Solutions for a healthy indoor environment

Healthy indoor air in schools is essential to increase the concentration and performance of students as well as their teachers, but also to combat high aerosol concentrations, virus spread and complaints such as odor nuisance, eye irritations, headaches and fatigue. To make the sector aware of this, the Fresh Schools Requirements Program was introduced in 2015. This program, renewed in 2021, sets specific requirements for air quality, among other things. In a typical classroom with about 30 students and one teacher, at least 650 liters of air must be refreshed per hour, with CO2 concentrations not exceeding 1,200 ppm. A "good" level even requires an air change of 950 liters per hour (max. 950 ppm CO2). To implement this properly, customization is required for each school. WOLF Energy Systems can provide this perfectly.

"Since 2015, many meetings have been organized to raise awareness in the industry about the importance of healthy indoor air," knows Tom Melching, technical consultant at WOLF Energy Systems. "This initially focused on concentration and learning performance. By reducing CO2 levels in the classroom, students can excel in learning. There was great interest in the market to get started with this, but unfortunately it stopped there. Not only because responsibilities were placed on school boards, which do not specialize in school ventilation, but mainly because financial resources were lacking. Although schools receive money from the government to maintain their housing, this money is for maintenance and not for innovation/improvement. Moreover, too often this money is still spent on outside consulting firms and/or teaching materials. Even now that as a result of COVID-19 the health aspect has been added to the importance of good school ventilation, real action is still lacking. A number of projects have been started, but these are 'drops in the ocean'. For real change, in addition to specific benefits such as SUVIS, central control is needed. Although the government must take the lead in this, there is also an important task for consultancies, installers and manufacturers. WOLF Energy Systems takes its responsibility in this, by guiding projects from A to Z."

'Open windows offer no guarantees'

At the onset of the COVID-19 pandemic, WOLF, with the support of the Hermann Rietschel Institute (TU Berlin), conducted research on aerosol dispersion in classrooms. For this purpose, a classroom of about 60 m² was simulated, on a summer morning and with an outside temperature of about 20°C. The classroom contained one teacher and 24 students, one of whom was infected with coronavirus. "In accordance with scientific advice, the windows in the classroom were left slightly open and then fully opened after 20 minutes," Melching says. "Based on an emission rate of 50 particles per second, it took only five (!) minutes for the aerosol particles from the infected person to move throughout the room."

The study mapped the distribution of airborne particles using a simulated gas that closely tracked the movement of air in the classroom. The volume of contaminated air increased as the distance between the infected person and the open window increased, reaching more than 900 contaminated particles per m³ in parts of the classroom. Fully opening all windows for five minutes provided sufficient air changes (15 air changes per hour) to reduce concentration levels to less than 100 particles per m³, minimizing the risk of contamination. However, the particle concentration increased again following the same pattern when the windows were put in the tilt position. 

"The simulation showed that slightly opening the windows gives a rather low air exchange rate. It is therefore more effective to fully open the windows," explained Prof. Dr. Ing. Kriegel, head of the Hermann Rietschel Institute. "Even with relatively small changes in parameters such as the wind speed, the time of year or the difference between indoor and outdoor temperatures, the particle concentration can rise far above the values observed in the simulation. With that, open windows offer no guarantee of preventing high aerosol concentrations and other pollutants in classrooms." Melching: "To ensure a healthy indoor climate under all conditions and in all seasons, the combination with a ventilation system is necessary. This applies not only to classrooms, but also to care centers, offices, hospitality venues and sports complexes, for example. For all areas where people spend long periods of time in one room and the risk of infection is therefore higher, we offer a customized ventilation solution. Thanks to our systems, windows no longer need to be fully opened, preventing drafts, temperature fluctuations and nuisance from noise, wind or rain. In addition, the filters in our systems protect the indoor air from fine dust and pollen."

A suitable solution for every situation

Popular in the range are the decentralized CGL edu WTW units, which continuously supply fresh outdoor air and extract polluted, CO2-loaded indoor air. "Thanks to the units, pollutants, odors, fine dust and, above all, moisture are effectively eliminated, while an aluminum counterflow plate heat exchanger guarantees a WTW efficiency of over 90%," Melching said. "In addition, we offer an extensive range of (semi)central WTW solutions, which can be installed above the ceiling, in the technical room or outdoors. For situations where the construction of a ventilation system is complex, we recommend the AirPurifier air purifier with fine dust and carbon filter, which eliminates fine dust, pollen and nuisance odors. The air is then post-filtered in a HEPA H14 high performance filter, which also efficiently removes all aerosols and viruses from the air. For air ventilation, additional windows can be opened."