How to reduce cooling costs by up to 30% with the Chimney Effect

In the current energy transition scenario, building envelope design is heavily weighted toward winter insulation. However, given the Mediterranean climate and record-breaking summer temperatures, the real challenge for designers and general contractors is controlling the summer heat load.

While traditional thermal insulation composite systems (ETICS) accumulate radiant heat on the façade and gradually transfer it into the building, ventilated façade technology exploits a principle of thermofluid dynamics to reverse this dynamic: the stack effect.

In-situ data collected by our technical office over 30 years of building envelope engineering confirms that properly activating this laminar airflow reduces energy costs related to operational cooling by up to 30%. Let's explore the physics behind this performance.

The physics of the chimney effect: a natural heat pump

The chimney effect is the natural convective motion of air that occurs within the technical cavity between the insulating panel and the external cladding (in stoneware, stone, or HPL).

The dynamics develop according to specific physical processes:

1. Radiation and thermal gradient: Under the direct influence of the sun, the external cladding panel heats up, increasing the temperature of the air contained in the cavity.

2. Density change: According to the laws of thermodynamics, the hot air becomes less dense and lighter than the outside air.

3. Flow trigger: This difference in density generates buoyancy (hydrostatic buoyancy). The hot air rises rapidly, exiting through the upper closing grilles of the façade and continuously drawing cooler air from the starting vents located at the base of the building.

This continuous cycle transforms the cavity into a true, zero-cost passive heat pump, requiring no electricity to operate.

Why the coat fails in summer and the ventilated facade wins

To understand the 30% savings on air conditioning, we need to analyze the behavior of materials under the summer sun.

In a traditional external thermal insulation system, the external finishing layer (thin plaster) has a very small mass. Under the July sun, the surface temperature of the insulation can easily exceed 70°C. Since there are no interruptions, this heat is transferred by direct conduction through the thickness of the insulation, saturating its thermal phase shift capacity and inevitably entering the home during the afternoon and evening hours.

In the VM Group ventilated facade, the dynamic is completely reversed:

1. Total shielding: The continuous flow of air in the cavity removes the thermal energy from solar radiation before it can reach the insulation panel.

2. Protected insulation: The thermal insulation (rock wool or glass wool) remains in the shade and at a temperature close to that of the ambient air, operating under the ideal thermal conditions for which it was designed.

3. Elimination of radiant heat: The load-bearing wall of the building remains cool, drastically reducing the need to turn on internal air conditioning systems.

Micrometric sizing: the VM Group engineering approach

The chimney effect isn't created "by magic" by simply distancing a sheet from the wall. If the cavity is too narrow, friction slows the flow of air; if it's too wide, internal turbulent motions are created that negate the upward thrust.

Our technical office calculates the effective ventilation cross-section based on specific variables:

• Building height: The taller the building, the greater the convective force (but air velocity must be managed).

• Solar Reflectance Index (SRI) of the sheet: The color and material of the external cladding determine how much heat will be generated in the cavity.

• Grid sizing: The inlet and outlet openings must ensure a minimum airflow of 300 cm2 per linear meter, while acting as a physical barrier against the intrusion of birds and rodents.

Design efficiency with VM Group

Choosing a VM Group ventilated façade means adopting a technology that enhances the value of your property over time, reducing the building's operational carbon footprint (to meet ESG parameters and LEED/BREEAM requirements) and ensuring total living comfort 365 days a year.

To receive a preliminary fluid dynamics analysis for your next project or to learn how to access Conto Termico 3.0 incentives, contact our Strategic Development specialists.