University of sulaimani
College of engineering
Water resource department
Ground water thermal energy storage
Supervisor: Dr. Haveen Muhammed Rashid
Students:
Sharo Shwan
Koyar Dlshad
Kaiwan Kwestany
Gashbin Abas
Academic year: 2021-2022
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Table of Contents
INTRODUCTION................................................................................................................................................... 3
TYPES OF UTES ................................................................................................................................................... 4
ATES ....................................................................................................................................................................... 4
BTES ....................................................................................................................................................................... 5
CTES ....................................................................................................................................................................... 6
CONCLUSION ....................................................................................................................................................... 7
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INTRODUCTION
We have utilized the underground since the beginning of mankind.
One very early observation was that the ground temperature was often
very different from the air temperature. It was found out that the
underground could serve as protection not only from enemies but also
from the coldest days of the winter and the hottest days of the summer.
The ground temperature at a certain depth below the ground surface
(10-15 m), which is not influenced by the season temperature
variation at the surface, is equal to the annual mean air temperature.
There are many examples, from various regions of the world, of
ancient underground buildings with comfortable temperatures around
the year.
Such buildings have often one outer wall while the others are
surrounded by rock or soil.
A more recent underground thermal storage technology, developed
during the last 40-50 years, means that thermal energy is actively
stored for the purpose of later extraction. So, heat is either injected
for later use (heat storage) or extracted from the ground (cold storage)
which is later used for cooling.
Such thermal energy storage is mainly for long-term storage or
seasonal storage of thermal energy
storage.
There are also combinations in which the storage is used for both
short-term and seasonal
storage.
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TYPES OF UTES
There are currently three common types of UTES:
 aquifer thermal energy storage (ATES)
 borehole thermal energy storage (BTES)
 rock cavern thermal energy storage (CTES).
Aquifer Thermal Energy Storage
The operation of Aquifer Thermal Energy Storage (ATES) means that
water is extracted from a well and is heated or cooled before it is reinjected into the same aquifer. So, the thermal energy is stored in the
groundwater and in the matrix around it.
There are usually several wells, for extraction and injection, and these
are separated in order to keep
them warm and cold water
from mixing. ATES systems
are
large-scale
systems
mainly for seasonal thermal
energy storage both heating
and cooling. In many cases,
the same ATES is used for
both heating and cooling.
Figure 1, ATES
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Advantages and drawbacks of ATES
The biggest advantage of the ATES is that it primarily uses renewable
energy. The system can operate almost endlessly with hot and cold
water, never running off energy in the process. The drawback of the
ATES is that the investment costs are high. Certain conditions must
be met as well: for instance, the soil must be suitable for the system.
The buildings themselves must be able to support it too. It is best to
make the necessary modifications during construction. The building
purpose is also important: ATES is less effective for residential
buildings.
Borehole Thermal Energy Storage (BTES)
Borehole systems are the most commonly used ground-coupled
technology for heating and/or cooling buildings. A rough estimation
is that there are about two million small-scale systems for singlefamily houses. These consist usually of one borehole drilled to 60200m. Such systems are “always” connected to a heat pump.
Figure 2, BTES
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Cavern thermal energy storage (CTES)
The other option for UTES involves man-made structures. These are
used when existing aquifer and sub-soil conditions are not favorable.
They are called cavern thermal energy storage (CTES), covering all
kinds of ‘cavities’ underground. The first is a tank buried
underground where an insulated tank is filled with water. The other
storage option is pit thermal energy storage in which a pit is dug,
lined, and filled with water or water/gravel. Underground caverns that
may be found in natural karstic formations or abandoned mines can
also be alternatives that can be used for UTES.
Figure 3, Different generic types of UTES
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CONCLUSION
Underground thermal energy storage (UTES) uses underground
reservoirs for storing heat and cold in different ways, depending on
geological, hydrogeological, and other site conditions. The two most
promising options are storage in aquifers (ATES) and storage through
borehole heat exchangers (BTES), TES through underground cavities
(CTES, cavern thermal energy storage) is a technology rarely applied
commercially.
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References
1. https://www.sciencedirect.com/topics/engineering/underground-thermal-energystorage#:~:text=Underground%20thermal%20energy%20storage%20(UTES,thermal%20energy%20storage%20is%20wate
r.
2. http://large.stanford.edu/courses/2013/ph240/lim1/docs/UTES_Nordell.pdf
3. https://www.ecologyandsociety.org/vol16/iss1/art22/
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