Carbon-emission calculation of electromechanical energy consumption of different structures during the construction phase

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1 Journal of Chongqing University (English Edition) [ISSN ] Vol. 12 No. 2 June 2013 doi: /j.issn To cite this article: WEI Xiu-ping, LAI Ji-yu, ZHANG Jin. Carbon-emission calculation of electromechanical energy consumption of different structures during the construction phase [J]. J Chongqing Univ: Eng Ed [ISSN ], 2013, 12(2): Carbon-emission calculation of electromechanical energy consumption of different structures during the construction phase WEI Xiu-ping, LAI Ji-yu, ZHANG Jin School of Transport and Civil Engineering, Fujian Agriculture and Forestry University, Fuzhou , P. R. China Received 23 April 2013; received in revised form 28 May 2013 Abstract: Due to the use of mechanical and electrical equipments in different buildings during construction phase, energy consumption produces large amounts of carbon emissions. Based on the energy use of China, we established a formula that was applicable to carbon-emission calculation, and discussed carbon-emission characteristics of concrete structures and steel construction. Owing to the difference of electrical and mechanical equipment used in construction phase, the results show that under the same conditions, the carbon emission intensity of a concrete structure building is much higher than that of a steel building. At last, we also put forward some emission reduction measures based on the calculation data of different buildings. Keywords: electromechanical energy; carbon emissions; concrete construction; steel construction; construction phase CLC number: TK01, TU Document code: A 1 Introduction a According to the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report, global warming is considered one of the most pressing threats to the existence of human race [1]. Buildings are major contributors to socio-economic development of a nation but also utilize a large proportion of energy during the construction phase. Due to the use of mechanical and electrical equipment in construction phase, it consumes a lot of energy, producing large amounts of carbon emissions. Worldwide, 30 to 40 of all primary energy is used for buildings and they are held responsible for 40 to 50 of greenhouse gas (GHG) emissions [2]. Though embodied energy constitutes only 10 to 20 Corresponding author, WEI Xiu-ping ( 魏秀萍 ): rihinna0504@gmail.com. Funded by Regional Transportation Integration Technology of FAFU (No. Pytd 12006); Science and Technology project of Fujian Education Department (No.JB 11046) to life cycle energy, opportunity for its reduction should not be ignored [3]. With the continuous improvement of living standards, the masonry structure and wooden structure have been unable to adapt to people s new requirements on the construction, while the high-rise and large span structure buildings have become a popular trend. Thus, based on the data of steel buildings and concrete structure buildings, we focused on the carbonemission calculation of electromechanical energy use in construction phase, so as to guide the construction enterprises to take specific reduction measures to achieve low-carbon production and good environmental benefits. 2 Calculation method Currently, carbon-emission calculation uses field measurement, mass balance method, and emission factors method and model [4]. The field measurement method has an extremely demand on the experimental conditions as well as the data processing. It is difficult to ensure the typicality and accuracy of sample data. The mass balance method is inapplicable when the activities process of 67

2 chemical composition is extremely complicated and full of mussy data is hard to be classified. In addition, the model method is difficult in regard to grasping the parameters representativeness of time and space, while the carbon-emission factors method is direct, simple, and highly reliable in obtaining activity data and corresponding carbon emission factors (CEFs) to calculate the carbon emissions. At present, there is no specific calculation tool for China s energy consumption contributing to carbon emission, and the emission factor used in China is internationally accepted from IPCC or the default value of Europe and other countries. As these tools are not designed based on China s situation, there exist differences between the types of fuel and emission factors. Based on China s energy use and the conversion formula of IPCC calculation method [5-6], we changed the computational tools. CE s AD unit MF kg / TJ FV kg / GJ AD unit CO factor kg / unit, 2e where CE(s) is the carbon emissions from stationary combustion, AD is the activity data, MF is the missions factors, FV is the fuel value, and CO 2e factor is the carbon dioxide equivalent factor. We used the low calorific value to count the fuel value and took the quantity of CO 2e as a unit of carbon emissions to calculate the GHG (including CO 2, CH 4, and N 2 O) emissions by multiplying the corresponding GWP (global warming potential) as the results of carbon emissions quantitative analysis. The GWPs of CO 2, CH 4, and N 2 O are shown in Table 1 [7]. Table 1 Global Warming Potential of greenhouse gas (GHG) GHG GWP of the time span 20 a 100 a 500 a CO CH N 2 O Carbon source analysis Life cycle energy analysis (LCEA) is an approach that accounts for all energy inputs to a building in its life cycle, including the energy use of manufacture, operation and demolition [8]. Life cycle assessment (LCA) is a tool that can be used to holistically evaluate the trends in construction stage and associated environmental impacts. In view of the above theories and characteristics of the LCA, the construction phase can be regarded as a micro-life cycle, and the stage for construction projects is divided into four parts including foundation construction, the main construction, roof construction, and decoration engineering. Every process uses a large number of mechanical and electrical machines and energy (coal, gasoline, diesel, and electricity, for example). Carbon emission sources are shown in Fig. 1. Fig. 1 Carbon emission sources of construction stage Total carbon emission of the steel and concrete building construction phase is denoted as CEM. Due to the use of earthwork and road construction machinery and consumption of energy, the carbon emission of foundation engineering construction stage is denoted as CEM1, that of the main engineering stage as CEM2, and that of the roofing and decoration engineering as CEM3. Therefore, CEM CEM1 CEM2 CEM3. In view of the use of different energy forms in a construction phase and the above formula, gasoline carbon emission factor is taken as F 1, diesel carbon emission factor as F 2, electricity carbon emissions as F 3, and energy use as Q 1, Q 2, and Q 3, so the carbon emissions formula can be changed into CEM F1 Q1 F2 Q2 F3 Q3. Electromechanical energy use in construction phase mainly comes from the use of electricity, diesel, and gasoline. The active data are primarily from the State 68 J. Chongqing Univ. Eng. Ed. [ISSN ], 2013, 12(2): 67-74

3 Electricity statistics, national energy consumption data and corporate budget document. 2.2 Determination of CEFs According to the standard IPCC methodology for GHG inventories (IPCC, 1997), CEF refers to the energy unit of a fuel type [9]. CEF, known as the coefficient of carbon emissions, is the statistical average of the carbon emissions generated by the production per unit of a product under normal economic and management conditions [10]. During the calculation process of carbon emissions, CEF is taken as a function of fuel type, combustion efficiency, process engineering, technical level, the degree of emission reduction and technological progress, and many other factors [11]. Based on China s energy use and IPCC methodology [7], we summarized the carbon emissions formula as follows. DEF/(kg/TJ)=C/(kg/GJ) CR 44/ , CO factor=def/(kg/tj) ALCA/(kJ/unit) 2e where DEF is the default emission factors, C is the carbon content, CR is the carbon oxidation rate, and ALCA is the average low calorific value Fossil fuel CEFs Through the 2006 IPCC Guidelines for National GHG Inventories [12] and General principles for calculation of total production energy consumption 2008 [13], the CO 2, CH 4, and N 2 O CEFs and the low calorific value of fuel source can be obtained. Meanwhile, considering the GHG global warming potential values (in the calculation, the GWP takes 100 a as the time span), the CEF for each fuel can be calculated as shown in Tables 2 and 3. Type of energy Unit Table 2 Fossil fuel carbon emissions factors in IPCC The average low calorific value/(kj/unit) The default carbon content/(kg/gj) CH 4 default value of emission factor/(kg/gj) Raw coal kg Washed coal kg Other coals kg Coal Products kg Coke oven gas m Blast furnace gas m Other gas m Natural gas m LNG kg Crude kg Gasoline kg Diesel fuel kg Fuel oil kg Refinery gas kg Other petroleum products kg N 2 O default value of emission factor/(kg/gj) J. Chongqing Univ. Eng. Ed. [ISSN ], 2013, 12(2):

4 2.2.2 Electricity CEFs As a secondary energy, electricity is closely related to the energy structure of different countries. The higher the proportion of thermal power generation is, the greater the CO 2 emission is from a unit of electrical energy [14]. A huge amount of carbon emission is due to the fossil energy consumption of electrical production. Since the power generation process of hydropower and nuclear rarely used carbon-containing fossil fuels, we only took account of thermal fossil energy consumption and carbon emissions from coalburning power to determine the carbon emission factor. Generally, thermal power uses different kinds of energy, mainly involving raw coal, coal gangue, coke oven gas, blast furnace gas, diesel oil, fuel oil, refinery gas, natural gas, petroleum products and other fossil fuels. Based on the energy use data from 2011 Power Statistical Yearbook [15], we obtained the main energy usage of coal-fired power in China, and calculated the corresponding emissions by the study of fossil fuel CEFs above. Details of the calculation are shown in Table 4. The above calculation shows that the total thermal power reached kw h in 2010, power plant consumption rate was 6.33, and the final power supply is kw h. The totaled emissions got to kg and the CEFs is 1.01 kg kw 1 h 1. Type of energy unit Table 3 Fossil fuel carbon emissions of China CO 2 emission factor/(kg/unit) CH 4 emission factor/(kg/ unit) N 2 O emission factor/(kg/unit) CO 2e factors/(kg/unit) A B C D=A+25B+298C Raw coal kg Washed coal kg Other coals kg Coal Products kg Coke oven gas m Blast furnace gas m Other gas m Natural gas m LNG kg Crude kg Gasoline kg Diesel fuel kg Fuel oil kg Refinery gas kg Other petroleum products kg J. Chongqing Univ. Eng. Ed. [ISSN ], 2013, 12(2): 67-74

5 Table 4 Electricity carbon emission factors Type of energy Unit Volume of energy use CO 2e factors/(kg/unit) Total carbon emission/kg Raw coal 10 7 kg Washed coal 10 7 kg Other coals 10 7 kg Coal Products 10 7 kg Coke oven gas 10 9 m Blast furnace gas 10 9 m Other gas 10 9 m Natural gas 10 9 m LNG 10 7 kg Crude 10 7 kg Gasoline 10 7 kg Diesel fuel 10 7 kg Fuel oil 10 7 kg Refinery gas 10 7 kg Other petroleum products 10 7 kg Sum Case calculation As shown in Table 5, we took the similar foundation conditions and covered area of concrete structures and steel buildings in Fuzhou as the cases. Combining the budget file of the project, we can see that the energy consumption of mechanical and electrical equipment in construction phase mainly comes from the use of gasoline, diesel, and electricity. By the way, we left out the amount of coal power machinery (such as industrial boilers), for they belong to the industrial carbon emissions. With reference to the Unified national construction machinery affecting cost quota 2012, we could obtain the data of carbon emissions via calculation. According to the project budget, the construction phase electromechanical energy consumption mainly comes from lifting machinery, transport machinery, processing machinery and welding machinery. As for the concrete structures building, it also covers the earthwork and road construction machinery, concrete and mortar machinery, and pumps machinery; and in steel building projects, it involves the use of power machinery. So we summarized the petrol, diesel and electric power consumption of electrical and mechanical equipment use in each project (Table 6). Table 5 Overview of case project Category Concrete structure Steel structure Project High-rise Steel structure residence factory Soil classification Secondary soil Secondary soil Foundation type Independent foundation Independent foundation Building area m m 2 J. Chongqing Univ. Eng. Ed. [ISSN ], 2013, 12(2):

6 Energy type Unit Table 6 Carbon emissions of concrete and steel buildings Total energy consumption of concrete structures/unit Total energy consumption of steel building/unit Carbon emission factors/(kg/unit) Carbon emission of concrete structures/kg Carbon emission of steel building /kg Gasoline kg Diesel fuel kg Electricity kw h Total Results and discussions Comparing concrete structures with steel structures, the area of concrete structure buildings is m 2, and the steel structure construction area is m 2. By calculating, we obtained that the concrete structure building produced kg/m 2 CO 2e and the steel building, released kg/m 2 CO 2e during the construction phase, which we defined it as the intensity of carbon emissions. The intensity of carbon emissions of concrete buildings is nearly 6 times higher than that of the steel structures. For concrete structure buildings, pumps machinery (51 ), transport machinery (44 ) and lifting (12 ) become the main sources of carbon emissions in construction phase. For steel structure buildings, welding machinery (47 ), other machineries (29, such as welding rod drying box and blower), and lifting machinery (12 ) are the main sources of carbon emissions. Carbon emissions from the vertical transport machinery and pumps machinery are the biggest difference between these two structures (Fig. 2). From the use of energy category, we could conclude that a unit carbon emission of gasoline is lower than that of diesel. Because of the higher price of gasoline, we should reduce the use of diesel fuel appropriately and choose the best type of energy, such as natural gas, high-quality gasoline, and highquality diesel. For the concrete structure, the total emission of the mechanical energy consumption generated from pump machinery, transport machinery and lifting machinery nearly reaches 97 in the construction phase. Therefore, to control the carbon emissions in construction phase, we should primarily consider improving the efficiency of the high pressure fuel pump, trucks, construction elevator, and crane. As for the steel structure, carbon emissions generated from the use of welding machinery, other machineries (such as welding rod, drying box, and blower), and lifting machinery account for 88. So we should focus on enhancing the efficiency of AC arc welding machine, spot welding, and blowers. In addition, it is revealed that the same kind of machineries have different types and specifications models. By Unified national construction machinery affecting cost quota 2012, the higher the model is, the more the energy is used, thus the greater the carbon emissions. In a word, under the premise of use requirements, we should prefer to select a smaller device model and specifications of mechanical and electrical equipment to ensure the efficiency, as well as to reduce the carbon emissions in the construction phase. 5 Conclusions Based on the carbon emission factor method, we got the carbon emission factor of fossil energy and electricity, then calculated the carbon emissions of concrete and steel structures in the construction phase, and proposed emission reduction measures. Meanwhile, CEFs used in this paper were appropriate for other building categories, such as municipal infrastructure construction projects. Moreover, the energy CEF determined by this method has a good applicability, which can be used as a reference in relevant situations. 72 J. Chongqing Univ. Eng. Ed. [ISSN ], 2013, 12(2): 67-74

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