Smart t stat with a a mod con

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scatgo
scatgo Posts: 98
in Thermostats and Controls

AI suggest its a bad idea. Claims the algorithm in a smart t stat will jam up the logic the mod con runs on like a 10 2 1 turn down ratio and outdoor sensor. Is t stat smart and AI dumb?

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  • Jamie Hall
    Jamie Hall Posts: 27,904

    Pretty much. The whole idea of the mod/con with outdoor reset is to modulate — hence mod — the boiler's output temperature so that it and the heating system is always running at just the right temperature and power to match the building heat loss demand. Ideally neither the boiler nor the circulation ever turns off.

    The whole idea of a mart thermostat is to ramp the building temperature up and down depending on who or what is using each space. That means, when the smart thermostat decides the space needs more heat, the boiler must put out enough more power to raise the temperature — overriding the control for optimum power output.

    The result may or may not show up as a measurable difference in energy use — most likely not — but neither gadget is working at its best.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    EdTheHeaterMan
  • EdTheHeaterMan
    EdTheHeaterMan Posts: 12,851

    There may be some credence to that statement.

    A smart thermostat keeps a log of its runtime (the time the thermostat is calling for heat) and makes adjustments based on that runtime.

    When a smart thermostat is connected to a standard on/off boiler or furnace control, the time it takes to satisfy the thermostat when the outdoor temperature is in the 50°F range is relatively short, since the full input of the burner heats the space in short order. The thermostat can obtain outdoor temperature information from the internet through its Wi-Fi connection.

    When the outdoor temperature drops, the call-for-heat cycle becomes longer, with longer on-times and shorter off-times.

    When you connect a smart thermostat to a modulating-input boiler, the amount of fuel supplied to the boiler or furnace changes based on the outdoor temperature. The smart thermostat has no way of knowing that the burner input is changing. As a result, the algorithm it uses to determine how to operate may no longer make sense, and the thermostat can behave in a way that is inconsistent with energy-efficient operation.

    Many smart thermostats have a way to disable the “learning” function, preventing the thermostat from making decisions based on the operating characteristics of an on/off burner when it is connected to a modulating burner.

    Think of it like two people trying to pass each other in a narrow hallway. One moves to the left while the other moves to the right. They end up blocking each other, so they immediately switch positions, only to find that they have blocked each other again. This continues until one person places their hands on the other’s shoulders and directs them to one side while moving to the other side themselves. Finally, they are able to pass each other and continue on their way.

    Having the heater and the thermostat both equipped with algorithms that save energy may be counterproductive if the two smart devices don't know how to communicate with each other. Eventually one of the smart devices will place the hands on the shoulder of the other device and move it out of the way so the system can continue on operating.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

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