effective sensible heat ratio can't be greater than 1.0

 RETURN

END FUNCTION CalcEffectiveSHR
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