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IBPSA 2021 Conference

We will be participating to theInternational Building Performance Simulation Association conference in Bruges in September this year.

Three paper will be presented, exposing part of the research done last year:

  • Urban Heat Island modeling with: Simulation of outdoor thermal comfort: A tweak with EnergyPlus
  • Spatialised computation of indoor comfort levels in semi-open spaces: Spatial distribution of thermal comfort: A case study in Paris’ station
  • Infrared radiation and polymer materials such as ETFE: A Spectral Model for Longwave Radiant Heat Transfer: Influence of New generation Polymers in BES
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Non-isothermal air flow in the urban environment

Amongst the team's current development themes: the calculation of air temperatures in urban environments.

In order to improve the prediction of the consumption calculations of buildings or the exterior thermal comfort, a thermal/aerodynamic coupling is necessary.It is all about taking into account the influence of building surface temperatures on the temperature of the outside air.

The complete anisothermal CFD calculation being prohibitive in computation time, a "weak coupling" approach is adopted, based on energy balances and valorizing the isothermal air velocity field systematically conducted in our studies.

The validation on an experimental dataset is underway (thanks again to our partners from the LaSIE in La Rochelle!).

Diagram of the heat balance on a mesh cell for the calculation of the air temperature.

 

Example of results: 3D air isotherms in a built environment.
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Urban scale infra-red radiation

Among the current development undertaken by the team: computing longwave radiation in the urban environment.

In order to improve the prediction of surface temperature levels for the calculation of building consumption or the evaluation of outdoor comfort, it is necessary to know the radiation view factors between surfaces of an urban scene.

View factor computation being time consuming, we will try to answer following question:

        How can we speed-up the process with a minimum trade-off on precision?

The possibilities yet considered are parallelism and k-means clustering.

Illustration du k-means clustering (source Wikipedia)
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Genetic optimization & natural ventilation

Amongst the team's ongoing research topics: optimizing the modeling of natural ventilation in dynamic thermal simulation.

In order to reduce the computational effort for the pressure coefficient computations by means of CFD simulations, we have to answer the following questions:

"Can we choose the wind directions a priori to limit the number of CFD calculations?"
"With a fixed number of CFD calculations, can we minimize the modeling error compared to a reference case?"

On the agenda : thegenetic optimization coupled to EnergyPlus.

Difference of pressure coefficients on a façade element between the classical approach and the coupled CFD+BES approach.

 

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Urban Heat Island modeling

In the beginning of 2021, we completed the development of a tool for simulating surface temperatures in an urban environment, using a weak coupling approach between temperatures and air velocities

The approach allows for comfort indexes computations at each point in space. It integrates the coupling of fluid mechanics simulations, together with sunlight and thermal dynamic regimes for the built environment.

Results of a case study around the Strasbourg train station (France) are presented next.

The following animation shows the evolution of comfort levels over the first week of the year Sit back and relax!

Hourly comfort levels during the first week of the year.
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Paris Est train station

Roofing and design variations: influence on interior thermal comfort

The study of comfort levels in the Paris Est train station development project was conducted using several steps / methods:

  • A coupling between CFD and dynamic thermal simulation for the calculation of natural ventilation with accurately calculated pressure coefficients
  • The detailed internal distribution of solar fluxes with Radiance software
  • Obtaining indoor comfort levels hour by hour for the whole year and their statistical analysis.

Some graphic results below.

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