Oversized aircon cooling design and humidity issue

[MEP.Learner]

hi Engineers,

I have a project in tropical country, and issue that aircon probably oversized and have humidity issue (more than 70% RH obtained), with mold growing on walls observed.
This may also due to hot humid air infiltration to the A/C space.
Would like to ask for advice and opinion how this can be solved.

From Trane aircon design notes that, when sensible heat ratio is lower due to certain reason (like space is at partial heat load), it will end up higher to obtain higher RH% which result in the mold issue.
See <attached> for illustration from the notes.
I am wondering, if any aircon setting can be adjusted to improve this situation.

As my system is a Chilled water system, with a adjustable fan speed FCU.
Would it help by adjusting the setting hoping to achieve lower SHR (sensible heat ratio) by getting lower off coil temperature and lower airflow air (so not too much over cooling).. so to meeting the space's SHR thus getting the moisture controlled.

Or is there is any moisture absorbing material that can be added to the system?

Appreciate if there is any valuable input. Thanks.

 

[SAK9]

If you are experiencing high RH due to oversizing,you need to address over sizing.The equipment is frequently short cycling and not operating long enough to remove the moisture from the room.There are few things like coil blank off,speed reduction which are easy fixes for capacity reduction,you need to give a better description of the area in question and the system serving the area for any meaningful advice.

 

[BronYrAur]

It is of course inefficient, but do you have the ability to reheat the air? If so, over-cool it to dehumidify and then reheat it back up to the desired discharge temp. This should be considered a temporary fix while you determine a permanent solution. It will waste a lot of energy and may be against local codes.

What is your chilled water temperature by the way? It is probably cold enough but you are probably throttling it to achieve your 65.4 deg discharge air temp. As SAK9 suggested, can you slow down the fan? Do that and keep your air as cold as possible.

 

[EnergyProfessional]

can you deliver less air at lower temp?
At a DAT of 64°F, you don't remove much if any water. A typical DAT would be 55°F. but this can vary based on what application we are talking about.
What room is that? People, production, server, waterfountain, or what?

If infiltration is part of the problem, there you go, you need to reduce that.

 

[Compositepro]

A separate dehumidifier will work much more efficiently than reheat. Even portable room units will work and provide an immediate fix.

 

[willard3]

Slow the air velocity down and drop the cw temperature.

 

[AdrienneGC]

How about ducting some fresh air into the return side of the air handler? This will do two things, it will increase the load on the equipment which will reduce short-cycling, and it will maintain a positive pressure in the building so no outdoor air is drawn into the space through any cracks or voids.


Adrienne Gould-Choquette, P.E.

http://www.adicotengineering.com