User Expression referencing Zone at system level

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I am looking to utilize a user expressions that will calculate the kW/CFM for a given system. Each system is a single zone system.

Is it possible to reference the zone "Assigned-Flow" in a user expression at the system level?

I am unsure if you are able to reference a child component.. I receive an error trying something along the lines of #CR("ZONE","ASSIGNED-FLOW").


pkrystyniak's picture
Joined: 2016-11-18
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I am not so sure you can reference children in the Keyword expressions. The DOE2.2 manual does not mention child referencing. I know you can reference child components using the Compliance Analysis modules - see the ComplianceAnalysis manual but not all those commands are available in the .inp Keyword expressions. For a single zone system, the SUPPLY-FLOW is the zone ASSIGNED-FLOW times the SIZING-RATIO. ASSIGNED-FLOW (times system SIZING-RATIO) in the zone takes precedence over supply flow keywords in the system. You might do testing querying the SYSTEM SUPPLY-FLOW with ASSIGNED-FLOW set in the zone and no system supply flow specified at the SYSTEM level.

Christopher R Jones, P.Eng.
T+ 1 416-644-0252

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Jones, Christopher2's picture
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Hi Patrick,
Like Christopher said, you can't reference children. There may be other ways to do what you're trying to do without referencing the zone ASSIGNED-FLOW.
HOWEVER, for single-zone systems that use the CONTROL-ZONE keyword, the control zone is a keyword of the local component (the system).
You can reference the ASSIGNED-FLOW (or other keywords) of a control zone accordingly:
If you knew, for example, that all your systems have 300 watts of fan power, you could enter this expression for SYSTEM:SUPPLY-KW/FLOW:
This won't be as helpful in cases where you have more than one zone assigned to a single-zone system. And you'll probably want to make the expression more elaborate using an IF-THEN to account for cases where there is no assigned flow in the control zone.


William Bishop, PE, BEMP, BEAP, CEM, LEED AP
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Bill Bishop's picture
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Everything from Bill and Chris is great input/advice.

To be contrarian and add a touch of mentorship philosophy, I'm just going to come out and say something I think others may (or should) be considering.

Sometimes automation is, all things considered, slower than just doing the math. It's my personal opinion (informed from a little experience) that system fan and circulation loop pump power inputs generally fall into that camp.

There are also very real dangers in allowing anyone who cannot demonstrably "do the math" to utilize such automation. Assuming everything works and proper training is provided, you might the risk of stunting their professional development and technical potential.

Some on this mailing list have achieved (and shown me!) some amazing feats around substantial automated energy model generation, and to the extent those of you have achieved something resembling a ROI for that time investment I have and always will applaud you, however I urge extreme caution for those considering such a deep dive effort on these philosophical grounds. For the same reasons, I would be hesitant to permit someone learning under my wing to leverage such automation before ensuring they know how to "kick the tires" and develop the inputs when the automation won't work/fit the situation.

As a corollary: If you need to document (i.e. spreadsheet) this math ANYWAY for something like LEED submission, then universally you're going to spend less time doing that once vs. automating it and then doing it manually anyway.


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Nicholas Caton2's picture
Joined: 2019-03-25
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I agree that blatant automation can be a dangerous game; especially if someone does not understand how to arrive at the same values manually. I do see a potential value with automation to develop dynamic parameters within a model. In some cases, trying to develop a way to automate things is slower than just doing the math. In other cases, dynamic calculations can potentially save time after a significant design change down the road.

In this case, the fan powers will have to be input manually regardless!

Thanks for everyone's input

Patrick Krystyniak
(212) 330-6174

Stantec Consulting Services Inc.
475 Fifth Avenue 12th Floor
New York NY 10017-7239 US


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pkrystyniak's picture
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