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EnergyPlus™ is a whole building energy simulation program that engineers, architects, and researchers use to model both energy consumption and water use in buildings.
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Erratic humidity control when >1 piece of HVAC equipment in a zone #8243

Open JimDirkes opened 4 years ago

JimDirkes commented 4 years ago

One air loop w/ DX coil + VRF fan coil = poor humidity control

I've defined a system with one zone, one air loop, one VRF system, all supposed to control to a specified temperature and relative humidity. Temp control is good. Humidity control is not even close

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mjwitte commented 4 years ago

Initial review of the code for SetpointManager:SingleZone:Humidity:Maximum shows that the zone node mass flow rate is being used to determine the humidity ratio setpoint, which would include flow from all HVAC inlets serving that zone. It should be the system node mass flow rate - which is currently hardwired to the first inlet node but never used. So, the ultimate fix may require an additional input to specify the system inlet node name as well.

Other similar setpoint managers may have the same issue.

A possible workaround for this case is to use SetpointManager:MultiZone:MaximumHumidity:Average which appears to grab the correct flow rates. This has not been tested.

JimDirkes commented 4 years ago

I tried the SetpointManager:MultiZone:MaximumHumidity:Average at Mike's suggestion, but it does not appear to help....

[cid:978f7059-4a16-400a-bd22-6287ffd7e7a0] James V Dirkes II, PE, BEMP, BCxP Team Lead - Building Performance 616 450 8653 Foresight Management https://fsmgmt.co/ LinkedIn https://www.linkedin.com/in/jim-dirkes-4134447/

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From: Michael J. Witte notifications@github.com Sent: Monday, August 31, 2020 8:55 AM To: NREL/EnergyPlus EnergyPlus@noreply.github.com Cc: Jim Dirkes Jim@fsmgmt.co; Author author@noreply.github.com Subject: Re: [NREL/EnergyPlus] Erratic humidity control when >1 piece of HVAC equipment in a zone (#8243)

Initial review of the code for SetpointManager:SingleZone:Humidity:Maximumhttps://github.com/NREL/EnergyPlus/blob/6729dbe590f6808441d17b9ac36ba9085de91c06/src/EnergyPlus/SetPointManager.cc#L5811-L5874 shows that the zone node mass flow rate is being used to determine the humidity ratio setpoint, which would include flow from all HVAC inlets serving that zone. It should be the system node mass flow rate - which is currently hardwired to the first inlet node but never used. So, the ultimate fix may require an additional input to specify the system inlet node name as well.

Other similar setpoint managers may have the same issue.

A possible workaround for this case is to use SetpointManager:MultiZone:MaximumHumidity:Average which appears to grab the correct flow rates. This has not been tested.

— You are receiving this because you authored the thread. Reply to this email directly, view it on GitHubhttps://github.com/NREL/EnergyPlus/issues/8243#issuecomment-683759687, or unsubscribehttps://github.com/notifications/unsubscribe-auth/APMLD75DESSGHDBHIUQ3IFDSDOMSPANCNFSM4QP4QTAQ.

rraustad commented 3 years ago

I think the bigger issue here is the 2 zone inlet nodes. Both will impose a sensible and latent load on the zone such that the predicted load is no longer accurate.