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The difference between setpoint calculation method A and B in a Xenta 121

Issue

There are two different methods used for calculating the setpoints in a Xenta 121 controller: method A and method B.

Environment

  • ZBuilder
  • NL220
  • LonMaker
  • Vista

Cause

Not knowing how each setpoint method is calculated in ZBuilder can lead to using the wrong method in certain applications.

Resolution

Method A

When nviSetpoint receives a valid setpoint, this value becomes the new, common setpoint. The cooling and heating setpoints are recalculated to be at the same distance from the new, basic setpoint as they were from the earlier basic setpoint. Therefore, method A removes any existing asymmetry. The controller calculates the different setpoints for heating and cooling in occupied and standby mode, from nviSetpoint, plus or minus half the neutral zone in occupied and standby modes, which are calculated from nciSetpoints. The controller uses the existing unoccupied setpoints in nciSetpoints for the unoccupied mode.

Below are the equations that go into calculating method A:
 

 

Method B

In standby mode you can choose method B to calculate the existing set-points. The result of method B will only differ from method A when the setpoints are placed asymmetrically around the mean value. With method B the asymmetry is kept. The controller calculates the different setpoints for heating and cooling in occupied and standby mode from nciSetpoints. The effective, absolute setpoint deviation is calculated as the mean value of the occupied_heat setpoint and the occupied_cool setpoint. The controller uses the existing unoccupied setpoints in nciSetpoints for the unoccupied mode.
 

Below are the equations that go into method B:

 

Note: If nviSetpoint is not being used, then just remove it from the above equation and calculate.
 

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Last update:
‎2018-09-06 03:48 PM
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