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Considering the comprehensive effect of building carbon emissions, cost savings is of great significance in nearly-zero-energy buildings (NZEBs). Previous research mostly focused on studying the impact of technical measures in pilot projects. The characteristics of different cities or climate zones have only been considered in a few studies, and the selection of cities is often limited. At times, only one city is considered in each climate zone. Therefore, this study selected 15 cities to better cover climate zone characteristics according to the variation in weather and solar radiation conditions. A pilot NZEB project was chosen as the research subject, in which the energy consumption was monitored and compared across different categories using simulated values by EnergyPlus software. Various NZEB technologies were considered, such as the high-performance building envelope, the fresh air heat recovery unit (FAHRU), demand-controlled ventilation (DCV), a high-efficiency HVAC and lighting system, daylighting, and photovoltaic (PV). The simulated carbon emission intensities in severe cold, cold, and hot summer and cold winter (HSCW) climate zones were 21.97 kgCO2/m2, 19.60 kgCO2/m2, and 15.40 kgCO2/m2, respectively. The combined use of various NZEB technologies resulted in incremental costs of 998.86 CNY/m2, 870.61 CNY/m2, and 656.58 CNY/m2. The results indicated that the HSCW region had the best carbon emission reduction potential and cost-effectiveness when adopting NZEB strategies. Although the incremental cost of passive strategies produced by the envelope system is higher than active strategies produced by the HVAC system and lighting system, the effect of reducing the building’s heating load is a primary and urgent concern. The findings may provide a reference for similar buildings in different climate zones worldwide.

The utility tunnel plays a vital role in improving city comprehensive bearing capacity, while whether the gas pipeline is set into the utility tunnel is a focus as chain and coupling accidents will happen in case of fire and explosion. In this study, a scaled-down gas chamber experiment was carried out, and full-scale two-dimensional (2d) and three-dimensional (3d) numerical models were compared. The combustion process of premixed gases could be roughly divided into four development stages, that is, (I) rapid development stage, (II) stable development stage, (III) jump stage, and (IV) oscillation stage. The over-pressure on different walls had the same development trend and the peak value appeared in the jump stage. When the methane-air premixed concentration was 9% and the ignition source was located at the center of utility tunnel (x = 0 m), the most unfavorable working condition occurred as its peak over-pressure was about 1.57 MPa with an increase rate of 70%. Similarly, when the ignition position was at the left end (x = −99 m), the peak over-pressure value was 1.51 MPa, which was 65% more than the initial value. While when the ignition position was not located at the center or ends of utility tunnel, the maximum wall pressure had a "double peaks" characteristic.When x = −80 m, the pressure jumped at 27 and 91 ms with the peak values up to 1.33 and 1.49 MPa, respectively. Arising findings provide guidance for assessing risks of setting the gas pipeline into utility tunnel and help to improve the safety design concept of utility tunnel. K E Y W O R D Scombustion and explosion, numerical simulation, over-pressure, premixed flame, utility tunnel INTRODUCTION BackgroundVarious municipal pipelines, including heating, electricity, water supply, drainage, gas, and communication pipelines can be set into the utility tunnel to construct the underground space of urban roads into a tunnel space. Particularly, gas pipeline is a carrier of natural gas transportation, demonstrating to be significant lifeline projects in cities. However, gas pipelines are susceptible to corrosion, natural disasters, external force excavation, geological changes and so forth which may cause gas leakage, combustion or even explosions. There was a total of 389 gas explosion accidents, and up to 116 accidents were caused by damaged gas pipelines by June 2017. Therefore, the gas pipeline network was expected to be incorporated into the utility tunnel to provide spatial protection, thereby effectively combating various risk factors and facilitating daily operation and maintenance. 1,2 The effect of premixed gas concentration and ignition position on explosion over-pressure needed to be analyzed, and propagation characteristics of explosion shock wave were urgent to be clarified.