Low enthalpy geothermal energy : technology review

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Gazo, F.; Lind, L. 2010 Low enthalpy geothermal energy : technology review Lower Hutt, N.Z.: GNS Science. GNS Science report 2010/20 53 p.

Abstract: Low enthalpy geothermal energy including ground and groundwater as an energy source is available widely across New Zealand. This report identifies technologies for low enthalpy geothermal energy use and conversion. Technologies for the use and conversion include: Equipment to convert heat to electricity; Equipment to pump heat from a lower temperature environment to a higher temperature environment. This can provide heat or cooling for various residential, commercial, manufacturing and industrial uses; Direct heat use technologies. Technologies documented for converting heat to electricity include the binary (Organic Rankine) and Kalina cycles. The binary cycle uses a hydrocarbon or refrigerant working fluid. The Kalina cycle uses an ammonia water mixture as the working fluid. Organic Rankine cycle equipment is a mature technology. Kalina cycle equipment is an emerging technology which is gaining some market penetration. Ground source heat pumps are a mature technology that are well established in a number of nations. There are innovative hybrid systems using combinations of ground loops, cooling towers, thermal storage ponds and solar energy collection systems that are being developed. These heat pumps can provide heating and cooling for space conditioning and water heating. There are also a wide range of commercial technologies and experience in direct use applications. Equipment available includes downhole pumps, heat exchangers, convectors, refrigeration, water heating and space conditioning equipment. Having reviewed the technologies it is considered that equipment technology research is not anticipated to yield significant benefits in the New Zealand environment. Rather determining the economic and technical advantages on technology development in other nations and appropriate technology modification or adoption is considered appropriate for New Zealand, which may or may not include whole system or specific component manufacturing. Increasing use of low enthalpy geothermal resources will likely depend on increased public technology awareness and commercial availability of equipment which has an operational track record that can be utilised under New Zealand conditions. (auth)