Humidity Control in a Comms Room

[GAJ87]

Hi

I am working on a site. it is a brand new built building. The building is now coming near the end of its complateion and will soon be handed over to the customer. i am commissioning a close control AC unit within the comms room in the basement of this building. I have set my humidity setpoint to 45%, my low alarm sepoint is 30% and my high is 70%. the humidity in this room seems to fluctuate alot and doesnt remain consistent at its setpoint. The comms room isnt live yet so there isnt much of a load in the room.

The supplier of the unit has told me that due to it being a newly built building and te fact that there is no real load in the room, the unit will not be able to maintain consistent humidity levels at 45% and that the RH reading will fluctuate.

My question is if anyone would know, why would this be the case? how could the fact it is a newly built building affect my RH reading? and how could no load in the room affect my rh reading?

[Neddy]

What's the diff for the set point? How much fluaction are you getting? Have you seen the humidifier bottle working? Is the room a sealed room?

[Brian_UK]

You haven't stated your operating temperature.

How stable is the room temperature in the empty state?

%RH follows the temperature so compare your readings with a psychrometric chart to see if you are getting any unstable conditions.

Had a situation many years ago where the humidity rose suddenly in a room being dried out around the same every day. Found a cleaner came to sweep up the dust. How did he control the excess dust? Simple, he threw a bucket of water over the floor before he swept it up.

You never can tell. ;)

[frank]

Without a heat load, the cooling isn't doing any real work, so the latent heat removal is minimal. This means that your design levels are not being reached.

At this point, your installed equipment is oversized, therefore, cooling and humidity control will be difficult due to on/off times of your kit.

It's like trying to set superheat on a freezer room when you have just had an ambient delivery.

[AlejandroJ]

A common mistake generally done is to only depend upon the monitoring the conditions at room level and not at rack level. ASHRAE recommends 9 temperature sensors per rack

[mikeref]

Without something to chew on, your A/C is going to power down and have bugger-all influence on Humidity.