Tips for going with a geothermal air conditioning solution
27 January 2017
WGE: Geothermal air conditioning systems are becoming a popular choice for new developments as they provide a more energy efficient result than traditional air cooled systems. WGE’s Alex Deluca says that geothermal systems offer a host of benefits, however there are tricks and tips designers need to be aware of before implementing them.
What is the geothermal solution?
The system utilises the stable temperatures of the earth as a heat rejection source for air conditioning. Systems can be either open or closed:
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Open systems extract water from the earth, use it to cool or heat the building via air conditioning equipment and then re-inject the water underground or discharge it into a water body.
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A closed system consists of an extensive pipe network underground to absorb heat from the earth in winter and reject heat to the earth in summer.
Typically open systems are cheaper to install (as there is less pipework to install and maintain) but they are vulnerable to variances in water quality and geological conditions. They also have high maintenance costs associated with the extraction and injection bores as well as filtration.
What are the benefits of geothermal air conditioning solutions?
Fundamentally, the main advantage is higher energy efficiency. The earth’s temperature is relatively stable at around 20oC, compared to relatively volatile air temperatures that typically range between 0o and 40oC. This makes it a much more effective way to reject excess heat compared to an air-cooled system or a water cooled system that rejects heat to ambient air.
Geothermal systems are also considered:
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highly sustainable
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yield lower running costs
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can result in a smaller plant footprint within the building and less plant noise radiating external to the building
Additionally, depending on the scale of the development and the local soil and groundwater conditions, a significant cost benefit can be achieved.
Tips for going with a geothermal solution
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Consider bore placement and life span before commencing. For open loop systems, the bore placement can be limited across the site and bore life span can also be dramatically impacted by water quality in open systems.
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Think about heat saturation. The design needs to be carefully modelled to ensure that the earth doesn’t get saturated with heat. In Perth, more heat is rejected than absorbed over an annual cycle and the net effect can cause a build-up of excess heat. Careful consideration of the ratio of the building to plot size is required to avoid this scenario.
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Get professional validation. Consultation from a qualified hydrogeologist is typically required to validate a geothermal application.
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Research your development’s Geothermal systems can incur a significantly higher capital cost from an infrastructure point of view when compared to conventional cooling towers or air cooled plant. Think about the longevity of your development and the payback period required for a geothermal solution.
Suitable applications
To maximise the energy efficiency benefits, there needs to be a central system to spread the cost of the infrastructure. Commercial projects where leasing arrangements or commercial contracts are in place governing delivery and maintenance of the system are perfect situations.
When considering geothermal for new developments, projects that are looking to utilise water cooled equipment such as office buildings, retail developments and large education or health campuses are well suited because geothermal systems can replace/supplement water cooled heat rejection systems (eg cooling towers). Additionally, campus sites typically have a greater ratio of plot size to building floor area which lends itself better to this type of cooling system.
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Source: Wood & Grieve Engineers - www.wge.com.au
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