OK, I am attempting to calculate the reuirements for creating a 3-ton, 90-day air conditioner using nothing but ice and an exchange loop between that ice and a heat exchanger in my house. I can calculate everything except knowing how much I can practically insulate a storage vessel, and, given that practical maximum insulation, what its given cooling loss, or more accurately, BTU absorption, would be each day during the lag time between when the coldest part of winter ends and air conditioning season begins, as well as the daily loss during the air conditioning season. Assume an approximately 40,000 gallon container of water that is 40ft. x 40ft. x 14ft. tall. Alternatively, I could use underground storage tanks like those at gas stations. That tank would be 12 feet in diameter and about 50 ft. long. Next, assume that I can freeze that water and that I can lower the temperature of the ice to 0 degrees F via the use of an ethylene glycol loop and simple outdoor heat exchanger run during the coldest parts of our winter (We can see -10 degrees F at times). Assume that I can freeze the water in the vessel without damaging it. Next, assume that I can insulate the tank equally well on all sides, whether it is rectangular or circular, and that the tank is buried 12-14 feet underground, well below the frost line, and I am assuming deeply enough that I can tap into the 52 degree F ground temperature year round. My question is this: Using conventional insulation technologies such as sprayed-on foam, fiberglass batting, reflective thermal blankets, etc., what would be the least amount of heat energy in BTU's that the ice block would absorb each day? In other words, I want to keep the ice block as cold as possible for a couple of months between the time winter ends and the air conditioning season begins. Let's also assume that the vessel, whether the equivalent of an underground swimming pool, or a fiberglass storage tank, has essentially no insulating value on its own. I realize this is a subjective question, since one could say something along the lines of "spray the foam on 3 feet thick" or "use 10 feet of fiberglass batting around the holding tank", but I am trying to get an achievable minimum heat absorption (and hence loss of cooling capacity) by the ice block each day. Thanks for any help.