The aim of this thesis is to develop a feasible, geo-solar heat pump in attempt to decrease the large loads put on Australia's power industry for cooling (and heating).
The following report analyses the potential benefits and presents a feasibility study of geo-solar heat pumps for Australia. A geo-solar system is one that utilises the sun's energy, and the earth's underground thermal properties to produce an economical and environmentally friendly cooling system. This thesis aims to combine concepts behind geothermal heat pumps and heat-driven chillers to develop a geo-solar heat pump suitable for use in an Australian climate.
For larger, commercial sized heat pump systems, it is proposed to combine solar absorption and ground sourced (or geothermal) air conditioning technology. The system rejects heat generated in the absorption chiller via geothermal ground loops rather than using a less efficient cooling tower.
Absorption chillers have typically low COPs of around 0.7. Geothermal ground loops offer significant advantages in terms of performance. By applying a general thermodynamic model of the system, it was calculated that the COP can be improved by 60%. These improvements are very significant. For a geo-solar absorption system operating during the day only, it is not yet a more feasible option compared to a solar absorption system due to the high cost of the geothermal ground loops. In order for the geo-solar absorption system to be feasible, the ground loop costs need to become cheaper or the system needs use the ground loops to provide over-night cooling.
Ground loop design is very site dependent. For example, if a particular project is situated close to a deep lake, it can use the lake to act as a heat sink for the ground loops. This would lower the cost significantly due to the absence of drilling costs thus making the geo-solar system more viable. Furthermore, overtime the market for ground sourced heat pumps is increasing allowing the cost of the ground loops to become more competitive. The future market for the ground loop technology will become larger which will encourage mass production and more competitive prices. However, while ground loop and drilling costs remain high, it is still possible for a geo-solar absorption system to be feasible. Theoretically, it was found that a geo-solar absorption system with capacity greater than 35kW is feasible if used over-night as well as during the day. If such demand exists, the originally proposed system can be modified for night use by using the ground loops assisted by thermal storage. For the 105kW system, the payback time for this system was determined to be 4.9 years, which is a very feasible result. This justifies the use of the ground loops whilst improving payback time by 1.6 years compared to the equivalent solar absorption system.
In order to validate the results and conclusions of this thesis, it is recommended that the performance improvements to the chiller be confirmed by measuring the COP increase of an existing solar absorption system when using lowered cooling water temperatures.
It is also recommended that simulations and experiments be conducted to confirm the theoretical night-time performance of the geo-solar absorption system proposed.