There are two main types of heat pump chillers available: air-to-water and water-to-water. Both types of heat pump chillers are capable of serving as part of an HVAC system, process equipment, or other applications. The main difference is how each transfers heat.
In an air-to-water heat pump chiller, air is used as the heat source. In heating mode, heat is absorbed from the ambient air and transferred to the water loop via refrigerant. In cooling mode, heat from the water loop is rejected into the refrigerant and then dissipated into the ambient air.
In a water-to-water heat pump chiller, water is used as the heat sync. The refrigerant in the system absorbs heat from the cooled space or process and transports it to the condenser, where it is transferred to a loop of water that is circulated through the system.