How much refrigerant does it hold?

[idontgetit]

So I get this question a lot from newer and some older techs a lot so I went on a quest to try and gather some info to share with them. I came up pretty dry actually, there are a couple of really great spread sheets out there that are for massive systems, but not much for the smaller stuff. It is not even particularly easy to find out how much a receiver holds which I found kind of odd in this day and age. Being kind of old school, whipping the calculator out and punching in the size and density gets me there, but it should be easier.

So I made up a small spreadsheet that does all the math in hidden cells that will give me an approximate number quick and easy. Goes from diameter to R2, then from in3 to ft3, then the density at 90 which is the ahri standard but a lot of the gas companies only make the 75 degree number readily available, go figure. so I waded through thermo tables to get the correct number and then added a line size calc into it as well. There are a lot of quick answers on the line sets but needed to be able to calc the condenser tubes for the low ambient applications as well.

I didn't bother with the evap or suction side of things as it is not a lot and the max so to speak is the pump down holding capacity so it is more of a "less than" result. One other doughnut in the middle of it all, when I checked it against a few mfg specs there were a few minor differences that look like just a bit of rounding in the formulas. This happens if you try and use "additional line numbers" for things like the condenser calcs. It might be fine to say X ounces per foot for a line set but if your trying to calc out 1/2 inch tubing in a big condenser you may find you have 800 to 1000 feet those extra digits can add up, even the difference in annealed vs hard drawn bore can add up, I am probably just to anal about it but I pulled the data for both.

Anyway, did I completely waste my time and there IS an app for it? I looked pretty hard for one and came up blank.

[Chuck]

I just use charts found in this document to get pump down capacity of receivers. If the exact size isn't listed you can extrapolate. The density of different refrigerants isn't that much different.

https://www.rchvacparts.com/dl/SECTI...CHNOLOGIES.pdf

[bunny]

I wouldn't discount the amount of refrigerant in the evaporator. I'd need to do some research, but I'd have to guess that somewhere near 50% of the internal volume of the evaporator is filled with refrigerant. Given the lower temperature, higher density (lbs/cu ft) of the liquid at the lower temperature, this can result in a significant amount of liquid in a larger evaporator.

Same for the condenser.

Now, regarding the suction line...you're right. Not that significant

Let's take a larger system, R-22, operating at -20F SST. Assume a 15F suction vapor temperature, and a 2-1/8'' suction line, with a 250' length (typical supermarket application).

The interior dimension of 2-1/8'' pipe is 1.985''.

The internal area of the pipe is Pi x radius squared...of the pipe will be (.9925) x (.9925) x 3.14 (pi) = 3.09 sq inches

Now, converting that to square feet, divide the square inches by 144 square inches/square ft: 3.09/144 = .02147 square ft

Multiply this by the pipe length: .02147 x 250 = 5.37 cubic ft

The density of R-22 at 10 psi and 15F is .43598 lb/cu ft

5.37 cu ft x .43598 lb/cu ft = a measly 2.34 lbs.

[idontgetit]

Actually there is significant differences in the refrigerant densities.

I just use charts found in this document to get pump down capacity of receivers. If the exact size isn't listed you can extrapolate. The density of different refrigerants isn't that much different.

https://www.rchvacparts.com/dl/SECTI...CHNOLOGIES.pdf

[idontgetit]

I am discounting the evap and suction for smaller and simpler systems that are going to pump down so the amount of refrigerant in the low side is minimal. I agree on e it is up and running, the mass flow rate is equal throughout the entire system so it will be pretty evenly split.

For larger systems the other spread sheets are a far better choice. Call this sheet for 100 lbs and lower which is what I was looking for in an app.

I typically ask them what the receiver holds and get the I dont know it doesnt say on the label response.

Several times I have explained PI r2 x length over 1728 times the listed density x 0.9 but I get a lot of blank stares.

I wouldn't discount the amount of refrigerant in the evaporator. I'd need to do some research, but I'd have to guess that somewhere near 50% of the internal volume of the evaporator s.

[Chuck]

Actually there is significant differences in the refrigerant densities.

Not in the real world. A pound or 2 in a system that holds 25 lbs makes no difference.

[bunny]

Not sure what your point is Chuck.

These are small receivers. A receiver that has a pump down capacity of 2.0 lbs would never be used on a system that requires a 25 lb charge. And, you'll see that the R-22 receiver has a pump down capacity of 2.4 lbs....a 20% higher capacity than the R-404A receiver. The difference? Liquid density.

But the point I was making is that refrigerant density increases as the temperature drops. Density of R-22 at 100F is 71 lbs/cu ft, but 85.9 lbs/cu ft at -20. So, the portion of the evaporator that is filled with liquid will have a greater weight per volume. So, in terms of calculating the system charge, the refrigerant in the evaporator ought to be considered....especially on a larger system.

[Chuck]

I meant plus or minus 2 lbs not that a system holding 25 lbs would have a 2 lb receiver, not sure where that came from.

My point is that there is really no need to be so exact in charge amounts in systems with a receiver. I look at a receiver and use a chart like the one found in that document, and put in 80% and walk away with absolutely no problem. Speaking of dedicated condensing units here. Total system charge at 80 to 90 percent receiver capacity is going to be totally fine.

And in markets we are looking at receiver level anyway, might be interesting for the engineers to know what the initial charge is, but out in the field we know how much gas to add.

I just don't see a huge need for what the op is developing.

[VanMan812]

I use the DuPont piping guide when I want to know the capacity of a receiver. Actually, I google the hell out of the receiver and or condensing unit first. If I don’t find anything, then I turn to the piping guide. Section 1, pg11.

I work on mostly smaller walk-ins, just a few HP at most with short line sets. For me, calculating the Total Equivalent Length on these systems usually doesn’t add up to anything substantial. So what I do is calculate the low ambient charge of the system if it has a head master or I just grab the receiver size and charge to 90%.

https://icemeister.net/backroom/wp-c...g-Handbook.pdf

[idontgetit]

. I look at a receiver and use a chart like the one found in that document, and put in 80% and walk away with absolutely no problem. Speaking of dedicated condensing units here. Total system charge at 80 to 90 percent receiver capacity is going to be totally fine.

I just don't see a huge need for what the op is developing.

That is indeed exactly what I am talking about, however your chart refrences only 3 refrigerants and we tend to deal with a lot more than that and the densities are far more broad.

You may put 155 lbs of 507 in a receiver but if it takes 422 your going to be a lot closer to 172 pounds for the same volume receiver. Not a big deal if you use the 422 number and put in 507 but if you go the other way it's going to be a problem.

I just figured by now there would be an app that you simply put your diameter and length in and it would spit out the capacity for various gases.

I already have made a spread sheet for the 8 gases we use most, I simply thought there might be a cleaner app since they have put charts etc for about every gas on the planet.

Been doin the math since 82, just looking to clean and speed it up is all and thought someone might have done it before.

[itsiceman]

Me oldest son is a Freshman ME student and got a rundown from a Sr. Mentor Student who told him not to take the Elective HVAC Class because it was too hard and useless lol
He couldn't believe it

[Chuck]

That is indeed exactly what I am talking about, however your chart refrences only 3 refrigerants and we tend to deal with a lot more than that and the densities are far more broad.

You may put 155 lbs of 507 in a receiver but if it takes 422 your going to be a lot closer to 172 pounds for the same volume receiver. Not a big deal if you use the 422 number and put in 507 but if you go the other way it's going to be a problem.

I just figured by now there would be an app that you simply put your diameter and length in and it would spit out the capacity for various gases.

I already have made a spread sheet for the 8 gases we use most, I simply thought there might be a cleaner app since they have put charts etc for about every gas on the planet.

Been doin the math since 82, just looking to clean and speed it up is all and thought someone might have done it before.

A receiver that size will have a level gauge or sight glasses, I don't see the need to calculate it just pump it down and fill it however full you want.