Thermal environment in architecture and the science of human activity

Many people set their air conditioners to 28°C in summer and 20°C in winter. But did you know that these recommended temperatures lack scientific basis? In Japan, it was Professor Hom Bahadur Rijal from the Faculty of Environmental Studies who introduced the “adaptive model” that links comfortable indoor temperatures with outdoor conditions. What does “true comfort” mean to him?

The field of architecture is built on three pillars: “design,” which shapes the building’s layout; “structure,” which focuses on its mechanical integrity; and “environment,” encompassing elements like heat, light, air, sound, and energy. Specializing in environmental studies—particularly thermal environments—Professor Rijal explores the relationship between climate and architecture.

“I research how to create buildings that make effective use of temperature, radiant heat, humidity, wind, and other factors for comfortable living,” he explains.

Architectural environmental studies cover a wide range of topics. These include indoor environments where people spend most of their time, semi-outdoor spaces like balconies, and outdoor environments from urban areas to natural landscapes. Professor Rijal’s focus on thermal comfort examines how to maintain optimal temperatures and humidity with minimal energy use. This includes studying human behaviors, such as adjusting clothing or opening windows in response to temperature changes.

“Our research emphasizes fieldwork,” he notes. “Recently, we’ve been collaborating with professors from universities across Japan to investigate thermal comfort behaviors in office spaces nationwide. By collecting large-scale data in real-life settings, we aim to develop guidelines for better living environments.”

Comfortable temperatures are influenced by regional and seasonal factors, especially in residential settings where occupants bear their energy costs. “People can adjust by wearing lighter clothing in summer and layering up in winter. The difference in temperature settings can be significant. We also record individual variations like age, gender, and hometown, as these factors matter,” he explains.

In 2015, a massive earthquake struck Professor Rijal’s home country of Nepal. Temporary corrugated metal shelters replaced many damaged buildings, creating extreme environments—sweltering in summer and freezing in winter. “In Nepal, there was another major earthquake 90 years ago, but no records remain. By documenting and publishing our findings, we can help prepare for future disasters,” he emphasizes.

Professor Rijal’s dedication to learning began in his childhood. “I was praised for my academic achievements,” he recalls. In Nepal, red powder is applied to the forehead during celebrations. “I vividly remember the joy of being honored with it for being among the top three students. It inspired me to study even harder.”

Growing up, he walked two hours each way to his elementary school along mountain trails. Initially aspiring to be an engineer, he moved to Kathmandu for further studies, where a friend introduced him to architecture. “I was told architects wear ties and work in offices, which seemed very appealing,” he says with a laugh. He eventually pursued architecture in a three-year college program in Nepal, benefiting from government-backed projects that allowed him to observe construction sites firsthand. His ambition led him to Japan, where he continued his studies through university and graduate school. That same friend who recommended Japan later became his wife.

Initially, choosing a research theme for his master’s degree was challenging. Around that time, global attention was turning to climate change and energy issues, particularly after the adoption of the Kyoto Protocol. “That’s when I developed an interest in environmental studies. But my proposals were often rejected by my supervisor,” he recalls.

A turning point came when he introduced his Nepalese village to a British student. “He was amazed by the photos and said he’d never seen anything like it.” This inspired Professor Rijal to propose studying Nepal’s climate, traditional architecture, and thermal comfort—a theme his supervisor finally approved. “There was little prior research, so I conducted surveys on the thermal environments and comfort levels across Nepal’s diverse regions.”

Nepal, with an area smaller than twice the size of Hokkaido, exhibits diverse climates based on elevation. In the arid Himalayan regions, flat-roofed homes made of sun-dried bricks dominate. In temperate areas, semi-outdoor spaces allow people to spend hot summer nights outside.

Professor Rijal is listed among the world’s top 2% of scientists by Stanford University and Elsevier and received the 2024 Architectural Institute of Japan Award (Paper). “It’s rewarding to see my work published and valued by others,” he says.

He encourages undergraduate students in his lab to present at conferences as early as their third year. “Their expressions change completely after presenting. It significantly impacts their careers, whether they pursue jobs or further studies.”

With modern cities heavily reliant on air conditioning, energy consumption is high, and poor ventilation can lead to increased CO2 levels, reducing productivity. “We should first harness the potential of the outdoor environment,” he suggests. “Open windows, use fans, and only rely on air conditioning when necessary.”

By integrating climate-conscious urban planning—like strategically placing parks and trees—Professor Rijal envisions cities that enable people to thrive in harmony with their environment.

The path to comfort in urban living might be simpler than we think: opening windows, feeling the breeze, or spending time in a park. Professor Rijal continues to explore landscapes where architecture, nature, and people coexist in harmony with the climate.