## 3 Results and Discussion
### Author Keywords Co-Occurrence Analysis  
The network analysis, which was done using keywords, was utilized in conjunction with the VOSviewer software to locate more than a few ranges and information on the study of ZEBs and energy efficiency toward sustainability. It was created by performing a co-occurrence analysis on the author's and index's keywords. The significance of this study was that it aided the researcher in revealing the evolution and structure of the research field [62]. Figure 5 illustrates the research interests on ZEBs and Energy Efficiency towards Sustainability (keywords co-occurrence). Figure 4: Geospatial distribution of research publications. There are six clusters on the basis of Figure 5 which are summarized as follows:  
1. Energy Efficiency Integrated Cluster (blue)  
Energy efficiency is integrated with energy consumption, buildings, net-zero energy, zero carbon, housing, and the environment in this cluster. Energy efficiency is becoming more well-known and extensively used; the key challenge is determining what will be proven to be the most successful and trustworthy in the longer term [62]. With such a diverse variety of proposed measures, the decision maker must balance environmental, energy, financial, and social issues in order to arrive at the best feasible option that ensures a building's highest potential energy efficiency while also fulfilling future expectations [63]. It is suggested that energy efficiency can be improved with the use of new creative efficient technology. Customers frequently face significant challenges as a result of a scarcity of fundamental resources, which are not always pecuniary in nature. It is also possible that the issue stems from a lack of understanding about one's options, where to go for help with concerns, and what to buy. Before making a purchase, the consumer must have access to the necessary information and tools in order to make informed judgments [64]. In order to evaluate a product and determine the total cost of ownership, the customer requires accurate and thorough information, such as energy consumption and performance. Furthermore, the energy-efficient buildings have a proper envelope and extremely good thermal properties, all heating and electric systems are managed efficiently, and heat recuperation is used [65]. 2. Sustainability Integrated Cluster (green)  
In this cluster, sustainability is integrated with energy, simulation, photovoltaic, efficiency, heat pump, solar energy, distributed generation, energy storage, renewable energy and economic. The heat pump offers major advantages in terms of achieving sustainability and environmental friendliness. In other words, a heat pump is a more energy-efficient  
Figure 5: Research interests related to ZEBs and Energy Efficiency towards Sustainability (keywords co-occurrence). and environmentally beneficial device for creating a comfortable interior environment. Furthermore, an Air Source Heat Pump (ASHP) is a cutting-edge heating system with several benefits such as low energy consumption, generally steady performance, significant energy-saving potential, and numerous social benefits [66]. The main disadvantage of ASHP is that its performance suffers in cold and harsh weather conditions. It is suggested that ASHP systems using solar-assisted technology be given as one option. These systems can provide solar energy to the ASHP system by utilizing direct solar irradiation as well as latent heat from the sun and the air [67]. While both air and solar energy are renewable and clean energy sources, they also align with the worldwide energy consumption trend of encouraging the use of sustainable and renewable energy sources. To increase sustainability, it is advised that well-established renewable energy technology such as PVs, wind turbines, solar thermal, heat pumps, and district heating and cooling be employed [68]. Furthermore, the issue of consistent regulation of energy efficiency standards around the world is a source of concern.