Presented by:
Gaurav Soni
14ESORE603
Contents
What is EATHE
Principle
Types of EATHE
Arrangements
Comparison of EATHE & air-conditioner
Literature Review
Methodology
Validation
Results & Discussion
Conclusion
References
What is EATHE
EATHE is one of the well defined ways to utilize the
geothermal energy.
The EATHE system utilizes the heat-storing capacity
of earth.
The fact that the year round temperature four meter
below the surface remains almost constant throughout
the year. That makes it potentially useful in providing
buildings with air-conditioning.
Principle
Earth acts as a source or sink
Cooling/Heating takes place due to a temperature
difference between the soil and the air
Types of EATHE
Open-Earth Air Tunnel Heat Exchanger (O-EATHE)
Closed-Earth Air Tunnel Heat Exchanger (C-EATHE)
O-EATHE
C-EATHE
Arrangements
EATHE in Series
EATHE in Parallel
Comparison of EATHE & Air-conditioner
S. No. Parameters EATHE Conventional Air
Conditioner
1. SPACE Require large space for Require less space for
installation installation
2. COOLING/HEATING EFFECT Give limiting cooling/ Give better cooling/heating
heating effect effect
3. REFRIGERANT Air CFCs etc.
4. ENVIRONMENT POLLUTION No pollution i.e. Eco Causes Global Warming &
friendly Ozone Layer Depletion
5. OPERATING COST Lower Higher
6. POWER CONSUMPTION Low High
7. MAINTENCE Low High
8. LIFE Long life Limited life
Literature Review
R. Misra et al. 2017 carried out CFD simulation using
ANSYS 15.0 on EATHE to investigate the effect of soil
thermal conductivity on EATHE for transient
conditions. They observed that better results were
obtained from EATHE for intermittent operation.
Dr. O.P. Jakhar et al. 2017 performed experimental
analysis of Simple and Hybrid EATHE in series
connection. They found that the average temperature
difference for simple EATHE was 11.00°C, and for
hybrid EATHE it was 16.27°C.
Mathur et al. 2016 investigated numerically the
recovery of soil temperature of an EATHE under
intermittent operation. They used different strategies
to improve the COP of the system and observed that
for better soil in next summer season EATHE system
must operate during winters for space heating.
Arshdeep Singh and Ranjeet Singh 2015 prepared
performance analysis of rectangular EATHE used for
cooling. They observed 13°C temperature drop in
summer and 5°C temperature rise in winter season.
Dr. O.P. Jakhar and Rajendra Kukana 2014 did
transient thermal analysis of EATHE using CFD
approach for summer season at Govt. Engineering
College Bikaner. They observed the temperature
difference of 17.8°C and 13.8°C for sandy soil and sandy
loam soil respectively. They used quarter segment of
pipe to reduce simulation time.
Methodology
Designing of Model
Validation
Effect of variation of different parameters
Comparison
Results and Discussion
Designing of Model
The model is drafted using CATIA V5R14 software.
The length of the model is same as of an actual EATHE
installed at Bikaner, which is as follows:
Inner Diameter Outer
SYSTEM Length (L) Thickness (t) Material
(Di) Diameter (Do)
EATHE 45.67 ft 40 mm 46 mm 3 mm Mild Steel
The ‘.igs’ file obtained from CATIA is imported in
ANSYS 15.0 for simulation.
The following five steps are involved in solving a CFD
FLUENT problem in ANSYS:
Geometry
Mesh
Setup
Solution
Results
Geometry
The geometry imported from CATIA, as shown in the
fig, is updated in FLUENT
The central portion of rectangle is the fluid region,
from which air flows, has 40mm width and 10 mm
thickness.
The adjacent both rectangles to fluid region define
steel having 3mm width and same thickness.
The remaining two rectangles define sand region
having same thickness of fluid region and width of 20
mm each.
The total length of the model is same as that of
installed in Bikaner, which is 45.67 ft.
Mesh
Meshing is defined as the process of dividing the
whole component into number of elements.
The details of mesh is as follows:
A fine mesh, as shown in fig, is obtained having
2242926 Nodes and 1876488 Elements.
In mesh tool different names are given to different
boundary surfaces of the geometry, viz. inlet, outlet,
wall sand, wall steel, wall fluid, sand steel interface,
and steel fluid interface.
After meshing the orthogonal mesh quality is
calculated, which is found to be 0.998.
The orthogonal quality of mesh varies from 0 to 1. The
value near 1 shows good quality of mesh and hence
desirable.
Setup & Solution
Energy and Turbulent flow models are turned on.
Materials are selected from fluent data base and
research papers.
Boundary conditions are provided to the system viz.
temperature of soil, inlet air velocity and temperature.
Solution is initialized with Hybrid initialization.
No. of iterations and reporting intervals are selected.
Starting the calculation.
Results
After completion of calculation, results are obtained.
The outlet air temperature is obtained using area-
weightage method.
Temperature of air is also noted down at different
points of pipe.
Validation
The results obtained from the simulation model are
compared with the results obtained from actual
EATHE installed at Bikaner.
The results are taken at three different velocities of 10,
12, and 14 m/s for three consecutive days of summer
season (June, 2017).
Velocity 10 m/s 324
322
322
320
Temperature (Kelvin)
320
Temperature (Kelvin)
318
316 318
314 316
312 314
310 312
308 310
306 308
304 306
302 304
0 2 4 6 8 10 0 2 4 6 8 10
Time (Hours) Time (Hours)
322
320
Temperature (Kelvin)
318
316
314
312
310
308
306
304
302
0 2 4 6 8 10
Time (Hours)
Velocity 12 m/s 324
324
322
322
Temperature (Kelvin)
Temperature (Kelvin)
320 320
318 318
316 316
314 314
312 312
310 310
308 308
306 306
304 304
0 2 4 6 8 10 0 2 4 6 8 10
Time (Hours) Time (Hours)
322
320
Temperature (Kelvin)
318
316
314
312
310
308
306
304
0 2 4 6 8 10
Time (Hours)
Velocity 14 m/s 324
322
322
Temperature (Kelvin)
320
Temperature (Kelvin)
320
318
318
316
316
314 314
312 312
310 310
308 308
306 306
0 2 4 6 8 10 0 2 4 6 8 10
Time (Hours) Time (Hours)
326
324
Temperature (Kelvin)
322
320
318
316
314
312
310
308
306
0 2 4 6 8 10
Time (Hours)
For velocity of 10 m/s, the error percentage for three
consecutive days is 6.21%, 5.28%, and 5.19%
respectively.
For velocity of 12 m/s, the error percentage for three
consecutive days is 4.71%, 4.35%, and 3.87%
respectively.
For velocity of 14 m/s, the error percentage for three
consecutive days is 4.54%, 3.76%, and 5.11%
respectively.
Results & Discussion
After validating our model. The variation of following
parameters are obtained:
Velocity
Tube Length
Tube Diameter
Tube Material
Thermal Conductivity of Soil
Velocity
The Outlet Air Temperature is calculated from
minimum velocity of 4 m/s to maximum velocity of 20
m/s with an interval of 2 m/s, at a constant inlet
temperature of 320K.
313
312
311
Temperature (Kelvin)
310
309
308
Outlet Air Temperature
307
306
305
304
0 5 10 15 20 25
Velocity (m/s)
Tube Length
The Outlet Air Temperature is calculated for an
increase as well as decrease in length by 5 and 10 feet,
at constant velocity of 10 m/s.
324
322
320
Temperature (Kelvin)
318
316
314
Inlet Temperature
312
310 Increased Length
308 Actual Length
306
304
302
0 2 4 6 8 10
Time (Hours)
Increased length by 5 feet
324
322
Temperature (Kelvin) 320
318
316
314
Inlet Temperature
312
310 Increased Length
308 Actual Length
306
304
302
0 2 4 6 8 10
Time (Hours)
Increased length by 10 feet
The average increase in temperature difference for 5
feet increased tube length is 1.88.
For 10 feet increased tube length it is 2.24.
324
322
Temperature (Kelvin) 320
318
316
314 Inlet Temperature
312 Decreased Length
Actual Length
310
308
306
304
0 1 2 3 4 5 6 7 8 9 10
Time (Hours)
Decreased length by 5 feet
The average decrease in temperature difference for 5
feet decreased tube length is 0.71.
324
322
320
Temperature (Kelvin)
318
316
314 Inlet Temperature
312 Decreased Length
Actual Length
310
308
306
304
0 1 2 3 4 5 6 7 8 9 10
Time (Hours)
Decreased length by 10 feet
The average decrease in temperature difference for 10
feet decreased tube length is 1.25.
Tube Diameter
The Outlet Air Temperature is calculated for an
increase as well as decrease in diameter of pipe by 5,
10, 15, and 20 mm, at constant velocity of 10 m/s.
324
324
322
322
Temperature (Kelvin)
320
Temperature (Kelvin)
320
318 318
316 316
314 314 Inlet Temperature
312 312 Increased Diameter
310 310
Actual Diameter
308 308
306 306
304 304
0 1 2 3 4 5 0 1 2 3 4 5
Time (Hours) Time (Hours)
Increased by 5 mm Increased by 10 mm
324
325 322
Temperature (Kelvin)
320
Temperature (Kelvin)
320 318
316
315 314 Inlet Temperature
312 Increased Diameter
310
310
308 Actual Diameter
305
306
300 304
0 1 2 3 4 5 0 1 2 3 4 5
Time (Hours) Time (Hours)
Increased by 15 mm Increased by 20 mm
The average decrease in temperature difference for 5
mm increased tube diameter is 0.22
For 10, 15, & 20 mm it is 0.62, 1.8, & 2.37 respectively.
325
325
Temperature (Kelvin)
Temperature (Kelvin)
320 320
315 315
310 310
305 305
300 300
0 1 2 3 4 5 0 1 2 3 4 5
Time (Hours) Time (Hours)
Decreased by 5 mm Decreased by 10 mm
325
325
Temperature (Kelvin)
Temperature (Kelvin)
320
320
315
315
Inlet Temperature
310
310 Decreased Diameter
305 Actual Diameter
305
300
300
0 1 2 3 4 5
0 1 2 3 4 5
Time (Hours)
Time (Hours)
Decreased by 15 mm Decreased by 20 mm
The average increase in temperature difference for 5
mm decreased tube diameter is 2.82
For 10 mm it is 4.85
For 15 mm it is 6.09
For 20 mm it is 6.65
Tube Material
The outlet air temperature is measured for different
tube materials at constant inlet temperature of 320K
and velocity of 10 m/s.
S. Tube Outlet S. Tube Outlet
No. Material Temperature No. Material Temperature
1 Steel 308.7 4 Gold 308.69
2 Copper 308.69 5 Titanium 308.73
3 Aluminum 308.69 6 Nickel 308.69
Thermal Conductivity of Soil
Let the thermal conductivity of soil for summer season
is reduced from 2.0 to 1.5 after operating EATHE for
five hours.
After six hours it is reduced to 1.0
After seven hours it becomes 0.5
The velocity of inlet air is 12 m/s.
324
322
320
Temperature (Kelvin)
318
316
314 Inlet Temperature
312 Experimental Outlet Temperature
310 Simulated Outlet Temperature
308
306
304
0 2 4 6 8 10
Time (Hours)
The average error percentage in temperature difference
for summer is reduced from 4.7% to 1.6% for velocity
of 12 m/s.
Let the thermal conductivity of soil for winter season is
increased from 1.26 to 1.75 after operating EATHE for
four hours.
298
296
Temperature (Kelvin)
294
292
290 Inlet Temperature
288 Experimental Outlet Temperature
286 Simulated Outlet Temperature
284
282
0 1 2 3 4 5 6 7 8
Time (Hours)
• The average error percentage in temperature
difference for winter is reduced to 0.8% for
velocity of 12 m/s.
Conclusion
The rectangular cross-section chosen in simulation model,
instead of circular cross-section, gives satisfactory results.
So, we can use rectangular element of a circular pipe for
obtaining good mesh quality.
The outlet air temperature increases with increase in inlet
air velocity and tube diameter, and also with decrease in
tube length, and vice-versa.
There is no effect of changing tube material on outlet air
temperature due to very small thickness of pipe.
It is observed that the thermal conductivity of soil
decreases in summer and increases in winter due to
continuous operating of EATHE for more than 3-4 hours.
References
R. Misra, Abhishek Agarwal, V. Bansal and D.K.
Jamuwa, ''Numerical Investigation of Dynamic
Interaction of Earth Air Tunnel Heat Exchanger with
Surrounding Soil during Continuous and Intermittent
Operation in Winter'', IJETSR, vol.-4, Issue 3, March
2017.
O.P. Jakhar, C.S. Sharma, R. Kukana, “Experimental
Thermal Performance Analysis of Simple & Hybrid
Earth Air Tunnel Heat Exchanger in Series Connection
at Bikaner Rajasthan India”, IOSR-JMCE, vol.-14, Issue
6, Ver. II, Nov.-Dec. 2017.
Anuj Mathur, Ankit Kumar Surana and Sanjay Mathur,
''Numerical Investigation of the Performance and Soil
Temperature Recovery of an EATHE under Intermittent
Operations'', Elsevier Renewable Energy, vol.-95, pp. 510-
521, April 2016.
Arshdeep Singh and Ranjit Singh, ''Performance Analysis
of Rectangular Earth-Air Tunnel System used for Air-
Conditioning of the College Classroom'', Journal of
Energy Technologies and Policy, vol.-5, no.-4,2015.
O.P. Jakhar and Rajendra Kukana, ''Transient Thermal
Analysis of Earth Air Heat Exchanger using CFD for
Summer Season'', STM Journals-Journal of Thermal
Engineering and Applications, vol.-1, no.-2, pp. 8-17, 2014.
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