Best AHU configuration to reduce reheat?
Best AHU configuration to reduce reheat?
(OP)
I have an industrial building in which the ahu's are being replaced. The units are 10,000 - 15,oo cfm units. The new units will be set to provide 100% OA during the occupied hours due to chemicals in the building, and minimum OA during the unoccupied hours. The new units will have VFD's. The building owner is concerned about reducing the amount of reheat. Also, due to funding, the only energy savings device on the new units will be the vfd's - as compared to using a heat wheel or the like. The ahu's will use chilled water and hot water.
The ahu vendor and building owner disagree on the the ahu configuration that will work the best. The vendor is suggesting a typical draw-thru unit with a single cooling coil and heating coil. He wants to use the control valves to control the load and use reheat when required.
The building user has suggested using a mixed air bypass unit or a unit with two cooling coils stacked on top of each other - a smaller one on top for the RA and a larger one on the bottom for the OA - the airstreams mix prior to the coil.
Any input on which is the better way to go?
The ahu vendor and building owner disagree on the the ahu configuration that will work the best. The vendor is suggesting a typical draw-thru unit with a single cooling coil and heating coil. He wants to use the control valves to control the load and use reheat when required.
The building user has suggested using a mixed air bypass unit or a unit with two cooling coils stacked on top of each other - a smaller one on top for the RA and a larger one on the bottom for the OA - the airstreams mix prior to the coil.
Any input on which is the better way to go?





RE: Best AHU configuration to reduce reheat?
If you are maintaining two chilled water inlet temperatures, two coil arrangement is good for better energy savings. (you need not pull down chilled water temperature for high humidity condition)
Otherwise I would go with the vendor.
RE: Best AHU configuration to reduce reheat?
RE: Best AHU configuration to reduce reheat?
Unless the owner could better explain his motives, I would rule for the defendant (vendor). -CB
RE: Best AHU configuration to reduce reheat?
for anyone here to make firm recommendations.
but it seems you have recipe for disaster brewing.
You need a engineer to ascertain client
technical requirements and translate
those into specification for vendor.
If 100% OA is a requirement, why bother
with expensive VFD's - better to
redistribute load if possible. Countless
VFD running at 100% capacity for
8hr x 365days x 15 yrs seems a
total waste of resources.
Have you considered pre-purge volumes??
Too many questions and few answers I am afraid.