[Equest-users] Appendix G Baseline Systems 6 and 8 - supply air temperature controls?

[Bishop, Bill]

I also created an input file template for System 6 which could be used for System 8 with some modification. Comments/mods are welcomed.

$ *********************************************************
$ **                                                     **
$ **                Performance Curves                   **
$ **                                                     **
$ *********************************************************

"G3.1.3.15 VAV Fan Curve fPLR" = CURVE-FIT
   TYPE             = CUBIC
   INPUT-TYPE       = COEFFICIENTS
   COEFFICIENTS     = ( 0.0013, 0.147, 0.9506, -0.0998 )
   ..


$ *********************************************************
$ **                                                     **
$ **               HVAC Systems / Zones                  **
$ **                                                     **
$ *********************************************************

SET-DEFAULT FOR ZONE
   TYPE = CONDITIONED
   MIN-FLOW-RATIO   = 0.3           $ Per G3.1.3.14
   ZONE-FAN-KW/FLOW = 0.00035       $ Per G3.1.3.14
   ZONE-FAN-RATIO   = 0.5           $ Per G3.1.3.14
   TERMINAL-TYPE    = PARALLEL-PIU  $ For all zones served by Sys 6 or Sys 8
   ..

SET-DEFAULT FOR SYSTEM
   TYPE             = PIU           $ For Baseline System 6 and System 8
   HEAT-SOURCE      = ELECTRIC      $ Per Table G3.1.1B and User's Manual p.G-23
   ZONE-HEAT-SOURCE = ELECTRIC      $ Per Table G3.1.1B and User's Manual p.G-23
   HEAT-SIZING-RATI = 1.25          $ Per G3.1.2.2
   COOL-SIZING-RATI = 1.15          $ Per G3.1.2.2
   COOL-SOURCE      = ELEC-DX           $ Per Table G3.1.1B
   MAX-SUPPLY-T     = 92            $ Per G3.1.2.8 (20F above room heat T-Stat
   HEAT-SET-T       = 62            $ = COOL-MAX-RESET-T plus 1F
   MIN-SUPPLY-T     = 56            $ Per G3.1.2.8 (20F below room cool T-Stat
   COOL-CONTROL     = WARMEST       $ Per G3.1.3.12
   ECONO-LIMIT-T    = 70            $ Per G3.1.2.7 and Table G3.1.2.6B by climate zone
   ECONO-LOCKOUT    = YES           $ (Seems like a reasonable baseline default)
   COOL-MIN-RESET-T = 56            $ = MIN-SUPPLY-T
   RESET-PRIORITY   = AIRFLOW-FIRST $ Per G3.1.3.12 and G3.1.3.14
   COOL-MAX-RESET-T = 61            $ Per G3.1.3.12 (5F above MIN-SUPPLY-T)
   OA-CONTROL       = OA-TEMP       $ Per G3.1.2.6 and Table G3.1.2.6A
   FAN-CONTROL      = FAN-EIR-FPLR                    $ Per G3.1.3.15
   NIGHT-CYCLE-CTRL = CYCLE-ON-ANY                    $ Per G3.1.2.4
   FAN-EIR-FPLR     = "G3.1.3.15 VAV Fan Curve fPLR"  $ Per G3.1.3.15
   REHEAT-DELTA-T   = 36            $ = MAX-SUPPLY-T minus MIN-SUPPLY-T
   ..

   $ Bill

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Bishop, Bill
Sent: Thursday, November 21, 2013 1:14 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Appendix G Baseline Systems 6 and 8 - supply air temperature controls?

ASHRAE Standard 90.1, G3.1.3.12 requires cooling supply air temperature reset for Systems 5 through 8.
G3.1.3.14 requires "supply air temperature setpoint shall be constant at the design condition" for Systems 6 and 8.
How should we interpret this and model it in eQUEST (for Systems 6 and 8)?

If the "design condition" in G3.1.3.14 means "peak design flow rate", I suggest the following cooling control settings:

-             COOL-CONTROL     = WARMEST

-             COOL-MIN-RESET-T = 56                    $ (assumes 76F cooling T-stat; 56F MIN-SUPPLY-T for 20F difference per G3.1.2.8)

-             RESET-PRIORITY   = AIRFLOW-FIRST

-             COOL-MAX-RESET-T = 61                   $ (5F reset per G3.1.3.12; assumes 76F cooling T-stat)

Using a RESET-PRIORITY of "TEMP-FIRST" resets the supply air temperature before the airflow, which does not satisfy the G3.1.3.14 requirement.
Using a RESET-PRIORITY of "TEMP-FIRST" or "SIMULTANEOUS" does not satisfy the G3.1.3.12 requirement, since temperature is reset well  before minimum cooling load conditions are reached.

Does anyone have an alternative/additional suggestion or interpretation?

Thanks,
Bill

William Bishop, PE, BEMP, BEAP, LEED AP | Pathfinder Engineers & Architects LLP
Senior Energy Engineer

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