So, how it works...
Whenever the temp of the water is greater than -27F then the ammonia is a gas that fills the tubes under slight pressure. When the temperature outside is cold enough (below freezing), the ammonia will condense on the walls of the copper tubing. The condensed ammonia drips down to the fridge where it absorbs the heat from the 300 gallons of water. It then boils to a gas again. The process continues until the water turns into a 300 gallon block of ice. The only moving part is a cutoff valve. It is shut at this point to prevent everything in the fridge from freezing. The ice will last until the next winter, or I should say that some of it will and maintain the fridge temps.
I would take it a few steps forward though. I would design it so that it was like a chest freezer so the door opened on the top. This would make it way more efficient. Then I would let the ice get much colder in the winter and have a fridge and a freezer section. The fridge section would have more insulation between it and the ice so that it doesn't get as cold. The freezer section would have no insulation on the part touching the ice.
Just so you know, 300 gallons take a lot of space and it weighs a lot. It weighs 2500 lbs and takes up 40 cubic feet. If you laid that down so that it was a chest fridge/freezer then you could make the water container 30 inches deep, 70 inches long and 33 inches wide. Then you need 16 inches all around for insulation. It would be a big unit but the storage would be shallow, maybe 13 inches deep for the fridge (so you can get a 2 liter bottle in it standing up). And deeper for the freezer section because that section is submerged with ice around it.
I found this in wikipedia.
In 400 BC Iran, Persian engineers had already mastered the technique of storing ice in the middle of summer in the desert. The ice was brought in during the winters from nearby mountains in bulk amounts, and stored in specially designed, naturally cooled refrigerators, called yakhchal (meaning ice storage). This was a large underground space (up to 5000 m³) that had thick walls (at least two meters at the base) made out of a special mortar called sārooj, composed of sand, clay, egg whites, lime, goat hair, and ash in specific proportions, and which was known to be resistant to heat transfer. This mixture was thought to be completely water impenetrable. The space often had access to a Qanat, and often contained a system of windcatchers which could easily bring temperatures inside the space down to frigid levels on summer days. The ice was then used to chill treats for royalty on such occasions.