HVAC stands for Heating, Ventilation, and Air Conditioning. HVAC systems are used in buildings to control the temperature, humidity, and air quality. These systems work to maintain a comfortable indoor environment for occupants by providing heating or cooling as needed. HVAC systems may also include air purifiers, humidifiers, and dehumidifiers to control indoor air quality. There are several types of HVAC systems, including central air conditioning systems, heat pumps, furnaces, and packaged systems. These systems can be powered by different energy sources such as electricity, natural gas, propane, or oil.