Results 1 to 9 of 9
  1. #1
    Join Date
    Jan 2016
    Location
    The triangle in the Keystone
    Posts
    1,221
    Post Likes

    Refrigeration day

    I remember reading about a “refrigeration day” a while back but I don’t remember the particulars. I believe the day is 18 hrs long?

    Can someone explain it for me. Defrosts, off cycle, etc.

  2. #2
    Join Date
    Dec 2014
    Posts
    2,858
    Post Likes
    You missed it! It was June 26th!

    18 hour runtime at design conditions. Plus 4x defrost at 45 min each. Plus drip time plus fudge factor, is how I think of it.

    Sent from my SM-G950U using Tapatalk

  3. #3
    Join Date
    May 2014
    Location
    Bay Area California
    Posts
    24,563
    Post Likes
    Maybe because you can't go home until the refer is back on line? Nothing like comfort cooling.


    Quote Originally Posted by VanMan812 View Post
    I remember reading about a “refrigeration day” a while back but I don’t remember the particulars. I believe the day is 18 hrs long?

    Can someone explain it for me. Defrosts, off cycle, etc.
    If you were a real tech, you'd solder a relay on that board and call it good to go.

    I do a triple evac with nitro to remove non condensables.

    I use 56% silver on everything except steel.

    Did you really need the " If you were a real tech " ??

  4. Likes icy78 liked this post
  5. #4
    Join Date
    Sep 2002
    Posts
    26,368
    Post Likes
    A refrigeration system must remove all the heat from the conditioned space in one 24 hour day. Because if it takes longer than a day - the heat will accumulate and the temperature of the space will rise.

    But there is more required in the operation of a refrigerating system than just cooling - because most refrigeration evaporators accumulate frost - as they operate below 32º F. - in order to cool the space to 40º or lower. So some time to melt the frost is also required. Whether it's off-cycle-defrost or powered defrost (electric, hot gas, reverse cycle, etc.) doesn't matter - every defrost method takes time to melt frost.

    That defrost-time must be subtracted from the standard 24 hours in a regular day. The resulting shorter-day is called: A Refrigeration Day.

    Just as an example: if the system requires four half hour defrosts per day - that would result in a 20 hour refrigeration-day for that system.

    What does that mean?

    Well; because 20 hours is only 80% of 24 hours - the condensing unit's rated capacity (which is based on the number of BTU's which will be removed while running 100% of the time) has to be at least 20% larger than heat load of the conditioned space.

    Because the condensing unit Still has to remove all the heat - but it has to accomplish that task in 20 hours instead of in 24 hours.

    Ignorance of this fact results in maybe the largest single problem with small site-built commercial refrigeration systems: the condensing unit is undersized.

    PHM
    ---------


    Quote Originally Posted by VanMan812 View Post
    I remember reading about a “refrigeration day” a while back but I don’t remember the particulars. I believe the day is 18 hrs long?

    Can someone explain it for me. Defrosts, off cycle, etc.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  6. #5
    Join Date
    May 2014
    Location
    Bay Area California
    Posts
    24,563
    Post Likes
    Oh, a refrigeration day. Looks like I'm forgetting more than I know.

    When I first got into the trade, the rule of thumb was to size the refer equipment to run 2/3's of the time.
    If you were a real tech, you'd solder a relay on that board and call it good to go.

    I do a triple evac with nitro to remove non condensables.

    I use 56% silver on everything except steel.

    Did you really need the " If you were a real tech " ??

  7. #6
    Join Date
    Jan 2016
    Location
    The triangle in the Keystone
    Posts
    1,221
    Post Likes
    Thread Starter
    Quote Originally Posted by Poodle Head Mikey View Post
    A refrigeration system must remove all the heat from the conditioned space in one 24 hour day. Because if it takes longer than a day - the heat will accumulate and the temperature of the space will rise.

    But there is more required in the operation of a refrigerating system than just cooling - because most refrigeration evaporators accumulate frost - as they operate below 32º F. - in order to cool the space to 40º or lower. So some time to melt the frost is also required. Whether it's off-cycle-defrost or powered defrost (electric, hot gas, reverse cycle, etc.) doesn't matter - every defrost method takes time to melt frost.

    That defrost-time must be subtracted from the standard 24 hours in a regular day. The resulting shorter-day is called: A Refrigeration Day.

    Just as an example: if the system requires four half hour defrosts per day - that would result in a 20 hour refrigeration-day for that system.

    What does that mean?

    Well; because 20 hours is only 80% of 24 hours - the condensing unit's rated capacity (which is based on the number of BTU's which will be removed while running 100% of the time) has to be at least 20% larger than heat load of the conditioned space.

    Because the condensing unit Still has to remove all the heat - but it has to accomplish that task in 20 hours instead of in 24 hours.

    Ignorance of this fact results in maybe the largest single problem with small site-built commercial refrigeration systems: the condensing unit is undersized.

    PHM
    ---------
    So is the refrigeration day 24hrs minus total defrost time? What about off cycle time?




    Sent from my iPhone using Tapatalk

  8. #7
    Join Date
    Dec 2014
    Posts
    2,858
    Post Likes
    Say you're selecting on an 18-hour run time.(Typical)( a smaller TD and a coil that's warmer than 32 degrees you may be able to get away with a 20 or 22 hour run time because you won't have defrost time)

    Then ,for example, if your total load is 100,000 BTUs in 24 hours you would then divide that by 18 hours as a start for selecting your equipment. So 5,550 btu/hr.


    In other words because you will have defrost time and recovery time after defrost then you will not have all 24 hours available to cool so you will have to size the equipment for that adjusted/ available, hourly run time.

    Sent from my SM-G950U using Tapatalk

  9. Likes VanMan812 liked this post
  10. #8
    Join Date
    Sep 2002
    Posts
    26,368
    Post Likes
    The proper design is to be adequate for worst-situation conditions. "off cycle time" is the way the system capacity is adjusted for less-than-worst-situation conditions. Off-cycle time is not something which has to be considered separately from defrost time.

    PHM
    --------


    Quote Originally Posted by VanMan812 View Post
    So is the refrigeration day 24hrs minus total defrost time? What about off cycle time?
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  11. Likes VanMan812 liked this post
  12. #9
    Join Date
    Oct 2011
    Location
    Chicagoland Area
    Posts
    7,985
    Post Likes
    Med 16 hours run time low temp 18 hours run time.
    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

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •