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IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 04 Issue: 05 | May-2015, Available @ http://www.ijret.org 92
THE DEVELOPMENT OF SOLAR ENERGY-GAS COUPLING SYSTEM
(SCADA) IN BUILDINGS
Xu Hui1
, Cai Yingling2
, Yang Huizhen3
1
College of Mechanical Engineering, Shanghai University of Engineering Science, Shanghai201620, China
2
3
Abstract
The system mainly use wall-mounted gas boiler and give priority in use of solar energy in order to maximize the utilization of
solar resources. The excess heat will be added to domestic water when the heat for floor radiant heating is enough. The PLC of
Siemens is set as slave computer in the monitoring system and it is used to collect thermal parameters such as temperature, flow
rate, etc. by temperature sensors, pressure sensors and flow rate sensors. WinCC is set as the host computer to monitor the
operating conditions of the entire system. Real-time tracing, monitoring and alarming function can be achieved based on the SQL
database, which has realized archive management of the date. The system has been debugged after the whole experiment platform
is completed, and the running state of the system shows that this system has high reliability and good stability.
Keywords: Solar Energy, Gas, PLC, WinCC, Database
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1. INTRODUCTION
Development of renewal energy and clean energy is
becoming an inevitable tendency of energy structure
transform, which is in conformity with China's current
situation. As one of the cleanest energy, solar energy is also
an inexhaustible source. However, the characteristics of
solar energy such as intermittent, instability, low energy flux
density, etc. lead to instability of the solar thermal system.
Wall-mounted gas boiler can very convenient and quickly to
provide hot water for daily life and heating to buildings, but
it’s not only benefit to realize the energy conservation and
environment protection goal but also consume lots of gas by
using wall-mounted gas boiler to heat the building alone.
Coupling the two kinds of clean energy (solar energy and
gas) can learn from each other. And this coupling not only
fully utilized the solar energy but also alleviate the shortage
of the non-renewable gas. Obviously, this method has great
potential for energy saving. The temperature of the fluid is a
critical parameter on the study of the solar energy-gas
coupling system and provides basis for mode switching of
the entire system. The measurement of temperature has
important significance for solar energy-gas coupling
system’s control and operation. Therefore, control method
and application of solar energy-gas coupling system will be
discussed in this paper[1-3]
.
2. OPTIMIZATION DESIGN OF SOLAR
ENERGY-GAS COUPLING SYSTEM
Solar energy-gas coupling system includes four main parts.
It is solar-collector system, auxiliary system of gas, terminal
system of users, monitoring system, respectively. The solar-
collector system is mainly used to collect solar energy and
ensure the system operate safely and normally. Auxiliary
system of gas is mainly used to make up the shortage of
solar energy when the weather is bad or large energy is
needed, and it can supply heating quickly. Terminal system
of users is mainly used to regulate and control the priority
level or complementary of hot water storage tank and gas
water heater. Monitoring system is mainly used to ensure the
whole system can be controlled and measured, and then
regulate and control the flow direction and flow rate of hot
water according to the needs of users. The hardware of the
system is mainly composed by plate solar collector, hot
water storage tank, wall-mounted gas boiler, heating fan coil
unit, three-way valve, pumps, etc[4-5]
.
Based on the previous research and standing on the
“shoulder” of the technology of solar energy storage and gas
application has becoming more and more mature, the solar
energy-gas coupling system was put forward in this article.
The system is different from the single traditional heating
mode or merely simple superposition of two systems. Based
on the data feedback of energy consumption monitoring
system, the water in the hot water storage tank will be
heated according to actual demands of users, based on the
local weather condition and take full advantage of the extra
heat of floor radiant heating which provided by solar energy
and gas, the efficiency of the entire system will be improved
by this way. The system has good practicability and requires
a small initial investment. Traditional heating system has
some shortages such as large area occupied, large amount of
resources consumption, etc. The most important defect in
ground source heat pump (GSHP) is the unbalance load of
summer and winter which lead to the imbalance of ground
temperature-field. According to the coupling system not
only these problems will be solved, but also the usage of
resource will be improved. The system schematic is shown
in figure 1.

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Water tank
Collector
Pump B1
Gas boiler
1 2 3 4 5
Pump B2
Floor radiant heating
Tee value1
Tee value2
1 Heating water inlet
2 Domestic hot water inlet
3 Gas inlet
4 Heating water outlet
5 Domestic hot water outlet
A
B
a
b
Cold water inlet
T1
T2
T4
T5
T6
Fig -1: Schematic diagram of solar energy-gas coupling system
3. DESIGN OF MONITORING SYSTEM
3.1 Regulations of the Solar Energy-gas Coupling
System Control
3.1.1 The Solar-Collector System
The water in the storage tank will be heated by hot water in
the solar-collector system. Temperature difference control
method is adopted in this circulation system. When the
temperature of heat media difference between the inlet
temperature named T1 and outlet temperature named T2 is
larger than 8℃(it can be set at the range of 5-8℃by the
users), the circulation pump (B1) of solar-collector will be
started after 3 minutes to accelerate the process of heat
transfer in order to meet the demands of users. When the
temperature difference is less than 3℃, delay 3 minutes and
then turn off circulation pump (B1) until the temperature
difference is in steady state. Only in this control method, the
frequent start and stop of the B1 pump caused by surge
temperature can be avoided. It’s unnecessary to run the
solar-collector system when the day is a rainy day or it’s a
foggy day. That is because the solar energy in these weather
of less open value for the system in this case. The solar-
collector system also will be turned off to avoid the
irreversible damage to the storage tank caused by excessive
temperature and influence the performance of the system in
late stage if the temperature of T4 is larger than 75℃. The
control flow chart is presented in figure 2.
Collector Water tank
Circulation
pump B1
Heating medium input
Heating medium
output
Fig -2: The flow chart of solar thermal system
3.1.2 The System of Domestic Hot Water
The hot water provided to the users will be offered by the
solar-collector system or the wall-mounted gas boiler
system. The hot water and cold water in the storage tank will
be stratified due to the density difference caused by different
temperature, and the hot water will in the upper of the
storage tank. The tee valve will be turned on in the direction
of (b) and provides domestic hot water to users directly if

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the temperature of T4 is larger than 60℃. However, if the
temperature of T4 is less than 60℃, the tee valve will be
turned on in the direction of (a) and the water in the storage
tank will be delivered to the wall-mounted gas boiler and be
heated, then it will be provided to users as domestic hot
water. There is a supply valve at the bottom of the storage
tank to replenish the water which has been consumed. The
control flow chart is presented in figure 3.
Water tank Tee value Temperature>Default Gas Boiler
Domestic hot water
Hot water N
Y
DHW outlet
Cold water inlet
Fig -3: The flow chart of domestic hot water system
3.1.3 Radiant Floor Heating System
After the water was heated by the wall-mounted gas boiler
and flow into the radiant floor heating system, if the
temperature of outlet water (T6) is larger than the upper
temperature in the storage tank (T4), it is worth recycling
the heat of return water. At this time, the tee valve will be
turned on in the direction of (B) and the water will flow into
the exchange coil to heat the water in the storage tank. This
heat recycle method can maximize the utilization of the heat.
However, if T6 is less than T4, the tee valve will be turned
on in the direction of (A) and the heat of return water will
flow into the wall-mounted gas boiler to be heated, and then
go to next cycle.
Gas boiler Pipe coiler
Heating return water
temperature>Water
tank outlet
temperature
Water tank
N
Y
Heating water
outlet
Tee value
Improve the water temperature by water tank
Fig -4: The flow chart of gas heating hot water system
2.2 Design of Controlling Software
Design of software for the slave computer is based on the
S7-200 of Siemens. The corresponding programs have been
completed by programming software of Siemens (STEP 7-
Micro/Win V4.0). There is variety of peripheral modules of
S7-200 of Siemens and these modules can combine lots of
controlling systems flexibility which can complete all
requirements. For example, this system is combined with
three EM231 RTD modules and one EM231 analog input
module. It is easily to maintain these kinds of system, and
these systems also have self-diagnosis function and can
monitor themselves very well. The working state for the
inner element of the system can be monitored by the
programs that have been written. The fault location can be
found easily and solved by this function coupling with the
targeted programs and its self-diagnosis function. The
maintenance time will be shortened and the maintenance
cost of the system will be cast[6]
. The structure control chart
of the system is presented in figure 4.

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The control procedure written by PLC has two control
mode, which is automatic model and manual mode. When
the automatic model is started, the circulation pump of solar-
collector (B1) and the circulation pump (B2) of domestic hot
water will be turned on and the tee valve 1/2 will be turned
on in the direction of (B/b) at the same moment to promote
the water in this loop heating system circulate. Three
minutes later, whether turn on or not the B1 pump is decided
by the temperature difference between outlet temperature of
solar-collector and the average temperature of the storage
tank, the start-stop type of domestic hot water will be
decided by the users’ demands, and the direction of the tee
valve is decided according to the temperature. When the
manual model is started, the start-stop type of pump B1 and
B2 and the direction of the tee valve are decided according
to users’ demands. Manual model is set to ensure users can
control avoided the problem that there is something wrong
with the automatic model.
Demand side of domestic
hot water
Demand side of heating
hot water
Water tank
Solar
energy
Gas
Residual
heating
Temperature difference control
Tee control
Monitoring and
control
Fig -5: Schematic diagram of the structure control of system
3.3 Design of Monitoring Software
The host computer monitoring system adopted in this system
(HMI）is developed by the configuration software
(SIMATIC WinCC7.0) of Siemens, and the data archiving is
completed by the normal database of Microsoft SQL Server
2000. This software also has the function of a Web browser
which can realize remote monitor and adjust the real-time
dynamic picture function. The software can communicate
with the slave computer by OPC (OLE for Process Control).
Main functions of this testing system will be described in the
following chapters.
(1) The simulation of the solar energy-gas coupling system:
the design of the interface for the solar energy-gas coupling
system will bring the workflow more intuitive to present in
front of the users. It includes circulation circuit of heating
collection, circulation circuit of the radiant floor heating and
circulation circuit of domestic hot water. This paper has
developed dynamic results of the critical parts for coupling
heating system with WinCC7.0, according to technological
requirements and simulates the real-time working state of
the entire system.
(2) Standardize the image design: automatic model and
manual mode have been designed according to design
principles and unprofessional user’s demands. The interface
of functional modules is very clear and the buttons is few. It
can reduce the invalid operation, disoperation etc. to ensure
the system operate security and stability. Monitor the key
variables such as temperature and pressure on-line and alarm
in time by the built-in alarming function of WinCC. The
configuration software will alarm and the B1 circulation
pump will be forced to turn off when the export temperature
of solar-collector is larger than 95℃or less than 5℃.

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(3) The Monitor Interface is Presented As Follows
Fig -6: Monitoring interface
3.4 Framework of the Monitoring System
The host computer collects the real time date from PLC in
this system. The monitoring system mainly includes
graphical interface, parameters detection interface, process
control and corresponding security mechanism. The
structure diagram for the monitoring system is shown in
figure 7.
Fig -7: The structure of monitoring system

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4. THE DESIGN OF SIGNAL SYSTEM AND
COMMUNICATION SYSTEM
Communication in this monitoring system is mainly
composed of two kinds: communicate between the
configuration software of WinCC and database;
communicate between the configuration software of WinCC
and the slave computer (PLC). However, WinCC cannot
communicate with PLC directly, the communication can be
achieved with OPC. Through connection the configuration
software of WinCC and database, WinCC will read directly
the date collected by the slave computer to the database, and
it is convenient to store and access to the data.
It’s necessary to build a communication between external
variables and the database when WinCC communicates with
the date. The external variables in this system mainly
include the import and export temperature of the solar-
collector, the import and export temperature of the heat
medium, the import and export temperature of gas, the flow
rate of the solar-collector, etc. We need to import external
variables into the software of PC ACCESS to ensure both
can communicate normally when WinCC communicating
with PLC. And the PPI communication protocol is used
between PLC and IPC, 9600 baud rate, RS232
communication mode, the local address 2, serial port address
COM2, data bit 8, stop bit 1, the rest is set to default setting.
5. EXPERIMENT MEASUREMENTS AND
ANALYSIS
Start the software of PLC, and load the relevant program in
the CPU of PLC after completing the preliminary inspection
work of solar energy-gas coupling system. Then start the
configuration software of WinCC, and check if or not the
communication between PLC and WinCC is effect. After the
communication is normal, enter the main interface of
monitoring system, and select manual mode, you can test the
relative part is normal or not. And you can switch to manual
mode to automatic mode after all equipment can work
normally. After switching to the automatic mode, the system
will be in accordance with the decision rule of automatic
mode to control the action of water pump and tee valve.
Now excerpt partial data of gas boiler heating system for the
following analysis, and the data record of gas heating loop
as shown in Table 1.
Table -1: The results of gas heating loop
Date Time Supply water
temperature ℃
Return water
temperature ℃
Gas consumption
m3
Cooling
water mL
Outside
temperature ℃
15-03-02 9:40:09 33.52 24.82 173 180 13.11
15-03-02 10:00:09 31.23 25.85 117 120 14.21
15-03-02 10:20:09 33.99 26.24 102 100 18.22
15-03-02 10:40:09 40.71 27.88 96 100 19.83
15-03-02 11:00:09 32.42 28.35 86 80 15.27
15-03-02 11:20:09 42.77 27.75 101 80 14.39
This test is the floor radiant heating test of wall-mounted gas boiler in winter, and the specific test process is shown in Fig.8.
Fig -8: Process of gas heating loop
12:20 14:20 16:20 18:20 20:20 22:20
10
20
30
40
50
60
70
80
Water-supply temperature
Return water temperature
Outside temperature
Gas consumption
Cooling water
Time
Temperature/℃
20
40
60
80
100
120
140
160
180
Gasconsumption/m3
20
40
60
80
100
120
140
160
180
200
Coolingwater/mL

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Fig.8 indicates that the consumption of gas and the emission
of condensate are more due to the low indoor temperature at
the time of the wall-mounted gas boiler has just opened. And
then the consumption of gas and the emission of condensate
are gradually decreasing with the gas system movement and
the indoor temperature increased. Due to the intermittent
operation of wall-mounted gas boiler, the supply water
temperature swells and subsides while the return water
temperature is stable. The detection system measured data,
such as temperature, flow rate and so on has a good stability
and accuracy form the above data.
6. CONCLUSION
Solar energy-gas coupling system can realize 24-hour non-
stop running, and it can also take advantages of solar energy
minimize the consumption of gas during the day on the
premise of guarantee the room comfort. This will lay the
foundation for establishing a scientific optimization method
of solar energy-gas coupling system through constructing
the solar thermal system and wall-mounted gas boiler
heating system, overcome the disadvantages of the produced
during the separate operation, improve the overall system
efficiency, achieve energy conservation and emissions
reduction. In this paper obtained the following conclusions:
(1) According to the design requirements of solar
energy-gas coupling system, the related
optimization design of the interface of monitoring
system based on the configuration software of
WinCC is carried out; users can more intuitive
operation and observation the system running state.
(2) By analyzing the data from the monitoring system,
the stability and accuracy of the system to collect
data is verified. This will provide a solid foundation
for solar energy-gas coupling system.
(3) Combined solar energy and gas has changed the
traditional heating mode which is solar energy or
wall-mounted gas boiler individual heating, and
achieve real energy conservation and emissions
reduction, which provides reliable basic data for
domestic leading technology of solar energy
coupling gas hot water and heating system
demonstration project in Shanghai area.
ACKNOWLEDGEMENTS
This project is sponsored by Shanghai University of
Engineering Science Innovation Fund for Graduate Students
(No.E1-0903-14-01020)
REFERENCES
[1]. De Winter F．Energy consumption impacts of backup
gas firing efficiency, tank standby losses, and pilot flame
energy consumption in“two-tank”solar-gas DHW systems,
subjected to the typical DHW consumption of the single
family home [J]. Renewable Energy, 1996, 9 (1-4):714—
719.
[2]. Sun Jindong, Tong Baohua. Analysis and comparison of
performance of residential water heater [J]. Journal of
Beijing Institute of Civil Engineering and Architecture,
2004, 20(2):45—49.
[3]. Chen Zhiguang，Qin Chaokui. Analysis of a hybrid
water supplying system with solar collector and fuel gas [J].
Acta Energiae Solaries Sinica, 2011, 32(11):1652-1655.
[4]. Zhang Chen. Research in Baoding area of solar wall
mounted gas boiler heating system [D]. Hebei University,
2014.
[5]. Mousa S Mohsen. On integrated solar water heating
system [J]. International communications in heat and mass
transfer, 2002, 29(1).
[6]. Yu Junjie, Zhang Wei. PLC and HMI Applications in the
Network Control[J],Control and Instruments in Chemical
Industry, 2014, No.3, pp344-346.
BIOGRAPHY
Xu Hui (1989- ), male, master of
engineering, research direction for
renewable energy application in buildings.
E-mail: 135177974@

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