What is "Thermostat hysteresis degrees"

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1

In the setup for a Virtual Thermostat used for zoned HVAC with Keen vents, there is a preference item for "Thermostat hysteresis degrees".
What exactly does this setting do or affect in the operation of the Virtual Thermostat?

2

It offsets the setpoint for when cooling/heating is turned on.
So if you want to heat your room, the thermostat would turn on heating when the temperature got below setpoint-hysteresis. It would not turn off until the temperature went above setpoint+hysteresis.

3

I forgot today cooling would be the opposite.

4

So for vents, this would narrow the temperature range during which the vents would be open if the hysteresis degrees were reduced. Thanks.

5

If you are using KeenectLite, no. It only uses the Hot and Cold setpoints on the virtual thermostat as desired temperature targets.
Then it figures out a proportion to be open using a formula: multiplier*(SetpointTemperature-ActualTemperature)+offset
I have been debating whether I make it so you can set different multipliers/offsets for different levels of need (Aggressive/normal/slow) Example would be that aggressive would have the vent more open when closer to the setpoint.
The other control question I have been debating is right now the vent goes to minimum if the temperature delta is less than zero. I am considering that it wouldn't go to the minimum until after it hits the setpoint (similar to the hysteresis idea)
Craig

6

In general hysteresis is the amount of offset between one direction and the other. "Probably useless information."

For a thermostat it is the amount the temperature must change to reverse direction.

example:
Assumptions:

  • Hysteresis = 2
  • Heating mode.
  • Temperature setting is 73

Actual temperature is 68 degrees....... heat is on ....... as the heat rises the thermostat is waiting for the temperature to reach 74 degrees (73 + 1/2 hysteresis).
The temperature reaches 74 degrees the heat goes off.

The room starts to cool......the heat is still off....... the thermostat is waiting for 72 degrees (73 - 1/2 hysteresis).
The temperature reaches 72 degrees.... the heat goes on.

So on rising temp the heat goes off at 74 degrees
On cooling the heat goes on at 72 degrees.

The difference is 74 - 72 = 2 = the hysteresis.

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7

My registers are in the ceiling pointed down, so I'd really appreciate an aggressive setting in KL, in order to blow hot air down vigorously as long as possible for best mixing with the room air.