– Moheet Vishwas
The degree of physiological ease we feel under our skin in an indoor environment is commonly attributed to the rather nonchalant-sounding term, “Thermal Comfort”. As easy as it may sound, it is hard to define and even harder to achieve.
Most people perceive thermal comfort to be synonymous with air temperature, but as far as engineering concoctions go, there is no single attribute that can accurately define the term in an indoor environmental space. It is, in fact, a culmination of six factors, or indicators, collectively contributing to the cause of ease. The six indicators are classified under two categories:
- Air temperature
- Relative humidity
- Air velocity
- Radiant temperature
- Metabolic heat
The indicators, in conjunction with the principles of heat balance and collected experimental data, are then used to develop one of the most recognised thermal comfort performance indicators – the Predictive Mean Vote, or PMV. The other well-known and popular thermal comfort model, called Adaptive Thermal Comfort (ATC) was created through numerous field studies to address concerns of indoor air temperature in relation to outdoor air temperature and thermal comfort.
In the Adaptive model, a building’s occupants dynamically interact with their environment. The model takes into account the many ways people perceive changes to their environment by applying a degree of control through fans or insulated clothing. It represents a simple method that relies on the indoor air temperature with respect to the outdoor air temperature as the main performance indicator. The PMV model, in comparison to the ATC model, is widespread in the Middle East region, since it is applicable to buildings that make use of mechanical ventilation systems as opposed to the adaptive model, which is used as a thermal comfort performance indicator in buildings that rely on naturally conditioned spaces. The PMV is essentially a scale that ranges from -3 (cold) to +3 (hot). It’s a mathematical model that was developed by P O Fanger between 1967 and 1972.
It is useful to have broad thermal comfort models, like the PMV, but it’s about time we developed newer models that suit the specific needs of buildings, such as schools or hospitals, and set new definitive standards. What we need is an approach that can couple thermal comfort with air quality to give comprehensive indoor environmental models.
Indoor environments are vital to the well-being and the progress of students in schools. Over the years, extensive research has helped prove the palpable correlation between the six indicators and indoor air pollutants, on one side and their apparent influence on the performance of students in schools, on the other. And while there is overwhelming evidence to prove that students perform better in schools with optimum indoor environmental conditions, it is important to understand the changing expectations of thermal comfort while evaluating schools for the same.
For instance, high concentrations of volatile organic compounds in schools lower attendance, poor ventilation rates or inadequate fresh air intakes affect academic performance and harmful inorganic compounds perhaps go one step farther in seriously jeopardising students’ future. There are studies that establish indirect associations, too, such as microbiological pollutants to the exacerbation of an asthmatic condition and respiratory illness, which results in reduced attendance and poor performance.
It’s time for these issues to be dealt with at a design level by developing energy-efficient thermal comfort models that are not just comfort-centric but also take into account the health of the occupants by factoring in the quality of air the students inhale.
Schools in the Middle East solely rely on mechanical ventilation systems, since the scorching heat of the summer is not conducive to natural ventilation. As per the norms, all mechanical ventilation systems have to comply with such comfort standards as specified in ASHRAE 55 or ISO 7730 for creating adequate indoor environments. The soaring temperatures during the extended summers in the Middle East mean most building designers resort to over-sizing the air conditioning systems. These systems constantly require energy-intensive environmental control strategies at the expense of compromising on climate-response methods, energy-efficient designs or innovative strategies in mechanical designs.
That is why the intelligent building control system is the need of the hour in schools. To begin with, the system is capable of meeting the objectives of a well-designed thermal comfort model. When implemented properly, it can also address every air quality issue that is plaguing schools.
Modern, well-designed HVAC systems, such as variable air volume units and demand-controlled ventilation regimes, need control systems in order to function in an effective manner. This highlights the need for automation to be synergised with thermal comfort models, indoor air quality and adequate mechanical ventilation systems. An automated control system for thermal comfort, based on the PMV and energy efficiency is an example of synergy. An integrated and adaptive control system with self-learning traits, based on the trends of the collected data, such as occupancy and activity schedules, is another. Also, advancements in data-gathering technologies, such as cloud computing and remote-server applications – accessed through mobile phone applications – mean that teachers can effectively over-ride functions as per the requirements of the students.
Another thermal comfort strategy worth considering in schools is combining active and passive cooling systems. To maximise energy savings, a mechanical ventilation system must have enough provision to allow for cooling through natural ventilation without affecting the indoor air quality. Advanced control systems can combine the two by making passive systems actively controlled. A simple control application that modulates motorised components to adjust shades, windows and louvres to open or close positions under the right ambient conditions can contribute to passive cooling and increased fresh air intake in classrooms.
An optimum air conditioning strategy would be one that doesn’t sacrifice a sustainable future for thermal comfort or indoor air quality. One cannot exist without the other, and the onus is on the government authorities in charge of regulating schools to bridge that gap and to find the right balance between the two. Technological advancements will gradually raise the bar to its absolute optimal standard, but firstly, the authorities and, in fact, the other stakeholders must be prepared to embrace innovations and implement them in existing and new schools. Provisions for thermal comfort and indoor air quality are critical for the well-being of students, and the teaching and non-teaching staff, but they also have to be energy efficient. There is irrefutable evidence in scientific literature and enough justification for improving and continuously monitoring indoor environmental standards through intelligent control systems in schools. The measures will help negate the health risks to students, encourage higher attendance in classrooms and improve academic performance.
The writer has a master’s degree in Energy Engineering and a bachelor’s degree in Electronics and Electrical Engineering. He works as an engineer in Dubai and can be contacted at firstname.lastname@example.org. Any ideas or views expressed are his own.