Romanian Journal of Physics 64, 819 (2019) INDOOR AIR QUALITY ASSESSMENT IN A CLASSROOM USING A HEAT RECOVERY VENTILATION UNIT T. CATALINA 1,2 , M. A. ISTRATE 1,2 , A. DAMIAN 1 , A. VARTIRES 1 , T. DICU 2 , A. CUCOŞ 2 1 Technical University of Civil Engineering, Faculty of Engineering for Building Services, Bucharest, 66, Pache Protopopescu Blvd. Bucharest, 021414, Romania E-mail: tiberiu.catalina@gmail.com, andrei.istrate85@gmail.com, adamian7@yahoo.com, vartires2@gmail.com 2 “Babeş-Bolyai” University, Faculty of Environmental Science and Engineering, “Constantin Cosma” Radon Laboratory (LiRaCC), Cluj-Napoca, Romania E-mail: tiberius.dicu@ubbcluj.ro, dinualexandra2007@gmail.com Received July 22, 2019 Abstract. The air quality inside buildings is a major problem in EU countries because of lack of any source of fresh air. The situation is even more dramatic in schools were many individuals breathe the same air for multiple hours a day increasing the risk of illness and reduced mental performances. Finding a solution for existing buildings is a challenging task as numerous factors must be considered: noise, weight of the system, required air flow, energy efficiency, costs, maintenance, etc. The present study reports on the analysis of a novel heat recovery ventilation unit inside a high school classroom. The analysis consists of measurement of the indoor environment quality especially on the radon concentrations and CO 2 level for one week. The polluted air is evacuated while a heat recovery ventilator introduces the fresh non- polluted air. This decentralized system is for the first time studied in the literature as most of the studies were focused on centralized systems for new buildings. If before the system installation the CO 2 levels were very high (>2500 ppm) and the radon concentrations medium (>150 Bq·m –3 ) at the end of the measurements it has been proven to be a perfect solution to reduce the indoor pollution. Key words: decentralized ventilation system, indoor air quality, radon, school environment. 1. INTRODUCTION We often talk about air pollution in the city, especially around roads. But several studies have measured air pollution in schools. It is not good to breathe the air of our EU schools – this is revealed in the European SINPHONIE project, which analysed indoor air in 114 schools from 23 European countries [1]. According to SINPHONIE project, every day, children breathe a cocktail of harmful pollutants, such as: benzene, radon and formaldehyde, in concentrations that exceed by far the limits set by World Health Organization (WHO) and National Agency for Food Safety, Environment and Labor – France (ANSES). For benzene, a substance resulting from combustion (including exhaust gases), 25% of schools exceed the threshold of