Energy and Environmental Engineering 5(1): 8-18, 2017 http://www.hrpub.org DOI: 10.13189/eee.2017.050102 CFD Study of Thermal Comfort in Urban Area Fidaros Dimitris 1,* , Baxevanou Catherine 1 , Tsagrasoulis Aris 2 , Bartzanas Thomas 1 , Kittas Constantinos 3 1 Center for Research and Technology, Hellas- Institute for Research and Technology, Greece 2 Department of Architecture, Polytechnic School, University of Thessaly, Greece 3 Department of Agriculture Crop Production and Rural Environment, School of Agricultural Sciences, University of Thessaly, Greece Copyright©2017 by authors, all rights reserved. Authors agree that this article remains permanently open access under the terms of the Creative Commons Attribution License 4.0 International License Abstract The reduction of energy consumption for cooling should be addressed on a city level since the urban environment where the building operates increases its cooling needs and deteriorates the heat pumps operation. In the present work, a Computational Fluid Dynamics (CFD) model is used to study the improvement of microclimate conditions in an urban agglomeration of the city of Volos, through bioclimatic interventions. The Boussinesq approximation is used in order to take into account the thermal buoyancy while the Discrete Ordinate (DO) model is used for the radiation transport. The ground temperature is calculated by solving an energy balance model while the ground is also considered an infrared diffusive radiation emitter. The planted surfaces are considered finite thickness heat sinks and the roofs and building walls are also took as finite thickness isothermal walls and heat sources (the heat pumps and electrical device operation, lighting and, residences presence). Trees are regarded as porous volumes. The surfaces of water elements are considered isothermal heat sink walls. The local microclimate before and after the bioclimatic interventions is presented by comparing the temperature and wind speed distributions as well as the thermal comfort indices for a typical summer day. Keywords CFD, Urban Environment, Thermal Comfort, Radiation, Bioclimatic Intervention 1. Introduction In the past, energy in buildings was consumed mainly for heating but today is also consumed to a high degree for cooling. This increase is due to: a) the development and widespread use of the cooling technology, b) the deterioration of the urban environment. Dense construction and lack of greenery are responsible for the development of the urban heat island. The reduction in energy consumption for heating can be dealt with on a building level, but the case of energy reduction for cooling should be dealt with on a city or neighborhood level. And this is because the urban environment, where a building operates, burdens considerably its cooling needs and the operation of the used heat pumps. The study of the microclimate developed in the urban core is a multivariate problem since the formation of the final pressure, air speed, temperature and humidity field depend upon factor such as: a) local climatic conditions, b) geometry and orientation of buildings, streets and openings, c) used materials in buildings, streets and public spaces, d) existence of greenery and water elements, e) the produced heat in buildings due to residents presence, device operation, lights and heat pumps etc. One way to describe this complex problem is through field measurements. However those measurements give information about specific points and require a large number of assumptions to be adopted in order to draw conclusions for a whole region. Nevertheless this does not reduce their value and the information they provide. Furthermore, those measurements can be used for validation of produced numerical models for the description of the developed microclimate [1, 2]. Measurement techniques are also used by numerical models for the preparation of the urban space computational grid [3]. The methods of Computational Fluid Dynamics (CFD), is another modern way to simulate the developed transport phenomena and to determine the urban microclimate behavior. Those methods can offer a full depiction of the developed microclimate in an area and even consider improvement scenarios by using appropriate materials, adding water elements and green areas, shaping public spaces etc. In this context, the flow field developed in an urban core was studied with CFD without taking into account the energy but focusing on the study of wind and turbulence modelling in paper [2]. A combination of measurements, CFD calculations for the flow aerodynamic and TRNSYS software for the thermodynamics are used in [4] in order to study bioclimatic measures aiming in the rehabilitation of specific open spaces in Tirana during winter and summer. The concept of different techniques coupling is also used in [5] where a CFD model is used for convective heat, air and vapor transfer with a Building Envelope Heat and Moisture (BE-HAM) model and a radiation model (RAD) for the study