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

On Sat, 6 May 2017 07:09:34 -0700 (PDT), 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

I'd skip the flow measurement and connect a tank(s) of known pressure
and volume to the piping and measure the temp & pressure after the
system comes to equilibrium.

IIRC, the largest argon tanks hold 330CF of gas at STP. If I did the
math right, assuming approx 10 miles of 5/8 tubing, 330 CF of STP gas
would settle at a couple or three atmospheres.

--
Ned Simmons

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-)

--
Ed Huntress

In article ,
rangerssuck wrote:

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?

Nitrogen is cheap and cheerful. CO2 might be another option, not sure if
it plays havoc with refrigerants (but you'd be pumping it back out
anyway - if you can handle the pressure sit's a nice cheap refrigerant
itself, IIRC.)

If you have the underfloor pipes evacuated/isolated and they are not
where the leaks are (which would seem like "throw in the towel" time to
me, or at least a much more expensive repair) you should be able to
carefully weigh a cylinder, connect it to the system, fill to the
pressure of your choice (using more cylinders if needed, just be sure to
weigh them) and then weigh the depleted cylinders - initial weight minus
final weight is the mass of gas you moved (far more precise than a CFM
meter, AFAIK) and if you know the temperature of the floor, the
pressure, and the mass of gas you should be able to get the volume
(metric units on the weight will make that easier.) Obviously (I hope)
you can't have leaks in your fill rig and have this work, nor will it
work with significant leaks in the pipes.

PV=NRT is the formula that springs to mind from a long time ago, where N
is the number of moles of gas (mass will get you to that, temperture is
in C, R is the gas constant, and Pressure and Volume.

V=(NRT)/P would be the form you want. Or, y'know, cheat:

http://www.webqc.org/ideal_gas_law.html

Nitrogen's molar mass is 28.014 g/mol

If this part of the system is truly leak free you might get better
numbers by waiting a day for the temperature to stabilize, since
expanding from the compressed tank will of course cool it somewhat,
though the mass of the floor will mostly shrug that off. And you
obviously want the most accurate/precise scale you can still weigh a
nitrogen tank on.

So long as pressures are not too high, the deviation between the "ideal
gas law" and real gasses is quite small - should certainly be enough to
get you a good solid estimate.

--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.

On Saturday, May 6, 2017 at 11:01:51 AM UTC-4, wrote:
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-)

--
Ed Huntress

As Ecnerwal said, a significant leak in the under-ice piping would be pretty much game over. This rink DID have significant leaks there, but 20-something years ago, they installed new pipes and a new slab on top of the old slab. I don't see any of the tell-tale signs of an under-ice leak - there's usually significant discoloration (of the ice) when that happens.

I'm not sure exactly what pressure these pipes run, but for sure, the lowest they can be is at the suction pressure of the compressor, which usually runs between 25 & 40psi, so 2 or 3 atm shouldn't be a problem.

As a bonus, once we've got it pressurized, we can watch for pressure drop over time to determine whether, in fact, the floor is leak-free.

I surely am hoping that we are on the low side of this range - this stuff is expensive.

On 05/06/2017 1:16 PM, rangerssuck wrote:
....

I surely am hoping that we are on the low side of this range - this stuff is expensive.


Well, how much _did_ you recover, you know? If _that_ number is big...

My only experience w/ rink refrigeration systems were all
ammonia-based...I suppose that is telling on their age!

--

On Saturday, May 6, 2017 at 11:27:49 AM UTC-4, Ecnerwal wrote:
In article ,
rangerssuck wrote:

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?

Nitrogen is cheap and cheerful. CO2 might be another option, not sure if
it plays havoc with refrigerants (but you'd be pumping it back out
anyway - if you can handle the pressure sit's a nice cheap refrigerant
itself, IIRC.)

I also don't know what the ramifications of filling the system with CO2 would be. I was planning Nitrogen or Argon - Nitrogen is almost certainly cheaper, but Argon would be good to have for other (tig) reasons. [while we're on that subject, here's a guy who is making his own liquid nitrogen. http://www.instructables.com/id/Home...gen-generator/ ]


If you have the underfloor pipes evacuated/isolated and they are not
where the leaks are (which would seem like "throw in the towel" time to
me, or at least a much more expensive repair) you should be able to
carefully weigh a cylinder, connect it to the system, fill to the
pressure of your choice (using more cylinders if needed, just be sure to
weigh them) and then weigh the depleted cylinders - initial weight minus
final weight is the mass of gas you moved (far more precise than a CFM
meter, AFAIK) and if you know the temperature of the floor, the
pressure, and the mass of gas you should be able to get the volume
(metric units on the weight will make that easier.) Obviously (I hope)
you can't have leaks in your fill rig and have this work, nor will it
work with significant leaks in the pipes.

Excellent plan. There BETTER not be significant leaks in the rink piping. I don't believe that there are - the pipes were replaced and a new slab was poured 20-something years ago. There were initial problems with this rink design - the R22 would find its way out of tiny leaks and react with the water in the concrete, eating the carbon steel pipes to death. - newer rinks use stainless pipes, or some other material that's run in continuous 200 foot runs.


PV=NRT is the formula that springs to mind from a long time ago, where N
is the number of moles of gas (mass will get you to that, temperture is
in C, R is the gas constant, and Pressure and Volume.

V=(NRT)/P would be the form you want. Or, y'know, cheat:

http://www.webqc.org/ideal_gas_law.html

Nitrogen's molar mass is 28.014 g/mol

If this part of the system is truly leak free you might get better
numbers by waiting a day for the temperature to stabilize, since
expanding from the compressed tank will of course cool it somewhat,
though the mass of the floor will mostly shrug that off. And you
obviously want the most accurate/precise scale you can still weigh a
nitrogen tank on.


I do have a good scale - will weigh down to grams in that range. The temperature measurement is part of the new control system I'm installing. There's already a sensor in the slab. I'm also installing new pressure transducers, so the bases really are pretty well covered.

I could actually hook up a data logger and watch that the temperature and pressure keep making sense over time. I'd expect that there will be some change as it settles, and then it would hold steady (assuming no leaks). If the pressure (vs temperature) slopes down over time, then we've got a problem..


So long as pressures are not too high, the deviation between the "ideal
gas law" and real gasses is quite small - should certainly be enough to
get you a good solid estimate.

Thanks loads for this. It's been a great help.


--
Cats, coffee, chocolate...vices to live by

Three of my favorite vices. We just yesterday rescued two kittens (maybe 5 weeks old) from a mini flash flood in my back yard.

Please don't feed the trolls. Killfile and ignore them so they will go away.

On Saturday, May 6, 2017 at 10:43:43 AM UTC-4, Ned Simmons wrote:
On Sat, 6 May 2017 07:09:34 -0700 (PDT), 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

I'd skip the flow measurement and connect a tank(s) of known pressure
and volume to the piping and measure the temp & pressure after the
system comes to equilibrium.

IIRC, the largest argon tanks hold 330CF of gas at STP. If I did the
math right, assuming approx 10 miles of 5/8 tubing, 330 CF of STP gas
would settle at a couple or three atmospheres.

--
Ned Simmons

Thanks - That's pretty much the same as what ecnerwal recommended, without the attached math. I'll probably just do what he said (which again, is pretty much what you said).

On Saturday, May 6, 2017 at 2:34:29 PM UTC-4, rangerssuck wrote:
On Saturday, May 6, 2017 at 11:27:49 AM UTC-4, Ecnerwal wrote:
In article ,
rangerssuck wrote:

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?

Nitrogen is cheap and cheerful. CO2 might be another option, not sure if
it plays havoc with refrigerants (but you'd be pumping it back out
anyway - if you can handle the pressure sit's a nice cheap refrigerant
itself, IIRC.)

I also don't know what the ramifications of filling the system with CO2 would be. I was planning Nitrogen or Argon - Nitrogen is almost certainly cheaper, but Argon would be good to have for other (tig) reasons. [while we're on that subject, here's a guy who is making his own liquid nitrogen. http://www.instructables.com/id/Home...gen-generator/ ]

If you've drained the system, and if you know it has leaks, what gas do you figure is in there now?

If it's drained and if any remaining drips of refrigerant have had time to evaporate in a leaking system, the pressure in there went to atmospheric pretty quickly. Then I would think that you're beginning to get air into that system, from that moment on.

--
Ed Huntress

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?

How long does it take to pump that thing down? What's the temp of the ice
in an ice skating rink?

On Saturday, May 6, 2017 at 2:32:40 PM UTC-4, dpb wrote:
On 05/06/2017 1:16 PM, rangerssuck wrote:
...

I surely am hoping that we are on the low side of this range - this stuff is expensive.


Well, how much _did_ you recover, you know? If _that_ number is big...

My only experience w/ rink refrigeration systems were all
ammonia-based...I suppose that is telling on their age!

--

We didn't get nearly enough - not enough to re-start the system. As I said, there have been non-insignificant leaks.

This rink was built in 1980. I am familiar with much newer facilities than this that run ammonia systems, though not under the ice. They have heat exchangers and run chilled glycol or brine under the ice.

On Saturday, May 6, 2017 at 2:47:02 PM UTC-4, wrote:
On Saturday, May 6, 2017 at 2:34:29 PM UTC-4, rangerssuck wrote:
On Saturday, May 6, 2017 at 11:27:49 AM UTC-4, Ecnerwal wrote:
In article ,
rangerssuck wrote:

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?

Nitrogen is cheap and cheerful. CO2 might be another option, not sure if
it plays havoc with refrigerants (but you'd be pumping it back out
anyway - if you can handle the pressure sit's a nice cheap refrigerant
itself, IIRC.)

I also don't know what the ramifications of filling the system with CO2 would be. I was planning Nitrogen or Argon - Nitrogen is almost certainly cheaper, but Argon would be good to have for other (tig) reasons. [while we're on that subject, here's a guy who is making his own liquid nitrogen. http://www.instructables.com/id/Home...gen-generator/ ]

If you've drained the system, and if you know it has leaks, what gas do you figure is in there now?

If it's drained and if any remaining drips of refrigerant have had time to evaporate in a leaking system, the pressure in there went to atmospheric pretty quickly. Then I would think that you're beginning to get air into that system, from that moment on.

--
Ed Huntress

Actually, we had it pumped down to -10 psi for three or so hours. That was over a week ago. I went in today and opened the system and unscrewed on of the valves (which is going to be replaced) and just got a little puff of positively pressurized gas. NOW it's atmospheric

The vast majority of the leakage is (I'm pretty sure) from the compressor shaft seals. Also, every one of the 50+ valves has leaky packing. There are at least two welded pipe connections that leak. I have a busy summer.

On 05/06/2017 1:50 PM, rangerssuck wrote:
....

We didn't get nearly enough - not enough to re-start the system. ...

Well, I wasn't thinking that; just perhaps sanity-check on volume numbers...

This rink was built in 1980. I am familiar with much newer facilities
than this that run ammonia systems, though not under the ice. They
have heat exchangers and run chilled glycol or brine under the ice.

Indeed, yes, these are brine-circulation system--they date back to
'60s/70s...

That'd be a lot more economical on refrigerant if so...

--

On Saturday, May 6, 2017 at 10:43:43 AM UTC-4, Ned Simmons wrote:
On Sat, 6 May 2017 07:09:34 -0700 (PDT), 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

I'd skip the flow measurement and connect a tank(s) of known pressure
and volume to the piping and measure the temp & pressure after the
system comes to equilibrium.

IIRC, the largest argon tanks hold 330CF of gas at STP. If I did the
math right, assuming approx 10 miles of 5/8 tubing, 330 CF of STP gas
would settle at a couple or three atmospheres.

--
Ned Simmons

That was my suggestion. Ideal gas law.
P*V=N*k*T. I think you could just use compressed
air. As long as you know the tank volume on your
compressor and have a good pressure gauge.
(T is in Kelvin)

George H.

On Sat, 06 May 2017 11:27:45 -0400, Ecnerwal wrote:

If this part of the system is truly leak free you might get better
numbers by waiting a day for the temperature to stabilize, since
expanding from the compressed tank will of course cool it somewhat,
though the mass of the floor will mostly shrug that off. And you
obviously want the most accurate/precise scale you can still weigh a
nitrogen tank on.

And if you have the time, you can test for total volume and leaks, too --
fill it, check the pressure, wait a day for temperature to stabilize,
then check the pressure once a day for as long as it's reasonable to
leave it pressurized -- if the pressure keeps going down and there's no
cold snap to account for it, then you've got a leak somewhere.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I'm looking for work -- see my website!

rangerssuck wrote:



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?
Pumped out as in evacuated? Get an industrial-size gas meter in working
condition. Connect to the evacuated system with a throttleing valve.
Record the gas meter's dial reading. Open the throttling valve slowly until
the moter starts turning. As the pressure in the pipes comes up, open the
valve more and more to keep the meter chugging along at a safe rate. When
the meter stops moving, you have the volume in cubic feet, roughly STP.

If you fill the system with a known pressure of gas, then vent out through
the meter, you will expand the gas in the system until it reaches
atmospheric pressure. If you filled it to 15 PSIG, then assuming an ideal
gas, venting to atmospheric pressure should release as much gas as the
system holds at atmospheric pressure, so again the reading = volume.
If you pressurize it to only 1 PSIG, then the meter reading would be 1/15th
of the actual volume. (All figures for sea level, not Denver.)



Jon

On 5/6/2017 11:27 AM, Ecnerwal wrote:
....
PV=NRT ... temperture is in C, ...

"K", not "C"

On 5/6/2017 2:34 PM, rangerssuck wrote:
....
I do have a good scale - will weigh down to grams in that range. ...

"That range" being 120 lb for a 220 cf tank/bottle/cylinder?

On 05/06/2017 1:16 PM, rangerssuck wrote:
....

I surely am hoping that we are on the low side of this range - this
stuff is expensive.

I'm sure they could probably imagine. If I were you, I'd track down the three or four previous contractors/maintenance/service people who left there and get whatever else bad news they found out about the needed repairs.

rangerssuck wrote:

On Saturday, May 6, 2017 at 2:32:40 PM UTC-4, dpb wrote:
On 05/06/2017 1:16 PM, rangerssuck wrote:
...

I surely am hoping that we are on the low side of this range - this
stuff is expensive.


Well, how much _did_ you recover, you know? If _that_ number is big...


My only experience w/ rink refrigeration systems were all
ammonia-based...I suppose that is telling on their age!

--

We didn't get nearly enough - not enough to re-start the system. As I
said, there have been non-insignificant leaks.

This rink was built in 1980. I am familiar with much newer facilities than
this that run ammonia systems, though not under the ice. They have heat
exchangers and run chilled glycol or brine under the ice.
Hmmm, how about converting the system to chilled glycol? You'd have to
replace the whole chiller, of course, but that could actually come out
cheaper than the refrigerant you would need. If the piping is of sufficient
diameter to support the required flow rate, it ought to work. You mentioned
leaky shaft seals, so maybe you are replacing at least the compressor.
Geez, shouldn't you be using a semi-hermetic, anyway?

Otherwise, a do-it-yourself conversion would require an evaporator/heat
exchanger and a circulator pump. This would obviously save thousands of $,
even with a relatively affordable refrigerant.

Jon

On Sat, 6 May 2017 14:21:09 -0700 (PDT), wrote:


That was my suggestion. Ideal gas law.
P*V=N*k*T. I think you could just use compressed
air. As long as you know the tank volume on your
compressor and have a good pressure gauge.
(T is in Kelvin)

You absolutely can NOT use the ideal gas law because none of the
gasses are ideal. The Van der Walls equation must be used. Learn all
about it he

https://opentextbc.ca/chemistry/chap...-gas-behavior/

John
John DeArmond
http://www.neon-john.com
http://www.tnduction.com
Tellico Plains, Occupied TN
See website for email address

On 05/08/2017 6:57 PM, Neon John wrote:
....

You absolutely can NOT use the ideal gas law because none of the
gasses are ideal. The Van der Walls equation must be used. ...

For the purposes here and at PT talking of, the correction will be of
only a few per cent, certainly within 10% or so.

--

On Monday, May 8, 2017 at 6:25:21 PM UTC-4, Jon Elson wrote:
rangerssuck wrote:

On Saturday, May 6, 2017 at 2:32:40 PM UTC-4, dpb wrote:
On 05/06/2017 1:16 PM, rangerssuck wrote:
...

I surely am hoping that we are on the low side of this range - this
stuff is expensive.


Well, how much _did_ you recover, you know? If _that_ number is big....


My only experience w/ rink refrigeration systems were all
ammonia-based...I suppose that is telling on their age!

--

We didn't get nearly enough - not enough to re-start the system. As I
said, there have been non-insignificant leaks.

This rink was built in 1980. I am familiar with much newer facilities than
this that run ammonia systems, though not under the ice. They have heat
exchangers and run chilled glycol or brine under the ice.
Hmmm, how about converting the system to chilled glycol? You'd have to
replace the whole chiller, of course, but that could actually come out
cheaper than the refrigerant you would need. If the piping is of sufficient
diameter to support the required flow rate, it ought to work. You mentioned
leaky shaft seals, so maybe you are replacing at least the compressor.
Geez, shouldn't you be using a semi-hermetic, anyway?

Otherwise, a do-it-yourself conversion would require an evaporator/heat
exchanger and a circulator pump. This would obviously save thousands of $,
even with a relatively affordable refrigerant.

Jon

I would like nothing more than a shiny new machine, but it aint happening. The entire load of RS-45 refrigerant is about $40,000 $9.50/lb. Compressor seals are the most expensive parts (York doesn't embarrass easily), but total parts cost will be under $8,000 to put the whole thing back in "pretty good" shape. Compare that to a 30 ton chiller, evaporator, pumps, 55,000 feet of pipe, 420 yards of concrete, etc, etc. I wish.

On Monday, May 8, 2017 at 7:57:30 PM UTC-4, Neon John wrote:
On Sat, 6 May 2017 14:21:09 -0700 (PDT), wrote:


That was my suggestion. Ideal gas law.
P*V=N*k*T. I think you could just use compressed
air. As long as you know the tank volume on your
compressor and have a good pressure gauge.
(T is in Kelvin)

You absolutely can NOT use the ideal gas law because none of the
gasses are ideal. The Van der Walls equation must be used. Learn all
about it he

https://opentextbc.ca/chemistry/chap...-gas-behavior/

John
John DeArmond
http://www.neon-john.com
http://www.tnduction.com
Tellico Plains, Occupied TN
See website for email address

Well, yes but...we're talking about approximately 2.25 cubic meters pressurized to about 2 atmospheres. Either way, though, I'll have P, n & t recorded to the best my instrumentation can give. Besides, I'm not buying refrigerant by the teaspoonful. If I get within a couple of hundred pounds, that's good enough.

On Sunday, May 7, 2017 at 6:01:12 AM UTC-4, wrote:
On 05/06/2017 1:16 PM, rangerssuck wrote:
...

I surely am hoping that we are on the low side of this range - this
stuff is expensive.

I'm sure they could probably imagine. If I were you, I'd track down the three or four previous contractors/maintenance/service people who left there and get whatever else bad news they found out about the needed repairs.

The only guy who worked on this system in the last 20 years died last month. We did have pretty extensive talks in the past couple of years, though. But he took all his knowledge to wherever lies beyond.

On 5/8/2017 7:57 PM, Neon John wrote:
... The Van der Walls equation must be used. ...

Not at the low pressures being used here.

On Monday, May 8, 2017 at 10:00:44 PM UTC-4, rangerssuck wrote:
On Sunday, May 7, 2017 at 6:01:12 AM UTC-4, wrote:
On 05/06/2017 1:16 PM, rangerssuck wrote:
...

I surely am hoping that we are on the low side of this range - this
stuff is expensive.

I'm sure they could probably imagine. If I were you, I'd track down the three or four previous contractors/maintenance/service people who left there and get whatever else bad news they found out about the needed repairs.

The only guy who worked on this system in the last 20 years died last month. We did have pretty extensive talks in the past couple of years, though. But he took all his knowledge to wherever lies beyond.

Oh, I have a pretty good handle on the "needed repairs." The problem is deciding which to do now and which can wait a while. Obviously the leaks need to be fixed. As I think I said, the compressor shaft seals are dripping oil, so they're a no-brainer but they eat up a LOT of money in parts (Someone's making big bucks at York). The valve stems all need repacking, some of the flanges need tightening, the gauge tubing all needs to be replaced, 3 of the 6 gauges (suction, discharge, oil for each of two compressors) are inoperable, and most importantly, the relief valves (two of them) are probably the originals from 1980. They should be replaced every 5 years. They both show signs of leakage. I have taken one of them off and it's full of gunky sludgy oil & dirt from being 6" off a very dirty floor.

I got a couple of the kids who work there to clean up the floor (if you're adding 20 gallons of oil a year, the oil must be going somewhere - in this case, most of it was on the floor turning to oil mud), and it made a huge difference in everyone's attitude about the project. Instead of felling like it's a disaster area, it now looks like a reasonable facsimile of a mechanical room.

I really took on this project thinking I was only going to update the control and monitoring system (that's my specialty). Things kind of spiraled from there.

When you're up to your neck in alligators, it's hard to remember that you came to drain the swamp.

So, I got to thinking that there might be a better place than AGL, Praxair or Aigas to get the nitrogen or Argon. A couple of minutes with google turned up a welding supply / gas supply about a mile from my house. They will rent a 330cf cylinder for $4.00 per month and fill it with nitrogen for $29 or argon for $65.

This is way cheaper than I would expect to pay at any of the big shops, and couldn't be much more convenient. A huge bonus.

"rangerssuck" wrote in message
...
So, I got to thinking that there might be a better place than AGL,
Praxair or Aigas to get the nitrogen or Argon. A couple of minutes
with google turned up a welding supply / gas supply about a mile from
my house. They will rent a 330cf cylinder for $4.00 per month and fill
it with nitrogen for $29 or argon for $65.

This is way cheaper than I would expect to pay at any of the big
shops, and couldn't be much more convenient. A huge bonus.

==========
Once it holds a vacuum I'd make a rough estimate of the volume with
dried compressed air, then a better one by evacuating it and filling
from a nitrogen tank nearest the estimated cf capacity. The (absolute)
pressure drop in the cylinder and the rise in the piping give you the
volume ratio. The more the gauges change, the better the resolution.
https://en.wikipedia.org/wiki/Boyle%27s_Law

-jsw

On Mon, 08 May 2017 19:45:11 -0500, dpb wrote:

On 05/08/2017 6:57 PM, Neon John wrote:
...

You absolutely can NOT use the ideal gas law because none of the
gasses are ideal. The Van der Walls equation must be used. ...

For the purposes here and at PT talking of, the correction will be of
only a few per cent, certainly within 10% or so.

Actually it will be much more significant than 10%. Why don't you set
up a model and calculate ideal and real gas laws and compare the
results before you continue to mislead this fellow.

even a 10% error is a huge amount of refrigerant for the tank size he
described.

Mine IS the voice of experience speaking.

John
John DeArmond
http://www.neon-john.com
http://www.tnduction.com
Tellico Plains, Occupied TN
See website for email address

On 05/09/2017 10:36 AM, Neon John wrote:
....

Mine IS the voice of experience speaking.
.....

Well, my ChE skoolin' tells me for these values it will be small.

But, with http://www.webqc.org/van_der_waals_gas_law.html @70F, 1 cf
enough N for about 2 atm yields P ~ 172580 Pa (~1.7 atm) while ideal gas
law for same is 173436 or about 0.5% difference.

Will have to get _very_ high pressures to make difference of any
significance and the point here isn't @ operating pressure but just a
measure of physical volume. In fact to get around 5%, took overall P~80
atm.

--

rangerssuck wrote:


I would like nothing more than a shiny new machine, but it aint happening.
The entire load of RS-45 refrigerant is about $40,000 $9.50/lb.
Compressor seals are the most expensive parts (York doesn't embarrass
easily), but total parts cost will be under $8,000 to put the whole thing
back in "pretty good" shape. Compare that to a 30 ton chiller, evaporator,
pumps, 55,000 feet of pipe, 420 yards of concrete, etc, etc. I wish.
What I was thinking, without knowing whether it would work, was to use the
EXISTING pipe in the floor for a glycol system. Now, maybe the pipes are
just too long for the glycol to flow through, but with 55,000 feet of pipe,
it seems there is PLENTY of surface to absorb heat. But, maybe the glycol
would need a lot of short pipes between manifolds, and the Freon system has
fewer, very LONG pipes, as it is absorbing heat by evaporation.

But, yes, the ONLY way it would make sense is if the existing pipe in the
floor could be used as is.

And, you can likely find a used but good 30 ton water-water chiller quite
easily on the used market. I'd start at HGR surplus. When you are talking
about $40K of refrigerant plus expensive repairs to a belt-driven compressor
which is certain to start leaking again sometime, it seems like a good idea
to look at alternatives. 30 tons is just NOT a great big chiller.

Jon

"dpb" wrote in message
news
On 05/09/2017 10:36 AM, Neon John wrote:
...

Mine IS the voice of experience speaking.
....

Well, my ChE skoolin' tells me for these values it will be small.

But, with http://www.webqc.org/van_der_waals_gas_law.html @70F, 1
cf enough N for about 2 atm yields P ~ 172580 Pa (~1.7 atm) while
ideal gas law for same is 173436 or about 0.5% difference.

Will have to get _very_ high pressures to make difference of any
significance and the point here isn't @ operating pressure but just
a measure of physical volume. In fact to get around 5%, took
overall P~80 atm.


This shows that the deviation of N2 isn't too bad at cylinder
pressure, perhaps less than the tolerance of uncalibrated gauges and
other experimental errors.
http://wps.prenhall.com/wps/media/ob...1/blb1009.html
-jsw

On 05/09/2017 4:40 PM, Jim Wilkins wrote:
....

This shows that the deviation of N2 isn't too bad at cylinder
pressure, perhaps less than the tolerance of uncalibrated gauges and
other experimental errors.
http://wps.prenhall.com/wps/media/ob...1/blb1009.html

Certainly for the present purposes, yes, indeed...

After just using the online calculator above to stick in a few values, I
wrote a Matlab script to solve the problem and generated one of the
curves in the link...with its builtin in nonlinear solver, it's
pretty-much a trivial exercise.

type neon

% the function to call for a given number moles, pressure and a starting
guess, x0

function [x,fval] = neon(p,n,x0)
[x,fval] = fzero(@pvdw,x0);

function vdw = pvdw(p)
T=(70-32)/1.8+273.15;
R = 8.3144621 ;
a=0.1408; b=0.00003913;
vdw=(p+n^2*a)*(1-n*b)-n*R*T;
end
end

The script

for
i=1:length(n),p(i,1)=neon(2000,n(i),2000);p(i,2)=p (i,1)/(n(i)*RT);end
[p(:,1)/10E5 p(:,1)/10E5*14.7 (p(:,2)-1)*100]
ans =
0.9717 14.2837 -0.7119
3.9322 57.8038 -2.5935
6.8193 100.2434 -3.8889
9.6970 142.5464 -4.4955


This is for roughly 1 to 10 atm at 70F and the deviation is only about
5% at 10 atm. I was looking at another dataset earlier when said 80
atm; got to thinking that was a little high. But, as the figures show,
these numbers are so near to the LH pressure axis as to not be
discernible from 1; the last column above converted the ratio to the
deviation in percent; the first column is atm, second psi corresponding.

I think rangers can safely ignore the effects, yes...

--

On Tuesday, May 9, 2017 at 8:37:03 AM UTC-7, Neon John wrote:
On Mon, 08 May 2017 19:45:11 -0500, dpb wrote:

On 05/08/2017 6:57 PM, Neon John wrote:

You absolutely can NOT use the ideal gas law because none of the
gasses are ideal. The Van der Walls equation must be used. ...

For the purposes here and at PT talking of, the correction will be of
only a few per cent, certainly within 10% or so.

Actually it will be much more significant than 10%.

Depends on which recommendations we're talking about. If the
test is to pump down, then fill from a lecture cylinder and measure
achieved pressure, and use the weight-before and weight-after of
the lecture cylinder to determine the gas quantity, then
the only pressure/volume relationships are on low-pressure
gas. The cylinder before/after pressure DOES need van der Waals
or other corrections, but if you go by cylinder WEIGHT, not
so much.

If you want to empty a 4.5 foot cylinder for the test, and don't have
a suitable balance to weigh that, and use the pressure gage, that's
a whole different scenario.

On Monday, May 8, 2017 at 7:57:30 PM UTC-4, Neon John wrote:
On Sat, 6 May 2017 14:21:09 -0700 (PDT), wrote:


That was my suggestion. Ideal gas law.
P*V=N*k*T. I think you could just use compressed
air. As long as you know the tank volume on your
compressor and have a good pressure gauge.
(T is in Kelvin)

You absolutely can NOT use the ideal gas law because none of the
gasses are ideal. The Van der Walls equation must be used. Learn all
about it he

https://opentextbc.ca/chemistry/chap...-gas-behavior/

Sure I learned that in my physics thermo classes.
(Helium is pretty close to idea... but spendy)
For a rough measure of volume (a few percent) I think air will be fine.
Temperature might be a bigger uncertainty.

George H.

John
John DeArmond
http://www.neon-john.com
http://www.tnduction.com
Tellico Plains, Occupied TN
See website for email address

On Tuesday, May 9, 2017 at 11:37:03 AM UTC-4, Neon John wrote:
On Mon, 08 May 2017 19:45:11 -0500, dpb wrote:

On 05/08/2017 6:57 PM, Neon John wrote:
...

You absolutely can NOT use the ideal gas law because none of the
gasses are ideal. The Van der Walls equation must be used. ...

For the purposes here and at PT talking of, the correction will be of
only a few per cent, certainly within 10% or so.

Actually it will be much more significant than 10%. Why don't you set
up a model and calculate ideal and real gas laws and compare the
results before you continue to mislead this fellow.

even a 10% error is a huge amount of refrigerant for the tank size he
described.

Mine IS the voice of experience speaking.

Huh, OK. It's not something I ever measured.
So for dry air at what pressure is the error ~10%?
(I guess I can google it.)

George H.

John
John DeArmond
http://www.neon-john.com
http://www.tnduction.com
Tellico Plains, Occupied TN
See website for email address

On Tuesday, May 9, 2017 at 9:29:09 AM UTC-4, Jim Wilkins wrote:
"rangerssuck" wrote in message
...
So, I got to thinking that there might be a better place than AGL,
Praxair or Aigas to get the nitrogen or Argon. A couple of minutes
with google turned up a welding supply / gas supply about a mile from
my house. They will rent a 330cf cylinder for $4.00 per month and fill
it with nitrogen for $29 or argon for $65.

This is way cheaper than I would expect to pay at any of the big
shops, and couldn't be much more convenient. A huge bonus.

==========
Once it holds a vacuum I'd make a rough estimate of the volume with
dried compressed air, then a better one by evacuating it and filling
from a nitrogen tank nearest the estimated cf capacity. The (absolute)
pressure drop in the cylinder and the rise in the piping give you the
volume ratio. The more the gauges change, the better the resolution.
https://en.wikipedia.org/wiki/Boyle%27s_Law

-jsw

That's a good one, but it requires that you know the actual cf in the tank first. I have no idea how accurately that gets measured when tanks are filled.

On Wednesday, May 10, 2017 at 11:31:19 AM UTC-4, wrote:
On Monday, May 8, 2017 at 7:57:30 PM UTC-4, Neon John wrote:
On Sat, 6 May 2017 14:21:09 -0700 (PDT), wrote:


That was my suggestion. Ideal gas law.
P*V=N*k*T. I think you could just use compressed
air. As long as you know the tank volume on your
compressor and have a good pressure gauge.
(T is in Kelvin)

You absolutely can NOT use the ideal gas law because none of the
gasses are ideal. The Van der Walls equation must be used. Learn all
about it he

https://opentextbc.ca/chemistry/chap...-gas-behavior/

Sure I learned that in my physics thermo classes.
(Helium is pretty close to idea... but spendy)
For a rough measure of volume (a few percent) I think air will be fine.
Temperature might be a bigger uncertainty.

George H.

John
John DeArmond
http://www.neon-john.com
http://www.tnduction.com
Tellico Plains, Occupied TN
See website for email address

Once again for all concerned (and I am overwhelmed and thankful for all the responses), We're not buying this stuff by the teaspoonful. It will be delivered in 800 pound (net) and 110 pound (net) tanks. I can return what I don't use. I'm really just trying to get a reasonable ballpark number to order with.

I expect to be running this test Saturday, so stand by for results.

"rangerssuck" wrote in message
...

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.
================================================== ==================================================

Just as a sanity check when you do the pressurize with nitrogen test, I get
a volume of 72 cu ft or 2039 L for 10 miles of 1/2" ID tubing. At STP, 0 C
and 101 kPa nitrogen has a density of 1.25 g/L so at STP 72 cu ft would
weigh 5.62 lbs (I'm ignoring the difference between room temperature and STP
for this estimate :-)). If you start at atmospheric pressure you would need
3x72 cu ft = 216 cu ft to reach 44.1 psig which should be completely safe
since the vapor pressure of R22 at 75 F is 132 psig. So you will need at
least a couple of tanks of nitrogen on hand to be safe, and a refrigeration
scale that can do 0.1 lbs at the weight of a full tank of nitrogen with
regulator should let you get an answer in the 5-10% range. Have fun.

--
Regards,
Carl Ijames