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
1345
Solar Research Center, Renewable Energy Directorate, Ministry of Science and Technology,
Republic of Iraq
2
Department of mechanical Engineering, SSET, SHIATS-DU, Allahabad, India
E mail1:aed.altaher@yahoo.com
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.
Index Terms— 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,
1
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 withstand a few
meters of water head.
 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.
II. COMPONENTS OF HEATING SYSTEM
The system components are cleared as shown in figure2.
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].
Figure 2 the evacuated tube collector, [15]
2.2 Thermal Radiator
A 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]
2. 1 Evacuated Tube Collector (ETC)
The part receiving the solar radiation and convert it to the
heat and transferring it into the solar system figure 3 is called
the vacuum tube itself is an enclosed, separate, small heat
system [13] it consists following components:
Figure 3 thermal radiators
 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%).
2.3 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 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
2
following specifications pump power (100watt), flow rate of
pump (0.11 litter/sec).
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 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.
Figure 4 thermal circulating water pump
III. MEASURING AND RECORDING DEVICES
3.1 Thermocouples
Thermocouples are used to measure temperatures at several
locations in the system as shown in figure 6, 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.
Figure 6 Positions of thermocouples, data logger and
solar meter [14]
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.
3.2 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
Figure 7 Pictures of thermocouples, data logger and solar
meter during the data recording
IV. THE OPERATING PROCEDURE OF THE
SYSTEM
Figure 5 recording device and store temperature data
The operating the system thereby the control unit which run
the circulating pump in case of existence of two conditions ,
the first is the temperature of the space must be less than
(22oC) 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 will stop then it will
3
work when the temperature decrease and become less than
(22oC) and so on depending on the control unit [14].
Figure 8 Picture of solar water heaters installed on the
roof of the building [14]
Figure 10 Temperatures scheme of the system for a day
30.01.2012
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.
Figure 9 Image hall meetings after the construction of the
system [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 (Tr) and the ambient temperature
(Ta) versus the local time.
Figure 11 Temperatures scheme of the system for a day
31.01.2012
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
4
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.
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.
VII. REFERENCES
[1] Francis de Winter "Solar Water Heating with Backup
Heating a Review" California, fdw@ecotopia.com.(2005).
[2] D. Frier, R.G. Cable "An overview and operation
optimisation of the kramer junction solar electric generating
system " ISES World Congress, Jerusalem (1999) 241–246.
[3] G. Francia " Pilot plants of solar steam generation systems
" Solar Energy 12 (1968) 51–64.
[4] D.R. Mills, G.L. Morrison "Compact linear fresnel
reflector solar thermal power plants " Solar Energy 68 (2000)
263–283.
Figure 12 Temperatures scheme of the system for a day
01.02.2012
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.
[5] M. Romero, M.J. Marcos, F. Baonzas, V. Fernandez "
Distributed Power from Solar Tower Systems: A MIUS
Approach. ISES Solar World Congress, Jerusalem, 1999,
286–295.
[6] P. Schramek, D.R. Mills " Potential of the heliostat field
of a multi tower solar array "Proceedings of the 10th
SolarPACES International Symposium on Solar Thermal
Concentrating Technologies, Sydney,2000, 157–163.
[7] D.Y. Goswami, F. Xu " Analysis of a new thermodynamic
cycle for combined power and cooling using low and mid
temperature solar collectors " J. Solar Energy Eng. 121
(1999) 91–97.
[8] D.Y. Goswami “Engineering of solar photocatalytic
detoxification and disinfection process" Adv. Solar Energy 10
(1995) 165–209.
[9] M.A. Green “Recent development in photovoltaics “Solar
Energy 76 (2004) 3–8.
[10] Geyer, Michael, and Stine, William B., "Power From the
Sun" (Power from the sun.net). J.T. Lyle Center (2001).
[11] Zekai Sen., "Solar Energy Fundamentals and Modeling
Techniques"Springer- Verlag, London Limited (2008).
[12] Salah AA. Masheiti “Modeling of lithium-bromide
(LiBr) chillers and organic Rankin cycle (ORC) powered by
low-temperature geothermal heat source Research" New
Castle University (2009).
Figure 13 Temperatures scheme of the system for a day
02.02.2012
[13] Wladyslaw Szczesny "Evacuated Tube Solar Collectors
Type" from- Website Seido-Manual, vissman’s guidelines,
BTF’S “Solar Patriot Manual”.
5
[14] Aed Ibrahim Owaid et al "Design and performance
Evaluation of a Solar Space Heating System using Evacuated
Tubes solar collector in Baghdad, Iraq climate "International
Journal of Advanced Research in Engineering and
Technology (IJARET), ISSN 0976 –6480(Print), ISSN 0976
– 6499(Online) Volume 5, Issue 3, pp. 115-129, March
(2014).
[15] Hyunjoo Han , Jeong Tai Kim , Hyun Tae Ahn , Sang
Jim Lee., "A Three-dimensional Performance Analysis of
all-Glass Vacuum Tubes with Coaxial Fluid Conduit "
International Communications in Heat and Mass
Transfer.(2008).
6