# Thermodynamics (sort of) for a non engineer

#### stryped

I have a 30 by 30 shop with insulation and 10 foot ceilings. I have been reading about geothermal and it got me curious. If I were to bury 1 inch PVC type pipe and ran water and radiator fluid or water and some type of alcohol like windshield washer fluid is there a formula to determine the amount I would need to cool this building? I thought about running it through a radiator. Mind you this is mainly just an experiment. Not looking to make it as comfortable as the inside of my house but to keep temp more comfortable in the hot summer season of southern ky.
I have 5 acres. I planned to build a pipe laying attachment for my tractor. I know the only problem will be depth. I can probably get the pipe between 1 and 3 feet underground. To help compensate, i could lay rigid insulation on the top side of the trench.

What do you think?

#### Andrew Mason

Homework Helper
I have a 30 by 30 shop with insulation and 10 foot ceilings. I have been reading about geothermal and it got me curious. If I were to bury 1 inch PVC type pipe and ran water and radiator fluid or water and some type of alcohol like windshield washer fluid is there a formula to determine the amount I would need to cool this building?
Why PVC pipe? You want to design a heat exchanger. That is a system that exchanges heat between the pipes and the ground. You will need to use pipes that conduct heat.

I thought about running it through a radiator. Mind you this is mainly just an experiment. Not looking to make it as comfortable as the inside of my house but to keep temp more comfortable in the hot summer season of southern ky.
I have 5 acres. I planned to build a pipe laying attachment for my tractor. I know the only problem will be depth. I can probably get the pipe between 1 and 3 feet underground. To help compensate, i could lay rigid insulation on the top side of the trench.
It will not work at all unless there is a temperature difference between the shop and the ground. You are not using a heat pump so you are simply cooling by conducting heat to or from the ground. In order for that to work at all you need to maximize temperature difference between the shop and the ground ie. between the surface temperature and the underground temperature.

AM

#### stryped

I am hoping there will be a temperarure differential or at least a lag.
The choice of plastic pipe is because it can be purchased in coils of several hundred feet and is relatively inexpensive. Copper does not come in coils of 1 inch diameter and if it did would be astronomical in price

#### Andrew Mason

Homework Helper
I am hoping there will be a temperarure differential or at least a lag.
The choice of plastic pipe is because it can be purchased in coils of several hundred feet and is relatively inexpensive. Copper does not come in coils of 1 inch diameter and if it did would be astronomical in price
You need a heat pump. You will not be able to cool or heat your shop without using a heat pump cycle. That requires a good refrigerant fluid, a compressor, a throttle and a heat exchanger. You certainly cannot do it with plastic pipes. Just look at the back of any refrigerator. Have you ever seen one with plastic piping at the back?

AM

#### stryped

Ok. Another thing I have wondered....
I actually have a used 2 ton heat pump in storage. I have often wondered, would burying the liquid and suction lines a certain amount increase efficiency by using the earth as a sort of heat sink to reduce the hot gasses? This is a regular heat pump, not a geothermal designed one.

#### Rive

You certainly cannot do it with plastic pipes.
He can. Plastic pipes are the standard (because of the reasons OP has already mentioned) as the ground part of such systems.

If I were to bury 1 inch PVC type pipe and ran water and radiator fluid or water and some type of alcohol like windshield washer fluid is there a formula to determine the amount I would need to cool this building? I thought about running it through a radiator.
The math is ~ the same as for heating: you have a temperature difference between the inside and outside, and with the data of the house it is possible to calculate the energy needed for heating (energy needed to be removed in case of cooling). With the temperature change of water you can calculate the water flow.

But if you look around there are plenty of homepages about such calculations for heating. It is easy to adjust them for cooling.

The radiator is tricky, expect excess moisture on the cooling surface. Also, three feet might not be enough/optimal, but if you have the right type of soil there you might get it cheaper with drilled wells.

#### jim mcnamara

Mentor
This is a great thread. Let's move it to DIY where it should be.

#### jim mcnamara

Mentor
Did you try youtube? This guy seems to be doing what you want. Note that geothermal cooling also works for heating in cold months. ...since we have a divergence of opinions here, @russ_watters could help, too.

#### jim mcnamara

Mentor
I lived nextdoor to a guy who installed Geothermal in New Mexico. Per Carl H: Minimum depth has to be well below the dry line in the soil. That's the point in the driest weather you have where the soil is still moist from capillary movement of deeper water upwards. Where I live this is 8 feet.

Also consider frost depth.

Find out what those depths are where you live before you do all this work. You may have shallow bedrock, too.
Your USDA county agent can tell you all of this stuff.

"Thermodynamics (sort of) for a non engineer"

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