very high chilled water flow effect.

[naifmbo]

will increasing the flow in ahu's coil for (say 300% the design value) decreases the heat transfer from the air to the water?

 

[cub3bead]

I know one problem you will likely encounter- erosion corrosion. The ahu's coil is likely copper or a copper alloy. Pushing the chilled water flowing velocity much above 8 fps will erode the tube material.

 

[TBP]

It's a zero sum game. You only have so many BTU/hr to work with. You can have a big delta-T with a smaller GPM, or increase the GPM and take a smaller delta-T. If you have a coil designed to handle 100 GPM with a 10*F delta-T, that's 500,000 BTU/hr. If you jack up the flow to 300 GPM, then if you only have that same 500,000 BTU/hr capacity available, then the delta-T drops to 3.3*F.

Other factors come into play as well, such as exceeding acceptable pressure drop across the coil, piping, valves, etc, which will probably show up as nasty erosion problems, as suggested by cub3bead.

 

[25362]

All this is because the heat transfer resistance is on the air side. The overall heat transfer coefficient, U, will, by definition, always be lower than the air side coefficient.

Thus, when applying the formula for heat, Q = UA.[Δ]T
you may notice that practically nothing changes when circulating more water than designed for.