| Most of the guys are running a foot temperature of 130f - 140f on the mod/cons for duct coils. I know more of the manufacturers are raising the foot temp from the factory set at 130f. If you want to turn it down you you may be required to use a password to get into the parameters for lowering the temp.
At 9% CO2 this is not a condensing range.
We cannot determine a 20f delta tee in a system unless it is designed as such. This means having the proper coil size for 140f water and of course the proper flow rate for a 20f delta-T. How many times does this happen in real life. We also assume a 20f delta-T in radiation which only happens at design water temperature. If the system was not designed, just installed BB on all exterior walls, what is that water temperature supposed to be? Who knows. For BB it is normally stated at 180f. That is at the designed flow rate. A system with a 20f delta-T at 180f water may only have a 10f delta-T at 140f. (Just guessing at this Delta-T). Try it sometime. Get a cold zone, cold boiler, and watch the delta-T change as the supply water temperature changes.
If you want a 20f delta-T in a duct coil you need to know what the spec's are from the manufacturer of the coil to match your heat loss. They can supply you with the flow rate, cfm and entering water temperature.
That means sizing the pump properly, sizing the pipe properly not just looking at the tapping on the coil, installing a circuit-setter for proper flow, and properly adjusting the fan. Unfortunately only has 3 or four speeds to choose from or variable fan. This is a better application.  |