Space plenums have cooling load

5 posts / 0 new
Last post

Hi All,

I have assigned all the space plenum as unconditioned. But it still shows
cooling load for those space, which increase the Space Cool in the report.
The plenums in the proposed model have much higher cooling load than the
baseline one. How could I modify it?

Thank you!

Jing

Jing Hong's picture
Offline
Joined: 2011-09-30
Reputation: 0

Hi Jing,

It seems unintuitive to assert that your proposed case plenums has increased cooling loads ? is there a good set of reasons for this?

I?m also unclear on what you mean by ?it still shows cooling load for those space? ? could you unpack this a little further?

Systems which use the plenums as a return air path could be a cause for why their loads are seen at the systems (though it sounds like you intend for them to be isolated). I might start with considering the sources of heat gains to your plenums, and determining what should be happening to direct/indirect heat gains to plenums over time. Should they be circulated back to systems responding to conditioned spaces? Common sources would include indirect gains from ceiling lighting fixtures, envelope (skin) loads (potentially exacerbated if spandrel glass is present), and internal loads transferred hourly from conditioned spaces below and from adjacent plenums.

If I had your model in-hand, I might scan for the presence of thermostat heating/cooling schedules being assigned to your plenum spaces, or assignments to a plenum space as a master zone for specific system types. Those could produce direct calls for airstream heating/cooling which otherwise wouldn?t be occurring.

~Nick

[cid:image001.png at 01D3D669.FC53D920]
Nick Caton, P.E., BEMP
Senior Energy Engineer
Regional Energy Engineering Manager
Energy and Sustainability Services
Schneider Electric

D 913.564.6361
M 785.410.3317
F 913.564.6380
E nicholas.caton at schneider-electric.com

15200 Santa Fe Trail Drive
Suite 204
Lenexa, KS 66219
United States

[cid:image002.png at 01D3D669.FC53D920]

Nicholas.Caton at schneider-electric.com's picture
Joined: 2016-02-26
Reputation: 0

Hi Nick,

Thanks for your reply. Coz my proposed U-value is worse than the baseline,
it is normal that the baseline has a bit lower cooling load than the
proposed. However, the plenum cooling load in the baseline is way much
lower than those in the proposed, which should not be.
I figured it out. First, I realized that I should use "Plenum" instead of
"unconditioned" . But it did not change too much. Second, I duplicated the
proposed model, saved as Baseline, and then modified it with baseline
information.
After modifying the model so many times, I might mess up some physical
characteristics of the Baseline model. Starting over is easier than keeping
debugging it. Especially, for a case, you cannot find the error for hours.
Hopefully, it is useful for some of you.

Jing

Jing Hong's picture
Offline
Joined: 2011-09-30
Reputation: 0

I?m happy to hear you found a resolution!

I do think it?s generally good practice to build your proposed/actual case fully before generating a prescriptive baseline, where the baseline inputs inevitably depend upon details and decisions of the proposed case. ?Starting over? with your baseline is a hard call to make before you?ve done it a few times and can perceive when that?ll be the path of least resistance.

~Nick

[cid:image001.png at 01D3D670.D4736590]
Nick Caton, P.E., BEMP
Senior Energy Engineer
Regional Energy Engineering Manager
Energy and Sustainability Services
Schneider Electric

D 913.564.6361
M 785.410.3317
F 913.564.6380
E nicholas.caton at schneider-electric.com

15200 Santa Fe Trail Drive
Suite 204
Lenexa, KS 66219
United States

[cid:image002.png at 01D3D670.D4736590]

Nicholas.Caton at schneider-electric.com's picture
Joined: 2016-02-26
Reputation: 0

I typically set the plenum space to CONDITIONED and the plenum zone to PLENUM. That seems to provide reasonable loads in the plenum.

Christopher R. Jones, P.Eng.
Technical Specialist
Sustainability & Energy

[cid:image003.png at 01D3D68E.B15898F0]
T +1 416-644-0252

2300 Yonge Street, Suite 2300
Toronto, ON M4P 1E4 Canada

wsp.com

Please consider the environment before printing...

Jones, Christopher2's picture
Joined: 2017-10-12
Reputation: 0