The Development and Application of an Electrostatic Air Cleaning Technology

George Richardson

January 2001

Department of Environmental Sciences, University of Plymouth, Plymouth, U.K.

in collaboration with

Neoventa AB, Kungälv, Sweden

and

A C & T Ltd., Plymouth, U.K.

There is a growing concern about the effects of indoor air particulate pollution, in relation to human health. The removal of indoor air pollution at its source is extremely difficult. Fine particles are continuously generated in outdoor air mainly by combustion processes. Coarse particles are constantly generated by activities indoors. There is a need for simple technology that can reduce these types of pollutants, which can work in conjunction with standard heating, ventilation and air conditioning (HVAC) systems.

A novel air cleaner was designed to harness the principles of electrostatic air cleaning, through the production of electrons. The electrostatic air cleaner (EAC system) needed to be tested to ascertain whether existing theories on the properties of electrostatics would apply. To investigate and develop the EAC system a series of experiments were conducted. The determination of the small air ion generating capacities using different voltages, the determination of the efficiency of carbon fibre thread as an electron emitter and an assessment of the concentration of hydrogen peroxide produced - through the use of new methodology and design of an enlarged interactive gas phase reactor (EIGPR) for use in a FT-IR spectrometer. To increase the understanding of the behaviour of particulate matter and other pollutants indoors, two investigations were conducted. Two nurseries in the city centre of Plymouth (UK) were monitored to assess variations in particles and 116 council owned properties in Torbay were assessed to ascertain the levels of particulates, humidity, temperature, house dust mites, damp and mould in private dwellings. To test the efficacy of the EAC system in a real life situation, the system was installed in a city centre office (Plymouth, UK) as part of a controlled trial.

The results from the nurseries and council houses confirm the problems people face with indoor air pollution. The studies showed that the EAC system needed to be able to cope with large variations in particle numbers and to be able to work in varying environmental conditions. The results from the investigation into the efficacy of the EAC system showed that with a 6.5 kV negative voltage generator, a reduction in fine and coarse particles would occur. Using carbon fibre threads as an emitter confirmed that they are the most suitable type of electron emitter. The results showed that the fibres do not deteriorate as quickly as needle type emitters and that dirt accumulation on the fibres only has a minor effect on the efficiency of the emitter. An analysis of electron chemical reactions using the EIGPR revealed that the EAC system could produce 0.44 ppb of hydrogen peroxide. Hydrogen peroxide has anti microbial properties, which would add to the improvement of air quality when the system is installed. The study of the city centre office showed that the EAC system could reduce fine particles by an extra 21 % in a room that already had an efficient air processor installed. The results from the development and application of the EAC system have led to a new design for an electrostatic air cleaner, termed a 'Full Electrostatic Air Cleaning system'. This system consists of a negative voltage generator and carbon fibre thread (the emitter) contained on a standard size ceiling tile. To aid the collection of particles, oxygen free radicals etc., the Full EAC system will be accompanied by a collector plate. This system will provide a weak electrostatic field within which indoor air will be cleaned of particulate matter.

© 2001 by George Richardson. All Rights Reserved

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