The promotion of prefabricated building is an important mission of"accelerating new-type building industrialization",an action plan for construction sector in China.It is widely believed to reduce energy consumption,construction waste,and pollutant emissions during the on-site construction stage.However,due to the lack of credible calculation methods and quoted parameters,quantitative assessment of its carbon emissions(CEs)is not yet feasible.This study focuses on the distinctive characteristics of prefabricated building during the construction process.It explores a process-based method for calculating the construction CEs,and conducts quotas of CE parameters for construction processes in a multi-story steel-framed building.Firstly,the construction processes for the building are clarified,including foundations,columns,primary beams,and secondary beams.Based on the differences of construction methods and component sizes,47 sub-processes are further summarized.The system boundaries of CEs for each construction process are delineated,identifying the types of energy and materials consumed,and appropriate data collection methods are adopted.Through the intensive monitoring of electricity signals using a self-developed power monitoring system,precise data collection for electricity consumptions by vanious construction machinery is achieved.By decomposing and meticulously recording the hoisting steps,the diesel consumption for hoisting the components by car crane is calculated,and further inspection shows that the calculation error is within 5％.Through on-site measurements,CE parameters for each construction sub-process are quoted.Among them,the CEs for constructing the ten types of foundations are in the range 17 72～151.26 kgCO2/foundation.The CEs for hoisting the first-and second-section columns are 10.52 kg CO2/column and 14.59 kgCO2/column,respectively.Based on the cross-sectional sizes,the steel columns are classified into three types,and the CEs for installing the first-and second-section columns are 38.16～44.17 kgCO2/column and 66.95～69.18 kgCO2/column,respectively.The hoisting of primary and secondary beams for the first to third floors is completed by car crane,resulting in CEs of 7.73 kgCO2/beam and 4.52 kgCO2/beam,respectively.For the fourth floor,the hoisting of beams is carried out by tower crane,resulting in corresponding CEs of 2.40 kgCO2/beam and 2.22 kgCO2/beam,which are significantly lower compared with those from the car crane.A total of 14 connection nodes are used for installing the primary beams,including three types.Among these,11 are connected by combination of bolting and welding,resulting in CEs of 42.34～125.96 kgCO2/beam,two are connected using high-strength bolts,resulting in CEs of 56.20～75.16 kgCO2/beam,and one uses only welding,resulting in CEs of 13.84 kgCO2/beam.A total of 11 connection nodes are used for installing the secondary beams,including two types.Of these,ten are connected using high-strength bolts,resulting in CEs of 10.39～43.49 kgCO2/beam,while one uses welding,resulting in CEs equal to that of the corresponding primary beams.The total construction CEs are accumulated by multiplying the above CE quoted parameters and the corresponding quantity data of each construction process.It shows that the construction of foundations,columns,primary beams,and secondary beams produce a total CE of 194.54 tCO2.Among these,the installation of primary and secondary beams contributes the highest proportions of CEs,at 42.4％and 30.7％respectively.Six construction sub-processes show contributions exceeding 5％of the total,including three for primary beam installation,two for secondary beam installation,and one for secondary beam hoisting.Feedback is provided on the national standard"Building Carbon Emission Calculation Standard"(GB/T 51366-2019)in this study.The standard recommends calculating construction machinery energy consumption using the working time and empirical energy consumption rate of the machines,and then converting it into corresponding CEs.However,due to the actual situation of work subcontracting and machinery operation,it is difficult to obtain the working time data at the construction site.This study proposes a process-based construction CE measurement method according to the characteristics of prefabricated building.For the practical operation,it can avoid the problem of being unable to collect data on some energy and material consumption due to subcontracting of construction works.For the measurement results,it can present the proportion of CEs contributed by each construction process,thereby assisting in determining the main sources of CEs from construction,comparing different processes,and optimizing construction plans for low-carbon solutions.The construction CE quoted parameters obtained from this study can be further combined with building information modeling and component production plans to optimize the data management for the production and engineering practice of prefabricated buildings.
维普
万方数据
