Head Calculation of a hot water circulating pump

[tj00343]

Hello,
I have the following hot water system. I have a water heater with a pressurized cold water inlet. A re circulation line is taken near the farthest fixture passed through a circulating pump and back to the heater inlet. When calculating pump head, do I calculate pressure drop in the entire circuit (Supply and Return )or through the return line only. I was thinking since the supply line is already pressurized and the pump is to provide enough pressure to circulate water back to the heater. Also do I leave any residual pressure at the heater.
Thank you

 

[jrmichler]

A system diagram that shows the entire system would be very helpful. Show the point of known pressure.

The pump head is only a function of the flow rate through the pump. System head loss calculations include everything that the water flows through, from the pump outlet around to the pump inlet. The point where the supply line connects is your point of known pressure. The system pressure decreases from there to the pump suction, increases by the pump head, then decreases from the pump discharge around to the point where the supply line connects.

 

[russ_watters]

Hello,
I have the following hot water system. I have a water heater with a pressurized cold water inlet. A re circulation line is taken near the farthest fixture passed through a circulating pump and back to the heater inlet. When calculating pump head, do I calculate pressure drop in the entire circuit (Supply and Return )or through the return line only. I was thinking since the supply line is already pressurized and the pump is to provide enough pressure to circulate water back to the heater.

Yes, you just need the loss in the re-circulation line.

Also do I leave any residual pressure at the heater.

I don't understand what you mean by that.