blow thru and draw thru AHU?
blow thru and draw thru AHU?
(OP)
How to choose the right type for any application ?
appreciate any assistance you can give.
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blow thru and draw thru AHU?
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RE: blow thru and draw thru AHU?
Steamguy2
www.SteamPlantEngineering.com - Discussion & resources for professionals in the Power Generation Industry
RE: blow thru and draw thru AHU?
In general if you have requirement for high airchanges per hour and the sensible and latent loads are not that high, blow thru will require less coling tons because the fan heat will be on the entering side of the coling coil, not on the leaving side. But be warned per above.
RE: blow thru and draw thru AHU?
lilliput1: thanks, your reply is very useful to me
RE: blow thru and draw thru AHU?
give yourself 15' clear downstream of humidifier to final filters
RE: blow thru and draw thru AHU?
As to blow through versus draw through, it (blow through design) is helpful in allowing placement of the heating coils (especially when hot water coils with their higher pressure drop)in the reheat position. Most fans are better utilized with higher pressure drops placed downstream of the fan.
The placement of the fan motor (unless in an unconditioned space not a part of the conditioned load, such as an external mount in a fully ducted system)does not affect the amount of heat imparted to the system, only whether it is absorbed by the coil before or after passing through the conditioned space. Sometimes, such as in dehumidification systems, placement of the fan motor within the airstream after the cooling coil is an advantage.
RE: blow thru and draw thru AHU?
RE: blow thru and draw thru AHU?
and I've got another in design
RE: blow thru and draw thru AHU?
I would typically use a plenum type fan as well for any air handling unit that included a discharge sound attenuator, final filter bank, humidifier or anything else that prohibited a direct duct connection to fan discharge.
In the State of Washington, hospital regulations require that steam injection type humidifiers be located a minimum of 15' downstream of the final filter bank. I agree.
In this region as well, I can't recall a new dual-duct system for at least 10 years, probably longer. The last one I rememeber was a VAV changover type that used both ducts for cooling in the summer. My boss at the time did that, and he received ample recognition. Although they go overboard in some areas, energy codes around here make us count BTU's quite carefully. We use single-duct terminal reheat with demand-based LAT and HWS temperature reset, CV in areas with pressure relationships, and VAV using FTU's in other locations. I too use twin supply fans, however, they are typically located in completely independent side-by-side custom AHU's equipped with isolation and cross-over dampers such that either side can feed both duct systems at about 75% of design air flow when the adjacent unit is out of service for any reason.
Regarding the "green" final filters downstream of a blow-thru DX coil, I recall discussions with the filter manufacturer about the influence of filter air pressure drop upon vapor pressure - no kidding. This was not news to them, but we never received a definitive answer and I was not in a position to conduct a research project.
For this same client, I later employed a dual temperature CWS sytem and 2 chilled water coils in series for the surgery AHU - again, a side-by-side arrangement. Base load chillers fed first coils and remainder of campus at normal CWS temperatures. Part load chiller fed second coils at depressed CWS temperatures during the summer, and the entire campus during the winter. Great way to go if geography permits. The improved ability to clean two shallow coils is another bonus.
Much more than 2 cents!
RE: blow thru and draw thru AHU?
it seems to me that draw thru is the safe selection for AHU (pls. correct me)