Trane's Ascend air-to-water heat pump model ACX combines chiller and heat pump technology to both heat and cool a building using electricity. In cooling mode, the model ACX moves heat from inside the building to the outside. In heating mode, a reversing valve changes the flow of energy to bring heat from outside of the building to the inside. The heat pump moves heat using a compressor, rather than simply generating heat. This technique can make heat pumps up to three times more energy-efficient than other forms of electric heating. As a result of its boiler-free heating, the model ACX achieves high energy efficiency for cooling and heating. The unit's heating efficiency exceeds ASHRAE standard 90.1-2019: 2.77 COP for heating and a cooling requirement of 9.215 EER.