Bacterial, fungal, and chemical emissions from air conditioning cooling coils

This study investigated the size-resolved emission rates of microbial aerosols emitted from commercial AC units and identified potential sources of bacterial and fungal growth and emissions of fungi within commercial HVAC systems. Commercial AC units in southern Connecticut were sampled and analyzed using spectrometry, quantitative polymerase chain reaction (qPCR) and next‐generation DNA sequencing technologies. Results from capture on multistage impactors and from real-time bioaerosol fluorescence spectrometer measurements indicated that microbial emissions from AC units into buildings do occur, including emissions of hazardous fungi. As the concentrations of the bacteria and fungi upstream and downstream of the AC coils were not significantly different (P = 0.10 and P = 0.49, respectively), and the fungal ecology between upstream and downstream air determined by PCoA and ANOSIM was also not statistically significant (P = 0.6), this suggested that AC coil biofilms were likely not the source of microbial emission within the system. The filters and heating coils located upstream of AC coils appear to be the source of fungal growth and emissions within the system. These emissions include potentially hazardous fungi such as Aspergillus, Stachybotrys, and Penicillium. As the use and implementation of air conditioning expands, it is necessary to study the filters and heating coils present in these HVAC systems as well as explore microbial mitigation techniques to diminish the emission into buildings of microbes that may be negatively affecting human health.

本研究针对商用空调机组排放的粒径分辨微生物气溶胶排放速率开展了系统调研，并明确了商用暖通空调（Heating, Ventilation and Air Conditioning, HVAC）系统内细菌、真菌滋生及真菌排放的潜在来源。本研究对康涅狄格州南部的商用空调机组进行采样，并采用光谱分析法、定量聚合酶链反应（qPCR）及下一代DNA测序技术开展分析。通过多级冲击采样器（multistage impactors）捕获样本及实时生物气溶胶荧光光谱仪（real-time bioaerosol fluorescence spectrometer）检测所得结果表明，商用空调机组确实会向室内排放微生物气溶胶，其中包含有害真菌。由于空调盘管上下游的细菌与真菌浓度无显著统计学差异（P值分别为0.10与0.49），且通过主坐标分析（Principal Coordinates Analysis, PCoA）与相似性分析（Analysis of Similarities, ANOSIM）解析的上下游空气真菌群落结构亦无统计学显著差异（P=0.6），这提示空调盘管生物膜大概率并非本系统内微生物排放的来源。安装于空调盘管上游的过滤器与加热盘管，才是本系统内真菌滋生及排放的潜在源头。此类排放物包含多种具有潜在健康危害的真菌，例如曲霉菌（Aspergillus）、葡萄穗霉菌（Stachybotrys）及青霉菌（Penicillium）。随着空调系统的应用与普及范围不断扩大，有必要针对这类暖通空调系统内的过滤器与加热盘管开展专项研究，并探索微生物减排技术，以减少可能危害人体健康的微生物向室内环境的排放。