[Equest-users] Dehumidification issue - REPOST

Wed Jun 7 13:29:00 PDT 2017

Hi Fred,

You say the system will snap into overcool-reheat mode when RA humidity exceeds the limit. However according to my hourly results, 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.

>From the eQUEST help on the zone cooling set point schedule : "If not specified, the program will assume that the zone has no zone-activated cooling control. If omitted, no cooling in zone."

What else would be activating the cooling if its not my zones or my max humidity set point?

[Bouthillette Parizeau]<http://www.bpa.ca/>

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

De : Porter, Frederick NOR [mailto:fporter at noresco.com]
Envoyé : 7 juin 2017 13:24
À : Ng, Jason <jng at bpa.ca>; equest-users at lists.onebuilding.org
Objet : RE: Dehumidification issue - REPOST

Your ZONES are COOLED. By the mixed air delivered to them from  the AHU, even if that cooling effect is not "controlled" zone by zone. Hence the term economizer COOLING. Your "zone cooling loads" are not ignored. They reheat the air to a balance point zone temperature, and if that temperature is less than the heating setpoint, whatever zone heating exists should turn on.

It's not clear how the mixed air temps, and economizer, and supply air temps are controlled in the real system, which will result in more or less cooling from the central air. In eQUEST, a central AHU will snap into overcool-reheat mode when the RA humidity exceeds the limit. It may be difficult to get the PVAVS AHU to NOT turn on the cooling coil for anything except dehumidification. Various combinations of cooling control settings might get close. If you try to use "WARMEST" SAT reset, that may require zone cooling setpoints, even if those don't affect any flows. eQUEST only uses the return air RELATIVE humidity to snap into overcooling, so if the zone temperatures vary from typical, the model dehumidification may not be controlled much like the actual dehumidification.

IF the AHU uses hot gas reheat during dehumidification, that can't be input directly in my version of eQ, it needs to be input as a parametric component; "HVAC System"/"Cooling Condenser"/"Max Condenser Recovery"

Good luck.

Fred

From: Ng, Jason [mailto:jng at bpa.ca]
Sent: Wednesday, June 07, 2017 9:00 AM
To: Porter, Frederick NOR; equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: [External] RE: 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=ZcWH4Itbr9glL8LTFtKYjWHiIRUBi3WlqwQq1lNfJJw&s=f27U_cD-nklke55AoHfhgvYUFBW7cty7yiznGVpAQio&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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