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Plate and Frame Heater Exchanger Temperature delivery accuracy

dfrudfru Member Posts: 26
I am working on a project where a plate and frame heat exchanger supplies domestic hot water to a series of guestrooms in a hotel. High temperature hot water supplies heat to the heat exchanger. We would like to maintain 120 degree F water at the supply side to the guestrooms. What type of accuracy would we expect at the outlet side +/-?

Any recommendations as to controls which we should consider to achieve good temperature control?


  • Firecontrol933Firecontrol933 Member Posts: 73
    Only thing I would suggest is that you get a licensed plumber to do it with good liability insurance.

    I'm not a plumber, but I am aware that the plumbing code is very specific about protecting the public from hot water scalding. If for any reason your system were to scald someone, even years or decades down the road, the chances of a lawsuit are good. I personally would want someone else to be on the receiving end of that.

    With that said. Your accuracy is only as good as the type, quality and responsiveness of the control used. Again I'm thinking the plumbing code spells out what kind of specifications the temperature control must meet.

  • hot_rodhot_rod Member Posts: 12,958
    Is there a storage tank involved, or is this a instantaneous type HX?

    You need an ASSE listed mixing valve to assure code compliance. Usually on large buildings with a wide flow range you will have a hi-lo mixing station. A high flow mixer piped with a smaller valve to accurately mix across low and high flow conditions. Google hi-lo mixing valves to get some data
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • dfrudfru Member Posts: 26
    I do not believe that the system has a storage tank.

    I was also thinking that a mixing valve would do the trick. But shouldn't the controls be able to maintain temperature without one?
  • Jamie HallJamie Hall Member Posts: 12,379
    dfru said:

    I do not believe that the system has a storage tank.

    I was also thinking that a mixing valve would do the trick. But shouldn't the controls be able to maintain temperature without one?

    A mixing valve really is required here. It would be nice to think that controls could do it alone, but it would be much easier -- and cheaper -- to do it with a mixing valve. Your control scheme would have to sense both temperature and flow at the output and be able to use both inputs to control the flow on the hot side. Could it be done? Sure. But -- at least in my opinion -- it's not the best way, never mind the simplest. And besides, you may find that code requires the valve...
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • SWEISWEI Member Posts: 7,356
    The controls have to move something physical in order to do their job. Generally that means moving a valve or varying the speed of a pump.
  • HenryHenry Member Posts: 962
    You cannot reliably supply hot water to a hotel using only a HX. Most hotels when using HX also use storage tanks. I debugged a hotel last year. Boilers are used unless the boilers provide heating then a HX is used. Boiler or HX supplies the tanks to have a minimum of 140F in the tanks. A high-low temperature thermostatic valve control output temperature to the rooms: 120F.
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