Quantification of environmental impacts of heat fluxes from built environments

A hydrology parameterization was implemented in the multilayer urban canopy model (BEP+BEM) to estimate the contributions of impervious surface evaporation at ground and roof level during and after precipitation events, and evapotranspiration from street vegetation in the surface energy balance. A temperature and moisture diffusion formulation was also adopted at rooftops to estimate the impacts of green roofs in the latent and sensible heat partitioning of complex urban environments. A cooling tower scheme was incorporated in the building energy model to represent the anthropogenic latent heat released by this type of technology. Additionally, an analytical expression for the drag coefficient as a function of building packing density was included. Urban canopy parameters from the Department of City Planning of New York City (NYC) were assimilated at 250 meters to improve the representation of the city morphology.;An evaluation with heat flux measurements from a field campaign at The University of Maryland Baltimore County indicates that the new formulation properly represents sensible and latent heat daily cycle with root mean square erros of 24.9 and 23.8 W/m2, respectively. A comparison with weather station information in NYC shows the model presents a tendency to overestimate by 1.5?C the maximum temperatures and underestimate by 4% moisture content during the day while improving the prediction during the night. The hydrology scheme introduces a slightly higher amount of sensible heat in the late afternoon and night principally in dry days. Latent heat produced by surface evaporation during rain events exceeds amount of heat flux produced by evapotranspiration. Evaporative cooling technology diminishes between 80 and 90% the amount of sensible heat which is transformed into latent heat. Streets constitute the main source of sensible and latent heat in residential and commercial areas. Sensible heat flux from roofs becomes more predominant during wet periods due to the larger water holding capacity of streets that enhances its latent heat production capabilities. Green roofs are able to reduce daytime near surface temperatures while increasing nighttime values due to a rise in the anthropogenic heat released by A/C systems. The increase of nighttime waste heat is related to the attenuation of the heat transfer from inside the building to the outside due to the presence of insulation layers at the bottom of the green roof installation.