Abstract
Deciphering the urban microclimate is a long-standing research topic which has been lately consolidated as a major interest in the built energy and environment community. Research investigates at a fast pace the physical laws and simulation techniques to better understand the urban built environment and the ways of improving it. The snap increase in the amount and breadth has come at a price of little systematization and appreciation of knowledge. With that in mind, this chapter provides a gentle overview of the Urban Weather Generator (UWG), a physics-based microclimate simulation paradigm developed and maintained over the past decade to quantify the energy interactions between buildings and urban climate. This chapter favours a consistent and progressive introduction of the main concepts and architectural treatments in the UWG over an exposition of the most related literature. Knowledge of changes in the urban environment and their effect on building energy performances can potentially support a better decision-making framework for civil engineering systems, particularly at the planning and design stage. We present the initial motivations, theoretical models, case studies, and practical achievements of the UWG that have thus far been made as well as the many challenges that await us in this nascent field. This chapter aims to give an insight into the importance of considering the urban microclimate as well as to stimulate further research.
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Notes
- 1.
The eagle-eyed reader might note that, technically, solving only two different sets of equations for night-time and daytime conditions would somewhat lead to discontinuities during the transition periods in the morning and evening, respectively. Although some small jumps in the temperature profile have been observed in our numerical trials, we treat this as a minor issue from the perspective of practical implementation. The discontinuities can be attenuated by the thermal inertia of the air body in the UBL and can be further reduced by adaptively shifting the transition times between day and night.
- 2.
UWG MATLAB version. https://github.com/Jiachen-Mao/UWG_Matlab.
- 3.
UWG Python version. https://github.com/ladybug-tools/uwg.
- 4.
Dragonfly. https://www.ladybug.tools/dragonfly.html.
- 5.
Ladybug Tools. https://www.ladybug.tools/.
Abbreviations
- A :
-
Area, m2
- A f :
-
Lateral heat exchange area, m2
- C :
-
Capacitance/conductance, W s K−1/W m−2 K−1
- C k :
-
Model parameter related to the diffusion coefficient
- c p :
-
Specific heat at constant pressure, J Kg−1 K−1
- c v :
-
Specific heat at constant volume, J Kg−1 K−1
- d :
-
Thickness, m
- E :
-
Turbulent kinetic energy, m2 s−2
- g :
-
Gravity acceleration, m s−2
- h :
-
Heat transfer coefficient, W m−2 K−1
- H rur :
-
Rural sensible heat flux, W m−2
- H urb :
-
Urban sensible heat flux, W m−2
- K d :
-
Diffusion coefficient, m2 s−1
- l k :
-
Length scale, m
- Q :
-
Heat flux, W m−2
- Q surf :
-
Sum of net radiation, sensible, and latent heat fluxes at the surface, W m−2
- R :
-
Resistance, K W−1
- t :
-
Time, s
- T :
-
Temperature, K
- T deep :
-
Annually average ambient air temperature of the site, K
- U :
-
Window U-factor, W m−2 K−1
- u circ :
-
Circulation velocity, m s−1
- u exc :
-
Exchange velocity, m s−1
- u ref :
-
Reference air velocity, m s−1
- V :
-
Volume, m3
- \( \dot{V} \) :
-
Volume flow rate, m3 s−1
- z :
-
Vertical space component, m
- z i :
-
Boundary layer height, m
- z r :
-
Blending height, m
- z ref :
-
Reference height, m
- θ :
-
Potential temperature, K
- θ ref :
-
Reference potential temperature outside the control volume, K
- ρ :
-
Density, kg m−3
- (ρc)l:
-
Volumetric heat capacity of the layer l, J m−3 K−1
- AEC:
-
Architecture, engineering and construction
- API:
-
Application programming interface
- CHTC:
-
Convective heat transfer coefficient
- DOE:
-
Department of Energy
- EPW:
-
EnergyPlus Weather
- HVAC:
-
Heating, ventilation and air conditioning
- MIT:
-
Massachusetts Institute of Technology
- RC:
-
Resistance-capacitance
- RSM:
-
Rural station model
- TEB:
-
Town Energy Balance
- UBLM:
-
Urban boundary layer model
- UC-BEM:
-
Urban canopy and building energy model
- UCL/M:
-
Urban canopy layer/model
- UHI:
-
Urban heat island
- UWG:
-
Urban Weather Generator
- VCWG:
-
Vertical City Weather Generator
- VDM:
-
Vertical diffusion model
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Acknowledgements
Over the years, this work has received financial support from the Singapore National Research Foundation through the Singapore-MIT Alliance for Research and Technology (SMART) Center for Environmental Sensing and Modeling (CENSAM), the MIT and Masdar Institute Cooperative Program, the Energy Efficient Buildings Hub of the US Department of Energy (DOE), the MIT Energy Initiative, the MIT Presidential Fellowship, the Leon Hyzen Fellowship and the George Macomber Chair Scholarship.
A special thank you goes to Chris Mackey (at Ladybug Tools LLC) for actively leading the development of the UWG Python version and Dragonfly over the years, as well as for his brilliant comments and fruitful supports during the writing of this chapter.
Finally, we would like to thank all the people who have helped us reach this far. The UWG would not have been possible without your enthusiasm and participations, which allow for potential technical updates and also make it more fun.
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Mao, J., Norford, L.K. (2021). Urban Weather Generator: Physics-Based Microclimate Simulation for Performance-Oriented Urban Planning. In: Palme, M., Salvati, A. (eds) Urban Microclimate Modelling for Comfort and Energy Studies. Springer, Cham. https://doi.org/10.1007/978-3-030-65421-4_12
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