Urban microclimate and its impact on building performance: A case study of San Francisco

Urban microclimate exerts an increasing influence on urban buildings, energy, and
sustainability. This study uses 10-year measured hourly weather data at 27 sites in San Francisco,
California, to (1) analyze and visualize the urban microclimate patterns and urban heat island
effect; (2) simulate annual energy use and peak electricity demand of typical large office buildings
and large hotels to investigate the influence of urban microclimate on building performance; (3)
simulate indoor air temperature of a single-family house without air-conditioning during the record
three-day heatwave of 2017, to quantify the divergence of climate resilience due to urban
microclimate effect. Results show significant microclimate effects in San Francisco with up to 11℃
outdoor air temperature difference between the coastal and downtown areas on September 1,
2017, during the record three-day heatwave. The simulated energy results of the prototype large
office and large hotel buildings using the 2017 weather data show over 100% difference in annual
heating energy use and 65% difference in annual cooling energy use across different stations; as
well as up to 30% difference in peak cooling electricity demand. The impacts on annual site or
source energy use are minimal (less than 5%) as cooling and heating in a mild climate are a
relatively small portion of overall building energy use in San Francisco. Results also show the
microclimate effects influence indoor air temperature of unconditioned homes by up to 5℃. Newer
buildings and homes are much less affected by microclimate effects due to more stringent
performance requirements of the building envelope and energy systems. These findings inform
that San Francisco microclimate variations should be considered in urban energy planning,
building energy codes and standards, as well as heat resilience policymaking.