HVAC Device: Economizer

The General Idea

The Wikipedia article on economizers is a good starting point.

Why Enthalpy Economizers Don't Work explains the role of humidity (though the title is a bit misleading). If that link doesn't work, try this.

HCC Implementation

Terms and Definitions

Economizer

An economizer is a device that will prevent the main HVAC device from switching on, and instead, turn itself on when conditions allow. Alternatively, it may work alongside the HVAC device to improve operational efficiency.

Changeover Delta

A changeover delta is the difference between indoor and ambient temperature which causes the economizer to turn on when the indoor or ambient temperature changes in the direction the economizer is configured to operate.

Target Temperature

A target temperature is the temperature which, when it is reached, causes the economizer to turn off.

Operation

The Economizer is connected to a Zone. Assuming the mode is set to cooling:

• When the ambient temperature is above the zone temperature less changeover delta , the Economizer can't operate and normal HVAC operation is in effect.
• When the ambient temperature drops more than changeover delta below the indoor temperature, the HVAC shuts off (if so configured) and the Economizer turns on.
• When the zone temperature reaches the target temperature, the Economizer turns off.
• Zone setpoint plays no role in economizer operation.

Example (Cooling Mode)

• Setpoint 27°C, changeover delta 1°C, target temperature 22°C.
• Ambient 30°C, zone temperature 29°C: HVAC takes care of cooling.
• Ambient 28°C, zone temperature 29°C: economizer shuts off the HVAC and starts taking care of cooling.
• Ambient 22°C: economizer shuts off.

Configuration

Please see home-climate-control.zones.${id}.economizer for the actual configuration.