A temperature control system includes a heating, ventilation and air conditioning (HVAC) system configured to control temperature in an environment. A sensor is configured to generate an electrocardiogram (ECG) signal for an occupant of the environment. An environmental sensor is configured to sense environmental data selected from a group consisting of temperature, air velocity, sun load and humidity. A heart rate variability (HRV) controller is configured to receive the ECG signal; identify inter-beat intervals based on the ECG signal; and control the HVAC system based on the inter-beat intervals and the environmental data.