Fancoil pressure drop

BC_3

Maybe the flow meter itself has a significant pressure drop? the pressure drp through some meters is huge as they approach max flow. They should have data on this. Maybe the spring check, although I wouldn't think that would contribute much.

Tom Hopkins

Pressure drop -- fancoil system

I have an ESP HE-50 hot water fancoil connected to a standard 75 gallon direct vent tank type water heater.

The mfgr calls for 5GPM through the fancoil which is 1/2" copper. Literature states that there is 5ft/hd drop through the fancoil. The rest of the piping is about 20' of 3/4" copper to and from the tank. 1 spring check. With a Grundfos 15-42 pump on high I am getting only 2.5GPM through the loop!

The pump curve of this unit tells me that at 2.5GPM I have about 16 ft/hd. Where is all this resistance coming from?

The two items I have considered are:

1) Because of space considerations I do not have 5 straight inches before and after the pump. The pump is just after a 90° elbow out of the fancoil. Does it matter that much?

2) I have returned the fancoil to the cold water inlet (dip tube) of the water heater. Is there that much resistance through the tank? Would it matter if I returned it to the drain fitting at the bottom of the tank where the hot water re-circ is located?

I'm pleased I put a flowmeter on the system to see what is really going on, but am suprised that I would need so much pump to get my flow rate.

Who's got insight on this one?

Thanks,

Jacob

tim smith

flow rate

I wonder if your flow meter is right. Was is the delta T of air side. What about checking your actual pressure drop across fan coil. either one of these can tell you what actual flow rate is. Tim

Tom Hopkins

Flow Meter

The flow meter itself is very accurate. A blue white graduated cylinder type. However it IS installed right after the pump where there may not be good laminar flow.

I do not have the ductwork connected yet so I do not have the delta T of the water in and out.