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  1. #1
    Join Date
    Jun 2003
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    Lenexa, KS
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    435

    Arrow Daikin Operation Question

    Howdy folks,

    Got a question for the Daikin guys out there... how does your VRV system maintain room setpoint?

    My understanding is that indoor fan coil units (all of them) are basically constant volume. Yes, you can change the speed on the controller if you want, but you would have to do that manually. I'm also told that the EEV on the indoor units tries to maintain the same superheat on the suction line on the outlet of the various fan coils. According to Daikin service manuals, the outdoor units revs compressors up and down trying to maintain the same evaporator pressure. So, I'm confused... how can you maintain the same saturated suction, fan speed and superheat all the time? How does the system change/react on change in room temp?

    Can somebody please help me connect the dots?
    "We are what we repeatedly do.
    Excellence, then, is not an act, but a habit."
    -Aristotle

  2. #2
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
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    14,915
    Quote Originally Posted by gschra11 View Post
    I'm also told that the EEV on the indoor units tries to maintain the same superheat on the suction line on the outlet of the various fan coils.
    I think you were misinformed on that point.
    If more government is the answer, then it's a really stupid question.

  3. #3
    Join Date
    Mar 2005
    Posts
    56
    The EEV in each evap maintains its own superheat, typically 1-5F. As EEV's open to lower the superheat (when load increases), the suction pressure rises, which tells the compressor to speed up. The reverse occurs when the load decreases. As the load is reduced or if fan speed is lowered, the EEV continues to close down to its programmed operating minimum if necessary. When room temp reaches setpoint, the valve closes almost full closed, but just a trickle open to prevent oil logging. The fan speed is also reduced a super low speed when satisfied.

  4. #4
    Join Date
    Jul 2006
    Location
    Anytown USA
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    2,060
    Quote Originally Posted by stopro1 View Post
    The EEV in each evap maintains its own superheat, typically 1-5F. As EEV's open to lower the superheat (when load increases), the suction pressure rises, which tells the compressor to speed up. The reverse occurs when the load decreases. As the load is reduced or if fan speed is lowered, the EEV continues to close down to its programmed operating minimum if necessary. When room temp reaches setpoint, the valve closes almost full closed, but just a trickle open to prevent oil logging. The fan speed is also reduced a super low speed when satisfied.
    Sounds about the same as the Sanyo/Panasonic Eco-I VRF system.

  5. #5
    Join Date
    Aug 2010
    Posts
    3,363
    So essentially the same as variable geometry car A/C compressor. The valve inside compressor uses case pressure to change compressor capacity by changing swash plate angle to maintain the same suction pressure while the TXV controls superheat.

    In ductless systems the feedback is to the VSD to change the speed rather than capacity.

  6. #6
    Join Date
    Aug 2011
    Location
    Chicago
    Posts
    51
    Went to a Daikin Training Seminar the more i listened the less I would want to burden a customer with one of those systems. Have n

  7. #7
    Join Date
    Aug 2011
    Location
    Chicago
    Posts
    51
    Have not had to work on one. Put a sungle evap system worked fine. Just think too many issues with multiple evap dx AC systems.

  8. #8
    Join Date
    Mar 2003
    Posts
    7,326
    have lots of vrv systems out there for years now, very, very few issues if installed properly. The controller sends the setpoints to the respective units. Each unit has its own sensors on board, and control to that. EEV's are controlled as necessary for each unit as is fan speed. The outdoor unit communicates with all of the indoor units for feedback and alrming, and essentially ramps the compressor/condenser fan(s) to maintain conditions atthe condensing unit.

  9. #9
    Join Date
    Aug 2011
    Location
    Chicago
    Posts
    51
    Still cant beat a chilled water system. Nobody cares about effeciency when its not working

  10. #10
    Join Date
    Jun 2003
    Location
    Lenexa, KS
    Posts
    435
    I guess I'm confused because Daikin tells me that the fan speed doesn't change... It only shuts the fan off when the thermostat is satisfied. Otherwise, it's a CAV system, with three user-selectable speeds that can be set by the user but have nothing to do with thermal demand.

    If the fan is constant, let's pretend I push my thermostat down 4 degrees because I want it cooler in the room. What does the system do to react? The return air going across the coil doesn't change... it still has the same amount of load on the coil, but now the thermostat is calling for more cooling. Does this drop the superheat? Does the suction pressure reset to make the leaving coil temp lower? Is the fan speed really constant?
    "We are what we repeatedly do.
    Excellence, then, is not an act, but a habit."
    -Aristotle

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