Ideal water velocity going to storage?

[pulse]

What is the target water velocity going to storage? I was thinking 2 fps.

 

[maple1]

That might be a tad high. I think I'm in the 1.5 range, with 1-1/4" near boiler piping & 6 GPM loading unit. Usually there are other constraints that would factor in first though. Like boiler output & GPM needed to move that & tapping sizes - then fps might just be what it is.

 

[pulse]

Ok

That might be a tad high. I think I'm in the 1.5 range, with 1-1/4" near boiler piping & 6 GPM loading unit. Usually there are other constraints that would factor in first though. Like boiler output & GPM needed to move that & tapping sizes - then fps might just be what it is.

Ok thanks. Eko 60 so max btu would be 200,000. Pump is a 3 speed 0010. I think needed gpm would be 20 at that output. If I figure right that would be a 2" to stay right around 2fps. That said I am initially planning on blocking one nozzle which will cut output in half, which would also cut needed gpm in half or less. I am plumbing a 1000 gallon tank horizontal using the 2 pipe configuration. I am trying to do as much as possible for stratification. 2" taps are fine I just want to make sure there is not going to be a problem if velocity goes below 2 fps.

 

[maple1]

I think flow on the load side is a bit more important to maintaining stratification, than flow on the boiler side, re. overall system performance. Maybe.

 

[jebatty]

Eko 60 so max btu would be 200,000. Pump is a 3 speed 0010. I think needed gpm would be 20 at that output.

That's only true if you need to move 200,000 btu when the boiler output is maximum, normally during the early to mid part of burn on a load of wood, and return to boiler from storage is at about 170F with boiler output at 190F.

Keep in mind that boiler output and btu's falls as the wood load burns down and flow can be much less than 20 gpm. Also, with delta-T of 30 flow only needs to be about 13 gpm to move 200,000 btu's, so when charging storage with a start temperature and return to boiler at 130F for example, flow can be much less than 20 gpm.

 

[pulse]

That's only true if you need to move 200,000 btu when the boiler output is maximum, normally during the early to mid part of burn on a load of wood, and return to boiler from storage is at about 170F with boiler output at 190F.

Keep in mind that boiler output and btu's falls as the wood load burns down and flow can be much less than 20 gpm. Also, with delta-T of 30 flow only needs to be about 13 gpm to move 200,000 btu's, so when charging storage with a start temperature and return to boiler at 130F for example, flow can be much less than 20 gpm.

Thank you for the reply. I realize 200,00 would be the max and probably not happen often. So do I size it for max and if so are there going to be any problems that will arise if flow goes below 2 fps.

 

[Pat53]

I'm not sure how fast mine flows to storage, but I put a 1 1/2" diffuser pipe into mine. Nothing but a threaded piece of pipe with 5/16" holes along the top and sides and a cap on the end with a small hole there also. So even if I want to run the circulator on high speed into storage, the incoming water will flow out evenly into the top of the tank only. Seems to work great.

Pat

 

[Bob Rohr]

2-4 fps is the common range for fluid velocity in hydronics.

Below 2 fps the fluid may not entrain any air and move it to the air purger, especially in vertical runs. Heat transfer in the heat emitters will drop at low velocity, the fluid needs to remain turbulent to get good heat exchange from the fluid to the wall of the emitter or heat source.

Above 4 fps you may start to hear the fluid flow, especially in metallic piping like copper or steel pipe.

Excessive velocity can also cause erosion wear in pipe and fittings.

Here is some reading from Idronics 16 if you want today that deep on the subject of flow velocity.