Air-conditioning is a subject that is now more frequently addressed due to both better comfort in an increasing number of countries and the effects of global warming. Now, even countries where demand for air-conditioning during summer months was limited, due to a cooler climate, require the operation of an air-conditioning plant for longer periods. The demand of heating is nevertheless significant and the most efficient system to provide heating is undoubtedly the heat pump. No other technology can provide net primary energy savings, economic benefits to users and reduced climate impact at the same time.