Estimating Thermal Comfort and Energy Use with Future Warmer Weather

The whole-building energy model estimates that the prototypical, unconditioned multifamily building in Honolulu, HI will be warmer and less comfortable in the future, but ceiling fans and design strategies to limit heat gain can help. While methods to model and present results of building energy and occupant thermal comfort with future weather are not standardized, this research demonstrates one approach with design guidance that may be applied today. The study quantifies increased future energy use if air conditioning is installed and intermittently used by residents.

The paper “Estimating Thermal Comfort and Energy Use with Future Warmer Weather” is authored by Associate Professor Wendy Meguro, Building Performance Group Leader, CannonDesign Elliot J. Glassman, and Climate Adaptation Specialist Josephine Briones. The team simulated a conceptual design for two multifamily five story residential buildings with an exterior walkway and 40 one-bedroom dwelling units per building.

Using the present day Honolulu TMY3 weather file, the unconditioned baseline multifamily building is estimated to be comfortable 88% of the time without fans, and 96% of the time with fans. The simulation estimates that the building will be significantly less comfortable in the future, as low as 75% of the time in 2050 and 58% of the time in 2080. Encouragingly, with fans, it is estimated to be comfortable 85–91% of the time in 2050 and 71–90% of the time in 2100.

In mixed mode operation, the building’s energy use intensity increases from approximately 90 kWh/m2/yr (29 kBtu/ft2/yr) today to approximately 107-132 kWh/m2/yr (34–42 kBtu/ft2/yr) in the year 2080.

The findings on poorer thermal comfort negatively impact health and productivity, particularly for populations who cannot afford air conditioning. Increased air conditioning energy use impacts demand on the electrical grid, onsite renewable energy system sizing, and the ability to meet greenhouse gas emissions targets.

Although the research focuses on this specific building, the design strategy recommendations apply widely to future residential buildings in Honolulu and the process may be replicated for different building types.

The research quantifies the impact of actions that designers may take now to prepare for future hotter temperatures: climate-appropriate building massing and orientation, exterior shading, glazing solar heat gain coefficient, limited glazed area, natural ventilation, and ceiling fans.

Design strategies increase thermal comfort and help meet the State’s GHG emissions reduction targets by reducing the need for mechanical cooling. If air conditioning is installed in the future, the building’s energy use intensity increases, but may be lessened through inclusion of the aforementioned design strategies and occupant education on prioritizing natural ventilation.

Designers should plan for future addition of air conditioning cooling in buildings and policymakers should implement policies to curb GHG emissions and reduce overheating in buildings.

This research was conducted through the UH School of Architecture’s Environmental Research and Design Lab as well as the Hawaii Sea Grant Center for Smart Building and Community Design. In kind support was provided by the UH School of Architecture and Sea Grant College Program. Additionally, we thank team members Charles Chaloeicheep, Zachary Stevens, and Eileen Peppard, Aiko Tells, and Darlyn Chau.

Funding was provided by the Office of Naval Research and the Hawaii Natural Energy Institute with resources from the State of Hawaii Energy Systems Special Fund §304A-C.

Read the full paper in the conference proceedings, p. 391-398.