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  1. #1
    Join Date
    Dec 2013
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    1/3, 2/3 Head Pressure Control?

    I have a variable-primary flow chilled water plant that has 4 chillers using 1/3-2/3 modulating valves for condenser water head pressure control. Can anyone shed light on how the valves work together to maintain head pressure?

  2. #2
    Join Date
    Apr 2017
    The Deep South
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    So, on an initial start command, the 1/3 valve will receive a call to open to minimum position. These are usually 0-10 or 2-10 VDC. Then based on head pressure, the valve will continue to open as the chiller puts heat into the condenser water. Usually around 40-50% signal, the 2/3 valve is enabled and then both valves will start opening. As tower water cools and head pressure drops, then the 2/3 valve closes first.

    Make sense?

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