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  1. #151
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    Re: Refrigeration 101



    Gary this is great info I do appreciate it could you tell me what is meant by " if the superheat is right at( design space temp) and the subcooling is not more than 15F/8.5K then the system has the right charge.



  2. #152
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    Re: Refrigeration 101

    It is reaaly nice way you put up required basic information of refrigeration...!!! Good one...!!!
    Last edited by frank; 30-01-2011 at 02:47 PM.

  3. #153
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    Re: Refrigeration 101

    Quote Originally Posted by chillyblue View Post
    If the superheat is high would the delta-T be much higher than when you have a normal superheat??

    Am i correct in saying you should have approx (commercial refrigeration) 3 to 6 Deg C temp difference (air on to air air off)

    Would the temp difference (air on to air off) be the same regardless of the high or correct room temp???

    I.e design room temp 0 deg C
    will the air on-off temp still be 3- 6 deg C difference when the room temp is 20 deg C
    And will it still be 3-6 deg C when the room is at 1 deg C

    CB
    Delta=T upper limit differs for various types of systems as well as for different design temperature and humidity requirements. And this goes beyond the scope of "Refrigeration 101".

    Suffice it to say that if you are familiar with the delta-T limit for a particular type of system, anything above this limit is an unambiguous indicator of an airflow problem.

  4. #154
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    Re: Refrigeration 101

    Sir,

    I am a commer to this site, well your version of refrigeration is so simple as it is communicable to every one.

    Thanks

    Chandramouli.G

  5. #155
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    Thumbs up Re: Refrigeration 101

    Thanks...I follow the reasoning...it helps to grasp the basic concept(s)...you're an excellent teacher...(where would we be without IT...finding such good answers from someone on the other side of the globe, with the click of a mouse)

  6. #156
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    Re: Refrigeration 101

    Quote Originally Posted by gwynn jones View Post
    Oh I very much agree -I work with a few lads who will fiddle with the TEV every call - makes even more trouble
    I remember working for a parts house where about 40-50% of the tev's we sold went to ONE tech.

  7. #157
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    Re: Refrigeration 101

    You dont sell/supply parker valves do you?

    It is true, txv rarely seldom need adjusting. Only adjusted maybe 2 from STD setting after installs, all rest had to be adjusted because last bloke wound it silly for who knows why...

    Is there any good threads about superheat checking/adjustment on multi evap systems? Seem to do alot of them where I'm at ATM mostly single evap/cond units previous.

    I have been using evap outlet shraeder valve for evap pressures where available and pipe temp probe at bulb location for each evap coil on system - but as not all systems have evap coil access can you use sst at comp?
    "Old fridgies never die, they just run out of gas!"

  8. #158
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    Re: Refrigeration 101

    Gary I have been using your TECH method for years it is really great especially when you are having a bad day and can't identify a starting point.

    I would encouage folk to get it and practiace it.

    Steve Wright CMS

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    Re: Refrigeration 101

    Hi Guys,

    You might be interested in the two e-books which I posted on the forum today for further reading. check them under refrigeration books.

    www.isentropictemptech.com

  10. #160
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    Question Re: Refrigeration 101

    I am new to the HVAC field. I am an electrician by trade and have just recently complete an Associate Degree in HVACR at a local community college. I have currently started a new position in the Refrigeration Department in the chemical plant at which I work. I was recently asked to look at a Trane VAV that has no HIM on the unit. The others in the shop tell me that the Trane Techs can interface with the VAV with a laptop. I would applicate any information that may help me trouble shoot this piece of equipment. Thanks!!

  11. #161
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    Re: Refrigeration 101

    Hi Gary ,
    I havn't been a member long and am currently in an apprentaship in the trade, i have about 6 months experience and things are clicking into place for a newby if that makes sense ha. I just want to say that your postings are brilliant and are helping me alot. Looking forward to reading some more many thanks
    Ben

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    Re: Refrigeration 101

    There seems to be some confusion about saturation, so perhaps some clarification is in order:

    For a given pressure, every liquid has a boiling temperature.

    For example, at atmospheric pressure (0 psi) water boils at 100C/212F. We could say this is it's "boiling temperature", or since we are turning it into a vapor we could say this is it's "evaporating temperature", or since vapor bubbles are forming we could call this it's "bubble point temperature". All mean the same thing.

    If we take hot steam at atmospheric pressure (0 psi) and cool it to that same 100C/212F it condenses to a liquid, so we could call this it's "condensing temperature", or since it is forming liquid droplets (dew) we could call this it's "dewpoint temperature".

    All of these terms describe the same temperature point for water at 0 psi, but also describe whether we are adding or removing heat.

    What if both liquid and vapor are present and we are neither adding nor removing heat? What do we call this temperature then? If we are simply describing the temperature at which the process could be driven in either direction (liquid to vapor or vapor to liquid) for water at 0 psi, we call this it's "saturation temperature".

    Which terminology we use depends on whether we are simply describing the temperature point or also describing the process... so...

    The saturation temperature for water at 0 psi is 100C/212F.

    The evaporating temperature for water at 0 psi is 100C/212F.

    The condensing temperature for water at 0 psi is 100C/212F.

  13. #163
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    Re: Refrigeration 101

    Taking this a step further, "dewpoint temperature" and "bubble point temperature" are terms we use to describe a mixture of refrigerants which have different saturation temperatures (zeotropic mixture).

    Let's say we have two refrigerants.

    The saturation temperature for refrigerant "A" at 0 psi is 10C/50F.

    The saturation temperature for refrigerant "B" at 0 psi is 15C/59F.

    If we mix these two together and are in the process of adding heat (at 0 psi), the mixture will start to bubble at 10C/50F and will finish evaporating at 15C/59F.

    If we are in the process of removing heat from the mixture (at 0 psi), it will start to form dew at 15C/59F and finish condensing at 10C/50F.

    The bubble point for this mixture at 0 psi is 10C/50F.

    The dewpoint for this mixture at 0 psi is 15C/59F.

    The difference between bubble point temperature and dewpoint temperature is called the "glide" which in this case is 5K/9F.

    Note that evaporating finishes at the dewpoint temperature, so when looking at the low side pressure, we want to know the dewpoint.

    Note also that condensing finishes at the bubble point temperature, so when looking at the high side pressure, we want to know the bubble point.

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    Re: Refrigeration 101

    And then there is pressure.

    If we raise the pressure, we raise the saturation temp. If we lower the pressure, we lower the saturation temp.

    The pressure/temperature (P/T) chart (aka comparator) for our refrigerant tells us the saturation temp for a given pressure. Or for zeotropic refrigerant mixtures, it tells us the bubble point and/or dewpoint.

    For those who confuse zeotropes with azeotropes, here's how I remember which is which:

    Just as theist means with religion and atheist means without religion, zeotrope means with glide and azeotrope means without glide.
    Last edited by Gary; 02-02-2011 at 04:25 AM.

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    Re: Refrigeration 101

    Thanks Gary - excellent.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  16. #166
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    Re: Refrigeration 101

    Re. Refrigeration 101
    great information...,would you like to emphasize some thing on setting the superheat on a refrigeration system.
    Fai

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    Re: Refrigeration 101

    Excellent explanation, thanks Gary

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    Re: Refrigeration 101

    If I recollect correctly, it is already explained as "Magoo rule" of 0,65xTD
    But more detailed is here:
    http://www.kueba.de/en-us/Tools/Küba...s/default.aspx
    Now, when I am officialy citizen off EU, I am looking for decent job! For any job offer please check my profile!

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    Re: Refrigeration 101

    I will concur with Gary. Keep away from the expansion valve. I've been at this a long time and have started up many supermarkets with long line ups of cases. very rarely do I have to touch a valve. Whats nice now is that some of the cases have sensors on the inlet and the outlet of the coil and supply and return air sensors. Back at the E-2 you can read superheats and splits. Makes it very convenient.

  20. #170
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    Re: Refrigeration 101

    G'Day its my 1st post to this sight , fairly new to the game , i am looking for a table of how many joules of energy each metal will absorb , i'm fairly sure there is something in arac but i can't find it , basicly table should state copper ***Kj per sq meter . Can any one help me
    Thanks

  21. #171
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    Re: Refrigeration 101

    Refrigerant flows very rapidly through the evaporator coil into the suction line. Many people believe that you can't have superheat until the liquid has all turned to vapor, but this is not true. Because of the velocity of the refrigerant flow it is possible to have liquid droplets surrounded by superheated vapor at the outlet of the evaporator... and in fact this is what happens. All of the liquid droplets are gone by the time there is 5-10F/3-5.5K superheat.

    We want the superheat at the evaporator outlet to be low enough to ensure that we are fully utilizing the coil, thus maximizing its ability to absorb heat, but we do not want liquid droplets to be sent back to the compressor.

    Similarly, it is possible to have vapor bubbles surrounded by subcooled liquid at the outlet of the condenser. All of the vapor bubbles disappear at about 10-15F/5.5-8.5K subcooling.

    We want the subcooling to be high enough to ensure that we are sending sufficient liquid to the metering device, but not so high that we are backing up liquid into the condenser, thus reducing its ability to reject heat.

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    Re: Refrigeration 101

    Thanks for such an informative post, I am new to the field and any advice and information is greatly appreciated

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    Re: Refrigeration 101

    Quote Originally Posted by Gary View Post
    There has been a big move towards self-diagnostic systems in recent years
    Funny you say that. I'm a sailboat owner. 5 years ago, my refigerator/freezer was not working on my boat. I pulled into a large and respectible marina and asked them if they would take a look at it. Well, they did not have time, but recommeneded that I replace the entire system from and air cooled condensor to a keel (water) cooled condensor. {hmm, a wholesale changeout on a system that is roughly 5 years old.} No, I'll pass. I ended up recharging it and made it work for another couple of seasons anyway. I now own a 30 lb can of 134a, gauges, nitrogen bottle w/ regulator, electronic leak detector and still cannot find the leak! Anyway, it's down to the bathtub pressure test.

    Aside from all that good fun, the refigeration concepts have been facinating to me have lead me on a pursuit to make a better refigeration system. As I dig deeper into this topic, I find myself refering back to the Enthapy charts. It seems as though only when you know the exact pressure and temperature do you know the state of the substance.

    To Gary's comment, my thought is that even though it is technically feasible to design a system that would diagnose itself, I doubt the Product Management or Marketing Department would allow it due to expense. That is my OPINION. Would you agree? I think we could have the ideal system if we could monitor and control the proper parameters. It is possible, and I just might do it with some help.

  24. #174
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    Cool Re: Refrigeration 101

    Quote Originally Posted by Gary View Post
    On a cap tube system there is a fixed amount of liquid flowing into the evaporator. When the load is heavy there is warmer air flowing through the coil and thus the liquid is all boiled off long before it reaches the outlet of the coil, thus the superheat is high when the load is heavy. If properly designed and charged, the superheat will be just right when the design temperature (design load) is reached.
    AH-HA Moment. Thank You, Thank You, Thank You.

    Now, I know why I over-charged the system during pull-down and found 350 PSI hi pressure and frosted lines when I came back.

  25. #175
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    Re: Refrigeration 101

    hey,

    im pretty new this forum, and i dont know how to create my own thread. anyway...im a student in my final year of my degree in construction project management, and i am doing a dissertation on air conditioning, but i dont know what to talk about. the title will most probs be "Air conditioning and Environmental issues" but i seriously dont know what to talk about, so i would appreciate if you guys could give me some advice, and point me the right direction?

    thank you
    Naeem

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    Re: Refrigeration 101

    Dear Gary,
    I have been encountered with aproblem of Oil nonreturning back to the compressor in an R22 system connected to an flake ice plant evaporating at -20C.The flaker is fed through 7nos TXVs and a hand regulating valve.I recon itis an TxV problem and what sort of superheats should yu allow. At the moment ir is set at 7 C.
    patrickj

  27. #177
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    Re: Refrigeration 101

    Quote Originally Posted by Gary View Post


    Are you measuring subcooling on the liquid line near the receiver?... or on the drip leg between the condenser and the receiver?
    On AC systems its the outlet side of the condenser, on refrigeration units its usually at the drip since I ususally can't get onto the outlet of the condenser. Wouldn't the liquid line just outside the reciever be the larger/greater subcooling difference?

    BTW, someone stoll my books, where can I get replacements?
    Rich

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    Re: Refrigeration 101

    Quote Originally Posted by Rich1281 View Post
    BTW, someone stoll my books, where can I get replacements?
    Rich
    Just click on my signature line.

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    Re: Refrigeration 101

    Subcooling should be measured on the liquid line after the receiver. Keep in mind that the liquid line cannot be cooler than the air surrounding it. If the liquid line is in the hot air stream leaving the condenser, it will measure abnormally high.

    Move down the liquid line until it enters an area that is surrounded by ambient air. That's where you measure the subcooling.

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    Re: Refrigeration 101

    First of all thank you Gary and all of you for sharing your knowledge.

    Second of all, picture this:
    - a sistem used in air conditioning: 5 C evap, 40 C cond, txv with no MOP, runing, in normal conditions with SH = 5k and SC = 4K, about 30 kw compressor capacity (it's a purely ipotetic system), R407c
    - according with txv producer (let's say Danfoss - TEZ 5 with orifice no.2), the valve has a capacity of 30 kw at a TXV DP of about 12bar; the capacity rises with the TXV DP rise
    - with a high load, the superheat rises, the txv opens and the TXV DP decreases thus it's capacity decreases, so the sistem capacity decreses too, leading to a increasing suply air temperature.
    What is wrong ?

  31. #181
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    Re: Refrigeration 101

    I think you are confusing TXV capacity ratings with system output.

    Let's say an elevator has a capacity rating of 10 people. Does that mean there are 10 people on the elevator? Nope.
    Last edited by Gary; 19-08-2011 at 03:02 PM.

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    Re: Refrigeration 101

    I'm well aware that the things are not going that way. The txv will open to increase the system capacity, to reduce the superheat and the thv dp will decrease. Then what is the table i've attached from Danfoss doc. saying ?
    Attached Files Attached Files

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    Re: Refrigeration 101

    The table is telling you the maximum flow (valve wide open) for a given dP... and you are still confusing capacity with output. Opening the TXV does not increase the capacity of the system, it increases the flow and thus the output.
    Last edited by Gary; 23-08-2011 at 04:33 PM.

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    Re: Refrigeration 101

    Quote Originally Posted by Gary View Post
    Subcooling should be measured on the liquid line after the receiver. Keep in mind that the liquid line cannot be cooler than the air surrounding it. If the liquid line is in the hot air stream leaving the condenser, it will measure abnormally high.

    Move down the liquid line until it enters an area that is surrounded by ambient air. That's where you measure the subcooling.
    Question Sir <Gary>

    Liquid line (on water chiller) should be subcooled liquid coming from condensor

    Sun beating down on tube-work

    I am expecting now saturated liquid (lots of flash gas)

    Could you explain for me please (technically or simply put)

    What is in this liquid line now ?

    R's chillerman
    If the World did not Suck, We would all fall off !

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    Re: Refrigeration 101

    Quote Originally Posted by chillerman2006 View Post
    Question Sir <Gary>

    Liquid line (on water chiller) should be subcooled liquid coming from condensor

    Sun beating down on tube-work

    I am expecting now saturated liquid (lots of flash gas)

    Could you explain for me please (technically or simply put)

    What is in this liquid line now ?

    R's chillerman
    I think you are grossly overestimating the solar input.

  36. #186
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    Re: Refrigeration 101

    Quote Originally Posted by chillerman2006 View Post
    Question Sir <Gary>

    Liquid line (on water chiller) should be subcooled liquid coming from condensor

    Sun beating down on tube-work

    I am expecting now saturated liquid (lots of flash gas)

    Could you explain for me please (technically or simply put)

    What is in this liquid line now ?

    R's chillerman
    Quote Originally Posted by Gary View Post
    I think you are grossly overestimating the solar input.
    Hi Gary

    could you explain further for me

    & obviously others would benefit from your expertise here

    R's chillerman
    If the World did not Suck, We would all fall off !

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    Re: Refrigeration 101

    Given the curvature of the liquid line, along with the reflective properties of the metal and the relatively small size, I suspect the solar heat gain would be negligible. I would certainly not expect lots of flashing.

  38. #188
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    Re: Refrigeration 101

    Quote Originally Posted by Gary View Post
    Given the curvature of the liquid line, along with the reflective properties of the metal and the relatively small size, I suspect the solar heat gain would be negligible. I would certainly not expect lots of flashing.
    Thankyou very much Sir,

    you have put to bed, once & for all a miss-conception which has been argued back & forth for far too long !

    R's chillerman
    If the World did not Suck, We would all fall off !

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    Re: Refrigeration 101

    A basic question, Gary.

    Given a system running in Cooling mode, how to raise evaporating temp (or pressure)? Different ways to do so?

    My condensing ~50C but evaporating ~ -3, quite low for an A/C.

    Try to open the TXV apperture until getting low limit SH but failed to raise Tevap muchly.
    Anything to do with indoor air flow rate? I was trying to maintain a 10% lower air flow rate than initial calculation for noise benefit.

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    Re: Refrigeration 101

    Quote Originally Posted by Uni View Post
    A basic question, Gary.

    Given a system running in Cooling mode, how to raise evaporating temp (or pressure)? Different ways to do so?

    My condensing ~50C but evaporating ~ -3, quite low for an A/C.

    Try to open the TXV apperture until getting low limit SH but failed to raise Tevap muchly.
    Anything to do with indoor air flow rate? I was trying to maintain a 10% lower air flow rate than initial calculation for noise benefit.

    Given a fully active evap coil, the pressure/temperature will depend upon the amount of heat being transferred from the air to the refrigerant. The more heat transfer, the higher the pressure/temperature.... and vice versa. The rate of heat transfer depends upon the surface area, the volume of air flowing through the coil and the temperature of the air flowing through the coil.

    It is a mistake to believe that a pressure/temperature is, in and of itself, too high or too low. In truth, the temperature/pressure may or may not be too high/too low for a particular design under a given set of conditions.

    In this case, the evap being the outdoor coil, on a cool day -3C is probably not low at all. It depends.
    Last edited by Gary; 06-09-2011 at 04:54 AM.

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    Re: Refrigeration 101

    Quote Originally Posted by Uni View Post
    Anything to do with indoor air flow rate? I was trying to maintain a 10% lower air flow rate than initial calculation for noise benefit.
    Thereby throwing the entire system out of balance. Air flow is IMPORTANT. Earplugs are cheap.

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    Re: Refrigeration 101

    Thanks for your insights, at least I know that my thought was not far off to explain the situation.
    Agree with you, airflow is so important and I hate forcing myself reducing it. But have to factor in noise level, can't make it quiet, cant sell.

    I considered Tevap low compared to initial calculated system balance. Such a low evap temp will affect system efficiency as well. Small compressor is now designed for high efficiency and is most efficient at approx Tevap ~ 5C or more. Stucked with airflow and coil size so could not improve it. And if you read my other post, it affects heating mode as well (high head pressure). Too much compromises just for noise.

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    Re: Refrigeration 101

    Off topic - needed removing
    Last edited by chillerman2006; 08-09-2011 at 03:59 PM.
    If the World did not Suck, We would all fall off !

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    Re: Refrigeration 101

    Gary, what do you think about using compressor superheat to analyse system performance? Checking discharge line temps and subtracting saturated liquid pressure. Something like 50 to 70 degrees as normal range.

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    Re: Refrigeration 101

    Quote Originally Posted by texas64 View Post
    Gary, what do you think about using compressor superheat to analyse system performance? Checking discharge line temps and subtracting saturated liquid pressure. Something like 50 to 70 degrees as normal range.
    Discharge superheat is directly related to compressor inlet superheat. The higher the inlet superheat, the higher the discharge superheat... and vice versa. I use inlet superheat and it tells me what I need to know. I don't know much about discharge superheat, because it is not something I use.

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    Re: Refrigeration 101

    Sorry to but in. I work on chillers for industrial. Supplying cooled water for various machines. A sub cooling of 15oc should be acheavable with any system there or about and 5oc superheat give or take. If you are not acheiving this its the same route. Gas charge/condensor fault/evap fault/ tev fault/ and abnormal ambient range. Your gauges are your friend and a simple logical reason. Look for signs like liquid return to compressor(bottom iced up) or tev iced up, mass dt across evaporater, low diff across condenser etc

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    Re: Refrigeration 101

    Oh and possibly water blockage on water side or pump failure all water / process side. Anything slowing down heat exchange

  48. #198
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    Re: Refrigeration 101

    In that case check pump curves - completely different game but very easy to grasp.

  49. #199
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    Re: Refrigeration 101

    Quote Originally Posted by spoon man View Post
    Sorry to but in. I work on chillers for industrial. Supplying cooled water for various machines. A sub cooling of 15oc should be acheavable with any system there or about and 5oc superheat give or take. If you are not acheiving this its the same route. Gas charge/condensor fault/evap fault/ tev fault/ and abnormal ambient range. Your gauges are your friend and a simple logical reason. Look for signs like liquid return to compressor(bottom iced up) or tev iced up, mass dt across evaporater, low diff across condenser etc
    Spoon Man

    a condensor has 3 jobs to do when rejecting heat

    de-superheating (specific heat rejection)
    condensing (latent heat rejection)
    subcooling (specific heat rejection)

    the last subcooling depends if the coil has been sized accordingly to subcool the refrigerant and to what degree, industrial refrigeration will subcool the already de-superheated/condensed refrigerant but most package chillers dont subcool to 15*c, in fact many struggle to reach 6*c

    Exactly what make/model are you referring to ??? @ 15*c many will be overcharged

    R's chillerman
    If the World did not Suck, We would all fall off !

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    Re: Refrigeration 101

    Subcooling at 15K is way too high, causing liquid to back up into the condenser, reducing it's effective area and therefore it's efficiency. I would recommend max 8.5K/15F subcooling or clear sightglass, whichever comes first.

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