I had the closed loop (water and methanol) on my geo system checked for freeze protection last year. The contractor told me the loop was good to -25 degrees F. I understand a heat pump isnt going to be able to operate with loop fluid temp even close to this temp, so I am not sure how this happened. It is my understanding that methanol does not conduct heat as well as water, but that it is close. I assume a loop only needs to be protected to about 15 degrees F. Am I losing a significant amount of efficiency in my geo system due to the high concentration of methanol in the loop? Just looking for ballpark number. Is it a 5% loss in efficiency or more like a 20% loss in efficiency? The loop has been like this for at least 4 years. In short, I am wondering if it is worth the high cost of getting a contractor to my home to correct the water/methanol concentration in the loop.
Can he refer to the way he came to that conclusion? It would mean you have 40% by volume in there. Looking at 21% vs 40 %, Not sure how much you would actually loose. The heat pump still takes the same amount of heat out of the water. The refrigerant circuit including the compressor does not know what is in the fluid. But pumping power might be slightly different, since you might need more fluid at higher viscosity.
He used a hydrometer to check specific gravity of the fluid in the loop. Water works well for transfering heat to the heat exchanger in the system due to its high heat capacity and thermal conductivity, but methanol has a lower heat capacity and thermal conductivity. Therefore, as the methanol concentration becomes higher, the heat capacity and thermal conductivity in the loop fluid go down. Unfortunately, I don't know of any rule of thumb as to how much higher concentrations of methanol in the loop fluid affect the effiency. I was hoping someone out their had a rule of thumb for effiency loss as methanol concentration gets higher in the loop fluid. Reference http://koolance.com/cooling101-heat-transfer for the exact heat capacity and thermal conductivity numbers if you are interested. I do agree that the higher viscosity of methanol is alsogoing to reduce effiency since you need more pumping power. I also agree that the heat pump will be able to take out the same amount of heat out of the water in the loop fluid. But if the loop fluid is only 60% water and the balance is 40% methanol, the heat pump will not be able to get as much heat out of the loop fluid as if the loop fluid was 79% water and the balance 21% methanol. Maybe I am overthinking this.
A 40% solution would be more flammable than a 20% solution. Not sure how much of a concern that would be.
Yep, I would not be sure why anyone would want to put that much methanol in there. I cost much more than water, is more flammable, and at a freeze point below 15 F the heat pumps shut down anyway....
Other than elevated risk of fire (which is real, I do believe), I can't see much downside to high methanol concentration. I'll defer to the northerners who actually work on systems with other than pure water in their loops, but my understanding is that methanol has low viscosity so little impact on pumping power. Before getting too wound up I'd ask for confirmation / methodology for measuring freeze protection point of the mixture. I assume there is some sort of specific gravity instrument (graduated float or swinging dial) that determines methanol concentration in loop fluid. I wouldn't know...entering loop water temps rarely dip below 60*F in Florida.
Get a small amount of the mixture and put it in the freezer. If it freezes your installer was wrong. The put a thermometer in there and check at what temperature is starts melting....it will give you some guidance.
