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    Re: Refrigeration 101



    Quote Originally Posted by ice_cold View Post
    Hello,
    Here is a question from a newbie of both the forum and the world of refrigeration!
    You see the terms evaporating temperature, condensing temperature in the literature. My question is where exactly these values are measured from? For example if we take the evaporating temperature; is it measured from the entrance or the exit of the evaporator?
    Thanks in advance!
    The evaporating temperature is the saturation temperature which corresponds to the low side pressure on a pressure/temperature chart.

    The condensing temperature is the saturation temperature which corresponds to the high side pressure on a pressure/temperature chart.
    Last edited by Gary; 29-11-2009 at 10:08 PM.



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    Re: Refrigeration 101

    Quote Originally Posted by Gary View Post
    The evaporating temperature is the saturation temperature which corresponds to the low side pressure on a pressure/temperature chart.

    The condensing temperature is the saturation temperature which corresponds to the high side pressure on a pressure/temperature chart.
    thank you, appreciated!

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    Re: Refrigeration 101

    yes! I have one of Gary's TECH books and they cut to the chase to real t/s, a great purchase if u can!!!
    just a pup on the porch:)

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    Re: Refrigeration 101

    Respected Gary
    Where I can get the books Tecch method troble shooting? Is there any agent in India?

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    Re: Refrigeration 101

    Last edited by Gary; 02-02-2011 at 01:54 AM.

  6. #106
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    Re: Refrigeration 101

    This thread is a wealth of good information. It is a shame that the people who need this info the most do not look at / subscribe to free sources of education such as this web site.
    Thanks
    From the west side of the pond.

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    Re: Refrigeration 101

    Hi, I have a quick question about connecting gauges, don't think it has been asked before. I always seem to release alot of gas when connecting guages to split A/C systems. Is there a nack to it, like pumping down a system before hand. Is it best to connect when the system is running or off, both high and low sides.

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    Re: Refrigeration 101

    Turn unit on cooling, close partially valve on smaller pipe and when pressure falls to around 1 bar disconnect your gauge. Open valve fully and put valve caps.

    Or buy Refco Quick Couplers.
    Last edited by nike123; 17-02-2010 at 06:20 AM.
    Now, when I am officialy citizen off EU, I am looking for decent job! For any job offer please check my profile!

  9. #109
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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, but as far as I know they haven't gotten it right yet... apparently their computers haven't learned how to subtract yet.

    On the other hand, I am retired now, so maybe things have changed since then.

    Hi gary sir
    Before 25 years ago self diagnosing systems are in market!! Ex: carrier 30 GT chiller. Now all commercial chiller manufactures are designing self diagnosing based refrigeration fundamentals. Some sample alarms such as- low suction super heat, high saturation suction temperature, low discharge superheat.etc.
    Your 101 is very useful, thanks a lot

    Moideen-dubai

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    Re: Refrigeration 101

    Quote Originally Posted by moideen View Post
    Before 25 years ago self diagnosing systems are in market!! Ex: carrier 30 GT chiller. Now all commercial chiller manufactures are designing self diagnosing based refrigeration fundamentals. Some sample alarms such as- low suction super heat, high saturation suction temperature, low discharge superheat.
    Something like e.g. - low suction superheat - is a symptom, not a diagnosis. In my opinion, these systems are not self-diagnostic.

    When they can say things like - insufficient evap airflow, or liquid restriction, or refrigerant overcharge, or inefficient compressor, etc, etc. etc... then I will be impressed.
    Last edited by Gary; 28-02-2010 at 06:25 AM.

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    Re: Refrigeration 101

    Quote Originally Posted by Gary View Post
    Something like e.g. - low suction superheat - is a symptom, not a diagnosis. In my opinion, these systems are not self-diagnostic.

    When they can say things like - insufficient evap airflow, or liquid restriction, or refrigerant overcharge, or inefficient compressor, etc, etc. etc... then I will be impressed.
    BTW, I know this can be done. I wrote a program to do this back in the 1980's. Nobody was interested.

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    Re: Refrigeration 101

    Gary,you're a legend.I always follow your post since i become a member and your ideas are great.

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    Re: Refrigeration 101

    I'm a legend in my own mind... lol

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    Re: Refrigeration 101

    Quote Originally Posted by Gary View Post

    When they can say things like - insufficient evap airflow, or liquid restriction, or refrigerant overcharge, or inefficient compressor, etc, etc. etc... then I will be impressed.
    Something like this:
    http://www.ecotechnics.it/en/product...lock-2000.html
    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

    Quote Originally Posted by nike123 View Post
    Yep... something like that.

    I had a couple diagnostic programs that I marketed on floppy disks back in the early 1990's. One for refrigeration and the other for A/C.

    Crude but effective. Programmers would have a good laugh, but it told you what was wrong with the system.

    Then they started putting USB connectors on printers and the printer function no longer worked. Started getting complaints that my programs wouldn't print the results, so I discontinued the products. I'm a service tech, not a programmer.
    Last edited by Gary; 21-03-2010 at 06:41 AM.

  16. #116
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    Re: Refrigeration 101

    i thnk a cooling effect on d finger will appear...due to d reason- d water on d finger will absorb latent heat of vapourization nd will vapourize...as a result d temp. of d finger will fall nd a cooling effect will b produced...

  17. #117
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    Re: Refrigeration 101

    good explanation welldone

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    Re: Refrigeration 101

    hi guys this is a great idea love it i will have to read the technical stuff again cos some of it leaked out my head already an i have learned some things as well an only been in game 20 plus yrs if i may be so bold as to make a small contribution even though most of you are super technical more than me not enough engineers stop and actually look at what there working on an do the stuff i was taught look at it listen to it and feel it there the most important tools we have you can see a design floor in a system and adjust for it you can hear a compressor straining under excessive load and you can feel if an evap is fully wet all the way accross and then ya can break out the super tools to fix it

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    Re: Refrigeration 101

    There seems to be a great deal of confusion about subcooling, so let's take a closer look:

    The vapor loses its heat and turns to liquid as it moves very rapidly though the condenser. This does not happen all at once, it is a gradual process.

    There is a point where the last vapor bubbles disappear and the mixture becomes solid liquid. Let's call this the "solid liquid point" or SLP.

    Technically, if there is enough refrigerant to modulate the superheat at the evap outlet, then the system will function properly, but this is not the full story. Vapor bubbles travelling through the TXV orifice over a long period of time will wear out and distort the orifice, so to ensure long life for the TXV we want solid liquid at its inlet.

    So... our minimum charge would have the SLP at the TXV inlet.

    At the other extreme, we do not want liquid backing up into the condenser as this takes up condensing space and drives up the high side pressure.

    So... our maximum charge would have the SLP at the condenser outlet.

    The problem with the minimum charge is that changing conditions could have vapor bubbles at the TXV inlet. The problem with the maximum charge is that changing conditions could have liquid backing up into the condenser.

    So... the ideal charge would have the SLP somewhere in between the TXV inlet and the condenser outlet. Thus, we want the SLP to be at the receiver outlet... which is why the sightglass is normally placed there, and why we want to measure subcooling there.

    If we monitor the subcooling while observing the sightglass, on a wide variety of systems, we will find that the last vapor bubbles disappear at about 10-15F/5.5-8.5K subcooling. Thus we can identify the SLP by measuring the subcooling at the receiver outlet, ensuring that (with all else functioning properly) we are neither undercharged, nor overcharged.

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    Re: Refrigeration 101

    Respected Gary,
    Thank you very much for your "Refrigeration 101", the highly informative article.
    May I ask you how can we check the heat absorbing capacity of a fin and tube evaporator, if we do not have any product details on it? Just we have the physical size of tube diameter, distance between end fins, fin spacing, fin thickness, number of tubes, number of elbows, fin width, refrigerant temperature, and cabinet temperaure. Also we know the fin and tube material, refrigerant and its properties. (forget about the oil film on the inner wall of the tube).
    Wishing you all the very best
    Thank you
    Rayin

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    Re: Refrigeration 101

    Gary that all sounds good there are actually 2 kinds of superheat evaporator and suction vapor since you failed to mention that. But lets do some
    transmission heat load calculations:
    If a wall has a u factor of .114 area of 90 square feet with a inside temp of 80 degrees what would the heat transmission be gary? In btu/hr

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    Re: Refrigeration 101

    There is only one kind of superheat... but lots of different places to measure it.

    Heat load calculations are outside the scope of this thread.

    If you would like to start a thread about heat load calculations... go for it.
    Last edited by Gary; 29-04-2010 at 03:52 AM.

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    Re: Refrigeration 101

    Quote Originally Posted by Gary View Post
    I was thinking it might be a good idea to set up a basic thread to send the newbies to:

    Refrigeration 101:

    Let's start from the beginning:

    Wet your finger and wave it in the air. What you are feeling is a refrigeration effect. When a liquid turns to a vapor it absorbs heat. In this case it is sucking the heat out of your finger.

    The opposite is also true. If that vapor then loses that heat, it will turn back into a liquid.

    In a refrigeration system, we force a liquid to become a vapor in the evaporator, thus absorbing heat from the refrigerated space.

    We then use a compressor to pump that vapor to the condenser.

    In the condenser we force that vapor to reject the heat and thus turn back into a liquid so that we can re-use it.

    We then meter the liquid back into the evaporator to complete the loop and do it all over again and again and again.

    How do we force a liquid to become a vapor?... or a vapor to become a liquid? By manipulating its boiling point.

    The boiling point is the temperature at which the liquid turns to vapor when heat is added. It is also the temperature at which a vapor turns to liquid when heat is removed.

    Boiling point = saturation temp = evaporating temp = condensing temp

    When we think of the boiling point of a liquid it is the boiling point at zero psi pressure. If we increase its pressure we raise its boiling point. If we decrease its pressure we lower its boiling point.

    In the evaporator we force liquid to become a vapor by lowering its pressure until its boiling point/evaporating temperature is lower than the air it is trying to cool.

    In the condenser we force the vapor to become a liquid by raising its pressure until its boiling point/condensing temperature is higher than the air it is trying to heat.

    Different substances have different boiling points at different pressures.

    We can tell what the boiling point/saturation temp/evaporating temp/condensing temp is at various pressures for common refrigerants by checking a pressure/temperature chart.

    Okay... let's go a step further: Superheat and subcooling.

    If we boil off a liquid into vapor and then add heat to that vapor its temperature will rise above the saturation temperature. This is called superheating the vapor. When its temp is 10 degrees above the saturation temperature it is superheated 10 degrees. When its temp is 20 above saturation it has 20 degrees of superheat, etc, etc.

    Similarly if we condense a vapor into liquid and then further cool the liquid this is called subcooling. When the temp gets 10 degrees below saturation it has 10 degrees of subcooling. When its temp is 20 degrees below saturation it has 20 degrees of subcooling.

    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.

    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.

    Many people believe that a TXV will maintain a fixed superheat, regardless of load. This is just simply not true. When the load is heavy the superheat rises and more liquid is fed to the evaporator. The superheat remains high as long as the load remains high. And again, the superheat is just right when the design temperature (design load) is reached. But the design temp will be reached sooner because of the extra refrigerant feed.

    As we see, when the load decreases the superheat decreases... so what happens when the filter gets dirty, or the evap coil... or the blower wheel? Less airflow means less load therefore the superheat drops, even though the refrigerated space may be at design temp.

    When the load is high the superheat is high, and when the load is low the superheat is low... even with a TXV.

    Everywhere, throughout the system, there are opposing forces balancing against each other, and it can be very difficult to tell which of these forces is out of balance.

    And yes, there is more... much much more... but that's enough for now.
    I didn't think starting a new thread for my mind blank was a great idea, and this was the closest thread i could relate my thread too.

    I am new into the refrigeration industry and I can't remember what a capillary system is.

    I have done a small search on google and have not made sense of the results. I was wondering if some one could explain a simple capillary system. Thanks...

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    Re: Refrigeration 101

    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

    capillary...

    Somewhere in the coil the flow of refrigerant is slower and also the pressure drops over the distance it has to traval? right?

    so does it travel this distance loosing pressure in a small coil pipe in hopes when the refrigerent gets to the evap (larger pipe coil) its lost enough enough pressure to have a zillion vapour droplets colleting heat? like a thermal expansion valve, but with out the sensor or valve?

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    Re: Refrigeration 101

    great job gary, i liked what i read.

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    Re: Refrigeration 101

    Gary,

    When you say "Generally speaking, a freezer should have 6-8F/3.5-4.5K superheat, a cooler should have 8-10F/4.5-5.5K superheat, and an A/C should have 12-16F/6.5-9K superheat."

    At what abient temp are we talking here?

    75 degree's?

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    Re: Refrigeration 101

    Quote Originally Posted by Deniver45 View Post
    Gary,

    When you say "Generally speaking, a freezer should have 6-8F/3.5-4.5K superheat, a cooler should have 8-10F/4.5-5.5K superheat, and an A/C should have 12-16F/6.5-9K superheat."

    At what abient temp are we talking here?

    75 degree's?
    Normally, the ambient temp would have relatively little effect on the superheat.

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    Re: Refrigeration 101

    Quote Originally Posted by Gary View Post
    In another thread Magoo has offered a rule for judging TXV superheat. He says the superheat should be 60-70% of the TD. This makes very good sense. I like it... a lot. :
    Acording Braydert's " Designing refrigeration installations" error-free performance of evaporator possible only with 0.5...0.7 of the TD.
    In some places will have to think ...

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    Re: Refrigeration 101

    Quote Originally Posted by Gary View Post
    If we monitor the subcooling while observing the sightglass, on a wide variety of systems, we will find that the last vapor bubbles disappear at about 10-15F/5.5-8.5K subcooling. Thus we can identify the SLP by measuring the subcooling at the receiver outlet, ensuring that (with all else functioning properly) we are neither undercharged, nor overcharged.
    How does SLP concept this relate to the concept of 'liquid cooling'?

    Where : LC = Tc,sat - Txv,in

    A few points to note:
    1. LC will vary as Tc,sat varies over the cycle range;
    2. The allowable subcooling (SC = Tc,sat - Tc,exit) differs for different condenser types. SC of 5.5-8.5K will be a problem for plate condensers (2-4K), & air-cooled condensers (~ 0K).
    3. In the quest for increased SC, be careful of not pushing up Tc,sat. Basically, Tc,sat levers up off the cooling medium temperature. There is a happy balance point for each system.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
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    Re: Refrigeration 101

    Quote Originally Posted by Gary View Post
    Normally, the ambient temp would have relatively little effect on the superheat.
    In my heat-pump trials, I have observed an influence on evaporator SH, due to ambient air temperature movements.

    If Ta,in falls during the range of test, SH will roll down a little more than if Ta,in is constant.

    If Ta,in rises during the range of test, SH can often end up being almost constant over the test duration.

    The influence can be in the range of ~ 1-3K, depending on the operating SH of the machine.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
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    Re: Refrigeration 101

    Quote Originally Posted by desA View Post
    In my heat-pump trials, I have observed an influence on evaporator SH, due to ambient air temperature movements.

    If Ta,in falls during the range of test, SH will roll down a little more than if Ta,in is constant.

    If Ta,in rises during the range of test, SH can often end up being almost constant over the test duration.

    The influence can be in the range of ~ 1-3K, depending on the operating SH of the machine.
    In your heat pumps, the ambient air would be the air entering the evaporator. As I interpreted the posters question, I believe he was referring to the air entering the condenser.

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    Re: Refrigeration 101

    Quote Originally Posted by desA View Post
    How does SLP concept this relate to the concept of 'liquid cooling'?

    Where : LC = Tc,sat - Txv,in

    A few points to note:
    1. LC will vary as Tc,sat varies over the cycle range;
    2. The allowable subcooling (SC = Tc,sat - Tc,exit) differs for different condenser types. SC of 5.5-8.5K will be a problem for plate condensers (2-4K), & air-cooled condensers (~ 0K).
    3. In the quest for increased SC, be careful of not pushing up Tc,sat. Basically, Tc,sat levers up off the cooling medium temperature. There is a happy balance point for each system.
    There is no doubt an ideal balance for each specific system... and I would not recommend SLP at the condenser exit for any system.

    What I have found works reasonably well for refrigeration systems in general is to have the SLP in between the condenser outlet and the TXV inlet.

    Generally, I would want the SLP to be near the receiver outlet and this is where I measure the SC. I suspect this is the very reason sightglasses are usually mounted near the receiver outlet.

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    Re: Refrigeration 101

    Quote Originally Posted by Deniver45 View Post
    Gary,

    When you say "Generally speaking, a freezer should have 6-8F/3.5-4.5K superheat, a cooler should have 8-10F/4.5-5.5K superheat, and an A/C should have 12-16F/6.5-9K superheat."

    At what abient temp are we talking here?

    75 degree's?
    This is the post I was referring to, Gary. There is a mix of applications & conditions here.

    It could be useful to split the air-breathing evaps from the closed-space evaps, in regards to the SH question - it will be less confusing.

    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

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    Re: Refrigeration 101

    Quote Originally Posted by desA View Post
    This is the post I was referring to, Gary. There is a mix of applications & conditions here.

    It could be useful to split the air-breathing evaps from the closed-space evaps, in regards to the SH question - it will be less confusing.

    I agree... both the question and the answer could have been more specific.


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    Re: Refrigeration 101

    Originally Posted by desA
    How does SLP concept this relate to the concept of 'liquid cooling'?

    Where : LC = Tc,sat - Txv,in

    A few points to note:
    1. LC will vary as Tc,sat varies over the cycle range;
    2. The allowable subcooling (SC = Tc,sat - Tc,exit) differs for different condenser types. SC of 5.5-8.5K will be a problem for plate condensers (2-4K), & air-cooled condensers (~ 0K).
    3. In the quest for increased SC, be careful of not pushing up Tc,sat. Basically, Tc,sat levers up off the cooling medium temperature. There is a happy balance point for each system.
    There is no doubt an ideal balance for each specific system... and I would not recommend SLP at the condenser exit for any system.
    Gary:
    What I have found works reasonably well for refrigeration systems in general is to have the SLP in between the condenser outlet and the TXV inlet.

    Generally, I would want the SLP to be near the receiver outlet and this is where I measure the SC. I suspect this is the very reason sightglasses are usually mounted near the receiver outlet.
    Based on thousands of experimental test points over the past few years, I would venture to say, in a direct system (no receiver), if no bubbles are present, then the system will be over-charged.

    Sub-cooled boiling & gas evolution in direct liquid lines are part & parcel of a liquid line's behaviour (R-134a). This may be different for a receiver-based system.

    The limiting system mass charge will be the one at which the Tc,sat value either jumps by 1-2K (non-linear jump), or where Tc,sat begins to climb rapidly. At this same instant, the pressure drop on the low-side reduces rapidly. These effects can be observed during refrigerant charge-determination trials. This seems to be a switch-over point from an evaporator-dominated system, to a condenser-dominated system.

    I'd say that basic rules-of-thumb are useful for field applications, but, for new designs, the system characteristics for each case, will need to be carefully evaluated.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
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    Re: Refrigeration 101

    Quote Originally Posted by Aik View Post
    Acording Braydert's " Designing refrigeration installations" error-free performance of evaporator possible only with 0.5...0.7 of the TD.
    This will very much depend on the magnitude of the TD itself.

    For instance:
    TD=10K ; SH = 0.5*10=5K; SH = 0.7*10=7K
    TD=20K ; SH = 0.5*20=10K; SH = 0.7*20=14K
    TD=30K ; SH = 0.5*30=15K; SH = 0.7*30=21K !!!

    That's asking for a fair-sized SH. In all likelihood, you'd have a tremendously high Tc,discharge temperature.

    The Magoo rule seems to be applicable in low TD applications & may need to be adjusted for high TD applications.

    Like everything in the rhvac game, some level of sound engineering judgement will need to be made in each specific application.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

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    Re: Refrigeration 101

    Gary...

    may I first thank you for posting this "refresher" and secondly thank you for continuing your input to the Refrigeration world after your "semi-retirement".

    I'm no fridgey...but at 33 and experienced it for 8 years, no quals gained, your "basics" brought it all back and has really urged me to follow the trade.

    I'm an automation eng by trade, I experienced 8 years as a services eng with ammonia gas in a food factory, working with Frick and Grasso screws in pumped overfeed systems to blast & spiral freezers plus -26c cold-storeage. Looking back I loved it! It was like a black art: food at 60+ degrees going into a box and coming out frozen!!! A magic box that I knew the code of; well I assumed I did. I was working in a role that I wasn't qualified for, had no proper experience of yet getting by... really dangerous looking back. Stupid or getting by? Stupid I'd say, but someone was assessing my skills and passing me capable!

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    Re: Refrigeration 101

    Quote Originally Posted by Gary View Post
    Yep... something like that.

    I had a couple diagnostic programs that I marketed on floppy disks back in the early 1990's. One for refrigeration and the other for A/C.

    Crude but effective. Programmers would have a good laugh, but it told you what was wrong with the system.

    Then they started putting USB connectors on printers and the printer function no longer worked. Started getting complaints that my programs wouldn't print the results, so I discontinued the products. I'm a service tech, not a programmer.
    Gary, do you still have copies of these programs?

    Is there any chance of a copy?

    Eggs

  40. #140
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    Re: Refrigeration 101

    With regards to this thread which I think has been very interesting t read, I am extremley new to this forum and to refrigeration all together. You seem to mention a lot about different heat loads, can someone please explain to me what a heat load is and how it would effect the refrigeration system?

  41. #141
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    Re: Refrigeration 101

    I am in school for HVACR, I will be graduating in Oct. I have used this site many times for research, and I am pleased with all of the info. I am struggling with the wiring diagrams (showing sequence of operation), any link you may have on basic wiring would be extremely helpful Thank You for your time Russell Peters (Cool Tool)

  42. #142
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    Re: Refrigeration 101

    Quote Originally Posted by Gary View Post
    OR

    You can weigh in the charge as marked on the nameplate.

    The manufacturer has done all of the work for you, setting up the system under tightly controlled conditions, determining the right charge, and then pulling all of the refrigerant out, weighing it and marking that weight on the nameplate.
    At what operating temperature would the refrigerant mass charge determination be most appropriate - startup Tc,sat 35'C; or hot end Tc,sat 70'C?

    I have no given mass charge to work off in this case & have to determine it in-house.

  43. #143
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    Re: Refrigeration 101

    Quote Originally Posted by Heeellp View Post
    That maybe true, but I am impressed. Gary, I have several quick questions if I may (homeowner). I know this is installation specific so I will try to keep it concise and compact. It deals with a problematic installation (as most do) and a dealer who can't seem to get it right. Can you try to steer me right? Thanks.

    3 ton heat pump (two speed ultra tech scroll compressor) split system. 95 % AFUE variable speed furnace matched coil System has had MANY problems since installation. TXV and heat pump replaced due to non-condensibles. Manual states: subcool 5-7 (no plus or minus for two speed pumps) and superheat values of 7-9 (no plus minus). After two years of somewhat adequate cooling I noticed it started running longer than usual cycles. Tech reluctantly came out again. Checked subcool (10-11) and superheat of 20. He added refrigerant until subcool was 9-10 and superheat was 10. He stopped. Please understand, I am a layman so go easy. Unfortunately I do no have the delta T for you. Ambient was around 80-82 degrees and compressor was on low speed. System runs way too long for these values (based on previous years of usage). It simply does not cool the house like it once did (added 44 bags of cellulose insulation in attic). Any ideas? Please?
    Found the issues as suspected. Techs would not adjust TXV. Field rep did. System runs much better. Thanks.......

  44. #144
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    Re: Refrigeration 101

    i would like to ask one question sir i have one refrigeration compressor make sabroe modl tsmc 108s using refrigerand 22 now adays it have loding problam it dosend get safishnt pumbing, then i open the compressor icant find eny mager problums but its oil pressur getting 4.5bar

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    Re: Refrigeration 101

    Hi Gary
    Good post,i could do with you in my tool bag so i can just pull you out and help me when im on site,im new to fridge game and im working on dryers mainly atlas copcos but it proving hard to get my head round and sort problems, cheers

  46. #146
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    Re: Refrigeration 101

    Quote Originally Posted by Gary View Post
    Just the opposite. High load increases SCT and low load decreases SCT... and SCT above ambient (cond TD) should remain within the 11-19K range.
    There will be relatively little change in subcooling as the liquid line temp will tend to rise and fall with the SCT and a TXV system stores sufficient surplus liquid refrigerant to compensate for variations in load without substantial changes in subcooling.

  47. #147
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    Re: Refrigeration 101

    Refrigeration System

    1/Refrigeration system overview
    *Propane Chiller: 57% Level
    *LPG OH Condenser: 80% Level, LPG T: -36C
    *Propane Economizer: 40% Level, PCV: 6 Bar, T Gas: 9.5C
    *02Propane Compressor:
    -PRO A -PROB
    .Capacity Control:
    Set point (Bar) O.5 0.5
    PID Out: 100% 100%
    .High Stage Capacity Control:
    Set point: 3.5 3.5 Bar
    PID Out: 100% 100%
    .Moy Amperes (Amp) 60.2 58.5
    .Suction Pressure (Bar): 0.82 O.91
    .Suction Temp (C) : -41.3 -41.2
    .Suction SH (C): 5.0 3.3
    .Intermediate Pressure (Bar): 4.0 4.4
    .Intermediate Temp (C) : 50.8 49.2
    .Intermediate SH (C): 55.5 51.6
    .Discharge Pressure (BAR) : 13.5 13.8
    .Discharge Temp (C) : 74.0 72.1
    .Discharge SH (C) : 34.7 31.8
    →Bypass Propane Condenser used in manual 0%
    *Propane surge drum:
    .Pressure: 14.5 Bar
    .Level: 52%
    *Gas Propane Exchanger:
    .Propane T: 34.75C
    .Gas T: 29.25 C
    2/ Refrigeration Skid:
    *Inlet Cold Separator: 26.4cC
    *Outlet Cold Separator: -28 C
    *Level Cold Separator: 40%
    *Set point TCV: -45 C (Bypass Cold Separator)
    *Gas / Liquid Exchanger :
    . Gas T: 36.75 C
    .LPG T : 8.85 C
    *Gas / Gas Cooler :
    .Gas T to sweet / sales gas Exchanger : 4 c
    .Gas T to propane chiller: -16 C
    →*we cant attend the cold Temperature -45C
    *Same times we have carryover of liquid on Propane Receiver
    Please help me to identify the problem and correct them.
    Last edited by frank; 30-01-2011 at 01:49 PM.

  48. #148
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    Re: Refrigeration 101

    hello im a newbie..i'll will enjoy this such a helpful tips on my work and profession..

  49. #149
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    Post Refrigeration and positive/megative air pressure

    Hi, i am just starting to learn about refrigeration and how it all works, although i am unsure of how positive and negative air pressure will affect a refrigeration system i was hoping that some1 could help me out with this.
    I am currently designing a filtered positive air system for a food production plant, up to now the positive air systems i have installed have been fed from the outside ambient air. on this system as the production room is to be kept at below 12degrees celsius and is 700cubic metres, going on the basis of using 8 air changes per hour. i am hoping to use two feeds with dampers, one from the outside and one from the refrigerated garage store next door to the production room which is kept at 5 degrees is 2,800 cubic metres. Will the negative air pressure created in the refrigerated garage area (which is 4x the size of the production room) affect the evaporators in this room, apart from making them work a little harder?? i am sorry if i havn't explained this very well this is my fist time writing a post. i can give more details if needed. Hope some one can advise. Thanks

  50. #150
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    Re: Refrigeration 101

    Quote Originally Posted by Gary View Post
    Think of the system charge as consisting of low side charge and high side charge.

    Assuming there is proper airflow through both coils (and that everything else is functioning normally):

    On the low side, at design refrigerated space temp, if the coil outlet superheat is right, then the low side charge is right.

    Coil outlet superheat varies with type of system. Generally speaking, a freezer should have 6-8F/3.5-4.5K superheat, a cooler should have 8-10F/4.5-5.5K superheat, and an A/C should have 12-16F/6.5-9K superheat.

    On the high side the subcooling should be no more than 15F/8.5K because this is the point at which liquid will start to back up into the condenser.

    On a cap tube/fixed orifice system, 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.

    Note that minimum subcooling is not a factor on cap tube/fixed orifice systems. They are critically charged.

    On a TXV system there is a minimum and maximum charge. When the superheat is right (at design space temp) and the subcooling is not more than 15F/8.5K then there is enough refrigerant in the system to do the job. This is the minimum charge.

    Additional refrigerant can then be added to bring the subcooling up to 15F/8.5K. This is the maximum charge.

    It is good practice to bring the charge up to maximum because vapor bubbles flowing through the TXV will wear out the needle and seat. This also provides additional refrigerant for heavy loads.
    Yes sir I'm a newbie but I like this, this is really great stuff.Thanks for all u do.

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