Online proceedings - EDA Publishing Association

7-9 October 2009, Leuven, Belgium
about 600W, up to 80% of the total heat. During other time of d i : Inner diameter of tube, m;
the day, the GCS dissipate 50%~60% of the heat, other heat
is dissipate to the decreased ambient air by the cabinet wall,
also the soil get time to recover. Above conclusion is proved
as well in result of long time test showed in figure 10.
Heat dissipated by soil will be reduced in winter as ambient
air temperature decreases to low level. The soil temperature
gets more time to recover back. In ultra low temperature
environment, the soil can also heat up the cabinet to proper
temperature; this will save a lot of heating energy. The test is
continued to verify it.
d o : Outer diameter of tube, m
Nu: Nuselt number;
λ p : Thermal conductivity of tube’s wall, w/mk
λ: Thermal conductivity of water, w/mk
For this GCS prototype, calculation result shows that R 1 is
close to 0.04 ℃/(Wm) and R 2 is close to 0.1℃/(Wm). Because
soil is high thermally inertial, figure 11 shows that R soil increases
gradually and becomes stable in a range finally. This value can
be use for fast engineering design. As R soil is the key design
parameter, it relate with many factor like property of the soil,
layout and size of tube, buried depth and etc., more research
should be carried out in the future work.
Fig 9 Transient curve of heat dissipated by soil in one day
Fig11 Transient thermal resistance curve of R soil
IV.
CONCLUSION
Fig 10 Transient curve of heat dissipated by soil for long time
It is necessary to set up an effective model for fast evaluation
of GCS cooling performance. As water-soil heat transfer process
is the most important part, this work start with the research
on R soil
. R
soil
is the thermal transfer resistance per unit length
of the tube:
R = L( T − T ) / Q − R − R (2)
soil ave soil
( )
R 1 πd i
h i
h Nuλ
/
1 2
= 1 (3)
= (4)
i
d i
R2 = ln( do / di ) / 2πλ
pL
Where,
L: Length of water-soil exchanger, m
Q: Heat dissipated by soil, W
R 1 : Thermal resistance from fluid to tube’s wall per unit
length (℃/Wm)
R 2 : Thermal resistance of tube’s wall per unit length
(℃/Wm)
T ave : Average temperature of fluid inside tube
T soil : Original soil temperature
A new geothermal cooling solution with good performance,
low noise and high energy efficiency for telecom outdoor
cabinet has been presented. The basic heat transfer behaviour of
the entire system (cabinet and GCS) is analyzed with transient
temperature data. With effective performance and low cost, this
GCS is more competitive compared with traditional cooling
solutions. It is necessary to carry out further research for design
and application.
REFERENCES
[1] Guizhi G., etc, “Simple calculation for GSHP heat-exchanger”,
Energy Conservation, 274(2005), pp.22-24.
[2] Li Xingrong, Zhang Xiaoli, Liang Biling,Yang Lin, “Diurnal
variation of Soil temperature and its vertical profiled in summer in
shenzhen city,” ScienceTechnologyandEngineering, vol.8,
pp5996-6000, 2009.
[3] “Soil cooling system for small site (KPN),|” ETNO annual report
2008, 7-3, pp.37.
[4] Hong Yuping, Ji Shengqin, Zhai Liqian, Chen Qiao, Claudio Bianco,
“Cooling System of Outdoor Cabinet using Underground Heat Pipe”
11-1978-1-4244-2056-8/08 2008 IEEE Intelec, 13-1.
©EDA Publishing/THERMINIC 2009 16
ISBN: 978-2-35500-010-2