Page 1 of 3 123 LastLast
Results 1 to 13 of 27
  1. #1
    Join Date
    Jun 2011
    Location
    Seattle WA
    Posts
    1,241

    Rule Of Thumb For Walk-In Charging?

    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?
    America; first we fight for our freedom,
    then we make laws to take it away.

    -Alfred E Newman

  2. #2
    Join Date
    Jul 2012
    Location
    Western KY
    Posts
    1,221
    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.

  3. #3
    Join Date
    Oct 2011
    Location
    Chicagoland Area
    Posts
    4,629
    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.
    Officially, Down for the count

    YOU HAVE TO GET OFF YOUR ASS TO GET ON YOUR FEET

    I know enough to know, I don't know enough
    Liberalism-Ideas so good they mandate them

  4. #4
    Join Date
    Nov 2004
    Location
    up in the hizzy
    Posts
    1,384
    Quote Originally Posted by LibertyTree View Post
    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.

  5. #5
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,692
    Quote Originally Posted by valdelocc View Post
    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

  6. #6
    Join Date
    Jan 2011
    Posts
    25
    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.

  7. #7
    Join Date
    Jun 2011
    Location
    Seattle WA
    Posts
    1,241
    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...
    America; first we fight for our freedom,
    then we make laws to take it away.

    -Alfred E Newman

  8. #8
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,692
    Quote Originally Posted by LibertyTree View Post
    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.

  9. #9
    Join Date
    Jan 2011
    Posts
    25
    Quote Originally Posted by jpsmith1cm View Post
    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.

  10. #10
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,692
    Quote Originally Posted by Kenscom View Post
    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.

  11. #11
    Join Date
    Jan 2011
    Posts
    25

    Smile

    Quote Originally Posted by jpsmith1cm View Post
    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.

  12. #12
    Join Date
    Jun 2011
    Location
    Seattle WA
    Posts
    1,241
    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.
    America; first we fight for our freedom,
    then we make laws to take it away.

    -Alfred E Newman

  13. #13
    Join Date
    Mar 2009
    Location
    Mid-Mo
    Posts
    3,595
    Quote Originally Posted by LibertyTree View Post
    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....

Page 1 of 3 123 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event