HVAC Filters Research Articles

Fine and ultrafine particle removal efficiency of new residential HVAC filters.

Particle air filters used in central residential forced-air systems are most commonly evaluated for their size-resolved removal efficiency for particles 0.3-10µm using laboratory tests. Little information exists on the removal efficiency of commercially available residential filters for particles smaller than 0.3µm or for integral measures of mass-based aerosol concentrations (eg, PM2.5 ) or total number concentrations (eg, ultrafine particles, or UFPs) that are commonly used in regulatory monitoring and building measurements. Here, we measure the size-resolved removal efficiency of 50 new commercially available residential HVAC filters installed in a recirculating central air-handling unit in an unoccupied apartment unit using alternating upstream/downstream measurements with incense and NaCl as particle sources. Size-resolved removal efficiencies are then used to estimate integral measures of PM2.5 and total UFP removal efficiency for the filters assuming they are challenged by 201 residential indoor particle size distributions (PSDs) gathered from the literature. Total UFP and PM2.5 removal efficiencies generally increased with manufacturer-reported filter ratings and with filter thickness, albeit with numerous exceptions. PM2.5 removal efficiencies were more influenced by the assumption for indoor PSD than total UFP removal efficiencies. Filters with the same ratings but from different manufacturers often had different removal efficiencies for PM2.5 and total UFPs.

Filter layer structure effect on the most penetrating particle size of multilayered flat sheet filter

In this study, four different HVAC filters were tested to evaluate the filter layer structure effect on the Most Penetrating Particle Size. Each filter consisted of two melt-blown (MB) layers and a thermal bond (TB) layer. The MB layers were constructed with fibers with diameters of 2 μm and 5 μm diameter while the TB layer exhibited a fiber diameter of 37 μm. The positions of the three layers (MB2, MB5, and TB) were varied along the air flow direction, and four different filters were considered as follows: Filter A (MB2 → TB → MB5), Filter B (MB5 → TB → MB2), Filter C (TB → MB2 → MB5), and Filter D (TB → MB5 → MB2). When particle loading was absent (clean filter), pressure drops and collection efficiencies were almost identical for the filters, thereby indicating that the filtration performance did not significantly change with the filter layer arrangement. However, particle loading test results showed that pressure drop and most penetrating particle size (MPPS) trends depended on the location of the MB2 layer. For Filter D, the pressure drop and the decreasing rate of the MPPS were the lowest. The pressure drop increased from 3.5 to 9.4 mmH2O and the MPPS decreased from 270 to 160 nm, when the particle loading increased from 0 to 1.55 g/m2.

Filtration efficiency and loading characteristics of PM2.5 through composite filter media consisting of commercial HVAC electret media and nanofiber layer

Abstract Pleated electret HVAC filters are often used in residences and commercial buildings to mitigate the particles that originate both indoors and outdoors. However, there are two concerns on the performance of electret media: 1. Low efficiency for particles in diameter of 10–30 nm at initial filtration condition, which represent the MPPS (most penetrating particle size), and 2. Significant efficiency reduction during the loading process due to the shielding of fiber charge. In this study, a composite filter media composed of a main layer of HVAC electret media on the top and a thin layer of nanofiber at the bottom was prepared and tested for its PM2.5 removal. In the initial efficiency tests, monodisperse nanoparticles ranging 8–500 nm were used to challenge the media. It was found that the nanofiber layer can enhance the efficiency for the MPPS (10–30 nm) of electret media significantly. In the loading performance, polydisperse NaCl particles which mimicked the size distribution of typical atmospheric PM2.5 were used to challenge the media. It was found the total efficiency reduction was less than 10% for particles with sizes 50–500 nm. This reduction due to the shielding of fiber charge was much less than the electret layer (>40%) without adding nanofibers. The observation of a decent performance over the loading process was expected since the composite media made full use of both the mechanical forces and electrostatic effects. Surprisingly, the overall loading FOM (figure of merit) of the composite media was close to that of electret media, indicating that there was only a minor tradeoff of pressure drop increase when adding the nanofiber layer. In conclusion, this type of combination provided a unique structure to take advantage of electret media and a nanofiber layer for PM2.5 removal in the application of pleated HVAC filters.

Modeling the impact of residential HVAC filtration on indoor particles of outdoor origin (RP-1691)

Much of human exposure to airborne particles of outdoor origin, including fine particles smaller than 2.5 μm (PM2.5) and ultrafine particles smaller than 0.1 μm (UFPs), occurs in residences. High-efficiency central HVAC filters are increasingly being used in residences, but questions remain about their effectiveness in reducing indoor PM2.5 and UFPs of outdoor origin in homes operating under realistic conditions (e.g., with HVAC systems operating only to meet heating or cooling demands). Here dynamic building energy and indoor air mass balance modeling are combined to estimate the impacts of 11 HVAC filters (minimum efficiency reporting value [MERV] 5 through high-efficiency particulate air [HEPA]) on indoor concentrations of PM2.5 and UFPs of outdoor origin in multiple vintages of prototypical single-family residences relying on either infiltration or mechanical ventilation systems in 22 U.S. cities. Results demonstrate that higher-efficiency HVAC filters can meaningfully reduce indoor proportions of outdoor PM2.5 and UFPs inside residences, but home vintage, climate zone, and ventilation strategy strongly influence the outcomes due to widely varying air exchange rates, HVAC system runtimes, and sources of ventilation air. Higher efficiency filters had a greater impact in older, leakier homes relying on infiltration alone and in new homes relying on supply-only mechanical ventilation systems designed to meet ASHRAE Standard 62.2.

Filtration performances of HVAC filters for PM10 and microbial aerosols— Influence of management in a lab-scale air handling unit

ABSTRACTFiltration performances of air handling unit (AHU) filters for particles and microbial aerosols were investigated. The influence of the AHU operational conditions on the behavior of microorganisms collected on the filters was also studied. A lab-scale AHU with two filtration stages was developed and validated for the study of downsized filters with industrial geometries. Three types of filters of different efficiency were considered: G4, F7, and F9, according to European standard EN 779. Two configurations of filters were studied: G4 pleated/F7 bag and F7/F9 bag. Filters were sequentially clogged by alumina particles, which provided a mineral fraction in the particulate cake, and then by micronized rice particles, which provided the fungus Penicillium chrysogenum and an organic fraction that acts as a substrate for microorganisms. Finally, a microbial aerosol composed of endospores of Bacillus subtilis and spores of Aspergillus niger was nebulized to contaminate filters. After clogging, periods of...

Analysis of the cost effectiveness of combined particle and activated carbon filters for indoor ozone removal in buildings

This study involved the development of a model for evaluating the potential costs and benefits of ozone control with combined particle/activated carbon filtration (referred to here as activated carbon filtration) in buildings. The modeling effort included the prediction of indoor ozone and ozone reaction products with and without activated carbon filtration in the HVAC system. Benefit-to-cost ratios were estimated for various types of buildings in 12 American cities in 5 different climate zones. Health benefits were evaluated using disability-adjusted life-years attributed to the difference in indoor ozone concentration with and without activated carbon filtration, and included city-specific age demographics for each simulation. Costs of activated-carbon filters included capital cost differences when compared against conventional HVAC filters of similar minimum efficiency reporting value rating (e.g., minimum efficiency reporting value 6–8), energy penalties due to additional pressure drop, and regional utility rates. When assuming a single-pass ozone removal efficiency of 60%, carbon filtration during the ozone season was beneficial and economically viable in commercial office buildings, long-term health-care facilities, and K–12 schools. Residential activated carbon filtration could be economically viable for conditions of higher ozone removal efficiencies, lower filter costs, and lower pressure drop across the filter.

Capture of Sub-500 nm Particles Using Residential Electret HVAC Filter Media-Experiments and Modeling

ABSTRACTElectret HVAC filter are widely used to remove airborne particles in residential or commercial indoor environments. Based on the International Commission on Radiological Protection (ICRP) deposition model, sub-500 nm particles have enhanced depositions in the tracheobronchial region and the alveolar region than particles larger than 500 nm. In this study, filtration efficiencies of five residential electret HVAC filters against monodisperse silver (Ag) and potassium chloride (KCl) particles with 3–500 nm diameters at face velocities ranging 0.05–1.5 m s–1 were investigated. For further understanding the effect of fiber charges on particle collections, electret media were discharged and the efficiencies acquired from pure mechanical mechanisms were compared with that of electret media. The figure of merit (FOM) of the five electret filter media was also investigated to further understand the effect of charge density on filtration performance. A theoretical model without parametric fittings used in literature was adopted and further modified by considering the polarization forces for charged particles. The modified model predicted the particle penetrations very well at low face velocities for all tested media and also well at high face velocities for the media with low charges. The discrepancy occurred for the media with high charges at higher face velocities was due to the nonuniform particle concentration distribution in the media layers. The validated model is able to be applied to improve the design for electret media for nanoparticle removal.

Characterizing the bacterial communities in retail stores in the United States.

The microorganisms present in retail environments have not been studied in detail despite the fact that these environments represent a potentially important location for exposure. In this study, HVAC filter dust samples in 13 US retail stores were collected and analyzed via pyrosequencing to characterize the indoor bacterial communities and to explore potential relationships between these communities and building and environmental parameters. Although retail stores contained a diverse bacterial community of 788 unique genera, over half of the nearly 118K sequences were attributed to the Proteobacteria phylum. Streptophyta, Bacillus, Corynebacterium, Pseudomonas, and Acinetobacter were the most prevalent genera detected. The recovered indoor airborne microbial community was statistically associated with both human oral and skin microbiota, indicating occupants are important contributors, despite a relatively low occupant density per unit volume in retail stores. Bacteria generally associated with outdoor environments were present in the indoor communities with no obvious association with air exchange rate, even when considering relative abundance. No significant association was observed between the indoor bacterial community recovered and store location, store type, or season. However, predictive functional gene profiling showed significant associations between the indoor community and season. The microbiome recovered from multiple samples collected months apart from the same building varied significantly indicating that caution is warranted when trying to characterize the bacterial community with a single sampling event.

Penetration of Sub-50 nm Nanoparticles Through Electret HVAC Filters Used in Residence

Pleated electret HVAC filters are often used in residence to mitigate the particles that originate both indoors and outdoors. These filters are usually tested with particles larger than 300 nm. However, residential particles can contain a significant amount of nanoparticles with size below 50 nm due to cooking, smoking, cleaning, wood burning, and outdoor infiltration. In order to characterize the nanoparticle removal by electret HVAC filters, penetrations of 3–50 nm silver nanoparticles through five different flat sheet electret media used in commercial residential HVAC filters were tested with face velocities of 0.05, 0.5, and 1.0 m s–1. Experimental results showed that all media had significantly high penetrations with 0.35–0.8 at the most penetrating particle sizes (MPPSs) for all three velocities, which were in the sizes of 10–30 nm. A model based on single fiber theory for particle penetration predictions was used and compared with the experimental data. Results showed that the model predicted the n...

Impact of Relative Humidity on HVAC Filters Loaded with Hygroscopic and Non-Hygroscopic Particles

The key characteristics of an air filter—flow resistance and filtration efficiency—are strongly affected by captured particles. The impact of exposing loaded heating, ventilating, and air conditioning air filters to a relative humidity (RH) other than that experienced during loading is investigated to develop an understanding of the role of RH throughout filter operation. Flat sheets of commercial filter media were loaded with hygroscopic, non-hygroscopic, or a mixture of particles in a laboratory apparatus. When filters loaded with hygroscopic particles in dry air were exposed to an elevated RH of 40%, the flow resistance reduced by up to 47%, depending on the filter being tested. Investigation of filter efficiency before and after changes in RH in the same samples shows reductions of up to 11 percentage points in the 130-nm size range. Further increasing RH causes additional drops in flow resistance and efficiency whereas reverting back to a lower humidity does not change the filter characteristics. The...

Building design and operational choices that impact indoor exposures to outdoor particulate matter inside residences

Much of human exposure to particles of outdoor origin often occurs inside homes where we spend most of our time. This work (1) reviews existing literature on the important parameters governing the infiltration and persistence of particles of outdoor origin in residences, (2) re-analyzes portions of data from recent experimental investigations of submicron particle infiltration and central HVAC system operation in single-family homes, and (3) combines these data to highlight particularly stark differences in particle infiltration factors and human exposures to submicron particles of outdoor origin that are driven by building envelope design, filter choice, and HVAC system design and operation (with an additional focus on data from one low-energy home). Results reveal that envelope design and construction, HVAC filter selection, and HVAC system operation can lead to variations in infiltration factors for submicron particles ranging by a factor of 60 or more from the most protective homes to the least protective homes. Moreover, an additional experiment performed in the most protective low-energy home (when relying on infiltration for ventilation air) was also responsible for the highest amount of outdoor particle infiltration when tested again while using an energy recovery ventilator connected to an outdoor air supply for ventilation air, suggesting that residential mechanical ventilation systems can adversely influence outdoor particle infiltration if improperly installed.

Impact of HVAC filter on indoor air quality in terms of ozone removal and carbonyls generation

This study aims at detecting ozone removal rates and corresponding carbonyls generated by ozone reaction with HVAC filters from various building, i.e., shopping mall, school, and office building. Studies were conducted in a small-scale environmental chamber. By examining dust properties including organic carbon proportion and specific surface area of dusts adsorbed on filters along with ozone removal rates and carbonyls generation rate, the relationship among dust properties, ozone removal rates, and carbonyls generation was identified. The results indicate a well-defined positive correlation between ozone removal efficiency and carbonyls generation on filters, as well as a positive correlation among the mass of organic carbon on filters, ozone removal efficiency and carbonyls generations.

Exploring the microbiome of the built environment: A primer on four biological methods available to building professionals

Building professionals are increasingly being called upon to conduct indoor microbial investigations as they remediate moisture-damaged buildings and design new, healthy, sustainable buildings. Characterizing the indoor microbial community present in the built environment is challenging and complicated by the vast array of biological methods available to building professionals. Furthermore, the particular biological technique employed to study an indoor environment can have a significant impact on the results obtained. This study evaluates the advantages and disadvantages of four biological methods suitable for indoor microbial investigations: culturing, quantitative polymerase chain reaction (qPCR), Sanger sequencing, and pyrosequencing. The results obtained from a study of four buildings are used to evaluate the merits of each bioanalytical approach. In each of the four study sites, the microbial-laden dust recovered on HVAC filters was used to provide a passive, long-term sample of the indoor air. Culturing of the microorganisms recovered from the dust was the least expensive method tested but provided a limited characterization of the microbial community present. qPCR provided the most specific information about the presence and quantity of target microorganisms but this method requires a priori knowledge of the species of interest and specifically designed primers that may not enumerate unanticipated species. Sanger sequencing provided microbial identification at the species level but lacked coverage to fully describe the microbial community present. Pyrosequencing provided in-depth sequence coverage of the microbial community present (to the genus level) but the vast dataset generated required increased computational analysis and data storage. Nevertheless, pyrosequencing when coupled with qPCR for target species quantification represents a viable approach that should become more accessible to building professionals as user-friendly software for analyzing sequencing results becomes available and more commercial laboratories offer these services.

The relationship between filter pressure drop, indoor air quality, and energy consumption in rooftop HVAC units

HVAC filters are commonly used to decrease exposure to particulate matter, yet little is known about the energy impacts and air quality consequences of high efficiency filters installed in commercial buildings. To explore these effects, system airflow, filter and coil pressure drop, fan pressure rise, and power draw were measured, and cooling capacity and compressor power were modeled for at least four filter pressure drops in 15 rooftop units equipped with and without fan speed control. Energy implications and clean-air-delivery-rate were estimated for a large dataset of filters divided into four efficiency (MERV) categories. Field measurements conducted on units without fan speed control showed that increased filter pressure drop decreased flow, cooling capacity, and power. For a unit with fan speed control, the same increase in pressure drop resulted in the same magnitude change of fan power but in the opposite direction, and other parameters were unchanged. Replacing MERV 8 with MERV 13/14 resulted in higher energy consumption (2–4%) during cooling mode for both unit types, energy savings during fan-only mode (8–13%) in units without fan speed control, and increased energy consumption in fan-only mode (11–18%) in the unit with fan speed control. Energy consumption increases were offset by improvement in clean-air-delivery-rate, especially for PM2.5 (2.9–3.8 times increase going from MERV 8 to MERV 13/14), with larger benefits achieved for the unit with fan speed control. A comprehensive understanding of the impact of filtration is essential to selecting the appropriate efficiency of filters that ensures low-energy use and a healthy indoor environment.

On-Site Particle and Gas Filtration Efficiencies of Air Handling Unit Filters in Industrial and Non Industrial Building

Air handling units are used to provide a mixture of fresh and recycled (recirculated) air to buildings. They include general ventilation filters for the removal of particles and gases in order to protect the components of the air handling units and to provide clean air to occupants. Standardised test methods exist for the laboratory performance assessment of particulate filters - EN 779 (2012) in Europe and ANSI/ASHRAE Standard 52.2 (2007) in USA - and gas phase filters - ANSI/ASHRAE Standard 145.2 (2011) in USA and draft International Standard ISO/FDIS 10121-2 (2012). Test results enable the comparison of filters against each other but they cannot be used to predict their in-situ performances because the laboratory loading pollutants are not necessarily representative of real pollutants. The EUROVENT 4/10 recommendation (2005) describes the measurement of the pressure drop and the filtration efficiency of HVAC filters on site (this may be one filter or a bank of filters depending on the size of the air handling unit) along with the airflow rate of the installation. It can then be verified that the efficiency of the filters is as expected and that the filters are correctly installed with no leakage or bypass. Results also give an idea about the particulate filter replacement frequency depending on their pressure drop. The EUROVENT 4/10 recommendation was used as a basis for the development of the ASHRAE Guideline 26 (2008) and the draft International Standard ISO/DIS 29462 (2011). For gas phase filters, no document covers the on site determination of the filtration efficiency. This paper presents examples of results obtained in-situ for both particulate and gas phase general ventilation filters (an original method is presented for gas phase filters) and shows that the methods used are suitable for the inspection of the air handling units in relation to their filtration function.

건축자재에 의한 실내 오존제거 및 제어에 대한 고찰

Recently, residents have been spending almost 90% of their time indoors, which presents a higher risk from inhalation of pollutants than when spending time outdoors. Therefore, controlling indoor air quality became important. It is reported that the lung diseases and mortality for occupants are increased when there is high density of ozone which is one of the pollutants among the indoor air. In addition, the reactions between ozone and building materials produce VOCs and formaldehyde. The studies to eliminate the ozone by building materials have been actively investigated. However, ozone removal and secondary pollutants from ozone reactions with building materials have not been reported in Korea. For this reason, the aim of this study is to introduce ozone removal by HVAC filters, various building materials, and eco-friendly building materials including the quantity of secondary pollutant emissions.

Characterizing Bioaerosol Risk from Environmental Sampling

In the aftermath of a release of microbiological agents, environmental sampling must be conducted to characterize the release sufficiently so that mathematical models can then be used to predict the subsequent dispersion and human health risks. Because both the dose-response and environmental transport of aerosolized microbiological agents are functions of the effective aerodynamic diameter of the particles, environmental assessments should consider not only the total amount of agents but also the size distributions of the aerosolized particles. However, typical surface sampling cannot readily distinguish among different size particles. This study evaluates different approaches to estimating risk from measurements of microorganisms deposited on surfaces after an aerosol release. For various combinations of sampling surfaces, size fractions, HVAC operating conditions, size distributions of release spores, uncertainties in surface measurements, and the accuracy of model predictions are tested in order to assess how much detail can realistically be identified from surface sampling results. The recommended modeling and sampling scheme is one choosing 3, 5, and 10 μm diameter particles as identification targets and taking samples from untracked floor, wall, and the HVAC filter. This scheme provides reasonably accurate, but somewhat conservative, estimates of risk across a range of different scenarios. Performance of the recommended sampling scheme is tested by using data from a large-scale field test as a case study. Sample sizes of 10-25 in each homogeneously mixed environmental compartment are sufficient to develop order of magnitude estimates of risk. Larger sample sizes have little benefit unless uncertainties in sample recoveries can be reduced.

Microbiomes of built environments: 2011 symposium highlights and workgroup recommendations

The air we breathe inside buildings dominates overall inhalation exposure to most air pollutants, whether of indoor or outdoor origin. The same is true for our exposure to microorganisms. Over the past three decades much has been learned about chemicals (in gas and particle phases) in building air, including typical levels, sources, fate, and control. Far less has been learned about the types, sources, and fate of microorganisms in buildings, and about how building design, and operation and maintenance affect microorganisms in buildings. Knowledge creation has been constrained by historical reliance on culture-based methods that can yield only partial or biased assessments of microbial community structure, sometimes dramatically underestimating uncultivable organisms, and failing to detect fragments of organisms that may themselves influence human health. However, in the past several years, advances in culture-independent analytical methods have significantly increased knowledge related to microbial communities and diversity in buildings. We are positioned to make even stronger gains in the coming years.

The Extraction of a Bacillus anthracis Surrogate from HVAC Filters

Developing a quick and inexpensive method to extract bacteria from HVAC filters can provide valuable information on the extent of contamination of a building after a release of pathogenic microorganisms. In order to identify the preferred extraction procedure of Bacillus thuringiensis HD1011 from a pleated filter with a minimum efficiency reporting value of 7, different agitation methods were varied systematically. This study shows that the vortex–shake extraction procedure was found to be significantly more efficient when preceded by sonication; the vortex–shake sequence had a mean of 0.49 (0.3–0.77) CFUs (colony forming units) compared to 1.3 (0.8–2.1) CFUs for sonicate–vortex–shake agitation. The control data suggested that growth was occurring when the filter was present in the bacterial solution, and this was investigated further. The data with no filter ever present produced a mean of 0.37 (0.14–0.47) CFU compared to the means of 0.85 (0.52–1.35) CFU and 1.07 (0.65–1.74) CFUs, respectively, for when the filter was present for agitation and when it was present for 24 h prior to agitation, indicating significant growth. Because these results suggest that germination could occur during the extraction procedure, all the results were quantified based on presence versus absence using a most probable number method.

Secondary pollutants from ozone reactions with ventilation filters and degradation of filter media additives

Prior research suggests that chemical processes taking place on the surface of particle filters employed in buildings may lead to the formation of harmful secondary byproducts. We investigated ozone reactions with fiberglass, polyester, cotton/polyester and polyolefin filter media, as well as hydrolysis of filter media additives. Studies were carried out on unused media, and on filters that were installed for 3 months in buildings at two different locations in the San Francisco Bay Area. Specimens from each filter media were exposed to {approx}150 ppbv ozone in a flow tube under a constant flow of dry or humidified air (50percent RH). Ozone breakthrough was recorded for each sample over periods of {approx}1000 min; the ozone uptake rate was calculated for an initial transient period and for steady-state conditions. While ozone uptake was observed in all cases, we did not observe significant differences in the uptake rate and capacity for the various types of filter media tested. Most experiments were performed at an airflow rate of 1.3 L/min (face velocity = 0.013 m/s), and a few tests were also run at higher rates (8 to 10 L/min). Formaldehyde and acetaldehyde, two oxidation byproducts, were quantified downstream of each sample. Those aldehydes (m/zmore » 31 and 45) and other volatile byproducts (m/z 57, 59, 61 and 101) were also detected in real-time using Proton-Transfer Reaction - Mass Spectrometry (PTR-MS). Low-ppbv byproduct emissions were consistently higher under humidified air than under dry conditions, and were higher when the filters were loaded with particles, as compared with unused filters. No significant differences were observed when ozone reacted over various types of filter media. Fiberglass filters heavily coated with impaction oil (tackifier) showed higher formaldehyde emissions than other samples. Those emissions were particularly high in the case of used filters, and were observed even in the absence of ozone, suggesting that hydrolysis of additives, rather than ozonolysis, is the main formaldehyde source in those filters. Emission rates of formaldehyde and acetaldehyde were not found to be large enough to substantially increase indoor concentrations in typical building scenarios. Nevertheless, ozone reactions on HVAC filters cannot be ignored as a source of low levels of indoor irritants.« less