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Water Cooled Condsener

I was working on a water cooled trane unit
My supper heat was 17 degrees
My subcooling was 15 degrres
I had 22 dregrees over my water coil
24 dregrees over my air flow coil
and 12 amp on a 17fla compresssor at the compressos

155 psig head pressure 55psig Suction
My water tempature was 52 degrees at my inlet and 74 dgrees at my outlet
My air tempature was 73 degrees at my return and 49 degrees at my discharge

This is a computer room maintaining a 72 degree room tempature. Upon arriving my air flow coil is frozen and I have to thaw it out. Came back the next day to change the filter and have been watching the unit for two days and it is working okay. Cycles on a t-87 honeywell on/off fan runs continueusly. The filter was a little drity but not plugged. It was a high efficency filter on the unit. This is a pelum return and the only thing I could come up with was low condnsing tempature and maybe not to put in a high efficency filter on this type of unit. Any thoughts on why the coil froze up?

Comments

  • larry_15larry_15 Member Posts: 55
    water cooled condensor


    I was working on a water cooled trane unit.
    My superheat was 17 degrees.
    My subcooling was 15 degrees
    I had 22 dregrees over my water coil.
    24 dregrees over my air flow coil
    and 12 amp on a 17fla compresssor at the compressos

    155 psig head pressure 55psig Suction.
    My water tempature was 52 degrees at my inlet and 74 dgrees at my outlet.
    My air tempature was 73 degrees at my return and 49 degrees at my discharge

    This is a computer room maintaining a 72 degree room tempature. Upon arriving my air flow coil is frozen and I have to thaw it out. Came back the next day to change the filter and have been watching the unit for two days and it is working okay. Cycles on a t-87 honeywell on/off fan runs continueusly. The filter was a little drity but not plugged. It was a high efficency filter on the unit. This is a pelum return and the only thing I could come up with was low condnsing tempature and maybe not to put in a high efficency filter on this type of unit. Any thoughts on why the coil froze up?
  • larry_15larry_15 Member Posts: 55
    water cooled condensor


    I was working on a water cooled trane unit.
    My superheat was 17 degrees.
    My subcooling was 15 degrees
    I had 22 dregrees over my water coil.
    24 dregrees over my air flow coil
    and 12 amp on a 17fla compresssor at the compressos

    155 psig head pressure 55psig Suction.
    My water tempature was 52 degrees at my inlet and 74 dgrees at my outlet.
    My air tempature was 73 degrees at my return and 49 degrees at my discharge

    This is a computer room maintaining a 72 degree room tempature. Upon arriving my air flow coil is frozen and I have to thaw it out. Came back the next day to change the filter and have been watching the unit for two days and it is working okay. Cycles on a t-87 honeywell on/off fan runs continueusly. The filter was a little drity but not plugged. It was a high efficency filter on the unit. This is a pelum return and the only thing I could come up with was low condnsing tempature and maybe not to put in a high efficency filter on this type of unit. Any thoughts on why the coil froze up?
  • larry_15larry_15 Member Posts: 55
    water cooled condensor


    I was working on a water cooled trane unit.
    My superheat was 17 degrees.
    My subcooling was 15 degrees
    I had 22 dregrees over my water coil.
    24 dregrees over my air flow coil
    and 12 amp on a 17fla compresssor at the compressos

    155 psig head pressure 55psig Suction.
    My water tempature was 52 degrees at my inlet and 74 dgrees at my outlet.
    My air tempature was 73 degrees at my return and 49 degrees at my discharge

    This is a computer room maintaining a 72 degree room tempature. Upon arriving my air flow coil is frozen and I have to thaw it out. Came back the next day to change the filter and have been watching the unit for two days and it is working okay. Cycles on a t-87 honeywell on/off fan runs continueusly. The filter was a little drity but not plugged. It was a high efficency filter on the unit. This is a pelum return and the only thing I could come up with was low condnsing tempature and maybe not to put in a high efficency filter on this type of unit. Any thoughts on why the coil froze up?
  • Eugene SilbersteinEugene Silberstein Member Posts: 1,380
    Here We Go!

    I have made a couple of assumptions about the system and then an evaluation, so feel free to respond if the assumptions are inaccurate.


    Assumption #1: Given the amperage rating of the compressor, I have assumed that the compressor is a 3 horsepower pump.

    Assumption #2: There is a water regulating valve on the condenser

    Assumption #3: The temperature difference between the evaporator outlet and the compressor inlet is 10 degrees (suction line superheat)

    Having said this, here is the story with the system.

    There are three possible causes for the coil freeze-up. They are system undercharge, system undercharge or system undercharge.

    Here's the deal:

    Item #1: Air conditioning systems should always operate with an evaporator saturation temperature above freezing. A low evaporator saturation temperature and pressure indicate a possible undercharge.

    Item #2: The evaporator superheat is high, also indicating a possible system undercharge.

    Item #3: The condenser subcooling is borderline low, also indicating a system undercharge.

    Item #4: Opeating pressures are low, indicating a possible system undercharge.

    Item #5: The water regulating valve is closing in an effort to increase the head pressure. This slows the water flow through the condenser, increasing the delta-t acorss the condenser. You have a 22 degree delta-t across the condenser, which should be about 10 degrees. This is also an indication of a system undercharge.

    Item #6: Frosting evaporator coils restrict airflow through the coil and increase the amount of time that the air is in contact withe coil. This will cause the delta-t across the evaporator coil to increase. Your 24 degree delta-t measurement agrees with this.

    So, all of these factors point to a system undercharge.


    Now with a completed pressure-enthalpy plot, we can see that the system (with a 3 horsepower pump) is producing a system (cooling) capacity of 4.6 tons.

    Since the evaporator coil is colder than design, the efficiency of this system is relatively high with a coefficient of performance of 5.7 (3.0 is normal for air conditioning systems) and an EER of about 19.

    The problem with the system being too efficient is the frosting of the coil. The initial frosting of the coil is very likely due to reduced load during off-peak system operation.

    In addition, the completed pressure enthalpuy plot for this system can provide information such as the net refrigeration effect, the heat of compression, heat of work, mass flow rate per ton, theoretical horsepower per ton, mass flow rate of the system, evaporator capacity, condenser capacity, compressor capacity as well as the items mentioned above.

    Sounds like magic?

    It's not. It's just that refrigerants behave in a predictable manner and because of that, we can predict how air conditioning and refrigeration systems will operate.

    Want to get in on the secret? No need... it's no secret.. check out this upcoming pressure enthalpy seminar, being taught by yours truly.
  • don_163don_163 Member Posts: 67
    thats was

    a great reply Professor...I'm shock that your class has not sold out by now.

    You must...Please!!! what ever it takes and do a video of
    this course.

    I'll be willin to put up a nice chunk of change.

    Lets see 4 x195 plus hotel room, travel expense,and time away from the job.

    Hmmm.. let me see what would this video be worth to me and my crew and then the trickle down affect it will have on my customer of a job well done.

    Hey professor lets talk??? Why you tease us?LOL!

    Ps.Forgot, Mr Holohan are you listening..Marketing Guru.


  • larry_12larry_12 Member Posts: 2


    Actually it is a 4 ton compressor copeland. And lookng at what you said maybe that it is not a low condensing tempature. However, the water coming in is low and the unit seam to run okay most of the time. It does not freeze up all the time, and I realize that if yoou have a low evaporator temp it start frosting up but this unit does not show sign of frost up unless it has the same filter in for a couple of months.
  • larry_12larry_12 Member Posts: 2


    Actually it is a 4 ton compressor copeland. And lookng at what you said maybe, it is not a low condensing tempature. However, the water coming in is low and the unit seam to run okay most of the time. It does not freeze up all the time, and I realize that if you have a low evaporator temp it start frosting up but this unit does not show sign of frost up unless it has the same filter in for a couple of months. If this helps any more, I am at a lost because it doesn't show the signs of a normal low charge system.
  • Eugene SilbersteinEugene Silberstein Member Posts: 1,380
    What does a dirty filter do?

    A dirty air filter reduces the amount of air that flows through the evaporator coil. With a reduction in air, the amount of heat the refrigerant in the evaporator can absorb is also reduced. If we add less heat to the refrigerant, the saturation temperature and pressure will drop.

    At 55 psig, you are already at a 30 degree saturation temperature, so freezing will likely occur. A light frost will likely begin to form, but will quickly melt when the compressor cycles off.

    You mentioned in your response that you are dealing with a 4-ton Copeland compressor. Just for the record, the tonnage is the system capacity, not the horsepower of the pump. From the information you provided, we were able to establish that the system was providing about 4.6 tons of cooling. This 4.6 is not the horsepower of the compressor, but the capacity of the system.

    Since you mentioned that the system is a 4-ton unit, my assumption that you have a 3 horsepower pump is pretty much right on point.

    Score another one for Pressure Enthalpy!

    Best of luck.
This discussion has been closed.

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