We may not realise it, but on average we spend about 90% of our day indoors, and we are very much affected, for better or for worse, by the environmental conditions we find inside buildings. Modern buildings are increasingly airtight, and thus their indoor air conditions are mostly determined by how well the HVAC system (heating, ventilation and air conditioning) works and caters to the needs of the human body.
When can we say the surrounding environmental conditions are satisfactory! Well, for a start, when we are comfortable. Some of the most relevant parameters that contribute to a general sensation of comfort are:
-Temperature
-Relative humidity
-Air speed
-CO2 concentration
-VOC (Volatile Organic Compound) concentration
-Micro-organism concentration.
All of these indicators together determine our comfort level, which is usually deemed acceptable if the PPD (Percentage of Persons Dissatisfied) index is below 10% [EN ISO 7730]. More practically, there are various national and international guidelines that regulate the allowable range for each parameter, although these are not mandatory in most countries.
For example, temperature is usually required to be between about 67 and 820F or 20 and 270C across the year, relative humidity between 40 and 60%, and indoor CO2 level lower than 1000 ppm.
When these values are outside of such limits, the human body suffers. Symptoms may vary greatly: headache, dizziness, nausea, eye, nose or throat irritation, dry cough, dry or itching skin, difficulty in concentration, fatigue, sensitivity to odours, hoarseness of voice, allergies, cold, flu-like symptoms, increased incidence of asthma attacks. When these symptoms affect the inhabitants of a building without any specific illness or cause being identified, their condition is called sick building syndrome.
Sick building syndrome is a serious ailment. Although studies suggest that about 30% of new buildings around the world may be subject to it, it is easy to underestimate its impact, as it might be difficult to trace symptoms from the occupants back to the true cause, the building itself. Effects are not immediate, and may appear only after prolonged or repeated exposure to the indoor environment. Moreover, some causes are more obvious than others.
Air temperature, for example, is the single parameter we can most easily identify as the cause of discomfort when it is outside of the normal range, however that is rarely the case, as a working heating/cooling system is the bare minimum to be expected in most buildings nowadays.
Relative humidity
Relative humidity, on the other hand, is the next major factor and it is usually downplayed, although it has a significant role in altering our perception of air temperature and affecting skin transpiration, as well as our internal energy balance. A suitable level of relative humidity prevents excessive skin, eye and respiratory tract dryness and enables us to breath and perspire more easily. This way, we can avoid subjecting our thermoregulation system to excessive effort that may cause discomfort. Other symptoms caused by breathing excessively dry air are headache, fatigue and irritability.
Managing humidity correctly also makes it possible to reduce any dust particles in the air by making them adhere to walls and floors. In a dry environment, they would remain suspended for longer, accentuating the feeling of dryness and discomfort.
Relative humidity also affects health of building occupants in other ways, through its impact on infectivity and indoor transmissibility of bacteria and viruses. Several laboratory studies have found that some airborne transmitted viruses – e.g. influenza virus – sharply decrease their activation rate at relative humidity above 40% (High Humidity Leads to Loss of Infectious Influenza Virus from Simulated Coughs – Noti et al.)
Another factor to consider is called mucociliary clearance, which is the self-clearing mechanism of the airways in our respiratory system. MCC works through a combination of a layer of mucous which traps the impurities we breathe in with the air, together with a wall of small cilia which slowly pushes the trapped pathogens to the oral cavity. Breathing air with low humidity level results in the inability of the cilia on the epithelial cells to move, compromising the response of the innate immune system. (“Low ambient humidity impairs barrier function and innate resistance against influenza infection” – Kudo E, Song E, et al. 2019).
Even, if other factors can participate in causing sick building syndrome, such a.s the lack of adequate fresh air intake or various materials and substances that release pollutants, the presence of relative humidity control, or lack thereof, has a major effect on its own on the health of building occupants.
Studies show that low humidity conditions alone can cause a reduction in the performance of workers carrying out office tasks such as reading, document editing and calculations. Moreover, controlling relative humidity between 40 and 60% can decrease the absenteeism rate of workers by about 7%. (Indirect health effects of relative humidity in indoor environments. – A V Arundel, E M Sterling, J H Biggin, and T D Sterling).
Solutions from CAREL to improve indoor air quality include-
Pre-configured control for AHU regulation: An air handling unit control and automation system can play a vital role in ensuring the correct personal comfort and health conditions are maintained in occupied rooms. The control system coordinates all of the unit’s components, which work together to achieve the desired ventilation with the lowest possible energy consumption. CAREL offers ready-to-use solutions that implement advanced logic to ensure that the right quantity and quality of air is introduced into rooms, when needed. Demand-controlled ventilation logic based on multiple parameters (CO2, VOC, PM 2.5-10), room pressurisation management, monitoring of absolute filter (HEPA) clogging, and advanced control of adiabatic humidification are fundamental strategies in achieving these goals.
The CAREL k.Air controller can ensure that the air handling unit operates in compliance with the most stringent hygiene standards, such as VDI6022, avoiding the unit itself from representing a risk for the proliferation of bacterial contamination.
Indoor air quality sensors
CAREL offers a complete range of sensors for measuring the most important parameters that determine indoor air quality: temperature, relative humidity, CO2 (carbon dioxide), VOC (volatile organic compounds), PM 2.5 and PM 10 (particulate matter). The measured parameters can be viewed directly on the display and/or used to control various mechanical ventilation and air purification systems, either via RS485 serial communication or a proportional signal. Integration of indoor air quality probes into the control of building ventilation systems helps combine the need to control energy consumption with the guarantee of a healthy and comfortable indoor environment. Maintaining an adequate indoor air quality level protects human health and productivity in shopping centres, offices, theatres, museums and other environments.
All in all, indoor air quality is a key factor in the correct design of HVAC systems in modern buildings. Proper relative humidity control, although often neglected, is one if the best tools we have to create an indoor environment that is good for human health and comfort, with a positive impact on the absenteeism and performance of occupants. As new knowledge and studies related to the not-so-new concept of indoor air quality emerge, there is the hope that guidelines and regulations all over the world will be updated and taken it into account when specifying how new HVAC systems should be designed.
Indoor air quality control is beneficial in its application to numerous types of buildings with a high level of human occupation, and not just hospitals and healthcare facilities. Also inside offices, supermarkets, schools and educational facilities, theatres and museums, hotels and our homes, health, not just comfort, are on the line.
Andrea Oscar Frisiero,
Application Specialist at CAREL HVAC Marketing Unit Commercial, is responsible for Indoor Air Quality and Climate Control application, focusing especially on healthcare segment.
