FI20207188A1 - Portable air purifier with reduced sound pressure - Google Patents

Abstract

Siirrettavä ilmanphuidtin (101) ilman pujdamisikse sämää pienhiukkasista (PM). Ilmanphuidtin (101) kaipsät kräkeketehoisen kärkeketehoisen käytäilmafiltre (HEPA filter) (105) ja HEPA filtern kaipätsätäää kaipäosin expanded polytetrafluoroethyleneiä (ePTFE). Menetelmä ilman pujdamisikse siirrettävällä ilmanpuihtistimella (101), joka kaipusi ePTFE-pohjaisen HEPA filter (105), joka metodö on olennaisesti hilijasempi kuin metodö, joka sistemas täläsiksen lasikuitupohjaisen HEPA-filtren tämö. The HEPA filter (105) is used for the ilmanphuittimessa (101), known as the HEPA filter.

Description

Portable air purifier with reduced sound pressure Field of invention The present invention relates to an apparatus for air cleaning and a method for reducing the sound pressure of a Portable air purifier according to the preambles of the independent claims 1 and 3 and according to the preambles of the dependent claims. Background of the invention Portable air cleaners (PACs) are small hand transportable air cleaning units used in occupied spaces (classrooms, offices, homes) to reduce the concentration of airborne particles and sometimes vapors and gases. They typically weigh 5-100 kg, are freestanding, use local electrical current, and can be placed anywhere in a room. The best ways to improve indoor air are to remove the pollutant sources and ventilate with clean outdoor air. Portable air purifiers can help when those methods are insufficient or not possible. Also known as air sanitizers, or air cleaners, Portable air purifiers are designed to filter the air in a single or a few rooms, not the entire house, like an HVAC system does. There are two basic types of technology that Portable air Cleaners use to remove particulate matter from the air: S Some Portable air Cleaners use fibrous media air filters to Capture particles in the same way that

O N MERV-rated filters Capture particles in a central HVAC system. In these units, there is often a N prefilter, which would have a lower MERV (Minimum Efficiency Removing Value) rating, and a + N 20 HEPA, which would have a much higher MERV rating. This is a simple technology, and it has the

I have an advantage that little can go wrong with it.

00 00 S Some Portable air Cleaners use electricity to make particles in the air adhere to plates or other

N N surfaces. Cleaners in this category include electrostatic precipitators (ESPs) and ionizers. Some of these devices may unintentionally produce ozone, which can be harmful.

Additionally, some Portable air purifiers offer ultraviolet germicidal irradiation (UVGI), a technology that uses ultraviolet (UV) light to damage microorganisms such as Bacteria and viruses, making them non-infectious. Portable air purifiers with pleated filters use fans to force air through a dense web of fine fibers that traps particles. Filters with very fine mesh are High Efficiency Particulate Air (HEPA) filters — those certified to collect typically more than 99.5 percent (E12) or 99.95 percent (H13) of particles of a certain size (0.3 microns in diameter—smoke and paint pigments, for example). HEPA filters can remove larger particles, too, including dust, pollen, and some mold spores while they're suspended in the air. HEPA filters can also very effectively reduce the number of smaller particles,

0.3 microns typically being the particle size which is most penetrable through the filter. There is a wide variation in the performance of air cleaners that is dependent on the specific air cleaner design and various indoor factors. The most widely used method in the United States to assess the performance of new air cleaners is the procedure described in the American National Standards Institute (ANSI)/Association of Home Appliance Manufacturers (AHAM) AC-1-2002. This method describes both the test conditions and the testing protocol. The protocol yields a performance metric that is based on the measured decay rate of contaminant concentrations with the air cleaner operating compared with the measured decay rate with the air cleaner turned off. The resulting metric, the clean air delivery rate (CADR), permits both an intercomparison of performance among various air cleaners and a comparison of air cleaner operation to other contaminant removal processes.

S N A problem with the current Portable air purifiers comprising a HEPA filter is their noise. The sound 7 preffure of a Portable air purifier depends on the power level where it is used and with exception - CADR (around 450 m?/h), the sound pressure can be similar to the one generated by a dishwasher. E Such noisy equipment cannot be used e.g. in bedrooms and thus the Portable air purifier power 8 25 may need to be turned considerably lower for the night time which obviously reduces the air S purification result.

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Brief description of the invention The object of the present invention is to provide a method so as to overcome or at least alleviate at least some of the prior art disadvantages. The objects of the present invention are achieved with method according to the characterizing Portions of independent claims 1 and 3 and according to the characterizing Portions of the dependent claims. After the Accidental Discovery of expanded polytetrafluoroethylene (ePTFE) in 1969, fibrous filters manufactured from it have been used to capture contaminants and other particles (since 1973). First HEPA filters based on ePTFE were introduced in 1994. A unique feature of ePTFE-based HEPA filters is their low operating resistance. This is assumed to arise from the "slip flow" principle caused by the much thinner fibers in ePTFE HEPA compared to conventional glass fiber HEPA. Nanofibers Bend air less and thus air sees lower resistance. The lower operating resistance means that less power is reguired to operate the fans pushing air through the filter which generates savings in power consumption. There are other advantages of using ePTFE HEPA filters in centralized ventilation systems, too and thus, despite their higher cost, ePTFE HEPA filtetrs are used in some special ventilation systems. Within almost 30 years of existence of ePTFE HEPA filters, their market share is still low, Mostly because of their higher cost. S The low operating resistance of ePTFE HEPA filters produces, however, another advantage which

O N according to our understanding has not been used as an advantage despite the long existence of 3 20 ePTFE HEPAs: the lower power requirement also means lower operating noise.

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I = It has to be noted that in centralized ventilation the machine rooms where fans are situated, are 3 typically placed far away from the terminals pushing air into the points where clean air is needed. S Placement in distance does not generate a need to considerably reduce the sound pressure.

O N Situation is very different with Portable air purifiers, where the fan is located in the apparatus (air purifier) itself. The dominant source of noise in a Portable air purifier is the fan and reducing the fan's power level (and rotation speed) reduces the noise level. Changing a glass-fiber based HEPA filter to an ePTFE filter allows fan power reduction because of the lower flow resistance (lower pressure drop across the filter) of the ePTFE filter. Sound is the term for the air pressure waves emitted by a vibrating object (such as an air purifier fan) which are picked up by the ear and perceived by the brain through our hearing sense. Noise is merely unwanted sound. Some People's sounds are other People's noise — but there are certain sounds that most people perceive as unpleasant and would call noise. Sound pressure is the actual change in air pressure caused by the vibrating source. A Portable air cleaner, like all other sound-emitting objects, has its sound/noise levels measured in decibels [dB], usually multiplied by an 'A' factor which accounts for the effect of human hearing on the sound. The dB(A) scale is logarithmic. That is, it goes up in powers of ten, rather than in single units. Thus an air purifier marked as 70dB(A) is actually ten times noisier than one marked as 60dB(A). Table | Sounds of different sources Source of sound Noise level in dB(A): Threshold of human hearing 0 Rustling leaves 10 Whispering 20 Fridge 50 Normal conversation 60 o 20 Dishwasher 55-70 O Small Orchestra 70 < Vacuum Cleaner 80 i Lawnmower 90 +

N E 25 Noise levels greater than 50dB can make normal conversation difficult and long-term exposure to © levels greater than 70db(A) can damage hearing.

S N The unique feature of the current invention is a Portable air purifier which comprises a HEPA filter

N and characteristic to the invention is that the HEPA filter mainly comprises fibers of ePTFE for filtration. The invented method describes air purification with a Portable air purifier and the characteristic feature is that the method for cleaning air with a fibrous filter is based on the use of ePTFE as the main filtration media. The current invention is also focused on the use of an ePTFE-based HEPA filter in a Portable air filter. "HEPAfilter" in this document means all classes of high-efficiency air filter in the E-, H- and U- classes as shown in the table below. Table II HEPA classes HEPA class Retention (averaged) Retention (spot) E10 > 85% - E11 > 95% - E12 > 99.5% - H13 > 99.95% > 99.75% H14 > 99.995% > 99.975% U15 > 99.9995% > 99.9975% U16 > 99.99995% > 99.99975% U17 > 99.999995% > 99.9999% Brief description of the figures In the following the invention will be described in greater detail, in connection with preferred embodiments, with reference to the attached drawing, in which:

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N a Fig. 1 shows a schematic view of the invented apparatus and method for measuring sound - pressure. +

N = Detailed description of the invention a < = Figure 1 shows a Portable air cleaner/purifier 101 for purifying air passing through the Cleaner 101 N 25 at least from particulate matter (PM). The air cleaner 101 comprises a fan 103 and a high efficiency

N particulate air (HEPA) filter 105. The air cleaner 101 may also comprise a prefilter 107 which may be placed either upstream or downstream the fan 103. Characteristic to the present invention is that the filter media of the HEPA filter 105 mainly comprises expanded polytetrafluoroethylene (ePTFE). The Portable air Cleaner 101 comprises a frame 109 where fan and filters are placed. The frame 109 may also be connected to wheels 111 for easy movement of the Portable air Cleaner 101. The Portable air Cleaner 101 of the present invention preferably removes at least 99.5 of the particles with 0.3 mm diameter passing through the air Cleaner 101 when the volumetric flow of air through the air cleaner 101 is at least 300 m?/h. Essential for the present invention is to create a Portable air purifier and a method for Purifying air with a Portable air purifier 101 based on the use of a HEPA filter 105 where the noise generated by air purification is essentially lower than with prior-art technology. This goal is achieved by using an ePTFE-based HEPA filter 105 instead of a glass fiber-based HEPA filter 105 typical for the prior art. "Essentially lower" noise generated by Portable air Cleaner -based air purification means in one embodiment of the present invention that when used in similar Portable air Cleaners 101, with essentially the same volumetric flow through the HEPA filter 105 and essentially similar particle removal efficiency of the HEPA filters 105 and minimum 500 m?/h volumetric flow through the air Cleaner 101, the sound pressure of ePTFE-HEPA based air Cleaner 101 is at least 3 dB(A) lower than the noise of conventional glass-fiber-HEPA based air cleaner, when the sound pressure is measured at the front of the air Cleaner 101, from the height of the center line of the air Cleaner 101, at 1.5m o distance from the front surface of the air Cleaner 101. The measurement set-up is schematically O 20 shown in Figure 1, showing means for sound pressure measurement 201 which are connected to a = measurement microphone 203.

N z In another embodiment of the present invention "essentially lower" means that the difference in N sound pressure in using glass fiber-based HEPA and ePTFE HEPA is at least 6 dB(A).

S N In yet another embodiment of the present invention "essentially lower" means that the difference N 25 in sound pressure in using glass fiber-based HEPA and ePTFE HEPA is at least 1 dB(A).

The invented method can be applied to any air purifier using a fibrous filter for air cleaning. The filter may be a pure mechanical filter, it may be an electret filter or it may be an electrically enhanced filter. What is characteristic of the present invention is the use of an ePTFE-based HEPA filter in a Portable air cleaning apparatus.

It is apparent to a person skilled in the art that as technology is advanced, the basic idea of the invention can be implemented in various ways. The invention and its embodiments are therefore not restricted to the above examples, but they may vary within the scope of the claims.

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Claims (6)

Claims

1. Portable air cleaner (101) for puryfying air passing through the cleaner (101) at least from particulate matter (PM), comprising a fan (103) and a high efficiency particulate air (HEPA) filter (105), characterized in that filter media of the HEPA filter (105) mainly comprises expanded —polytetrafluoroethylene (ePTFE).

2. Portable air cleaner (101) as in claim 1, characterized inthat portable air cleaner (101) removes at least 99.5 of the particles with 0.3 um diameter passing through the air cleaner (101) when the volumetric flow of air through the air cleaner (101) is at least 300 m?/h.

3. Method of cleaning air with a portable air cleaner (101) based on the use of a HEPA filter (105), characterized in that the method of cleaning air is essentially more silent than a method based on the use of a conventional, glass-fiber-based HEPA filter due to the use of ePTFE as the HEPA filter media.

4. Method of cleaning air as in claim 3, characterized in that when used in similar portable air cleaners (101), with essentially same volumetric flow through the HEPA filter (105) and essentially similar particle removal efficiency of the HEPA filters (105) and minimum 500 m?/h volumetric flow through the air cleaner (101), the sound pressure of ePTFE-HEPA based air cleaner (101) is at least 3 dB(A) lower than the noise of conventional glass-fiber-HEPA based air cleaner, when the sound pressure is measured at the front of the air cleaner (101), from the height of the center line of the o air cleaner (101), at 1.5m distance from the front surface of the air cleaner (101).

N & = 20 5. Method of cleaning air as in claim 3, characterized in that when used in similar portable air s cleaners (101), with essentially same volumetric flow through the HEPA filter (105) and essentially z similar particle removal efficiency of the HEPA filters (105) and minimum 500 m%/h volumetric flow N through the air cleaner (101), the sound pressure of ePTFE-HEPA based air cleaner (101) is at least = 6 dB(A) lower than the noise of conventional glass-fiber-HEPA based air cleaner, when the sound O 25 pressure is measured at the front of the air cleaner (101), from the height of the center line of the air cleaner (101), at 1.5m distance from the front surface of the air cleaner (101).

6. Use of a HEPA filter (105) in a portable air purifier (101), characterized in that the filter media of the HEPA filter (105) comprises mainly fibrous ePTFE material.

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