Impact of Gradual Step Changes in Temperature on Thermal Comfort in Hot Climates

Abstract

Thermal comfort affects the interaction that building occupants have with the environment, both inside and outside the building. It is a key determining factor of energy usage in the building. Buildings can become more energy efficient if appropriate consideration is given to leverage the occupants’ thermal comfort tolerance. This research examined the impact of the exposure to temperature graduation by step changes when people make their way from extremely hot outdoor temperatures to the air-conditioned interior spaces of a building. It assessed the occupants’ perceptions of thermal comfort and examined possible energy savings, by adjusting the thermostat setpoint in the transitional and steady occupancy spaces within the building. The study was conducted with groups of students and staff members in two university campuses in Saudi Arabia: King Abdulaziz University (KAU), and Umm Al-Qura University (UQU). Overall, this PhD research enriches the existing body of knowledge by providing detailed insights into thermal comfort, energy efficiency, and building design considerations in hot climates, particularly in the context of buildings in the education sector of Saudi Arabia. The research employed a case study comparative analysis approach. The study used survey questionnaires to collect quantitative and qualitative thermal comfort perception data from the building occupants. The data from nearby weather stations combined with sensors installed in the building were used to measure the environment of the spaces that the subjects transitioned through, on the way to their destination (i.e., classrooms). Firstly, data was collected under the existing air-conditioning (AC) operation settings in the buildings. This was the base-case scenario. Thermostat adjustments were then introduced to the air conditioning systems to create a step change in temperature from the exterior spaces to the transitional spaces with a difference of 3°C in temperature to the destination spaces (i.e., classrooms). Finally, the temperature was increased by an additional 1°C in both the transitional spaces and destination spaces. The results of the study have shown that a gradual change in temperature reflects positively on building occupants’ comfort sensation in both the transitional and destination spaces. The study participants didn’t experience any increase in discomfort in the transitional spaces. Moreover, they reported feeling more comfortable in the destination spaces. Thermal comfort perception of the occupants was assessed in all three scenarios. A noticeable improvement in the occupants’ thermal comfort was observed in the destination spaces. Basic energy use estimation analysis results indicated that the changes applied to the AC system within the temperature ranges acceptable to the participants would lead to a significant reduction of energy use by the AC system, mainly due to reducing operational loads from the transitional spaces. This research has provided valuable insights on the impact of temperature step change on occupants’ thermal comfort in the context of Saudi Arabia, which generally has a desert climate, with a long and hot summer, a situation very common to the Middle East region. The findings of this study have important implications for researchers, building designers, building managers, owners, and occupants. While the two case study buildings were the existing buildings within the university campuses, with no opportunity to modify the layout of spaces or the physical fabric, some extrapolations from the data can be made to provide guidance to the design of future similar facilities. In particular, building occupants would benefit directly from these research outcomes as they would experience a more comfortable temperature range in the building. Building owners would benefit due to reduction in energy use/cost. The difficulty of reaching female participants and the impact of Covid-19 on the experiment were some of the limitations that impacted this research. This however has opened up more opportunities for future research, such as including female occupants in studies, which could provide valuable insights into how gender influences thermal comfort preferences and responses. Future research could also focus on optimising building design and operation strategies to accommodate new restrictions and enhance HVAC systems' efficiency in sparsely occupied institutional buildings.