Replacing chiller barrel
Currently replacing a chiller barrel (25 yrs old) on a continental 10 ton water cooled chiller (converted to air cooled some yrs ago) providing water to three air handlers in a one story building. It had corroded causing water and refrigerant mix (killed the compressor of course). While talking to the maintenance supervisor who handles all the equptment in the building except this unit, we decided that refrigerant in the water would cause a rise in pressure. The system is not running but gauges show 60 psi in the water system. The super says that the psi should be no higher than 10 psi. That sounded low to me. What say you. I'll be calling continental direct, but thought I'd put it out there to see what the pros have to say.
Also any suggestions on purging the water from the refrig lines? There are no access points at the rooftop condensor. We blew the lines with nitro until there was no apparent water coming out. Have been running a 5cfm pump for two days and am getting tired of babysitting it. Any suggestions?
10 to 15 psi pressure on the loop should be about right. It would be normal for it to go up a few psi when the chiller is off because of expansion.
60psi is likely the relief setting and in most cases a cause for concern on a one story building. Make sure that your expansion tank has a level or that the precharge is correct.
Now that the temperatures across the loop are equallized you could drain some pressure (water) out and see if it stays constant over time.
As far as removing the moisture you did good by blowing it out with nitrogen. Now you have to keep up the vacuum and warm any low spots or traps with your torch.
If your oil is turning cloudy too frequently try to make a moisture trap with an old replacable core drier shell, some fittings and dry ice. Construct it so that the vapor passes over the dry ice chamber and the water freezes on to it and doesn't go into the vacuum pump oil. The first day you may want to break your vacuum occasionally to help carry the moiture out. (R-22 works good)
gotta get the water out of all the piping. drill holes at all the low points, braze em over later. you gotta borrow, or make, a cold trap. mind your pump oil, change when it emulifies.
Recharging water loop
Thanks for the help!
I like the idea of the cold trap. Sounds like it could have saved me a lot of time! I'll use it next time. My micron gauge showed 700 microns last night, so hopefully, the end is near.
I'm thinking of changing the water in the loop, as it probably contains refrigerant and now probably acid. Is this just a matter of recharging with city water until the loop is full. Do I charge until the sight glass in the expansion tank registers?
What is a precharge?
Precharge is the pressure that that is pumped into a compression type expansion tank. You've probably seen a tank with a round sight glass and a flange on one end. These tanks have a rubber bladder to keep the air and water seperate. When you put one into service you have to pump air into the bladder equal to the system pressure. On a 1 or 2 story, or any facility with pumps on the roof, you would set your make-up water and precharge to about 15psi. This way you maintain a reasonable NPSH and allow for thermal expansion. Some times the tank location requires that much more air be pumped in. I use a standard inflator to pump the air into the schrader under the 1" pipe plug.
The common expansion tank with the tube sight glass will generally be at a correct level and pressure when there is little or no level when the system is at 0psi. This is a rule of thumb for the 1 or 2 story and can vary wildly for other systems.
If you have an expansion tank with the tube sight glass remember to keep the valves closed to the sightglass except when taking readings. The upper stem packing will always dry out and you will lose air. Also important, DO NOT HAVE AUTOMATIC VENTS ON THIS TYPE OF SYSTEM. The air and water are in contact and will breath. The vents will remove air that has given up oxygen and eventually new water with excess O2 will come in creating new oxidation.
No opinion on changing the loop contents...No Opinion....!? I am getting old..
Purge, or recover :-) the refrigerant in the water system. The refrigerant blew into the water side until it equalized, then the system filled with water as some of the pressure relieved. You can verify with a leak detector.
Originally Posted by AGi
Keep driers (high water type) handy for a couple of changes and possibly a couple of oil changes on the compressor. Consider a suction line filter/drier to capture the goop created by the oil and water mix in the system.
Worst problem you could have on a chiller.
After some circulation take a water sample and have it analyzed to see if there is anything happening in the loop. You may need inhibitors.