Summer comfort and dual-flow ventilation to cope with heat waves

Overheating is becoming a major housing issue

Improved energy efficiency in buildings has profoundly changed the thermal behavior of homes. New constructions and renovated buildings now benefit from high levels of insulation and airtightness, reducing heating needs in winter.

These characteristics can, however, increase the risk of overheating during the summer. Once heat has accumulated in the home, its removal becomes more difficult, especially during heat waves when nighttime temperatures remain high.

The phenomenon is particularly pronounced in urban areas. According to data presented in Zehnder's white paper, urban heat islands can locally increase surface temperatures by an average of 4 to 6°C, and even up to 10°C during the most extreme episodes. This situation limits the natural cooling of buildings and reduces occupant comfort.

The limitations of traditional cooling solutions

Faced with intense heat, opening windows remains one of the most common reflexes. However, this solution quickly shows its limitations when outside temperatures remain high throughout the day and night.

Natural ventilation does not protect against pollen, noise, or air pollution. In some urban or residential settings, safety regulations may also restrict the prolonged opening of windows.

The white paper also examines conventional air conditioning systems. While they allow for rapid cooling, they involve additional energy consumption, expel heat to the outside, and can indirectly contribute to exacerbating the urban heat island effect.

Anticipate heat gains from the design stage

For Zehnder, managing summer comfort must be considered from the building's design stage. The company relies on the "Cooling Ladder" concept, developed by Munster Technological University and then adapted to its technical recommendations.

This approach is based on prioritizing actions to limit heat accumulation before resorting to active cooling solutions.

The first step is to reduce external heat gain through vegetation and landscaping around the building. Next come design choices that limit heat gain, particularly through the use of appropriate solar shading and by utilizing the thermal inertia of materials.

Reference document: HVAC - Heating, Ventilation and Air Conditioning

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Dual-flow ventilation as a lever for summer comfort

Ventilation plays a central role in this strategy. The white paper highlights the benefits of dual-flow ventilation in ensuring continuous air renewal while improving indoor comfort.

Thanks to the automatic bypass function, dual-flow ventilation systems can promote passive cooling by taking advantage of periods when the outside air becomes more favorable, particularly at night. This airflow management helps limit heat buildup in the home while preserving indoor air quality.

For design offices, installers and designers, this approach is part of a logic of energy sobriety which aims to reduce the need for mechanical cooling.

When air treatment complements passive strategies

During prolonged heat waves, passive measures alone may no longer be sufficient to guarantee occupant comfort. Zehnder then recommends integrating air treatment directly into the ventilation system.

In its offering, this function is ensured by the ComfoClime system, coupled with the ComfoAir Q ventilation unit. This air/air heat pump acts on the incoming fresh air in order to temper and dehumidify it before it is blown into the dwelling.

The goal is to maintain more stable indoor conditions while limiting energy consumption. This solution also has the advantage of integrating with the ventilation system without requiring a visible outdoor unit, unlike many traditional air conditioning systems.

A guide for construction professionals

With this publication, Zehnder hopes to provide food for thought to architects, design offices, developers, installation companies and individuals facing rising summer temperatures.

The document emphasizes that summer comfort does not rely on a single technology but on a combination of measures integrated at the building level. In a context marked by increasingly frequent heat waves and evolving energy performance regulations, controlling overheating has emerged as a key issue in housing design, on par with indoor air quality and energy consumption reduction.