High Humidity in project

[lestopliego]

Hi everyone:
Does anyone know about equipment to control humidity? Im working on a Guatemala project where humidity is around 80% and because of that, the size of the equipment goes all the way up. I would like to know if anyone has worked with 3000 CFM dehumidifier's and how to connect it to the HVAC system.

[teddy bear]

Why do you need a 3000 cfm dehu instead of five 600 cfm dehus? The high efficiency Hi-E Dry 195 is on these units. Also the Ultra-Aire XT150H is high efficiency dehu that is made connect to a 5-10 ton a/c.
Staging smaller dehus is much more effective than one large device.
Regards TB

[lestopliego]

Thanks a lot for your help; i should add that is a 5059 sq. ft. area and my design sheets give me a load of 50 tons for the AC. These loads are high because the humidity. i was planning on using two 25 ton equipment of 10,000 cfm, and i wanted at least 25% of that flow going into a dehumidifier. What do you guys think? I live in a desert area and this is my first time working with humidity.

[pmeunier]

I suggest reading "Causes of High Relative Humidity Inside Air Conditioned Buildings" at www.aiha.org

System and building configuration make a huge difference as to how much dehumidifier capacity you need.

[tnhikr44]

Not knowing the application (type of facility), the amount of required outside air and calculated loads it is hard to say. I am no engineer, but at nearly 4 cfm per square foot (based on 400 cfm per ton) those numbers seem way way high to me. Sounds like a recipe for a cool wet building to me.

I have to add that on all the buildings I have ever worked on in 20 years, the cooling coils were exclusively responsible for moisture removal. Other than portable dehumidifiers here and there on 'lost' buildings, I have never seen dehumidifiers as part of a newly designed system. Typically I see extra cooling capacity built in for humidity control and extra re-heat capacity for temperature control (sub-cooling to remove moisture, re-heat to maintain space temperature).
I would like to know how these systems turn out. Please post results when the systems are up and running.

[lestopliego]

Yes i will, im reading the book "pmeunier" sugested. The problem with dehumidifiers is that it seems vendors dont want to sell these products....they ask for so many info...they make you fill these sheets...there must be an easier way....im not saying its easy...maybe a rule of thumb or something...ill keep you updated.

[bob_scheel]

Thanks a lot for your help; i should add that is a 5059 sq. ft. area and my design sheets give me a load of 50 tons for the AC. These loads are high because the humidity. i was planning on using two 25 ton equipment of 10,000 cfm, and i wanted at least 25% of that flow going into a dehumidifier. What do you guys think? I live in a desert area and this is my first time working with humidity.

Seasons 4, Munters, and Desert air all make air handlers that are designed to manage humidity as well as temperature. Lennox also makes RTU's that have reheat coils to allow dehumidification and humidity control.

It is far more energy efficient to have a single air handler perform both functions. Don't know what your fresh air requirements are, but in general it is easier to control humidity if the AC is closely matched to the current load. In practice this means that variable capacity in the AC system is a plus if your load is variable. At first glance having 2 25 ton units might not be ideal unless they have at least 4 stages of cooling each.

[cnay20]

Use the cooling coil to dehumidify and then a reheat coil for supply air.

[teddy bear]

Use the cooling coil to dehumidify and then a reheat coil for supply air.

Sounds like a simple dehumidifier. They remove 2 pints/pounds per KWH. The modern dehumidifiers like Ultra-Aire/Santa Fe/Quest remove upto 8 pints/lbs. per hour. Thats a fraction of the cost plus they are off the shelf plug and play system. Setout the web sites for more tech info.
Regards TB

[cnay20]

What I was trying to say is that if you only use a cooling coil and cool the air to a certain temperature....lets say you use the cooling coil to get 50F DB air off the coil and then reheat to 70F. The outgoing air would be 70DB with 50% RH. Doing it this way you would not need a humidifier and it could all be done in the AHU.