[Equest-users] Economizer issue

[Keith Swartz]

Regis,

I have a theory why your gas consumption goes up when you incorporate the discharge air temperature reset, but I don't know how to get around it. Perhaps someone more familiar with the DOE-2.2 code and algorithms can chime in. I believe it has to do with the difference between discharge air temperature and mixed air temperature.

Based on the economizer examples in the DOE-2.2 documentation "Volume 3: Topics" (p. 121-124) the economizer is controlled to a mixed air temperature setpoint. (TAPPXX in the FORTRAN code below.)

[cid:image001.png at 01CCC6D7.8A359F20]

I suspect that the economizer control is not changed by resetting the discharge air temperature setpoint. Perhaps the mixed air temperature setpoint is back-calculated from the discharge air temperature setpoint by subtracting the fan heat. I don't know for sure. Raising the discharge air setpoint might be causing the heating coil to come on and warm the air from the mixed air temperature to the higher discharge air temperature. That's my theory.

I have not found a way to access the mixed air temperature setpoint through eQUEST. Do any of you people more familiar with DOE-2 know of any BDL lines that could be added to the .inp file to adjust the mixed air temperature setpoint so that the economizer will not overcool?
________________________________
Keith Swartz, P.E., LEED AP

Energy Engineer / Senior Project Manager
Energy Center of Wisconsin
455 Science Drive, Suite 200, Madison, WI 53711
Phone: 608.238.8276 x123
Fax: 608.238.0523

The Buildings Team
Design decisions through energy, economics and emissions analysis.
www.ecw.org/Buildings<http://www.ecw.org/Buildings>

Energy Center University
Your gateway to sustainable design training and online education programs.
www.ecw.org/university/<http://www.ecw.org/university/>
From: Regis Bruant [mailto:RBruant at B2Qassociates.com]
Sent: Thursday, December 29, 2011 2:36 PM
To: equest-users at lists.onebuilding.org
Cc: Joshua Doolittle
Subject: [Equest-users] Economizer issue

Hi everyone,

I am trying to implement an economizer based on OA enthalpy on a baseline model that has an economizer set on OA temperature and have issue because I have an unexpected increased in gas usage on the proposed case.

The system I am working on consists of a VAV box containing a heating and cooling coil respectively attached to a Hot water loop and a chilled water loop (operating from March to October). It has terminal reheat coils at the zone level.

-The baseline economizer system is set on Outdoor air temperature high limit of 50F because of the low discharge air temperature of 52F.
-The proposed case economizer is set on an enthalpy high limit of 23BTU (and an OA temperature high limit of arbitrarily 100F because we want the economizer to be only limited by the enthalpy). The discharge air temperature was also reset because the system will be economizing with air temperature higher than the initial discharge temperature of 52F. It was reset from 52F to 63F as the Outdoor temperature varies from 52 to 73F.

Results:

-1st run: When running the discharge air setpoint reset based on OAT alone, we obtain substantial electrical and gas usage gain.

-2nd run: When running the discharge air setpoint reset based on OAT + the economizer based on OA enthalpy, we obtain even higher gain in electrical consumption but a lower  gas usage gain.

Results numbers:
Baseline:
Elec: 14,582,599 kwh
Gas: 646,752 therms
1st run:
Elec: 14,439,619 kwh
Gas:587,782 therms
2nd run:
Elec: 14,319,200kwh
Gas: 607,876 therms

I do not understand why there is a gas usage increase on the 2nd run in comparison to the 1st run.

Has anyone been through the same issue? It would be very helpful to share any kind of info.

Thank you for your time,

Regis Bruant
Intern
B2Q Associates, Inc.
146 Main Street #2
North Andover, MA 01845
Office: 978.208.0609 x212
Fax: 978.719.6339
Mobile: 978.810.1858
Email: rbruant at B2Qassociates.com<mailto:rbruant at B2Qassociates.com>
www.b2qassociates.com<http://www.b2qassociates.com/>

The contents of this e-mail and any attachments are confidential and the property of the B2Q Associates, Inc. The e-mail contents are only to be used by the intended recipient of the e-mail. If you are not the intended recipient then use, disclosure, copying, distribution or reliance on the e-mail is prohibited. All professional advice from us should be obtained in writing (not e-mail).

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20111230/94e51466/attachment-0002.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image001.png
Type: image/png
Size: 54344 bytes
Desc: image001.png
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20111230/94e51466/attachment-0002.png>