Dust in ventilation ducts : accumulation, measurement and removal

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Doctoral thesis (article-based)
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57, [122]
Report / Helsinki University of Technology, Laboratory of Heating, Ventilating and Air Conditioning. A, 9
This thesis focuses on dust accumulation in, and removal from, recently installed supply air ducts and on the bristle behaviour of rotating duct cleaning brushes. The results of dust accumulation, measured using three different methods, were compared and the amount of dust in newly installed air ducts was evaluated. The vacuum test was found to be an efficient method of collecting dust samples on the duct surface. The vacuum test and the gravimetric tape method gave approximately the same results when the measured dust accumulation on the duct surfaces was 0.1-1.0 g/m2. The gravimetric and optical tape methods can be used to evaluate cleanliness of new ducts when the amount of dust accumulation is 0.1-1.0 g/m2. The effect of protection measures on dust accumulation was studied. The mean amount of accumulated dust after construction was 0.9 g/m2 in cleanliness category P1 ducts, which have special requirements for oil residues and protection measures against contamination during construction, and 2.3 g/m2 in cleanliness category P2 ducts, which have only minor protection requirements and are for normal use. The results show that dust accumulation in category P1 ducts was significantly lower (P < 0.008) than in category P2 ducts. The highest mean amount of dust accumulation was found in the middle of the ducts and the lowest amount near the air handling units. The efficiency of two dry air duct cleaning methods applied to new air ducts was compared. Mechanical brushing and compressed air cleaning methods were found to be efficient in removing dust from the newly installed air duct surfaces. Mechanical brushing was more efficient in metal ducts, while the compressed air cleaning method was more efficient in plastic ducts. The mean amount of residual dust on the duct surfaces was below 0.4 g/m2 after duct cleaning. However, neither of the cleaning methods studied was efficient enough to clean ducts that had a high level of residual oil (216-338 mg/m2) on the duct surfaces. A mathematical model to simulate the behaviour of a single bristle of a rotating duct cleaning brush was developed. The results of the simulation were compared with those obtained from a laboratory test. The simulated and experimental results were found to be in reasonable agreement. The dependence of the normal force and the contact angle as a function of various parameters was studied. The simulation and experimental results showed that the normal force and contact angle increase as a function of the rotation speed. Further, the thickness of the bristle was found to have a strong effect on the normal force. Air drag has only a slight effect on the deflection of the bristle. The model can be used as a first step in the systematic design of brushes. However, further theoretical and experimental research is needed to determine the dependency, for instance, between the brush tip normal force and its cleaning efficiency.
duct, dust, cleanliness categories, duct cleaning, bristle model, normal force, contact angle, air drag
Other note
  • Holopainen R., Asikainen V., Pasanen P. and Seppänen O., 2002. The field comparison of three measuring techniques for evaluation of the surface dust level in ventilation ducts. Indoor Air 12, number 1, pages 47-54. [article1.pdf] © 2002 Blackwell Publishing. By permission.
  • Holopainen R., Tuomainen M., Asikainen V., Pasanen P., Säteri J. and Seppänen O., 2002. The effect of cleanliness control during installation work on the amount of accumulated dust in ducts of new HVAC installations. Indoor Air 12, number 3, pages 191-197. [article2.pdf] © 2002 Blackwell Publishing. By permission.
  • Holopainen R., Asikainen V., Tuomainen M., Björkroth M., Pasanen P. and Seppänen O., 2003. Effectiveness of duct cleaning methods on newly installed duct surfaces. Indoor Air 13, number 3, pages 212-222. [article3.pdf] © 2003 Blackwell Publishing. By permission.
  • Holopainen R. and Salonen E.-M., 2003. Modelling bristle behaviour in rotating brush duct cleaning. Helsinki University of Technology, Department of Mechanical Engineering, Laboratory of Heating, Ventilating and Air Conditioning, Report B75. [article4.pdf] © 2003 by authors.
  • Holopainen R. and Salonen E.-M., 2003. Large deformation analysis of a rotating bristle in brush duct cleaning. In: 1st CEACM Conference on Computational Mechanics (CMM-2003). Gliwice / Wisła, Poland, 3-6 June 2003, paper 060P, published on CD-ROM.
  • Holopainen R. and Salonen E.-M., 2004. Rotating brush behaviour in duct cleaning. Energy and Buildings – REHVA Scientific, accepted for publication, in a shortened form, on 25th February 2004. [article6.pdf] © 2004 by authors and © 2004 Elsevier Science. By permission.
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