In my last column, I began to review how the controller varies power to the heater. I'll conclude this series with power feedback, heat and cool cycle times, balancing heat and cool, and controlling cooling zones. Power Feedback. Suppose your zone is running at 25 percent power and the tem- perature is right on setpoint. Then, suppose line voltage falls some 20 percent. This results in a heater power drop of 36 percent because of the square law dependence of power on voltage. Sooner or later, the temperature falls.
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