I'm now curious. If there is a deep secret facility somewhere, how long does it take for heat to dissipate through the rock. Let's say you dig 500m deep and through some layer of ground water that you use to cool down any air from ventilation to ambient temperature. Let's say it's a 10MW facility. Unless there is good data on the temperature of a wide area prior to the installation, you wouldn't notice this as the heat would dissipate over a wide area and even 10MW would not make a dent compared to what the sun radiates on a square km for example.