1、476 ASHRAE TransactionsABSTRACTIn the United States and Canada, the initiation of air system cleaning is based on visual inspection, which is subjec-tive and impractical for major cleaning work. The association for the prevention and study of contamination (ASPEC) in France has published a guide on
2、objective sampling methods (numerical evaluation method) for keeping non-porous air systems clean. However, the sampling methods have some defi-ciencies. The objectives of this study were to reproduce in the laboratory different levels of cleanliness in non-porous ducts of HVAC systems, to compare a
3、 new method for sampling surface dust in ducts with those methods cited in the literature, and to compare the numerical evaluation method (objective method) to the visual method (subjective one). For each of the simulated cleanliness conditions, a committee of specialists did a visual assessment bas
4、ed on a scale of 3, where level 1 meant normal, 2 meant above normal, and 3 meant serious. According to these assessments, the established initiation criteria correspond to 0.2 grams per square meter (0.00066 ounces per square foot) for the NADCA method, 0.3 g/m (0.00098 oz/ft) for the ASPEC method,
5、 and 0.6 g/m (0.002 oz/ft) for the new method. These criteria are significantly differ-ent (p0.05) from one another. When replacing the visual method, any of the surface sampling methods can be used, inso-far as the corresponding initiation criterion is applied, but these results need to be evaluate
6、d in real ducts with real dust before being used as cleaning initiation criteria. INTRODUCTIONVentilation systems can be potential sources of pollutants due to the accumulation of dust in their air systems. Building managers have to consider a wide range of proposals from specialized cleaning compan
7、ies and have difficulty arriving at a decision because there is no recognized or standardized method for assessing a systems dust contamination. Ventila-tion systems must therefore be maintained under optimal cleanliness conditions. For the optimal maintenance of facil-ities, it is important to be a
8、ble to measure the amount of dust that has been deposited in ventilation networks. In all cases, an objective diagnosis avoids unnecessary network cleaning, but if decontamination is required, allows the cleaning methods to be chosen (ASPEC 2004).In the United States and Canada, the initiation of ai
9、r system cleaning is currently based on visual inspection (Lavoie and Lazure 1994; Brosseau et al. 2000). However, this is subjective and rather impractical for major cleaning work. In 2006, the American National Air Duct Cleaners Associa-tion (NADCA) published criteria for cleanliness acceptance af
10、ter cleaning. However, these criteria are inadequate if you want to know when to start cleaning HVAC system networks (NADCA 2006). As well, these criteria can only be applied on rigid and non-porous surfaces, meaning smooth surfaces (e.g., metallic surfaces).The Association pour la prvention et ltud
11、e de la contamination (ASPEC, association for the prevention and study of contamination) in France has published a guide on methods for keeping the non-porous air systems of clean rooms and related controlled environments clean (ASPEC, 2004). In this guide, the initiation criteria for tertiary envir
12、on-ments (office buildings) and the methods used are reported for different countries. Table 1 presents these criteria (ASPEC 2004).This table shows that the criteria are accompanied by different dust sampling methods, thus making comparisons Cleaning Initiation Criteria for Heating, Ventilation and
13、 Air-Conditioning (HVAC) Systems in Non-Industrial BuildingsJacques Lavoie Ali Bahloul, PhD Yves ClouttierJacques Lavoie and Ali Bahloul are researchers in the Research Department and Yves Clouttier is an engineering physicist in the Research and Expertise Support Department at the Institut de Reche
14、rch Robert-Sauv en Sant et en Scurit du Travail in Montreal, Quebec, Canada.AB-10-0132010, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions (2010, Vol. 116, Part 2). For personal use only. Additional reproduction, dist
15、ribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission.2010 ASHRAE 477difficult. According to ASPEC, these methods can be applied only to rigid and non-porous ducts of sufficient dimensions, i.e., larger than 30 cm (11.8 inches) in diamete
16、r for round components; in addition, the ducts must be horizontal; and finally, the walls must be dry (ASPEC 2004). Sampling must be done on a layer of dust distributed on the bottom surface, and not on an accumulation of dust (ASPEC 2004). Further-more, the sampling methods have some deficiencies,
17、mainly the absorption of moisture from the air by the cellulose ester membranes, and the adhesion of dust on the walls of the cassettes and sampling tubes. One method that would eliminate these two problems would involve weighing a complete sampling cassette such as the IOM cassette (SKC Inc. Eighty
18、 Four, PA, USA) equipped with a polyvinyl chloride membrane. However, this surface sampling method has not yet been evaluated. We will compare this cassette with the sampling systems mentioned in the liter-ature in order to choose the most accurate method.The objective of this project is therefore t
19、o propose a methodology for measuring the dust contamination of ducts in order to compare the numerical value to the value obtained from the visual evaluation corresponding to the limit value that determines the need for cleaning.METHODOLOGYThe steps in this project are: to develop a dust contami-na
20、tion chamber and technique, to choose the most appropriate surface sampling method for dust, and to determine a limit concentration for initiating cleaning.Development of the Dust Contamination ChamberA preliminary study led to the development of a chamber for the laboratory simulation of dust conta
21、mination of ducts. Figure 1 presents a diagram of this chamber.This chamber was designed with smooth and non-porous surfaces. It is also equipped with a PALAS RBG 1000 dust generator (Karlsruhe, Germany). The standard dust used is the dust recommended by ASHRAE (ASHRAE 1992). It consists of:72% fine
22、 test dust (Arizona road dust).23% carbon powder (Molocco black).5% No. 7 cotton linters.However, to optimize this system, different improve-ments will have to be made in order to improve its perfor-mance. The following modifications will be made to the system (Sippola and Nazaroff 2004; Sippola and
23、 Nazaroff 2005):maximum extension of the sectionselimination of asperities and interior jointsreplacement of the fan in order to eliminate leaksChoice of Sampling MethodsTwelve control substrates (aluminum filters 47 mm (1.9 in) in diameter, MSP Corp., Shoreview, MN, USA) uniformly distributed over
24、the entire surface of the base were used for each dust contamination test. Figure 2 presents their location on the plate.Table 1. Criteria for Initiating the Cleaning of Non-Porous DuctsCountryCleaning initiation criterion based on surface densityg/m2(oz/ft)Cleaning initiation criterion based on thi
25、ckness m (mil)Post-cleaning acceptance criterion g/m2(oz/ft)Sampling methodL/min (cfm)United States (NADCA 2006)- - 0.075 (0.00025)Surface sampling on membrane at 15 L/min(0.53 cfm)(open cassette)Great Britain(HVAC 1998)Blowing: 1 (0,0033)Exhaust: 6 (0.02)Blowing: 60 (1524)Exhaust: 180 (4572)0.1 (0.
26、00033)Surface sampling on membrane at 15 L/min(0.53 cfm)Finland(FiSIAQ 1995)Blowing: 2 (0.0066)Exhaust: 5 (0.016)- -Surface sampling on membrane at 15 L/min(0.53 cfm)(sampling tube)France(ASPEC 2004)Blowing: 0.4 (0.0013)Exhaust: 6 (0.02)- 0.1 (0.00033)Surface sampling on membrane at 15 L/min(0.53 cf
27、m)(sampling tube)2010, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions (2010, Vol. 116, Part 2). For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not per
28、mitted without ASHRAEs prior written permission.478 ASHRAE TransactionsThree sampling methods were chosen for the dust contam-ination chamber. The first principle was the NADCA principle (NADCA 2006). It involves vacuuming dust over a predefined 100 cm (15.5 in) duct surface from a template 0.381 mm
29、 (0.039 in) thick and of collecting it on a preweighed 0.8 m (0.03 mil) cellulose ester membrane in an open cassette 37 mm (1.46 in) in diameter (SKC Inc. Eighty Four, PA, USA), in order to determine the difference in surface density (Figure 3).The second sampling method was the ASPEC method (ASPEC
30、2004). It consists of a 0.8-m (31.5 mil) pore size cellulose ester membrane in a 37-mm (1.46 in) closed cassette (SKC Inc. Eighty Four, PA, USA) connected to a beveled tube. The aspirated duct surface is 50 square centimeters (7.75 square inches). Figure 4 presents this method.The third method was t
31、he method recommended by the IRSST. It uses an IOM cassette (SKC Inc. Eighty Four, PA, USA). In the latter, the entire 25-mm-diameter (0.98 in) cassette including a 0.8-m (0.031 mil) pore size polyvinyl chloride membrane is weighed (SKC Inc. Eighty Four, PA, USA). This avoids underestimations of the
32、 weight. To be able to compare this method to the NADCA method, the cassette is slipped onto a template, leaving a 1.5-mm (0.06 in) space between the sampling cassette and the aspirated surface. Figure 5 presents this latter method. All the sampling flows were 15 L/min (0.53 cfm).Experimental PlanNi
33、ne (9) samples (3 per method) were collected each time in the dust chamber in order to compare the methods (paired Students t-tests over a bilateral distribution). In total, 22 different tests were compiled. The statistical tests were performed on the natural logarithms due to the log-normal distrib
34、utions of the data. Mulhausen and Damiano (1998) esti-mated that 6 to 10 measurements are required to suitably esti-mate a mean and a standard deviation. Furthermore, the total number of samples required, to demonstrate a significant difference between two averages, for a chosen error limit of 10% a
35、nd a 95% confidence level, equal 5 (BOHS 1993). These tests were conducted by varying the fan operating time and the amount of dust in the generator. The average velocity of the air in the dust contamination chamber, measured with a hot-wire anemometer (TSI Inc., model 8384, Shoreview, MN, USA), was
36、 0.59 (0.15) m/sec (116.4 feet per minute (29.4) (calcu-lated using 50 measurement points). The precision of this instrument is 3%. Weighing was done using the standard IRSST method whose minimum reported value is 25 g (8.8 X 10-7oz) (IRSST 1985).Visual InspectionIn parallel with this dust sampling,
37、 a committee of experts from different disciplines related to air quality did a subjective evaluation based on visual assessment of the dust contamina-tion. In addition to the four people in charge of this activity, this committee consisted of four other specialists (chemist, certified industrial hy
38、gienist, building engineer and microbiologist), all Figure 1 Diagram of the actual dust chamber in millimeters (inches).Figure 2 Distribution of control substrates.Figure 3 NADCA method.2010, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published
39、in ASHRAE Transactions (2010, Vol. 116, Part 2). For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission.2010 ASHRAE 479from the IRSST. This assessment, based on direct visualization of de
40、posits of concentrations unknown to the committee, involved a 3-level scale, where level 1 or normal, is character-ized by clean ducts or ducts with a thin uniform layer of dust; level 2 or above normal, is characterized by a uniform layer and localized accumulations; and level 3 or serious, is char
41、acterized by significant accumulations (NAIMA 1993; Goyer et al. 2005). Level 2 corresponds to the limit concentration (or concentration range) for initiating cleaning.RESULTS AND DISCUSSIONInitiation CriterionTable 2 presents the results of the corrected weighings of the control substrates. The min
42、imum value used for concen-tration calculations was the methods reported minimum value, 25 g (8.8 X10-7oz) divided by the square root of 2 (Rao et al. 1991; Finkelstein and Verma 2001).The paired Students “t” comparison tests on the normal logarithms between the first third and second third of the s
43、urface (p0.185), between the first third and third third (p0.279), and between the second third and third third (p0.393) are all non-significant. The deposits are therefore considered as uniform over the entire surface.Table 3 presents the comparisons of the average votes of the committee of experts
44、 in relation to the average weighings for each of the methods evaluated, including the control substrates. Therefore, for an average vote of 1.6/3, or approaching level 2 which is characterized by a uniform layer and localized accumulations, the corresponding values are 0.2 g/m (0.00066 oz/ft2) for
45、the NADCA method, 0.3 g/m (0.00098 oz/ft2) for the ASPEC method, and 0.6 g/m (0.002 oz/ft2) for the IRSST method. These methods are all significantly differ-ent (p0.05) from one another. Despite the fact that there is generally a significant difference between the weighings for the control substrate
46、s and the IRSST method, the same value is obtained for these two methods, or 0.6 g/m (0.002 oz/ft2) for a vote of 1.6. We were therefore able to demonstrate, because of this study, the strengths and weaknesses of the three methods for sampling dust on ventilation duct surfaces. We recommend using th
47、e criterion in the IRSST method, which is 0.6 g/m (0.002 oz/ft2), since it is the highest result for the three meth-ods. However, for the time being, we do not think that this criterion can be used in actual situations and requires subse-quent validation. The same comment also applies to the other t
48、wo criteria. The latter can be used, insofar as the limits and scopes are taken into consideration. Perhaps under real dust contamination conditions, one of these methods can provide different results that will result in it being favored.Regarding the subsequent validation of the three criteria, ano
49、ther study has been undertaken and we can state that, for the time being, these methods work very well in real ducts, whether they are admission or exhaust ducts. It also seems that these methods work in evaluating the cleanliness of the differ-ent components of HVAC systems, and on rigid and non-porous surfaces (e.g., metallic surfaces). LIMITATIONS OF THIS STUDYThis study was carried out under laboratory conditions with standard ASHRAE dust (ASHRAE 1992). Clearly, the method favored by the IRSST requires adjustments before commercial use. Among
