I have 5 well tanks, one for each geo unit. Yes, this is a big house! Once the water exits the pressure valve on the output side of the geo unit, the pressure drops to zero, and it is a gravity feed out the wall of the house and flows by gravity in a 4 in" PVC pipe to the pond. It dumps above the surface of the water (important) at the edge of the pond. It doesn't have to be below the frost line because the water is always moving. It won't freeze in the pipe. I see on some of the posts that someone is using 15 gallons/ min. WOW! I think they must be quoting close loop anti-freeze flows. The nice thing about open loop is, because the water is both warmer in the winter and cooler in the summer than closed loop, you don't need nearly as much flow to get the desired effects. My basement unit is a 5.5 ton unit, and it has a flow regulator pegged at no more than 7 gallons/ min. A closed loop would probably be in that 15 gallon /min range to get the heat or cooling effects needed.
Think about some of the posts hear. Some are talking about the coils freezing into huge blocks of ice at the bottom of the pond in the winter. Well ice is 32F and your geo unit is trying to extract heat from it! Not that efficient. In the summer, assuming you aerate the pond, once it de-stratifies, will be in that 70F range (Michigan weather) and that’s your source of cooling! Sure, the geo unit uses a compressor cycle, but you need a lot of flow too achieve good cooling. Frankly for heating, I'd rather bury the coils 4-5 ft in the ground. At least there, in cooling mode, you can use the cool earth as your heat sink.
Of course, I'm a big open loop advocate, in the winter; my input water is 50F, in the summer, its 50F. For me it's the only way to go.
