Supply Humidity Control

[IanogPM]

Hi,

I am trying to run a simple CAV model in which the supply temp and humidity vary to control the room between 17-21 and 45 +/-10%, I havent been able to dehimidify the air with the cooling coil dispite numerous attempts, does anyone have an idea how to do this or tip on the subject?

Regards,
Ian

[farahghanem]

Just came across this, and it is really sad to see a question left unanswered like this... I seem to be running into the same issue.

Some more help on these forums would be appreciated.

[Complex Potential]

ApacheHVAC isn't exactly my specialism but I have dabbled.

From what I remember, you will first need to use a psychrometric chart to determine the min/max moisture addition/removal that's required throughout the simulation period to keep the RH values in the space where required.

On the dehum side, the simplest method is to then overcool the air down to the required moisture content and then reheat using proportional controllers with the sensed variable connected to the return flow, remembering to ensure that the cooling coil contact factor is included and realistic.

For humidification, a steam chamber is probably your best bet, again with a proportional controller sensing the return flow.

It's possible that some of the "pre made" system types that can be imported may be already set up to do this but I haven't really dabbled much since they were introduced.

Hope this helps.

CP

[bbrannon4]

What CP suggests is correct. Cooling coils are used to sub cool and dehumidify and spray chambers to humidify, just as in the real world. Many prototype HVAC systems have dehumidification built in (07a for example), but humidification is less common. It's fairly simple to add it in though. Just add the spray champer and control the outlet condition based on a measured RH value, as you would for temperature.

[farahghanem]

Thank you both for the input on this.

However, this is were the problem is actually at. Using prototype system 7 I have set the dehumidification control to demand over-cooling from the coil, however, the issue is that I keep getting high RH values in both leaving and ENTERING air temperatures... it is making me think there might be an issue with the weather file i'm using for this project (i have loaded the weather file several times to make sure it is the one being used for the simulation.)

Unfortunately the problem is not easy to describe in writing, if someone would like to take a look at the cab file please let me know.