Bear in mind that this is only one well, so the system is running with 1/3 to 1/4 of expected final cooling capacity. It is handling the heat absorbed by the (so far poorly-insulated) system from the 90+ degree air, plus the 45 Watts of heat generated by the water pump and the blower. These heat sources will eventually be spread across all wells in the system, so it is encouraging to see a 5-6 degree F drop in cabinet air temperature below ambient. The heat from the server is not in the system yet, but it certainly seems that as we scale the system to 3 or 4 wells, it might handle that additional heat.
Notice near the peak temperature of the second day in this chart (click for a full-size version), I turned off the water pump for a few hours to demonstrate the cooling effect that the system has on the air temperature:
Other points worth noting: The air temperature (blue dotted line) reaches the temperature of the water passing through the coil (not shown, but roughly equal to the blue dotted line) even with the blower at the lowest setting. This tells me the fan-coil unit is plenty large for what it's cooling right now.
However, the water temperature (not shown) never gets very close to the soil temperature. This tells me the water isn't spending enough time under ground and/or the PEX tubing in the ground loop is too good of a thermal insulator. PEX is about twice as good as soil at conducting heat, so I don't think the problem is so much the choice of material as it is the length of time the warm water is exposed to it.
You can see quite a temperature swing in the soil as we dump heat into it. So heat IS successfully transferring from the cabinet air to the soil. As we add more wells, this temperature swing will be proportionately reduced as the wells share the absorption of heat energy. So with four wells, instead of being raised from 71 to 83 (a 12 degree increase), we can expect the soil to be raised from 71 to 74 (a 3 degree increase).
