Cooling Water in Hard Soil: Data and Questions

[ETworker]

TL;DR Summary

We’re working in Ethiopia setting up water supply schemes. The one we are currently working at has a water temp of 51° C coming out of the borehole. We are thinking to cool the water by a pipe loop in between the borehole and storage tank.

Here’s the data is can supply.
Water temperature entering ~51°C.
desired water exit temperature ~38-40°C
Water flow ~approx. 300L/min.
Pipe Inside Dia.- 51mm
Pipe Material- HDPE PN16
We would bury the pipe around 1 meter deep. Deeper is not feasible as the trenches would be hand dug in an area with hard soil.
Ground Temperature. This is a hard one. Use a temperature of 26°C. If you think it should be way different feel free to change.
We’re wondering how many meters of pipe to bury to cool said water.
Let me kno of any questions or info i missed.

 

[berkeman]

TL;DR Summary: We’re working in Ethiopia setting up water supply schemes. The one we are currently working at has a water temp of 51° C coming out of the borehole. We are thinking to cool the water by a pipe loop in between the borehole and storage tank.

Here’s the data is can supply.
Water temperature entering ~51°C.
desired water exit temperature ~38-40°C
Water flow ~approx. 300L/min.
Pipe Inside Dia.- 51mm
Pipe Material- HDPE PN16
We would bury the pipe around 1 meter deep. Deeper is not feasible as the trenches would be hand dug in an area with hard soil.
Ground Temperature. This is a hard one. Use a temperature of 26°C. If you think it should be way different feel free to change.
We’re wondering how many meters of pipe to bury to cool said water.
Let me kno of any questions or info i missed.

Welcome to PF.

I'm not very familiar with what you are doing, but I have a few clarifying questions please.

Why is the borehole water so hot? Where is this water coming from? And what is the final application for this water? it seems like the 40C water that you are wanting is pretty hot unless you need home heating (which seems like an unlikely application in that region of the world).

What have you found in your research so far about using the ground for cooling water? Have you found articles like this introductory one at Wikipedia? https://en.wikipedia.org/wiki/Ground-coupled_heat_exchanger

Also paging @russ_watters @Chestermiller

 

[256bits]

TL;DR Summary: We’re working in Ethiopia setting up water supply schemes. The one we are currently working at has a water temp of 51° C coming out of the borehole. We are thinking to cool the water by a pipe loop in between the borehole and storage tank.

We would bury the pipe around 1 meter deep. Deeper is not feasible as the trenches would be hand dug in an area with hard soil.
Ground Temperature. This is a hard one. Use a temperature of 26°C. If you think it should be way different feel free to change.

Would the hard soil mean that it is very dry?
A low heat capacity and heat conduction of the soil can limit the success of the proposed system.

Guessing at the soil temperature is a non-starter, as calculations would not reflect reality.
One should be able to drive a temperature sensor to depth to obtain readings.
Preferably, you need to find the depth at which the ground temperature is stable, although not absolutely necessary as long as the temperature of the soil is not fluctuating widely due to heat penetration from solar irradiation.

 

[russ_watters]

This question is not answerable without testing the soil's thermal conductivity with a test loop. There is far too much variation between soil types.

 

[Lnewqban]

Welcome, @ETworker !

Please,see:
https://en.wikipedia.org/wiki/Cooling_pond

https://en.wikipedia.org/wiki/Cooling_tower

 

[Chestermiller]

Isn't the hotter water going to heat up the ground around the buried pipe, which would substantially reduce the rate of cooling. Isn't the ultimate sink for the heat going to be the air above ground?

 

[256bits]

Isn't the hotter water going to heat up the ground around the buried pipe, which would substantially reduce the rate of cooling. Isn't the ultimate sink for the heat going to be the air above ground?

True.
Whether he needs 10 feet of buried pipe or a mile of it cannot be answered with the information given.
All he has is the required amount of heat flow.
It might be just as advantageous to lay out some pipe above ground.

 

[Baluncore]

It might be just as advantageous to lay out some pipe above ground.

With an exposed above-ground pipe array, water could be cooled during the night, and stored for later use.
During the day, well water could be boost heated, using the same pipes. The heated water could then be employed as a source of energy, working against ground or air temperature.