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 loop-fields 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

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