Example of Geothermal Cooling with Ground Source Heat Pumps in South-East Asia
01.12.2017«Geothermal Energy Development for a Green Economy» is a key factor not only in industrial countries but also in developing and emerging economies. IEA Geothermal, the International Technology Collaboration Programme on Geothermal Energy of the International Energy Agency, organised a workshop on this crucial topic in Hanoi (Vietnam) on 13-14 November 2017. Host and Co-organiser was the Vietnam Institute of Geosciences and Mineral Resources (VIGMR). About 100 experts from worldwide participated in the event to share information and highlight the opportunities and benefits of geothermal energy deployment.
In most Asian countries, the interest in Geothermal Energy is rapidly increasing in recent times. One of the main topics is the development and establishment of geothermal direct use and heat pump applications. In several Asian countries, there is a seasonal change between a cooling and heating demand. On the other hand, a constant cooling demand dominates in the tropical regions. Kasumi Yasukawa, deputy director of the Renewable Energy Research Center of the Fukushima Renewable Energy Institute, Japan, introduced into the topic «cooling with ground source heat pumps (GSHP) in tropical regions» and presented lessons learned from South East Asian Countries. This project is part of the CCOP-GSJ Groundwater Project Phase III (CCOP = Coordinating Committee for Geoscience Programmes in East and Southeast Asia).
There are important reasons for the development and use of GSHP for cooling applications in tropical Asian countries: Increasing population, expanding industry, an urban heat island phenomenon and a very high electricity demand for air conditioning.
Picture 1: Reduction of electricity demand and heat island phenomenon by the utilisation of geothermal cooling (Source: Genchi et al., 1999; taken from Yasukawa, 2017).
A series of concerns regarding the utilisation of geothermal cooling with GSHP systems have to be investigated. The major questions are if such systems are applicable in tropical regions, if the heat exchange rate is sufficient (in closed systems), and if local drillers are able to drill without cementing.
Picture 2: Comparison of the monthly mean atmospheric and subsurface temperature in different climatic regions. Blue line = cold climate, purple = moderate climate (example Tokyo) and red = tropical climate. Green lines = different underground temperatures.
The comparison of the atmospheric and subsurface temperature in the tropics reflects that the underground is – in general – too warm to store waste heat from geothermal cooling. A solution is to use the effect of «cold» ground water which infiltrates in the underground in high mountain regions and flows towards the nearshore regions with the densely populated Asian (Mega-) Cities.
Picture 3: water saturated sediments in the area of Asian cities.
The underground in this regions consists of water saturated, unconsolidated sediments. The advection effect of the ground water will additionally enhance the heat exchange rate in the borehole. To take full advantage of this, a bare borehole is needed: a borehole heat exchanger with no cementing, no casing ad no bentonite mud circulation. This can be achieved by drilling with a Polymer.
In the CCOP project, numerous underground temperature profiles from recharge, intermediate and discharge zones have been measured and compared with atmospheric temperatures in different regions of the participating countries. The influence of the cold water flow from the infiltration areas can be tracked clearly everywhere.
The experiment example from Hanoi (Vietnam) shows that in the Hanoi region the GSHP system has a relatively high performance. This is due to the bigger difference between the atmospheric and underground temperature. Furthermore, winter time is cool and humid in Hanoi, so that the GSHP system can be used for heating and/or drying.
Summary of the GSHP demonstration experiments of the CCOP project for cooling applications in Tropical Asia:
The experiment example in Kamphaengphet, Thailand was installed in an office building and the system performance and subsurface heat exchange capacity were monitored over a year. The cooling system achieved a COP of 3 and is working well. The borehole was in this case completed with «normal» cementing and casing.
Picture 4: Atmospheric and underground temperatures at the location of the experiment in Kamphaengphet (Thailand).
Experimental operation of GSHP systems for cooling only has been conducted in Thailand, Indonesia and Vietnam. The main lessons learned regarding the efficient and economic utilization of such applications are that all systems worked well and reliable and with an acceptable COP. The efficiency is much higher than by a new air conditioning system. The best performance can be achieved with boreholes without bentonite, cementing, and casing. In addition, important for the efficient and economic utilization are the careful setting and adjustment of the system parameters and the availability of locally manufactured materials. Currently, most materials have to be imported from Japan etc.
More information about the CCOP project on Geothermal cooling with GSHP in tropical regions can be found here: http://www.ccop.or.th/page/GSJ-GW. An introduction into this topic is also given here http://www.aist.go.jp/fukushima/en/unit/SGHT_e.html.
The presentation from Kasumi Yasukawa and all other presentations from the International Geothermal Workshop in Hanoi are available on the website of IEA Geothermal: http://iea-gia.org/publications-2/working-group-publications/2017-asian-workshop-presentations/.
As follow up event, IEA Geothermal and IGA will hold an Asian Geothermal Symposium in conjunction with the GeoTHERM fair in Offenburg on 28th February 2018.
Dr. Katharina Link (Geo-Future GmbH, Frauenfeld), Leiterin Working Group «Direct Use of Geothermal Energy» der IEA Geothermal
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