[Equest-users] NEW (?) eQUEST DOAS workaround using plenum spaces

Keith Swartz kswartz at ecw.org
Wed Nov 6 14:34:14 PST 2013


Hats off to you, Bill. It looks like a clever solution.

I have noticed that for some HVAC systems the wizard creates one big plenum over all the spaces and for other systems it creates individual plenums over each space below. If one big plenum was created, then you would have additional steps of breaking up the plenum and adding interior walls.

Keith Swartz, PE, BEMP, LEED AP
Senior Energy Engineer | Energy Center of Wisconsin | Madison.Chicago.Minneapolis
608.210.7123 | www.ecw.org<http://www.ecw.org/>

From: Bishop, Bill [mailto:bbishop at pathfinder-ea.com]
Sent: Wednesday, November 06, 2013 2:29 PM
To: Bishop, Bill; Hall, Brendan; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] NEW (?) eQUEST DOAS workaround using plenum spaces

Correction - ceiling surfaces are created for the conditioned spaces below the plenum spaces, so the change to "air wall" is made for the space below, not in the plenum space. You do, however, need to change the plenum zones to "conditioned" in order to assign OA to them. I'm also thinking it might make sense to assign thermostat schedules to one or more DOAS plenum zones, to control whether the DOAS is in heating or cooling mode. You could use schedules with lower heating, higher cooling temps and/or larger throttling range and/or different t-stat type, in order to avoid increasing the reported unmet load hours.

~Bill

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Bishop, Bill
Sent: Wednesday, November 06, 2013 2:47 PM
To: Hall, Brendan; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] NEW (?) eQUEST DOAS workaround using plenum spaces

You make no changes to the plenum space geometry as it is normally created via the eQUEST wizard, except to make sure there is a ceiling, and change the ceiling surface TYPE to "Air". I used the "Default Air Wall Construction" which has a U-value of 2.7 Btu/ft2-hr. I'm not sure about DESIGN-COOL-T and DESIGN-HEAT-T. I think you would want them to represent the DOAS SAT, so that the system(s) serving the occupied zones below can be autosized accordingly (as described in the DOE-2 help menu). I just noticed that you have to use "Adjust Loads" for the zone SIZING-OPTION for this effect to be included.

~Bill

From: Hall, Brendan [mailto:BHall at karpinskieng.com]
Sent: Wednesday, November 06, 2013 2:34 PM
To: Bishop, Bill; equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: RE: NEW (?) eQUEST DOAS workaround using plenum spaces

I'd say that is a pretty clever approach. Would you just add the geometry as a normal plenum zone with exterior/interior walls and such or would you just have them exist as plenum zones with only one heat transfer surface in common with each the zone(s) its serving? Wouldn't you want DESIGN-COOL-T AND DESIGN-HEAT-T to be the same as the zone it is serving? Then you could set the u value of the air wall high so that any cooling or heat that the DOAS provides would then be effectively transferred into the occupied spaces. I think in that scenario it might act as a quasi supply plenum? Not sure without actually trying it. Just my first thoughts, maybe you have already considered all that and the way you described works better.


Brendan Hall,  PE, LEED AP BD+C
Engineer, Mechanical
karpinski
ENGINEERING
3135 Euclid Avenue
Cleveland, OH  44115
P  216.391.3700<tel:216.391.3700> Ext 3111
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W www.karpinskieng.com<http://www.karpinskieng.com/>



From: equest-users-bounces at lists.onebuilding.org<mailto:equest-users-bounces at lists.onebuilding.org> [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Bishop, Bill
Sent: Wednesday, November 06, 2013 1:17 PM
To: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: [Equest-users] NEW (?) eQUEST DOAS workaround using plenum spaces

I doubt I'm the first to think of this but I don't recall it being discussed on the List. Simply put, you can model a DOAS system by assigning it to the plenum spaces above occupied spaces, and putting all OA loads in the plenum zones.
I propose the following workaround for modeling dedicated outdoor air systems (DOAS) in eQUEST/DOE-2.2:

-          Model all shells/floors with plenum spaces if they are served by a DOAS

-          Change the plenum zones ZONE: TYPE to "Conditioned"

-          Leave the plenum zone COOL-TEMP-SCH and HEAT-TEMP-SCH as "undefined" (no zone control over the DOAS operation)

-          Pick DESIGN-COOL-T and DESIGN-HEAT-T values for the plenum zones that match the likely DOAS supply air temperature range

-          Create the DOAS as a new SYSTEM (TYPE = [whatever is appropriate])

-          Assign the DOAS to the plenum zones above the conditioned zones that it actually serves

-          Assign outdoor air only to the plenum zones, representing the outdoor air requirement of the conditioned zones below

-          Create/modify internal walls between plenum zones and zones below, making them "Air walls"

This method has the following advantages:

-          No exceptional calcs or separate models needed (but see "Conditioned area" comment below)

-          All DOAS systems can be modeled as designed, within normal eQUEST constraints

-          A single DOAS system can supply ventilation air to multiple zones/systems

-          DOAS system operation and ventilation supply can be independent of the other systems serving the zones

-          Return air temperature to the DOAS closely follows that of the occupied zone, for accurate heat recovery simulation

-          Zonal systems "see" the space load from ventilation air that is not supplied at a "zone-neutral" temperature

-          DCV can be modeled, but people need to be assigned to the plenum spaces instead of the occupied spaces below (which might also be a disadvantage of this method)

-          No ventilation load changes need to be made to create the LEED Baseline from the Proposed design model, but the plenum zones need to be assigned to the baseline systems that serve the zones below.

...but has these disadvantages or does not solve these problems:

-          Conditioned floor area reported (such as in LS-C) is incorrect. Subtract the area served by the DOAS (as reported on SV-A).

-          Latent heat transfer is not simulated across interior walls. Ideally, latent loads should be assigned to the plenum spaces to represent the portion of non-ventilation latent loads handled by the DOAS.

-          Plenum space FLOOR-WEIGHT may need to be adjusted for realistic lag time and peak load damping (I haven't thought this out yet)

Please discuss!

~Bill

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

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