underground temperature

[DanielCHall]

I would like to monitor ground temperature (10' below surface) with a BAS. This is for control of a heat pump loop.

I would appreciate any helpful ideas.

 

[DRWeig]

Hi Daniel,

I've dealt with a number of underground temp monitors but not quite as deep (a couple of our customers have installed BAS controls in NFL stadiums that contain snow-melting equipment). You should be able to drive a 10' piece of rigid conduit down with a sealed cap on the end, and inside the pipe you can put a stainless sheathed sensor immersed in some thermally conductive compound, with the rest of the pipe filled with polyurethane or something to reduce the thermal contribution of air in the pipe and help keep moisture to a minimum. Here are potential problems:

1. You'll need to take steps, such as moisture-resistant splices and good sealing techniques to keep moisture from migrating down the conductors to your sensor and ruining it. The stadium fellows made their splices in a conduit body using moisture-resistant connectors, then filled the whole thing with a silicon sealant. Worked good in almost all instances.

2. In instances where it doesn't work perfectly and you get some seepage into one lead or the other, you can wind up with a better unintentional ground than you'd expect, which can cause problems with non-isolated transmitters. Use a signal isolator and you're pretty much guaranteed to be trouble free.

3. I'd use an RTD instead of a thermistor -- they are much more resistive to moisture effects.

Holler at me (DWeigel@kele.com) if you have trouble finding parts.

Best wishes with your project!

Old Dave