MIT International Journal of Mechanical Engineering, Vol. 4, No. 1, January 2014, pp. 54–57
ISSN 2230-7680 © MIT Publications
54
Performance Testing Methodology of a
Hybrid Solar Water Heater-cum-room
Lighting Room Heater
Vishal Bhasin
Faculty Department of Mechanical Engineering
K.I.M.T., Moradabad, U.P. INDIA
Email: vishalbhasin02@gmail.com
ABSTRACT
A multipurpose hybrid solar water heater and room heater cum room lighting system have been designed and fabricated. The
present system is not only provided the continuous hot water supply round the year but in winters it is feasible for space heating
with good lighting around the place of installation (a room of 8 ×10 m2 approximately). In the present article the methodology
for the performance evaluation of hybrid solar water heater and room heater cum room lighting system has been discussed with
the design of the system. The system simply deals with a solar parabolic concentrator, a water storage tank with a capacity of 50
liters, and a rectangular loop of aluminium pipe. Besides this, some additional benefits are presented over the designs of solar
hybrid systems used for water and space heating.
Keywords: Solar water heater, parabolic concentrator, space heating, lighting.
I. INTRODUCTION
There are various hybrid systems which perform for water
heating and space heating individually. Solar water heating
system (SWH) is renewable energy technology and has been
used in numerous countries of the world. Solar heater is a device
which is used for heating the water, for producing steam for
domestic and industrial purposes by utilizing the solar energy.
Solar energy is the energy which is coming from the sun in the
form of solar radiations, when these solar radiations falls on
absorbing surface, then they gets converted into the heat, this
heat is used for heating the water. This energy is absolutely free
and the supply is unlimited in the day whenever there is sunlight.
Hot water is important for bathing and for washing, utensils
and other domestic purpose in urban as well as in country areas.
Solar Water Heaters (SWHs) of 100-300 liters capacity are suited
for domestic use and easily heated water to a temperature of 6080°C. A 100 liters capacity SWH can replace an electric geyser
for residential use and may save approximately 1500 units of
electricity annually. The use of 1000 SWHs of 100 liters capacity
each can contribute to a peak load saving of approximately 1
MW. A SWH of 100 liters capacity can prevent the emission of
1.5 tonnes of carbon dioxide per year [1]. The efficiency of
solar thermal conversion is around 70% when compared to solar
electrical direct conversion system which has an efficiency of
only 17% [2]. K.S. Ong et al., reports the result of outdoor tests
conducted on natural and forced convection heat pipe solar water
heating systems. The natural convection system performed better
than the forced convection system and is cheaper [3].
A. Solar Hybrid System
The solar hybrid system is the system that converts solar
radiations coming from the sun into thermal energy and
electricity using solar collector and photovoltaic panels
respectively with an advantage of higher overall efficiency. PV
panels are the semiconductor devices with a basic unit of solar
cell can be easily installed for electricity generation and is
available in the market in the form of a group of cells known as
modules. These modules are able to combine to form panel of
any requirement. For hot water requirement it is not practical to
convert solar energy into electrical energy and then into thermal
energy as this reduces the efficiency of a system to the large
amount. Since this solar water heater can easily utilize the solar
energy for hot water requirement with higher efficiency and the
control of the system can be maintained using electricity
available with PV modules. The system which generates
electrical energy as well as thermal energy are known as a hybrid
system. Zhaohui Qi concluded on comparing with traditional
solar powered water heater and cooling machine, the hybrid
system is more suitable for household usage, and the utilization
of solar energy is more effective [4]. Hybrid photovoltaic/thermal
solar systems can simultaneously provide electricity and heat,
achieving a higher conversion rate of the absorbed solar radiation
than standard PV modules [5]. R.Z. Wang et al stated that the
MIT International Journal of Mechanical Engineering, Vol. 4, No. 1, January 2014, pp. 54–57
ISSN 2230-7680 © MIT Publications
hybrid system is capable of heating 60 kg water to about 90 °C
as well as producing ice at 10 kg per day with a 2m2 solar
collector.[6]
B. Solar Water Heaters
Solar water heaters use the sun to heat either water or a heattransfer fluid such as a water-glycol antifreeze mixture in
collectors generally mounted on a roof. Performance varies
depending on how much solar energy is available at the site,
and on how cold the water temperature is coming into the
system [7].
There are various types of SWH and it can be classified into
various categories as shown below:
Fig. 2. Classification of SWH
Passive solar water heaters are typically thermosyphon systems
based on gravity. The chief advantage of these systems is that
they don't need controls, pumps, sensors, or other mechanical
parts, so maintenance requirements are minimal. Active solar
water heaters use pumps to circulate water or some other fluid
from the collectors, where the water is heated by the sun, to the
storage tank. Active systems fall into two general groups: indirect
systems, which use a fluid with a low freezing point (such as
propylene glycol) in the collector loop, and direct systems, which
use water in the loop. Direct SWH is also known as open loop
SWH as the regular fresh water supply is needed for the operation
of SWH [8]. In a forced circulation electric fluid pump is
generally used for the circulation of fluid in the circuit for
effective heating in solar water heating.
Flat plate collectors consist an array of metal pipes having a
property to absorb solar radiations which are most widely used
in SWH [1].
Fig. 2. ETC Solar water heater installation
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To reduce the collector losses ETC type SWH are used which
are made of double layer glass tubes evacuated for providing
insulation. The collector is made of double layer borosilicate
glass tubes evacuated for providing insulation. Nowadays
various types of CPC are in the market and few of the collectors
in this category are parabolic trough, compound parabolic
concentrator, parabolic dish, and cylindrical parabolic
concentrator etc. Batch collectors are used as solar water heaters
in which a storage tank is placed in an insulated plywood box
having a glazed glass plate at an inclination of 200C towards
south.
C. Space Heating
Solar space heating systems can be either active or passive.
Passive systems use building components such as floors, walls,
and sun spaces to collect and store heat. Active space heating
systems are based on hardware such as rooftop collectors to
collect and distribute heat. They use air or a liquid that is heated
in the solar collectors and then transported by small electric
fans or pumps or by thermosyphon effects, to storage. Solar
heat is stored in water tanks or rock bins to provide heat during
sunless periods. A common heat delivery system also can be
used when adding active space heating to an existing house.
But in all cases, the backup heating system should be capable
of supplying 100% of the home.s heating requirements for
periods of cloudy weather when the less solar heat is available.
Active solar space heating, while commercially available for
almost as long, significantly lags behind solar water heating in
the market due to its relatively higher costs as well as special
requirements for utilization [9]. Solar heating systems for
combined domestic hot water preparation and space heating are
similar to solar water heaters in that they use the same collectors
and transport the produced heat to a storage device. Unlike solar
hot water applications, solar space heating cannot be used to
preheat [10].
D. Space Lighting
Solar lighting can be defined as any use of sunlight or sky light
for illuminating the interior of a building. The use of natural
light for illumination in buildings has great potential for energy
conservation. The sun is the source of all daylight illumination
in the form of beam sunlight and diffuse sunlight in the
atmosphere. This solar radiation can be brought directly into
the building as daylight, or it can be converted into electricity
on site with the electricity being converted into electric light
[11]. Solar lighting can be used as standalone street PV lights
as well as the small home lighting system. A solar home lighting
system aims at providing solar electricity for operating lights
and/or fan or energizing a DC operated portable TV set for
speci?ed hours of operation per day. A Solar lantern is a lighting
system consisting of a lamp, battery and electronics, all placed
in a suitable housing, made of metal, plastic or ?ber glass, and a
PV module. The battery is charged by electricity generated
through the PV module. The lantern is basically a portable
lighting device suitable for either indoor or outdoor lighting,
MIT International Journal of Mechanical Engineering, Vol. 4, No. 1, January 2014, pp. 54–57
ISSN 2230-7680 © MIT Publications
covering a full range of 360 degrees. An LED based solar lantern
system aims at providing solar electricity for operating LED
lights for speci?ed hours of operation per day [11].
II. EXPERIMENTAL SETUP
The test was conducted on the roof of mechanical engineering
department building at the Moradabad Institute of Technology,
Moradabad (28051'N, 78049'E), U.P., India. The schematic
diagram of natural circulation direct type hybrid SWH is shown
in Figure 4.
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A. Solar Collector
The Solar collector is the main component of the system which
collects the solar energy in the form of sun rays and transmit the
radiant heat to the working fluid. The system consists of a solar
collector of aluminium frame structure of approx. 100 cm 2
having 10 aluminium pipe of the inner diameter of 9 mm placed
at a distance of 12 cm each. These tubes are placed in parabolic
form having slight angular curvature with a maximum focal
length of approximately 20cm and along with it the structure is
coated with black paint to increase absortivity.
B. Storage Tank
For testing purpose a small storage tank of circular cross section
of vertical type of capacity 50 liters is used. The efficiency of the
system is mostly depends on the type of insulation provided to
the storage tank. It is insulated to reduce heat loss during poor
ambient conditions. The system mounted on a rigid structure and
firmly fixed to the roof to prevent damage in high winds. The
solar collector was connected with the properly insulated storage
tank via PVC pipes in a closed loop and the fluid to be heated
was transferred directly to the solar collectors which then circulates
naturally within the circuit pipes via storage tank i.e. no pump
was installed in the circulation of fluid. The collected hot water
in storage tank can be made available for usage.
C. Instruments Used
Fig. 3: Main components of Hybrid SWH cum room heater
The system comprises of four major components i.e. solar
collector, water storage tank and connecting tubes including
heating element. The detailed specifications are given in the
table below.
Table 1: Specification of the system tested
System Parts
1. Collector
Frame structure
Rectangular loop
Material
Aluminium
Type
Curved
Concentration ratio
2
Aluminium Tubes
10
Nos.,
diameter)
300
120x90 cm
Tilt Angle
Cross Section
2. Storage Tank
Capacity
3. Connecting
Pipes
Material
4.
Specifications
(9
The ambient temperature,inlet temperature and outer temperature
of fluid is measured using a thermocouple meter with an accuracy
of ±1 °C. The aluminium frame is kept at an angle of 300 in
sunlight with its collector facing south. The solar insolation (mW/
cm2) on the horizontal surface can directly measure by a standard
device 'SURYA-MAPI' (CEL-201) with an accuracy of 1 mW/
cm2. The thickness of the pipe and its inner and outer diameter
is measurable by micrometer having an accuracy of 0.01mm.
The flow rate of fluid passing through a solar collector can be
measured by a stop watch and graduated beaker.
III. TESTING METHODOLGY
mm
50 liters
PVC, Aluminium
Diameter
15 mm
Auxiliary Power
Halogen light (300Watt)
The storage tank and working fluid tubes are filled with water
as the working fluid. Due to the absorption of solar radiation
the working fluid which is transmitting through the solar collector
started to get heated. Thus the temperature of the outlet fluid
from the collector was more than inlet fluid to collector. At
equilibrium condition i.e. after maintaining the equal discharge,
the temperatures at the inlet and outlet fluid was measured
alongwith the ambient temperatures at every 30 minute interval.
When the sun rays fall on the solar collector the working fluid
inside it gets heated. This heated water started to move upwards
and thus natural circulation of fluid gets started as thermosyphon
effect and the heated water is collected in the storage tank. The
variation in inlet fluid temperature, outlet fluid temperature, and
ambient temperature thus measured at particular interval of time.
To optimize the cost of SWH two methods are generally used,
one is to install the system of lower capacity of particular
requirements and fulfill the remaining need of hot water using
backup and another method is by providing proper insulation to
MIT International Journal of Mechanical Engineering, Vol. 4, No. 1, January 2014, pp. 54–57
ISSN 2230-7680 © MIT Publications
storage tank so that hot water can be used during night or early
morning. For this an element is placed along with SWH which
can supply additional energy during odd hours and thus collector
efficiency and overall efficiency of the system was measured
by economic analysis. The same element can also be used for
lightening of room and room heating [12].
A. Thermal Performance
It is not easy to determine the hot water needs of a family.
Generally, we estimate the consumption at 50 liters at 50°C per
day per person, but those figures can change by as much as
20% [13]. The daily needs of hot water can also be evaluated
using this formula:
Where, Vp = volume needed per person per day
Np = number of people
Thw= heated water temperature
Tsw = stored water temperature
Tcw = cold water temperature
Consider a family of 4 people having daily water requirement
of 50 LPD. During a winter season inlet water temperature is of
15°C and the hot water requirement is of temperature of 50°C
with a stored water temperature of 70°C. According to above
formula the total hot water requirement is approximately 190
LPD. During the summer season if the inlet water temperature
increases up to 30°C the hot water requirement reduces to 150
LPD using the same formula.
B. Efficiency Calculation
The instantaneous efficiency of the flat plate collector with an
alternative working fluid was calculated using the heat gained
by water with respect to the actual solar energy received by the
flat plate collector.
Heat gained by the water = m Cp T
Input solar energy (solar energy falling on the collector) = IA
The overall efficiency of the system = (heat gained by the water
/input solar energy) = (m Cp T)/ (IA)
Where, m = weight of water (gram), Cp = specific heat of water
(joule/gram °C), T = temperature difference (outlet
temperature-inlet temperature, °C), I= solar insolation (joule/
hour. m2), A = area of the collector (m2)
IV. RESULT DISCUSSION
In typical north Indian weather conditions, on a sunny winter
day, one sq. m. In the collector area can be expected to heat
approximately 50 liters of water by a temperature of 30- 40° C.
Typical flat plate collectors made in the country have an area of
around 2 sq. m and are thus capable of heating around 100 liters
of water in a day and this proportion serves as a benchmark [7].
The thermal performance of Thermosyphon flat plate solar water
57
heating system is investigated and water as a working fluid on
both sunny day and cloudy day. For economical feasibility the
system was installed in a way such that it can be used for other
purposes as the heater element which serves as a backup for the
system during night can also be served as a room heater at the
same time in colder regions and along with it also used as room
lighting. Thus the multi function system will obtain at the same
cost without any degradation of energy.
V. CONCLUSION
Testing methodology and performance of new hybrid solar water
heater were studied in Moradabad, India at 28051'N, 78049'E.
The system consists of parabolic type simple aluminium structure
solar collector of 2.25 m2 which is flexible in nature and can be
installed easily. The overall efficiency of the system can
improved using an electric back up and the hybrid nature of the
system improves its applications by using it as a room heater as
well as for room lighting. In that way the demand of hot water
supply, space heating as well as room lighting can be fulfilled
by using the present system.
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