Assisting low energy consumption building design

To gain professional experience with MINES ParisTech

Maxime Trocm is a doctor of MINES ParisTech since the 26th of November 2009

His PhD thesis took place within the framework of a partnership between the Center for energy and processes of MINES ParisTech and VINCI (World largest construction company). The work was conducted full time in the R&D department of VINCI Construction France.

 

After a motivating six month internship at the CEP and engineering school graduation, Maxime Trocmé was desirous to acquire more competence on building eco-design. This doctoral thesis was a way to fulfil this wish in a theoretical (building models) and practical way (real building studies). Since it took place within the frame work of a CIFRE convention, it was also an opportunity to gain professional experience.

Thermal modelling tools

Various studies and real life instances show that a high performance level, e.g. primary energy consumption below 50 kWh.m-² per year (including heating, cooling, domestic hot water, lighting and ventilation), can be reached through appropriate architecture design combined with high insulation, free cooling and heat recovery on exhaust air. This last technology is particularly affected by airflows across the building envelope caused by low air tightness. Thermal modelling tools need therefore to deal with this issue precisely.

A multizone model has been developed to compute building airflows in order to evaluate them with a higher degree of precision in the frame of a simplified simulation tool that can be used in early design phases. This model is based on the well-mixed zones assumption and mass conservation principles. The air flow rate between two zones is expressed as a function of the pressure drop between those two zones. Wind pressure and buoyancy effects are the causes of pressure drops. Several types of connections are implemented: cracks, ventilation inlets, large openings. This model has been implemented in the thermal building simulation tool COMFIE, developed at the CEP.

Two case studies are presented. First, the case of a residential building, a project of Vinci Construction France where the influence of air tightness on heating loads is studied. Then the case of a concept building, EFFIBAT®, being developed by Vinci Construction France and MINES ParisTech. This building is an urban dwelling including an atrium. Natural ventilation is used to cool the building at night in summer and the model aims at evaluating the resulting comfort level.

 


The simulation tool was developed and validated. Its use on real cases was of great importance to assess their thermal performance precisely. Moreover it was linked to a LCA (Life Cycle Assessment) that evaluates environmental impacts from building construction to demolition. Several impacts (e.g. CO2 emissions, resource depletion or water consumption) could therefore be evaluated with regard to the new model results.