HVAC Filters Research Articles

A Study of the Effectiveness of Indoor Plants for Removal of Volatile Organic Compounds in Indoor Air in a 7-story Office Building

PP-30-142 Background/Aims: People have been intrigued by the use of potted plants indoors for air cleaning since a 1984 publication of NASA research claiming that certain plants can remove formaldehyde from indoor air. A study was conducted in a 7-story, 4600 M2 office building in a highly polluted Asian city. The building, housing 500 workers, contains about 900 plants from 5 carefully selected species. The plants are integrated into the building ventilation strategy, with the expectation that they remove a wide range of Volatile Organic Compounds (VOCs). The aim of this work was to ascertain whether VOCs are effectively removed by the indoor plants. Methods: Measurements of a range of 29 VOCs commonly found in office buildings (carbonyls; cleaning solvents, bathroom products; office products and supplies; building materials; plant materials and wood; plasticizers; outdoor air) were made outdoors, in the rooftop greenhouse, on 2 floors, and in the building exhaust air, following the sequential flow of ventilation air through the building. An air washer is installed between the ventilation air inlet and the greenhouse to clean outdoor air. Particulate matter (PM2.5) was also measured indoors and outdoors. Results: Indoor formaldehyde levels in the building increased by almost 5-fold from ambient levels to 30 μg/m3 (chronic 8 hours reference exposure level = 9 μg/m3) on floor 3, doubling during transit through the greenhouse containing 160 plants. Hexanal, nonanal, and octanal, odorous VOCs, were measured on floors 3 and 5 at roughly 10 times documented odor thresholds. Methylene chloride increased about 30-fold in the indoor air. 1,4-dichlorobenzene, bathroom deodorizer, was measured throughout the building, increasing by a factor of 10 between the greenhouse and floor 5. PM2.5 indoors was reduced to 7% (30 μg/m3) of the outdoor 380 μg/m3 due to efficient HVAC filters. Conclusion: Overall, VOC and aldehyde concentrations increased despite the use of selected potted plants, suggesting low overall effectiveness for VOC air cleaning.

Evaluation of HVAC filters as a sampling mechanism for indoor microbial communities

HVAC filters are in place for extended periods of time and can serve as integrated air samplers. This paper presents a comparison of bacterial and fungal concentrations and communities in HVAC filter dust and other sampling locations in occupied residences and in the unoccupied UTest House. A DNA-based, culture-independent approach was utilized to characterize the microbial communities. Microbial concentrations and communities in HVAC filter dust samples were not statistically different from those in high surface dust samples in occupied homes. Despite the general similarity in the communities, Proteobacteria were present in greater proportion in HVAC filter dust samples than in surface dust samples suggesting the air origin of this phylum. Gram-positive bacteria were present in greater proportion in occupied residences than in an unoccupied test house, confirming the potential association of this group with occupants. HVAC filter microbial communities were not different from those present in a composited month-long indoor air sample providing preliminary evidence that filters could be a viable option for long-term investigation of airborne biological contaminants.

The Effects of Filtration on Pressure Drop and Energy Consumption in Residential HVAC Systems (RP-1299)

The use of high-efficiency HVAC filters is a common strategy to control exposure to airborne particulate matter in residential buildings. However, high-efficiency filters generally have a higher pressure drop and are widely assumed to have large energy penalties. In this paper, we explore the underlying theoretical energy implications of high-pressure-drop filters and we present the results of a four-month-long period of detailed energy monitoring of two air-conditioning systems in a test home in Austin, Texas. A theoretical analysis shows that the magnitude of potential energy impacts associated with high-efficiency filters are overall likely to be small and can result in either a net savings or additional expenditure, depending on the system. The measured results in the test systems confirm these findings, and energy consumption generally did not differ with high-efficiency filters compared to low-efficiency filters. These results suggest caution when assuming that high-efficiency filters require more energy than low-pressure-drop filters in residential HVAC systems.

Optimizing the Recovery of Surrogates for Bacterial Bioterrorism Agents from Ventilation Filters

AbstractHeating, ventilating, and air‐conditioning (HVAC) filters have the potential to serve as long‐term integrated samplers for biological particles that may be released intentionally or unintentionally into a public building. Methods for eluting bacteria that are surrogates for potential bioterrorism agents from HVAC filters were tested for their ability to recover as high a percentage of culturable bacteria as possible. A solution of 0.02% Tween‐80 in water was an effective eluent for Bacillus globigii (BG) spores whereas phosphate‐buffered saline was the most effective eluent for vegetative bacteria. Hand shaking was a more effective agitation method for high recovery rates than vortexing or mechanical shaking. The results indicate that BG spores can be eluted successfully while maintaining essentially 100% culturability. The recovery of the vegetative bacteria Mannheimia haemolytica and Yersinia ruckeri was 80% or higher under optimal conditions. The culturability of the vegetative bacteria eluted from HVAC filters declined substantially within as little as 2 h after the bacteria were loaded onto the filter. The culturability of the BG spores eluted from filters exhibited an exponential decay subsequent to loading with a half‐life of 8–9 days.

Background culturable bacteria aerosol in two large public buildings using HVAC filters as long term, passive, high-volume air samplers

Background culturable bacteria aerosols were collected and identified in two large public buildings located in Minneapolis, Minnesota and Seattle, Washington over a period of 5 months and 3 months, respectively. The installed particulate air filters in the ventilation systems were used as the aerosol sampling devices at each location. Both pre and final filters were collected from four air handing units at each site to determine the influence of location within the building, time of year, geographical location and difference between indoor and outdoor air. Sections of each loaded filter were eluted with 10 ml of phosphate buffered saline (PBS). The resulting solutions were cultured on blood agar plates and incubated for 24 h at 36 degrees C. Various types of growth media were then used for subculturing, followed by categorization using a BioLog MicroStation (Biolog, Hayward, CA, USA) and manual observation. Environmental parameters were gathered near each filter by the embedded on-site environmental monitoring systems to determine the effect of temperature, humidity and air flow. Thirty nine different species of bacteria were identified, 17 found only in Minneapolis and 5 only in Seattle. The hardy spore-forming genus Bacillus was the most commonly identified and showed the highest concentrations. A significant decrease in the number of species and their concentration occurred in the Minneapolis air handling unit supplying 100% outdoor air in winter, however no significant correlations between bacteria concentration and environmental parameters were found.

Ozone removal by HVAC filters

Residential and commercial HVAC filters that have been loaded with particles during operation in the field can remove ozone from intake or recirculated air. However, knowledge of the relative importance of HVAC filters as a removal mechanism for ozone in residential and commercial buildings is incomplete. We measured the ozone removal efficiencies of clean (unused) fiberglass, clean synthetic filters, and field-loaded residential and commercial filters in a controlled laboratory setting. For most filters, the ozone removal efficiency declined rapidly but converged to a non-zero (steady-state) value. This steady-state ozone removal efficiency varied from 0% to 9% for clean filters. The mean steady-state ozone removal efficiencies for loaded residential and commercial filters were 10% and 41%, respectively. Repeated exposure of filters to ozone following a 24-h period of no exposure led to a regeneration of ozone removal efficiency. Based on a theoretical scaling analysis of mechanisms that are involved in the ozone removal process, we speculate that the steady-state ozone removal efficiency is limited by reactant diffusion out of particles, and that regeneration is due to internal diffusion of reactive species to sites available to ozone for reaction. Finally, by applying our results to a screening model for typical residential and commercial buildings, HVAC filters were estimated to contribute 22% and 95%, respectively, of total ozone removal in HVAC systems.

Evaluation of Culturable Particle Load on HVAC Filters Before and After Remediation: A Pilot Study

This pilot research was performed to evaluate a quantitative method for culturing particles on HVAC filters. The reasons were to compare relative concentrations of culturable fungi found in two separate rooms of a six-floor building and to re-evaluate culturable fungi in the same building after remediation efforts. The evaluated quantification method involved shaking samples of filter materials in sterile saline followed by plating out. The pilot study consisted of two phases. Firstly, a case study comparison of two HVAC filters from a building with a history of indoor air quality concerns in the space served by one of the filters. The second, following remediation efforts in the same building. This involved the quantification of culturable fungal particles on each of ten filters serving ten separate areas of the building. Statistical analysis of the phase I results indicated a significantly greater number of viable particles on the complaint filter than on the non-complaint filter following culture and quantification on either malt extract agar (p=0.02) or potato dextrose agar (p=0.03). Phase II results suggested a factor of four decrease in culturable fungal load following remediation. This limited study was performed for preliminary assessment of the use of a filter quantification method to estimate relative airborne fungal load. The results suggest that more work is merited but limitations in the scope of the research and the statistical power of the analysis mean further conclusions regarding method efficacy cannot be drawn.

Enhancement of the Performance of Low-Efficiency HVAC Filters Due to Continuous Unipolar Ion Emission

Our novel concept utilizing continuous emission of unipolar ions, which has been recently proven to enhance the efficiency of facepiece respirators, was applied to conventional HVAC filters. Laboratory study demonstrated that the air ion emission in the vicinity of a low-efficiency HVAC filter significantly improves its performance. For example, the collection efficiency of two commercial HVAC filters challenged with 1μm PSL particles jumped from 5–15% (measured with no ion emission) to 40–90% (when the ion output rate was ∼ 1012 e−/sec). The enhancement effect depends on the filter type and, generally, on the distance from the ion emitter to the filter surface. The results were explained as follows. The air ions with high mobility are deposited on the fibers forming a macroscopic electric field, which shield out some incoming unipolarly charged particles due to repelling forces. The field estimate has shown that this explanation is feasible. The enhancement effect seems to have a good potential to be emp...

Penetration of Particles into Buildings and Associated Physical Factors. Part I: Model Development and Computer Simulations

The PM2.5 standard proposed by the U.S. Environmental Protection Agency (EPA) has stimulated research on the relationships between particulate matter concentrations and the exposures and subsequent health responses of sensitive subpopulations, such as the elderly. Since individuals in these subpopulations may spend more than 90% of their time indoors, understanding the relationship between outdoor particle concentrations and those found in indoor microenvironments is critical. This research resulted in a time-dependent indoor air quality model incorporating all potential particle sources and loss mechanisms. Monte Carlo simulations of the model identified the mechanisms, such as particle loss during penetration through the building envelope, that modify the outdoor particle size distribution during transport into the interior of a building, calculated indoor-to-outdoor (I/O) concentration ratios, and estimated penetration factors as a function of particle size. Indoor particle generation and transport of outdoor particles through the HVAC system were the most important contributors to the indoor concentration in residential and commercial buildings, respectively. The most significant removal mechanisms included ventilation through and particle removal by the HVAC filter if an HVAC system was present, or particle deposition on indoor surfaces if an HVAC system was not present. The modeled I/O concentration ratios varied between 0.05 and 0.5, depending on particle size and type of ventilation system, and agreed well with published experimental results. Penetration factors less than unity were calculated for particles with aerodynamic diameters larger than 0.2 θ m if the air exchange rate and steady-state I/O concentration ratio were correlated during the simulations. An additional correlation between the air exchange rate and particle deposition velocity is required if penetration factors less than unity are to be modeled for particles with aerodynamic diameters smaller than 0.2 θ m. These results

Penetration of Particles into Buildings and Associated Physical Factors. Part I: Model Development and Computer Simulations

The PM2.5 standard proposed by the U.S. Environmental Protection Agency (EPA) has stimulated research on the relationships between particulate matter concentrations and the exposures and subsequent health responses of sensitive subpopulations, such as the elderly. Since individuals in these subpopulations may spend more than 90% of their time indoors, understanding the relationship between outdoor particle concentrations and those found in indoor microenvironments is critical. This research resulted in a time-dependent indoor air quality model incorporating all potential particle sources and loss mechanisms. Monte Carlo simulations of the model identified the mechanisms, such as particle loss during penetration through the building envelope, that modify the outdoor particle size distribution during transport into the interior of a building, calculated indoor-to-outdoor (I/O) concentration ratios, and estimated penetration factors as a function of particle size. Indoor particle generation and transport of outdoor particles through the HVAC system were the most important contributors to the indoor concentration in residential and commercial buildings, respectively. The most significant removal mechanisms included ventilation through and particle removal by the HVAC filter if an HVAC system was present, or particle deposition on indoor surfaces if an HVAC system was not present. The modeled I/O concentration ratios varied between 0.05 and 0.5, depending on particle size and type of ventilation system, and agreed well with published experimental results. Penetration factors less than unity were calculated for particles with aerodynamic diameters larger than 0.2 θ m if the air exchange rate and steady-state I/O concentration ratio were correlated during the simulations. An additional correlation between the air exchange rate and particle deposition velocity is required if penetration factors less than unity are to be modeled for particles with aerodynamic diameters smaller than 0.2 θ m. These results

Air filters from HVAC systems as possible source of volatile organic compounds (VOC) – laboratory and field assays

The emission of volatile organic compounds (VOC) from air filters of HVAC systems was to be evaluated. In a first study carbonyl compounds (14 aldehydes and two ketones) were measured by reacting them with 2,4-dinitrophenylhydrazine (DNPH). Analysis was done by HPLC and UV detection. In laboratory experiments pieces of used and unused HVAC filters were incubated in test chambers. Filters to be investigated were taken from a filter bank of a large HVAC system in the centre of Berlin. First results show that – among those compounds – formaldehyde and acetone were found in higher concentrations in the test chambers filled with used filters in comparison to those with unused filters. Parallel field measurements were carried out at the prefilter and main filter banks of the two HVAC systems. Here measurements were carried out simultaneously before and after the filters to investigate whether those aldehydes or ketones arise from the filter material on site. Formaldehyde and acetone significantly increased in concentration after the filters of one HVAC system. In parallel experiments microorganisms were proved to be able to survive on air filters. Therefore, a possible source of formaldehyde and acetone might be microbes.

A methodology to investigate the particulate penetration coefficient through building shell

Dust penetration coefficient was defined to quantify the ability of building fabrics, door gap and window louver in reducing the amount of outdoor particulate matter brought into the building by infiltration. An office premises were selected as the controlled environment in this study. In order to minimize the impact of other factors, continuous measurements were conducted at night when the air conditioning units were turned off and when no indoor generation term was available. Exponential decay curves of the indoor particulate levels were obtained from which the penetrating coefficients were determined. Indoor dust removal mechanisms were discussed in the paper and within the experimental conditions, the dust penetration coefficients varied from 0.69 to 0.86. A cascade impactor was also used in the experiment to collect particle size distribution in the range of 0.43–10 μm. The size distribution was extended to the range of 0.05 μm by extrapolation technique. The modal size of the particulate matter (by mass conc.) was found at about 1 μm reflecting the inability of HVAC filter in removing dust around this size range. The dust penetration coefficient and size spectrum are useful for building researchers in quantifying influence of HVAC unit and building fabrics on indoor particulate characteristics.

Bioaerosol filtration efficiency of clean HVAC filters and shedding of micro-organisms from filters loaded with outdoor air

Bioaerosol filtration efficiency of clean HVAC filters and shedding of micro-organisms from filters loaded with outdoor air