On Saturday, May 6, 2017 at 10:09:36 AM UTC-4, rangerssuck wrote:
I have an unusual problem staring at me. I'm doing maintenance of an ice skating rink, and we have decided to replace the R22 with RS-45 as part of a general upgrade. The system was full of leaks and was constantly losing significant and costly amounts of R22.

This is a liquid overfeed system and as such, the refrigerant runs through the pipes under the ice surface. These pipes are buried in concrete and nobody knows how large they are. The people who installed this are long gone, and there is zero access to the piping after the large feed and return lines enter the concrete.

I need to determine how much refrigerant we need to buy. I have heard estimates ranging from 4000 pounds to 7000 pounds from various experts in the field. That extra 3000 pounds is almost $30,000, so it would be good to get a better feel for a real number. The refrigerant pipes in a typical rink are about 10 or 11 miles long (seriously), and are (sometimes) 5/8 OD thinwall steel, but that's a variable.

The R22 has been removed from the system - unfortunately, the quantity recovered really has no bearing on the actual capacity as there had been considerable leakage.

So, given that I have a system that's shut down and pumped out, and that I can isolate the rink floor pipes from the rest of the system and there are service valves accessible, does anyone know how I might determine the volume of these pipes?

I was thinking, perhaps, of filling with nitrogen at some regulated flow rate and watching for a pressure rise and then doing some magic calculations I haven't thought about since high school. Does that make sense? can anyone offer specifics?

I'd appreciate any help any of you can offer.

Thanks.

jpb

Because the system is leaking, you'd first have to determine the leakage rate, so you can correct for it when you fill it with a measured amount of gas (is there some reason you can't just use air?). If the rate is low, the following plan ought to give you an approximate idea of the system's volume.

It suggests a leakdown test that you'd do first: seal off the exhaust end and Fill the pipes with air, ignoring the quantity. Pump it to, say, 1.2 atmospheres of pressure, as a guess. Monitor the leakdown rate by sampling the pressure drop. If the rate is low, you can then pump it up again with a measure quantity of air, to the same pressure above atmospheric, and use that volume to calculate the volume at one atmosphere with Boyle's Law.

I can't guess what the operating pressure is, but your sample for the leakdown test should be somewhere in the same range, I would guess. Or, if the system runs right around atmospheric, cross your fingers that it will hold up with a little overpressure.

Good luck! It's an interesting challenge. If the leakdown rate is too high, events will occur too quickly to get an accurate measure this way. I'm not going to do the math to distinguish "high" from "low." That's why you're getting paid. d8-)

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Ed Huntress