Smart Thermostats enhance home automation systems by enhancing comfort and providing additional convienece or functionality. A smart home theromstat can save money on heating and cooling costs by creating custom schedules and allowing the user to adjust the heat or air conditioning when they're away or on the way back to the home, cottage or office. In some cases this can happen automatically.
WiFi Smart Thermostats can work on their own using only your WiFi network and Internet connection for cloud connected alerts, programming or control.
ZWave or Zigbee Smart Thermostats are designed to work with an appropriate smart home hub. The hub then becomes the orchestrator of the system, allowing remote control, schedule programming and alerts. A smart hub can also tie HVAC events to other scenes or triggers. For example you may wish to turn off the system FAN in case of a fire so smoke doesn't blow around the house. At the same time you may turn on all the automated house lights.