coil spec : TD or LMTD

[mechman]

good day
what is the norm to spec a coil, TD or LMTD?

[B G Scott]

Depends what you are considering, are you building a coil or just applying a pre-engineered coil

[mechman]

specifying performance for pre engineered coil

[B G Scott]

Ok then you can only consider the TD as the LMTD has already been appraised by the engineer who designed the coil.
The coil selection is based on the SHR for the design and in imperial units the TD will be selected in the following range.

SHR 0.95 - 0.80 5 to 8 deg F Below ADP (apparatus dew point)
SHR 0.80 - 0.50 8 to 15 deg F Below ADP

All other factors will be tabulated by the engineer who designed the coil and correction factors for capacity against evaporating temperature will be published with the coil specification.
If this is for A/C applications then consideration of entering dry and wet bulb conditions will also have to be applied to the selection process.