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  1. #1
    Join Date
    Jun 2006
    Location
    Omaha, Nebraska
    Posts
    861

    Rack Cond Fan Cycling in the Summer?

    I say summer because it's always like summer here. It gets down to 72 Deg on a cold night. Would the rack save money by having some fans cycle off during low load or should they be set to run continuously if the ambient is above 70?

    In the states you pay about a fifth of what electricity costs here. Commercial customers pay 41 cents per kW here so every watt counts.

  2. #2
    Join Date
    Mar 2009
    Posts
    174
    You should try floating the condensing temps to save power year round. It is a large savings and easy to set up on most controlers.

  3. #3
    Join Date
    Jun 2006
    Location
    Omaha, Nebraska
    Posts
    861
    Quote Originally Posted by cold spell View Post
    You should try floating the condensing temps to save power year round. It is a large savings and easy to set up on most controlers.
    You're talking about a reset schedule where the condenser setpoint changes with the ambient temp? What kind of numbers are you talking about as far as setpoints?

  4. #4
    Join Date
    Mar 2009
    Posts
    174
    for most racks I use 10 deg for low temp and 13 deg for medium temp. 70 deg min 100 deg max.

  5. #5
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,671

  6. #6
    Join Date
    Jun 2006
    Location
    Omaha, Nebraska
    Posts
    861
    I'm looking at the program in EZset for ComTrol and it doesn't give me an option to change the ambient setpoints, only the condenser min and max setpoints.

    When you say 13 for medium temp, that means saturated condensing temp runs 13 degrees above ambient?

  7. #7
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,671
    Yes. SCT would run at that TD.

    You may have to change the condenser strategy. Totally different. I have exactly zero experience with microthermo, but all other controllers allow it to happen.

  8. #8
    Join Date
    Mar 2009
    Posts
    174
    On comtrol it is PSI/ambient modified control input and single setpoint PID control method.

  9. #9
    Join Date
    Jun 2006
    Location
    Omaha, Nebraska
    Posts
    861

    Update

    For now, I've decided to not let the fans cycle off. Ever. Almost every 5 year old+ coil on my island is eaten away 1" at the bottom. All I can figure is:

    A. Acid rain drips to the bottom when fan is not running and eats away the aluminum.

    B. Rain washes salt from coil to the bottom and salty rainwater then eats away the aluminum.

    The corrosion is always at the bottom where rain would collect during the off cycle. Either way, it seems that leaving the fans on would prevent this. I have a 150 ton condenser that was almost completely clogged with chunks of aluminum and oxide dust in just 4 years! See my update on how to remove the corroded coil section from a Bohn condenser...

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