Open Or Closed

J Matthers_2

is actually on a geo system and should be a sealed tank with an air space per design. I set it up as a closed system with 12psi, no air gap (full tank), expansion tank and a Spiro vent. Worked great until I added water via the fill valve to the system last summer to purge air from the hydro coil for the air handler in my attic. I forgot about it until the first night of heating season. Just about to fall asleep and Ka-bloowie. I knew just what had happened. The buffer blew its screw top. The pressure relief had blown as well but I must have way overfilled when I purged compromising the expansion tank. The nylon screw cap was married to the tank via a treaded rubber gasket which was ripped during the action. I called the company to get a replacement and was told by a tech that the top wasn’t really needed and the system would work fine without the top sealed. It has run as such since. I also asked what options I had to get the temp off the buffer tank down lower to provide cooled water to my AC coils. He suggested adding 10% glycol and there is the rub. As Hotrod has told me, glycol likes a closed system. In order to glycol this baby I need to get rid of the oxygen.

If I replace the rubber gasket to seal the tank leaving the air space. And the oxygen is consumed through reaction with the ferrous and inhibitors, will the airspace bother anything. As the tank is set up the air occupying the space can not travel to other parts of the system unless in solution and as I understand from reading Dan’s books, the tank will be the point of no pressure. If no oxygen can get in I should be ok with the glycol.

I think.

J Matthers_2

open or closed system

Open or closed system? The buffer tank shown below is filled to ¾ capacity with all piping terminating below the surface of the water. There is no pressure in the system. Circ pumps are pumping away from the buffer tank making the tank the area of low pressure. . There is a spirovent on the low pressure side of the pumps after the tank. Theoretically, the pressure is greater throughout the rest of the system so this is the only place air would come out of solution and would not go into solution.

As I think about this, the tank would only be the area of low pressure when the pumps were on but that is true in a closed pressurized system as well. Would air go into solution in the tank when the pumps are off and the tank is at 14.7 psi?

What if the system were pressurized slightly with the air gap in the buffer tank? Would this cause the air in the tank to go into solution when not being pumped?

I suspect that with the air gap it can’t be a closed system but will air go into solution and find its way to other parts of the system?

If not, will it act as a closed system as far as turning the water since the piping all terminates below the water line?

Robert O'Connor_3

How ironic, I just repiped a system two weeks ago designed by Rich Trethewey in 1984 that was almost the identical setup. There was a hwh pumping into a flat plate hx, then from the flat plate it went into a copper buffer tank that was 3/4 full. there was no air serperation to speak of, or purging method for that matter. The system was VERY airbond before the repipe, not sure if it's because of the not filled buffer or lack of proper purging. In my eyes, the system is very similar to running a hot water loop of a steam boiler condensate... only that the steam vents open during not use to allow 14.7 to enter the loop... flow checks, and a tight system keep the wawter loop from siphoning (also loop must be no higher than 30 feet above the boiler) is the buffer tank in your senario closed above the water line? if so then atmospheric pressure can never enter it. The only time the air would go into the system is if 1) there is an automatic water feeder which could add water and displace the air 2) if your loop is above 30 from buffer to top or three if there is a leak on the air side of the buffer tank. IMO the air is in the buffer tank to allow for expansion.

J Matthers_2