Rule Of Thumb For Walk-In Charging?

[LibertyTree]

Hi, I was wondering if there is a rule of thumb for charging up new walk-in freezer/refrigerator units. I have heard that you put in a small amount then charge by the sight glass. If this is so, how do you know how much refrigerant to start with? Is there a rule of thumb for compressor horsepower? How do you guys do it?

[Tommy knocker]

Most manufactures will provide total charge weight, based on receiver capacity. Heatcraft publishes a manual with total charge weights by model #. Charging to a full sight glass will not get you a full charge, especially with ambient above 65-70 degrees where you would be way short on charge. Several good threads on here about this subject with alot of good tips and information.

[2sac]

Not really a rule of thumb. Depends on the condensing unit being inside or outside, is there a headmaster or fan cycle control? Receivers sized properly, You may need to add or subtract a "winter charge" if condenser is not sized properly. Clear the sight glass. There is a formula depending on what ambient, condenser size, pipe size to add for headmaster. Sorry I do not have this info with me.

[valdelocc]

Hi, I was wondering if there is a rule of thumb for charging up new walk-in freezer/refrigerator units. I have heard that you put in a small amount then charge by the sight glass. If this is so, how do you know how much refrigerant to start with? Is there a rule of thumb for compressor horsepower? How do you guys do it?

if the condenser is inside then clear the sight glass plus a couple of ounces and you good to go.

[jpsmith1cm]

if the condenser is inside then clear the sight glass plus a couple of ounces and you good to go.

And, if it is outside, read and follow this http://sporlanonline.com/90-30-1_072012.pdf

[Kenscom]

Charging to a clear sight glass can only be used if the expansion valve is not oversized and the proper oriface is installed. A heat exchanger on liquid to suction will change things too. Most walk ins I see under 1 horse do not have a sight glass on them. If the installed equipment is properly sized and a receiver is present then a clear sight glass works most of the time. With headmaster without a checkvalve on condenser outlet the condenser will need to fill up before head rises much on low ambiant operation. If the equipment does not have a pumpdown and it has a headmaster on it, a suction accumulator will be required to keep valves in the compressor.

[LibertyTree]

Awesome, thanks for the replies fellas. This is very helpful. If someone can dig up a chart that can help calculate charge with lineset length, outdoor ambient, compressor horse etc. I would appreciate it. Also, what about when there are (2) fan coils to one outdoor unit? Someone else engineered and installed this system (refrigerator/Freezer with 2 outdoor units and 4 fan coils) and I'm going to start it up. I have done the small ones before but never one that's as big as a house...

[jpsmith1cm]

Awesome, thanks for the replies fellas. This is very helpful. If someone can dig up a chart that can help calculate charge with lineset length, outdoor ambient, compressor horse etc. I would appreciate it. Also, what about when there are (2) fan coils to one outdoor unit? Someone else engineered and installed this system (refrigerator/Freezer with 2 outdoor units and 4 fan coils) and I'm going to start it up. I have done the small ones before but never one that's as big as a house...

Size of the equipment really doesn't matter.

Larger equipment, IMO, is easier to deal with. You may actually have a receiver level gauge to use as a charging indicator if the equipment is large enough.

I've never taken the time to add up line set lengths and all that jazz. Just look at it, take a reasoned and educated guess, add 100-200 pounds and order that for start-up. You can always return unused refrigerant.

I think that you're over thinking this thing. It's a refrigerator, not brain surgery.

Hook up a charging hose, add some gas, fire it up and go from there.

[Kenscom]

Size of the equipment really doesn't matter.

Larger equipment, IMO, is easier to deal with. You may actually have a receiver level gauge to use as a charging indicator if the equipment is large enough.

I've never taken the time to add up line set lengths and all that jazz. Just look at it, take a reasoned and educated guess, add 100-200 pounds and order that for start-up. You can always return unused refrigerant.

I think that you're over thinking this thing. It's a refrigerator, not brain surgery.

Hook up a charging hose, add some gas, fire it up and go from there.

The size of the receiver will list maximum weight of water it will hold. This can be converted to refrigerant weight by specific gravity and used as the maximum charge that will fit in the receiver for service. This will determine the maximun charge for most equipment. It is very rare that the receiver will not hold the charge for service. The min charge can only be calculated by volume of liquid line, condenser etc.

[jpsmith1cm]

The size of the receiver will list maximum weight of water it will hold. This can be converted to refrigerant weight by specific gravity and used as the maximum charge that will fit in the receiver for service. This will determine the maximun charge for most equipment. It is very rare that the receiver will not hold the charge for service. The min charge can only be calculated by volume of liquid line, condenser etc.

The amount of refrigerant in the receiver is largely immaterial for an operating system other than that a liquid seal is maintained at the receiver outlet at all times.

Larger, built up systems can have miles of hidden piping, making it impossible to compute the charge by measuring the lines and also impossible to pump the entire system down for servicing.

The biggest priority is to maintain temperature. The best way to do that is to ensure that quality liquid is delivered to the TEV at all times.

Limiting yourself to the receiver's capacity as determined by the method you describe isn't going to work in all cases.

Example. I'm commissioning systems today. The listed receiver capacity of one system at 80% is 702#. The system contains 1350# of R-22 with a 20-25% running receiver level. By your logic, I should remove almost half of the system's charge. That would result in a quarter of a grocery store not maintaining proper product temperatures.

[Kenscom]

The amount of refrigerant in the receiver is largely immaterial for an operating system other than that a liquid seal is maintained at the receiver outlet at all times.

Larger, built up systems can have miles of hidden piping, making it impossible to compute the charge by measuring the lines and also impossible to pump the entire system down for servicing.

The biggest priority is to maintain temperature. The best way to do that is to ensure that quality liquid is delivered to the TEV at all times.

Limiting yourself to the receiver's capacity as determined by the method you describe isn't going to work in all cases.

Example. I'm commissioning systems today. The listed receiver capacity of one system at 80% is 702#. The system contains 1350# of R-22 with a 20-25% running receiver level. By your logic, I should remove almost half of the system's charge. That would result in a quarter of a grocery store not maintaining proper product temperatures.

You are exactly correct! I had no idea the guy needed help on a grocery store walk in with miles of hidden pipe. I was thinking engineered system for cooler/freezer. Sorry about that.

[LibertyTree]

Thanks for the help guys, really appreciate it. I ended up starting the units up a few days ago (3 hours away) The electricians were supposed to have the electrical done, it wasn't... As the day dwindled away they managed to get one unit wired. It didn't fire up the fan coils. I had to spend a couple of hours getting the wiring sorted out and by that time it was almost dark-thirty so I had to stay the night. Next morning the other unit had not been wired... Took almost all day to get that done too. Unfortunately one of the cooler fan coils had a pinhole leak that prevented it from pulling down past 2000 microns. Couldn't start that one up. Anyhow, I pulled the freezer down to 500 microns (took 5 hours.) I called the tech rep to ask about the amount of refrigerant to add after the sight glass is clear to backflood the compressor in winter conditions. Apparently that compressor (Copeland Discus) needs 4 pounds of refrigerant per horsepower. I added said amount and everything went well.

[ryan1088]

Thanks for the help guys, really appreciate it. I ended up starting the units up a few days ago (3 hours away) The electricians were supposed to have the electrical done, it wasn't... As the day dwindled away they managed to get one unit wired. It didn't fire up the fan coils. I had to spend a couple of hours getting the wiring sorted out and by that time it was almost dark-thirty so I had to stay the night. Next morning the other unit had not been wired... Took almost all day to get that done too. Unfortunately one of the cooler fan coils had a pinhole leak that prevented it from pulling down past 2000 microns. Couldn't start that one up. Anyhow, I pulled the freezer down to 500 microns (took 5 hours.) I called the tech rep to ask about the amount of refrigerant to add after the sight glass is clear to backflood the compressor in winter conditions. Apparently that compressor (Copeland Discus) needs 4 pounds of refrigerant per horsepower. I added said amount and everything went well.

4 pounds per horsepower??!? I have ever heard that. What if......it has a headmaster? What if it doesn't? Big difference in charge there....

[LibertyTree]

4 pounds per horsepower??!? I have ever heard that. What if......it has a headmaster? What if it doesn't? Big difference in charge there....

Thats what the 1 tech guy from Coldzone told me, I hope he wasn't a retard

[Tommy knocker]

The amount of refrigerant in the receiver is largely immaterial for an operating system other than that a liquid seal is maintained at the receiver outlet at all times.

Larger, built up systems can have miles of hidden piping, making it impossible to compute the charge by measuring the lines and also impossible to pump the entire system down for servicing.

The biggest priority is to maintain temperature. The best way to do that is to ensure that quality liquid is delivered to the TEV at all times.

Limiting yourself to the receiver's capacity as determined by the method you describe isn't going to work in all cases.

Example. I'm commissioning systems today. The listed receiver capacity of one system at 80% is 702#. The system contains 1350# of R-22 with a 20-25% running receiver level. By your logic, I should remove almost half of the system's charge. That would result in a quarter of a grocery store not maintaining proper product temperatures.

I don't think he has a whole store rack here. Sounds like a couple walk ins. Excellent info you have provided but maybe a bit above this thread. A simple WI with a couple fan coils receiver capacity method most efficient for initial charging IMO.

[LibertyTree]

I don't think he has a whole store rack here. Sounds like a couple walk ins. Excellent info you have provided but maybe a bit above this thread. A simple WI with a couple fan coils receiver capacity method most efficient for initial charging IMO.

It is a couple of walk ins. albeit large ones. I do appreciate that info as well, I hope to get into the really large stuff soon

[jpsmith1cm]

4 pounds per horsepower??!? I have ever heard that. What if......it has a headmaster? What if it doesn't? Big difference in charge there....

I agree.

Tech guy might need a lesson.

[jpsmith1cm]

I don't think he has a whole store rack here. Sounds like a couple walk ins. Excellent info you have provided but maybe a bit above this thread. A simple WI with a couple fan coils receiver capacity method most efficient for initial charging IMO.

Whole rack or a couple of walk-ins.

It doesn't matter.

Charging by receiver capacity is a nice start, but if you aren't delivering quality liquid to the TEV, you aren't keeping temp, and you may not be able to pump it down into itself. Fact of life.

I used those racks as an example, but I can find others where charging to receiver capacity would severely undercharge the unit without going to a full rack system.

[LibertyTree]

I agree.

Tech guy might need a lesson.

I certainly hope not... The job is 3 hours away and that service call would really suck. Box got down to temp just fine, everything seemed to be going great.

[KB Cool]

How do you calculate the new micro channel coils additional charge with Head master?