 The refrigerant flows through insulated pipes between the evaporator and the condenser, allowing for efficient thermal energy transfer at relatively long distances.The simpler heat pumps tap the atmosphere as heat source; for better performance and greater energy flow, ground water or geothermal energy will be tapped, but this requires more expensive installation.The heat can be released directly into the air (this is simpler and cheaper), or through the water plumbing of central heating or to provide domestic hot water.