Ground Source Geothermal Heat Pumps:
Significant Pilbara Energy Reductions and Environmental Benefits
Dr Anthony Horton (EnviroCarb) and John Houdalakis (Subthermal Solutions)
Rising energy costs and increasing evidence of a link between greenhouse gas emissions and climatic
effects are drivers for the rapid development of technologies that are renewable and energy efficient.
One of the fastest growing areas of technological development is in improving the efficiency of
heating, ventilation and air conditioning (HVAC) equipment and systems in buildings (Michaels
Engineering, 2008). In residential and commercial buildings, these systems account for more than 40%
of electricity and more than 90% of gas consumption. Therefore, improving the efficiency of these
systems can realise savings in energy, expenditure and emissions (Michaels Engineering, 2008).
Geothermal is emission-free energy that is extracted from the earth’s or ocean’s constant
temperature. It is one of the few energy sources that is available 24 hours a day, seven days a week
and
has
the
potential
to
solve
Australia’s
future
energy
issues.
The four types of geothermal energy that are under development in Australia are as follows:
1. Hot Rock (or Enhanced Geothermal Systems / EGS) geothermal electrical generation energy
2. Hot Sedimentary Aquifer (HSA) geothermal energy
3. Direct heat projects
4. Ground Sourced heat pumps–Water to Air systems.
Our focus is ground source geothermal heat pump (GSGHP) systems, which are one of the fastest
growing alternatives to traditional HVAC systems and equipment. They are a highly efficient
renewable energy technology which relies on the principle that at depth, the earth has a relatively
constant temperature which is warmer than the ambient temperature in winter and cooler in summer
(Omer, 2008). GSGHP’s collect heat from the ground outside homes or commercial buildings and
concentrate it for heating purposes, and collect the heat inside and pump it outside for cooling
purposes (Heinonen, 1996).
This technology is well established in North America and some parts of Europe (Omer, 2008). Thermal
energy is transferred between the earth and the GHP using fluids that circulate within loop fields
(comprising polyethylene pipes) that are placed in boreholes (vertically), horizontal trenches or in
surface water bodies (Huttrer, 2007). Within the GSGHP itself, thermal energy is exchanged with a
refrigerant which circulates past fan coils or radiating tubes to emit or absorb heat at strategic
locations within the building (Huttrer, 2007). The heat pump refrigerant can also be circulated through
a loop-field, although this practice is less common. In a domestic setting, the GHP can heat water as a
by-product of the space heating/ cooling process or on demand (using the entire output of the heat
pump) (Huttrer, 2007).
Typical GSGHP System Configurations
Different applications of closed and/ or open loop GHP configurations can be considered depending
on a number of factors (Huttrer, 2007). Some common configurations are shown in Figure 1. In a
closed loop system, water or water/ refrigerant is circulated continuously in a buried pipe, the
diameter and length of which depend on the amount of heating and cooling required, the
temperature, amount of moisture and thermal conductivity of the ground, and the system design. In
an open loop system, water is pumped out of a water body, passed through a heat exchanger and
discharged downstream into the source (Huttrer, 2007).
Figure 1: Common GSGHP configurations (Oak Ridge National Laboratory, 2008).
Closed Loop Configurations
Horizontal Closed Loops
Horizontal closed loop systems are most widely used for smaller scale installations where the amount
of available space is not a concern (Huttrer, 2007). The pipes are buried in trenches, and up to six pipes
can be buried in each trench. Recent technological advances in drilling have given rise to horizontal
drilling which enables the pipes to be pulled through; this method is gaining popularity because loopfields can be installed underneath existing structures and it minimises the area of ground disturbance
(Huttrer, 2007).
Vertical Closed Loops
These systems are most widely used at smaller sites that have limited available land area, and are
particularly commonly installed in commercial and educational settings (Huttrer, 2007). The borehole
depths range from 30-100 metres, and 30-100 metres of loop per tonne of heat exchange may be
required depending on the site soil, rock and groundwater conditions. In the majority of vertical closed
loop installations, a number of holes are drilled, the loops are placed in the holes and joined in either
parallel or series configurations (Huttrer, 2007).
Surface Water Closed Loops
If a water body with sufficient depth and flow is present at the site, closed loops can be located on the
bottom (Huttrer, 2007). The circulating refrigerant gives rise to very good heat exchange with the
surrounding water, without needing to excavate to bury the pipes as is required on land. These
systems are inexpensive to install, efficient and have no documented adverse effects on aquatic
ecosystems (Huttrer, 2007).
Open Loop Configurations
Standing Column Wells
These systems are used where bedrock and ground water are close to the surface (Huttrer, 2007).
Standing column wells can be up to 500 metres deep and 15- 20 cm in diameter. Standing column
wells pump water from the bottom of a well, through the heat pump and return the water near the
surface of the well. The temperature of the return water is moderated by the temperature of the
water in the well (Huttrer, 2007). In the event that the temperature of the return water is too high or
low, a small amount of water can be bled, allowing inflow of ground water at ambient temperature
into the well, which in turn returns the well water to the acceptable temperature range (Huttrer,
2007).
Energy Efficiency of GSGHP Systems
The efficiency of these systems is measured in terms of heating and cooling respectively (Omer, 2008).
Heating efficiency is expressed as a coefficient of performance (COP); the higher the COP the more
efficient the system. A residential GSGHP system may have a COP of 3.4 which means that for every
unit of energy used to power the system, 3.4 units are put back into the home as heat (Omer, 2008).
This efficiency compares favourably to the efficiency of a natural gas furnace which has been reported
as 0.92 (Omer, 2008). The cooling efficiency is measured as an energy efficiency ratio (EER); the higher
the EER the more efficient the system. COP and EER are dependent on a number of factors, and the
initial cost of GSGHP’s is greater than traditional systems, however the energy savings can be used to
pay back the difference in a relatively short time (e.g. a few years) (Omer, 2008).
A heat pump can save up to 30- 40% of the electricity typically used for heating in homes (Omer, 2008).
In mild and moderate climates, heat pumps can provide two to three times more heating than the
equivalent amount they consume in electricity (Omer, 2008). Ground source heat pumps are more
efficient than air source heat pumps especially in climates with similar heating and cooling loads
(Omer, 2008).
Environmental Benefits of GSGHP Systems
GSGHP’s operate with nature to provide clean, efficient and energy saving heating and cooling all year
round (Omer, 2008). They use less energy than alternative heating and cooling systems which relieves
pressure on the earth’s natural resources. GSGHP’s are housed within the building/ house envelope
and underground and therefore do not cause a loss of visual amenity, operate quietly, and do not emit
pollutants (Omer, 2008). These systems have a high coefficient of performance (COP) and therefore
the emissions of CO2, SO2 and NOx (all linked to greenhouse gas emissions and global warming)
associated with traditional electricity generation are reduced (Omer, 2008).
Consumers
From a consumer’s point of view, GSGHP’s offer heating, cooling and hot water at a reduced cost and
that is reliable, efficient and environmentally sound (Omer, 2008). They can be installed in new
buildings or retrofitted in existing buildings (Omer, 2008).
Utilities
GSGHP’s assist utilities to stabilise demand loads and to become more competitive with other energy
sources. They are rapidly becoming the most reliable and competitive heating systems that are
currently available (Omer, 2008).
Financial Savings
Whilst some GSGHP systems can be more expensive to install than natural gas, oil or electric heating,
they are very competitive with any type of heating/ cooling combination system (Omer, 2008). A
closed loop GSGHP system may cost approximately $20000 to install, however the annual operating
costs may be as low as $850 compared to approximately $2000 for conventional heating/ cooling
systems (Petrov, 1997). The savings that can be achieved will vary according to a number of factors
including the size of the house, its typical heat loss and level/type of insulation, the size of the system,
its COP and the local climate and energy costs (Omer, 2008).
Global Warming Impacts Compared to Other Heating/ Cooling Systems
GSGHP’s offer significant emissions reductions in commercial and residential buildings (Omer, 2008).
They use renewable energy stored in the ground near the surface. The use of this renewable energy
replaces the need for primary fuels (by approximately two thirds) which emit greenhouse gases and
contribute to global warming when burnt (Omer, 2008). Conventional fossil fuel systems have been
reported to produce 1.2- 36 times the equivalent CO2 emissions of GSGHP’s, and when used, GSGHP’s
can reduce emissions by 15-77% (Omer, 2008).
On a life cycle cost basis, GSGHP’s are competitive, particularly in climates where air conditioning is
the traditionally favoured cooling system (Omer, 2008). Purely in terms of greenhouse gas mitigation,
there is unlikely to be a currently available technology that has the same potential to mitigate
emissions by as much as GSGHP’s (Omer, 2008).
Economic Aspects of GSGHP Systems
There is little doubt that GSGHP systems can have a significant economic impact at a national level
(Hughes, 2009). In the United States, more than 600,000 units have been installed, and if the Federal
Government set a target to use no more non-renewable primary energy in 2030 than it did in 2008,
GSGHP systems could account for 35-40% of this target due to the aggressive deployment of these
systems. In addition, it is estimated that US$33-38 billion could be cut from annual utility costs (at
2006 costs) (Hughes, 2009). Tax credits have been offered for residential and commercial building
owners since they were enacted in 2008 (Hughes, 2009). Since 2007, rural electric co-operatives have
been able to receive 35 year loans from the Department of Agriculture Rural Utilities for the
infrastructure outside the building (Hughes, 2009).
The Federal incentive discussed above covers 30% of the expenditures in the year the incentive is
taken up (maximum $2000) if the system was installed prior to 1 January 2009 (Geothermal Genius,
2009). The incentive is available for primary residences or second homes until December 2016. In
terms of commercial buildings, a tax credit of 10% of the installed cost is available until 2016
(Geothermal Genius, 2009).
Current Barriers to the Rapid Growth of GSGHP Systems
There are a number of barriers that are currently limiting the growth of GSGHP systems as follows
(Hughes, 2009):
- High initial cost of GSGHP systems to consumers.
- Lack of consumer knowledge/ trust/ confidence in the benefits of GSGHP systems.
- Lack of policymaker and regulator knowledge/ trust/ confidence in the benefits of GSGHP systems.
- Limitations of system design and business planning infrastructure.
- Limitations of GHP installation infrastructure.
- Lack of new technologies/ techniques to improve the cost and performance of GSGHP systems.
Ways to Facilitate the Rapid Growth of GSGHP Systems
There are a number of actions which can encourage the rapid growth of GSGHP systems as follows
(Hughes, 2009):
- Compile independent, statistically valid data on the costs and benefits.
- Assess the benefits of aggressive deployment on a national scale.
- Streamline and deploy nationwide programs that provide GSGHP infrastructure.
- Develop and deploy programs that can provide universal access to GSGHP infrastructure.
- Develop tools and data analysis techniques that facilitate the lowest life cycle cost GSGHP
infrastructure.
- Expand the number of areas where high quality GSGHP design and installation infrastructure exists.
Case Study One: Cornell University Lake Source Cooling System (Ithaca, New York USA).
Lake Source cooling is one of the most significant environmental initiatives undertaken by a United
States university (Cayuga Lake Watershed Network, 2014). The system was installed in 2000 to
upgrade the campus central chilled water system with a design based on energy conservation, and
uses the cold deep waters of Cayuga Lake (Figure 2). Although requiring a capital outlay of $58.5
million, it provides Cornell University with cooling without the need for refrigeration equipment. It
also reduces the energy burden, and other issues associated with the refrigerants that have replaced
chlorofluorocarbons (Cayuga Lake Watershed Network, 2014).
Figure 2: Cornell University’s cooling system that uses Cayuga Lake (Cayuga Lake Watershed Network,
2014).
Case Study Two: GSGHP Systems in Western Australia.
Several examples of GSGHP systems exist in the commercial, educational, and high-end residential
domains in greater Perth, Western Australia. Several large projects are currently at various stages of
rollout having leveraged the former Australian Government’s Community Energy Efficiency Program
(CEEP). Moreover, demand from commercial facilities for cost effective delivery of sustainable HVAC
services is fuelling growth in the deployment of these systems, in line with internal sustainable/
efficiency policy initiatives and desired savings to operational expenditure.
Recent examples include relatively large capacity systems being installed to not-for-profit facilities,
including several of Bethanie Group’s Aged Care Facilities, the Multiple Sclerosis Society, and the
Centre for Cerebral Palsy, where energy savings in the order of 70% or greater are expected. Regional
Western Australia has seen a growth in the deployment of GSGHP systems, with regional councils
having been able to access the CEEP grant. Increasingly local governments throughout Western
Australia are retrofitting recreational facilities with geothermal systems for pool heating and air
conditioning requirements, where offsets to both gas and electricity consumption are expected to be
significant.
The land development sector in Western Australia is increasingly showing interest in the opportunities
of geothermal energy; in order to combat rising headwork and infrastructure and development costs,
and improve corporate image and the sustainable outlook of portfolios, many if not all sustainability
programs and efficiency initiatives have moved to a district scale deployment. The prospect of district
geothermal HVAC deployment is therefore closer than ever, with at least one urban redevelopment
deployment having occurred.
Conclusions
GSGHP systems can offer a wide range of benefits if home and commercial building owners are willing
to look beyond the installation costs. These benefits can be realised for a long period of time and
therefore present a very unique selling proposition for these systems when compared to traditional
HVAC or other heating/ cooling systems. While currently there are barriers to the implementation of
GSGHP systems, these barriers should not be viewed as insurmountable given the economic and
environmental paybacks that can be achieved. In the context of the Pilbara where energy supply
infrastructure and maintenance is extremely expensive, the implementation of these systems at a
district scale should be prioritised.
References
Cayuga Lake Watershed Network (2014). Cornell University’s Lake Source Cooling and Cayuga Lake
Modelling
Projects.
http://www.cayugalake.org/cornell-university-s-lake-source-cooling-lsc-
project.html accessed 17 May 2014.
Geothermal
Genius
(2009).
Geothermal
in
the
Golden
State.
http://www.geothermalgenius.org/states/california.html accessed 17 May 2014.
Heinonen, EW, RE Tapscott, MW Wildin and AN Beall (1996). Assessment of anti- freeze solutions for
ground- source heat pumps systems. New Mexico Engineering Research Institute NMERI 96/ 14/
32580 p. 156.
Hughes, P. (2009). Geothermal (Ground- Source) Heat Pumps- Market status, barriers to adoption and
actions to overcome barriers. National Driller. October 2009 10-12.
Huttrer, G. (1997). Geothermal Heat Pumps; An Increasingly Successful Technology. Renewable
Energy. 10 (2/3) 481-488.
Michaels Engineering (1998). Performance, Emissions, Economic Analysis of Minnesota Geothermal
Heat Pumps. Final Report. Minnesota Department of Commerce St. Paul Minnesota. April 2008.
http://www.cleanenergyresourceteams.org/files/EEE-GHP-Final-Rev.pdf Accessed 16 May 2014.
Oak Ridge National Laboratory (2008). Geothermal (Ground Source) Heat Pumps: Market Status,
Barriers to Adoption, and Actions to Overcome Barriers. December 2008. ORNL/ TM- 2008/232. Oak
Ridge National Laboratory. https://www1.eere.energy.gov/geothermal/pdfs/ornl_ghp_study.pdf
Accessed 16 May 2014.
Omer, AM. (2008). Ground- source heat pumps systems and applications. Renewable and Sustainable
Energy Reviews. 12 (2) 344-371.
Petrov, RJ, RK Rowe and RM Quigley (1997). Selected factors influencing GCL hydraulic conductivity.
Journal of Geotechnical and Geoenvironmental Engineering. 123 (8) 683-695.