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How to get the Cold (inlet) water temperature?

asked 2015-07-23 12:03:12 -0500

georges's avatar

updated 2016-04-23 17:55:59 -0500


Hi, I am quite new to EnergyPlus, and have been using DOE up until now. I want to find out, how does EnergyPlus calculate the Cold (inlet) water temperature? I googled a bit, and looks like the term EnergyPlus uses is: "Water Mains temperature" instead of "Cold water temperature". I found an equation for EnergyPlus 8.3 Water Mains temperature in here:

The thing that I am confused of, is lack of pipes depth input.

DOE2 uses the following equation to calculate the Cold (inlet) water temperature ("Carslaw and Jaeger semi-infinite medium conduction equations"):

It has an input for both the pipes depth and soil type. It is also used to calculate the hourly cold water temperature while EnergyPlus one, seems to give only the daily value.

I would be very grateful for any clarification on this would.

Thank you.

EDITED on 10pm (UTC -5:00).

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There is a lot of discussion on this topic, you might see if one of these existing posts answer your question.

David Goldwasser's avatar David Goldwasser  ( 2015-07-23 12:58:23 -0500 )edit

Thank you for the reply David. Maybe I should have been more precise from the very start: I am actually looking for a ground temperature so that I could calculate the cold (inlet) water temperature for domestic hot water loads. I am quite new to EnergyPlus, in DOE2, this variable is defined as: cold (inlet) water temperature. Does this change your reply? From what I have seen by the link you provided these are mostly "Ground Heat Transfer in EnergyPlus" questions.

georges's avatar georges  ( 2015-07-23 15:58:06 -0500 )edit

@georges, can you edit your question to reflect your comment above? That way other users can understand better what you are asking for. Thanks!

Neal Kruis's avatar Neal Kruis  ( 2015-07-23 16:40:18 -0500 )edit

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answered 2015-07-23 16:36:56 -0500

updated 2015-07-23 18:32:34 -0500

Try using the Site:WaterMainsTempearture object. You can use Calculation Method = "Correlation" to have EnergyPlus calculate what the inlet water temperature based on the outdoor temperatures of your climate.

The article you reference seems to be a similar correlation (E3.3) that uses the Kusuda-Achenbach equation with an assumed depth of 10ft. This correlation was originally intended for undisturbed ground temperatures (i.e. ground far away from buildings).

The EnergyPlus correlation is based on work developed by Christensen and Burch based on actual water mains temperatures. You can see that the correlations actually have a very similar form, but I'd generally trust the EnergyPlus correlation over the other.

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Hi Neal. Thank you for the reply. Would you please take a look at the edited version of my initial reply? Thank you and I apologize once again for not clarifying the issue from the very start.

georges's avatar georges  ( 2015-07-23 17:04:16 -0500 )edit

Thank you Neal. Do you know whether or not there is an hourly version of the Christensen and Burch formula? I can not use the daily one.

georges's avatar georges  ( 2015-07-24 02:33:44 -0500 )edit

Hi Neal. Do you happen to know at which depth does Christensen and Burch formula calculate the water mains temperature? Thank you.

georges's avatar georges  ( 2015-07-28 05:26:52 -0500 )edit

As each building has inlet mains at different depths, I believe the correlation is independent of depth. I think the depth variable is in the noise of the data they collected.

Neal Kruis's avatar Neal Kruis  ( 2015-07-28 09:26:49 -0500 )edit

Thank you Neal.

georges's avatar georges  ( 2015-07-28 09:43:22 -0500 )edit

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Asked: 2015-07-23 12:03:12 -0500

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Last updated: Jul 23 '15