Re: [EnergyPlus_Support] Help trying to procure minimal cooling load during winter from VAV system

["Michael J. Witte" <mjwitte@xxxxxxxx>]

This simulation uses SET POINT MANAGER:SINGLE ZONE MIN HUM and SET POINT 
MANAGER:SINGLE ZONE MAX HUM to control the humidifer and cooling coil, 
respectively.  The two set point managers are controlled off of different zones 
which are both set to 50%RH.

Reporting "AHU3 FAN OUTLET NODE:System Node Humidity Ratio Max" and "AHU3 
HUMIDIFIER OUTLET NODE:System Node Humidity Ratio Min" reveals that the two are 
fighting each other during the winter design day.  The min hum setpoint is 
higher than the max hum setpoint, so that is why the cooling coil kicks in and 
dries the air, but the humidifier gets the last word and adds the moisture back 
in.

How to fix this?  In this case, since both zone humidistats are set to the same 
RH, you could run both set point managers off of the same zone.  But you'll 
need to select which zone gets the good control and the other zone will go off 
RH setpoint, because the two zones apparently have different humidity loads.  
Another option might be to put some spread in the RH setpoints.  For example, 
set the max hum zone humidistat at 51% and the min hum zone at 49%.  But this 
could still result in fighting, because the min hum zone will always get the 
last word with the humidifier.

Mike


On 5 Apr 2005, at 15:10, Elmer Morrissey wrote:

> 
> 
> Hello all,
> 
> I am trying to uncover a system to service two zones with 50% rh and 
> 21oC for minimal plant use. I have attempted to implement a VAV 
> system with a heat recovery unit before the mixing box. 
> 
> Note: After the mixing box, there is a cooling coil, humidifier and 
> a supply & return fan. I have uploaded the file, it is called 
> AHU3_BenchmarkMetricHR.idf
> 
> However, the results indicate increased cooling coil load during the 
> winter months when utilising a heat recovery unit vs `no heat 
> recovery unit'. This seems to occur when the cooling coil turns on. 
> Can anyone spot why the cooling coil strips moisture during the 
> winter months (only for the humidifier to add moisture directly 
> after it)?
> 
> I appreciate any help you can give me
> 
> Kind regards
> 
> -Elmer
> 
> 
> Elmer D. Morrissey,
> Informatics Researach Unit for Sustainable Engineering (IRUSE),
> Department of Civil & Environmental Engineering/Environmental 
> Research Institute (ERI),
> National University of Ireland, Cork (UCC),
> Ireland.
> 
> ph:   00-353-21-490-2913
> fax:  00-353-21-427-7648
> 
> 
> 
> 
> 
> 
> The primary EnergyPlus web site is found at:
> http://www.energyplus.gov
> 
> The group web site is:
> http://groups.yahoo.com/group/EnergyPlus_Support/
> 
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> in the Files area of the Support Web Site.
> 
> Yahoo! Groups Links
> 
> 
> 
> 
> 
> 
> 
> 
> 



========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support      
EnergyPlus-Support@xxxxxxxx




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