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3-pipe fan coil unit system

1964 dormitory - has a 3-pipe heating/chilled water system. Hot and chilled water go out to fan coil units but only 1 return comes back. I had never seen this. Why was it done this way? It appears to be a changeover system so why not just go with 2-pipes? Thank you.

Comments

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,056
    @feisenhower
    Those systems were designed to run both heating and cooling at the same time. They may be ok in the summer or winter but spring and fall with both systems running your returning cool water to the boiler or hot water to the air conditioning. Not good in my opinion.

    So they get run as a changeover system which as you said can be done with just two pipes

    Let me take a guess that this system is 1950s-mid 1960s?????????