[Equest-users] Dehumidification issue - REPOST

Wed Jun 7 13:29:18 PDT 2017

To go back to Jason’s original specific questions:

1.       How does eQUEST control the maximum humidity allowed in the supply airstream?
There is direct control of humidity in the supply airstream. Humidity is controlled by the “system” RH, which is really a return air RH.

2.       How could one possibly explain a cooling load/consumption without any cooling set point schedules in any of the zones supplied by my system and zero moisture removed from the air?
In a SINGLE ZONE system, the supply air temperature is controlled to meet zone temperature setpoint schedules. In a VAV/PIU, PVAV, CVRH system, i.e. the type of system you say you are modeling, the supply air is controlled in a variety of ways, but the simplest, and eQUEST default, is a constant 55F AHU “SAT”, i.e., discharge air temperature. If the MAT > SAT – fan dT, there will be a cooling load on the coil. If the MA WBT < SAT, which might be the case in your location, there can be sensible cooling w/o any condensation.

From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of David Eldridge via Equest-users
Sent: Wednesday, June 07, 2017 1:03 PM
To: equest-users at onebuilding.org
Subject: [External] Re: [Equest-users] Dehumidification issue - REPOST

Jason, I think one mix-up may be the lingo – if the zones or supply air have heat removed, then it is being cooled even if the cooling is provided for dehumidification purposes, or if the economizer is operating and the zones are cooled as a byproduct of dehumidification.

Where is the 60% RH setpoint entered? The system could still supply lower humidity air to the spaces in order to maintain RH in the zones. I don’t see why this would require the coil to operate though, unless the packaged system requires one control zone that has a temperature control schedule. If none was provided is one made by default?

David

David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP
Grumman/Butkus Associates

From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Ng, Jason via Equest-users
Sent: Wednesday, June 07, 2017 10:00 AM
To: Porter, Frederick NOR <fporter at noresco.com<mailto:fporter at noresco.com>>; equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: Re: [Equest-users] Dehumidification issue - REPOST

Hi Frederick,

To clarify, my zones are not cooled (no cooling schedules, i.e. no set point for cooling to be met, my zone cooling loads are ignored). The system has a cooling coil that is sized to take the dehumidification load only. The system does not attempt to maintain a maximum temperature in the zone.

[Bouthillette Parizeau]<https://urldefense.proofpoint.com/v2/url?u=http-3A__www.bpa.ca_&d=DwMFAw&c=ilBQI1lupc9Y65XwNblLtw&r=3xdcdPfNRiIRbdcNOFLTvgBFEa2F6BAz_UMLqgqXn6k&m=w1NEVziC4VmLmVJepE8gLOcGVr7oG7LrS3R7mSinOsY&s=PwSyRZlcGKiJYVKIO66R0vfqogVvHe4TAV9h75ODiX4&e=>

Jason Ng_ing. M.Sc.A.
jng at bpa.ca<mailto:jng at bpa.ca> | t: 5143833747x2813

De : Porter, Frederick NOR [mailto:fporter at noresco.com]
Envoyé : 7 juin 2017 10:46
À : Ng, Jason <jng at bpa.ca<mailto:jng at bpa.ca>>; equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Objet : RE: Dehumidification issue - REPOST

Jason,
You state that this “system” will “dehumidify air only (no cooling…” Exactly HOW does it dehumidify, if not by cooling and condensation?
Fred

From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Ng, Jason via Equest-users
Sent: Wednesday, May 24, 2017 7:14 AM
To: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: [External] [Equest-users] Dehumidification issue - REPOST

Hello all,

I posted this awhile back and received no response. Testing my luck again and hoping someone will have some insight!

Hello list,

I thought the dehumidification calculation would be a relatively straightforward calculation for QUEST, however, I have some results that are a bit puzzling.

I have a simple all-electric packaged VAV system that serves living quarters of an in-patient clinic. The system has 50% OA and uses an economizer. The system is designed to heat and dehumidify air only (no cooling, none of my zones have cooling set point schedules). My dehumidification set point is 60% RH. The building is located in Chibougamau, Quebec (quite north) where cooling and dehumidification requirements are relatively small, but still exist.  According to the SS-N report, the maximum RH is never surpassed for my system.

This is all fine and great until you start digging a bit deeper into the hourly results of the system in question. In my hourly data report I have the following variables : Total central heating/cooling coil outputs, dehumidification reheat heat output, return air humidity ratio, mix air humidity ratio, humidity ratio of air leaving cool coil, Moisture added or removed from air for (de)humidification, and maximum humidity set point. The strange thing I noticed is that my return air humidity ratio and mix air humidity ratio NEVER surpass my maximum humidity set point, yet I still have loads on my cooling coil during the summer, and moisture removed from the airstream. Furthermore, I noticed that there are 815 hours during which there is a load on the cooling coil, but no humidity is removed from the airstream whatsoever (mix air humidity ratio = humidity ratio of air leaving cool coil). My team here has experienced these results in more than 1 simulation that have a system with only dehumidification requirements on the cooling side.

So my questions are:

1.       How does eQUEST control the maximum humidity allowed in the supply airstream?

2.       How could one possibly explain a cooling load/consumption without any cooling set point schedules in any of the zones supplied by my system and zero moisture removed from the air?

Any insights would be much appreciated!

Many thanks.

  [Bouthillette Parizeau] <https://urldefense.proofpoint.com/v2/url?u=http-3A__www.bpa.ca_&d=DwMFAw&c=ilBQI1lupc9Y65XwNblLtw&r=3xdcdPfNRiIRbdcNOFLTvgBFEa2F6BAz_UMLqgqXn6k&m=QRUn_fz_LOs_iOHt_0-lov2KxZe7ZclvRy6XedxQqHM&s=Xl2kZgukQwhwIiwsR-cVKoQgFE-OJwy5oJyK0Zr8kzQ&e=>

Jason Ng_ing. M.Sc.A.
jng at bpa.ca<mailto:jng at bpa.ca>   |  www.bpa.ca<https://urldefense.proofpoint.com/v2/url?u=http-3A__www.bpa.ca&d=DwMFAw&c=ilBQI1lupc9Y65XwNblLtw&r=3xdcdPfNRiIRbdcNOFLTvgBFEa2F6BAz_UMLqgqXn6k&m=QRUn_fz_LOs_iOHt_0-lov2KxZe7ZclvRy6XedxQqHM&s=ltbl3nk22R3GJG3At72nnGWr5THYZpEEzk6UvPZ2Cj8&e=>  |  t: 5143833747x2813

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