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, Montr?al
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 (
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 r?sidentiel, institutionnel et des affaires
Bureau de l'efficacit? et de l'innovation ?nerg?tiques
Minist?re de l'?nergie et des ressources naturelles
5700, 4e Avenue Ouest, B-406
Qu?bec (Qu?bec) G1H 6R1
T?l?phone : 418 627-6379, poste 8060
T?l?phone sans frais : 1 877 727-6655
T?l?copieur : 418 643-5828
http://www.efficaciteenergetique.mrn.gouv.qc.ca
