Results 1 to 8 of 8
  1. #1
    Join Date
    Jan 2007
    Location
    USA
    Posts
    37
    Rep Power
    0

    Differance Of Opinion



    I HAVE ALWAYS BEEN TOLD WITH AN EVAP. CONDENCER YOU SHOULD ALWAYS RUN THE WATER FIRST THEN THE FANS AND THAT MAKES SENCE. I WAS JUST TOLD BY ANOTHER ENGINEER FAN FIRST THEN WATER.,IAM ALMOST SURE THAT IS WRONG. ANY HELP ON THIS?



  2. #2
    Join Date
    Dec 2005
    Location
    Norfolk, England
    Age
    66
    Posts
    132
    Rep Power
    19

    Re: Differance Of Opinion

    Hi, I like water first and the fans start on a presure switch at about 8.5 bar. on Ammonia systems. All the systems that I know about and have worked on work this way around.
    All the best Arthur.

  3. #3
    Join Date
    Aug 2005
    Location
    USA
    Posts
    5,326
    Rep Power
    25

    Re: Differance Of Opinion

    Water first & fans last...

    The majority of the condenser capacity is created by the water flow. The fans add only just a bit of capacity.

    If you turn on the fans first, the condensing temperature can raise fairly quick. Then if the water pumps start, the discharge pressure drops quickly. Then the water pump shuts off and the coil dries off. Very soon the water pumps start again and the coil is wetted once more. This results in very rapid scale buildup on the coils if the water is not perfect and results in very poor control of the discharge pressure.

    If the water starts first the discharge pressure tends to stabalize unless the entering wet bulb temperature increases. In cold weather you have a steam plume that some people object to, but I rarely hear complaints on this point.
    If all else fails, ask for help.


  4. #4
    Join Date
    Jul 2006
    Location
    USA
    Age
    73
    Posts
    867
    Rep Power
    26

    Re: Differance Of Opinion

    Quote Originally Posted by US Iceman View Post
    The majority of the condenser capacity is created by the water flow. The fans add only just a bit of capacity.
    Here I have to (gently) disagree with my esteemed colleague.

    When a Evap Condenser is operated without water or fans, the only condensing is done by convection. Not very effective.
    With the water on and no fans, the water temperature rises quite quickly. There is some evaporation (evidenced by the steam plume), but the water temperature rises.
    With the fans on the water temperature is reduced, and the air and water moving over the coil forces condensing below dry bulb.
    I agree with the water first. I have a customer who insists in cycling the pump. As I was leaving the last time he was acid washing the condenser. In fact I think that except in cases of very disproportionately sized components or very cold climates, the water pump should NOT be cycled.
    My disagreement is with the contribution of the fans. I believe they play a major role in the efficient of the condenser. However this is from experience. I have no hard figures to back that up.

  5. #5
    Join Date
    Aug 2005
    Location
    USA
    Posts
    5,326
    Rep Power
    25

    Re: Differance Of Opinion

    Quote Originally Posted by NH3LVR
    Here I have to (gently) disagree with my esteemed colleague.
    Ouch!

    I agree with what you said, but I'm not changing my mind. Let me explain.

    My thoughts and comments were based on the condenser operation in the cooler weather which is where we see fan (& pump) cycling occur. In cooler weather with the warm(er) water flowing over the condenser coils the natural convection currents are pretty high.

    Which is why you can see systems operate at stable discharge pressures in cool weather without the fans.

    What I was thinking of is the system reaction to pumps starting or fans starting to control discharge pressure. In the winter, starting the fans tends to bring the discharge pressure down slowly. This of course depends on how many fans you start too. However, if you start the pumps (with the fans off) the discharge pressure drops rapidly.

    This is where my comment was drawn from about the fans having less capacity/impact than the pumps. I did not explain myself too well the first time I guess.

    When the load or entering wet bulb temperature begin to increase this mode of operation (fans only, no pumps) tends to be insufficient to prevent the discharge pressures from raising. This is where the fan operation comes into play. The fans simply provide forced convection currents so that the high humidity air in the condenser box is removed and replaced with lower humidity air.

    I hope I clearned that up (with egg on my face).
    If all else fails, ask for help.


  6. #6
    Join Date
    Jul 2006
    Location
    USA
    Age
    73
    Posts
    867
    Rep Power
    26

    Re: Differance Of Opinion

    Quote Originally Posted by US Iceman View Post
    Ouch! (with egg on my face).
    Do not worry about egg on the face. (I have not had any on mine since last Thursday)

  7. #7
    Join Date
    Dec 2004
    Location
    Weihai,China
    Posts
    807
    Rep Power
    20

    Re: Differance Of Opinion

    Water pump and fan start at the same time,and then start compressor after a designated seconds. No need to separate them. It's my understanding
    I hear...I forget;I see...I remember;I do...I understand

  8. #8
    Join Date
    Aug 2005
    Location
    USA
    Posts
    5,326
    Rep Power
    25

    Re: Differance Of Opinion

    Quote Originally Posted by Lc_shi
    Water pump and fan start at the same time,and then start compressor after a designated seconds. No need to separate them. It's my understanding
    If the normal operation occurs in the summer or moderate weather I think this is OK to do. If you start the pumps and fans together during the winter, you will have big problems.
    If all else fails, ask for help.


Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •