Merits of 4 fps flow

[MarauderX]

Currently we are designing condenser water piping (40-90 degrees F water) to be flowing at 4 feet per second or less. Sure it is great for acoustics, but the piping ends up being upsized a lot along the way, and it will cost more. Another senior engineer is insisting this method of design. Will there be significant operation savings?

By the way, this is a project for the U.S. government.

http://www.eypmcf.com

 

[BigInch]

The bigger the pipe, the less energy is spent moving fluid around. As the cost of energy of a pump system's life is many many times the cost of the pump and usually the pipe too, bigger is almost always better. Do an economic analysis and determine the optimum pipe size. I'm betting that it will be close to the size you need for a velocity of 4 fps, but that depends on exactly how much pipe you do need.

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"Pumping systems account for nearly 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[katmar]

As BigInch says - run the numbers. The optimum velocity is generally higher in larger pipes than in smaller pipes so it is unlikely that an arbitrary "4 fps" will give you the best design in all cases.

If your pipe is at 40F you may need to include the cost of insulation in your economics.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[cvg]

length of piping may also have an impact. If the piping run is short, higher velocities may not result in significant head losses

 

[MarauderX]

Thanks for the responses thus far.
There is a lot of piping for the building, as this is a geothermal project of about 1500 tons. We are sizing the piping up from 12" to 16", and the branch piping is typically 4" for as little as 27 GPM.

It seemed a little arbitrary to size all of the risers & major runs (including the below ground piping) at 4 fps. I had always learned that it was better to keep the same pressure through the system.

http://www.eypmcf.com

 

[cvg]

for large, underground watermains (12" and larger) - I was taught to keep the velocity below 8 fps.

 

[Zapster]

How slow can you go? Look at the transport velocity for any debris or solids that may come out of solution. If corrosion could be an issue, the ideal velocity is somewhere above that transport velocity and below a velocity where erosion or damage to passivating films is a concern.

Slow is not always better.

 

[BigInch]

8 might be a little fast in a building with light weight heat exchange equipment and somebody around to hear any water hammering, which at times can become problematic even above 6 fps.

**********************
"Pumping systems account for nearly 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

http://virtualpipeline.spaces.live.com/