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Thread: HVAC Controller

  1. #1

    HVAC Controller

    Hi:

    Why do the HVAC controller daily schedules force a 2 deg C separation between heat and cool setpoints? They force the cool setpoint to be a higher temp for some reason??
    So in the winter, the house will be fine, but the then hot in the summer? Or cold in the winter but fine in the summer?

  2. #2
    Senior Member
    Join Date
    Oct 2013
    Posts
    400
    The differential is called "deadband" Its the area of temperature where nothing occurs. It stops systems from short cycling Kinda of like a dog chasing its tail. You never want systems constantly switching over or short cycling.Its generally used when a stat is in auto mode.

  3. #3
    I understand the deadband/hysteresis concept, but I'm surprised to see it implemented like this then. So if you start with the t-stat in auto mode with say 23C heat setpoint and 25C cool setpoint, and then flip the mode to cooling mode, the setpoint will be 25C? But if you switch to heat mode, the setpoint becomes 23C?
    If that is true, then they force the cool setpoint to be a higher temp for some reason? So in the winter, the house will be cozy, then too hot in the summer?

    Bottom line: How do you actually maintain a single steady setpoint temperature regardless of season or mode, without human input/adjustment?

  4. #4
    Authorized Lutron Contributor
    Join Date
    Apr 2013
    Posts
    407
    There is not a way (using either the TouchPRO or HVAC controller) to only have 1 set point for both heating and cooling. This is to prevent the HVAC system from constantly switching between heating and cooling.
    Last edited by Brian S.; 12-05-2013 at 09:39 AM.

  5. Thanks ekimla thanked for this post
  6. #5
    Authorized Lutron Contributor
    Join Date
    Jun 2013
    Posts
    19
    Quote Originally Posted by ekimla View Post
    I understand the deadband/hysteresis concept, but I'm surprised to see it implemented like this then. So if you start with the t-stat in auto mode with say 23C heat setpoint and 25C cool setpoint, and then flip the mode to cooling mode, the setpoint will be 25C? But if you switch to heat mode, the setpoint becomes 23C?
    If that is true, then they force the cool setpoint to be a higher temp for some reason? So in the winter, the house will be cozy, then too hot in the summer?

    Bottom line: How do you actually maintain a single steady setpoint temperature regardless of season or mode, without human input/adjustment?
    If the setpoint that is comfortable for you is 24C then set your heat setpoint to 23C and your cool setpoint to 25C. In systems with a single setpoint this is what they are doing the in background when you select 24C. The reason we expose both is that it allows you to control how wide the hysteresis is. Some people may find a wider range of temperatures acceptable and would prefer to save the energy/money on heating/cooling. For me for example, I always want my heat setpoint at 22C when I am home because I never want it to get colder than that in the winter. But my cool setpoint is set to 26C because I don't mind it being warmer in the summers. This way I can leave my system in auto and know that my house will always be at a comfortable temperature for me, while at the same time I am saving energy on cooling by not trying to maintain my house at 24C.

  7. Thanks ekimla thanked for this post
  8. #6
    Just want to say thank you for the responses and changes made in the 7.0 software which redefines the terminology in the software to eliminate the ambiguity and confusion! It's totally clear now.

  9. Thanks Chris Y. thanked for this post

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