Air conditioning and environmental protection : Are they really incompatible ?
By Pierre Famery, of Elcimaï Environnement
What does the future hold for global warming ?
Global warming is already a reality in our country. According to Météo France, the annual average temperature since 1990 has consistently been higher than the average observed during the 1961–1990 period. 2022 was the hottest year in France since the beginning of the 20th century, and 2023 ranks second, with temperatures 1.4°C higher than the norms of the previous three decades.
The situation is similar worldwide, and the Paris Agreement’s goal—to keep the global average temperature rise as close as possible to 1.5°C above pre-industrial levels—is clearly on track to fail.
How can we combat global warming ?
In our regions, the challenges are mounting. Beyond outdoor conditions, the use of buildings (classrooms, hospitals, housing) is being disrupted. We must therefore provide concrete answers to the following questions : how can we address this situation while ensuring an acceptable level of summer comfort for occupants ? To what extent will this—or will it not—have an additional impact on the environment ?
Until now, certain passive solutions have been favored as alternatives to air conditioning : building renovation, bioclimatic design, regulatory changes, etc. And yet, how many thermal simulation models used in design have proven inaccurate compared to the building’s actual use and the experiences of its occupants ? How many building owners have had to deal with dissatisfaction among their staff or users due to obvious summer discomfort ?
The goal is not to reject or slow down the active production of cooling capacity, but to conduct a thoughtful analysis in order to propose innovative, sustainable, carbon-neutral hybrid solutions that align with responsible management.
Summer comfort refers to a building’s ability to maintain a temperature that is not uncomfortable during heat waves. The RE2020, which took effect on January 1, 2022, introduced metrics such as hours of discomfort, when the indoor temperature exceeds 26°C or 28°C depending on conditions.
Energy-intensive and not very low-carbon, the principles of air conditioning (reversible heat pumps or chilled water systems), long favored, no longer seem to be the only or the best solution, and passive cooling solutions, such as green roofs, natural ventilation, or sunshades, are certainly beneficial but also insufficient.
The focus must now be on implementing and promoting a range of measures that take into account both the natural environment—proximity to the sea or the presence of a water table, thermal winds day and night, the effects of urban heat islands, etc.—as well as the building’s configuration and use, starting from the design phase. Create cooling zones in outdoor spaces such as green corridors and arbors, ensure the building’s orientation relative to the sun and winds, allow for cross-ventilation at night, rigorously study choices regarding the building envelope (wall thickness and height, number and type of openings, thermal mass of floors and interior partitions), and organizing spaces according to their use (number of occupants, presence or absence of office equipment, activity level, etc.) are all actions that, when combined, will help ensure comfort in the summer.
But this approach must also be supplemented, and this is where design firms come in. The combination of passive solutions with efficient active technologies appears to be the preferred path to pursue and develop.
New Technologies : Thalassothermy and Aquathermy
Among these technologies, thalassothermy and aquathermy offer underestimated potential. Geothermal energy using geothermal heat pumps also allows heat to be extracted from a building in the summer, stored in the ground, and released in the winter. These solutions offer the possibility of cooling one or more buildings, or even an entire neighborhood, using a chilled water loop. Is it necessary to emphasize the energy efficiency of water-cooled condensation compared to air-cooled condensation for a thermodynamic machine ? Our 20,000 kilometers of coastline, our seas, our lakes, our groundwater, and the many rivers that flow through our territory (representing 80 billion cubic meters of runoff and floodwater per year for metropolitan France, according to the National Water Data Network) enable a wide range of innovations in cooling, given that water withdrawals, discharges, and other impacts on biodiversity are strictly regulated to manage environmental consequences. Thus, in a city crossed by a waterway, it is possible to establish an urban cooling network, an energy-efficient and sustainable solution. This is the case in Paris, where the cooling network operates using the Seine.