Author Topic: DIY Geothermal sizing for shed  (Read 18845 times)

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Atokatim

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DIY Geothermal sizing for shed
« on: September 28, 2014, 12:49:42 PM »
Well, here I am again with another project that has sparked my interest.  Since I am testing all of my projects on my shed, I am looking to build a geothermal heating / cooling system for my shed.  I don't have a massive budget for this so I need to keep as much cost down as possible.

Luckily, I work at a hose shop and get get just about any industrial hose for quite cheap.  The problem I have right now is sizing the system for the shed.  I like to keep it around 73 in my shed year round and my little 5000 BTU AC works pretty good in the summer and a 1500W space heater plus my solar heater works pretty good in the winter.  The size of the shed is 16 x 20 feet.  The walls and ceiling are well insulated and sheetrocked.

So to start, I need to figure how big of trenching I need to dig.  I live in West Tennessee and the ground here is pretty tough to dig.  I am sure I can find someone with a small backhoe to help me dig the trenches, but I need to know how long, how wide, and how deep to go.

The next step is powering the pump and fan.  I have just finished installing solar panels that track the sun to my shed.  For the past 2 hours, I have been running a solid 10A load to test everything.  Batteries are staying topped off even with the small 10A load.  My goal is to keep the pump and fan draw no more than 10A @ 12V DC.  I have a new radiator and a fan that I never used on my car and a 12V pump that draws around 3A and the flow is 5 gallons per minute.  I would figure this would be more than sufficient to use as the water to air exchanger.

Any feedback is appreciated!

drbob

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Re: DIY Geothermal sizing for shed
« Reply #1 on: September 28, 2014, 02:38:36 PM »
you are at about 1/2 ton or 6,000 btu.  400 feet of 3/4" hdpe pipe should be adequate for an exchange loop.  now you will need a heat pump of 1/2 ton capacity if you can find one.     

Mary B

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Re: DIY Geothermal sizing for shed
« Reply #2 on: September 28, 2014, 05:17:25 PM »
Might have to go vertical if it is that hard to trench, 2 200 foot wells...

XeonPony

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Re: DIY Geothermal sizing for shed
« Reply #3 on: September 28, 2014, 07:11:02 PM »
800 feet per ton, 3gpm, easy to make a small heat pump, get some exchangers from ebay get a cheap older 6kbtuh air conditioner and a bit of brazing.
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drbob

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Re: DIY Geothermal sizing for shed
« Reply #4 on: September 28, 2014, 08:07:52 PM »
Might have to go vertical if it is that hard to trench, 2 200 foot wells...
A 50 trench should be plenty long enough, you can put the pipe in the trench slinky style, and if you go vertical the rule of thumb is 200' of bore per ton so a single 100' bore should work

Frank S

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Re: DIY Geothermal sizing for shed
« Reply #5 on: September 28, 2014, 09:26:30 PM »
If you trench you will need to know at what depth for your area the ground temperature remains at a constant or near constant.
 this depth is different depending on winter average lows and summer average highs .
 Some northern areas have a frost line that goes several feet deep, on the same token some Sun baked desert areas can have 85° ground temps at 10 ft down
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thirteen

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Re: DIY Geothermal sizing for shed
« Reply #6 on: September 28, 2014, 10:03:32 PM »
Any mining close to you they maybe able to tell the ground temp where you are.  13
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Atokatim

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Re: DIY Geothermal sizing for shed
« Reply #7 on: September 29, 2014, 11:54:46 PM »
I don't have any way to tell the temps around my area at any depth.  I was not expecting to have to dig as much surface area as my house for a small 16 x 20 insulated shed! 

Since the trench length would have to be that long, that may not be an option since my septic system has the first branch about 25ft away from my shed where I want to set this up.  My neighbor's yard is about 5ft to one side and my solar panels are about 20 feet from his property line.  This is about a 25ft square that I have to play with if I get right on the edge of his property.  He may not like that too much.

So with the provided space, lets say 20ft x 20ft area, that is not large enough to do a trench style geothermal piping setup?  That is larger than my shed!

EDIT * :  Also....another question..  Moving water through pipes underground at specific rates is what I am trying to accomplish correct?  What do I need a heat pump for?
« Last Edit: September 30, 2014, 12:00:18 AM by Atokatim »

Frank S

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Re: DIY Geothermal sizing for shed
« Reply #8 on: September 30, 2014, 01:00:07 AM »
The chart in the following link may help you it shows the temps at about 6 feet down
http://www.earthrivergeo.com/geothermal-hvac-loop-systems-information.php
.
  But should you go with a bore hole or  more than one you can check the temps very easy with a laser temperature gun
 Assuming a dry bore take readings at each 5 to 10 feet  depths  once the readings  become the same as the previous you will have reached the depth of constant  ground temperature to a certain degree of accuracy.
 If you can have the bores made about 8" in diameter you could run 2 or possibly as many as 4 pairs of tubes  but the efficiency of thermal transference will diminish  with  too many pairs in the same borehole.
 Some recommend  back filling with 1/4 to 3/8 pea gravel  to near the top of the bore then finishing off with a grout that meets local code,where the bore is down to the water table to enhance thermal conductivity.
 IMO' this can be both good and bad . Should the water table go down the gravel will offer very little  thermal transference.
   What little on the subject that was covered  back when I was a college kid the  most reasonable argument I remember was in the event a borehole penetrated an aquifer not just near surface ground water the bore should be filled with gravel only just a little above the lowest expected  water level then several feet of sand then filled with Bentonite  or thermally-enhanced grout
  A bore where there is nothing but rock will require a  thermally-enhanced grout for the entire depth of the bore.
  But the driller or the installer should know what is required.
  Also your county extension agent will or should have an archive of information.
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drbob

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Re: DIY Geothermal sizing for shed
« Reply #9 on: September 30, 2014, 07:01:03 AM »
the easiest way to get ground temperature is to measure the temperature of your well water.
The heat pump is needed to convert the heat you capture from the earth to a higher temperature to warm your structure.
Geothermal heating  systems are more actually earth source heat pumps or ground source heat pumps or geo source heat humps or ground water heat pumps.  The term "Geothermal" just sounds more GREEN  and GREEN sells.
Your 5000 btu air conditioner is an air source heat pump.   It pumps the heat out of your structure. The refrigerator in your house is also a heat pump. It moves heat from the cabinet and puts it into your house.

Atokatim

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Re: DIY Geothermal sizing for shed
« Reply #10 on: September 30, 2014, 07:36:02 PM »
I don't have a well and apparently drilling one costs a significant amount!  I got quoted on one 100ft hole at $1500....  Quite expensive. 

So maybe I am not understanding this whole geothermal system...  I thought it is basically a system that moves water / eco friendly antifreeze through polyethylene tubing through geothermal loops under ground.  The water is run through a water to air heat exchanger (radiator) via a fan which cools or warms to the temperature the water returned from underground is.   I have seen other systems that use freon which is WAY over my head in building and expense.

According to the graphs that were listed in a previous post, the temperature at 6ft below the surface is around 60 degrees F.  That is quite chilly for the winter time, but great for the summer time.  Is that where the "heat pump" comes into play?  It uses more electricity during the winter, but heats more efficiently?

Atokatim

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Re: DIY Geothermal sizing for shed
« Reply #11 on: October 01, 2014, 12:35:08 AM »
I am interested in attempting to drill my own well for the geothermal feed but am a little worried I will not hit water after hours of work and money spent on PVC piping.  I called a local drill company who quoted me $1500 for a 100ft well and asked about how deep I would need to go to hit the water table.  He told me it was about 120ft down.  Based on my research about the water table in my area, I would only have to go down 80 feet and could pump 150 to 300 gallons per hour.  I don't need anywhere close to that amount for what I am doing so maybe I can get lucky at 30 or 40 feet?

I have read and watched all the video's on drillyourownwell.com and am tempted to try it.  Problem is, my shed and house are at the top of my property and the rest slopes down to a pond / swamp about 80 to 100 yards away.  About 100ft from the shed, I have a semi flat area of land that is about 20 feet lower than where my shed sits.  That would probably be the ideal spot to attempt a drill, but I would not be able to get electricity down there for the pump and it is 100ft away from the shed making it even farther for the cool water to have to travel which will result in less efficiency and higher running costs.  Would it be possible to hit water from higher up so I can get closer to the shed?

joestue

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Re: DIY Geothermal sizing for shed
« Reply #12 on: October 01, 2014, 01:17:29 AM »
common sense would dictate drilling a deeper well closer to the shed, if you have to pump water 100 feet then that's the same friction, and pipe, as drilling a 100 foot deeper well.

are you expecting to hit an impermeable layer at 100 feet down?
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Frank S

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Re: DIY Geothermal sizing for shed
« Reply #13 on: October 01, 2014, 12:51:06 PM »
Atokatim; it now sounds like you are considering an open loop system.
 For an open loop system you need a suitable means of disposal or a 2nd well preferably a dry well to pump the water back into BUT! before you consider an open loop system #1 If the water is going to be returned to another well. the water needs to be tested for mineral content, high iron 7 salts can foul or plug up the return well as well as cause scale deposit build up in your heat pump ,  heat ex-changer & tubing . An open loop system requires more maintenance than a closed loop system.
 the return water must not be aerated as this  would help to release the minerals in the water.
 #2 If an open loop system is installed with drainage disposal the well needs to have plenty of reserve water to operate the system. Also over time an open loop system may lower the water table and neighbors wells may be effected as well.
 #3 an open loop system may be cheaper initially to install but more often than not  prove to be far more expensive than a closed loop system in a very short time.
   #4    A closed-loop system presents absolutely no environmental impact to the earth or our aquifers and this is recognized by environmental authorities. As such, no special permitting or licensing is required for most areas . In some localities, all or parts of an open-loop installation may be subject to local ordinances, codes, covenants or licensing requirements.
 #5 When in doubt check with your county extension Agent or a local Mechanical Engineer.
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Bruce S

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Re: DIY Geothermal sizing for shed
« Reply #14 on: October 01, 2014, 02:17:09 PM »
The geothermal at 60 F is also a relative thing.
60F in the winter might sound chilly, until you come in from the outside and it's 2F, then that 60F is blissful.
Normally where I'm at the cold water comes in at about 45F during the winter, our frost free depth is only 24" . So if I were to have a closed loop system to raise our incoming cold water from 45F to 60F that would be a lot!
 
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Atokatim

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Re: DIY Geothermal sizing for shed
« Reply #15 on: October 01, 2014, 07:19:24 PM »
I sometimes spend hours in my shed working on electronics that are extremely small.  So I am sitting in one spot and trying to pick up components that are the size of the tip of a pen with tweezers.  That would be tough to do in 60 degree temps for me.  I like it around 68 to 70 in the winter which is comfortable for me.  Wearing a jacket and messing with the small electronic components is also not an option because the jacket can interfere with the space I am working on and move components out of sequence if it bumps them.

An open loop well sounds like it would be least expensive and easier for me to do, but I think a close loop system will be better for me in the long run.  Problem with a closed loop system is the vertical shafts would have to be way deeper than I can drill by hand and way too expensive to hire someone to do it for me.  I also don't have much room for a horizontal shaft due to my septic drain offs in my back yard.  I really wish I could dig a 4" hole in my back yard 100ft down, but I don't think I can supply enough water or force to do that in my area.  What I would like to do is try a 3/4" pipe and see how far I can go with that.  If I can hit a water table with the smaller pipe, maybe I can get lucky with a 4" pipe?  I am sure I could get 1 loop in a 4" hole.  Not sure about the effectiveness of the tubing being so close together though.

EDIT :

Here are some sources in my area from awhile back :
http://pubs.usgs.gov/wri/wrir88-4182/pdf/wrir_88-4182_a.pdf - page 26 (brighton, tn) - This is my town.

http://pubs.usgs.gov/wri/wri834011/pdf/wrir_83-4011_a.pdf - page 15 (Covington, TN) close to my house

drbob

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Re: DIY Geothermal sizing for shed
« Reply #16 on: October 02, 2014, 07:17:08 AM »
I would recommend that you go with an open loop system.  If your well water temps are 60 degrees it is possible to heat that structure with 25 gallons per hour.  If you have a good well at your house a 1/2 gpm draw off your well should be no problem.   No need to put in a new well, no need to install a closed loop.   Just use what you already have.
here is a quick calculation for you to ponder.
25 gallons of water X 8.33 # per gallon = 208# X 25 degrees extracted = 5200 btu from absorption add in the heat from the compressor and you should end up with 7500 - 8500 btuh.    IF you can get a heat pump that small.

I heat my house in northern Wisconsin with an open loop heat pump.  I get 50,000 btu with a 6.5 gpm flow with 52 degree water.   Been doin it for 26 years.   I have no problems heating my house at outside temps of -35f.   I have no other heat source, never have.

drbob

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Re: DIY Geothermal sizing for shed
« Reply #17 on: October 02, 2014, 10:11:02 AM »
McQuay / Dalkin Enfinity 007 console water source heat pump may work well for you  for heating and cooling.  Climate Master also has trc series console heat pumps that will also do a good job.  I have seen these on EBAY from time to time in the $700 to $900 price range.     Either can be used with open or closed loop systems.

These are commonly used in motels and schools 

Atokatim

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Re: DIY Geothermal sizing for shed
« Reply #18 on: October 02, 2014, 10:53:01 AM »
So a heat pump is basically a window unit that uses water instead of air to cool or heat the discharge?  I already have a window unit that I am trying to not use to save electricity.

drbob

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Re: DIY Geothermal sizing for shed
« Reply #19 on: October 02, 2014, 10:58:26 AM »
yup you got it.  heat pumps come in many variations.   they ALL use electricity.   

Atokatim

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Re: DIY Geothermal sizing for shed
« Reply #20 on: October 02, 2014, 11:29:40 AM »
Is there an advantage to converting a window unit to use water to cool the discharge instead of air?  Will the compressor not have to work as hard and save power?

drbob

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Re: DIY Geothermal sizing for shed
« Reply #21 on: October 02, 2014, 02:08:23 PM »
400% advantage

joestue

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Re: DIY Geothermal sizing for shed
« Reply #22 on: October 02, 2014, 02:24:17 PM »
You can take a household dehumidifier and construct a water-freon heat exchanger without breaking the refrigerator loop. you will have to be pretty creative to do it but it is possible, provided you don't need to pressurize the water side more than a few psi.

they typically pull 8-10 amps from the 120 line. replacing the fan with a more efficient unit might be in order, most of them are an induction motor operating at less than 40% efficiency.
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Atokatim

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Re: DIY Geothermal sizing for shed
« Reply #23 on: October 02, 2014, 02:30:58 PM »
So what about an outside central heat and air unit that is not a heat pump?  I tried misting years ago and it was not efficient due to the water usage.   I could save a bunch if I could get the outside coils in water all the time at 60 degrees.

I have also head that the compressor can lock up if the temps outside are 60 or lower.  If that was the case, wouldn't that be the same for cooling the coils in 60 degree water?

joestue

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Re: DIY Geothermal sizing for shed
« Reply #24 on: October 02, 2014, 02:35:12 PM »
an outside central heat and air pump that is not a heat pump is... what is it?

well the biggest problem with heat pumps is you have to work harder to move heat from 40F air to 70F coils but the other problem is the reduced capacity of the refrigeration system because it wasn't designed to operate at those low temps.
so for example, i could probably get more heat out of my dehumidifier-converted heatpump by switching from r-410 to propane, which would raise the pressure in the low side, and the heat capacity of propane is higher than r-410.*
however, to do so would overload the compressor in higher temperature operation (which mine will never see btw)

*this might be true if the propane they sell here boiled at -40c, it doesn't, it boils at 29C because its half butane.
« Last Edit: October 02, 2014, 02:39:29 PM by joestue »
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Atokatim

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Re: DIY Geothermal sizing for shed
« Reply #25 on: October 02, 2014, 03:04:24 PM »
It does not have the ability to heat the house using the freon.  The pump cannot run the system backwards for heat. 

So it is possible to convert a dehumidifier to be a heat pump?  I am getting a little confused.  I know an ac unit pulls humidity from the air while also removing heat and transfers it to the outside coils.

I am trying to heat and cool my shed using the least amount of money...either up front expense and / or long term.  I am quite creative and will engineer just about anything I think I can build from scrap parts.

EDIT :

I have an old window unit that died on me this year I am guessing due to low freon.  The coils freeze up right where they come into the front coil.  It never gets to the point to be able to cool.  I paid $300 for it and it lasted 2 years :(
« Last Edit: October 02, 2014, 03:09:09 PM by Atokatim »

drbob

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Re: DIY Geothermal sizing for shed
« Reply #26 on: October 02, 2014, 04:58:26 PM »
I am afraid a do it yourself geothermal heating system just may not work for you. 

joestue

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Re: DIY Geothermal sizing for shed
« Reply #27 on: October 02, 2014, 05:04:58 PM »
the pump doesn't run backwards what is going on is there's a solenoid valve that swaps the evaporator coils with the condensing side
looks like this: http://www.ebay.com/itm/Alco-Freon-Reversing-Valve-with-Coil-Source-1-02529133700-/120890623693

a dehumidifier is a heat pump, the air flows through the evaporator first and then immediately flows through the condenser.
you can separate the two fairly easily and install a second fan.
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Atokatim

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Re: DIY Geothermal sizing for shed
« Reply #28 on: October 02, 2014, 05:52:28 PM »
It may not, but if I spend $300 to $500 on a system that does work, great!  It was a success!  Better than spending $20,000.  If it does not work, I am still good because I did not spend 1/3 of the cost of my house and I have more toys to tinker with later on.  Maybe I could even invent an efficient way to make it work. 

I don't have thousands of dollars to do it professionally, but if I can save a little money to start with, I can take that savings and invest it into the correct equipment which will change the small savings into a larger savings...

Bruce S

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Re: DIY Geothermal sizing for shed
« Reply #29 on: October 03, 2014, 09:36:02 AM »
Quick question.
Do you have windows in your shed?
IF so you could use the beer can method of assisted heating  :)
Here's a couple to look at.
http://www.instructables.com/id/How-to-Build-a-Soda-Can-Heater/
The second one is also the website of a very long and trusted poster!!
User's name here is Gary Gary
http://www.builditsolar.com/
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Atokatim

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Re: DIY Geothermal sizing for shed
« Reply #30 on: October 03, 2014, 10:06:15 AM »
I already have a solar heater on my shed made from over 200 cans and double pane glass.  Been using it for a few years.  It is enough to knock the chill off on sunny winter days.  There is not many of those for some reason.

Atokatim

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Re: DIY Geothermal sizing for shed
« Reply #31 on: October 03, 2014, 02:10:48 PM »
Another thing I was looking into for the heating was evacuated tubes, but those things are expensive!  They also only work during the day unless I store a BUNCH of water which is not something I can do since I don't have enough space. 

Relying on the sun only for heat during the winter is not feasible since night is the coldest time and there is no sun :P  I am looking at finding some kind of heat pump setup that I can do some testing with even if it is a small setup.

I just found a 500ft roll of 1/2" HDPE tubing for under $100.  Is 1/2" ID too small?

XeonPony

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Re: DIY Geothermal sizing for shed
« Reply #32 on: October 05, 2014, 06:44:20 PM »
Not if you do allot of perallel loops, but have fun balancing it all!
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