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Old 08-06-2011, 10:43 AM   #16
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how does a modulating furnace modulate?


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Originally Posted by Jackofall1 View Post
Really that sounds like something from Star Trek or Back to the Future, I would have thought it would be Proportional, Intregral and Derivative (PID) controlling the functionality between the output, variable and setpoint.


Mark

PWM has been around for a long time.

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Old 08-06-2011, 10:58 AM   #17
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how does a modulating furnace modulate?


I always thought PWM'er (an inexpensive alternative to a VFD) was the device that would drive the ECM motor to variable speeds and the PID is what drives both the PWM'er and the voltage output to the gas valve, is this not the case in residential mod furnaces?

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Old 08-06-2011, 12:14 PM   #18
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how does a modulating furnace modulate?


VS blowers can be controlled by either PWM or by temperature.

PID can be used to control the PWM of a thermostat.

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