Just run a pump and dump system, using your endless supply of pond water as heat transfer fluid. You could still run a dx coil indoors if you wanted to. Pipe your suction line underground, and if the pond water is cold, it would pick up some heat underground on the way in. You could even use copper pipe if you wanted more heat transfer. Much safer, less refrigerant, way less expensively accomplished. Spend some extra money on a hx and pump.
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