Abstract
Energy recovery ventilators (ERVs) are widely used to reduce energy losses caused by ventilation and improve indoor air quality for recently-constructed buildings. It is important for spaces with high occupancy density and longer residence times, such as classrooms. In classrooms, the ERV size is typically estimated by the target number of students in the design phase, but the design air volume flow rates (m3/h) of the ERV can decrease over time owing to filter degradation such as increased dust loading. In this study, field tests are conducted in a classroom to investigate filter degradation through a visual inspection and by measuring the air volume flow rates at the diffusers connected to the ERV. In addition, variations in carbon dioxide (CO2) concentrations are also measured to verify the effects of filter degradation on the indoor CO2 levels over the entire test period, which includes filter replacement, as well. As the tests are conducted during classes, several adjusting methodologies are proposed to match the different test conditions. The results show that the total air volume flow rate of the ERV increases after the filter replacement (546 to 766 m3/h), but it again decreases as time elapses (659 m3/h). Accordingly, the indoor CO2 concentration decreases after the filter replacement by more than 300 ppm (1404 to 1085 ppm), clearly showing the effect of filter degradation. However, this CO2 concentration remains similar for four months after the replacement, and the total air volume rate decreases again. An interpretation is made using computational fluid dynamics analysis that the measured CO2 concentrations are affected by airflow patterns. The airflow in the cooling system may dilute CO2 concentrations at the measuring location. Thus, periodic filter replacement and management are important to ensure the desired ERV air volume rates and consequently the desired indoor CO2 concentrations.
Highlights
With an increased requirement for reducing building energy consumption, buildings have become more airtight, and the infiltration rates have decreased [1]
The number of students is changed over the filter replacement period, and the electric heat pump (EHP) mode is changed between the second and third time points
The existing filters mounted in the Energy recovery ventilators (ERVs) system for the past three years were replaced by new ones, and the resulting air volume flow rates and CO2 concentrations were measured
Summary
With an increased requirement for reducing building energy consumption, buildings have become more airtight, and the infiltration rates have decreased [1]. A decrease in air exchange rates of a building is good for energy conservation, but the contaminated air may remain indoors for a long time, such as PM2.5, radon, formaldehyde, nitrous oxides, volatile organic compounds and carbon dioxide (CO2), which are harmful to the health of the occupants [2,3,4,5]. High levels of CO2 concentration are observed in a space with high occupancy density. This may cause problems such as headaches, fatigue, eye symptoms, throat symptoms and breathing difficulties. Consequences of such problems may be more serious when the room is used for mental work. Several studies reported negative effects of high CO2 level on educational attainment [7,8,9,10,11,12]
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