Geothermal cooling

shookbrad · 07/31/2006, 05:05 PM

Ok here is what I am going to try. I am going to burry a 55 gallon blue poly drum about 3 feet from the surface. (The top will be three feet the entire depth will be 6â€™ since the drum is 3â€™ tall) I plan on plumbing an intake and out take. I will put a pump in the sump pumping water into the drum and forcing the water out back into the sump. A Closed loop basically.

Does anyone know how to calculate heat transfer rates for water? I am curious as to how fast I need to pump the water. I am burying a thermometer about 4â€™ this afternoon so I will know the exact ground temp. I believe it will be around 76.

Any input will be great. The drum is food grade so I donâ€™t have to worry about chemicals.

daytonians · 07/31/2006, 05:18 PM

I think you would be better off digging a hole about that size, and then just putting a few hundred feet of tubing surrounded with P-gravel. You will have much more heat transfer due to the greater amount of surface are exposed.

If you happed to live where you will hit water, such as a natural spring or going deep enough to be below the water table, it will work much better.

RobbyG · 07/31/2006, 05:36 PM

I would be worried that the container may leak or that it could get contaminated by FW, Mud or pesticides during a rain storm.

I like the hose idea better and it will definetly transfer a lot more heat and is less likely to get contaminated. The only problem I see is that your hole is just way to shallow to get the real benefits. I think you need to be much deeper to take advantage of the lower temps.

shookbrad · 07/31/2006, 06:51 PM

I will dig as deep as I can. Maby it would be a good Idea to fill the barrel up with tubbing and then p gravel. I would have greater heat dispursement, etc. It only rains about three times a year here and the ground is so hard the water runs off and does not soak more than 6" to 12" into the ground.

I really am not too worried about the barrel leaking as they are designed to withstand the blazing heat and sun here in West Texas. I know the Oil field uses them to store chemicles deep in the earth and in the sun, and the EPA is way more strict and concerned with barrel leakage than anyone else.

42 · 07/31/2006, 07:37 PM

If you run the water through tubing in a barrel of gravel then it can be modeled as water flowing throug a pipe with a constant surface temperature. How are you with thermodynamics?

Itâ€™s best if we can fix all of the variables but one and calculate for that. So you can decide what your inlet and outlet temperatures are (what outlet temperature you would like that is), the length of pipe you are going to run and we could calculate the required flow rate using a method based on something called the logarithmic mean temperature difference. Also need to know the heat transfer coefficient of the pipe, or approximate it.

shookbrad · 07/31/2006, 08:57 PM

I would like a temp of 78 out. I do not know what the ground temp is yet. I am in the process of measuring that. I would say If you can give me the formula I can put it in Excel and play around with different pipe lengths and heat transfer coefficient of pipe and pipe diameter.
Any suggestions on what would be good tubing to use?

Barto · 07/31/2006, 09:33 PM

There is a large and informative thread in the DIY forum about this subject. Maybe someone with more luck than I have can find it using search function.

42 · 07/31/2006, 10:58 PM

All the units need to be SI for these formulas so temp in deg C or Kelvin, length in metres etc.

Ts = surface temperature of the pipe (deg C)
Ti = inlet temperature of the water (deg C)
Te = exit temperature of the water (deg C)
h = heat transfer coefficient of the pipe (w/m^2.K)
A = surface area of the pipe (pi x diameter x length) (m^2)
Qdot = rate of heat transfer (kW)
LMT = log mean temperature difference
massflow = mass flow rate of the water (kg/s)
Cp = specific heat of the water at the average water temperature (Ti-Te)/2, found from tables. It is 4.182 kJ/kg.K at 20 degrees Celcius or 293 K

DeltaTe = Ts â€“ Te
Delta Ti = Ts â€“ Ti

LMT = (DeltaTe â€“ DeltaTi) / ln(DeltaTe/DeltaTi)

Qdot = h x A x LMT

Qdot = massflow x Cp x (Te â€“ Ti)

Rearranging for the mass flow rate gives:

massflow = (h x A x LMT) / (Cp x (Te â€“ Ti))

This is making some big assumptions about the earth around the pipe conducting the heat away and staying at a constant temperature. Ideally you would look at the heat transfer through the soil also.

shookbrad · 11/19/2006, 08:53 PM

Ok, Here are pics of the tank in the ground. I could only get the top of the barrel about 20" below the surface. I was worried that would not be enough. So far is seams to be deep enough.

I will post temperature data soon.

07/31/2006, 05:05 PM	#1
shookbrad Registered Member Join Date: Aug 2005 Location: Odessa, TX Posts: 411 Blog Entries: 1	Geothermal cooling Ok here is what I am going to try. I am going to burry a 55 gallon blue poly drum about 3 feet from the surface. (The top will be three feet the entire depth will be 6â€™ since the drum is 3â€™ tall) I plan on plumbing an intake and out take. I will put a pump in the sump pumping water into the drum and forcing the water out back into the sump. A Closed loop basically. Does anyone know how to calculate heat transfer rates for water? I am curious as to how fast I need to pump the water. I am burying a thermometer about 4â€™ this afternoon so I will know the exact ground temp. I believe it will be around 76. Any input will be great. The drum is food grade so I donâ€™t have to worry about chemicals.

07/31/2006, 05:18 PM	#2
daytonians Registered Member Join Date: Jun 2003 Location: Cincinnati, Ohio Posts: 394	I think you would be better off digging a hole about that size, and then just putting a few hundred feet of tubing surrounded with P-gravel. You will have much more heat transfer due to the greater amount of surface are exposed. If you happed to live where you will hit water, such as a natural spring or going deep enough to be below the water table, it will work much better. __________________ Thanks, Matt I'ld rather be in Daytona! Avatar: Photo taken with model Asia Williams posing on my car. Current Tank Info: 45 Gallon, LR, power head, custom hood with 140 watts PC light & 175 MH, basement has 29 g. fuge with 6" sand & caluerpa, 20 g. cryptic fuge with 4 inch sand bed & LR, carbon & Phos remover, 55 gallon sump.

07/31/2006, 05:36 PM	#3
RobbyG Registered Member Join Date: Jun 2005 Location: 600 Ft From the Reef Posts: 2,099	I would be worried that the container may leak or that it could get contaminated by FW, Mud or pesticides during a rain storm. I like the hose idea better and it will definetly transfer a lot more heat and is less likely to get contaminated. The only problem I see is that your hole is just way to shallow to get the real benefits. I think you need to be much deeper to take advantage of the lower temps. __________________ The Optimist says the glass is half full, the Pessimist says it’s half empty, an engineer only see's a glass that’s twice as big as it needs to be! Current Tank Info: Insanely Automated Low Power Consumption 90 Gal Oceanic Bow System/Aquatronica Touch Controller/AQ Dosing Pump/AQT LEDS/AQ SMS/Seq Dart Pump/ASM G3/Ozotech Ozonizer/Koralin 1502/Chiller/Typhoon3 Ro/S.Squirt /Phos React/Rmt DSB

07/31/2006, 06:51 PM	#4
shookbrad Registered Member Join Date: Aug 2005 Location: Odessa, TX Posts: 411 Blog Entries: 1	I will dig as deep as I can. Maby it would be a good Idea to fill the barrel up with tubbing and then p gravel. I would have greater heat dispursement, etc. It only rains about three times a year here and the ground is so hard the water runs off and does not soak more than 6" to 12" into the ground. I really am not too worried about the barrel leaking as they are designed to withstand the blazing heat and sun here in West Texas. I know the Oil field uses them to store chemicles deep in the earth and in the sun, and the EPA is way more strict and concerned with barrel leakage than anyone else. __________________ No, That fish is not new. He's just use to the tank now. Current Tank Info: 220G, 107G Cylender, 42G Hex

07/31/2006, 08:57 PM	#6
shookbrad Registered Member Join Date: Aug 2005 Location: Odessa, TX Posts: 411 Blog Entries: 1	I would like a temp of 78 out. I do not know what the ground temp is yet. I am in the process of measuring that. I would say If you can give me the formula I can put it in Excel and play around with different pipe lengths and heat transfer coefficient of pipe and pipe diameter. Any suggestions on what would be good tubing to use? __________________ No, That fish is not new. He's just use to the tank now. Current Tank Info: 220G, 107G Cylender, 42G Hex

07/31/2006, 07:37 PM	#5
42 Registered Member Join Date: May 2004 Location: Perth, Western Australia Posts: 29	If you run the water through tubing in a barrel of gravel then it can be modeled as water flowing throug a pipe with a constant surface temperature. How are you with thermodynamics? Itâ€™s best if we can fix all of the variables but one and calculate for that. So you can decide what your inlet and outlet temperatures are (what outlet temperature you would like that is), the length of pipe you are going to run and we could calculate the required flow rate using a method based on something called the logarithmic mean temperature difference. Also need to know the heat transfer coefficient of the pipe, or approximate it.

07/31/2006, 09:33 PM	#7
Barto Alleged Lounge Moron Join Date: Jan 2006 Location: BigSkyCountry Posts: 459	There is a large and informative thread in the DIY forum about this subject. Maybe someone with more luck than I have can find it using search function. __________________ "Outliving our pets is the price we pay for the unconditional love they give us" ~Barto's Mom~ AUGUST 2009 TOTM! Current Tank Info: no more fish tanks, nothing, nada, gone!

07/31/2006, 10:58 PM	#8
42 Registered Member Join Date: May 2004 Location: Perth, Western Australia Posts: 29	All the units need to be SI for these formulas so temp in deg C or Kelvin, length in metres etc. Ts = surface temperature of the pipe (deg C) Ti = inlet temperature of the water (deg C) Te = exit temperature of the water (deg C) h = heat transfer coefficient of the pipe (w/m^2.K) A = surface area of the pipe (pi x diameter x length) (m^2) Qdot = rate of heat transfer (kW) LMT = log mean temperature difference massflow = mass flow rate of the water (kg/s) Cp = specific heat of the water at the average water temperature (Ti-Te)/2, found from tables. It is 4.182 kJ/kg.K at 20 degrees Celcius or 293 K DeltaTe = Ts â€“ Te Delta Ti = Ts â€“ Ti LMT = (DeltaTe â€“ DeltaTi) / ln(DeltaTe/DeltaTi) Qdot = h x A x LMT Qdot = massflow x Cp x (Te â€“ Ti) Rearranging for the mass flow rate gives: massflow = (h x A x LMT) / (Cp x (Te â€“ Ti)) This is making some big assumptions about the earth around the pipe conducting the heat away and staying at a constant temperature. Ideally you would look at the heat transfer through the soil also.

11/19/2006, 08:53 PM	#9
shookbrad Registered Member Join Date: Aug 2005 Location: Odessa, TX Posts: 411 Blog Entries: 1	Ok, Here are pics of the tank in the ground. I could only get the top of the barrel about 20" below the surface. I was worried that would not be enough. So far is seams to be deep enough. I will post temperature data soon.