Dust Build-up Research Articles

Reducing PV soiling and condensation using hydrophobic coating with brush and controllable curtains

Abstract Solar photovoltaic technology faces many challenges in climates that are characterized by arid nature with high dust frequencies and high relative humidity levels, which make dust build-up extremely problematic. Soiling and condensation affect the performance of PV systems and greatly degrades their power output. Covering the PV panels during non-operation will greatly improve the overall efficiency and reduce the PV soiling. In the present study, a motorized curtain is developed to cover the PV module surface during nights and dust storms. This system successfully reduced the impact of the condensation and the accumulation of soiling that could affect the performance of the PV panels and reduce their efficiencies. This study also experimentally investigates utilizing a superhydrophobic (Laboratory prepared nano-coating) and a superhydrophilic coating on the PV module surface to reduce the impact of soiling. These two proposals could heavily reduce the frequency of cleaning the PV panel; therefore, reducing water consumption; particularly for areas with limited water supply. This study uses experimental data as a method to demonstrate the impact of dust, humidity, and nano-coating on the performance of PV Panels. In addition, PVsyst was used to demonstrate and verify the soiling impact on the performance of PV modules.

CFD modeling and laboratory studies of dust cleaning efficacy of an efficient four stage non-clogging impingement filter for flooded-bed dust scrubbers

Fibrous-type filters are used to capture dust particles in mining and other occupations where personnel are exposed for prolonged periods. Dust cleansing devices including flooded-bed dust scrubbers use these mesh-type multi-layered filters. These filters trap dust particles efficiently on their surface and inside their mesh. However, their continued operation leads to dust build-up and clogging. This results in increased resistance of the filter and lowered airflow rate through the scrubber. This could potentially enhance the exposure of the miners. A non-clogging self-cleaning impingement screen type dust filter was designed by the authors for use in mining and industrial dust cleansing applications. The filter guides dirt-laden air through rapidly turning paths which forces it to shed heavier particles. The particles impact one of the impermeable solid metallic filter surfaces and are removed from the airstream. A full cone water spray installed upstream prevents any surface build-up of dust. This paper summaried the computer models generated to show the filter operations and laboratory experiments including optical particle counting to establish the cleaning efficiency.

Experimental investigations for dust build-up on low-iron glass exterior and its effects on the performance of solar PV systems

The performance of solar photovoltaic (SPV) power plants is adversely affected by soiling losses caused by natural dust deposition on the module surface. The size and density of dust particles vary depending on the location. Thus, it is essential to investigate the impact of dust collection on SPV module performance. This work investigates the effect of dust build-up on the low-iron glass surface and the performance of SPV modules. To analyze the characteristics of these dust particles, low-iron glass samples have been chosen, which resemble a front glass surface of the SPV module. To study the holistic pattern of the natural dust accumulation of a particular area, low-iron glass samples have been placed with three different positions like vertical, horizontal, and local tilt angle for Building Integrated Photovoltaic Systems (BIPV) and rooftop PV power plant applications. The mineralogical study of dust particles provides insight in determining the transmittance loss from the glass surface of solar PV modules due to the local soiling loss. Furthermore, the electrical power output of the SPV modules has been monitored at various levels of dust accumulation. Moreover, these findings indicate that natural dust deposition at selected site locations significantly reduces energy generation from PV modules.

Observation of coherent mode induced by a molybdenum dust on EAST

The influence of a molybdenum dust buildup on plasma edge turbulence has been studied in the EAST tokamak. The motion of the dust from the upper divertor region is detected by a fast visible CCD camera, the XUV spectrometer arrays, and the EUV spectrometer. The MoXV emission intensity sharply increases compared with the spectral lines of various ionization states of other elements, which implies that the dust particles are the molybdenum impurities. The radial distribution of Mo14+ ion simulated by a simplified 1D transport model indicates that the molybdenum dust mainly deposits in the pedestal bottom region. Moreover, it is observed that the coherent mode (CM) appears at ρ = 0.94 after the molybdenum impurities enter the main plasma region. The influx of molybdenum impurities results in increasing pedestal electron density and decreasing pedestal electron temperature in contrast to that before the event of impurities dropping. It is also found that the electron density gradient in the pedestal increases when the ablation of the molybdenum impurities is observed in the pedestal region. The qualitative experimental results indicate that the onset of CM is likely related to the increase of the density gradient and edge collisionality in the pedestal. In comparison to the density gradient, the enhancement of CM amplitude largely depends on the increase of the edge collisionality.

On the build-up of dust aerosols and possible indirect effect during Indian summer monsoon break spells using recent satellite observations of aerosols and cloud properties

Association of higher (lower) rainfall with lower (higher) Aerosol Optical Depth (AOD) is consistent with the understanding that increased washout (build-up) and shorter (longer) life-time of aerosols occur in wetter (drier) conditions. Given the life-time of aerosols, it is imperative to examine how aerosols impact active/break (wetter/drier than normal) spells, prominent intraseasonal variability (ISV) of Indian summer monsoon (ISM), through their composite analysis using recent satellite observations of aerosols and cloud properties, circulation and rainfall. Dust aerosols can act as CCN and participate efficiently in cloud processes during active phase. During breaks, build-up of desert dust transported by prevalent circulation, is associated with lower cloud effective radius implying aerosols’ indirect effect where they can inhibit cloud growth in the presence of reduced moisture and decrease precipitation efficiency/rainfall. Correspondingly, correlation albeit small, between intraseasonal anomalies of AOD and rainfall is negative, when AOD leads rainfall by 3–5 days implying that indirect aerosols impact is effective during breaks, though it is not the dominant responsible factor. During breaks, lower shortwave flux at top of atmosphere hints at dust-induced semi-direct effect. As breaks are permanent features of ISM, incorporation of dust-induced feedbacks in models, is essential for improved ISV simulation and ISM prediction.

The ALPINE-ALMA [CII] survey

We present dust attenuation properties of spectroscopically confirmed star forming galaxies on the main sequence at a redshift of ∼4.4 − 5.8. Our analyses are based on the far infrared continuum observations of 118 galaxies at rest-frame 158μm obtained with the Atacama Large Millimeter Array (ALMA) Large Program to INvestigate [CII] at Early times (ALPINE). We study the connection between the ultraviolet (UV) spectral slope (β), stellar mass (M⋆), and infrared excess (IRX =LIR/LUV). Twenty-three galaxies are individually detected in the continuum at > 3.5σsignificance. We perform a stacking analysis using both detections and nondetections to study the average dust attenuation properties atz ∼ 4.4 − 5.8. The individual detections and stacks show that the IRX–βrelation atz ∼ 5 is consistent with a steeper dust attenuation curve than typically found at lower redshifts (z < 4). The attenuation curve is similar to or even steeper than that of the extinction curve of the Small Magellanic Cloud. This systematic change of the IRX–βrelation as a function of redshift suggests an evolution of dust attenuation properties atz > 4. Similarly, we find that our galaxies have lower IRX values, up to 1 dex on average, at a fixed mass compared to previously studied IRX–M⋆relations atz ≲ 4, albeit with significant scatter. This implies a lower obscured fraction of star formation than at lower redshifts. Our results suggest that dust properties of UV-selected star forming galaxies atz ≳ 4 are characterised by (i) a steeper attenuation curve than atz ≲ 4, and (ii) a rapidly decreasing dust obscured fraction of star formation as a function of redshift. Nevertheless, even among this UV-selected sample, massive galaxies (logM⋆/M⊙ > 10) atz ∼ 5 − 6 already exhibit an obscured fraction of star formation of ∼45%, indicating a rapid build-up of dust during the epoch of reionization.

Effects of current mismatch due to uneven soiling on the performance of multi-crystalline silicon module strings

Photovoltaic (PV) module operation is critical in PV systems for optimum generation of electrical power. Modules installed in the field suffer uneven soiling caused by bird droppings and dust build-up on their front surface. This study investigated the impact of partial shading caused by non-uniform soiling on the electrical characteristics of multi-crystalline silicon (mc-Si) modules and strings, and compared this with simulated I-V parameters. Light and heavy uneven soiling on mc-Si solar cells resulted in current mismatch which can be simulated. The effects of partial soiling on the I-V characteristics of mc-Si module strings were experimentally measured and agreed with the simulated results.

Household cleanliness and urinary phthalate concentrations among toddlers in the HOME Study

PDS 62: Chemicals and metals: exposure and biomarkers, Johan Friso Foyer, Floor 1, August 28, 2019, 10:30 AM - 12:00 PM Background/Aim: Household dust can contain butylbenzyl phthalate (BBzP) and di-2-ethylhexyl phthalate (DEHP), which may adversely impact childhood health. Cleaning may lower dust phthalate concentrations, but the relationship between household cleanliness and urinary phthalates among toddlers is unknown. We evaluated the association between household cleanliness and concentrations of monobenzyl phthalate (MBzP), a metabolite of butylbenzyl phthalate, and the sum of di(2-ethylhexyl) phthalate metabolites (∑DEHP) among toddlers in the HOME Study. Methods: We measured phthalate metabolites in serial urine samples collected from 312 Cincinnati, Ohio area toddlers at ages 1, 2, and 3 years (n=714 samples collected from 2004 to 2009). During home visits, we assessed household cleanliness and classified homes into three groups based on dust buildup, presence of debris, and evidence of cleaning. We used linear mixed models to evaluate associations between repeated measures of household cleanliness and log-transformed phthalate metabolite concentrations adjusting for creatinine and covariates. Results: Overall, toddlers living in homes with less evidence of cleaning and heavier dust and debris buildup had higher urinary concentrations of MBzP and ∑DEHP. Compared to urine samples collected from toddlers living in clean homes (n=412), those collected from toddlers living in homes with only some (n=285) or no evidence of housecleaning (n=37) had 14% (95% CI= -3%, 35%) and 58% (95%CI= 9%, 130%) higher MBzP concentrations, respectively, as well as 10% (95% CI= -4%, 26%) and 39% (95%CI= 2%, 90%) higher ∑DEHP concentrations. We found statistically significant trends in the relationship of household cleanliness with urinary MBzP (p= 0.016) and ∑DEHP (p= 0.042) concentrations. Conclusions: Household cleaning may lower toddlers’ phthalate body burden. Future intervention studies will be useful to test the efficacy of cleaning methods.

Dust settles, we don’t: The electrodynamic screen—A self-cleaning technology for concentrated solar power mirrors and photovoltaic panels

ABSTRACT

An empirical model to predict road dust emissions based on pavement and traffic characteristics

The relative impact of non-exhaust sources (i.e. road dust, tire wear, road wear and brake wear particles) on urban air quality is increasing. Among them, road dust resuspension has generally the highest impact on PM concentrations but its spatio-temporal variability has been rarely studied and modeled. Some recent studies attempted to observe and describe the time-variability but, as it is driven by traffic and meteorology, uncertainty remains on the seasonality of emissions. The knowledge gap on spatial variability is much wider, as several factors have been pointed out as responsible for road dust build-up: pavement characteristics, traffic intensity and speed, fleet composition, proximity to traffic lights, but also the presence of external sources. However, no parameterization is available as a function of these variables.We investigated mobile road dust smaller than 10 μm (MF10) in two cities with different climatic and traffic conditions (Barcelona and Turin), to explore MF10 seasonal variability and the relationship between MF10 and site characteristics (pavement macrotexture, traffic intensity and proximity to braking zone). Moreover, we provide the first estimates of emission factors in the Po Valley both in summer and winter conditions. Our results showed a good inverse relationship between MF10 and macro-texture, traffic intensity and distance from the nearest braking zone. We also found a clear seasonal effect of road dust emissions, with higher emission in summer, likely due to the lower pavement moisture. These results allowed building a simple empirical mode, predicting maximal dust loadings and, consequently, emission potential, based on the aforementioned data. This model will need to be scaled for meteorological effect, using methods accounting for weather and pavement moisture. This can significantly improve bottom-up emission inventory for spatial allocation of emissions and air quality management, to select those roads with higher emissions for mitigation measures.

Herschel-ATLAS: revealing dust build-up and decline across gas, dust and stellar mass selected samples – I. Scaling relations

We present a study of the dust, stars and atomic gas (HI) in an HI-selected sample of local galaxies (z<0.035) in the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) fields. This HI-selected sample reveals a population of very high gas fraction (>80 per cent), low stellar mass sources that appear to be in the earliest stages of their evolution. We compare this sample with dust and stellar mass selected samples to study the dust and gas scaling relations over a wide range of gas fraction (proxy for evolutionary state of a galaxy). The most robust scaling relations for gas and dust are those linked to NUV-r (SSFR) and gas fraction, these do not depend on sample selection or environment. At the highest gas fractions, our additional sample shows the dust content is well below expectations from extrapolating scaling relations for more evolved sources, and dust is not a good tracer of the gas content. The specific dust mass for local galaxies peaks at a gas fraction of ~75 per cent. The atomic gas depletion time is also longer for high gas fraction galaxies, opposite to the trend found for molecular gas depletion timescale. We link this trend to the changing efficiency of conversion of HI to H2 as galaxies increase in stellar mass surface density as they evolve. Finally, we show that galaxies start out barely obscured and increase in obscuration as they evolve, yet there is no clear and simple link between obscuration and global galaxy properties.

The impact of atmospheric wet deposition on roof runoff quality in an urbanized area

Understanding the sources of chemical components in roof runoff can help to prevent water quality problems in rooftop rainwater harvesting. To identify the contribution of wet deposition to the mass of components in roof runoff, the samples from air, rainwater, dust buildup and roof runoff were collected from an urban site in Shenzhen of China in 2011–2012. The results indicate that: (1) wet deposition has a dominant contribution to the mass of total organic carbon (TOC), NH4+, NO3–, Cl– and organic acids in the roof runoff, while the mass of NH4+, acetic acid and formic acid in the roof runoff may be greatly reduced by the neutralization between the components with alkaline dust buildup on the rooftop; and (2) wet deposition partially contributes to the mass of Na+, K+, Mg2+, Ca2+, F– and SO42– in the roof runoff, while other factors like dust buildup on the rooftop and chemical reactions also have a non-negligible impact. Furthermore, TOC, NH4+, NO3– and organic acids in the wet deposition are mainly influenced by the atmospheric pollution due to fast increase in fossil fuel consumption (e.g. vehicle emissions). Therefore, the effects of wet deposition should be carefully considered for rooftop rainwater harvesting in urbanized areas.

Optically transparent and environmentally durable superhydrophobic coating based on functionalized SiO2 nanoparticles

Optical surfaces such as mirrors and windows that are exposed to outdoor environmental conditions are susceptible to dust buildup and water condensation. The application of transparent superhydrophobic coatings on optical surfaces can improve outdoor performance via a ‘self-cleaning’ effect similar to the Lotus effect. The contact angle (CA) of water droplets on a typical hydrophobic flat surface varies from 100° to 120°. Adding roughness or microtexture to a hydrophobic surface leads to an enhancement of hydrophobicity and the CA can be increased to a value in the range of 160°–175°. This result is remarkable because such behavior cannot be explained using surface chemistry alone. When surface features are on the order of 100 nm or smaller, they exhibit superhydrophobic behavior and maintain their optical transparency. In this work we discuss our results on transparent superhydrophobic coatings that can be applied across large surface areas. We have used functionalized silica nanoparticles to coat various optical elements and have measured the CA and optical transmission between 190 and 1100 nm on these elements. The functionalized silica nanoparticles were dissolved in a solution of the solvents, while the binder used was a polyurethane clearcoat. This solution was spin-coated onto a variety of test glass substrates, and following a curing period of about 30 min, these coatings exhibited superhydrophobic behavior with a static CA ≥ 160°.

The dust budget crisis in high-redshift submillimetre galaxies

We apply a chemical evolution model to investigate the sources and evolution of dust in a sample of 26 high-redshift ($z>1$) submillimetre galaxies (SMGs) from the literature, with complete photometry from ultraviolet to the submillimetre. We show that dust produced only by low-intermediate mass stars falls a factor 240 short of the observed dust masses of SMGs, the well-known `dust-budget crisis'. Adding an extra source of dust from supernovae can account for the dust mass in 19 per cent of the SMG sample. Even after accounting for dust produced by supernovae the remaining deficit in the dust mass budget provides support for higher supernova yields, substantial grain growth in the interstellar medium or a top-heavy IMF. Including efficient destruction of dust by supernova shocks increases the tension between our model and observed SMG dust masses. The models which best reproduce the physical properties of SMGs have a rapid build-up of dust from both stellar and interstellar sources and minimal dust destruction. Alternatively, invoking a top-heavy IMF or significant changes in the dust grain properties can solve the dust budget crisis only if dust is produced by both low mass stars and supernovae and is not efficiently destroyed by supernova shocks.

Shrouded plasma spray of Ni–20Cr coatings utilizing internal shroud film cooling

It is widely reported that oxidation during plasma thermal spraying leads to degradation in the coating corrosion and wear resistant properties. A number of shrouding systems have been developed to minimize oxidation to enable production of low oxide content coatings while spraying in air. The shroud design in this work was based on a detailed review of the mechanisms of oxidation during plasma spraying and the result of past shrouded plasma spray trials and simulations. It incorporated a novel film cooling concept within the shroud which was intended to cool the inner shroud wall and reduce energy loss from the plasma jet, while at the same time causing vaporized material to condense in the gas film and flow out of the shroud rather than building up on the shroud walls. Coatings were sprayed without the shroud, with the solid shroud alone (no shroud gas flow) and with various settings of internal and external shroud gas flows. The effect of these variables on the coating quality and oxide content was assessed by XRD, SEM and microhardness testing. The solid shroud was found to be effective in reducing in-flight oxidation but less effective in reducing layer to layer oxidation during spraying. High external shroud gas flows had the most significant effect on reducing coating oxidation. The internal shroud gas flow used to generate the film cooling effect was ineffective in significantly reducing internal dust build-up within the shroud and had no definitive effect on the coating properties. The shroud operation and mechanisms of oxidation are discussed to highlight areas of improvement for future designs.

A REST-FRAME OPTICAL VIEW ONz∼ 4 GALAXIES. I. COLOR AND AGE DISTRIBUTIONS FROM DEEP IRAC PHOTOMETRY OF THE IUDF10 AND GOODS SURVEYS

We present a study of rest-frame UV-to-optical color distributions for z~4 galaxies based on the combination of deep HST/ACS+WFC3/IR data with Spitzer/IRAC imaging. In particular, we use new, ultra-deep data from the IRAC Ultradeep Field program (IUDF10). Our sample contains a total of ~2600 galaxies selected as B-dropout Lyman Break Galaxies (LBGs) in the HUDF and one of its deep parallel fields, the HUDF09-2, as well as GOODS-North and South. This sample is used to investigate the UV continuum slopes beta and Balmer break colors (J_125-[4.5]) as a function of rest-frame optical luminosity. The [4.5] filter is chosen to avoid potential contamination by strong rest-frame optical emission lines. We find that galaxies at M_z<-21.5 (roughly corresponding to L*[z~4]) are significantly redder than their lower luminosity counterparts. The UV continuum slopes and the J_125-[4.5] colors are well correlated. The most simple explanation for this correlation is that the dust reddening at these redshifts is better described by an SMC-like extinction curve, rather than the typically assumed Calzetti reddening. After correcting for dust, we find that the galaxy population shows mean stellar population ages in the range 10^8.5 to 10^9 yr, with a dispersion of ~0.5 dex, and only weak trends as a function of luminosity. In contrast to some results from the literature, we find that only a small fraction of galaxies shows Balmer break colors which are consistent with extremely young ages, younger than 100 Myr. Under the assumption of smooth star-formation histories, this fraction is only 12-19% for galaxies at M_z<-19.75. Our results are consistent with a gradual build-up of stars and dust in galaxies at z>4, with only a small fraction of stars being formed in short, intense bursts of star-formation.

The unbiased measurement of ultraviolet spectral slopes in low-luminosity galaxies at z ≈ 7

The ultraviolet (UV) continuum slope β, typically observed at z ≈ 7 in Hubble Space Telescope (HST) WFC3/IR bands via the J − H colour, is a useful indicator of the age, metallicity and dust content of high-redshift stellar populations. Recent studies have shown that the redward evolution of β with cosmic time from redshift 7 to 4 can be largely explained by a buildup of dust. However, initial claims that faint z ≈ 7 galaxies in the Hubble Ultra Deep Field WFC3/IR imaging (HUDF09) were blue enough to require stellar populations of zero reddening, low metallicity and young ages, hitherto unseen in star-forming galaxies, have since been refuted and revised. Here we revisit the question of how best to measure the UV slope of z ≈ 7 galaxies through source recovery simulations, within the context of present and future ultra-deep imaging from HST. We consider how source detection, selection and colour measurement have each biased the measurement of β in previous studies. After finding a robust method for measuring β in the simulations (via a power-law fit to all the available photometry), we remeasure the UV slopes of a sample of previously published low-luminosity z ≈ 7 galaxy candidates. The mean UV slope of faint galaxies in this sample appears consistent with an intrinsic distribution of normal star-forming galaxies with β ≈ −2, although properly decoding the underlying distribution will require further imaging from the ongoing HUDF12 programme. We therefore go on to consider strategies for obtaining better constraints on the underlying distribution of UV slopes at z ≈ 7 from these new data, which will benefit particularly from the addition of imaging in a second J-band filter: F140W. We find that a precise and unbiased measurement of β should then be possible.

Control analysis for solar panel dust mitigation using an electric curtain

An energy efficiency and control analysis is given for application of a transparent electric curtain for dust mitigation on a solar panel. The electric curtain technique has been proposed by NASA as an effective active method for dust removal from solar panels in planetary and lunar exploration, and this method also has potential for mitigation of dust build-up on terrestrial solar panels in dry environments. Since energy expenditure rate required for electric curtain operation can be significantly higher than the energy capture rate from a solar panel, a control scheme for activation and deactivation of the electric curtain is necessary to achieve optimal net energy capture. The control method examined in the current paper is one in which the electric curtain is activated when the panel output voltage decreases to a fraction V ′ o n of the clean panel output voltage and deactived when the output voltage exceeds a second output voltage fraction V ′ o f f . A combination of theoretical and computational approaches is used to determine how the energy efficiency changes with change in the threshold voltage ratios. A scaling analysis is developed that identifies a single key dimensionless parameter that influences the efficiency results. Optimal values of turn-on and turn-off voltage ratio are determined in terms of this parameter, and it is demonstrated that the efficiency decreases rapidly as the turn-off voltage ratio is raised above the optimal value. All of the efficiency predictions for a given mitigation velocity profile are collapsed onto a single curve with appropriate choice of the scaling parameters, which is then used to develop an optimal control criterion.

Particle removal from a surface by a bounded vortex flow

A bounded vortex flow consists of an axisymmetric vortex that is confined top and bottom between two plates (the “confinement plate” and “impingement plate”, respectively) and surrounded laterally by a swirling annular slot jet. The bottom of the vortex terminates on the boundary layer along the impingement plate and the top of the vortex is drawn into a suction port positioned at the center of the confinement plate. The circumferential flow within the annular jet is important for supplying circulation to the central wall-normal vortex. This flow field is proposed as a method for mitigation of dust build-up on a surface, where the vortex–jet combination supplements the more traditional vacuum port by enhancing the surface shear stress and related particle transport rate. The paper reports on a computational study of the velocity field and particle transport by a bounded vortex flow. Fluid flow computations are performed using a finite-volume approach for an incompressible fluid and particle transport is simulated using a discrete-element method. Computations are performed for different values of two dimensionless parameters – the ratio of the plate separation distance and the average radial location of the jet inlet (the dimensionless confinement height) and the ratio of flow rate withdrawn at the suction outlet and that injected by the jet (the flow rate ratio). For small values of the flow rate ratio, the impinging jet streamlines pass down to the boundary layer along the bottom surface and then travel up the vortex core. By contrast, for large values of flow rate ratio, the annular jet is quickly entrained into the suction outlet and no wall-normal vortex is formed. Particles are observed to roll along the impingement surface in a direction determined by the fluid shear stress lines. Particles roll outward when they lie beyond a separatrix curve of the surface shear stress lines, where particles within this separatrix curve roll inward, piling up at the center of the flow field. A toroidal vortex ring forms for the small confinement height case with flow rate ratio equal to unity, which yields double separatrix curves in the shear stress lines. The inward rolling particles intermittently lift up due to collision forces and burst away from the impingement surface, eventually to become entrained into the flow out the suction port or resettling back onto the impingement surface.

Validation of the Criteria for Initiating the Cleaning of Heating, Ventilation, and Air-Conditioning (HVAC) Ductwork Under Real Conditions

Dust accumulation in the components of heating, ventilation, and air-conditioning (HVAC) systems is a potential source of contaminants. To date, very little information is available on recognized methods for assessing dust buildup in these systems. The few existing methods are either objective in nature, involving numerical values, or subjective in nature, based on experts’ judgments. An earlier project aimed at assessing different methods of sampling dust in ducts was carried out in the laboratories of the Institut de recherche Robert-Sauvé en santé et en sécurité du travail (IRSST). This laboratory study showed that all the sampling methods were practicable, provided that a specific surface-dust cleaning initiation criterion was used for each method. However, these conclusions were reached on the basis of ideal conditions in a laboratory using a reference dust. The objective of this present study was to validate these laboratory results in the field. To this end, the laboratory sampling templates were replicated in real ducts and the three sampling methods (the IRSST method, the method of the U.S. organization National Air Duct Cleaner Association [NADCA] and that of the French organization Association pour la Prévention et l’Étude de la Contamination [ASPEC]) were used simultaneously in a statistically representative number of systems. The air return and supply ducts were also compared. Cleaning initiation criteria under real conditions were found to be 6.0 mg/100 cm2 using the IRSST method, 2.0 mg/100 cm2 using the NADCA method, and 23 mg/100 cm2 using the ASPEC method. In the laboratory study, the criteria using the same methods were 6.0 for the IRSST method, 2.0 for the NADCA method, and 3.0 for the ASPEC method. The laboratory criteria for the IRSST and NADCA methods were therefore validated in the field. The ASPEC criterion was the only one to change. The ASPEC method therefore allows for the most accurate evaluation of dust accumulation in HVAC ductwork. We therefore recommend using the latter method to objectively assess dust accumulation levels in HVAC ductwork.