"Over time, a building that is poorly designed to withstand heat could lose value"

In a Switzerland that is warming rapidly, the fight against heat is becoming a major concern. It is clearly so for the real estate sector, which has focused its efforts over the past decades on insulating buildings against winter cold. By threatening the comfort, even the habitability, of some buildings during the summer, this development is now pushing the main players in the sector to adapt, some even developing their own solutions, such as GEFISWISS.

Six years ago, at the initiative of its CEO Boris Clivaz, the French-speaking Swiss asset manager specializing in sustainable, local real estate created STEEN Sustainable Energy, a start-up intended to shake up the codes of heating and cooling buildings through one concept: anergy. "This principle can be summarized quite simply: recovering thermal wastes that were until now unused and transforming them into a new energy source," explains Boris Clivaz. We discuss it with him to conclude this series of interviews devoted to ways of combating ever more stifling summer heat.

Has the issue of warming urban centers been underestimated by authorities for too long?

Yes, clearly. For decades, our entire construction culture — insulation, heating, airtightness — has been solely oriented towards winter. The question of summer comfort has largely been underestimated in Switzerland, unlike in southern European countries, which have historically developed strategies aimed at protecting themselves from heat.

Today, with climate warming and the intensification of urban heat islands, this approach is showing its limits. Several studies show that a significant portion of the building stock could become uninhabitable in summer without appropriate measures. As recent work highlights, summer performance depends as much on the building itself as on its environment — neighborhood, density, vegetation. It is therefore essential to integrate adapted measures now.

Do you observe concrete consequences on the value of a property poorly protected against heat?

Yes, clearly. Some early signals are noticeable, such as requests for rent reductions in apartments suffering from summer overheating. This phenomenon is likely to increase, as tenants are becoming more and more sensitive to these issues, particularly vulnerable populations such as seniors. Ultimately, a building poorly designed for heat could suffer a loss in value, as is already the case for properties insufficiently insulated against the cold.

It is not only a climatic issue, but often a problem of building design (orientation, glazed surfaces, lack of solar protections, etc.). It is important to emphasize that the implementation of passive measures — such as a façade modification — may require authorization and can therefore be subject to opposition.

Anergy consists of recovering and pooling so-called “lost” energies, such as waste heat from buildings, extracted air or infrastructures.

How do you assess the financial needs to upgrade the existing stock and should we fear that these needs will contribute to increasing rents that are already unaffordable in some Swiss cities?

We must distinguish two approaches in the energy transition:

• an "ideal" approach, which consists of deep renovation of both the energy systems and the complete envelope of a building;
• a more pragmatic approach, focused mainly on energy systems.

Complete renovation of the existing stock indeed represents very significant investments. The CRML (Center for Risk Management of Lausanne) mentions an investment equivalent to 13% of the net asset value of real estate funds in order to achieve the climate objectives set for 2050 and beyond. At GEFISWISS, we have historically favored well-insulated buildings, integrating, whenever possible, effective thermal management solutions, notably geocooling.

The challenge will be to find a balance between improving comfort, economic constraints and social acceptability. The risk of upward pressure on some rents exists, but it can be limited thanks to progressive and intelligent solutions.

What is anergy, the concept behind your entity STEEN Sustainable Energy?

Steen has developed multi-source energy systems based on the principle of anergy, which allows energy to be phased over time. The system consists of recovering and pooling so-called "lost" energies, such as waste heat from buildings, extracted air or infrastructures.

These systems make it possible to produce heat and cold simultaneously at a distance thanks to an optimized infrastructure — notably via a simplified network — thus reducing costs compared to traditional networks.

Geocooling fits fully within this logic: it is a passive, decarbonized cooling solution that consumes very little electricity. It should therefore not be confused with traditional air conditioning systems.

Is this technology the best response to cooling urban centers?

There will never be a single system capable of covering all needs, and the answer will never be purely technological. However, this approach constitutes an essential building block to meet the growing need for urban cooling. By combining different solutions — anergy, geocooling, etc. — it will be possible to achieve an excellent level of comfort.

Between so-called "active" or "passive" cooling, what concrete solutions exist to reduce the effects of warming urban centers on the built environment?

Priority should be given to passive solutions, as they are the most sustainable approaches to limit building overheating. This primarily involves reducing solar gains through appropriate protections, such as blinds, shading devices or thoughtful façade design.

The building's thermal inertia also plays an essential role: a high thermal mass allows heat to be stored and limits indoor temperature variations. As for natural ventilation, particularly night ventilation, it helps to evacuate heat accumulated during the day.

One should not neglect occupant behavior, which will play an important role in heat management.

Added to these elements are limiting heavily exposed glazed surfaces as well as the choice of materials and colors, since darker surfaces tend to absorb more heat. Today, these principles are widely recognized and constitute the first line of action in facing issues related to thermal comfort.

Beyond the scale of the building, measures must also be implemented at the urban scale. Greening spaces, suitable roof treatments and reducing urban heat islands help limit temperature increases in cities and improve the overall comfort of inhabitants.

Active solutions, such as air conditioning, should however remain limited. Although effective in the short term, they lead to a significant increase in electricity consumption and place strong pressure on energy networks, especially during summer heat peaks.

Finally, occupant behavior should not be neglected, as it will play an important role in managing heat. Simple actions, such as closing shutters during the hottest hours, ensuring adequate ventilation or correctly using available passive devices, concretely contribute to improving thermal comfort.

Is it ultimately more difficult to reduce nuisances linked to heatwaves than those associated with severe cold?

Yes, because as I explained in the preamble our entire construction culture has historically been designed to cope with cold. We know how to heat efficiently, insulate buildings and optimize energy systems. In contrast, heat management is a more recent challenge. It requires rethinking building design and avoiding simple but problematic solutions, such as individual air conditioning, which represents an energy dead end.

We are now in a phase of learning and transition. Feedback shows that occupants now complain more about heat in summer than about cold in winter. This confirms that the challenge of summer comfort is becoming central.

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