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Geothermal Energy Systems Engineering

28 December 2023

Geothermal resources have a wide range of temperature, pressure, potential brine or steam flow rate, and dissolved mineral composition. The UC projects focus on modelling, design, and economical analysis of practical Organic Rankine Cycle (ORC) power plants. Learn more about UC's Geothermal Energy group.


Geothermal resources have a wide range of temperature, pressure, potential brine or steam flow rate and dissolved mineral composition.

High temperature resources with high pressure and ample water flow can be used for power plants in the hundreds of megawatts range. These resources require geologic investigation, drilling, often in the range of 2000m, and reservoir engineering.

But, at the end of the well is the power plant, and there is a lot of research yet to do to economically and technically develop lower temperature resources.

The UC projects focus on modelling, design and economic analysis of practical Organic Rankine Cycle (ORC) power plants.

Large ORCs over several MW are currently used in geothermal power generation. These systems are designed for the specific brine conditions and a standard heat rejection temperature.

Our research focuses on the modelling of the ORCs for smaller, low temperature systems.

We need to prospect lower energy resources with knowledge of the new types of ORC that could use them.

We need to understand the off-design performance of existing plants to make design and operational strategy adaptations as the resource characteristics change over time (as they do). 

We need to understand the different types of expanders that can be used in small ORCs to model turbines, design, manufacture and test them.

We need to provide educational opportunities for Mechanical Engineers to upskill in thermal systems engineering through post-graduate study so they can contribute to the anticipated rapid development of geothermal energy around the Asia-Pacific region.

  • Sid Becker
    Heat Transfer and Heat Exchanger Performance
  • Susan Krumdieck
    Platform Development, Energy Systems, Energy Economics and Policy
  • Mark Jermy
    Fluid Dynamics, Scaling Experimental 
  • Mathieu Sellier
    Computational Methods, Scaling Mechanisms

External partners

  • Dr. H.C. Jung
    Curtin University, System Modelling, Component Modelling, Turbine Design
  • Dr. Nick Baines
    Concepts NREC, Turbine and Turbomachinery 
  • Hezy Ram
    Ram Power, Geothermal Project Development

Research and Development

Geothermal power generation at a large scale has undergone steady development for many decades, largely through R&D by the world leader, Ormat Technologies Inc, USA.

High temperature, high volume hydrothermal resources can be flashed to drive conventional steam turbines.

Brine and condensate from the steam turbines are the heat source for Organic Rankine Cycle (ORC) power plants using multi-stage axial turbines. ORCs can be built to fit binary or bottoming applications from 5 to 25 MW.

The first stage of development is 'prospecting' for the potential power generation capacity of a given resource. This involves modelling the thermodynamics, heat transfer, and energy conversion of the plant and the components.

Development Process for Low Temperature and Small Scale ORC Power Plants

Exploration and reservoir engineering provide the data used for thermodynamic cycle design which provides a concept of the size and type of plant that could be developed for a given resource.

If the concept is viable, then the pre-feasibility and feasibility analysis must be carried out by engineers with specialist capabilities in thermal systems engineering.

The feasibility study provides estimates of the economic return, and selection of working fluid and component equipment, particularly the expander.

If a feasible design can be found with an expander available for the working fluid and plant conditions, then a detailed design and simulation of the performance of the final plant can be carried out.

Finally, if the decision is made to invest in the manufacture of the components and purchase or manufacture of the turbine, the engineering for delivery of the project, commissioning and sign-off will be carried out.

Significant research contributions can be made in the area of low-temperature resources where the generation potential is under 1 MW.

The research approach emphasises flexibility and lean design with economic evaluation and streamlined thermo-economic modelling at each development stage described in the basic structure shown below.

It is essential that realistic engineering analysis be carried out at each stage from inception and resource evaluation to manufacture, construction and commissioning.

One very important lesson learned so far is that ORC plant engineering must be carried out by expert engineers with a high level of thermal systems engineering knowledge and experience in modelling and simulation at all levels.

There is no one simple tool that can be used by non-engineers to design an ORC power plant.

Critical Role of the Expander in Development Potential

The thermodynamic potential of a heat resource is characterized by the temperature and mass flow rate and enthalpy, plus the allowed minimum temperature if applicable. A thermodynamic cycle analysis characterises the potential for power generation.

The potential end use for energy is characterised by the power developed, the shaft speed, torque and conversion efficiency. The only way that it is possible to match up the potential heat resource with the possible end use is through an expander.

The figure below illustrates how the expander characteristics must be selected to perfectly match the pressure ratio, mass flow rate, shaft speed and work developed in the thermodynamic cycle. 

Turbine Development Research

The turbine is the essential energy conversion component of an ORC. There are currently very few turbines available worldwide for ORC applications.

The team is investigating the possibility of designing, developing and manufacturing ORC turbines. 

The University of Canterbury Erskine Fellowship was awarded to Dr. Nick Baines of Concepts NREC in 2014.

Dr Baines taught a final-year elective course on turbomachinery. He also worked with the team to help them understand the long development process for any kind of turbomachinery.

The first step is to model the turbine in a basic way to select the size and type for a specific thermodynamic cycle. The next step is to use CFD and FEA modelling to develop a blade geometry and nozzle geometry that will work for the specific working fluid at the thermodynamic inlet and outlet conditions, shaft speed and flow rate for the application.

The figure below shows a CFD model of a 100 kW Sunstrand Gas Turbine operated with R134a refrigerant as modelled by Choon-Seng Wong.

The next step is to manufacture the turbine and test it in a compressed air test bench to get empirical data about the performance, the losses, and the rotor dynamics.

After this step the process is repeated and the design refined.

Finally, after several iterations, the turbine balance of the plant is developed and the turbine must be tested in the ORC cycle with the particular refrigerant and flow rate.

The team has built a compressed air test bench and is working on manufacturing the first ORC turbine in the 5-10 kW range.

Heat Exchangers

Heat exchangers are well-known devices, however, the experience with them as boilers for organic fluids is limited.

The heat exchanger research at UC focuses on modelling and design for boiling and condensing of refrigerants and 'lean design' of heat exchangers that is not oversizing.

In addition, the relationship between heat exchanger design and ORC operation conditions and overall ORC performance is being investigated.

Selection of the ORC working fluid, as with the thermodynamic cycle and the expander and pump also has a major influence on the size and cost of the heat exchangers.

The group use Engineering Equation Solver (EES), ASPEN Tech, FLUENT, COMSOL and other programmes to model ORC components. 

Geothermal and Waste Heat Development Opportunities

Industrial research is aimed at understanding the opportunities for developing waste heat and geothermal.

The investment opportunity assessment process shown below describes the four different types of waste heat projects that could be pursued.

All types of projects require specialist engineering modelling and design as well as project management and commissioning. The lowest risk project would involve selection, importing and installing of an appropriate turn-key system that has already been developed for the exact heat resource and cooling situation.

An off-the-shelf ORC would be the right size and work between the same temperatures as the resource, but the waste heat development engineers would need to design, manufacture and install heat extraction equipment and a cooling tower or air-cooled heat exchanger.

If an expander-generator were available commercially for the exact working fluid, pressure etc. for the resource, then the balance of the plant could be designed and built to use that expander.

Many heat resources and end-uses are still in the category that requires a custom build, including a turbine designed specifically for the conditions in the thermal cycle developed for the resource. In all but the turn-key situation, the ORC cycle and heat exchangers must be designed.

One aspect of the team research is to investigate both the thermodynamic efficiency and the cost efficiency as a function of design and operation variables.

Research Projects

  • Experimental ORC power plant to study dynamic thermal system performance with different refrigerants, test different expanders and develop design knowledge.
  • Design relations experimentally developed for different refrigerants and zeotropic mixtures.
  • 100 kW pilot plant thermal system and detail design.
  • 10-100 kW radial turbine design for R245fa.
  • Compressed air radial turbine test platform.
  • Dynamic modelling for control system design and simulation.
  • Plant and component modelling for a thermo-economic feasibility study.
  • Development standard for ORC technology.
  • Economic and energy return on investment in ORC technology.

  • Budisulistyo, D., S. Krumdieck, Thermodynamic and economic analysis for the pre- feasibility study of a binary geothermal power plant, Energy Conversion and Management, (2015).
  • Gunby, N.R., S. Krumdieck, H. Murthy, S. L. Masters, S. S. Miya, Study of precursor chemistry and solvent systems in pp-MOCVD processing with alumina case study, Physica Status Solidi a, 1Vol 212, No. 7 (2015), 1519-1526, DOI 10.1002/pssa.201532309.
  • Jung, H-C, S. Krumdieck, An experimental and modelling study of a 1 kW organic Rankine cycle unit with mixture working fluid, Energy, 81 (2015)  601-614. 
  • Jung, H-C, Krumdieck, S., Rotordynamic modelling and analysis of a radial inflow turbine rotor-bearing system, International Journal of Precision Engineering and Manufacturing, Vol. 15 No. 11. (2014) 2285-2290. 
  • Jung, H-C, S. Krumdieck, T. Vranjes, Feasibility assessment of refinery waste heat-to-power conversion using an organic Rankine cycle, Energy Conversion and Management, 77 (2014) 396-407.
  • Jung, H-C, S. Krumdieck, Modelling of organic Rankine cycle system and heat exchanger components, International Journal of Sustainable Energy, (2013).  
  • Sohel, M.I., M. Sellier, L. Brackney, S. Krumdieck, An iterative method for modelling the air-cooled organic Rankine cycle geothermal power plant, International Journal of Energy Research, Vol. 35 Issue 5 (2011) 436-448.
  • Sohel, M. Imroz, Mathieu Sellier, Larry J. Brackney, Susan Krumdieck, Efficiency improvement for geothermal power generation to meet summer peak demand, Energy Policy, Vol 37,9 (2009) 3370-3376.
  • Masuri, S.U., M. Sellier, Effects of Physicochemical parameters on colloidal potentials, Applied Mechanics and Materials, 564, (2014) 222-227.
  • Lee, D., S. Krumdieck, S. Davies, Scale-up design for industrial development of a pp-MOCVD coating system, Surface & Coatings Technology, 230 (2013) 39-45.
  • Krumdieck, S., S. Davies, C.M. Bishop, T. Kemmitt, J.V. Kennedy, Surface & Coatings Technology, 230 (2013) 208-212.

Conference Papers (peer-reviewed)

Education: Special Topics Courses

Energy Systems Engineering (ENME405) 

A wide-ranging coverage of sustainability issues, demand side management, energy auditing, fossil and nuclear transition, renewable energy technologies, policy and society.

Geothermal Energy Technology (ENME481)

Special topics course covering:

  • natural research
  • resource engineering
  • economics and development issues
  • scale deposition
  • toxic mineral issues
  • ee-injection, thermodynamics
  • heat exchangers
  • thermal system modelling
  • working fluids
  • turbomachinery
  • and lots of case studies.

Turbomachinery (ENGR408)

  • Physics and design fundamentals and modelling for pumps, compressors, and turbines.
  • Hydroturbines, radial inflow and axial turbines. 
  • Aerodynamics, losses, testing, vibrations, stability and system design and control.

Geothermal Development (ENME605)

  • Resource consenting.
  • Drilling and exploration.
  • Investing and environmental compliance.
  • Community and cultural negotiations.
  • Technology.
  • System design.
  • Issues of working fluids.
  • Thermal system modelling.
  • Reservoir management and plant control.
  • Government policy.
  • Economics.
  • Contracting.
  • Engineering.
  • Commercial supplies and construction.
  • Power grid integration.
  • Safety and natural hazards.

Green Energy Team (2014)

Christina Crowley, Dareth Ny, Theo Wordsworth, Fraser McConnel.
The team worked on behalf of potential ORC power developers and investors. They worked with the postgraduate talent on various aspects.

They completed a prospecting investigation of ORC conversion for the waste heat from diesel generators.

Dareth modelled the thermal cycle, investigated selection of working fluid, selection of turbine and pump, and design of heat exchangers.

Christina carried out an industry review of available technologies including getting quotes.

Theo developed an investment analysis approach and Fraser worked on the marketing and customer interface.

ORC B Team: (2013)

Nathan Marks, Muhamad Ghazali, Michael bush, Christopher Mills.
Final Year Project: Gas Turbine Bottoming Cycle
The student team was sponsored by the AGGAT programme and mentored by Ben Friskney of Page Macrae.

The mission was to design and build an ORC power plant that would run as a bottoming cycle on the exhaust heat from a Capstone Gas Turbine.

The gas turbine burns diesel fuel and can generate up to 35 kW of electricity. The bottoming cycle ORC generates up to 1kW.

Team Turbo: (2013)

Amerul Abd Kadir, Darren Burrows, Morgan Boyd, Rebecca Gray, Robbie McIvor.
Turbine Testing Unit.
The students completed two objectives feasibility study for the design of an ORC system that could be used for expanders up to 100kW.

This turbine test bed was required to be built with currently available equipment in New Zealand.

The test bed would provide for an R&D facility in New Zealand at scale.

The team also developed a database of available ORC components from New Zealand suppliers, and with the cost, footprint and performance of the components, built a Prospecting Advisor Model in Matlab that can give a preliminary estimate to evaluate potential resources.

Green Energy Team: (2012)

David Meyer, Eugene Robson, Chris Horn, Aidan Davey
Final Year Project: Design and Build an 1-5 kW ORC

The final-year student team is sponsored by Page Macrae Engineering. Their mission is to design and build a working ORC in the Mechanical Engineering Department Thermo lab.

The ORC will use the exhaust heat from the department’s new Capstone Gas Turbine.

Resource Prospecting Team: (2012)

Max Watters, Alex Finch, Keziah George, Ben Tomlin
Final Year Project: Thermal Resource Assessment Tool

The final year Mechanical Engineering student team is sponsored by AGGAT. Their mission is to develop the thermodynamic energy mapping tool that can be used to characterise the development potential of low-temperature geothermal and waste heat resources. The analysis includes modelling of the suitable extraction heat exchangers including fouling and scaling factors.

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