Hello omerizm,
I think you misinterpret what I'm talking about when I use the term "efficiency". I'm speaking of how cool the
nutrient solution gets, not how efficient the compressor is. I know that adding any amount of tubing to the inside of the frig is not going to change how well the compressor works. I'm only concerned with how cool I can get the nutrient solution, and how much it costs to get it there. The key to making it efficient (cooling the nutrient solution) is in getting the warm nutrient solution to transfer as much heat with the cool air inside the frig as possible. Then it will depend on the size (volume of water) of the reservoir and the outside temperature (I grow outside) weather it can cool down the entire volume of water (nutrient solution) to a sufficient temperature, and be able to maintain that water temp all day long. That is what it takes to be efficient to me. Of coarse another factor in how efficient it will be in cooling the nutrient solution is how well insulated the reservoir and outside tubing will be. I didn't really mention that because it's easily enough to do, and I already have planed on doing that regardless.
And although the thermostat can help adjust the water temp, I can assure you my water temp in my reservoir will be no ware near the temp on the thermostat in the fridge (unless it's winter, maybe early spring). The thermostat will need to be set to its coldest setting and remain there all summer. Considering that the fridge will be outside during the hottest parts of the summer that will be 120-125 degrees fahrenheit during the day, and between 100-110 at night. There is no way to bring it inside and just run the lines outside, there is simply no place to put it inside, other than the garage and it's hotter in there than it is outside. Also I have no set plan of what I will be growing this summer, but suffice it to say as many things as I can. That would include more than one reservoir needed. With the amount of money I have for materials being the largest deciding factor in how much I will be able to grow. With reusing as much as I already have, but I want to try some new setups.
Like I said the key to making it efficient is getting as much heat out of the nutrient solution as possible. I have already designed a cooling box witch is pretty much just like a large ice chest. With the reservoir inside here and ducting the cold air from a small refrigerator or window AC unit, that will make the heat transfer more efficient. And kind of like keeping the entire reservoir inside the refrigerator, instead of only running some coils through it.
I designed this cooling box to work with the heat sinks that I was working on as the cooling source, but it's very adaptable and functional. It will even be able to work with the geothermal coil trench design I have as the cooling source. How well and how efficient it works with that cooling source at cooling the
nutrients depends mostly on how deep the trench is, how long the coiling tube is, volume of the reservoir, and how well the tube transfers heat. I even have another cooling device design that I'm planing to test this summer, with or without using the cooling box. I'm looking forward to seeing how efficient that will be. Building on what the original person built I can make some improvements, but it's supposed to work well as is in our climate.
P.S. Also another thing to consider is using air stones in the solution. Obviously pumping hot air into the reservoir is not going to be beneficial. So the placement of the air
pump, lines and how long the lines are is all going to make a difference.