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  1. #1
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    How much gas should this system take?



    http://www.instructables.com/id/Home...ridgeAir-con-/

    This is my quick home made job of a freezer . I didnt know how much gas to put in so i put in about 70grams .

    I might have to measure all the pipe work to get an exact amount but how far of the mark am i with 70grams?

    whats the calculations i need. its 1/4 pipe .

    Yes i know this is not the best designed system . like i said it just quickly put it together for something to do .



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    Re: How much gas should this system take?

    As with most experiments you need to experiment with the quantity required at the design conditions.
    Brian - Newton Abbot, Devon, UK
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    Re: How much gas should this system take?

    Evaporator and condenser in the same cooler. Going to find there will be alot more hot water than cold water with the space allowed. Suction pressure will have to be under 5 psi.
    To the optimist, the glass is half full. To the pessimist, the glass is half empty.

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    Re: How much gas should this system take?

    As much gas you need for the correct SH at optimum pressures (LP/HP). That's the most precise definition I think. You can't calculate this, just trial and error
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: How much gas should this system take?

    Thanks for your replys .
    Mikeref , There are fully air tight . but yes the condenser side gets hotter than it does cool . I have a slow flow going through it with fresh water and it works fine. or change the water every 15mins.
    Not the most ideal unit , even with a bigger condenser , that facts of life is its easier to heat than to cool .

    So theres no real calc for this ? 12 metres of pipe at 1/4 size . I guess will all the variables you cant really just pull a standard figure .

    Im fiddling around with the "metering device" and ive gotten it to -4.8 . more like average -1 . thats with out water . Water has alot more heat energy than i realized . Compared to air .

    I the gas charge is abit more hard to fiddle around with
    IT runs great with just still air . even a fan behind it all good .

    So to cool the water down better i just need a bigger condenser ?

    Next challenge idea is to feed 3/4 clear hose over the coil . So the coil is inside the bigger pipe . then fill it with water . Ice it up then have a fan blowing past the coil.

  6. #6
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    Re: How much gas should this system take?

    Quote Originally Posted by Simeonx1 View Post
    Thanks for your replys .
    Mikeref , There are fully air tight . but yes the condenser side gets hotter than it does cool . I have a slow flow going through it with fresh water and it works fine. or change the water every 15mins.
    Not the most ideal unit , even with a bigger condenser , that facts of life is its easier to heat than to cool .

    So theres no real calc for this ? 12 metres of pipe at 1/4 size . I guess will all the variables you cant really just pull a standard figure .

    Im fiddling around with the "metering device" and ive gotten it to -4.8 . more like average -1 . thats with out water . Water has alot more heat energy than i realized . Compared to air .

    I the gas charge is abit more hard to fiddle around with
    IT runs great with just still air . even a fan behind it all good .

    So to cool the water down better i just need a bigger condenser ?

    Next challenge idea is to feed 3/4 clear hose over the coil . So the coil is inside the bigger pipe . then fill it with water . Ice it up then have a fan blowing past the coil.
    Air heat loads change with temperature but are about 1 Kj/kg so one kilogram of air requires 1 Kilojoule of heat to warm it by 1 degree Centigrade.

    Water is a lot denser and is about 4.19 Kj/kg so 1 Kilogram of water requires 4.19 Kilojoules of heat to warm it by 1 degree Centigrade.

    3 X more heat required.

    All the best

    taz

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    Re: How much gas should this system take?

    .

    What are you using as a valve?

    untitled.JPG

    It looks like a ball valve? .

    If I was you I would put a reciever on it and then you could charge it with any amount of liquid (within reason)

    taz

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    Re: How much gas should this system take?

    .

    Not much help maybe because it does not go as low as 1/4 but this old chart says
    3/8 Liquid is 0.0595 per metre. All the best taz.
    Line size
    O.D.
    Refrigerant
    Liquid
    Line
    Hot Gas
    Line (55C)
    Inches
    kg/m
    gm/m
    134a
    0.0595
    2.2322
    3/8
    22
    0.0580
    3.2740
    R507 404A
    0.0506
    4.6133

  9. #9
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    Re: How much gas should this system take?

    Quote Originally Posted by Simeonx1 View Post
    So theres no real calc for this ? 12 metres of pipe at 1/4 size . I guess will all the variables you cant really just pull a standard figure .
    According to my calcs, 1/4" tube with a wall thickness of 0.76mm has an internal area of 0.000018551 Square Meters. Unless I've botched things, this should hold 18.55ml/M which is 22.3713g/M based on the density of R134a being 1.206g/ml

    My calcs for 3/8" tube work out at 49.01ml/M which for R134a is 59.1g/M (which is pretty close to taz24's table, so I'm probably not far off).

    So you've got ~58ml in the system give or take measurement error (how accurate are your scales?)

    I'd have thought you wanted the evaporator completely (or almost) full of liquid and the condenser mostly full of gas.

    Assuming you've split the tube 50/50, the evap would take about 91.57ml

    How big and long are your hoses?

  10. #10
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    Re: How much gas should this system take?

    This chart might be useful (or maybe not)

    Tube OD (mm) Thick (mm) ID (mm) Circ(mm) Square (mm) Area (ID/mm) L/M Surface Area OD / M Surface Area ID / M
    3/16" 4.76 0.76 3.24 14.95 3.74 8.24 0.008245 0.014954 0.010179
    1/4" 6.35 0.76 4.83 19.95 4.99 18.32 0.018322 0.019949 0.015174
    5/16" 7.94 0.81 6.32 24.94 6.24 31.37 0.031371 0.024944 0.019855
    3/8" 9.52 0.81 7.90 29.91 7.48 49.02 0.049017 0.029908 0.024819
    1/2" 12.70 0.81 11.08 39.90 9.97 96.42 0.096421 0.039898 0.034809
    5/8" 15.87 0.89 14.09 49.86 12.46 155.92 0.155924 0.049857 0.044265
    3/4" 19.05 0.89 17.27 59.85 14.96 234.25 0.234247 0.059847 0.054255
    7/8" 22.23 1.14 19.95 69.84 17.46 312.59 0.312590 0.069838 0.062675
    Last edited by BradC; 23-02-2012 at 03:50 AM.

  11. #11
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    Re: How much gas should this system take?

    Thanks for that information guys.

    The value im using for a metering device is a little hand valve that goes on the end of your gauges , so you can keep the refrigerant in the gauge line from escaping , Its the law to have these on your gauges in Australia.

    The gauge line im using is a normal r22/134a not to sure about to ID , probably 3/8 ?

    Ill measure the pipe length in a sec ,

    How would i go about doing the liquid receiver ? A piece of 3/4 copper 200mm long after the condenser ?

    Im going to turn the esky into the condenser and have the evap coil inside a 300mm piece of duct connected to my fan . The condenser will be a longer pipe length when i finish with it and water would fill the whole esky ,

  12. #12
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    Re: How much gas should this system take?

    Thanks for that information guys.

    The value im using for a metering device is a little hand valve that goes on the end of your gauges , so you can keep the refrigerant in the gauge line from escaping , Its the law to have these on your gauges in Australia.

    The gauge line im using is a normal r22/134a not to sure about to ID , probably 3/8 ?

    Ill measure the pipe length in a sec ,

    How would i go about doing the liquid receiver ? A piece of 3/4 copper 200mm long after the condenser ? Would i have to make it like a real one. So vapor goes in the top and liquid is fed to the tx from the bottom of the receiver .

    Im going to turn the esky into the condenser and have the evap coil inside a 300mm piece of duct connected to my fan . The condenser will be a longer pipe length when i finish with it and water would fill the whole esky ,
    Last edited by Simeonx1; 04-03-2012 at 08:56 AM.

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