Pumping to (a low loss header)

Chuck_17

I don't normally do this (I am a pump away adherent) but I am thinking about zones with pumping to a low loss header.
I just want make sure I am not missing something (other than paying attention to the pressure on the suction of the pumps).
Why:
Replacing a hot water boiler. The original steam system was converted to hot water. The supply going out of the boiler room is 4" (this is not that big a building - less than 25 GPM at 20 deg). The returns are smaller and come back to the boiler rooms more individually.
So:
If I use the 4" main as a low loss header, I can put zone pumps on the returns and add zoning to the system (it currently has one pump/zone).
Or I could piping more traditionally with one pump and put zone valves on the returns.
I like the zones pumps better just because it may be easier to control the water temperature in the big 4" pipe.
Either way the boiler would be on a secondary loop with it's own pump.

EBEBRATT-Ed

The piping resistance around the boiler loop will have virtually no resistance with 25 gpm in a 4" pipe that could carry 250-300 gpm so it probably doesn't matter how you pump it. You could put the expansion tank and pump on the boiler return and pump away from the expansion tank. This puts the discharge into the boiler. Because the boiler loop has no resistance there is no danger of the relief valve opening

Zman

It sounds like you may have an old gravity system. I either event, you should be fine pumping as you suggest. I your case it sounds like the advantages of zoning outweigh the minimal concerns of pumping into the tank.

delta T

'pumping away' is always good practice, but always keep in mind what you are trying to achieve by doing so. As @EBEBRATT-Ed pointed out, the piping is so large that you will not ever experience enough pressure drop across the pump to make any difference anywhere in the system (assuming you are using reasonably sized pumps of course).

Honestly I think your biggest problem would be that there is so little velocity in that large piping that it will lose heat on its way to the emitters. Insulation?

I think you are on the right track using pumps for zoning in this scenario given that it will allow you much better control of each zone. I would make sure to install a globe valve (not a ball valve) after each pump to be able adjust the flow on each zone.

EBEBRATT-Ed

@delta T
your right about the low velocity. LV will make it difficult to get the air out as well.