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Outdoor Reset Coordination Between Mod Con Boiler and Buffer Tank

tomtech
tomtech Member Posts: 10
I've installed a Navien Mod Con Boiler and a Buffer Tank. I have piped the buffer tank with a 3 pipe design and have panel Rads with TRV's , low mass radiant floors and wall, and a high mass radiant slab, all designed around the same supply temperature. With the various types of emitters I have a number of micro zones and that is the reason for the buffer tank. I am utilizing a TEKMAR 256 to monitor/control the temperature of the buffer tank. The T256 provides the Boiler demand to the boiler and utilizes ODR. I have also setup the boiler to operate on an ODR strategy. My question is what is the best way to coordinate the ODR strategy of the boiler and buffer tank. I currently have set the reset curve of the boiler higher than the reset curve of the buffer tank but with the 3 pipe design of the buffer tank this defeats the purpose of the 3 pipe design when a zone/zones are calling for heat and the boiler is providing system supply directly to the zones and buffer tank. I am considering matching the ODR of both the boiler and the buffer tank but am wondering if anyone has a better experience and suggestion.

Comments

  • hcpatel78
    hcpatel78 Member Posts: 151
    I have similar setup as yours . i have Two pipe buffer with MOD CON setup. In warm weather like above 45 my ODR sets the water temperature around 98 and floor is not getting heated enough (Floor Sensor set at 76) resulting thermostat keep calling for heat and water temperature is not enough to bring the floor temperature at 76.
    When my boiler SWT set above 100 or so it not a problem. So in cold(below 45) my ODR works perfect with this setup.
    I am also looking for the solution of this ...
    Thank you,
    Hiren Patel
  • tomtech
    tomtech Member Posts: 10
    The setup that I am now going to try is as follows. I have chosen identical ODR curves for the boiler and the buffer tank. I have also selected the differential for the T256 to be 16deg F. Therefore the T256 provides a boiler demand (TT signal) with the buffer tank at 8degF below the target buffer tank temperature ODR curve. I have chosen a burner on temp for the Navien boiler to be 4degF below the Navien ODR curve. The burner off temp for the Navien will be set to 10deg F (2 degrees above the T256 upper differential). This I think will provide the control needed to coordinate the 2 ODR strategy's for the boiler and buffer tank as long as the performance of the 10K sensors are close to similar. When the buffer tank sends a TT signal / boiler demand the Navien programing should allow the boiler to fire immediately and on the upper side of the buffer tank temperature the Navien should still be firing when the T256 stops the boiler demand TT signal. sometimes it helps to write these issues out and then the answer appears more obvious.
  • hcpatel78
    hcpatel78 Member Posts: 151
    edited December 2020
    Do you have aquastat on Buffer tank?
    Thank you,
    Hiren Patel
  • tomtech
    tomtech Member Posts: 10
    The TEKMAR 256 acts as an aquastat