This Small Business Innovation Research (SBIR) Phase I project will develop an earth heat exchanger that has a lower installation cost, lower operating cost, and smaller footprint than the currently available ground source heat pumps. High ground loop installation costs are the primary barrier to broader acceptance of ground source heat pump technology despite its efficiency advantage. By replacing the circulating liquid pipes with a "heat-pipe" arrangement which consists of a closed pipe containing a saturated working fluid which is cyclically evaporated and condensed at different locations within the heat-pipe, heat transfer efficiency between the earth and the heat pump refrigerant is increased. A heat-pipe heat exchanger would require no electricity in heating mode and only a very small amount of electricity in cooling mode. A novel working fluid which has a low vapor pressure, is non-toxic, inexpensive, and is not a potential ground water contaminant has been identified. Successful completion of this project will result in a heat-pipe exchanger that is more economical to install and operate. The broader/commercial impacts of this research are increased adoption of ground source heat pumps, the most efficient means of heating and cooling. The heat-pipe will have a lower internal thermal resistance and will use a larger pipe diameter than CLPS which will increase the contact surface area per unit length. This will allow less boring/trenching, will simplify installation, and will lower installation costs. A significant reduction in the cost and footprint of installations could increase adoption in both new building and retrofit applications. World demand for HVAC equipment will rise more than five percent per year through 2012, exceeding $70 billion. The US market is growing at 3.2% per year and exceeded $14B in 2009. The new technology will be licensed to heat pump manufacturers
