[Equest-users] Modeling Active Chilled Beams in eQUEST v3.64

Daniel Caporizzo DanielMC at BVHis.com
Tue Oct 28 07:12:21 PDT 2014

A few questions on this approach:

Do you need to have a separate plenum zone for each "regular" zone? Currently my model is set up with one plenum zone for each floor. If it's the only way to get it to work, then I will probably have to backtrack to the wizard edit mode. Not ideal but with this model I tried to minimize how much work I did in detailed edit mode.

Did you set up the OA-FROM-SYSTEM for the zones' system or just set the OA requirement for each of the zones to 0 so only the plenums have OA? Do you need to assign the people to the plenum zones as well? I assume equipment and lighting loads would stay within the "regular" zone - correct me if this is not the case.

Thank you for the catch on the static, I thought I had picked that up but I must have missed it.


From: Bishop, Bill [mailto:bbishop at pathfinder-ea.com]
Sent: Friday, October 24, 2014 11:47 AM
To: Daniel Caporizzo; equest-users at lists.onebuilding.org
Subject: RE: Modeling Active Chilled Beams in eQUEST v3.64


As an alternative to using dummy zones, I suggest trying an alternative workaround ("plenum method") I have advocated for, which may be appropriate depending on how you would design your active chilled beam system. (If your system would be constant volume, without a separate DOAS, you could just model it with the Induction Unit system type. If you want to allow for variable flow, and/or separate DOAS unit, read on.) I have had luck modeling DOAS by creating separate systems (as they are designed) and assigning them to the plenum spaces above the occupied spaces. The description of how to do this, and the merits and potential drawbacks, can be found in the "NEW (?) eQUEST DOAS workaround using plenum spaces" thread in his archive: http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/2013-November/thread.html. It would be an easy alternative for you to try modeling in your schematic model, as you have few zones and they all have plenum zones above them. Also, note that while you said your static is the same in both models, you have 1" static on supply and exhaust for the heat recovery portion of the DOAS systems, which you did not include in the VAV model. This is about 90,000 kWh as shown on the ERV reports.


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

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From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Daniel Caporizzo
Sent: Thursday, October 23, 2014 2:19 PM
To: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: [Equest-users] Modeling Active Chilled Beams in eQUEST v3.64

Hi everyone,

I am working on a project where I have to compare the energy usage between a primarily VAV system and an active Chilled Beam system. I started with the VAV system and modeled the building that way, and then made a copy to utilize active Chilled Beams. The building is a 5 story, new 400,000 SF office building.

I have heard different opinions on how to properly model this in eQuest. So far I have tried using induction units with no separate DOAS but my fan energy consumption came out at least 3x what I had for VAV. I then tried induction units with a DOAS set as their "outside air from system" but this didn't help as much. Another option, and what I am currently using is the following: Fan coil units for each zone and a VAV unit for the DOAS.

-        Each zone is set to its own FCU system

-        Building is split down the middle for main AHUs, so each DOAS serves half the building's fan coils.

-        Each DOAS system is set up with a dummy zone whose zone has the OA requirement of its system's FCUs. The dummy zone has no cooling or heating schedule (including these causes a lot of unmet hours) either.

-        FCUs are set to a secondary CHW loop with a 6 degree delta and 58 deg F supply temp, the DOAS are set to a 44 deg F and 12 degree delta on the main CHW loop. I have set my FCU with 64 deg F LAT for cooling and 83 deg F LAT for heating; these are numbers I have seen on other chilled beam designs but it was not for an office application.

-        DOAS systems each have an enthalpy wheel due to amount of OA

-        FCU air-side economizer is default at Fixed-Fraction - I noticed that changing this will drastically increase the amount of space heating energy consumption. I have tried to match it to OA enthalpy or OA temperature (what the AHU will likely be) and it is at least a 2x increase in heating energy.

-        Zoning is purely based on perimeter and core since the project is in early schematic phase.

I am very new to designing chilled beams so I am unsure if my numbers are coming out correctly. In comparison to the VAV model, my heating energy is very low (it is low in both models, which is another issue). I also noticed that my fan energy does not drastically change between systems, when the chilled beam should have a much smaller air handler. (Although my static is set the same in both models)

Has anyone had any experience with modeling chilled beams that they are willing to share?

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