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  1. Replies
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    In your example, the defrost clock terminals 1...

    In your example, the defrost clock terminals 1 and 4 would be in series with the thermostat on the left of this schematic: This is a classic pumpdown control scheme for a refrigeration system.


    ...
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    How does a refrigeration tech get a vacation in...

    How does a refrigeration tech get a vacation in the summer? ;)
  3. The Scotsman CM/CME evaporators are like that. ...

    The Scotsman CM/CME evaporators are like that.

    As for replating, I have only seen it done one time about 25 years ago on a Manitowoc G-series, back when their evaporators were failing so bad they...
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    This has already been done. It's called a window...

    This has already been done. It's called a window air conditioner. ;)
  5. If you compare the basic suction line sizing for...

    If you compare the basic suction line sizing for R22 vs R410A for this job, your capacity loss due to the suction line pressure drop is actually less with the higher capacity R410A system.

    With...
  6. Thread: Pro forum

    by icemeister
    Replies
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    I checked the Membership Committee records and...

    I checked the Membership Committee records and you were accepted for Pro Technical membership on Aug 10, 2017. That was during a period for which the site lost a lot of data due to a server crash...
  7. Basically, yes but you need to add a bit more...

    Basically, yes but you need to add a bit more detail for it to be realistic.

    There are other sources of superheating of the refrigerant vapor after it leaves the evaporator in addition to the...
  8. My father did a lot of supermarket installations...

    My father did a lot of supermarket installations back in the 50's for A&P (when our mutual friend Perley Barker was in charge in their Boston office). In those early days evacuation wasn't a...
  9. Looks good! :cheers:

    Looks good! :cheers:
  10. Now you've got it. Good job!

    Now you've got it. Good job!
  11. This is a good example of how to plot the...

    This is a good example of how to plot the compression line (constant entropy) on a PH chart. (Start watching at about 4:00 and end at 5:30) He explains it very well and has a good playlist on...
  12. I'll go over plotting a constant entropy curve...

    I'll go over plotting a constant entropy curve once more:

    To plot a constant entropy curve you start at the point representing the entrance of the compressor. Call this point 1.
    From point 1,...
  13. The subcooling looks right. Good. Now try to...

    The subcooling looks right. Good.

    Now try to follow what I said about the constant entropy lines.
  14. You're not following the constant entropy line...

    You're not following the constant entropy line for the compression. It looks like you just drew a random line and called it good. Just start at the compressor inlet point 1 and follow the constant...
  15. Referencing the R404A diagram, your subcooling...

    Referencing the R404A diagram, your subcooling line is all the way to the left so it's indicating you have 78F of subcooling, which I'm sure you didn't intend to do. Try doing it again except start...
  16. I've seen those far too often. They were...

    I've seen those far too often. They were probably taught to purge the system rather than pull a vacuum too.
  17. It's true that manufacturers of condensing units...

    It's true that manufacturers of condensing units tend to run their TD's on the high side, some as much as 30-35F, but when you're selecting your own condenser you have the freedom to choose your own...
  18. Yep, the condenser is figured the same as the...

    Yep, the condenser is figured the same as the evaporator except it's upside down.
  19. You know everything you need to figure ot the...

    You know everything you need to figure ot the head pressure, you just know you know it. ;)

    You need to design a system for a walk-in cooler. Start at the beginning, with a pencil and paper. What...
  20. I agree with you description of a TXV. What...

    I agree with you description of a TXV.

    What does it do? It controls superheat.

    How does it do that? By regulating refrigerant flow.
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    I would consider using a Heresite coating. Some...

    I would consider using a Heresite coating. Some manufacturers like possibly Heatcraft or Trenton will have this done on special order or you can send your parts directly to them to be coated (which...
  22. That's when you're dealing with air...and the...

    That's when you're dealing with air...and the answer you got was not correct. Even when dealing with air (psychrometrics) ,enthalpy is the heat content at a given point in Btu/lb, which has nothing...
  23. https://www.youtube.com/watch?v=GokBgQ1LgDI

    https://www.youtube.com/watch?v=GokBgQ1LgDI
  24. You can ask what is "h" at a specific point but...

    You can ask what is "h" at a specific point but it means nothing. "Δh" can be the heat absorbed by the evaporator, rejected by the condenser and more.

    Ask what is the "Δh" between point 1 and 4...
  25. Concentrate on understanding Enthalpy as it's...

    Concentrate on understanding Enthalpy as it's what is important in refrigeration.

    Enthalpy by itself is just a number and as such not particularly useful. Even when comparing two refrigerants'...
  26. Good advice. The Sporlan article I posted in...

    Good advice. The Sporlan article I posted in Post #287 is an example of a refrigeration cycle analysis which gets about as deep in thermodynamics as any of us would ever get. It never mentions...
  27. [QUOTE=idontgetit;25744392] You're going in...

    You're going in circles, so I'm done. Bye
  28. [QUOTE=idontgetit;25744342] I agree that it...

    I agree that it regulates flow, however the it regulates the flow to maintain constant superheat, not to maintain constant pressure.

    I specifically stated that the TXV senses evaporator pressure...
  29. Probably the best example of how a PH diagram can...

    Probably the best example of how a PH diagram can be used is here:
    https://sporlanonline.com/literature/education/5-200.pdf
  30. Enthalpy is basically the heat content expressed...

    Enthalpy is basically the heat content expressed in Btu/lb. It's represented on the Mollier diagram as "h". By itself it really doesn't tell us much, but when two enthalpy quantities are compared,...
  31. Either you have no idea how a thermostatic...

    Either you have no idea how a thermostatic expansion valve actually works or you simply like to argue. :rolleyes:

    It does use evaporator pressure as one of the three components which modulate the...
  32. This is the same diagram with the addition of...

    This is the same diagram with the addition of liquid subcooling and evaporator superheat:


    809840
  33. By the term "enthalpy diagram" do you mean a...

    By the term "enthalpy diagram" do you mean a pressure/enthalpy (PH) diagram...ie, a Mollier diagram?


    809834


    These diagrams are useful as a graphical representation of a refrigeration cycle...
  34. We each have our own way of describing the same...

    We each have our own way of describing the same thing. So be it.



    No need to argue this one. This answer is simply no. ;)



    This would be my opening statement to that argument, were we to...
  35. Now you include the change of state from liquid...

    Now you include the change of state from liquid to vapor framed by your molecular movement model. Why didn't you mention it before? It's quite relevant to what we were discussing here...ie, what...
  36. Sorry, but I don't agree with the near adiabatic...

    Sorry, but I don't agree with the near adiabatic compression thing.

    For the expansion and the refrigerant getting colder due to the reduced internal friction, that may fit a scenario where you...
  37. You're correct in saying the expansion process is...

    You're correct in saying the expansion process is adiabatic, meaning the enthalpy or heat content remains constant. Compression however is not adiabatic, it's isentropic where the entropy remains...
  38. The flooded chiller is a good example. I ...

    The flooded chiller is a good example. I learned a lot peering into sightglasses when with D/B. ;)

    Once, although I wasn't part of the service department, since I was in the area that day I was...
  39. If you're viewing HVAC-Talk using a cell phone...

    If you're viewing HVAC-Talk using a cell phone the software detects that and switches to mobile mode which does't have the full editor for posts, so that's why you can't find how to do attachments.
    ...
  40. I can link you to the one on my website I based...

    I can link you to the one on my website I based it on: https://icemeister.net/backroom/icemeisters-ramblings/air-cooled-condenser-sizing-selection

    But you have to be registered and logged in to...
  41. You'll have to get the Journal. ;) I don't...

    You'll have to get the Journal. ;)

    I don't think they would appreciate me posting their copyrighted material here. The RSES Journal's editor used to be the editor of Contracting Business, so he...
  42. valdelocc is referring to an article I wrote for...

    valdelocc is referring to an article I wrote for the July issue of the RSES Journal.
  43. I don't know how regularly it might be, but I...

    I don't know how regularly it might be, but I hope to do more refrigeration-related articles in the future.
  44. With today's mandated higher SEER residential A/C...

    With today's mandated higher SEER residential A/C units it's probably not worth the effort to gain any additional subcooling than what the standard unit already gets via its built-in subcooling...
  45. I'm looking for a good example of how to show the...

    I'm looking for a good example of how to show the thermodynamics of a liquid subcooler on a rack system. I may have to rest to pencil and paper. LOL
  46. I think you know the answers now but you're still...

    I think you know the answers now but you're still don't have a clear picture in your mind of what's going on.

    The thing is, nobody (unless you're a research scientist) really knows what we're...
  47. An little side-note relating to this topic for...

    An little side-note relating to this topic for all the market techs out there who typically see mechanical subcoolers on their racks, did you know that the capacity boost that is gained from a...
  48. I want to clarify what you're saying about the...

    I want to clarify what you're saying about the flash gas cooling the remaining liquid.

    By its traditional definition, flash gas is the result of the boiling or flashing off of a portion of the...
  49. You're forgetting that the heat is not only due...

    You're forgetting that the heat is not only due to the higher temperature liquid entering the TXV, when this liquid reaches the low pressure of the evaporator it is suddenly becomes what is...
  50. Look at it this way... The mechanism or...

    Look at it this way...

    The mechanism or driving force to induce boiling is a temperature difference (ΔT). You then ask, "What temperature difference?"

    It's the difference between the...
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