Dehumidify with no reheat????

[moshmont]

I have some air handlers that have economizers & preheat with only a hot deck & cold deck outlets on them. The problem I'm having is trying to keep the humidity down at 50% during the hot & humid summer days were having.
I'm running my hot deck at 85 degrees & my cold deck at 50 degrees just to keep room temperatures at about 72 with the humidity at 87% outside & 64% inside.
Is there any way I can false load in order to lower my inside humidity?

Thanks.

[thegoodlistener]

Are the economizers open and is there anyway you can slow your fan speed down?

[Control Man]

In HOT / HUMID weather decrease the amount of outside air , no need to try and cool / dehumidify OUTSIDE air while exhausting return air that has less humidity.

[flange]

with a leaving air of fifty, you may be cooling the space to quickly with an airstream that has a high rh anyway. you need to look at conditions on your handy dandy psyche chart. do the decks mix at the ahu or at each space? you could close to minimum oa, assuming its high than exhaust, and then since your return is lower than oa, use the hot deck to false load by cracking that damper open a tad raising your leaving air a few degrees. make sure bldg is positive vs oa though so infiltration doesnt come in to play and upset the apple cart.warm humid air seeping in due to being negative will create bigger issues such as condensation on those pesky fifty degree suplly diffusers.

[DeltaT]

Sounds like you just need mechanical refrigeration to dehumidify. Make sure that your economizer is not opening at all, especially during the night. The calibration of the dry bulb sensor may be off allowing the economizer to open, which is not what you want.

I'd make sure the hot deck is closed and off with no heat involved in the coil as it would unfluence the cold deck if they are close. Then slow down the fan some to get more exposure time for the air to dehumidify. Watch your drain to see if the water increases.

All this is going to take about 2 to 3 days to take effect so have patience. I'm assuming this is a large area that is being cooled. Also make sure there is no other humidity influence within or close to the space being conditioned.

That's what I'd do.

[pringlel]

If you are going to attempt to dehumidify with no reheat. Very good capacity control is key Hot gas bypass would help you reduce your capacity and still stay on line. If you dont have the load to support your min cooling requirements, then you may entertain stand alone dehumidifiers or reheat installed, If staged heat I would try to get your first staging of heat to match your min cooling capacity

[HvAckid82]

why not lower the temp of the coil?? say 44-46. That will make a big difference.

[moshmont]

So far... I lowered the coil temp to about 42, closed the economizer & exhaust dampers leaving the return dampers @ 100% & then lowered supply & return fans. This seems to be working fairly well but I'm wondering how it will be when I get a huge load increase on the temperature. I work for a music school with 2 big concert halls & things like to shift when it goes from empty to full.

[teddy bear]

Originally Posted by pringlel

If you are going to attempt to dehumidify with no reheat. Very good capacity control is key Hot gas bypass would help you reduce your capacity and still stay on line. If you dont have the load to support your min cooling requirements, then you may entertain stand alone dehumidifiers or reheat installed, If staged heat I would try to get your first staging of heat to match your min cooling capacity

I was wondering how long it would take to mention dehumidifiers. There a line of commercial dehumidifiers that can assist in humidity control. Quest and Hi-E Dry are the brands. The are high efficiency and ductable.
Regards TB

[pringlel]

Originally Posted by teddy bear

I was wondering how long it would take to mention dehumidifiers. There a line of commercial dehumidifiers that can assist in humidity control. Quest and Hi-E Dry are the brands. The are high efficiency and ductable.
Regards TB

Definitely should be more efficient because your reusing the heat from the condenser.

[moshmont]

UPDATE:

After closing my economizers, slowing the fan speeds, lowering my chilled water temp. to 42 degrees & raising my hot deck temp to about 90 degrees I've been able to keep around 74 degree room temps. with 50% humidity.

Thanks all for your help.
It's been almost a week & things are looking good!

Ray