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Thread: superheat

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    superheat



    hiya ya all, i have a new split system going in and don,t know how to measure the superheat, is it at the condensor or compressor or evaporator, it is a fan coil unit with tev fitted but i have to adjust infield and ain,t done it before HELP PS GAS IS R22



  2. #2
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    Re: superheat

    Why are you fitting a system with R22 in it as they were phased out two years ago.

    Ian

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    Re: superheat

    My question as well, you cannot purchase new R22 equipment in the UK officially.
    Brian - Newton Abbot, Devon, UK
    Retired March 2015

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    Re: superheat

    Again all this is according to application and installation. From the sound of it you could use a little classroom time before throwing yourself to the wolves.

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    Re: superheat

    Quote Originally Posted by scott12 View Post
    hiya ya all, i have a new split system going in and don,t know how to measure the superheat, is it at the condensor or compressor or evaporator, it is a fan coil unit with tev fitted but i have to adjust infield and ain,t done it before HELP PS GAS IS R22
    Hellou Scott ,

    If you give me your e maill adress i will sent to you same docu. about superheating .
    My maill is gianirns@yahoo.com.

    All the best.

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    Re: superheat

    Quote Originally Posted by scott12 View Post
    hiya ya all, i have a new split system going in and don,t know how to measure the superheat, is it at the condensor or compressor or evaporator, it is a fan coil unit with tev fitted but i have to adjust infield and ain,t done it before HELP PS GAS IS R22
    Super heat is the temperature difference between the temp measured by the gauge pressure (saturation temp), and the evaporator outlet. The evap pipe outlet will be warmer then the saturation temp read off the gauge. How much warmer it is, is the superheat (extra heat the vapour picks up).
    Too high a superheat, means not enough refrigerant liquid in the evap, so the system is not efficient. Too low a superheat means a flooded evap and extra liquid which might come back to the compressor which is bad for it.

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    Re: superheat

    Quote Originally Posted by scott12 View Post
    hiya ya all, i have a new split system going in and don,t know how to measure the superheat, is it at the condensor or compressor or evaporator, it is a fan coil unit with tev fitted but i have to adjust infield and ain,t done it before HELP PS GAS IS R22
    To Determine Superheat:

    1. Take the low side pressure reading from your gauges and convert it to temperature using chart or

    gauge.

    2. Then take the temperature of the Suction line as close to the condensing section as possible stay at least 6 inches from compressor.

    3. Take the difference between the above readings (Suction line temp – Saturation temp)

    4. When ambient air temp (Outside air temp) is 75-85 degrees the superheat should be 12-15 degrees, if the ambient temperature is 85 degrees or over the superheat should be 8-12 degrees.

    5. If superheat is low then flooding the evaporator. Note: Do not adjust charge yet.

    6. If superheat is high then starving the evaporator. Note: Do not adjust charge yet.

    7. Do not adjust charge until sub-cooling is checked.

    Note: When charging a system using superheat, you are basically charging the unit to the amount of air that is crossing the evaporator.

    Note: Do not adjust charge based on superheat on systems with thermal expansion valves (TXV’s). TXV’s control the superheat. You can, however, check the superheat to see if the TXV is working properly.

    To Determine Sub-Cooling:

    1. Take the high side pressure and convert it to temperature using chart or gauge.

    2. Then take the temperature of the liquid line as close to evaporator as possible before the metering device.

    3. Take the difference between the above readings. (Saturation temp – Liquid line temp). Note liquid line temperature at the evaporator should be within 2 degrees of liquid line temp at condensing unit. If not could be restriction or line set too long.

    4. Sub-Cooling should be around 12-15 degrees

    5. Then using the information from superheat and sub-cooling we can have some idea where to look for a problem.

    Example:
    Suction line temp is ------- 60 degrees @ condenser
    Suction Pressure is ------ 76 psi ---- 45 degrees saturation temperature
    60 degrees – 45 degrees = 15 degree superheat

    Liquid Pressure is ------------226 psi --------110 degrees saturation temperature
    Liquid line temp is -------------95 degrees @ evaporator before metering device

    110 degrees – 95 degrees = 15 degree sub-cooling

    Possible Diagnosis using Superheat and Sub-Cooling:

    If superheat is high and sub-cooling is low:
    Charge must be adjusted. System undercharged.

    If superheat is low and sub-cooling is high:
    Charge must be adjusted. System overcharged

    If superheat is high and sub-cooling is high:
    Could have blockage in coil, orifice or line set.

    If superheat is low and sub-cooling is low:
    Orifice could be too big, there is no orifice in the unit of the orifice is stuck and refrigerant is by-passing it.

    To Determine Delta T (Temperature difference across the coil):

    1. While unit is running take the temperature of the air in the supply plenum near the coil (approx 12 inches.)

    2. Then, while the unit is still running, take the temperature of the air in the return plenum near the unit.

    3. Then take the difference between the above readings.

    4. Should be around 15-18 degrees.

    5. If to low then coil might not be seated in pan correctly or air bypassing coil. (Assuming superheat and Sub-Cooling are OK.)

    6. If too high then you might not be getting enough air across coil. Obviously this can cause the coil to freeze.
    The difference between genius and stupidity is that genius has its limits.

    Marc

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    Re: superheat

    Marc
    your info must have come from a manual for a specific piece of kit as some of the points are some what unusual especially the bit that states the superheat should be different dependent on ambient temperature.

    If this guy is talking about a split which more than likely has a capillary tube how is he going to adjust the superheat anyway.

    Ian

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    Re: superheat

    It's what i was given when i first started asking about superheat and subcooling when i joined the site. im sure the guy should get the jist of it.
    The difference between genius and stupidity is that genius has its limits.

    Marc

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    Re: superheat

    Quote Originally Posted by scott12 View Post
    hiya ya all, i have a new split system going in and don,t know how to measure the superheat, is it at the condensor or compressor or evaporator, it is a fan coil unit with tev fitted but i have to adjust infield and ain,t done it before HELP PS GAS IS R22

    There are two methods.
    One accurate one crude.

    The crude way is to measure the temp of the pipe just after the TEV, then measure the temp of the pipe just out of the evap.
    The temp at TEV will be the coldest and the out temp should indicate crudly the amount of superheat.
    This method should only be used if access to gauges is not possible.

    The more accurate method is to fit your gauges and measure the temp on the low side. Then measure the temp of the suction line at the outlet of the evap.
    The difference will be the accurate superheat temp.

    taz.

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