In the field of energy strategy, the technical efficiency of buildings has improved significantly (+25% between 2000 and 2017). However, the overall increase in surface areas has often offset these gains, illustrating what is known as the rebound effect.
In response to this, the sector is exploring new approaches that complement technology to address climate challenges. Among them, sobriety through intensity of use and “Slow Heat” are emerging as relevant and accessible levers.
Far from being a constraint, this approach to sobriety offers an opportunity to rethink our practices in order to gain resilience and coherence.
Rethinking standards: the “Slow Heat” approach
The traditional heating model generally aims to maintain a uniform temperature of 19 to 21 °C throughout all spaces. Although standardized, this method consumes a significant amount of energy to heat the air, sometimes regardless of actual occupancy.
The concept of Slow Heat offers a different perspective: focusing on people’s thermal comfort rather than systematically heating entire buildings.
This approach suggests a range of solutions that can be adapted to specific needs:
- Class A (Passive): adaptation through clothing, the creation of protected zones (partitioning), and natural acclimatization.
- Class B (Contact heating): heat provided through conduction (heated vests, heated seats, hot water bottles).
- Class C (Localized radiation): the use of radiant heat sources in close proximity.
- Class D and E (Convection): heating the air in the room or building, used as a complement when necessary.
The goal is to personalize comfort. It involves allowing a more precise and individual control: for example, using a 360 W radiant heater at one’s workstation can provide excellent thermal comfort in a cooler overall environment, while reducing overall energy consumption.
The human factor and adaptation
The comfort of occupants is central to this approach. Research on this topic, notably conducted by groups from ULB, provides interesting insights into our capacity to adapt.
Feedback shows that after an adaptation period of around 28 days, thermal perception evolves:
- A reduction can be observed in the gap between the actual temperature and the perceived comfort temperature (with the average temperature decreasing from 21 °C to 17.5 °C).
- The body reactivates its natural thermoregulation mechanisms (physiological acclimatization).
- A balance appears to be around 16 °C for activities and 14 °C for sleep.
These observations suggest that comfort is not a fixed condition, but a dynamic state. By giving users more control (choice of heating solutions, adaptation of clothing), a more positive relationship with their environment is encouraged.
Intensity of use: optimizing existing space
Beyond temperature, sobriety also invites us to rethink how we use our spaces. Analyses show that the average occupancy rate of offices in Europe is often between 35% and 40% during working hours.
Intensity of use aims to make better use of existing buildings in order to limit the need for new carbon-intensive construction:
- Optimization: Sharing and increasing the flexibility of workspaces offer significant potential to reduce the required surface area (estimated between 50% and 70% in some Swedish studies).
- Soft densification: Expanding or reorganizing existing buildings improves efficiency per square meter without the carbon impact of new construction.
- Mutualization: Encouraging people to gather in heated shared spaces (shared lounges, third places) is a social practice that helps optimize energy consumption.
Guidelines for the future: the CLEVER 2050 scenario
To guide both real estate and personal strategies, the CLEVER 2050 scenario provides reference values that are compatible with planetary limits, which can be seen as “consumption corridors”:
- Living space: aiming for 32 to 40 m² per person.
- Hot water: an average of 18 to 25 liters per person per day.
- Specific electricity use: 500 to 700 kWh per person per year for appliances.
These indicators encourage “sufficiency”: aiming for what is truly necessary. In some cases, adopting more frugal behaviors can be more effective from an environmental perspective than major renovations, which carry a high material carbon cost.
Conclusion: supporting the transition
Technical solutions already exist and are often accessible and low-tech. The real challenge lies in supporting people through this transition.
Sobriety is a progressive approach that transforms our relationship with energy: we move from a logic of automatic supply to one of tailored comfort.
It is an invitation to experiment step by step, to rediscover a conscious and sustainable control over our thermal well-being.
