DIY Ground Source Heat Pump – Part 3: An Improved Drilling Rig

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by Tim Fulton on September 1, 2009

To make his life a bit easier, AC Hacker decided to build an electric drilling rig.  He did dig a few holes with the manual drilling rig and it worked fine.  However, he calculated that he needed around 200 feet of borehole and decided to make something better.


The frame of the drilling rig is made mostly out of square tubing with some plate here and there.


The head for the drilling rig consists of another close fitting square tube that slides over the frame tube.  This allows the head to be moved up and down with the red wench you can see in the last picture.  Attached to the head is a 1/4 horsepower 25:1 gear motor.


Attached to the gear motor is a home made flexible coupling.  This dampens shock loads and allows for some misalignment in the system.  The coupling is made from two flanges, a rubber disk, some bolts with nyloc nuts, and rubber and regular washers.  This coupling has gone through a few design changes and this is the one AC Hacker has settled on (for now at least).


The last piece we have here is a fancy water connection.  The drill shaft must rotate, but you don’t want your water hose to rotate with it.  So, AC Hacker constructed this swivel adapter.  It is made from a PVC compression T, two sealed bearings and a piece of pipe. Construction details of the swivel can be found here.



In addition to the drilling rig, AC Hacker made a few other hand made tools.  The pointed tool works well for chipping through clay and the bladed tool works well for cutting through roots.  He also made the shop vacuum extensions shown above that works well for removing dirt and even rocks from the holes.  These tools have allowed him to drill 11 of the 16 holes that are necessary for his heat pump system.

For more details about the tools or project check out AC Hacker’s forum thread that tracks all of his progress.


1 Bill June 21, 2010 at 3:51 pm

How deep did he makes these holes? I understand 250 ft is needed for each Ton. Does that agree with what ACHacker found?

2 Chris S August 19, 2014 at 1:12 pm

150 to 250 ft is needed for each refrigerant Ton, depending on the conductivity of the soil. Almost all soil runs in the 175-225 ft per Ton range to a good rule of thumb is 200 ft. Roughly the first 5 ft of hole doesn’t count however, as it will be strongly influenced by air temperature.
Looks like he did 16 holes 12 ft deep. That should reliably provide 1/2-3/4 Ton. Toward the lower end of that range in the extreme temperatures (dead of winter, dog days on summer), and higher end in the spring and autumn (where the system is most efficient due to the lower temperature differences).

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