[Equest-users] Air wall heat transfer - custom values?

[Chris Baker via Equest-users]

Bill, I smell what you're stepping in.

This is interesting because I recall Nick's team submission for the equest energy modeling competition in which all the ventilation was natural /displacement with the delta-T's affecting the airflow in some interesting ways.

Determining a "thermal conductivity" multiplier that you could factor into DOE2's equation for determining the Delta T would seem like a good way forward but this is getting into uncharted territory for me, personally, and more going under-the-hood into limits of DOE2.

But that thermal conductivity variable is further back (or down) in the calculation so you would have to use 2.7 as a known value and work backwards from there (running the Delta-T calcs backwards in an engineering sense) then recalculate the Delta T forwards again with your new value for thermal conductivity factored in with the intended value.

Because, in essence, that would be the goal -  A more accurate model - Which would require a more accurate delta-T for an air-wall system as it applies to a given scenario/schema.

And the adjacent zone(s) will always be a part of how it plays out in the final simulation.

Nick and I skyped about the nature of the air-wall systems a couple years ago but it was more of just a basic brainstorming session and I remember getting a headache at some point.

Chris Baker
CCI Alliance of Companies
Fort Wainwright, AK

From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Bishop, Bill via Equest-users
Sent: Friday, February 03, 2017 10:31 AM
To: equest-users <equest-users at lists.onebuilding.org>
Subject: [Equest-users] Air wall heat transfer - custom values?

One of the interior wall types in DOE-2 is "AIR", for which there is a default library member "Default Air Wall Construction" with heat transfer of U = 2.7 Btu/h-ft2-°F. The help menu describes this as the recommended value but gives no reference for it. How might we come up with a range of values?
I frequently model air walls for everything from open doors to transfer grills to stairwells etc. It is also critical to my method of modeling DOAS systems where I assign the DOAS to plenum spaces and the zonal systems to the spaces below.
There are many situations where I suspect the default 2.7 value is too small, such as the DOAS system method I described, or any time you have forced air systems on either or both sides of the air wall. Other examples could be displacement ventilation systems, or high bay systems with fans to avoid stratification.
The relevance of changing the number is that higher values simulate higher rates of mixing of air, and can impact the unmet hours substantially if the zone temperatures separated by the air wall have a high delta-T between them.

What say you, simulationists?
Thanks,
~Bill

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

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