Chlorofluorocarbons (CFCs) and other ozone layer-depleting refrigerants are still in use in many HVAC systems, violating the 1987 Montreal Protocol and the 1997 Kyoto Protocol. Researchers in Iran have studied the potential for natural refrigerants as well as zeotropic and azeotropic refrigerants to replace CFCs, hydrochlorofluorocarbons and hydrofluorocarbons in geothermal heat pumps to reduce energy use and Schematic of a closed loop mode of the geothermal heat pump. Source: AIP Publishingoperating costs.

These heat pumps exploit the earth’s subsurface temperature in mid-50s degrees Fahrenheit by using a vapor compression cycle equipped with buried pipes in horizontal trenches or vertical boreholes. Geothermal heat pumps extract heat from the ground during winter and dissipate heat to the ground in summer by circulating fluid such as water through buried pipes. This design exploits the moderate temperatures in the ground to boost efficiency and reduce the operational costs of heating and cooling systems.

An hour analysis program was used to calculate the heating and cooling loads in a 14-story residential building. Results were fed to an engineering equation solver to model the thermodynamic cycle of an open and closed loop ground source heat pump with different known refrigerants.

Natural materials, including ammonia and n-butane, were identified as the most economical and environmentally friendly replacement refrigerants for geothermal heat pumps.

The research, conducted by scientists from Imam Khomeini International University and Islamic Azad University, is published in the Journal of Renewable and Sustainable Energy.