This. HVAC controls most work as a team, otherwise they end up fighting each other. As a simple example, picture an office building in which each room has a t

This. HVAC controls most work as a team, otherwise they end up fighting each other. As a simple example, picture an office building in which each room has a temperature sensor and air supply. If a room says "Oh, it's hot here!" The system will try to send cooler air. Now, imagine that in one of those rooms, there's a little lady who's a little cold. The system however, is in cooling mode, because the room is slightly warmer than the temperature setpoint. The lady won't have it a decides to bring an electric heater. Now she is heating her room and feels more comfortable. From the point of view of the system, her room is much warmer than it should be. As a consequence, the system sends even more cooler air to her room. The lady now has to crank up her electric heater to counteract this increase in cooler air...