First tests

While waiting for the auger extensions to arrive, I drilled a test well to 30" depth, installed some K-type thermocouple probes, and back-filled the hole. I don't have much experience with auger drills, and I almost expect a broken wrist by the end of this project!

I picked up this inexpensive digital temperature gauge and a handful of removable thermocouples at www.sweetmarias.com. Evidently, they use K-type thermocouples to monitor the temperature of coffee beans while they're roasting. K-type thermocouples have a very wide temperature range, so they're handy for that. I'm discovering that I probably shouldn't expose the sensors directly to damp soil because it makes the readings a little flaky. They're only supposed to be used up to 80% relative humidity, so I should plan on sealing them in something waterproof I guess. Also, I'll need to extend the 36" leads now that I've ordered extensions for the auger bit!

The K-type thermocouples are convenient and cheap, but since the temperature range is so wide, the accuracy isn't very high (+/- 4 degrees F). I know I should consider 1-wire temperature sensors and a real-time monitoring/logging system, but that's a project, and I don't want to get bogged down in something that might distract me from the task at hand. If there's time...!

After waiting a day for soil temperatures to equalize, I was pleased to discover that the building provides enough shade throughout the day that the ground temperature at a 2-inch depth is about 10 degrees cooler than the ambient air. At 30", it's only in the mid-to-upper 60's in 87 degree weather.




Here is the cabinet that the server will live in. It will be a tight squeeze because the server is pretty deep (front-to-back). If it's as tight as I expect, I'll probably need to duct the hot air directly out the back wall of the cabinet behind the server and pipe it through the fan-coil unit outside the cabinet. I'm more comfortable with the coil outside anyway so we can keep the server completely isolated from the coolant and condensation.






I considered a radiator from a PC water-cooling system, like the 2-fan or 3-fan units from Black Ice. But they are designed to radiate heat, not cool the air, so they aren't designed to direct condensation away from the coils. Instead, I settled on a 9"x9" surplus fan-coil unit.




The cabinet is only 8 cubic feet, so if I can get a couple hundred CFM from my fans, I'll be turning over all the air and passing it through the coils every few seconds.