## 1 Introduction  
Energy balance is one of the most important indexes for assessing green buildings [1]. After sustainable architectural design became mainstream in the world of building development [2], more and more projects began to consider, refer to, and even be based on green building evaluation. Among all of the green building evaluation indexes, building energy balance is one of the most intuitive, efficient, and recognizable [3]. Therefore, determining how to improve building energy balance is one of the first aspects to consider when engaging in green building design. Improving active energy access and reducing passive energy consumption can improve building energy balance. Improving access to active energy [4] enhances efficiency through the use of solar panels, heat and light-shading louvers, and so on. Reducing passive energy consumption [5] reduces unnecessary daily energy loss via passive regulation courtyards, composite walls, etc. By increasing sources and reducing consumption, building energy balance can be improved. The i-Yard 2.0 was Beijing Jiaotong University's entry in the 2018 Solar Decathlon China competition [6; 7]. In terms of design, it is quite different from a passive house, low-energy house, and the nearly zero energy houses that can be seen in green buildings. For example, the \"zero house\"is a nearly zero energy house built in the suburbs of Beijing in 2019 [8]. Research on energy-saving strategies and design methods used in passive houses was published by [PERSON] and other Chinese scholars in 2020 [9]. The i-Yard 2.0 is a net-zero energy house that achieves energy self-sufficiency via solar energy [10]. The net-zero energy house uses renewable energy to completely supply the annual energy consumption of the building via a variety of active and passive designs and efficient energy savings equipment [11]. For example, the [PERSON] heritage center, built in the United States, realized net-zero energy consumption through a comprehensive strategic design [12]. A net-zero energy house can not only maximize energy consumption throughout the lifecycle of the building and achieve complete energy self-sufficiency, but also indirectly improve the ecological environment. To address problems such as city population size, scarce resources, the environment, and China's aging population [13], the object market of the design was a senior residential house in a new town development. This was not a study of the net-zero energy design as applied to a type architecture, such as the 2020 work by [PERSON] and other Chinese scholars who studied the development of an American net-zero energy structure that took the form of an education building [14]. Nor was it similar to the 2019 work by [PERSON] and other Chinese scholars who studied the technology of net-zero energy houses in hot summer and cold winter regions [15]. Rather, the present work was based on China's increasingly acute population aging problem, and thus targeted a net-zero energy design for senior residential housing. The i-Yard 2.0 is quite specific in its design, and thus not entirely suitable for all types of residential housing. \"I-Yard 2.0,\" the name of the entry, is a continuation of the 2013 entry in the same competition. The \"1\" represents the \"3i\" technology system--industrial, individual, and intelligent. Industrial construction and modular assembly can greatly reduce the construction cycle of net-zero energy houses, but this type of structure requires more thermal insulation and treatments to guarantee air-tightness at the junctions of building modules. For example, in 2018, [PERSON] and other Chinese scholars studied the thermal insulation and air-tightness of the joints of net-zero energy houses [16]. A variety of modular space combinations can meet different individual needs, breaking the homogeneity of traditional net-zero energy residential building spaces. Intelligent design provides a superior solution strategy for senior occupants and comprehensively improves the daily user experience of the elderly.