Copper maximum flow rate and manufacturer specifications

[SteveJ]

This is kind of a continuation of the https://www.hearth.com/econtent/index.php/forums/viewthread/72159/ thread.
Issue with maximum velocity as specified by copper.org (http://www.copper.org/applications/plumbing/techref/cth/cth_3design_size.html )
Below 140F up to 5 ft/s
Above 140F up to 3 ft/s

Chart show conversion for type K copper using inside diameter (http://www.sizes.com/materls/pipeCopper.htm ) to find cross sectional area and using 1 cu ft of water is 7.48 gallons (http://dnrc.mt.gov/wrd/water_rts/wreneral_info/wrforms/615.pdf )

The values agree well with the “Zoning Made Easy†rules of thumb (http://www.bellgossett.com/literature/files/810.pdf ). For example, the 4 gpm quoted in the zoning made easy for 0.75" pipe corresponds to a velocity of about 3 f/s from chart in attached image.

However, using manufacturer specifications for indirect water heater (Amtrol Boilermate http://www.amtrol.com/media/documents/boilermate/9040-586_01_09_BoilerMate_Indirect_IO.pdf – not to pick on Amtrol – I just have one!), the WH-7 series has 0.75†fittings and heat exchanger and the pump curve calls for a minimum of 5gpm flow. The minimum flow exceeds the recommended velocity for the 0.75†Cu fittings on the tank…What is wrong with my math?

PM me if you would like a copy of the Excel 2007 workbook used to generate the attached plot.

Thanks,
Steve

 

[heaterman]

Nothing wrong with your math. Just run 1" CU to the boiler mate and reduce it at that point.

I could never understand the logic of a high head heat exchanger in the boiler mate indirects. But it's definitely less expensive for them to manufacture that way.

Cheaper is seldom gooder in the hydronic world. Something somewhere is always compromised.

 

[peakbagger]

Heres a link to everything you ever wanted to know about copper

Its the Copper Tubing Handbook

http://www.copper.org/publications/pub_list/plumbing.html

There is a section on recomended velocities.

 

[in hot water]

2- 4 fps is the ideal range for air removal. Below that velocity the air will not be carried along, above that velocity the air purgers will not function as well, we test our air purgers up to 10fps.

It has more to do with noise and fitting wear when you run higher velocities. Some times commercial water piping is sized around higher velocity but it is a very intermittent flow, like a urinal flush valve for instance.

Most of the indirects that use finned copper, cupornickle or stainless coils use a small diameter tube so they can easily wind them into a bundle. Corrugated stainless tube is a new concept but has a fairly high pressure drop with that shape inside.

The smooth coil indirects that use enamaled steel or stainless can form a large diameter coil. Both types have pros and cons. I prefer the large smooth coils for larger flow capacity and less scale build up, but at the expense of the fins surface area.

Seeing as an indirect coil is generally not flowing for more that 15- 30 minutes, the higher velocity should not cause problems. if it ius a coil for heating or boiler input to a tank, running perhaps 24 hours some day, I'd lean towards the 2-4 fps rule.

Here are some examples f the various types of coils.

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