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Calculating Temperature Drop In Water, Air Over Time Period


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#1 gravelld

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Posted 02 November 2015 - 11:00 AM

I've been searching in Engineering Toolbox but I can't find this. Maybe it's very difficult to calculate?

Given a material, mass of the material, the temperature of the material, heat loss from the material and the ambient temperature is it possible to work out what the temperature of the material will be over different periods? Any variables I've missed?

Bonus points for reducing the heat loss over time as the temperature delta declines.

I'm trying to work out e.g. what the drop in temperature of water in 15mm copper pipes over a certain length would be over a certain time period. We have very long dead legs and I want to work out if it is practical to have usable hot water in the pipes if people have showers, say, 30mins apart.

I'm also interested in applying this to the air temperature of a room (ignoring ventilated losses).

#2 SteamyTea

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Posted 02 November 2015 - 11:02 AM

One of the easier things to work out.
http://www.ugrad.mat...ffeqs/cool.html

If you give a few more details, we should be able to work it out.

Is it purely theoretical or do you already have a water store you want to calculate?
If you already have a store, it is very easy.

Just read the second part.

Fill the pipe up with hot water, measure the temperature drop every minute for 15 minutes.
Plot that in excel, chart it and find then best fit trend line (should be exponential).
Extend the trend line backwards and forwards and you should get the right formula (make sure you show the formula)

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Edited by SteamyTea, 02 November 2015 - 11:14 AM.


#3 gravelld

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Posted 02 November 2015 - 11:16 AM

I knew you'd come up trumps ST. Thanks, I guess I just wasn't using the right keywords.

I don't really want to have to measure (pipes are in the loft) so I'm hoping I can use the above to work out the theoretical drop.

Edited by gravelld, 02 November 2015 - 11:17 AM.


#4 PeterW

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Posted 02 November 2015 - 12:04 PM

If you PM me an email address I will send you a copy of CIT - its produced by NMC and contains simple and complex heat loss and freeze point calcs for pipes and tanks

Cheers

Peter

#5 tonyshouse

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Posted 02 November 2015 - 12:09 PM

Pipes will always loose all their heat even if insulated, showers use so much water that the pipes will be replenished very fast

Best plan to minimise losses would to use thinnest possible pipes

Maximum cost and waste use a circulator and hot water return, even having it on a timer may help you.

#6 PeterW

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Posted 02 November 2015 - 01:22 PM

Posted the software for you :)

http://www.ebuild.co...s-cit-software/