Chilled water is provided by either a ground source or air source heat pump. A surface cooling system requires water at a higher temperature than that needed by an air conditioning system. This increases the efficiency of the air source heat pump.

Where ground loops are installed the benefits are even greater. During the summer the ground temperature would be around 15°C at a depth of 2 metres. When coupled with a ground source heat exchanger this chilled water can be used directly in the surface cooling system, making it almost free to run, with the benefit of recharging the ground, storing energy until needed by the heat pump.