Combining Models for Urban Microclimate and Building Energy for Early Stage Design

People: Jianxiang Huang (HKU), Phil Jones (Cardiff-HKU), Rong Peng (HKU)

 

Sustainable design decisions need to be better coordinated at building and street scale. Often, improvements of outdoor environment are at odds with building energy performance. Aligning apartment buildings parallel to wind direction, for instance, can enhance outdoor breeze under hot climate, yet it may hinder natural ventilation performance inside each apartment. Cities configured to maximize building solar heat gains, e.g., cities in Northern China, may restrict solar access on streets and discourage walking and outdoor activities. In practice, these rather intricate decisions are often made with intuition, personal experiences, or guess work, which may not meet sustainability goals for the built environment as a whole.

To our knowledge, design tools that can support sustainable design of both building and street scale do not exist; rarely are there models that can simultaneously predict indoor energy consumption and outdoor microclimate. The Computational Fluid Dynamics tools, despite many merits, cannot be easily coupled with other simulations software and it is computationally expensive. Building energy models, such as DOE, Ecotech, or IES VE takes in weather data measured at airport or remote rural stations that differ considerably from the conditions in urban areas.

The goal of the proposed study is to develop a usable, simple, accessible, and flexible software platform to support early stage urban design and building design. To this goal, the proposed study will combine two simulation software together. One is VIRVIL, a building energy tool developed at Cardiff University (Jones et al., 2013) and it has been developed into a SketchUp Plugin (WSA, 2014); the other is a multizone microclimate model developed at the University of Hong Kong (Huang et al., 2015). The reason why these two tools are chosen is because both aim at providing rapid assessment at early stage of design, and each are flexible enough to be coupled with other tools.

The combined software platform will allow seamless assessment of environmental parameters across building and street scale. On the one hand, it allows more accurate prediction of building energy used in dense urban areas. The combined model can take into account of localized meteorological factors such as radiative trapping in deep street canyons, heat island effect, and shading from neighboring buildings. On the other hand, the combined model will be better equipped to assess microclimate variations in dense cities, which are driven by not only surface heat gains or natural wind, but also anthropogenic heat sources from building HVAC systems and vehicles.