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Re: [EnergyPlus_Support] Humidity control in an Autosized AHU



Are you saying you don't have enough capacity to maintain RH, or that 
the system is not actively controlling to the RH set point? I assume you 
already have a humidistat in the control zone. What type of system are 
you using? If you are using a chilled water coil, the simple 
controller's control variable should be set to TEMPandHUMRAT and a 
single zone max hum set point manager is required to place the set point 
at the cooling coil outlet node. Report out the temperature set point 
after the cooling coil, when the RH rises above the set point, the 
temperature set point should start to drop. The higher the humidity 
rises above the set point, the lower the temperature set point after the 
cooling coil. If this happens, the system is actively controlling to the 
RH set point and it is a capacity issue. If you are using DX 
System:AirLoop object, the Run on Latent Load field should be set to YES 
and the dehumidification control type field should be set to COOLREHEAT. 
A single zone max hum set point manager is also required to place the 
humidity set point at the cooling coil outlet node. If you are using a 
Furnace or Unitary System, all that is required is setting the high 
humidity control field to YES in the furnace or unitary system object.

Elmer Morrissey wrote:

> Hello all,
>
> I am having major difficulty maintaining 50% RH in a single zone
> supplied by a simple AHU.
>
> Fresh air- -> Fan -> CC -> HC -> Hum -> -----------TRH -> Zone->-----
> ------exhaust
>
> The max humidity ratio is assigned after the cooling coil while the
> minimum humidity ratio is set after the humidifier. I am looking at
> a typical design day in a British climate and it should not be
> overtaxing.
>
> Unfortunately, the RH is not maintained during the summer months
> (even though I oversized the system sizing object). The average RH
> is around 57%. During the winter, RH values slip around mid-day for
> a four hour period that I cannot explain.
>
> I've taken a look at the setpoint output from the CSV file for the
> max and min humidity ratios and it seems to me like they just are
> not be applied within the model. I am aware that humidity control is
> not the strongest area in E+ but is there any way of creating a file
> that would work for an autosized run?
>
> Can anyone help or point out some things I may have overlooked?
>
> Kind regards
>
> -Elmer
>
>  


-- 
Richard A. Raustad
Senior Research Engineer
Florida Solar Energy Center
University of Central Florida
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Cocoa, FL  32922-5703
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Fax:     (321) 638-1439 or 1010
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