Study on Performance Test Method of Solar Assisted Gas
Heating System
Y Wang
1,2
, W X Gao
2,*
L Yang
2
, W Y Zhou
2
and Q Wang
2
1
School of Environmental Science and Engineering, Tianjin University, Tianjin,
No.92 Weijin Road, China
2
North China Municipal Engineering Design&Research Institute CO., LTD., Tianjin,
No.16 Guiyuan Road, China
Corresponding author and e-mail: W X Gao, wenxuegao@163.com
Abstract. In this study, a test method for thermal performance of solar assisted gas heating
system was taken as research object, basing on the existing relative test standards in China,
test system was set up, and test parameters and test method for thermal performance of the
heating system were put forward. Daily useful energy captured by solar collector, heat output
of the gas boiler, heat loss rate and energy efficiency coefficient of system were proposed to
analysis the thermal performance of the hybrid system.
1. Introduction
In view of the thermal performance test of solar assisted gas heating system, the relevant regulations
and standards, available in China, were mainly concentrated in a single heat source or very few
combined heating systems. Among them, for solar water heater, the relevant national and industrial
regulations and standards were mainly related to the basic standards, technical conditions,
performance evaluation standards, solar collector, water storage tank, supplementary heat source and
so on, thereinto the main standards for performance test were shown in Table 1. For gas boiler,
current performance test was carried out mostly according to the standards “Gas-fired heating and hot
water combi-boilers” (GB 25034-2010) and “Minimum allowable values of energy efficiency grades
for domestic gas instantaneous water heaters and gas-fired heating and hot water combi-boilers” (GB
20665-2015), principle product standards were shown in Table 2.
For solar assisted gas heating system, the existing standards were insufficient for the integrated
test indexes and interaction between different heat sources can not be truly reflected. At the same
time, in Europe energy labelling and ecodesign requirements for space heaters, combination heaters,
packages of space heater, temperature control and solar device and packages of combination heater,
temperature control and solar device were issued in 2013 [1-4], that provided a reference for the test
of multi-energy hybrid heating system.
Wang, Y., Gao, W., Yang, L., Zhou, W. and Wang, Q.
Study on Performance Test Method of Solar Assisted Gas Heating System.
In Proceedings of the International Workshop on Materials, Chemistry and Engineering (IWMCE 2018), pages 189-193
ISBN: 978-989-758-346-9
Copyright © 2018 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved
189
Table 1. Principle test regulations and standards for solar water heaters in China.
Number of standard
Name of standard
GB 50495-2009
Technical code for solar heating system
GB/T 25966-2010
Specification of domestic solar water heating systems with electrical auxiliary
heat source
GB/T 6424-2007
Flat plate solar collector
GBT 17581-2007
Evacuated tube solar collectors
GB/T 23889-2009
Specification of air source heat pump assisted domestic solar water heating
systems
GB/T 4271-2007
Test methods for the thermal performance of solar collectors
Table 2. Principle test standards for gas water heater in China.
Number of standard
Name of standard
GB6932-2001
Domestic gas instantaneous water heaters
GB18111-2000
Gas storage water heater
GB25034-2010
Gas-fired heating and hot water combi-boilers
GB20665-2015
Minimum allowable values of energy efficiency grades for domestic gas
instantaneous water heaters and gas-fired heating and hot water combi-boilers
2. Test system
The solar assisted gas heating system studied in this paper consisted of a solar heating unit and a gas
heating unit. In order to carry out the test for thermal performance of the system, a solar assisted gas
heating test platform was set up. The test devices and arranged test points were shown in Table 3 and
the flow chart of test system in Figure 1.
Table 3. Test devices and test parameters.
Test devices
Test parameters
Electromagnetic
flowmeter
Working mass flow of solar collector, L min
-1
;Water flow of domestic hot water,
L min
-1
; Water flow of space heating loop, L min
-1
;
Wet type
flowmeter
Gas flow, m
3
;
Temperature
sensor
Return water temperature of solar heater, °C ; Supply water temperature of solar
heater, °C ; Leaving water temperature, °C ; Tap water temperature, °C ; Supply
water temperature of space heating, °C ; Return water temperature of space
heating, °C ; Outlet hot water temperature of gas boiler, °C ; Inlet hot water
temperature of gas boiler, °C ; Outlet water temperature of gas boiler in space
heating loop, °C ; Inlet water temperature of gas boiler in space heating loop, °C ;
Water temperature in the upper part of tank, °C ; Water temperature in the middle
part of tank, °C ; Water temperature in the lower part of tank, °C ;
Electricity meter
Electricity consume of system, kwh; Electricity consume of gas boiler, kwh;
Electricity consume of solar collector, kwh; Electricity consume of pump in space
heating loop, kwh.
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190
Figure 1. Test system 1-solar collector; 2,18,19,28- electromagnetic flowmeter;
3,5,8,12,50-regulating valve; 4,22,31-pump; 6,30,47-pressure gauge; 7,29-expansion tank;
9,10,11,13,14,16,20,23,26,33,37,39,41,43,46,48- temperature sensor; 15-water tank;
17,21,24,27,34,38,40,42,44,45- electromagnetic valve; 25-plate-type heat exchanger; 32,36-
three-port valve;35-gas fired heating and hot water combi-boilers; 49-gas flowmeter.
3. Test conditions
Test should include at least 1 day to meet the following conditions: daily solar radiation was 10 MJ
m
-2
≤H≤25 MJ m
-2
; water temperature in the storage tank was t
b1
=15±2°C before test, and that was
t
e1
=50±2°C after; average ambient temperature was 0°C ≤t
ad
≤39°C ; reference gas was selected as test
gas (15°C , 101.3kPa); and the ambient wind speed was v≤4 m s
-1
.
4. Test method
(1) Before the beginning of test, storage tank should be full filled with cold water of 15±0.5 °C , and
solar collector was covered with sun visor.
(2) At the beginning of the test, sun visor was removed, water temperature of storage tank and test
time were started to be recorded; meanwhile outdoor ambient temperature t
ad
, the humidity d and
wind speed v were monitored in real time, and the electricity consumption N
1
and gas using amount
V
g1
were recorded at the same time, as well as the accumulated solar irradiation received by the solar
collector.
(3) During the test, flow rate of medium in solar circulation system was set at a constant discharge
between 6 L min
-1
and 10 L min
-1
, and the medium temperature at the entrance and exit of solar
collector, t
in1
and t
out2
, were recorded at least every 15s.
(4) When the solar irradiation accumulated to 10 MJ m
-2
, the combined operation of gas boiler and
solar heater was started; water out from boiler was set at 60°C ; storage tank was equipped with a
mixing pump, water intake and outlet were placed at the bottom and the top of this tank respectively,
mixing pump was run continuously during the whole period of test; when the water temperature in
the middle part of tank arrived at 50°C , gas boiler was closed, the mixing loop was stopped, and the
test was over.
Study on Performance Test Method of Solar Assisted Gas Heating System
191
5. Analysis of thermal performance
5.1. Daily useful energy captured by solar collector
60
1
outiiniiim
n
i
m
s
ttc
Q
(1)
In it, Qs was daily useful energy captured by solar collector, kJ; c
m
was specific heat capacity of the
solar cycle medium, kJ (kg °C )
-1
; ρ
m
was density of the solar cycle medium, kg L
-1
; υ
i
was flow rate
of the solar cycle medium, L min
-1
; τ
i
was measure interval, s.
Converted to the daily useful energy captured by solar collector, Q
s17
, kJ, under daily solar
irradiation of 17 MJ m
-2
, calculated as formula (2),
1
17
17
Ess
HQQ
(2)
In it, H
E
was accumulated solar irradiation received during the test, MJ m
-2
.
5.2. Heat output of the gas boiler
Under dry type flowmeter measuring, gas heat output was converted into gas heat input in the
reference condition according to formula (3); When the wet type flowmeter was used, the gas density
should be corrected by formula (4), and in it d was replaced by d
h
.
(3)
1
622.0
gassgah
ppppppdd
(4)
In them, Q
g
was heat output of the gas under 15°C , 101.3kPa and dry state, kJ; H
i
was low caloric
value of reference gas under 15°C and 101.3kPa, MJ Nm
-3
; V
g1
was consumption volume of gas, m
3
;
p
g
was gas pressure, kPa; t
g
was gas temperature, °C ; d was relative density of dry test gas,
dimensionless; d
r
was relative density of reference gas, dimensionless; p
s
was saturated vapor
pressure at t
g
, kPa; 0.622 was relative density of water vapor in ideal state, dimensionless.
5.3. Heat loss rate of system
1
1711
1
gsbe
QQtVc
(5)
In it, η was heat loss rate of system, %; c was specific heat capacity of water, kJ (kg °C )
-1
; ρ was
density of water, kg L
-1
; V was volume of storage tank, L; ∆t
e1b1
was temperature rise of water in
storage tank, ∆t
e1b1
=t
e1
-t
b1
, °C .
5.4. Energy efficiency coefficient of system
1
211111
tcegbe
QcVcNtVcCTP
(6)
In it, CTP was energy efficiency coefficient of system, dimensionless; N
1
was electricity
consumption of system, kwh; c
1
was standard coal coefficient of electricity, kg tce kwh
-1
; c
2
was
standard coal coefficient of gas, kg tce m
-3
; Q
tce
was calorific value of standard coal, kJ (kg tce)
-1
.
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192
6. Conclusions
Through the study of test method for thermal performance of solar assisted gas heating system, it
contributed to help consumers to specify the energy efficiency of hybrid heating system, and to
understand the thermal performance of different types of water heaters more directly. Thermal
performance of hybrid system was analysis, test method and test parameters were put forward in this
research, so as to choose heating water equipment more better, and directly promote the energy
efficiency of heating equipment and the application of renewable energy and energy saving
technology.
7. References
[1] European Commission 2013 No.811/2013 Energy labelling of space heaters, combination
heaters, packages of space heater, temperature control and solar device and packages of
combination heater, temperature control and solar device p 77-81
[2] European Commission 2013 No. 812/2013 Energy labelling of water heaters, hot water
storage tanks and packages of water heater and solar device p 123-127
[3] European Commission 2013 No. 813/2013 Ecodesign requirements for space heaters and
combination heaters p 156-159
[4] European Commission 2013 No. 814/2013 Ecodesign requirements for water heaters and hot
water storage p 173-177
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