No experience, but just thinking out loud; if you'd install a ground water well and put a sizeable container with water (and/or long PVC pipes going back and forth to act as makeshift heat exchanger )  in the datacenter and constantly pump water through the containers, it should remove quite a bit of heat at relatively low cost. Basically cooling the room with ground water.  Where I live ground water has a constant 15C temperature, but I think its the same everywhere. Drilling water wells is surprisingly cheap. Water containers can be found cheap. PVC piping costs next to nothing.  A power efficient pump with sufficient flow will cost you a bit, but the savings compared to AC Im sure would make it worth it.

Oh, and should you have a pool.. use the warm water to heat your pool. You could swim all winter