HRU (Heat Recovery Unit) is a type of HVAC system that is used to recover heat from the exhaust air and transfer it to the fresh air intake. This helps to reduce the energy consumption of the system and improve the overall efficiency. AHU (Air Handling Unit) is a type of HVAC system that is used to condition the air in a space. It is responsible for controlling the temperature, humidity, and air quality of the space. It also filters the air and distributes it to the space. AHU is typically used in larger spaces such as commercial buildings, while HRU is typically used in smaller spaces such as residential homes.