Passive cooling of telecom shelter using solar chimney with Earth

Passive cooling of telecom shelter using solar chimney with Earth
Recent Advances in Energy, Environment, Biology and Ecology
Passive cooling of telecom shelter using solar chimney with
Earth-air heat exchanger
BOUBEKEUR DOKKAR1,a, BELKHIR NEGROU1, NASREDDINE CHENOUFF1,
NOUREDDINE SETTOU1, ABDESSLEM BENMHIDI2
1
Laboratoire de Valorisation et Promotion des Ressources Sahariennes
University of Kasdi Merbah
BP 511 Route Ghardaia 30000 Ouargla
ALGERIA
E-mail: Boubekeur.ogx@ gmail.com.
2
Linde Gas Algeria, centre of Ouargla,
Z.I Route Ghardaia 30000 Ouargla
ALGERIA.
Abstract:- Passive ventilation systems are being increasingly proposed as an alternate to mechanical ventilation
systems because of their potential benefits in terms of operational cost, energy requirement and carbon dioxide
emission. This paper presents passive cooling system for base transceiver station (BTS) in neighboring Ouargla
city (south of Algeria). There are numerous ways to promote this cooling technique, and in the present study the
use of solar chimney together with earth-air heat exchanger (EAHE) is introduced to remove undesirable interior
heat from telecom shelter. Consequently, theoretical analyses have been conducted in order to investigate the
cooling and ventilation through combined solar chimney and underground air channel. In winter, only solar
chimney is used for shelter cooling. In summer, the solar chimney can be perfectly coupled with the underground
cooling system. CFD commercial code (Fluent 6.3) is used to predict the thermal performance, and fluid flow in
two-dimensional solar chimney and underground channel. The obtained results show that flow increase at shelter
inlet causes a marked improvement in cooling in all Shelter area, which indicates that we can design a shelter
without conventional air conditioning.
Key-words:-Telecom station, passive cooling, solar chimney, heat exchanger.
Natural convection is the transport of heat by buoyancy
induced flows. The literature on natural convection
within enclosures is vast and the selected few are
available in Refs. [1–3]. This is the simplest and most
cost effective cooling method. However, in remote
desert with high ambient temperatures, this method
proves its inability to maintain the desired internal
temperature. Forced air convection is also of relatively
low cost and simple in design, but it provides about
56% as maximum surface temperature reduction [4], so
does not achieve the satisfactory results for cooling
systems with high heat flux.
Concerning cooling systems using phase change heat
transfer where the latent heat transfer of working fluid
is used for removing heat. In this technique, A.
Shammuga et al. [5] were developed and experiment
two-phase closed thermosyphon heat exchangers to
provide thermal management in telecom shelters. This
thermal system absorbs the equipment dissipated heat
1 Introduction
Cellular mobile service is a rapidly expanding and a
very competitive business worldwide, including
developing countries. Mobile network operates by
connecting between Base transceiver stations which
contain sophisticate electronic components; however,
significant improvement in the microelectronic devices
performance requires development of very efficient
cooling systems. Generally, dissipating heat rates
(ranging from 500 to 10,000 W depending on the size
and type of equipments) is removed by using
conventional air conditioners which consume large
amount of electrical energy. In addition in remote areas
large engine generators are required to supply power to
air- conditioner. A large variety of passive cooling
techniques have been proposed. They include standard
ventilation and novel methods that use sensible and
latent heat storage systems. Standard ventilation
includes natural convection and forced air cooling.
ISBN: 978-960-474-358-2
134
Recent Advances in Energy, Environment, Biology and Ecology
during the hottest part of the day, stores it as latent heat
and releases it through thermosyphons during the night
to the ambient. It is seen from the ambient temperature
curve for the month of May that the maximum
temperature is 40.90 ◦C. The enclosure temperature is
maintained at an average temperature of 37.67 ◦C and
the maximum reaches 38.70 ◦C. It is seen that the phase
change temperature of PCM increases above its melting
temperature (29 ◦C) during the period 11.00 a.m. to
5.00 p.m. This is due to the fact that the storage
capacity of the PCM is insufficient to take all the heat
loads of the day during the month of May.
In the same way, A. Samba et al. [6] were investigating
the impact of the thermosyphon loop by comparing two
types of cooling system: the traditional cooling system
(air convection) currently used by France Telecom and
the thermosyphon loop cooling. They conclude that the
maximum heat load of the telecommunication
equipment is limited about 250 W for the traditional
cooling system, while it is about 600W for the
thermosyphon loop cooling system.
Another technique, commonly used in green building,
remedies the inconvenient of natural and forced
convection systems. It is composed of solar chimney
and earth-air heat exchanger which is characterized by
its simplicity and high removed heat rate [7-10]. In
addition, it has low electricity consumption, so it is very
convenient in remote area where photovoltaic is used to
provide shelter [11]. The present paper investigates the
possibility of using solar chimney and earth-air heat
exchanger system to cool mobile telephone BTS in the
neighboring of Ouargla city (south of Algeria).
North face
V
Fig. 1: Computational domain
2.2 Governing equations
Air flow across the shelter is carried by both air input
velocity and the temperature gradients. Heat and mass
transfer are then partly due to natural convection and
forced convection. In this work, we consider the
laminar regime, air as Newtonian fluid and neglecting
viscous dissipation. Internal gain is assumed as heat
flow at bottom shelter border. The phenomenon is
governed by the conservation equations (mass,
momentum and thermal energy) which are respectively
written in condensed form as follows [10]:
2 Mathematical model
2.1 Computational domain
Fig. 1 shows the base case computational domain which
is assumed as bi-dimensional, it includes shelter and
solar chimney placed on the south side at an angle α
equal to Latitude. For the Earth-air heat exchanger is
taken only as shelter inlet boundary condition. The size
of solar chimney is similar to that adopted by Z.
Akchiche [10]. The shelter mesh consists of (240 × 225)
and the chimney as (120 × 60).
With: ρ density (kg/m3), μ cinematic viscosity
(kg/m.s), cp calorific capacity (J/𝑘𝑔.𝐾), λ thermal
conductivity J/m2.
Natural convection effect is considered in the
momentum equation by varying the density expressed
according to thermodynamic reference state (density ρ0
and temperature T0) by the Boussinesq approximation
as follows:
ISBN: 978-960-474-358-2
135
Recent Advances in Energy, Environment, Biology and Ecology
With β is the isobaric expansion coefficient of the
fluid:
The flow in the Earth-air exchanger is similar to flow in
circular pipe; it is governed by the conservation
equations (continuity, momentum, energy). In order to
simplify calculation, we consider only velocity and
temperature at the exchanger outlet as shelter input
conditions.
2 Numerical procedures
Fig. 2: Shelter indoor temperatures along year 2013
The shelter energy audit without cooling system is
simulated by Trnsys 16 software. In order to fix the
boundary conditions, this software simulation is used to
determine shelter indoor temperature (lateral walls and
zone) for the worst state which reaches the highest
temperature.
3.2 Effect of Earth-air heat exchanger
For shelter with passive cooling system, Fluent software
is used to plot shelter indoor temperature contours. Fig.
3 shows that temperature remains high in whole zone its
maximum fall is not greater than 2 °C, this is due to the
lack of pushing system to facilitate the passage of air
flow within Shelter. So, at shelter inlet, natural
convection does not give a significant result for passive
system. In Fig. 4, we see that the temperature in the
zone records a significant fall. This shows that the flow
with 0.009 m/s and temperature at 15°C caused by
earth-air heat exchanger at shelter inlet gives a positive
effect on improving cooling.
By introducing the passive cooling system, the
governing equations of flow across the shelter are
solved by using a general-purpose CFD code (Fluent
6.3). Upwind scheme is chosen for numerical
discritization and coupling betweens velocity field and
pressure is insured by the SIMPLE algorithm [12].
Under relaxation is activated to accelerate convergence
up to reaching steady state at 10-6 as residual error.
3 Results and discussions
3.1 Indoor temperature of shelter
For shelter without cooling system, Trnsys software is
used to plot shelter indoor temperature curves at
instantaneous state along the year. Fig.2.illustrates
temperature curves of lateral walls and zone which
shows that the worst case occurs in the day of
21/07/2013. The high indoor temperature reaches 83 °C
which is taken as boundary conditions on the lateral
walls.
Fig. 3: Temperature contours for shelter without EAHE
ISBN: 978-960-474-358-2
136
Recent Advances in Energy, Environment, Biology and Ecology
Fig. 5: Temperature contours for shelter with EAHE,
V=0.1 m/s, OS=0.4m
Fig. 4: Temperature contours for shelter with EAHE,
V=0.009 m/s, OS=0.25m
3.3 Effect of flow rate and velocity
4 Conclusion
Fig. 4 shows that the temperature in the zone reported a
very significant drop. This shows that increased flow by
increasing the inlet open space at the shelter and the
solar chimney have a positive effect on improving
cooling.
A passive cooling system incorporating solar chimney
and earth-air heat exchanger system for cooling
telecommunication enclosures is viable and reliable for
shelters installed in desert and tropical regions. It
requires less power; therefore it is a highly efficient
system for remote areas where there is no power grid
and the maintenance is minimal. In addition, it is a low
cost cooling system and eco-friendly.
Temperature in the middle of the shelter does not
exceed 29 °C. It indicates that we can design a shelter
without conventional air conditioning with condition
that we use batteries operating at temperatures up to 29
°C.
For future work, we plan to integrate other techniques
to further reduce of temperature. It consists by
combining the present cooling system with vertical
chimneys placed on the outer sides of the shelter lateral
walls to minimize external gains of sun radiations.
Fig. 5, there is a marked improvement in cooling covers
almost any shelter space. This is explained by the effect
of the flow rate increase by the simultaneous increase in
the velocity and the open space (OS) at shelter inlet to
reach respectively V=0.1 m/s and OS=0.4 m.
Temperature in the middle of the shelter does not
exceed 29 °C. It indicates that we can design a shelter
without conventional air conditioning with condition
that we use batteries operating at temperatures up to 29
°C because the batteries currently used on the site are
designed to a maximum temperature of 25 °C.
References :
[1]
K.R. Kirchartz, H. Oertel, Three dimensional
cellular convection in rectangular boxes, Journal of
Fluid Mechanics 192 (1998), pp. 249–286.
[2] T. Fusegi, et al., Transient 3-D natural convection
in a differentially heated cubical enclosure, in:
Proc. ASME/JSME Thermal Engineering Conf,
Nevada, 1991, pp. 83–88.
[3]
ISBN: 978-960-474-358-2
137
S.B. Sathe, Y. Joshi, Natural convection liquid
cooling of a substrate mounted protrusion in a
Recent Advances in Energy, Environment, Biology and Ecology
square enclosure: a parametric study, Journal of
Heat Transfer 114 (1992), pp. 401–409
[4]
C.W. Argento, et al., Forced convection air
cooling of a commercial electronic chassis: a
experimental and computational case study, IEEE
Transactions on Components Packaging and
Manufacturing Technology Part A 19 (2) (1996),
pp. 248–257.
[5] A. Shanmuga Sundaram, R.V. Seeniraj, R. Velraj,
An experimental investigation on passive cooling
system comprising phase change material and twophase closed thermosyphon for telecom shelters in
tropical and desert regions, Energy and Buildings
42 (2010),pp. 1726–1735
[6]
Ahmadou Samba, Hasna Louahlia-Gualous ,
Stéphane Le Masson b, David Nörterhäuser, Twophase thermosyphon loop for cooling outdoor
telecommunication equipments, Applied Thermal
Engineering 50 (2013) ,pp.1351-1360
[7]
Akchiche Zineb, Étude de comportement d’une
cheminée solaire en vue de l’isolation thermique,
Magister thesis in energetic and process, university
of Ouargla Algeria, 2011.
[8]
M. Maerefat, A.P. Haghighi, Passive cooling of
buildings by using integrated earth to air heat
exchanger and solar chimney, Renewable Energy
35 (2010), pp. 2316-2324.
[9] Ramadan Bassiouny, Nader S.A. Korah, Effect of
solar chimney inclination angle on space flow
pattern and ventilation rate, Energy and Buildings
41 (2009), pp. 190–196.
[10] Alemu T. Alemu, Wasim Saman, Martin Belusko,
A model for integrating passive and low energy
airflow components into low rise buildings, Energy
and Buildings 49 (2012), pp. 148–157.
[11]
Pragya Nema, R.K. Nemab, Saroj Rangnekar,
Minimization of green house gases emission by
using hybrid energy system for telephony base
station site application, Renewable and Sustainable
Energy Reviews 14 (2010), pp. 1635–1639.
[12]
Patankar Suhas. Numerical heat transfer and fluid
flow. Washington D.C: Hemisphere; 1980.
ISBN: 978-960-474-358-2
138
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertising