Труды Всемирного конгресса Международного общества солнечной энергии - 2007. Том 2
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Proceedings of ISES Solar World Congress 2007: Solar Energy and Human Settlement
882
(DAC) of the data-logger is the manipulated variable. This
variable is used to control the output voltage of a Goodwill
Model 3080 series DC power supply. The power supply has
a specially designed interface that is used to control its
output voltage by using another voltage source. In this case,
the remote voltage is supplied by the DC source of the
DAC. The DC power supply is connected to a switching
power controller made of thyristors and a Hioki power
meter which monitors the power. The power controller thus
controls the input power to the electrical hot plate.
Fig. 1: The hardware setup for power control.
2.2 Control Structure
A combined feedforward and feedback structure is
employed to control the input power to the hot plate in
order to simulate the special case of daily incident solar
radiation on a clear day. This is shown in Fig. 2.
Fig. 2: A diagram of a combined feedforward and feedback
control structure.
The incident solar radiation varies according to the
approximation [9]
on
GMT
sin
Δ
πt
II
T
⎛⎞
=
⎜⎟
⎝⎠
(1)
where
I
is the clear day solar radiation,
on
I
is the
solar constant,
t is the time (= 0 for the sunrise hour) and
TΔ is the day length which is given by
TGMTGMTΔ= −
(2)
where
sunset
GMT and
sunrise
GMT are the Greenwich
meridian time at sunset and at sunrise, respectively. To use
Eq. (1) to give the received or required power, a simulated
optical efficiency
sop
η and a simulated capture area
C
A
are incorporated into the relation to yield
sop C on
R
GMT
sin
Δ
t
QηAI
T
π
⎛⎞
=
⎜⎟
⎝⎠
(3)
where
R
Q
is the required power.
The feedforward function that relates the manipulated
voltage to the required power is a third order polynomial
given as
93 72 3
mp R R R
1
4.0 10 2.6 10 1.7 10
6.0 10
VQQQ
−−−
−
=− × + × + ×
+×
(4)
where
V is the manipulated control voltage. Any
difference that may occur between the required power and
the measured power as monitored by the power meter is
eliminated by an integral feedback action. A Visual Basic
computer program was written to implement this control
structure.
2.3 Software Design
It is a requirement that the values of the measured power
and those of the required power are displayed in real time
-
3 SOLAR COLLECTOR TECHNOLOGIES AND SYSTEMS
883
whilst the control algorithm is being implemented. The
software should also facilitate the saving of data for
analysis at a later stage. The software for these
requirements was designed with these considerations in
mind. A flowchart of the process is shown in Fig.3. Fig. 4
shows a screenshot display of the results generated from
the power controller software as it runs in real time. The
figure displays the values of the required and the measured
power both as two text labels and as a graphical picture
box.
3. RESULTS AND DISCUSSION
The power control structure was tested as the heat transfer
fluid was being circulated through a copper spiral coil
absorber in thermal contact with the electrical hot plate.
This was done in order to transfer the energy flux of the
electrical hot plate to the fluid while avoiding damage to
the element of the hot plate during the tests. This was
because the thermostatic control of the hot plate had been
removed to allow for full control of the hot plate by the
power control algorithm. Fig. 5 shows a graph of the
experimental results obtained from the tests that were
carried out on 24
th
February, 2005.
Fig. 3: A diagram showing a flowchart of the mode of
implementation of the power control software.
Fig. 4: A screenshot display of the results from the power control software running in real time.
Proceedings of ISES Solar World Congress 2007: Solar Energy and Human Settlement
884
Fig. 5: Results from the combined feedforward and
feedback tests that were carried out on 24
th
February, 2005.
The duration of the experiment depicted by Fig.5 was
performed for approximately 2 hours from around 11:20
hrs to 13:20 hrs. A peak power of 700 W was obtained at
around 12:20 hrs which is the solar noon in the simulation.
An integral gain of 0.00015 W/Vs was used to eliminate
any offset errors. The plot of Fig. 5 shows that the
measured power of the electrical hot plate follows the
sinusoidal variation of the required power very well.
In order to test the robustness of the power control structure
and to simulate the power on a day with variable radiation
conditions as opposed to a clear day, a random noise function
was added to Eq. (1). It is expected that this function will
introduce a situation of a turbid day such that the incident
radiation is variable. The results obtained from a test carried
out on 28
th
February, 2005 are shown in Fig. 6.
The figure shows that even though the required power was
made to vary randomly as the solar radiation was simulated,
it was tracked fairly satisfactorily by the measured power.
The simulation was performed over a period of 5 hrs from
08:45 hrs to 13:45 hrs. This is because the slowest
simulation speed-up factor of 0.02 was chosen from the
graphical user interface (GUI) of the power controller
software. An upward kink in the power trace at 09:30 hrs
corresponds to a change in the simulated optical efficiency.
This is effected by changing the value in the GUI. The
downward power variations at about 11:15 hrs and 12:30
hrs are due to induced changes in the simulated optical
efficiency.
Fig. 6: Experimental results obtained from the combined
feedforward and feedback structure. The simulated
radiation conditions were made to be variable and
the experiment was carried out on 28
th
February,
2005.
4. CONCLUSIONS
A combined feedforward and feedback structure has been
implemented in Visual Basic to control the power supplied
to an electrical hot plate. The structure facilitated that the
daily variation of solar radiation is followed by the program.
The results show that the measured power follows the
required power obtained from a simplified daily solar
radiation model. Based on this closeness of the two types of
power, it is clear that the control system is working well.
The design can thus be used as cheap solar radiation
simulator for the design of solar concentrators and for
characterizing a TES system when a solar concentrator is
unavailable to capture the solar radiation.
5. REFERENCES
(1) Morrison, G. L., Burdihardjo, I., Behnia, M., 2004.
Water-in-glass evacuated tube solar water heaters.
Solar Energy 76, 135-140.
(2) Smyth, M., Eames, P. C., Norton, B., 2003. Heat
retaining integrated collector/ storage solar water
heaters. Solar Energy 75, 27-34.
(3) Buddhi, D., Sahoo, L. K., 1997. Solar cooker with
latent heat storage: design and experimental testing.
Energy Conversion and Management 38, 493-498.
Power (W)
Time
(
hh:mm
)
Measured Power
Required Power
3 SOLAR COLLECTOR TECHNOLOGIES AND SYSTEMS
885
(4) Ekechukwu, O. V., Ugwuoke, N. T., 2003. Design and
measured performance of a plane augmented box-type
solar energy cooker. Renewable Energy 28, 1935-1952.
(5) Hüseyin Öztürk, H., 2004. Experimental dermination of
energy and exergy efficiencof the solar parabolic
cooker. Solar Energy 77, 67-71.
(6) Sharma, S. D, Iwata, T., Kitano, H., Sagara, K., 2005.
Thermal performance of a solar cooker based on an
evacuated tube solar collector with a PCM storage unit,
Solar Energy 78, 416-426.
(7) Morrison, G. L., Di, J., Mills, D. R., 1993.
Development of a solar thermal cooking system.
School of Physics, University of Sydney, Australia,
Internal Report No. 1993/ FMT/ 1.
(8) Mawire, A., van den Heetkamp, R. R. J., McPherson,
M., Zhandire, E., 2005. Data Acquisition and Control of
a Thermal Energy Storage and Cooking System. In
Proc. of EUROCON 2005, 361-364, Serbia &
Montenegro, Belgrade, November 22-24, 2005.
(9) Chaabene, M., Annabi, M., 1997. A dynamic model for
predicting solar performance and optimum control.
Energy 22, 567-578.
(10) Castro, M. A., 1988. Simulaciόn de Centrales de
Energía Solar. Aplicación a la gestiόn energética, PhD
thesis ESII Madrid, Spain.
(11) Global Environmental Outlook 1, 1997. United
Nations Environmental Programme, Global State of
the Environment Report, Chapter 2: Regional
Perspectives, Oxford University Press, Oxford.
(12) Hewlett Packard, 1997. HP 34970A, Data Acquisition/
Switch Unit User’s Guide. Hewlett Packard Company,
Colorado.
APPLICATION OF SOLAR COMBISYSTEM FOR ARCHITECTURE
Lu Chao, Zhu Dunzhi, Liu Jun
Beijing Solar Energy Research Institute Co.Ltd
No.10 Dayangfang, Beiyuan Road
Beijing 100012, China
appleluchao@sina.com
ABSTRACT
The solar space heating is an important realm of the
renewable energy application in new village construction.
Combined with the biomass fuel and the radiant-floor
heating system, an advanced solar combisystem which
designed for new rural residential building is presented in
this paper. System configuration and work principle are
described; the cost and economic analysis of solar heating
are given. So it provides abundant experience for the
further development of solar space heating technique.
1. INTRODUCTION
With the fast development of the domestic hot water system,
solar space heating technology has been stepped into the
people life and would become one of the development
directions of solar thermal utilization in the future. The
demonstration of the Beijing new village construction is
held by Beijing government. The aim is to develop
folk-custom tour which principal part is countrymen and
construct the new village integrated the inhabitancy,
reception and sightseeing. The item use the solar space
heating technology combined with the biomass to solve the
energy demand of space heating and domestic hot water.
It is meaningful to extend solar combisystem and utilization
of biomass in new village construction. As reproducible
energy, solar energy and biomass is a kind of inexhaustible,
clean energy. It can not only reduce hothouse gas and
contamination made by conventional energy and realize
energy localized and circulation of agriculture castoff, also
change energy configuration and county environment,
which can make the development quickly and improve the
living standard of the people and build a new county.
2. SOLAR COMBISYSTEM
Solar space heating technology is extended on a large scale
in developed counties. 15,360,000m
2
solar collectors, 20%
were used for the solar space heating system, were installed
in Europe and 20-60% of the normal regulations energy
was saved in 2005[2]. The solar space heating system is
approximately increased 120,000 sets every year.
Fig. 1: The building with solar combisystem.
3 SOLAR COLLECTOR TECHNOLOGIES AND SYSTEMS
887
Solar space heating system, a way to provide the energy for
space heating and hot water to residents, is one of the new
technical extensions in solar thermal applications. It is also
called solar combisystem. The system is made up of three
sections: solar collectors, storage tank and consumers.
Differences between solar combisystem and solar domestic
hot water system are as follows. (1) Heating load varies
fluctuantly according to the season temperature; (2) The
temperature difference of water supply and backwater is
great. Moreover, there is obviously contradiction between
solar radiation and heating load. When solar radiation is
higher in May to October, it needn’t any heating load, while
it need lots of heating load in winter or night, there is
seldom solar radiation. So some questions should be think
over such as auxiliary, solar fraction, preventing frostbite or
overheat of the system and design of exchange tank.
3. COST AND ECONOMY ANALYSIS OF SOLAR
COMBISYSTEM
Give an example: solar combisystem in new village
construction. The building area is 175m
2
and the heating
load is 31.6W/m
2
. The flat plate collectors are used for heat
collecting components. We suppose that the average heat
efficiency is 50% in non-heating seasons while 45% in
heating seasons and the domestic hot water is needed
300kg/d in non-heating seasons. So the syatem proceeds
with the different scale, which shown in Table 1, could be
calculated according to the above hypothesis.
It is clear from the above analysis that the project cost is
not direct proportion to the collector area. The system is
much smaller, the cost of the collector is much higher, that
is the heat gain of the same cost is much smaller. The
investment proceeds of the system is increased sharply
when the collector area is increased from 10m
2
to 30m
2
, but
the increasing range is decreased when the collector area is
larger than 30 m
2
According to the investment callback
time, static callback time of solar space heating instead of
electricity or natural gas is much shorter than the life of the
system, while the investment proceeds is higher relatively,
so it is valuable to extend sweepingly. As we all know,
social benefit and economic benefit is the main criterion to
the investment proceeds, thus integrated factors should be
think over before extent some techniques. Much auspice is
needed to be given by all levels government to extend the
solar space heating technology in new village construction.
4. INTRODUCTION OF SOLAR COMBISYSTEM
The work principle flowchart of solar combisystem is
shown as Figure 2. Difference in temperature circulation is
used in the solar collecting system and empty mode is used
to prevent frostbite and overheat. Two temperature sensors
are set at the upper pipe of the collectors and the underside
of the storage tank. The solar circulating pump begins to
work when the difference in temperature of two sensors is
TABLE 1: COST, PROCEEDS YEALY AND INVESTMENT CALLBACK TIME OF SOLAR COMBISYSTEM
Area of solar collectors m
2
10 20 30 40 50
System cost yuan 23000 31000 38000 45000 52000
Valid heat gain yearly MJ 21729 29892 38055 45665 52339
Collector cost per meter square yuan/ m
2
2300 1550 1267 1125 1040
Heat gain per meter square MJ/ m
2
1589 1203 1074 979 916
Heat gain yearly/cost MJ/yuan 0.94 0.96 1.00 1.01 1.01
Proceeds yearly instead of electricity yuan/year 3218 4427 5636 6763 7752
Static callback time instead of electricity year 7.15 7.00 6.74 6.65 6.71
Proceeds yearly instead of natural gas yuan/year 1380 1899 2417 2901 3325
Static callback time instead of natural gas year 16.66 16.32 15.72 15.51 15.64
Note:1)Price of electricity is 0.48yuanˋkwh and the efficiency of the system is 90%;
2)Heat value of natural gas is 35.17MJ/m
and the price is 1.9yuanˋm . The efficiency of the system is 85%.
Proceedings of ISES Solar World Congress 2007: Solar Energy and Human Settlement
888
higher than the upper limit, while the solar circulating
pump stops when the difference in temperature is lower
than the lower limit. The pump stops when temperature of
the collectors reaches the prevent frostbite caution
temperature in winter, thus the water in the solar collectors
flows back to the tank under the gravitation, which could
be empty the collectors and pipes to prevent frostbite.
Similar, the pump stops and the water in the collectors
flows back to the tank, once the temperature of tank is
higher than the initial highest temperature. So the system
could be empty and prevent overheat because the solar heat
cannot be sent to the system and the solar collectors
temperature will reach at stagnation temperature. Besides,
the pump connects with the manual switch, so the
consumer could stop the solar system according to the
demand of the hot water.
1üsolar collectors 2übiomass boiler
3üthe heat water storage tank 4üthe domestic hot water tank
5üdomestic hot water 6üradiant-floor heating system
7üsolar circulating pump 8ücirculating pump of radiant-floor
9üautomatic exhaust valve 10üvalve
11üball cock 12üelectric auxiliary
Fig. 2: Sketch map of solar combisystems.
The multiple tank used in the system is quite special. The
closed domestic hot water tank is nested in the open heat
water storage tank to compose the sleeved heat exchange.
The heat water storage tank, designed to the open mode, is
suit for the empty mode system and make the system
configuration simple and the cost low. The closed domestic
hot water tank exchange the heat through the tank surface
and the shower water is provided by the pressure of the
water supply net. Water quality of the domestic hot water is
ensured because the tank is the porcelain enamel tank and
is separated from the solar collecting and space heating
system. Meantime, the capacity heat exchange is used to
ensure the demand of hot water when the temperature of
the heat storage tank is low and enhance the ability of
providing hot water. So the multiple tank could increase
the quantity of providing domestic hot water remarkably.
Furthermore, the solar collecting system and the solar
space heating system are all direct system without
exchange equipment, which could decrease the work
temperature of the system and increase the solar collecting
efficiency.
Another advantage of the heat water storage tank is vertical
bed inside, which work principle is using the water density
difference in different temperature to produce different
temperature area in the same tank. The solar collectors
connect with the underside of the vertical bed tank, the
space heating system connects with the middle of the tank
and the domestic hot water tank is set in the upper of the
vertical bed tank. The work temperature of the solar
collecting system and the radiant-floor heating system is
lower in the heating season, while the accessorial boiler is
used to ensure the high temperature in the tank top to
provide enough domestic hot water.
The advantage of the radiant-floor heating system is as
follows: (1) The heat comes from the underground, then
transfers to the room and form a comfortable
circumstance; (2) The providing water temperature of the
radiant-floor is low to fit the solar collecting system with
high efficiency; (3) There is a good effect for the
radiant-floor to storage heat to decrease the volume of
the heat water storage tank. Moreover, the space heating
system could be stopped at night in the saving energy
building and the thermal capacity of the ground could
ensure the room temperature.
The biomass boiler is used to be the auxiliary. The biomass
is transformed to the commercial energy though the high
technology, which could not only decrease the villagers
expend on energy but also improve the atmospheric quality
and turn the waste to the useful energy resource. So it is the
highlight to combine the solar combisystems and the
biomass fuel in this demonstration.
To sum up, the system life, maintenance and safety are the
3 SOLAR COLLECTOR TECHNOLOGIES AND SYSTEMS
889
main factors to be though over in the design. It is embodied
as follows: (1)Use the high efficiency solar collectors with
selective coat to achieve high solar fraction; (2)Use the
vertical bed tank to ensure the demand of space heating and
domestic hot water; (3)Use the toughened glass and unitary
absorbed strip and no connection in the collectors, which
ensure the long life of the system; (4)Use the porcelain
enamel tank to keep the domestic hot water quality; (5)Use
the biomass boiler to be the auxiliary.
5. TEST RESULTS OF SOLAR COMBISYSTEM
Though the test from December 2005 to January 2006, it is
shown that the room temperature is over 18 when the ć
providing water temperature of the radiant-floor heating
system is 35̚40 , the room temperature would deć crease
2̚3 when the radiantć -floor heating system stops and the
circumstance temperature is −5 ̚ −9 and the room ć
temperature is 12̚14 in sunshine day while 10ć ̚12 ć
in cloudy day when the auxiliary stops. The whole test
indicates that the solar combisystem with empting the
system and preventing frostbite could work safely in winter,
even power cut accidentally.
6. CONSLUSIONS
(1) The solar space heating technique is mature and will be
applied sweepingly in the future. The technique, combined
with the radiant-floor heating technology, is suit for the low
story building.
(2) Considered the economy, the solar energy is suit to
instead of electricity or oil and the solar combisystem is
suit to use in the large demand of hot water in non-heating
season. Otherwise, the investment proceeds is mainly
embodied on social benefit and environmental benefit.
(3) The solar combisystem, with the biomass fuel, is one of
the good measures to solve the energy using in the village.
7. REFERENCES
(1) Renewable energy sources in figures, Federal Minnistry
for the Environment, Berlin, 2005
(2) Overview 2000, Solar Combisystems, IEA SHC-
TASK26, 2000
A STUDY ON ENERGY GAIN ON EVACUATED COLLECTOR TUBE WITH CYLINDRIC
ABSORBER ON BUILDING SOUTHERN FACADE
Min Zijian
Information Engineering College
Capital Normal University
Beijing 100037, China
Ge Hongchuan
Beijing Eurocon Solar Energy Tech. Co., Ltd.
Beijing 100083, China
Ma Yiqing
Special Education College Of Beijing Union University
Beijing 100025, China
ABSTRACT
According to the Clear-Day Modelˈdaily energy gain and
its annual variation of single evacuated collector tube with
cylindric absorber in three different installation on building
southern facade are studied. The solar energy gain of
vertical installed tube and east-west horizontal installed
tube comparing with local latitude tilted installed tube are
presented. During the summer season the east-west
horizontal installed tube has more solar energy gain than
the vertical installed tube.
1. INTRODUCTION
With increasing application of sun energy collectors that
are southern face or incline southern face on building roofs,
it is important to study the daily energy gain and annual
variation gain of sun energy collector. The investigation is
very useful in the design of buildings and sun energy
collectors. In this paper the daily and annual variation gain
of single vacuum cylindric tube that installed with vertical
or east west horizontal on building southern facade has
been studied, and it compared with the tube witch installed
incline southern face on building.
The daily and annual absorbed energy by full circular
coating integral collector storage evacuated tube (ICSET)
with glass-covered outer diameter of 100mm under specific
conditions are analyzed quantitatively, and the results are
also applicable to analyze others with different dimensions.
2. MODEL AND FORMULAE
In the Ref.[1] paper (He Ge 1997), concepts of solar
irradiance ratio and absorber energy factor on the surface of
evacuated collector tube absorbers are presented
respectively. The distribution of solar irradiance ratio that
varies with incident angles on various points on the surface
of cylindric absorber in a glass-covered tube was measured.
In follows, we only discuss the direct solar irradiance ratio
for simplicity. According to definition, the absorbed energy
factor of an evacuated tubular collector f can be expressed
as follows:
f= ∫ R(γ , ψ )¢( (θ
r
) ds (1)
where R(γ , ψ ) is solar irradiance ratio of one point on the
absorber, ¢(θ
r
) is solar absorptance of coating on the
absorber, and the integral is taken over the lit surface of
whole absorber.
In Ref. [1], the authors have measured solar irradiance ratio
3 SOLAR COLLECTOR TECHNOLOGIES AND SYSTEMS
891
on the absorber surface including various influences, such
as reflection, absorption and transmission of glass covered
tubes as well as repeated reflections between absorber and
glass-covered layer. For convenience of comparison, all the
lit area of the absorber is converted into the diameter of
cylindric absorber in glass tubes with unit length.
The coordinate system for the relative position of the sun to
tilted plane and angles defined in Ref.[2] (Duffie et al 1980)
are adopted in this paper. The clear-day model of radiation
proposed by Jordan (ASHRAE, 1977) is adopted also. On a
clear day, the direct radiation affects the absorbed energy of
evacuated collector tubes (ECT, see Ref.[1]). This model
has a wide available range, it fit suitably with that in low
latitude and somewhat humid regions, but would be
generally 10-20% greater in high latitude and dry regions.
We calculated daily and annual absorbed energy of single
ICSET installed vertical or east-west horizontal southern
facade or southward with the tilted angles same with
northern latitudes at 40° and 50°. The absorbed energy
calculated only for direct radiation when incident angle θ
r
<85° and solar altitude α
s
>0°. The energy obtained by ECT
in unit length at certain time in a day is:
q=I
DN
hf (2)
The daily-absorbed energy of the evacuated tube is:
E =∫ qhd¹ (3)
where ¹ is time angle.
The annual absorbed energy of ECT is the sum of daily-
absorbed energy all the year round.
3. RESULTS AND DISCUSSION
Fig. 1 gives instantaneous energy gain of single evacuated
collector tube(SECT) with cylindric absorber in unit
length in three different installation at north latitude 40e ,
on spring equinox(1-1), summer solstice(1-2), autumnal
equinox(1-3) and winter solstice(1-4) in a year. The
Daily absorbed energy gains and the ratios of south-north
axial installed tube(ns-tube) tilted at 40e, horizontal
installed tube on southern façade(h-tube), vertical
installed tube on southern façade(v-tube) are shown in
table 1 respectively.
1-1 on Spring Equinox
1-2 on Summer Solstice
1-3 on Autumnal Equinox