[Bldg-sim] [DOE22] ERV, air side economizer and ERV-RUN-CTRL = WHEN-MIN-OA

Julien.Dutel at mern.gouv.qc.ca Julien.Dutel at mern.gouv.qc.ca
Fri Nov 7 12:04:28 PST 2014


Context:
I'm trying to understand how DOE2.2 (EXE48r) deals with ERV plus an airside economizer on a PSZ unit (constant volume only). I've studied the economizer alone (OA-CONTROL =OA-TEMP), the ERV alone, than two others runs with both (ERV+economizer), one  with ERV-RUN-CTRL = WHEN-MIN-OA, one with ERV-RUN-CTRL = WHEN-FANS-ON.

Runs parameters :

********* 1- Econo only *********
OA-CONTROL        = OA-TEMP
DRYBULB-LIMIT     = 68
MAX-OA-FRACTION   = 0.8
ECONO-LOCKOUT     = NO
**************************

********* 2- ERV Only **********
OA-CONTROL         = FIXED

RECOVER-EXHAUST   = YES
ERV-RECOVER-TYPE  = SENSIBLE-WHEEL
ERV-SENSIBLE-EFF  = 0.6
ERV-RUN-CTRL      = WHEN-FANS-ON
***************************

*********** 3- Both (WHEN-FANS-ON) ******
OA-CONTROL        = OA-TEMP
DRYBULB-LIMIT     = 68
MAX-OA-FRACTION   = 0.8
ECONO-LOCKOUT     = NO

RECOVER-EXHAUST   = YES
ERV-RECOVER-TYPE  = SENSIBLE-WHEEL
ERV-SENSIBLE-EFF  = 0.6
ERV-RUN-CTRL      = WHEN-FANS-ON
*****************************************

*********** 4- Both (WHEN-MIN-OA) ******
OA-CONTROL        = OA-TEMP
DRYBULB-LIMIT     = 68
MAX-OA-FRACTION   = 0.8
ECONO-LOCKOUT     = NO

RECOVER-EXHAUST   = YES
ERV-RECOVER-TYPE  = SENSIBLE-WHEEL
ERV-SENSIBLE-EFF  = 0.6
ERV-RUN-CTRL      = WHEN-MIN-OA
**************************************

Results:

The WHEN-FANS-ON strategy (ERV + economizer) has the same cooling hours load that the ERV alone, but a little lower annual cooling energy (-2%).
With the WHEN-MIN-OA strategy : same cooling hours load, but a lower annual cooling energy (-21%). The 21% reduction in cooling energy compare to the 2% means the economizer plays an important role in the WHEN-MIN-OA strategy. On the other side, the runs have the same cooling hours when there is an EVR (no matter the control strategies). So with WHEN-MIN-OA, the ERV doesn't seems to stop when the economizer is active (which is not what the dictionary says)...

[cid:image001.gif at 01CFFA9C.20D62120]
note : annual OFF hours not represented. Runs make with a PSZ, Constant Volume, 56% OA fraction, Montréal


Question 1)

In the DOE2 file SYS.LIS we can read that
*****************************************************************
c              Required and maximum mixed-air temperature drop                  ERV1    28
      dTreqd = TR - TAPP                                                        ERV1    29
      dTmax  = TR - DBT                                                         ERV1    30
c              reqd OA fraction to meet setpoint                                ERV1    31
      IF (dTmax .GT. dTreqd)  THEN                                              ERV1    32
        PO = dTreqd / dTmax                                                     ERV1    33
      ELSE                                                                      ERV1    34
        PO = 1.0                                                                ERV1    35
      ENDIF                                                                     ERV1    36
*****************************************************************

Q: In a AHU with an ERV and an economizer, can we consider that the economizer "Outside air" become the heat exchanger outlet air (in the FORTRAN code above, "DBT" would become the heat exchanger outlet air temperature )?


Question 2)
In the dictionary we can read that, ERV-RUN-CTRL = WHEN-MIN-OA means that the ERV operates only when the outside air dampers are at their minimum position (i.e., the economizer is inactive). In other hand, in the file SYS.LIS we can read that:
***********************************************************
c            Check if ERV active                                             ERVnt  152
      SELECT CASE (<rv:RUN-CTRL>)                                               ERVnt  153
        CASE (1)  ! When fan on                                                 ERVnt  154
          RON = 1.                                                              ERVnt  155
        CASE (2)  ! When OA at minimum                                          ERVnt  156
          IF (OAfrac .GT. OAerv)  THEN                                          ERVnt  157
            RON = 0.                                                            ERVnt  158
          ELSE                                                                  ERVnt  159
            RON = 1.                                                            ERVnt  160
          ENDIF                                                                 ERVnt  161
************************************************************
with :
OAfrac   Fraction of supply flow thru ERV and economizer
OAerv    Fraction of supply flow thru ERV only

Q: Considering MIN-OA-METHOD = FRACTION-OF-DESIGN, does the "OAerv" variable mean the design minimum OA fraction ?

Question 3)
A last one question more macro about the ERV-RUN-CTRL = WHEN-MIN-OA strategy:
Because with ERV-RUN-CTRL = WHEN-MIN-OA, the ERV stop when the economizer is active (that what is says in the dictionary);
because the economizer is active when outside air dampers are NOT at their minimum position (inlet economiser air temperature < return air );
because the inlet economizer is the outlet heat exchanger (I'm not sure with DOE2, but this is what the reality is)

Q: does DOE22 select what would be the best choice for the mixed air temperature between these two configurations:
the ERV is active with economizer inactive (outside air dampers at their minimum position) ;
the ERV is inactive with economizer active (outside air dampers position to maximize the mixed air temperature) ?

Thank you


Julien Dutel, ing., CEM, CMVP.
Direction des secteurs résidentiel, institutionnel et des affaires
Bureau de l'efficacité et de l'innovation énergétiques
Ministère de l'énergie et des ressources naturelles
5700, 4e Avenue Ouest, B-406
Québec (Québec)  G1H 6R1
Téléphone : 418 627-6379, poste 8060
Téléphone sans frais : 1 877 727-6655
Télécopieur : 418 643-5828
 http://www.efficaciteenergetique.mrn.gouv.qc.ca<http://www.efficaciteenergetique.mrn.gouv.qc.ca/>

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