Air-conditioning controllers should have a much smaller hunting range
than that. Cooling systems are not common in the UK, but even bi-metal
thermostats, for heating systems, had a built in heating element, so the
thermostat would switch off much faster than would be the case it you
had to wait for the air in the room and the hysteresis of the switch.
Substituting on for off, that should work for cooling as well.
Whilst this produces a de facto pulse width modulation, electronic
controllers explicitly pulse width modulate based on the analogue value
of the process variable, when it is close to the set point. Mine has a
default pulse frequency of 1.6666... mHz, although it is adjustable
between about 0.8333 mHz and 3.3333 mHz, in 0.8333 mHz steps. The
hunting range is really too small to resolve on an alcohol analogue
thermometer.
--
David Woolley
Owner K2 06123
On 02/09/14 18:34, Don Wilhelm wrote:
If performed in an air conditioned space, consider the hysteresis in the
thermostat controlling the AC (if the thermostat is set for 72 degF, it
may come on when the room temperature reaches 74 degF and turn off when
the room temperature drops to 70 degF - it all depends on the
characteristics of the thermostat).
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