Reheat Application

[psychro]

If one is retrofitting (new ahu,new controls,new insulation) a large VAV system which have humidity problems, would you try to solve it by installing a new terminal reheats or would you rely on the new AHU and controls upgrade without the reheat terminals.
I beleive that if the AHU is selected correctly and the controls are designed correctly, the humidity problems should be eliminated unless the problem resides outside the HVAC System. All the insulation chwr&chws and duct work is been replaced also. The application is for 50%RH.

Thanks for your comments.

 

[ChasBean1]

The existing has DX or chilled water cooling? What does the new AHU have?

 

[AbbyNormal]

Are the majority of the zones having problems with high humidity?

Have you re-run the load on the system, and checked the SHR of the coil? Don't just look at design dry bulb and coincidental wet bulb, look at design ambient dewpoint parameters. Such info should be in newer ASHRAE handbooks, there is also a Humidity Control Design GUide that ASHRAE sells that was authored by Lew Harriman and others that has some good information. Probably get it at ASHRAE site or even

http://www.masongrant.com

.

I relocated 5 years ago from an extreme cold climate to a hot humid climate. They only applications here where I find that I need reheat, are where there are high latent loads due mainly to high occupant densities, like a night club, or where there is a high amount of outside air, if not even 100% outside air. I have never required reheat in an office building application.

What solves most of my humidity problems here, and I am always in cooling mode, is positive pressure with dry air.

I would try and determine why there is a humidity problem first before adding reheat.

 

[lilliput1]

Are you getting too much outdoor air?

 

[imok2]

psychro Have you considerd a heat wheel to dehumidify OSA before it get to the cooling coil? Try this web site for more info

http://www.xetexinc.com/energy_recovery/products/heat_wheels.html