A Simple 3-Dimensional Urban Energy Balance Model and Outdoor Scale Model Experiments

A Simple Urban canopy Model for Meso-scale simulation (SUMM) was proposed. The surface geometry employed in the model is composed of uniform buildings with square horizontal cross-sections, which are regularly arranged. The constituent faces of the model are a roof, a floor and 4 vertical walls. The physical properties of each face can be given individually. The model can predict the local heat balance at the constituent faces. One of the outstanding points of the current model is the radiation scheme, in which the multi-reflections inside the street canyons, the complicated sunlit/shade distributions, and view factors among constituent faces are theoretically calculated without any time-consuming procedures. A network-resistance formulation is employed in the estimation of local sensible heat transfer. The heat transfer coefficient is the key parameter, but the values are not currently well known. To estimate this parameter and to validate the numerical model, 1/50 outdoor scale model experiments were done. The hardware model is made up of cubic concrete blocks (15cm×15cm×15cm) and the fetch of the model is enough long (about 13 times of the building height). The estimated local heat transfer coefficients in nearly neutral conditions agree well with the results of previous wind channel experiments. Using the estimated heat transfer coefficients, local heat balances and surface temperatures were evaluated by comparison with the observations.