Estimating groundwater temps

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Hi everyone,

I have a situation where I want to estimate the seasonal variance in the potable domestic water supply as a function of atmospheric drybulb temperatures. I *think* eQuest has some algorithm to derive 12 (monthly average) temperatures from the weather file data for makeup/DHW purposes... however after scanning the 2.1e engineers manual and a first pass at trying to find some helpful entry in the resource manual, I'm coming up dry so far.

I'm trying hoping to source the equations & assumptions used for this estimation, so that I can modify it to fit my project. I'm not specifically married to matching eQuest's output - any similar process/formulae would be welcome.

Any suggestions?

~Nick

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Nick Caton, P.E., BEMP
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Schneider Electric

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Hey there Nick,
Weather files such as TMY2 and TMY3 include monthly ground temperature data. I don't know how the data is generated but I believe it's based on methodology in ASHRAE Handbook - Fundamentals.
According to the help documentation, the DHW-INLET-T and DHW-INLET-T-SCH default to the monthly ground temperatures from the weather file. You can create a custom hourly report block to report the ground temperature -ground temp is one of the global variables. You can also use DOE2 weather utilities to convert weather files to readable text files. For example, STAT.BAT generates a summary of statistical data that includes the monthly ground temperatures.

Happy Thursday,
~Bill

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If you want to get real accurate, the percentage of hot water to cold water varies seasonally as well.

Users like hotter water in the winter to warm up (hand wash and showers), and colder water in the summer because it?s more refreshing.

Not sure there?s a good reference out there for this, but thought I would muddy the waters some more ?.

Fred

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Fred Betz's picture
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Hi Nick,

I wrote an Openstudio measure on the subject in which I included a supporting excel file that will help you calculate that. You can just download the xlsx in the right column here and ignore the rest:
https://bcl.nrel.gov/node/83628

E+ engineering documentation for the Burch and Christensen correlation:
?https://bigladdersoftware.com/epx/docs/9-0/engineering-reference/water-systems.html#water-mains-temperatures.

Cheers,
Julien
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