Increase flow rate in closed loop water system

[zipp]

I have a closed loop water system with a high return pressure subsequently giving me a low flow rate. The delta across the supply to return is only 20 PSIG (supply 60 return 40). I have tried increasing the supply pressure but this has added more problems with little increase in flow rate. The system has no reservoir and has a makeup water supply attached to the return leg. Does this system need a reservoir where the return discharges at the top and pump suction at the bottom? If this is the case than will it still be considered a closed loop system?

 

[TBP]

The only thing that will give you a flow in a closed loop system is the pump, and that will only add it's energy to whatever the suction pressure is. If the pump has 60 PSI discharge pressure when it has a 40 PSI suction pressure, then 20 PSI differential is all you're going to get. If you increase the suction pressure to 100 PSI, you'll have 120 PSI discharge. Differential pressure is the only thing that will give you a flow. The higher the delta-P, the greater the flow in a given piping system.

If more flow is required, the you need a pump with more GPM, at whatever head is required to overcome the resistance of the system. Watch the velocity in your piping, as you can quite easily encounter erosion problems in a system that constantly circulates.

If you add an open tank to the system, you'll require a LOT more pumping power to get the same flow, as the pump will now only have whatever suction head is available from the tank.

What exactly does this system do? If the water is being heated, you can have air popping out of solution, and collecting at high points in the system, unless there's an air separator installed in the proper location in the loop. It also matters where the make-up is fed, etc.

 

[JLAU]

Hi Zipp,

installing an open circulating tank may give you severe corrosion problems as air will be introduced into your water. But you also need an expansion tank to get rid of any entrapped air in the system. Properly designed you can use this to control your suction pressure in the system.

I agree with TBP that you need a larger pump (flow) to increase your flow rate, and also that you should give attention to your piping that the velocity does not give cause to erosion.

JLAU