Moisture re-evaporation control in comm bldgs, do they have something like this?

[ICanHas]

Commercial buildings often have the fan going whenever its occupied and I read this paper on moisture re-addition problem when call for cool ends.

http://www.cdhenergy.com/presentations/CIBSE-ASHRAE%20Scotland%202003%20Part-Load%20Dehumidification.pdf

Residential usually have the fan cycle with the coil, but reevaporation is always an issue that's brought up. I know that if I leave the fan always on and compressor cycles off, I could FEEL the moist as soon as compressor kicks off and I think it smells a little funny too.

Even without advanced modulation and such, why don't they use something that simply cuts off air flow through wet coil by diverting the air like this? It couldn't be that complicated at all

http://i51.tinypic.com/2mebapt.png

[kevinnn]

The reason is a French guy, his name is Count DE MonE. It depends on what kind of system. A coil that stops refrigerating should stop producing condensate quickly leaving the coil to dry quickly. I think that reintroduction of moisture may take place more from condensate pans that hold water because they are not pitched enough rather then a wet coil. IMO they don't make systems like that is the benefits of this system design would not warrant the extra cost for extra material, space, etc on a system where the fan continues to run when a call for cool ends. No doubt that a system like that would cut down on reintroduction of moisture but to what extent? To one that would justify the extra cost of a design to by pass the coil. Such a design may exist? It probably would be more in material cost and labor, (bigger) ( sorry for the bad joke at the begining).

[genduct]

Commercial systems have continuous fan because of the need for continuous ventilation ( fresh air) Having the moisture evaporate back into the supply air is just the cost of providing that needed fresh air.

[ICanHas]

Commercial systems have continuous fan because of the need for continuous ventilation ( fresh air) Having the moisture evaporate back into the supply air is just the cost of providing that needed fresh air.

Which is why I was asking about cooling coil bypass instead of turning the fan off.

[flange]

There are indeed systems that can do that, but rarely are used, its called face and bypass. Its a more common use in heating of outside air, but there were and are some applications that have evap coil bypass. For commercial cooling, not used.

[fixitman]

There are also dedicated outdoor air systems that provide the minimum outdoor air separately from the rest of the HVAC. These are seldom used when the cooling is delivered with forced air, though - more often with systems like radiant cooling or chilled beams.