Mode Switching with Implicit Dual Set Points – Flair

Understanding Implicit Dual Set Points

When Mode is set to "Auto Heat/Cool", Flair will create two implicit set points: a heating set point and a cooling set point that are by default, 2F below and above the average home set point. The 2F is called the Heat Cool Mode Hysteresis.

• The heating set point is 2F below the average home set point
• The cooling set point is 2F above the average home set point

Note: You will not see heating or cooling set points in Flair. They are implicit.

In this example, for an average home set point of 72F, the implicit dual set points are 2F above and below the set point. Flair will switch when the average home temperature is 3F above or below the cooling or heating set point.

Rooms Set Points

Each room with a hold will get its own implicit dual set points. By default, these are 2F above and below the set point that is displayed in a room.

Note: these are not heating and cooling set points, but instead used as the current set point of the room for Smart Vent operation.

In this example, Janie's Bedroom has a hold of 71F and the Hallway has a hold of 72F. Flair will create implicit dual set points for each room as follows:

Janie's Bedroom

• 69F: used when the system is heating
• 73F: used when the system is cooling

Hallway

• 70F: used when the system is heating
• 74F: used when the system is cooling

Rooms without holds will use implicit dual set points based on your default home set point shown at the top of the Flair app. Flair creates dual implicit set points around the default home set point and rooms will use these values.

Vent Operation

Like all thermostatic systems, Flair uses an operating range (or hysteresis band) for knowing when to open and close Smart Vents. By default this is 1F around the set point. We call this the Vent and Thermostat Hysteresis. For a set point of 72F, the operating range is 71F to 73F.

The 1F Vent and Thermostat Hysteresis is also applied when using implicit dual set points.

This example shows how Vents operate for an average home set point of 72F where implicit dual set points are 70F and 74F.

Note: While Vent and Thermostat Hysteresis is not used for mini split set point handling per se, it is used in the calculation for mode switching.

Mode Switching

Flair uses the sum of the Vent and Thermostat Hysteresis (default 1F) and the Heat Cool Mode Hysteresis (default 2F) as the mode switching value. By default, the mode switching value is 3F (1F + 2F). Professionally, this is called the auto changeover differential.

Mode switching occurs when the average home temperature of Active rooms moves 3F above or below the average home set point (of Active rooms).

If the home is heating, when the room temperature rises 1F above the cooling set point, Flair will switch to cooling. If the home is cooling, when the room temperature drops 1F below the heating set point, Flair will switch to heating.

This example shows when switching occurs based on a 72F average home set point.

Note: Heating and cooling set points will adjust when the default home set point is changed. For rooms with holds, Flair will switch modes based on a consensus of how far each room is from its individual heating and cooling set point.

Auto Heat/Cool Example

The graph below represents a home's temperature over two hours. The example is for a home where the temperatures fluctuating from morning to night. The blue areas represent when the system is in cool mode and the orange area represents when the system is in heat mode. The home begins in cool mode, switches to heat mode, and then switches back to cool mode again. Let's see why.

• The average home set point is 72F.
• Flair calculates a heating set point of 70F and a cooling set point of 74F (2F around the average home set point).
• The mode switching temperatures are 69F and 75F (3F around the average home set point).

The timeline starts with the system in cool mode (blue). As the home temperature dips more than 1F below the heating set point, the system switches to heat mode (orange). Next, the home temperature begins to rise, and once it rises more than 1F above the cooling set point, the the system switches to cool mode (blue).

If the home temperature continues to drop below 69F again, the system will switch to heat mode.

What Values are Adjustable?

These values are used for calculating modes switching:

• Heat Cool Mode Hysteresis: the default value is 2F. This determines how Flair calculates the heat to and cool to set points. Closer heating and cooling set points will maintain tighter temperature control and use more energy. Set points further apart will result in a wider temperature range and use less energy.
• Vent and Thermostat Hysteresis: the default value is 1F. This determines the operating range around a set point for when Smart Vents open and close. A tighter range will maintain tighter temperature control and Smart Vents will open and close more often (this could increase battery usage). A wider range will allow a wider temperature range and Smart Vents will open and close less often.