ACERMI, certification: a partner for summer confort

Summer confort

Faced with ever-warmer summers and longer heatwaves, designing high-performance buildings that are adapted to hot weather is now a major issue. Summer comfort—or discomfort—is thus a core focus of the French 2020 environmental regulation (RE2020).

Which became effective on January 1, 2022. It incorporates greenhouse gas (GHG) emissions from construction products (which the environmental and health declaration datasheet (FDES) makes it possible to characterize) and emphasizes the performance of the building envelope and its insulation. It has significantly higher requirements than those of RT2012, particularly regarding the bioclimatic need (Bbio) indicator for energy efficiency. As a key indicator in establishing a building's ability to provide real comfort to its users or inhabitants in summer and winter, Bbio corresponds to the bioclimatic needs of a building: warm in winter, cool or cold in summer. Bbio defines the thermal indicators (heating, cooling and lighting) of new buildings, regardless of the heating and cooling methods, and thus makes it possible to assess energy efficiency for an entire building. It is an indicator of good bioclimatic design.

Advantages of both summer and winter insulation

With this tighter regulation, the right selection of insulators is, more than ever, a necessity to reduce energy consumption while maintaining, or even improving, perceived comfort. People usually associate insulation with protection against cold. But it is also provides an excellent barrier against heat. It therefore has a positive impact in summer because it increases comfort and decreases the use of costly and harmful air conditioning. Summer and winter, the use of ACERMI-certified products guarantees the overall thermal performance of a building in winter conditions as well as for summer comfort.
A guarantee of efficiency.

Summer - Winter

Understanding the physics of summer comfort

With RE2020, the assessment of summer comfort takes on major importance. RT2012 set the standard indoor temperature (TIC)—the maximum indoor temperature reached in a stretch of 5 consecutive days by correlating it with that of a reference building (Ticref). TIC must be less than Ticref. Feedback on RT2012 brought to light the summer discomfort in many new buildings, leading to the conclusion that Ticref was inadequate in addressing the subject. This is all the more problematic since global warming is already causing unusually hot summers, with increasingly long heatwaves.
RE2020 introduces a new, finer and stricter approach. A new indicator has been adopted to keep track of summer discomfort: the degree-hours of discomfort (DH). This indicator is similar to a meter that sums, over the year, each degree of discomfort perceived each hour. The objective is to assess the impact of heatwaves on discomfort perceived by occupants and to reduce the energy consumption requirements associated with the use of cooling devices: air conditioning, fans, etc.

The Th-D calculation method defines a period that generally extends from May to October (depending on the weather zone) and compares, over the entire period, the indoor operative temperature (Top) with discomfort thresholds set at 26°C at night and 26–28°C in the day. Beyond these thresholds, each additional degree is considered a discomfort for the occupant. The DH indicator therefore quantifies the excess temperature perceived compared with the set threshold and is measured in °C.h (degree-hours). RE2020 also introduces the concept of adaptive comfort, varying the tolerance threshold from day to day to include the human body's ability to adapt to high temperatures after a succession of hot days, up to a limit of +2°C above the 26°C threshold.

Specifically, two DH thresholds are set to assess a building: DH_max and DH_min. If DH is less than DH_min, this RE2020 criterion is considered to be met. Conversely, a DH higher than DH_max means that the building design does not meet the regulatory standard and must be reviewed. Finally, if the DH is between the DH_min and DH_max, the building is considered to be potentially uncomfortable, and a cooling factor, proportional to the difference (DH-DH_min), is applied to the indicator.

DH thresholds

RE2020 is clearly more precise and rigorous. It imposes new constraints on contracting authorities, building designers and construction professionals. It is also an opportunity to highlight the professionalism of each stakeholder, the quality of the materials and the merits of ACERMI certification.