The Indoor Environmental Quality from the Past to Future Challenges

Keywords: Indoor Environmental Quality, Thermal comfort, Indoor Air Quality, Visual Comfort, Acoustic Comfort

The interest in indoor environmental quality conditions has deep and ancient roots

Concerning indoor air quality (IAQ), it is necessary to distinguish comfort from health risks. The suspensurae of large baths, like Rome's Caracalla, used metals to keep the exhausts from the hypocaustum from getting to the hot rooms and contaminating the air. In the Middle Ages and up until the 19th century, the miasma theory was widespread, according to which vapours and toxic fumes from decomposition processes, stagnant water, or contaminated soil spread through the air, and anyone who breathed them could fall ill with malaria, plague, and cholera. In the 19th century, the germ theory by Louis Pasteur and Robert Koch demonstrated that many infectious diseases were caused by specific microorganisms transmitted directly or through contaminated surfaces, food, and water, not by toxic vapours. Today, air quality is a crucial issue that strongly affects the design, management, and maintenance of HVAC systems.

Concerning thermal issues, the evolution of the history of ideas has a fil rouge consisting of the double relationship between life and death and hot and cold. It is customary to attribute the introduction of a blood-based theory to Empedocles. The blood is conceived as synthesising the four elements, and it does not fill entirely the vessels; instead, it moves within them due to heat. In this way, air occupies the free space inside the vessels and follows the oscillations of blood, determining the inspiration and expiration. Aristotle developed a cardiocentric theory, adopting and modifying Empedocles' ideas. The heart contains the body's natural fire, and the blood, through the vessels, is the heat carrier from the heart, whereas the lungs are responsible for breathing. In the second half of the 2nd century AC, Galen established that there was no air in the blood vessels and theorized the existence of blood capillaries. Early in the 17th century, the Italian doctor Sanctorio Sanctorius began studying the body's metabolic rate and thermoregulation, yielding the first significant findings that helped to establish modern thermophysiology. Sanctorius was among the first to introduce physical measurements in medicine. He discovered the perspiratio insensibilis, one of the heat transfer mechanisms between humans and their surroundings, using a scale he had invented. In those years, some instruments for measuring temperature were invented, including alcohol thermometers. In 1775, Blagden recognised the significance of latent heat loss in the energy balance of the human body. Among the pioneers of studies on the human response to the thermal environment, we certainly remember Lavoisier and Laplace, who carried out (1780) a series of experiments on the production of thermal energy in animals, deducing that there is a relationship between thermal dispersion and respiration. In 1890, the collaboration between the physicist Atwater and the chemist Rosa gave birth to the first calorimetric chamber. This apparatus, where the subject stayed for a long time, allowed to show the equivalence of energy contained in the food and thermal energy dispersed. This occurrence demonstrated that man can be considered a thermodynamic system. Claude Bernard initially postulated the human body's homeostasis in 1865, but Cannon didn't define it until 1932. The evolution of thermal environment studies in the twentieth century reveals the interdisciplinarity of skills. While heat and cold conditions received much emphasis in the first half of the century, comfort conditions also received attention in the post-war era.

Visual comfort has been studied since the 18th century, mainly focusing on the distribution of daylight to improve visibility conditions and reduce visual fatigue. Following the development of electric lighting in the early decades of the 20th century, the first artificial lighting standards were published. Their primary goals were to maximize productivity and safeguard workers' visual health.

Studies on acoustic problems in indoor environments are more recent. American physicist Wallace Sabine was appointed in the late 1800s to enhance the acoustics of Harvard University's Fogg Lecture Hall. During his studies, he developed the reverberation time formula, which became fundamental for the design of indoor environments and contributed to the birth of acoustics as an applied science. Then, the acoustic comfort idea was expanded to include residential and non-residential buildings, ultimately leading to the current understanding. Acoustics was also well known to the ancients, but essentially about theatres like the one in Epidaurus.

Indoor air quality and thermal comfort have been the subject of parallel studies for centuries, as have acoustic and visual comfort in the last century. The ASHRAE Standard 62-2: 2003 [1] referred to the ASHRAE 55: 1992 [2] concerning thermal comfort issues, whereas the ASHRAE 62-1: 2004 [3] stated: “For the purposes of the Indoor Air Quality Procedure acceptable perceived indoor air quality excludes dissatisfaction related to thermal comfort, noise and vibration, lighting, and psychological stressors”.

The first studies focused on the mutual interaction among IAQ, acoustic, thermal, and visual comfort (what is now called indoor environmental quality IEQ) appeared early in the third millennium. As an example, Chiang et al. [4] investigated the impact of the four IEQ components on a sample of elderly subjects living in a care centre, also considering those subjective issues that play a crucial role in the indoor comfort conditions assessment.

As shown by the articles included in this issue, which also highlight the regulatory facets of the subject, research on the four components of Indoor Environmental Quality (IEQ) has advanced dramatically over the last 20 years. The Standards specifically provide indices or indicators of indoor environmental quality for every component, including the well-known PMV/PPD indices for thermal comfort. Unfortunately, there is no overall IEQ index, which could be very useful for assessing the overall quality of the environment. A global indicator could be a weighted average of the indicators related to the four aspects of IEQ. In the case of thermal comfort, the PMV index is enough, as it is also representative of the PPD. Conversely, there is no one metric for visual and acoustic comfort, and a careful choice is required. The best indicator (or indicators) for indoor air quality (IAQ) is up for debate, and no agreement will likely be established. Therefore, a reasonable choice may be to define an indicator for three comfort aspects, excluding IAQ. One possible solution could be to select the worst among the specific indices of the four aspects. In this case, while reaching an agreement on the IAQ index would still be necessary, a deterministic approach would be adopted, one that does not consider the different weights of each aspect of the overall perception. Recently, the Aldren project [5], aimed at key stakeholders in the non-residential building renovation sector, proposed the TAIL index, which considers 12 characteristic parameters of IEQ. These include only the air temperature for thermal comfort, the sound pressure level for acoustic comfort, the daylight factor and illuminance for visual comfort, and for air quality, the presence of mold, relative humidity, ventilation rate, and concentrations of CO₂ and certain pollutants. It is an interesting attempt, although the choice to consider only the air temperature seems unusual. However, TAIL should be tested on a significant sample of people before it can be accepted as an indicator of the sector it was developed for. However, further research is necessary and is one of the future challenges.

Since 2000, the relationship among IEQ, building design, and energy saving has also been consolidated from a regulatory and legislative point of view. This relationship, highlighted in Figure 1, has given rise to a set of standards that fall under the mandates of the EPBD (Energy Performance of Buildings Directive), released in 2002 and 2010. In particular, as is well known, the 2018 version addresses air quality and, more generally, thermal and visual comfort, while the 2024 version explicitly mentions indoor environmental quality, specifying that Member States must consider it in the design of new buildings and major renovations of existing ones.

Figure 1. The relationship among IEQ, building design and energy saving.

The topic of indoor environmental quality also affects other fields, such as ergonomics. Specifically, IEQ concerns both the physical and organizational factors of Ergonomics/Human Factors, as shown in Figure 2.

Figure 2. Ergonomics/Human Factors Areas (https://iea.cc/about/what-is-ergonomics/).

As previously mentioned, the Human Factor plays a crucial role in evaluating indoor environmental quality as well as energy saving and cannot be overlooked when assessing aspects related to comfort. The evaluation of IAQ, which cannot be limited to comfort but must also consider health risks, also falls within the scope of Ergonomics, as this field also focuses on risk prevention.

The strong link between IEQ and sustainability in buildings should not be overlooked. The New European Bauhaus: beautiful, sustainable, together is an EU policy and funding initiative launched by the European Commission in 2021 that promotes sustainable solutions for transforming the built environment and lifestyles as a part of the green transition. "If the European Green Deal has a soul, then it is the New European Bauhaus, which has led to an explosion of creativity across our Union": these words by Ursula von der Leyen may sum up a project that strives for a sustainable future wherein buildings ensure the health and inclusion of their occupants and, as a result, a suitable indoor environment quality. The New Bauhaus, as a creative and interdisciplinary movement, also represents a challenge for engineers and technicians who are often used to working in contexts where creativity is considered an obstacle.

LEED, Breeam, and Well rating systems also address sustainability. However, they lack a unique IEQ indicator. Often, they do not explicitly consider the specific aspects of IEQ but instead account for them within credit categories that are not specific to each individual aspect.

Historic buildings deserve separate consideration, as ensuring adequate levels of IEQ is not always easy due to frequent constraints we cannot overlook. It is our responsibility as technicians to identify alternative solutions that guarantee IEQ while maintaining the building in compliance with the Venice Charter and any subsequent documents, including the CEN 16883 standard [6]. And this is a great challenge too!

References

[1]     ASHRAE (1992). Thermal environmental conditions for human occupancy. ANSI/ASHRAE Standard 55-1992. Atlanta: ASHRAE.

[2]     ASHRAE (2003). Ventilation and acceptable Indoor Air Quality in Low-Rise Residential Buildings, ASHRAE Standard 62.2. Atlanta: ASHRAE.

[3]     ASHRAE (2004) Ventilation for acceptable Indoor Air Quality. ANSI/ASHRAE Standard 62.1. Atlanta: ASHRAE.

[4]     Chiang, C.M., Chou, P.C., Lai, C.M., Li, Y.Y. (2001). A methodology to assess the indoor environment in care centers for senior citizens. Building and Environment, 36, 561-568.

[5]     ALDREN – ALliance for Deep RENovation in Buildings, https://aldren.eu/.

[6]     CEN (2017). Conservation of cultural heritage - Guidelines for improving the energy performance of historic buildings. Standard EN 16883. Brussels: CEN.