The EcoCute is an energy efficient electric heat pump, water heating and supply system that uses heat extracted from the air to heat water for domestic, industrial and commercial use. Instead of the more conventional ammonia or haloalkane gases, EcoCute uses supercritical carbon dioxide as a refrigerant. The technology offers a means of energy conservation and reduces the emission of greenhouse gas.

The name of the EcoCute comes from the Japanese phrase, which literally means “natural refrigerant heat pump water heater”. Eco is a contraction of either ecology or economics. literally “supply hot water.”

Modern chemical refrigeration techniques developed after the proposal of the Carnot cycle in 1824. Jacob Perkins invented an ice-making machine that was used in 1843, and built a refrigerator that used water and sulfuric acid in 1850. In Japan, Fusanosuke Kuhara, founder of Hitachi, Ltd., made for air conditioning and its use as a refrigerant. In 1930 Thomas Midgley, Jr. discovered dichlorodifluoromethane, a chlorinated fluorocarbon (CFC) known as freon. CFCs, which has been successfully replaced with traditional refrigerant substances, including CO 2, for use in heat pumps and refrigerators. But from the 1980s CFCs began to lose weight when their damaging effects were detected. Two alternative types of refrigerant, hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs), also lost favor when they were identified as greenhouse gases (additionally, HCFCs were found to be more damaging to ozone layer than originally thought). The Vienna Convention for the Protection of the Ozone Layer, the Montreal Protocol and the Kyoto Protocol for the complete abandonment of such refrigerants by 2030. In 1989, the international concern about the effects of chlorofluorocarbons and hydrochlorofluorocarbons on the ozone layer, scientist Gustav Lorentzen and SINTEF patented a method for using CO 2 as a refrigerant in heating and cooling. Further research into CO 2 refrigeration was conducted at Shecco (Sustainable Heating and Cooling with CO 2) in Brussels, Belgium, leading to increasing the use of CO 2 refrigerant technology in Europe. In 1993 the Japanese company Denso, in collaboration with Gustav Lorentzen, developed an automobile air conditioner using CO 2 as a refrigerant. They demonstrated the invention at the June 1998 International Institute of Refrigeration / Gustav Lorentzen Conference. After the conference, CRIEPI (Central Research Institute of Electric Power Industry) and TEPCO (The Tokyo Electric Power Company) approached Denso about developing a prototype air conditioner using natural refrigerant materials instead of freon. Together they produced 30 prototype EcoCute units for a year-long experimental installation at locations throughout Japan, from the cold climate of Hokkaido to Okinawa hotter. After this successful feasibility study, Denso obtained a patent to compress CO 2 refrigerant for use in a heat pump from SINTEF in September 2000.

In Japan in 1998, water heating () accounted for 33.8% of typical domestic energy consumption, with air conditioning and heating energy accounting for another 26.9% and 2.3%. Most of the remaining 37% was spent on electrical appliances, a field where 21st century innovations in energy conservation. This is the most difficult area for energy conservation, leaving a gap in the market for the EcoCute. By January 2005, 26 Japanese companies were producing more than 450 models of EcoCute machines, and sales of domestic units increased 130-150% each year between 2001 and 2005. Denso first introduced the EcoCute outside Japan at the COP9 Milan, Italy on December 9 , 2003. From 2007, Denso began concentrating on marketing the EcoCute in the EU.

An EcoCute machine or system consists of a heat pump and hot water storage unit. The components are serially concatenated with sealing refrigerant CO 2 gas in circulation. Not including upstream losses of input energy source, the EcoCute’s COP is 3.8 in industrial use, while electric power water heating is 1.0, and gas boiler is 0.88 including pilot light loss.

is a registered trademark (No. 4575216 – Japan) of Kansai Electric Power Company.