- DIY Ground Source Heat Pump
- DIY Ground Source Heat Pump – Part 2: Making A Drilling Rig
- DIY Ground Source Heat Pump – Part 3: An Improved Drilling Rig
- DIY Ground Source Heat Pump – Part 4: Selecting in Ground Tubing
- DIY Ground Source Heat Pump – Part 5: Welding Plastic
- DIY Ground Source Heat Pump – Part 6: Testing Plastic Welds
- DIY Ground Source Heat Pump – Part 7: Digging Trenches
- DIY Ground Source Heat Pump – Part 8: Building The Loop Field
With a capable drilling rig, AC Hacker turned to selecting parts for the rest of the system. Specifically, we’ll be looking at selecting the tubing that must be laid in the ground.
PVC and CPVC are not a good choice. They both get brittle eventually and will crack under pressure. Pex would be a good material. However, with the way it is made, it is not possible to weld it together. Copper would also work well, but it is very expensive.
So, that left AC Hacker with what he had read about many small residential systems using, HDPE (high density polyethylene). Its that black water tubing you’ve probably seen at the home improvement store. AC Hacker found that HDPE comes in two schedule ratings, 40 and 60. The 40 was too thin to think about using as he feared it might be crushed by the weight of the soil on it. But, the schedule 60 looked like it would be up to the job.
The next hurdle is that HDPE needs to be welded together. AC Hacker looked into what kind of tools would be needed for this. He found McElroy makes a tool called the MiniMc that is made specifically for welding plastic pipe. The bad thing is it costs $2000. He also found that even renting it was very expensive.
Since that would blow the budget for this project out of the water, AC Hacker decided to look into how hard it is to weld the tube without this tool. He picked up a teflon skillet from the local junk store and heated it up on his stove at home. He placed a couple short pieces of HDPE on the skillet and monitored the skillet’s temperature with an IR thermometer. At about 300°F (149°C) he noticed a bead forming around the tube. He picked two pieces up and pushed them together. The above was his first result. So, plastic welding is indeed possible without the very expensive tool.
For more details about the tools or project check out AC Hacker’s forum thread that tracks all of his progress.