ISSN 2319-8885
Vol.03,Issue.04,
March-2014,
Pages:0544-0549
www.semargroup.org,
www.ijsetr.com
Effect of Successive Cloudy Days on Operating the Solar Space Heating System
using Evacuated Tubes Solar Collector in Baghdad-Iraq Climate
AED IBRAHIM OWAID1, MOHAMMAD TARIQ2, FALAH. I. MUSTAFA3, KHALIL ALWAN4, TARIK YASSIN5
1
Solar Research Center, Renewable Energy Directorate, Ministry of Science and Technology, Republic of Iraq,
Email: [email protected].
2
Dept of Mechanical Engineering, SSET, SHIATS-DU, Allahabad, India.
3
Solar Research Center, Renewable Energy Directorate, Ministry of Science and Technology, Republic of Iraq.
4
Solar Research Center, Renewable Energy Directorate, Ministry of Science and Technology, Republic of Iraq.
5
Solar Research Center, Renewable Energy Directorate, Ministry of Science and Technology, Republic of Iraq.
Abstract: In this paper, the effect of successive cloudy days on operate solar space heating system using evacuated tube solar
collector is tested. The system is designed and constructed for heating of a meetings hall by area 47.5 m2 for a period of six
hours in Iraq under the ministry of science and technology because of acute shortage of electric power, especially the energy
consumed for heating in winter in the official working hours for government departments and the private sectors .In this paper
we have tested effecting of the serialized cloudy days on operate the system through the little solar radiation that received by
evacuated tube solar collector in cloudy days..
Keywords: Cloudy Days, Evacuated Tube Collector, Thermal Radiator, Solar Energy, Solar Space Heating.
I. INTRODUCTION
The sun is a source of nearly all forms of energy on the
earth .Our earth receives a continuous stream of energy
from the sun. On a clear day, the earth receives 1 kw/m2,
when overhead a clear day of solar energy for a few hours
per day. Perhaps 4 to 8 kwh/m2 /day can be collected [1].
The environmental pollution and the energy crisis have
brought serious problems to the world environment and
sustainable development. The applications of solar energy to
electricity generation and heat collection/refrigeration
become important, and have received considerable attention
[2–9]. When dealing with solar energy, there are two basic
choices. The first is photovoltaic, which is direct energy
conversion that converts solar radiation to electricity. The
second is solar thermal, in which the solar radiation is used
to provide heat to a thermodynamic system, thus creating
mechanical energy that can be converted to electricity. In
commercially available photovoltaic systems, efficiencies
are on the order of 10 to 15 percent, where in a solar thermal
system, efficiencies as high as 30 percent are achievable
[10] to replace fossil fuel usage as much as possible with
environmentally friendly, clean, and renewable energy
sources. Among these sources, solar energy comes at the top
of the list due to its abundance and more even distribution in
nature than other types of renewable energy such as wind,
geothermal, hydropower, biomass, wave, and tidal energy
sources [11]. As solar energy is dispersed form of energy,
an effective method of collection is very important. The flat
plate collector is the simplest and one of the cheapest means
of collecting solar energy for use in system that require
thermal energy at low temperatures (< 100°C). It is well
known that Evacuating Tube Collector (ETC) permit the
use of a vacuum of sufficient magnitude about (5×10 –3pa) to
eliminate convection and conduction heat transfer losses.
The vacuum may help to protect a selective surface used on
the absorber against performance degradation over the life
of the collector. In addition, these collectors generally
require a minimum amount of material per square meter of
collector and thus provide for the possibility of lower costs.
These evacuated tubes collectors perform well in both direct
and diffuse solar radiation and offer the advantage that they
work efficiently with high absorber temperatures [12].
The evacuated tube solar collectors perform better in
comparison to flat plate solar collectors, in particular for
high temperature operations. However, previously, it
provided no real competition for flat plate solar collectors,
because of difficulties in manufacturing and maintenance of
the metal-to-glass vacuum seal. One of the most significant
developments is the use of double-glass evacuated tubular
solar water heaters, which now comprise 65% of 6 million
m2 / year solar collector market in China. The mechanism of
this type of solar water heater is driven by natural
circulation of the fluid in the collector and the storage tank.
It consists of all-glass vacuum tubes, inserted directly into a
storage tank, with water in direct contact with the absorber
surface. The limitation of this concept is that it can only be
used for a low-pressure system, as the tubes can only
Copyright @ 2014 SEMAR GROUPS TECHNICAL SOCIETY. All rights reserved.
AED IBRAHIM OWAID, MOHAMMAD TARIQ, FALAH. I. MUSTAFA, KHALIL ALWAN, TARIK YASSIN
withstand a few meters of water head.
II. COMPONENTS OF HEATING SYSTEM
The system components are cleared as shown in figure1.
Where the system consist of two solar heaters from the type
– Evacuated tube – with (32) tubes and storage capacity of
(263) liter for each heater, two solar panels with power (80
watt), solar charger (solar charger rating 12 v d.c /14 amp),
battery type (Deep cycle 200 amp. h), electrical reflector,
compensation water tank with capacity (1000) liter,
conducting water tubes type (1/2” C.P.V.C SCH 80),
(Chlorinated Polyvinyl Chloride), circulating pump with
(100 watt) power. Two thermal radiators, control unit
consists of two parts, the first is fixed within the space
which is responsible for measuring and control the space
temperature, and the second to be fixed on the solar heater
to measure the internal temperature for hot water of the
storage tank solar heater [14].
Vacuum: The vacuum between inner glass (absorber tube)
and outer glass tube ensures optimum heat insulation;
convection and conduction losses are eliminated. This
enables the vacuum tube collector to make use of the solar
radiation, regardless of low ambient air temperature range.
Figure 2: The evacuated tube collector, [15].
B. Thermal Radiator
As shown in figure 3, hot-water radiator consists of a
sealed hollow metal container (cast iron) filled with hot
water by a pressure pump. As it gives out heat, the hot water
cools and down to the bottom of the radiator and is forced
out of a pipe at the other end.
Figure 1: Meetings hall with components of the heating
system [14].
A. Evacuated Tube Collector (ETC)
The part receiving the solar radiation and convert it to the
heat and transferring it into the solar system figure 2 is
called the vacuum tube itself is an enclosed, separate, small
heat system [13] it consists following components:
Glass Tube: Glass tube is made of a strong borosilicate
glass, high quality tempered glass that can sustain even a
very high impact.
Absorber: Active area of the solar collector, which absorbs
the solar radiation and converts it to heat and then
transforms it into water inside tube. Thus it is the most
important part of the collector. It is selectively coated with a
long lasting aluminum nitride layer so it absorbs the arriving
solar radiation almost completely (>92%).
Figure 3: Thermal radiators
C. Circulating Pump
Water pump centrifugal three-Quicken installed on the
base in the roof of the building under the geyser solar it drag
a water recurrent is of radiators inside the building via
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.04, April-2014, Pages: 0544-0549
Effect of Successive Cloudy Days on Operating the Solar Space Heating System using Evacuated Tubes Solar Collector in
Baghdad-Iraq Climate
plastic tubing thermal thermoplastic pipe type CPVC
(Chlorinated polyvinyl chloride) to reservoirs hot water for
both solar water heaters, installed on the roof of the building
which is the following specifications pump power
(100watt), flow rate of pump (0.11 litter/sec).
Figure 5: Recording device and store temperature data
Figure 4: Thermal circulating water pump
III. MEASURING AND RECORDING DEVICES
A. Thermocouples
Thermocouples are used to measure temperatures at
several locations in the system as shown in figures 5, 6, 7
according to their purpose:
 Three thermocouples type K (1, 2, 3) to measure the
inlet and outlet temperatures of water in the tank and
ambient with measuring range (– 50 to 150oC).
 Three thermocouples type K (4, 5, 6) to measure the
temperature of entry and exit of water to and from the
space and inner space temperature.
The thermocouples are connected to electrical digital
reader. The thermocouples were calibrated according to the
company that manufactured these thermocouples and the
errors are found to be 0.4oC for K-type.
Figure 6: Positions of thermocouples, data logger and
solar meter [14].
B. Recording Device and Store temperature Data
 Accurately measures 12 channels of temperature
independently
 Records data onto an SD card in Excel format for easy
transfer to a PC for analysis
 Data logging capability up to 20,000 records using a
2G SD card
 Manual store and recall of up to 99 records
The 12-channel meter has automatic temperature
compensation and is designed to work with the six most
popular thermocouple types: J, K, T, E, S, and R. Data
logging capability up to 20,000 records using a 2G SD card,
with user-programmable sampling rate from one second up
to one hour. Data is recorded onto a standard SD memory
card instead of a built-in memory, offering unlimited data
storage. The removable SD card is easy to transport and
Figure 7: Pictures of thermocouples, data logger and
solar meter during the data recording.
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.04, April-2014, Pages: 0544-0549
AED IBRAHIM OWAID, MOHAMMAD TARIQ, FALAH. I. MUSTAFA, KHALIL ALWAN, TARIK YASSIN
insert into a computer’s memory card slot or SD card reader
for upload. Data is provided in Excel, allowing you to easily
analyze the information without the need for additional
software. Data can also be streamed directly to a computer
using the RS-232 port on the meter.
IV. THE OPERATING PROCEDURE OF THE
SYSTEM
The operating the system thereby the control unit which
run the circulating pump in case of existence of two
conditions , as shown in the figure 8 and 9 the first is the
temperature of the space must be less than (22 oC) and the
other is the inlet temperature of the hot water in the middle
of solar collectors storage tanks must be more than (40oC),
where the system working continuous till the space
temperature becomes (22oC), it
Figure 8: Picture of solar water heaters installed on the
roof of the building [14].
Figure 9: Image hall meetings after the construction of
the system [14].
will stop then it will work when the temperature decrease
and become less than (22oC) and so on depending on the
control unit [14].
V. RESULTS AND DISCUSSION
The system operated in the cloudy and partial cloudy
days, we observed that the system worked for six hours with
keeping the required space temperature (22ºC) for the first
cloudy day on 30.01.2012, depending on the energy stored
from the previous day as shown in figure 10, that represents
the relation between the entry temperature (T i) for the hot
water to the hall, the exit temperature (T o) for the water
from the hall, the hall temperature (T r) and the ambient
Figure 10: Temperatures scheme of the system for a day
30.01.2012.
Figure 11: Temperatures scheme of the system for a day
31.01.2012.
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.04, April-2014, Pages: 0544-0549
Effect of Successive Cloudy Days on Operating the Solar Space Heating System using Evacuated Tubes Solar Collector in
Baghdad-Iraq Climate
temperature (Ta) versus the local time. As for the next
cloudy day we observed from the figure11, that the system
worked six hours without reaching the required space
temperature (22ºC) because of the decreasing of the water
temperature in the solar heater storage tanks because of the
decreasing in the solar radiation rate from the previous day
(i.e. little energy gained) that were lead to never rise the
water temperature in the solar heater tanks , so the lost
energy in the space which resulted from the decreased
temperature rate is not enough to rise the space temperature
to the required temperature.
The operating of the system for the next sunny day on
02.02.2012 as shown in the figure 13, the energy gained
from the solar radiation started to rise the hot water
temperature in the storage tanks gradually and the system
doesn’t work at the first morning hours due to the
decreasing of the hot water temperature in the storage tanks
and due to the decreasing of solar radiation rate on the
previous day and the heat lost at the night , the system
started the operating at half past eleven o’clock after the
energy accumulation and when the hot water temperature in
the tanks became lager than the calibrated hot water
temperature , the system operating continued till the official
work end at 2 pm o’clock but without reaching the required
space temperature.
Figure 12: Temperatures scheme of the system for a day
01.02.2012.
The continued operation of the system for the next day
cloudy to partial cloudy day on 01.02.2012, and through the
figure 12 has observed that the system worked sporadically
and for varying periods, where it works when the hot water
temperature becomes more than the calibrated hot water
temperature in the storage tanks and this happens when the
high rate of solar radiation. The system stop working at low
temperature hot water in the storage tank and this because
the energy lost from the space is more than the energy
gained from the solar radiation and it was due to
disappearance of the sun because the air partially cloudy .
after the 12 o’clock at noon has observed that the system
continuous to work to the end of the official working hours
because the air become sunny , the energy gained from the
solar radiation was more than the energy lost from the space
and this leads to the increasing of the hot water temperature
in the tanks more than the calibrated temperature and thus
the continuation of the work of system without interruption
but the energy resulted from the temperature difference not
enough to raise the space temperature to the required
temperature.
Figure 13 Temperatures scheme of the system for a day
02.02.2012.
VI. CONCLUSION
The system have operated normal work in the first
cloudy day by the stored energy from the solar radiation
from the previous day, but it was effected in the second
cloudy day on the work where the control unit operated the
system at that day without reaching the temperature of the
hall to the desirable temperature (22oC), because there is
little energy gained from solar radiation in the first cloudy
day.
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International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.04, April-2014, Pages: 0544-0549