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SUPPORTING INFORMATION

Environmental life cycle assessment and economic techno-

economic analysis of domestic hot water systems in China

Wei Liu*, Cheng Chen, Huijuan Wu, Chunhui Guo, Yuedong Chen, Wenqiu Liu,

Zhaojie Cui*

26 pages, including 12 Figures and 24 Tables

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List of Figures

Figure S1. The distribution of all the climatic regions for buildings in China... . .1

Figure S2. The solar resource map of China.........................................................2

Figure S3. The six power grids of China..............................................................4

Figure S4. Natural gas pipeline map of China......................................................5

Figure S5. Stage and order of the texts for ASHP DHW systems......................12

Figure S6. The relation of the ratio of two COPs (COPuse/COPheating) and the

ambient temperature.....................................................................................................13

Figure S7. Life-cycle impacts of DHW systems in the hot region (region 1) of

China............................................................................................................................17

Figure S8. Life-cycle impacts of DHW systems in the warm region (region 2) of

China............................................................................................................................18

Figure S9. Life-cycle impacts of DHW systems in the hot summer and cold

winter region (region 3) of China.................................................................................19

Figure S10. Life-cycle impacts of DHW systems in the severe cold region

(region 5) of China.......................................................................................................20

Figure S11. Life-cycle costs of DHW systems in all climatic regions of China.24

Figure S12. The composition of the life-cycle costs of DHW systems in all the

climatic regions of China.............................................................................................24

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List of Tables

Table S1. Detailed information of five climatic regions in China........................1

Table S2. The solar irradiance per month in cities in different climatic regions in

China..............................................................................................................................3

Table S3. The LCA results of 1 kWh electricity from different power grids in

China..............................................................................................................................4

Table S4. Pipeline transmission distance of natural gas in some cities in China..5

Table S5. Upstream materials and corresponding components and data sources

for natural gas water heater (12 L/min)..........................................................................6


for electric water heater (60L)........................................................................................7


for ASHP water heater (150L).......................................................................................7


for ETS water heater (145L)..........................................................................................8


for FPS water heater (100L)...........................................................................................8


for auxiliary system........................................................................................................9

Table S11. The abiotic depletion potential of several materials...........................9

Table S12. Energy efficiency grades of gas DHW systems................................10

Table S13. Energy efficiency grades of electric DHW systems.........................10

Table S14. Energy efficiency grades of ASHP DHW systems...........................11

Table S15. The SPF and tested COP of the ASHP DHW systems (standard

COP=3.8) in different regions......................................................................................11

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Table S16. The actual using COP of ASHP DHW systems in different regions.

......................................................................................................................................13

Table S17. Energy efficiency grades of solar DHW systems.............................14

Table S18. Heat load of domestic hot water in different regions........................14

Table S19. Natural gas consumption of gas DHW systems................................15

Table S20. Electricity consumption of electric DHW systems...........................15

Table S21. Electricity consumption of ASHP DHW systems.............................15

Table S22. Electricity consumption of solar DHW systems...............................16

Table S23 LCA results of the ASHP DHW systems..........................................20

Table S24 Overview of all the high sensitivity coefficients (>10%) for LCA

results of DHW systems in the cold region (Beijing for solar systems)......................22

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1. The climatic regions for the buildings in China

1.1 Thermal engineering zones for civil buildings

In order to clarify the relationship between architecture and climate, the general principles for

civil building design (GB 50352-2005) divides China into seven main climatic zones, 20 sub-

climatic zones, and proposes different architectural designs for each zone [1]. In terms of thermal

engineering of buildings, there are five main zones, shown in Figure S1.

Figure S1. The distribution of all the climatic regions for buildings in China.

Detailed information of each climatic region is listed in Table S1, including water supply

temperature, outdoor temperature, and season time.

Table S1. Detailed information of five climatic regions in China.

Season Temperature/Time

Region 5severe cold

Region 4cold

Region 3hot summer and

cold winter

Region 2warm

Region 1hot summer and

warm winter

Summer

Water supply 15℃ 16℃ 20℃ 18℃ 22℃

Outdoor 22℃ 22.5℃ 26.8℃ 21.3℃ 27℃Days 92 122 122 122 213

Month 6、7、8 6、7、8、9 6、7、8、96、7、8、9

4、5、6、7、8、9、10

Springand

Water supply

10℃ 10℃ 12℃ 12℃ 17℃

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autumn

Outdoor 16℃ 15.5℃ 19.4℃ 15.7℃ 21.2℃Days 91 91 91 121 61

Month 5、9、10 4、5、10 4、5、104、5、10、11

3、11

Winter

Water supply 4℃ 4℃ 5℃ 5℃ 12℃

Outdoor -2℃ 0℃ 9℃ 8.8℃ 15℃days 182 152 152 122 91

Month1、2、3、4、

11、12

1、2、3、11、12

1、2、3、11、12

1、2、3、12

1、2、12

1.2 Solar resource in China

The actual operation of solar DHW systems is closely related to the solar irradiation in different

regions. In the winter and rainy weather with lower temperatures, auxiliary electricity is needed to

compensate for the gap between the heat demand of hot water and the heat provided by solar energy.

According to the annual solar irradiance, China can be roughly divided into resource-rich belts, rich

belts, general belts and poor belts, as shown in Figure 2. In this study, 14 representative cities were

selected to analyze the environmental impact of solar DHW systems, which basically covers the

distribution of solar energy resources in different regions. The solar irradiances per month in these

cities are listed in Table S2.

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Figure S2. The solar resource map of China.

Source: https://solargis.com/maps-and-gis-data/download/china

Table S2. The solar irradiance per month in cities in different climatic regions in China.Month January February March April May June July August September October November December

Solar irradianceper month （kWh/m2）

Region 1：Guangzhou（113.3°E,23.1°N)

78 66 71 80 105 104 128 120 115 117 96 87

Region 2：Kunming（102.7°E，25.0°N)

114 126 160 170 158 131 124 130 117 104 104 105

Region 3：Shanghai（121.4°E,31.2°N)

65 77 97 122 144 124 148 140 118 103 73 65

Region 3：Changsha（112.9°E，28.2°N)

46 54 60 87 119 117 158 147 113 89 65 57

Region 3：Chengdu（104.0°E，30.7°N)

46 51 81 101 118 118 124 119 80 62 48 41

Region 4：Beijing（116.3°E,39.9°N)

67 85 122 146 170 155 145 137 118 96 67 57

Region 4：Qingdao（120.3°E,36.1°N)

71 87 126 150 177 163 154 149 130 106 73 65

Region 4：Xian（108.9°E,34.3°N)

59 71 91 121 146 143 158 144 102 77 57 51

Region 4：Kashi（76.0°E,39.5°N)

66 81 115 149 181 206 212 187 150 116 78 59

Region 4：Qamdo(97.2°E,31.2°N)

109 106 134 153 179 182 190 174 153 125 112 114

Region 4：Lhasa（91°06′E.29°36′）129 129 159 164 193 192 189 169 156 141 129 129

Region 5：Changchun（125.2°E,43.9°N)

64 86 127 149 172 175 155 145 126 92 62 51

Region 5：Urumchi（87.6°E,43.8°N)

46 62 108 151 188 195 187 175 138 97 52 39

Region 4：Xining（101.8°E,36.6°N)

83 100 135 162 181 175 179 164 128 110 88 74

Region 4：Nakchu（92.1°E,31.5°N)

114 119 159 156 180 189 195 187 154 124 109 112

Notes: The data come from the meteorological database installed in the Meteonorm V7.

2. Energy supply in different regions of China

2.1 Distribution of China’s power grid

The electric power industry of China is the world’s largest electricity producer. Most of the

electricity in China comes from coal, accounting for 66% of the total electricity generation in 2016

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https://solargis.com/maps-and-gis-data/download/china

[2]. China has six power grids, including Northeast power grid, North power grid, Northwest power

grid, Central power grid, East power grid and Southern power grid, shown in Figure S3.

Figure S3. The six power grids of China.

Source: http://www.cdmc.org.cn/2009/isgf/e-why.asp

The inventory data of electricity were obtained from the Chinese reference life cycle database

(CLCD). The LCA results of 1 kWh electricity from different power grids are shown in Table S3.

Table S3. The LCA results of 1 kWh electricity from different power grids in China.

Indicator Unit

LCA results per kWh electricityNortheast

power grid

North power grid

Northwest power grid

Central power grid

East power grid

Southern power grid

PED kg Sb-eq 8.81E-07 7.77E-07 5.83E-07 4.68E-07 5.95E-07 5.47E-07

ADP MJ 6.47E-03 6.42E-03 4.96E-03 4.01E-03 5.36E-03 4.14E-03

WU kg 17.46 15.91 12.42 10.85 12.43 11.05

AP kg SO2-eq 4.63E-04 4.34E-04 3.49E-04 2.74E-04 3.33E-04 2.72E-04

EP kg PO43--eq 1.33 1.24 0.96 0.77 0.94 0.78

GWP kg CO2-eq 3.70 3.81 2.81 2.35 3.71 2.95

PCOP kg formed ozone 6.27E-06 5.61E-06 4.80E-06 3.88E-06 4.39E-06 3.90E-06

ODP kg CFC-11-eq 1.39E-09 1.20E-09 8.47E-10 7.35E-10 2.445E-09 3.59E-09

CHTP CTU 3.67E-10 2.44E-10 1.98E-10 1.12E-10 2.49E-10 2.74E-10

NCHTP CTU 4.53E-10 3.22E-10 3.01E-10 2.34E-10 5.89E-10 7.03E-10

ETP CTU 8.20E-10 5.66E-10 4.98E-10 3.45E-10 8.39E-10 9.77E-10

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http://www.cdmc.org.cn/2009/isgf/e-why.asp

2.2 Pipeline distance of natural gas in China

In this study, the inventory data of natural gas production were obtained from the CLCD, in

which the differences of natural gas production in different gas fields were not considered. However,

the distances of gas transmission to different locations were calculated. The map of natural gas

pipeline of China is shown in Figure S4. Through investigation on the natural gas sources, the

distances of gas transmission were calculated for all locations, listed in Table S4. The inventory data

of gas pipeline transmission were obtained from the CLCD.

Figure S4. Natural gas pipeline map of China.

Source: http://tupian.baike.com/458128/2.html?prd=zutu_before

Table S4. Pipeline transmission distance of natural gas in some cities in China.

Region City Natural gas source Gas transmission distance/km

1 Guangzhou Lunnan, West-East natural gas transmission project 4600

2 Kunming East of Sichuan and Burma 500

3Shanghai West-East natural gas transmission project 4000

Chengdu Sichuan 400

4Beijing Shanganning Basin 900Xian Shanganning Basin. 500

5Changchun Daqing and Liaohe 400

Urumchi Turkmenistan, Central Asian gas pipeline 2500

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Note：The selected cities can represent the furthest and the nearest distances of the pipeline transmission in

the regions 3, 4 and 5.

3. Bill of materials for DHW systems in China.

The bill of materials (BOM) was constructed based on the investigation on several major

manufacturers of water heater, their suppliers, and users. The BOMs of DHW systems included the

materials of both water heaters and auxiliary system. It is important to note that the BOMs of water

heaters are for the most common types of DHW systems in China. For example, materials used in the

heat exchanges of gas water heaters were assumed to be oxygen-free copper not stainless steel (Table

S5). Materials used in the storage tanks of electric, FPS and ASHP water heaters were assumed to be

ceramic-lined steel (Table S6, S7, S9). Materials used in the storage tanks of ETS water heaters were

assumed to be stainless steel (Table S8). Refrigerants charged in ASHP water heaters were assumed

to be R22 (70%) and R134a (30%) (Table S7). The inventory data of material extraction and and

processing (M&P) were obtained from the CLCD, the Ecoinvent database, and investigation.

Table S5. Upstream materials and corresponding components and data sources for natural gas water heater (12 L/min).

Component Material Mass/kg Data source for M&P

Fan, gas-collecting hood, bolt Cold-rolled carbon steel 4.1 CLCDOuter casing Zinc plated carbon steel 2.5 CLCDHeat exchanger Copper 2.1 CLCDCombustor, discharge pipe Stainless steel 2.5 EcoinventFoil sealing for discharge pipe Aluminum 0.2 CLCDDisplay pane Glass 0.3 CLCDController and electronic parts Polypropylene (PP) 0.3 CLCDCoating of gas pipe and electric wire Polyvinyl chloride (PVC) 0.15 CLCDWater inlet/outlet pipe, angle valve, gas pipe Stainless steel 1.8 Ecoinvent

Pipe connection Copper 0.2 CLCD

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Table S6. Upstream materials and corresponding components and data sources for electric water heater (60L).

Component Material Mass/kg Data source for M&PWater tank Cold-rolled carbon steel 13.26 CLCDErosion resistant coating of tank Ceramic powder 0.54 Enterprise surveyOuter casing Zinc plated carbon steel 2.70 CLCDInsulation foam Polyurethane foam 0.51 EcoinventAnode Magnesium 0.40 CLCDHeating pipe Stainless steel 0.80 EcoinventMaintenance cover Polystyrene (PS) 0.80 CLCD

Other plastic parts Acrylonitrile butadiene styrene (ABS) 0.60 Ecoinvent

Safety relief valve Copper 0.15 EcoinventAngle valve, expansion bolts Stainless steel 0.45 EcoinventWater inlet and outlet pipes Polypropylene random (PPR) 0.15 CLCDExhaust water pipe PVC 0.10 CLCD

Table S7. Upstream materials and corresponding components and data sources for ASHP water heater (150L).


Water tank Cold-rolled carbon steel 32.2 CLCDErosion resistant coating of tank Ceramic powder 1.615 Enterprise survey

Outer casing of tank Zinc plated carbon steel 13.1 CLCDABS 1.2 Ecoinvent

Pipe connection, safety relief valve Copper 0.9 CLCDWater pipe Carbon steel 0.5 CLCDHeating pipe Stainless steel 0.6 EcoinventAnode Magnesium 0.5 CLCDInsulation foam Polyurethane foam 2.2 EcoinventRefrigerant R22 or R134a 0.98 EcoinventEvaporator, condenser Copper 2.6 CLCDEvaporator Aluminum 1.1 CLCDMotor, compressor-outdoor unit Cold-rolled carbon steel 13 CLCD

Outer casing of outdoor unit

Zinc plated carbon steel 7.5 CLCDPP 1.5 CLCDPolyethylene (PE) 0.8 CLCD

Pain for outer casing

Xylene 0.018 CLCDEthyl acetate 0.015 CLCDButyl acetate 0.024 EcoinventPigment powder 0.028 CLCDWater 0.1064 CLCDAcrylic resin 0.112 Ecoinvent

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Table S8. Upstream materials and corresponding components and data sources for ETS water heater (145L).


Evacuated tube

High borosilicate glass 60.0 EcoinventCopper 0.002 CLCDAluminum 0.0012 CLCDStainless steel 0.001 EcoinventWater 0.010 CLCDNatural gas 1.8 CLCDElectricity 5.0 CLCD

Water tank Stainless steel 5.47 EcoinventOuter casing Zinc plated carbon steel 7.51 CLCDInsulation foam Polyurethane 4.0 EcoinventHeating pipe Stainless steel 0.5 EcoinventAnode Magnesium 0.5 CLCDHolder Zinc plated carbon steel 15.0 CLCDTube saddle, cell box ABS 1.6 EcoinventFixed rope and hook, angle valve Stainless steel 1.5 EcoinventWater inlet/outlet pipes PPR 0.3 CLCD

Table S9. Upstream materials and corresponding components and data sources for FPS water heater (100L).

Component Material Amount Data source for M&P

Water tank Cold-rolled carbon steel 26.0 kg CLCD

Outer casing Zinc plated carbon steel 9.0 kg CLCDABS 0.8 kg Ecoinvent

Pipe connection Copper 0.5 kg CLCDWater pipe Carbon steel 0.5 kg CLCDHeating pipe Stainless steel 0.6 kg EcoinventAnode Magnesium 0.5 kg CLCDInsulation foam Polyurethane 1.8 kg EcoinventErosion resistant coating of tank Ceramic powder 1.3 kg Enterprise surveyCollector-holder Zinc plated carbon steel 15.0 kg CLCDCollector-frame Aluminum 3.0 kg CLCDCollector-glass cover Sun glass 8.0 kg EcoinventCollector-tube Copper 7.0 kg CLCDCollector-insulation Glass wool 1.5 kg CLCD

Collector-plate core

Aluminum 2.16 kg CLCDTitanium sponge 0.012 m3 CLCDOxygen 0.001 m3 CLCDArgon 0.001 m3 CLCDNitrogen 0.001 m3 CLCD

Electricity 1.11 kWh CLCD

Water 1.48 t CLCD

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The BOM of auxiliary system only covers the shower system and hot water pipes, shown in

Table S10.

Table S10. Upstream materials and corresponding components and data sources for auxiliary system.

Component MaterialMass/kg Data source for M&P

Shower nozzle, nozzle base ABS 0.25 EcoinventShower pipe Stainless steel 0.6 EcoinventWater mixing valve Copper 0.7 CLCDHot water pipe PPR 1.5 CLCD

The abiotic resource depletion impact score can then be calculated as follows:

ADP=EFADP•Amt (S1)

where ADP is the abiotic resource depletion impact score for the material (kg antimony-equivalents)

per functional unit; is the amount of the material extracted (kg) per functional unit; EFADP is the

abiotic depletion potential of the material (kg antimony-eq/kg material), which is associated with the

resources abundances and extraction rate of the material. Table S11 lists EFADP the in CLCD for

several materials in this study.

Table S11. The abiotic depletion potential of several materials.

Material UnitEFADP in the CLCD

Steelkg Sb-eq kg-1 1.66E-06

Cooperkg Sb-eq kg-1 2.50E-03

Aluminum

kg Sb-eq kg-1 2.53E-05

Coalkg Sb-eq kg-1 9.08E-07

Natural gas

kg Sb-eq kg-1 9.83E-06

Crude oilkg Sb-eq kg-1 9.87E-06

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4. Energy efficiency of DHW systems

4.1 Gas DHW systems

According to the national standard of energy efficiency for gas DHW systems in China, the

energy efficiencies are divided into three grades under both 100% and 50% of the rated heating load.

In this study, the average of energy efficiencies under the two heating loads was used to as the actual

energy efficiency of gas DHW systems, shown in Table S12.

Table S12. Energy efficiency grades of gas DHW systems.

Heating load (%) Energy efficiency (%) Data SourceGrade 1 Grade 2 Grade 3

100 98 89 86 GB 20665-2015 [3]50 94 85 82no specific 96 87.5 84 This study

4.2 Electric DHW systems

According to the national standard of energy efficiency for electric DHW systems in China, the

energy efficiencies are divided into five grades under specific test conditions. The actual energy

efficiency depends on the using condition, and around 0.6-0.9. Li et al. [4] divided the actual energy

efficiencies of electric DHW systems into five grades based on the field test, shown in Table S13.

These test results were employed as the actual energy efficiencies of electric DHW system in this

study.

Table S13. Energy efficiency grades of electric DHW systems.

Energy efficiency grade Inherent energy coefficient (ε) in 24hin GB 21519-2008 [5]

Energy efficiency (%) in this study [4]

1 0.6 902 0.7 823 0.8 744 0.9 685 1.0 60

Notes: ε=Q/Q0, Q is the electricity consumption of electric DHW system in 24h under specific test conditions, and

Q0 is the baseline of electricity consumption of electric DHW system in 24h under specific test conditions.

4.3 ASHP DHW systems

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As for ASHP water heaters, the coefficient of performance (COP) is employed to evaluate the

energy efficiency grades in the national standard, which gives the heat output (in watts) divided by

the electrical input (also in watts), shown in Table S14. However, the COP is measured under very

specific conditions in the laboratory, and the real performance of ASHP is highly dependent on the

temperature difference between the external heat collector and the output to the home. In practice,

COP drops by between 0.6 and 1.0 for every 10 difference, giving 0.6-1.0 kWh less heat output℃

per kWh of electrical input [6]. Several field trials around the world have shown that the values of

seasonal performance factors (SPFs) lie in the range of 3.0–3.5 for ASHP.

Table S14. Energy efficiency grades of ASHP DHW systems.

Type Heating mode Energy efficiency grades (COP)[7]1 2 3 4 5

Ordinary Single heating, cycle heating 4.60 4.40 4.10 3.90 3.70Static heating 4.20 4.00 3.80 3.60 3.40

Low temperature Single heating, cycle heating 3.80 3.60 3.40 3.20 3.00

Given the disparity between the COP values published by manufacturers and the SPF values in

real-world testing, it is vital to estimate the actual energy efficiencies of ASHP systems with

different EEGs installed at different locations in this study. According to the experimental of Xu et

al. [8], the tested COP (standard COP=3.8) has a linear relation with the ambient temperature (Ta) as

flows:

COP=0.1Ta-26 (S1)

For other ASHP DHW systems, the tested COP (standard COP=X) can be estimated based on a

modified formula as flows:

COP=X/3.8•(0.1Ta-26) (S2)

The SPF of ASHP DHW systems can be estimated based on the ambient temperature in Table

S1 and the standard COP in Table S14. Table 15 list the SPF and the annual COP of ASHP DHW

systems (standard COP=3.8) in different regions.

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Table S15. The SPF and tested COP of the ASHP DHW systems (standard COP=3.8) in different regions.

RegionSpring and autumn Summer Winter

COP ambient temperature/K SPF ambient temperature/K SPF ambient temperature/K SPF

1 294.35 3.435 300.15 4.015 288.15 2.81

5 3.62

2 288.85 2.885 294.45 3.445 281.95 2.19

5 3.07

3 292.55 3.255 299.95 3.995 282.15 2.21

5 2.84

4 288.65 2.865 295.65 3.565 273.15 1.31

5 2.45

5 289.15 2.915 295.15 3.515 271.15 1.11

5 2.17

Figure S5. Stage and order of the texts for ASHP DHW systems.

However, the tested COP is still not the actual using COP of ASHP DHW systems in China.

According to the standard in the EU, the performance tests of ASHP DHW systems consists of six

principal stages: heating up period (A), determination of standby input (B), determination of the

energy consumption and the COP (C), determination of a reference hot temperature and the

maximum quantity of usable hot water in a single tapping (D), test to determine the temperature

operating range (E), and safety tests (F). The COP in the stage C could indicate the using efficiency

in practice. The COP in the standard in China tests the heating process of inlet water from 15℃ to

55 , similar the heating up period, which is higher than the COP in use stage. Shu et al. ℃ [9] tested

the COP in the two stage and found that the COP in the use stage was only 78% and 37% of the COP

in the heating up period when the ambient temperature changed from 20 to 15 . Based on the℃ ℃

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experimental data, the relation of the ratio of two COP (COPuse/COPheating) and the ambient

temperature was establish by data fitting, shown in Figure S6.

255 260 265 270 275 280 285 290 2950.3

0.4

0.5

0.6

0.7

0.8C

OP

use/C

OP

heat

ing

Equation y = Intercept + B1*x^1 + B2*x̂ 2Plot BWeight No WeightingIntercept -15.88927 ?8.00843B1 0.10746 ?0.05806B2 -1.72554E-4 ?1.05045E-4Residual Sum of Squares 0.00171R-Square(COD) 0.98478Adj. R-Square 0.96956

Figure S6. The relation of the ratio of two COPs (COPuse/COPheating) and the ambient temperature.

Based on the relation equation and the tested COP of ASHP DHW systems, the actual using

COP of ASHP DHW systems in different regions could be calculated. The results are listed in Table

S16.

Table S16. The actual using COP of ASHP DHW systems in different regions.

RegionCOP

EEG 1 EEG 2 EEG 3 EEG 4 EEG 51 3.20 3.05 2.90 2.75 2.462 2.62 2.49 2.37 2.24 2.013 2.37 2.25 2.14 2.03 1.814 1.81 1.72 1.62 1.53 1.435 1.57 1.48 1.40 1.32 1.24

4.4 Solar DHW systems

According to the national standard, the coefficient of thermal performance (CTP) is used to

classify the energy efficiency of solar water heaters into three grades, which is given as a coefficient

compositing the heat-collecting efficiency of collectors and the heat loss of water tanks, and

measured under very specific conditions.[10] The CTP cannot directly indicate the overall energy

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efficiency of solar DHW systems. According to a large sample survey on ETS DHW systems [11,

12], the average heat collecting efficiency could be divided into three grades, shown in Table S17.

Based on our investigation, the empirical annual heat collecting efficiency of ETS DHW systems is

0.25–0.60, and the heat loss rate of ETS DHW systems is 0.10–0.30, the expected value of the

annual energy efficiency of ETS DHW systems is 0.40. We assumed that the annual energy

efficiency is proportional to the heat collecting efficiency, and then the annual energy efficiency of

ETS DHW systems with three grades can be estimated, shown in Table S17. As an emerging DHW

systems in China, there is almost no information on the actual energy efficiency for TPS DHW

systems, then we assumed that the annual energy efficiency of TPS DHW systems is 95% of that of

ETS DHW systems in the same energy efficiency grade.

Table S17. Energy efficiency grades of solar DHW systems.

TypeEnergy efficiency grades

Data source1 2 3

Close-coupled (including ETS) 0.50 0.32 0.10

CTP in GB 26969 [10]Remote-storage direct(including PFS) 0.48 0.30 0.10

ETS 0.65 0.50 0.42 Heat collecting efficiency [11, 12]

ETS 0.45 0.40 0.32 Annual average energy efficiency in this studyPFS 0.43 0.38 0.30

5. Energy use of DHW systems in the use stage

5.1 Heat load of hot water

Based on the temperature of inlet and outlet water and the hot water consumption, the heat load

of hot water in different regions can be calculated as Eq. 1 and shown in Table S18.

Table S18. Heat load of domestic hot water in different regions.

Region

Spring and autumn Summer Winter A whole year

Water/L

Heat load/MJ

Water/L

Heat load/MJ

Water/L

Heat load/MJ

Water/L

Heat load/MJ

1 9150 845 31950 2013 13650 1663 54750 4521

S14

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247

248

249

250

251

252

253

254

255

256

257

258

259

260

261

262

2 18150 2058 18300 1460 18300 2767 54750 62863 13650 1548 18300 1307 22800 3447 54750 63024 13650 1663 18300 1614 22800 3543 54750 68205 13650 1663 13800 1275 27300 4242 54750 7180

Notes: The temperature of inlet and outlet water in different regions is present in Table 1. The temperature of

outlet water (domestic hot water) is set as 39℃ in spring and autumn, 37℃ in summer, and 41℃ in winter

based on our questionnaire survey.

5.2 Energy use of DHW systems

Based on the heat load of DWH and the actual energy efficiency of DHW systems, the energy

consumption of DHW systems with different EEGs in different regions can be calculated as Eq. 2

and Eq. 3, shown in Table S19-S22.

Table S19. Natural gas consumption of gas DHW systems.

RegionNatural gas consumption (m3/yr)

EEG 1 EEG 2 EEG 31 131.31 144.9 150.072 182.57 201.45 208.653 183.04 201.98 209.194 198.08 218.57 226.385 208.55 230.12 238.34

Table S20. Electricity consumption of electric DHW systems.

Region Electricity consumption（kWh/yr）EEG 1 EEG 2 EEG 3 EEG 4 EEG 5

1 1395.3 1531.5 1697.0 1846.8 2093.02 1940.0 2129.2 2359.4 2567.6 2910.02 1945.0 2134.8 2365.6 2574.3 2917.54 2104.9 2310.2 2560.0 2785.9 3157.35 2216.1 2432.3 2695.2 2933.1 3324.1

Table S21. Electricity consumption of ASHP DHW systems.

Region Electricity consumption（kWh/yr）EEG 1 EEG 2 EEG 3 EEG 4 EEG 5

1 530.9 557.4 586.7 619.3 692.22 669.3 702.7 739.7 780.8 872.72 544.8 572.0 602.1 635.6 710.44 1045.7 1103.8 1168.8 1241.8 1324.65 1272.7 1343.4 1422.5 1511.4 1612.1

S15

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264

265

266

267

268

269

270

271

272

273

274

Table S22. Electricity consumption of solar DHW systems.

Region CityElectricity consumption of ETS

(kWh/yr)Electricity consumption of FPS

(kWh/yr)EEG 1 EEG 2 EEG 3 EEG 1 EEG 2 EEG 3

`1 Guangzhou 241.1 299.7 405.6 399.2 454.1 614.62 Kunming 222.5 327.5 509.9 497.7 635.2 909.6

3Shanghai 583.8 668.2 837.1 827.2 910.0 1092.6Chengdu 813.9 899.5 1047.5 1039.1 1110.8 1283.9Changsha 775.5 860.4 996.3 988.6 1056.9 1204.8

4

Beijing 606.6 679.3 853.3 840.9 959.0 1193.3Xian 732.1 814.9 997.4 987.1 1079.9 1290.0

Qingdao 561.6 639.3 799.5 788.1 896.6 1136.0Kashi 578.8 654.6 809.0 797.7 891.6 1041.8Lassa 192.0 300.1 507.0 493.9 614.6 856.1

5

Changchun 643.1 754.6 945.7 933.3 1048.4 1278.5Urumchi 741.6 830.2 990.9 984.0 1077.0 1257.5Naquin 293.8 425.2 664.9 648.5 784.8 1015.9Xining 480.6 609.7 821.3 807.1 925.0 1161.9

6. LCA results of DHW systems

6.1 LCA results of DHW systems in different regions

The LCA results of DHW systems in the climatic regions 1 (hot summer and warm winter), 2

(warm), 3 (hot summer and cold winter), and 5 (severe cold) of China are shown in Figure S7-S10.

S16

275

276

277

278

279

280

G E A T P

2

4

6

8P

ED

(GJ)

G E A T P

19.0

19.5

20.0

20.5

WU

(t)

G E A T P0.4

0.6

0.8

1.0

1.2

AD

P(g

Sb-

eq)

G E A T P0

1

2

3

AP

(kg

SO

2-eq

)

G E A T P

0.1

0.2

EP

(kg

PO

3-4-e

q)

G E A T P

0.1

0.2

0.3

0.4

0.5

GW

P(t

CO

2-eq

)

G E A T P

0.5

1.0

1.5

2.0

2.5

OD

P (m

g C

FC-1

1-eq

)

G E A T P1.0

1.5

2.0

2.5

3.0

3.5

4.0

PO

CP

(g fo

rmed

ozo

ne)

G E A T P

4

6

8

10

NC

HTP

(10-7

CTU

)

G E A T P2

4

6

8

10

12

CH

TP(1

0-9C

TU)

G E A T P8

12

16

20

HTP

(10-9

CTU

)

G E A T P2

4

6

8

10

ETP

(CTU

)

Figure S7. Life-cycle impacts of DHW systems in the hot region (region 1) of China.

S17

281

282

283

G E A T P

2

4

6

8

10P

ED

(GJ)

G E A T P18.5

19.0

19.5

20.0

20.5

21.0

21.5

WU

(10

kg)

G E A T P

0.6

0.8

1.0

1.2

AD

P(k

g S

b-eq

)

G E A T P0

1

2

3

4

AP

(kg

SO

2-eq

)

G E A T P0.0

0.1

0.2

EP

(kg

PO

3-4-e

q)

G E A T P0.0

0.2

0.4

0.6

0.8

GW

P(t

CO

2-eq

)

G E A T P0

1

2

3

4

OD

P (m

g C

FC-1

1-eq

)

G E A T P1

2

3

4

5

PO

CP

(g fo

rmed

ozo

ne)

G E A T P

4

6

8

10

NC

HTP

(10-7

CTU

)

G E A T P2

4

6

8

10

12

CH

TP(1

0-7C

TU)

G E A T P

12

16

20

HTP

(10-7

CTU

)

G E A T P2

4

6

8

10

ETP

(CTU

)

Figure S8. Life-cycle impacts of DHW systems in the warm region (region 2) of China.

S18

284

285

286

G-sh G-cd E-e E-c A-e A-c T-sh T-cd P-sh P-cd2

4

6

8

10

12P

ED

(GJ)

G-sh G-cd E-e E-c A-e A-c T-sh T-cd P-sh P-cd

19

20

21

22

WU

(t)

G-sh G-cd E-e E-c A-e A-c T-sh T-cd P-sh P-cd0.6

0.8

1.0

1.2

AD

P(k

g S

b-eq

)


1

2

3

4

5

AP

(kg

SO

2-eq

)


0.1

0.2

0.3

EP

(kg

PO

3-4-e

q)


0.2

0.4

0.6

0.8

GW

P(t

CO

2-eq

)


0.5

1.0

1.5

2.0

2.5

OD

P (m

g C

FC-1

1-eq

)


2

3

4

5

6

PO

CP

(g fo

rmed

ozo

ne)


4

6

8

10

NC

HTP

(10-7

CTU

)


4

6

8

10

12

CH

TP(1

0-7C

TU)


8

12

16

20

HTP

(10-7

CTU

)


4

6

8

10

ETP

(CTU

)

Figure S9. Life-cycle impacts of DHW systems in the hot summer and cold winter region (region 3)

of China.

S19

287

288

289

290

G-cc G-u E-ne E-n E-nwA-ne A-n A-nwT-cc T-u T-nqP-cc P-u P-nq

4

8

12

16

20P

ED

(GJ)


19

20

21

22

23

WU

(t)

G-cc G-u E-ne E-n E-nwA-ne A-n A-nwT-cc T-u T-nqP-cc P-u P-nq0.6

0.8

1.0

1.2

1.4

AD

P(g

Sb-

eq)

G-cc G-u E-ne E-n E-nwA-ne A-n A-nwT-cc T-u T-nqP-cc P-u P-nq0

2

4

6

AP

(kg

SO

2-eq

)

G-cc G-u E-ne E-n E-nwA-ne A-n A-nwT-cc T-u T-nq P-cc P-u P-nq

0.1

0.2

0.3

0.4

0.5

EP

(kg

PO

3-4-e

q)

G-cc G-u E-ne E-n E-nwA-ne A-n A-nwT-cc T-u T-nq P-cc P-u P-nq

0.2

0.4

0.6

0.8

1.0

1.2

1.4

GW

P(t

CO

2-eq

)G-cc G-u E-ne E-n E-nwA-ne A-n A-nwT-cc T-u T-nqP-cc P-u P-nq

2

4

6

8

PO

CP

(g fo

rmed

ozo

ne)


0.5

1.0

1.5

OD

P (m

g C

FC-1

1-eq

)


4

6

8

10

NC

HTP

(10-7

CTU

)


4

6

8

10

12

14

CH

TP(1

0-7C

TU)


8

12

16

20

THTP

(10-7

CTU

)


4

6

8

10

12E

TP(C

TU)

Figure S10. Life-cycle impacts of DHW systems in the severe cold region (region 5) of China.

6.2 LCA results of AHTP DHW systems

R134a and R22 are two main refrigerants used in ASHP DHW systems. The LCA results of the

ASHP DHW systems with the two kinds of refrigerants are shown in Table S23.

Table S23 LCA results of the ASHP DHW systems.

LCA results R22 R134A R22/R134AADP/kg Sb-eq 3.06E-06 3.12E-06 98.1%WU/kg 54.80 54.80 100.0%PED/MJ 16.11 16.11 100.0%AP/kg SO2-eq 6.51E-03 6.52E-03 100.0%EP/kg PO4

3-eq 5.42E-04 5.42E-04 100.1%GWP/t CO2-eq 1.37 1.34 102.0%POCP/kg formed ozone 9.97E-06 1.09E-05 91.2%ODP/kg CFC-11-eq 3.12E-06 4.84E-09 644.21

S20

291

292

293

294

295

296

CHTP/CTU 1.86E-09 1.86E-09 99.9%NCHTP/CTU 2.20E-09 2.20E-09 100.4%THTP/CTU 4.07E-09 4.06E-09 100.2%ETP/CTU 1.64E-02 1.64E-02 100.1%

6.3 Sensitivity analysis

Table S24 lists all of the high sensitivity coefficients (no less than 10%) for LCA results of

DHW systems in the cold region of China.

S21

297

298

299

300

Table S24 Overview of all the high sensitivity coefficients (>10%) for LCA results of DHW systems in the cold region (Beijing for solar systems).

DHWsystems Stage Inventory data ADP AP PED EP GWP WU PCOP ODP CHTP NCHTP total HTP ETP

Gas

Materials extraction

and processing

Copper of heat exchanger 46.3% 0.4% 0.4% 57.6% 0.1% 0.2% 2.7% 2.6% 76.3% 49.9% 67.7% 75.0%Copper of mix water valve 7.3% 0.5% 0.1% 8.9% 0.0% 0.0% 0.4% 0.4% 11.8% 7.8% 10.5% 11.6%

Cold-rolled carbon steel 0.6% 1.5% 0.7% 0.3% 0.3% 0.0% 12.4% 1.0% 0.2% 14.4% 4.8% 0.3%Zinc plated carbon steel of

casing 6.1% 1.0% 0.5% 0.3% 0.2% 0.0% 7.7% 0.7% 0.2% 10.7% 3.6% 0.4%

Use

Gas consumption 33.3% 44.0% 97.9% 7.1% 10.0% 0.2% 14.0% 93.5% 2.8% 7.9% 4.4% 4.2%Emissions from gas

burning 0.0% 47.3% 0.0% 18.8% 87.9% 0.0% 52.6% 0.0% 0.0% 0.0% 0.0% 0.0%

Water consumption 0.4% 13.1% 4.0% 2.9% 1.9% 99.7% 1.6% 1.8% 0.1% 0.5% 0.3% 0.2%

Electric


and processing

Carbon steel of water tank 2.1% 0.1% 0.2% 0.2% 0.2% 0.1% 10.0% 1.6% 1.6% 36.2% 22.9% 2.4%Copper of connection 3.7% 0.0% 0.0% 0.8% 0.0% 0.0% 0.0% 0.1% 14.1% 2.8% 7.1% 12.0%

Copper of mix water valve 7.0% 0.0% 0.0% 1.6% 0.0% 0.0% 0.1% 0.2% 26.2% 5.2% 13.3% 22.4%Polyurethane foam for

insulation 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 10.0% 0.4% 0.0% 0.4% 0.2% 0.2%

UseWater consumption 0.4% 0.4% 0.4% 0.6% 0.4% 87.4% 0.4% 0.9% 0.4% 0.4% 0.4% 0.4%

Electricity consumption 71.4% 99.5% 99.6% 97.0% 99.7% 12.6% 76.3% 94.8% 57.1% 47.1% 51.0% 61.7%

ETS


and processing

Glass of evacuated tube 2.9% 1.5% 0.8% 2.5% 0.9% 0.0% 4.4% 38.2% 2.0% 7.7% 6.5% 11.5%Stainless of water tank 39.6% 0.4% 0.4% 1.7% 0.4% 0.0% 4.8% 10.3% 44.4% 53.3% 51.4% 42.6%

Zinc plated carbon steel of holder 34.5% 0.8% 1.1% 1.4% 1.0% 0.1% 20.0% 4.3% 5.0% 30.2% 24.7% 6.3%

Polyurethane foam for insulation 0.0% 0.1% 0.1% 0.3% 0.0% 0.0% 36.7% 1.5% 0.1% 0.5% 0.4% 0.5%

Copper of mix water valve 4.9% 0.0% 0.0% 5.0% 0.0% 0.0% 0.1% 0.3% 29.9% 2.6% 8.5% 22.0%



FPS


and processing

Zinc plated carbon steel of casing 20.3% 0.4% 0.6% 0.5% 0.5% 0.1% 18.2% 4.2% 0.8% 24.6% 10.3% 1.3%

Carbon steel of water tank 1.3% 0.4% 0.6% 0.3% 0.5% 0.1% 19.3% 3.7% 0.4% 21.8% 9.0% 0.7%Copper of mix water valve 53.9% 0.1% 0.2% 33.9% 0.1% 0.3% 2.2% 5.0% 84.6% 39.7% 66.6% 83.2%



ASHP Materials extraction

134a charge 15.4% 0.1% 0.1% 0.3% 0.0% 0.0% 8.6% 69.3% 0.6% 4.6% 2.8% 0.8%Copper of heat exchanger 27.8% 0.0% 0.0% 13.4% 0.0% 0.1% 0.7% 0.5% 70.6% 18.8% 42.6% 66.8%

S22

301302

and processing

Zinc plated carbon steel of casing 19.0% 0.2% 0.3% 0.4% 0.3% 0.1% 9.7% 0.8% 1.1% 21.1% 12.0% 1.9%

Carbon steel of water tank 1.8% 0.3% 0.4% 0.3% 0.3% 0.1% 14.9% 1.0% 0.9% 27.0% 15.1% 1.5%Carbon steel of compressor 0.7% 0.1% 0.1% 0.1% 0.1% 0.0% 5.9% 0.4% 0.4% 10.7% 6.0% 0.6%Copper of mix water valve 4.4% 0.0% 0.0% 2.1% 0.0% 0.0% 0.1% 0.1% 11.2% 3.0% 6.8% 10.6%



S23

303

7. Techno-economic analysis of DHW systems

The life-cycle costs of DHW systems in all the climatic regions in China are shown in Figure

S11.

G E A T P G E A T P G E A T P G E A T P G E A T PRegion 1 Region 2 Region 3 Region 4 Region 5

0.0

0.5

1.0

1.5

2.0C

ost(Y

uan

pers

on-1 d

-1)

Figure S11. Life-cycle costs of DHW systems in all climatic regions of China.

Notes: The baseline is the costs of the DHW systems with the average prices of electricity or natural

gas and freshwater in the region.

The composition of the life-cycle costs of DHW systems in the cold region was shown in Figure

S12.

G E A T P0

20

40

60

80

100

cost

com

pone

nt(%

)

Initial costs Energy Water Maintenance and recovery

S24

304

305

306

307

308

309

310

311

312

313

Figure S12. The composition of the life-cycle costs of DHW systems in all the climatic regions of

China.

S25

314

315

316

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