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Thread: Heating and cooling mode changeover algorithm

  1. #1

    Heating and cooling mode changeover algorithm

    Anyone have any ideas on the best way to automate heating/cooling mode changeovers? I figure it might be at least partly dependent on outdoor temperature and season and gps and of course indoor temperature.

  2. #2
    Super Moderator
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    The TouchPRO or HVAC Controller can both be configured to control heat pumps.

    On the HVAC Controller, the dip switches are used to specify whether the changeover valve is for cool or heat.
    On the TouchPRO, you can do the same using the internal configuration menus on the unit.

    For more information, see the install guides of both devices:
    HVAC Controller (Page 1, pane 3, tables 2/3): http://www.lutron.com/TechnicalDocum...ry/041-299.pdf
    TouchPRO (Page 7, option 190): http://www.lutron.com/TechnicalDocum...y/041-338B.pdf

  3. #3
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    This somewhat a foggy area. We have some very large residences that actually use a chiller for air conditioning and a boiler for heat utilizing the same coils. In a case like this the switch over needs to be done by a professional. There is valves that need to be manually switched. One would never want to shock a boiler with ice cold water. If you explain in a little more detail your exact scenario and what your trying to accomplish I may have some valuable input

  4. #4
    The application I am talking about is a standard forced air furnace and air conditioner. No heat pump, or aux heat source.

    The algorithm I'm asking about would mainly apply in the spring and autumn when the outside temperature bounces from too hot to too cold. i.e. now. During these months you constantly flip from heating to cooling or dressing down and dressing up.

    In my mind, an automated home means the home owner just selects a single temperature setpoint they want, without having to comprehend the technicality of changing the mode from heating mode to cooling mode. Having a heating setpoint and a separate cooling setpoint is confusing for normal people.

    Heat/cool combo mode is awkward too because it has two different thresholds for temperature - a min and max. If the min or max are exceeded, then the system applies corrective heating and cooling as required to return the interior temperature to within the min/max. This is not smart control, even if you automate it!

    In my mind real climate control properly changes to the heating or cooling modes (where appropriate and) when appropriate, in order to maintain a single setpoint temperature. I would think this can only be accomplished by understanding the heat loss rate from inside to outside, among other parameters like maybe season, gps, forecast, etc...

    To properly change the system mode from heat mode to cool mode, you might require a PID controller that measures the outdoor temperature? So if the temperature outside is rising fast (large dT/dt) but is less than the home setpoint, the controller would know to inject very little, if any, heat into the home. Similarly if the outside temperature is dropping fast, but is higher than the home setpoint, the controller would know to remove very little if any heat into the home.

    It seems odd to me that thermostats today still do not factor the outdoor temperature into the heating/cooling decision. The temperature differential between inside and outside is important - It determines how much Mother Nature is working towards your setpoint goal.

    Perhaps there is thermostat on the market that already does this? Or perhaps I am totally off track!

  5. #5
    Having had some more time to ponder this and see the improvements in the 7.0 software, I think I can now add some clarity to my cryptic posts above...

    the software let's you select the temp range by setting a min and max.

    I think I'd like a feature that let's you shift this range up and down based on the outdoor temperature.

  6. #6
    Senior Member
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    Our Honeywell VisionPro 8000 thermostats are capable of being set up to automatically transition between heating and cooling modes. They're also integrated with one of their wireless outdoor temperature sensors.

    The one thing missing is the ability to use rapidly dropping outside temps to cool the interior. During the Spring->Summer and Summer->Fall transitions we get hot days with much cooler nights. The system doesn't have a way to take advantage of that. Instead I just open a few windows and allow for some convection.

    As for single setpoint, I'm not sure that would be ideal. The temperatures for "comfort" differ based on outside conditions. It's perfectly reasonable to have interior temps of 76F when it's much hotter and/or humid outside. But it'd be stifling to have it 76F inside when it's much colder/dryer outside. So different setpoints for different modes come into play.

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  8. #7
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    Thanks friends for sharing nice information
    Last edited by calvan; 12-30-2015 at 08:44 AM. Reason: correction

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