A Question About Thermostats

[From Bruce Gregory (980913.1750 EDT)]

In my house, the thermostat is set to 65 F. During the summer, the
temperature in the house never drops below 70 F. Is the thermostat
controlling the temperature?

Bruce Gregory

[From Bill Powers (980913.2056 MDT)]

Bruce Gregory (980913.1750 EDT)--

In my house, the thermostat is set to 65 F. During the summer, the
temperature in the house never drops below 70 F. Is the thermostat
controlling the temperature?

Yes.

This is what is known as a one-way control system. It is organized to
maintain the condition "perception not less than reference signal." It is
irrelevant whether any effort happens to be necessary to maintain the
controlled condition. Even in the winter, the furnace can spend half of its
time off. What matters is that a control system physically exists, that it
is in the correct relationship to its environment, and that it is turned on.

Best,

Bill P.

Best,

Bill P.

Whether or not the thremostat is controlling the temp depends on whether it has
the capability to turn on the Air conditioner.

If it only controls the Heater it can't reduce the temp below the heat load
that the house builds up during the summer days. It prevents the heater from
adding any additional energy to the house, but it cant take any away.

In this case it does NOT function as a control device.
Dave

Primum Non Nocere
            Hippocrates

[From Bill Powers (980913.0403 MDT)]

Dave (no last name or time-date stamp) --

Whether or not the thremostat is controlling the temp depends on whether

it >has the capability to turn on the Air conditioner.

This depends on your definition of what it _should_ be controlling. If you
designed the system without any air conditioner, then presumably what it
should be controlling is T >= Tref. When the reference temperature is 65
and the actual temperature is 75, the controlled variable is at its
reference level, because 75 IS greater than or equal to 65. The reference
condition is satisfied.

If you designed the system to maintain the reference condition T = Tref,
then clearly your design is incorrect if you left out the air conditioner.

Best,

Bill P.