[Equest-users] Modeling DOAS with a dummy zone

[Charles Land]

I would also check the outside air per person under the zones.

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Haddad, Kamel
Sent: Wednesday, March 30, 2011 1:02 PM
To: Jeremy Poling; brians at murraypc.com; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Modeling DOAS with a dummy zone

I would also add here that you can sign the OA for the system either based on "Sum of Zone OA" or "Set by Critical Zone".

When you size using "Set by Critical Zone" the system OA will be greater than the sum of the zone OA requirements to compensate for the diversity in the OA requirements of the zones.

Kamel Haddad


________________________________
From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Jeremy Poling
Sent: March 30, 2011 12:38
To: brians at murraypc.com; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Modeling DOAS with a dummy zone
Brian,

First: here's what the help file says about how the system comes up with OSA flows:

OA-FROM-SYSTEM
Takes the U-name of the system that supplies dehumidified make-up air either directly, or through the corridor, to apartments or hotel rooms. Make sure that minimum outside air of a make-up air system assigned to the corridor matches the sum of the minimum outside air flow rate of the apartments or hotel rooms. In the input, define the make-up air system prior to the apartment or hotel room system. Several Error and Warning messages are present to prevent incorrect simulations and only simple sizing calculations are available for OA-FROM-SYSTEM referenced SYSTEMs.  In previous versions of DOE-2.2 (before 44c) and 2.1E, if a SYSTEM had an OA-FROM-SYSTEM specified, the referencing SYSTEM value for MIN-OUTSIDE-AIR was reset to the MIN-OUTSIDE-AIR of the referenced OA-FROM-SYSTEM; this has been removed and replaced with the action as described next. The sum of the OA requirements for all SYSTEMs that reference an OA-FROM-SYSTEM is used to set the referenced OA-FROM-SYSTEM value for MIN-OUTSIDE-AIR, SUPPLY-FLOW as well as adjust the referenced OA-FROM-SYSTEM directly served ZONE maximum and minimum flows for both heating and cooling.  Additionally the referenced OA-FROM-SYSTEM has its calculated/specified cooling (total and sensible), heating, and preheat capacities adjusted if its SUPPLY-FLOW was increased.  If the referenced OA-FROM-SYSTEM and its ZONEs have sufficient minimum OA specified (greater than that required by the referencing SYSTEMs) no adjustments are made.  If any adjustments are made a warning is issued that informs the user of the adjustments and recommends the project be re-run with the values in the input corrected.  Also, errors are issued (and the simulation terminated) if the referenced OA-FROM-SYSTEM is either an incorrect type (a zonal system or a system that cannot have outside air) or the referenced OA-FROM-SYSTEM is not placed into the input file before all referencing SYSTEMs.


There could also be a couple of places causing the system OSA to exceed the sum of the zone OSA for each system, depending on how you set the model up:


*        If your project has a specified elevation greater than 0 then eQuest will be correcting airflows for elevation.  ASHRAE Fundamentals directs that if you're less than 1,000 ft above sea level you can usually ignore elevation effects on CFM values, therefore if that applies you can zero out that value (see below)

[cid:image001.png at 01CBEEDD.E6B759F0][cid:image002.png at 01CBEEDD.E6B759F0]


*        If you're looking at the proposed model, make sure you don't have any sizing factors in place for the system (unless you intend to run the calculations that way).

[cid:image001.png at 01CBEEDD.E6B759F0][cid:image003.png at 01CBEEDD.E6B759F0]

Jeremy R. Poling, PE, LEED AP+BDC

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Brian Smith
Sent: Wednesday, March 30, 2011 11:13 AM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Modeling DOAS with a dummy zone

Thanks for your replays to my email, it was very much appreciated. I tried modeling the doas system with a dummy zone and OA from system. While looking at my Air side reports I found that the DOAS system OSA equaled the sum OSA from each zone in each system (fine that's logical). But each system has its own OSA total which is larger than the sum of OSA requirements of its zones (not sure why). Whether I model a doas dummy or not the individual system still require the same amount of OSA. Therefore with the dummy air totals added to the system air totals my building needs more OSA and consumes more BTU's. Not sure what all this means but It would seem bad? Any insights, does this sound right? This makes me think if I could eliminate this Dummy Doas system and zones, and work in the components of DOAS into the other systems I would at least find a different result, but right?


Regards,
Brian Smith, Mechanical Design Engineer
Murray & Associates, P.C.
T/907.780.6151 F/907.780.6182
www.murraypc.com

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