Summer comfort and energy efficiency in hot periods: interest of mixed mode cooling and need for occupant feedback


In the current context of global warming, severe problems of buildings overheating during summer in temperate and hot climates arise. As a result, these hot periods increase the use of air conditioning and thus increase energy consumption and peak electricity demand globally. However, to address both comfort in hot climates and energy savings issues, alternative and original so-called combined passive and soft cooling solutions exist, such as natural ventilation and ceiling fans that consume much less energy. Furthermore, the COVID-19 crisis highlights the importance of building ventilation with clean air in the foreground of natural ventilation. Some cooling solutions combining passive and soft cooling solutions with active, more energy-consuming systems can drastically reduce energy consumption. Nevertheless, although those mixed-mode solutions begin to be well-known today, their uses still need to be improved in the building field, especially in temperate and tropical climates. The notion of performance through both the energy and the comfort aspects is a critical issue. However, quantifying energy consumed through an indicator is relatively easy to reach. In that case, it is challenging to quantify and ensure thermal comfort in diverse hot climates considering a mixed-mode cooling solution combining passive, soft and active systems. Indeed, comfort considerations are not the same in function of the cooling system and the occupant habits. For example, it has been notably shown that the occupants’ comfort expectancy is much higher when using Air Conditioning (AC) than for Naturally ventilated (NV) buildings. Mixed mode cooling solution being at the edge of those AC and NV ones, comfort should be quantified in accordance. Two other challenges appear then. First, suppose the energy performance guarantee is primarily studied in the state of the art in heating conditions. In that case, energy performance guarantee in cooling conditions remains less investigated, especially in the presence of natural ventilation and the use of ceiling fans providing a consequent air velocity. Second, considering comfort in the verification protocols is usually not considered in those works.

This session explores these combined cooling strategies, some occupant feedback and performance indicators. The presentation will be based on cases study in different climate conditions: one tropical climate (Koppen Tropical wet savanna (Aw)) and two temperate climates, Cfa and Cfb in Koppen Classification.  The first part of the session will focus on windows and ceiling fan occupant behaviour model coupling methodology with Building Energy Models. This presentation will rely on a tropical case study. Then, an innovative approach to better understand hot discomfort will be highlighted based on the measurement of global human responses. This presentation will lie on an application to end users of mixed-mode cooled buildings under tropical climate conditions. Thirdly, a Windows coach for office workers will be introduced. The coach’s objective is to advise occupants on the proper action to take on their windows (open or close) to optimise their thermal comfort, IAQ and energy efficiency. Feedback on two summers’ experimental campaigns for occupant thermal comfort in a naturally ventilated building in a continental climate has been used to design the coach. This feedback will be presented. Finally, these works led to a new research project, CoolDown, funded by the French National Research Agency (ANR). It aims to develop new tools and methodologies to target energy and comfort performance in mixed-mode cooled buildings from early design to on-site performance. COOL-DOWN methodology will be introduced in the last presentation and will serve as a starting point for the discussion of this session.


    • to present new tools and methodologies for resilient cooling using successively or simultaneously natural ventilation, ceiling fan and air conditioning
    • to introduce several examples of some cooling strategies proposed to maximise occupants controlled comfort for occupants while minimising energy use during summer, hot periods seasons or heat waves
    • to anticipate the impact of the climate change
    • to introduce the COOL-DOWN framework


  1. Windows and ceiling fan occupant behaviour model coupling methodology with building energy models, a tropical case study. Maxime BOULINGUEZ, Université La Réunion – PIMENT, France
  2. An innovative approach to better understand hot discomfort, based on the measurement of global human responses, including physiological and sensory indicators – application to end users of mixed mode cooled buildings under tropical climate conditions. Gwénaëlle HAESE, CSTB, FRANCE

    Maxime BOULINGUEZ, Université La Réunion – PIMENT, FRANCE

  3. An IAQ and thermal comfort coach prototype to improve comfort and energy consumption thanks to adequate management of natural ventilation: development and first feedback results.
    Arnaud JAY, CEA Liten – INES, FRANCE

  4. Towards an alternative cooling: Optimisation of the successive use of the cooling systems from passive to active – Development of design and control strategies of the hybrid cooling.
    Arnaud JAY, CEA Liten – INES, FRANCE
    Gwénaëlle HAESE, CSTB, FRANCE
    Maxime BOULINGUEZ, Université La Réunion – PIMENT, France


  1. Arnaud JAY, Grenoble Alpes – CEA Liten – INES, FRANCE
  2. Gwénaëlle HAESE, CSTB, FRANCE

-90 minutes

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