2011 International Conference on Alternative Energy in Developing Countries and Emerging Economies
- 292 -
Abstract
--This research goal was to study the feasibility of
a greenhouse cooling technique by the earth tube system
(ETS) in climates of northern Thailand. The study focused
on temperature and relative humidity changes as well as the
ability of heat transfer to the underground from an even-
span greenhouse during daytime. The investigation found
that the ETS fairly decreased the temperature, especially in
the summer, by 4
o
C while the maximum coefficient of
performance (COP) was 3.56. In the winter and the rainy
seasons, the ETS could decrease the greenhouse
temperature approximately by 3
o
C and 2
o
C while the
maximum COP was 1.84 and 0.77, respectively. In addition,
the cooling potential of the ETS was depended on the
temperature difference of the inflow and outflow air
through the earth tube as a result of the amount of solar
radiation and water vapor in the atmosphere for different
climates
Index Terms
-- Agricultural Greenhouse, Earth-to-Air
Heat Exchanger, Earth Tube System, Northern Climate
N
OMENCLATURE
COP Coefficient of performance
ETS Earth tube system
GH Greenhouse
Q
out
Heat removal from greenhouse (W)
RH Relative humidity
T
in
Inflow air temperature of earth tube system (
o
C)
T
out
Outflow air temperature of earth tube system (
o
C)
T
s
Soil temperature at 1 m (
o
C)
T
out
Outflow air temperature of earth tube system (
o
C)
W
in
Power input from blower (W)
I.
I
NTRODUCTION
In hot climate, the greenhouses (GH) always have a
relatively high temperature where the cooling is
necessary. The utilization of soil temperature under earth
surface is an alternative passive cooling method that uses
low energy. The underground is able to be a large heat
sink with temperature almost constant. When the tube or
pipe is buried in the ground at the various depths, the tube
surface acts as an intermediate heat exchanger between
the air flow through the system and soil texture. This
method is called the earth tube system (ETS) or the earth-
to-air heat exchangers (ETAHE).
This work was supported by the Commission on Higher Education,
Thailand under the program Strategic Scholarships for Frontier
Research Network for the Ph.D. Program Thai Doctoral degree.
At present, the researches of the ETS are carried out
widely in different climates for example in Europe,
America and Asia. These studies would be implemented
in buildings, residential homes, and agricultural GHs. The
researchers in [1]
–
[9] reported that the ETS could
decrease the air temperature of the buildings and GHs.
Anyway the temperature reduction is depends on
different climates for example in hot and dry weather the
temperature is reduced similar to composite climate. In
addition to the temperature study, the ETS has been
studied focusing on more parameters which affect the
system potential such as ground surface temperature,
buried depth, thermal diffusivity, thermal conductivity of
tube and soil, tube length, air flow rate and cooling
performance.
In Thailand, researchers in [10]
–
[12] studied the ETS
in the residential homes and buildings concerning the
effectiveness of temperature decrease, the optimum
design on pipe diameter, total length and the suitable
depth.
The results demonstrated that the indoor
temperature was reduced by ETS during daytime but the
thermal comfort was not appropriate for human.
In GH
application, the advantages of ETS are regardless of the
human thermal comfort so that the principle design and
functional system is not complicated. Therefore, the ETS
has potentiality in the agricultural GH. This research aims
to study the cooling feasibility of the ETS focusing on the
temperature and relative humidity changes including the
ability of heat transfer during daytime in the experimental
GHs under various weather conditions of Chiang Mai.
II. M
ATERIAL AND
M
ETHOD
A. Experimental greenhouse
In order to compare the results between cooling and
non-cooling, the experiments were carried out in 2 nearly
identical greenhouses (GHs). The first greenhouse was
the model GH with the ETS and the second one was the
control GH without the ETS. Two GHs were an even-
span type, covered by poly-ethylene plastic and located in
north
–
south orientation. The configurations were 3m
wide, 5m long, 3m high with 0.6 m roof ventilators. The
research was situated in Mae Hia Agricultural Research,
Demonstrative, and Training Center, Chiang Mai
University, Thailand.
The Feasibility Study of Cooling by Earth Tube
System in Agricultural Greenhouse
for Northern Thailand Climates
S. Mongkon*, S. Thepa*, P. Namprakai* and N. Pratinthong*
* Division of Energy Technology, School of Energy Environment and Materials
King
Mongkut’s University of Te
chnology Thonburi, (
Thailand
)
