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Water density calculation, from temperature in F?

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Member Posts: 10
Hi, I've been looking for a function that takes temp in F and returns the specific
weight in lbs/f3. I can find lookup tables, and found this https://antoine.frostburg.edu/chem/senese/javascript/water-density.html but was wondering if there is a simple formula for calculating this? It can be an approximation, so long as it is suitable for hydronics. Thanks

Read some of the idronics, but may I may have missed it.

• Member Posts: 23,727
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There is no really simple formula -- lookup tables should be more than adequate. Remember that the maximum density is a 39 F, not at freezing.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
• Member Posts: 10
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Yes the problem with a lookup table is you get a figure for 39F, one for 40F and so on. If you need 39.7, then you have to workout the slope of the graph and approximate the value. Its doable but a bit rubbish.

I'm trying to write some web/javascript pages, that can calculate thermopsyphoning. I got the calcs from an old book posted somewhere on this forum.

Thing is, i really don't want to re-invent the wheel here.
• Member Posts: 23,727
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I think I have seen a formula out there somewhere... it runs to a number of non-linear terms. Great fun. Within 10 degrees of freezing, the relationship is highly non-linear, and you would need fairly closely spaced points for your interpolation. Above about or so , the relationship becomes much more linear (though never quite) and a simple interpolation between points even as much 5 degrees apart will be adequate to three significant digits -- which is all you need. Writing an interpolation routine for your program should be trivial.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
• Member Posts: 22,536
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Try engineeringtoolbox.com. They usually have tables but also show the formula or math.

Modern HydronicHeating and Cooling has a chapter on water properties. The HDS software has a module for density also.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 10
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bingo! Thanks that is perfect.
• Member Posts: 7,273
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I think Salt water freezes are 27 degrees F.  Mad Dog 🐕