Winter nighttime overcooling and atmospheric stability changes resulting from building energy retrofit

Building retrofitting can reduce energy consumption and greenhouse gas emissions. The impacts of enhancing building thermal performance (e.g. improve insulation and air tightness) extend beyond individual buildings via altered anthropogenic heat emissions from buildings (Q_F,B) to the outdoor climate. These dynamic feedbacks have been widely explored for summertime heat mitigation, but outdoor air temperature impacts from wintertime urban canopy changes in Q_F,Bare little studied.

Here, we couple a neighbourhood-scale urban climate model (SUEWS) and a building energy model (EnergyPlus) to evaluate the impacts of building energy retrofitting on outdoor thermal environment across 16 US climate zones. The results show energy retrofitting exacerbates the nighttime overcooling and change the boundary layer stability due to reduced Q_F,B. This cooling effect is more pronounced in areas with low wind speeds (i.e. seasonal median ≤ 0.5m s^-1) and higher aerodynamic resistance (e.g. Denver and Albuquerque), causing nocturnal temperatures to drops by >1.5℃. Whereas, with higher wind speeds (e.g. New York and Buffalo) there are much smaller temperature decreases and less periods with stable condition. These findings highlight the challenge of balancing building energy savings with impacts on the outdoor thermal environment and demonstrate how background climate shapes the influence of building design and operations on urban climate.