A validated numerical investigation of the ceiling fan's role in the upper-room UVGI efficacy

We measured indoor air speeds generated by ceiling fans in 78 full-scale laboratory tests. The factors were the room size, fan diameter, type, speed, direction (up or down), blade height, and mount distance (i.e. blade to ceiling height). We demonstrated the influence o f t hese f actors, s howing t hat t he m ost s ignificant ar e speed, diameter and direction. With other factors fixed, t he average r oom a ir s peed i n t he o ccupied z one increases proportionally with fan air speed and diameter. Blowing fans upwards yields lower but far more uniform air speeds than downwards. We show that for the same fan diameter and airflow, f an type h as l ittle effect on the air speed distribution in the region outside the fan blades. We developed several new dimensionless representations and demonstrate that they are appropriate for comparisons over a wide range of fan and room characteristics. Dimensionless linear models predict the lowest, average, and highest air speeds in a room with a median (and 90 th percentile) absolute error of 0.03 (0.08), 0.05 (0.13), and 0.12 (0.26) m/s respectively over all 56 downwards tests, representing common applications. These models allow designers to quickly and easily estimate the air speeds they can expect for a given fan and room. We include all measured data and analysis code in this paper. Highlights:• Measured air speed distribution in 78 full-scale laboratory tests • Average air speeds increase in direct proportion to fan rotational speed and diameter • Blowing fans upwards yields lower but more uniform air speeds than downwards • At equal diameter and airflow, fan type doesn't affect air speeds in most of the room • Developed easily applied models to predict indoor air speeds with ceiling fans Graphical Abstract 2

Section: Review Of Prior Studies Investigating Ceiling-fan Driven Airmentioning

confidence: 99%

Ceiling fans: Predicting indoor air speeds based on full scale laboratory measurements

Raftery

Fizer²,

Chen

et al. 2019

“…The spatial distribution of fluence rate in the upper room, which is also needed for CFD predictions of upper-room UVGI, is available from a previous publication [13]. In a companion paper with the same title as the present paper, but referred to as Part II, the efficacy of upper-room UVGI was predicted from simulations using both Eulerian and Lagrangian CFD [14]. These predictions were made without knowledge of the results from the present experimental study.…”

Section: Discussionmentioning

confidence: 99%

“…w. (12. 5250 cfm (0.77, 1.4, and 2.5 m 3 /s) respectively, based on methodology published by U.S. EPA [16]. Further details for this fan are given in a companion paper [14]. We did not conduct experimental tests without a ceiling fan operating because upper-room UVGI efficacy may vary significantly depending on the amount of mixing caused by heat sources (such as people, computers, and radiators), HVAC systems, differences in indoor and outdoor temperatures, and wind velocity [17e19].…”

Section: Room-size Test Chambermentioning

confidence: 99%

See 1 more Smart Citation

Influence of ceiling fan's speed and direction on efficacy of upperroom, ultraviolet germicidal irradiation: Experimental

Rudnick¹,

McDevitt²,

Hunt³

et al. 2015

Self Cite

a b s t r a c tIncreasing a ceiling fan's speed from its lowest setting of 61 rpm, which resulted in 0.77 m 3 /s of airflow, to its highest setting of 176 rpm, which resulted in 2.5 m 3 /s of airflow, or having the fan blow either upward or downward had no statistically significant effect on the efficacy of upper-room ultraviolet germicidal irradiation (UVGI). This outcome suggests that air circulation due to the ceiling fan was sufficient and that any additional increase would not improve efficacy. Numerous experimental studies on upper-room UVGI in which fans were used to provide air mixing have been published. However, none have quantified the air movement produced by these fans or described their tests in sufficient detail to allow results to be compared to predictions using computational fluid dynamics (CFD). The present work provides the required information. In addition to the usual boundary conditions needed for CFD, we made experimental measurements of UV susceptibility of the microorganisms used in the upper-room UVGI tests. We measured UV susceptibilities for Mycobacterium parafortuitum and Bacillus atrophaeus spores to be 0.074 and 0.018 m 2 /J, respectively. In a previous publication, we reported the spatial distribution of fluence rate, which is also needed for predicting efficacy from CFD. In a companion paper referred to as Part II, upper-room UVGI efficacy was predicted by both Eulerian and Lagrangian CFD and compared to the experimental results from the present study.

“…The decay of airborne microorganism was indispensable factor in both empirical and theoretical models of airborne transmission, which was difficult to be quantified [2,40,41]. Inlet air filter to remove the effect of background concentration was indispensable in the use of tracer bacteria without specificity in UVGI studies [42][43][44]. Whereas, the lack of biological characteristics for particles or narrow application of microbial surrogate in clean or isolated room prevented it to be an ideal substitution of airborne microorganism.…”

Section: Introductionmentioning

confidence: 99%

A tracing method of airborne bacteria transmission across built environments

Wang

Zheng

et al. 2019

A B S T R A C TDisease transmission across built environments has been found to be a serious health risk. Airborne transmission is a vital route of disease infection caused by bacteria and virus. However, tracing methods of airborne bacteria in both lab and field research failed to veritably express the transporting process of microorganism in the air. A new tracing method of airborne bacteria used for airborne transmission was put forward and demonstrated its feasibility by conducting a field evaluation on the basis of genetic modification and bioaerosol technology. A specific gene fragment (pFPV-mCherry fluorescent protein plasmid) was introduced into nonpathogenic E. coli DH5α as tracer bacteria by high-voltage electroporation. Gel electrophoresis and DNA sequencing proved the success of the synthesis. Genetic stability, effect of aerosolization on the survival rate of tracer bacteria, and the application of the tracer bacteria to the airborne bacteria transmission were examined in both lab and field. Both the introduced plasmid stability rates of tracer E. coli in pre-aerosolization and post-aerosolization were above 95% in five test days. Survival rate of tracer E. coli at 97.5% ± 1.2% through aerosolization was obtained by an air-atomizer operated at an air pressure of 30 Psi. In the field experiment, the airborne transmission of E. coli between poultry houses was proved and emitted E. coli was more easily transmitted into self-house than adjacent house due to the ventilation design and weather condition. Our results suggested that the tracing method of airborne bacteria was available for the investigation of airborne microbial transmission across built environments.