Background Art Throughout this description and the claims which follow, unless the context requires otherwise, the word"comprise', or variations such as"comprises"or "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

During the winter months in extremely cold climates, the capacity of the air to contain moisture in the form of water vapour is very low. When this air is heated inside a building to provide comfort for the occupants, the water vapour content of the air, expressed as grams of water vapour per kilogram of dry air does not change.

However, at the increased temperature inside the building, the capacity of the air to contain water vapour has increased dramatically. The relative humidity of the air, defined as the ratio of the water vapour content of air to the capacity of air to contain water vapour is therefore very low. As an example, if the outside air were saturated with water vapour at-20°C, the water vapour content of the air would be 0.64 g/Kg dry air. If this air is then heated to 20°C inside the building without change of water vapour content, the relative humidity inside the building would be approximately 4.5%.

The occupants of the building experience a severe drying effect from air of such a low relative humidity. Symptoms include dry skin, irritated nasal passages, headaches and respiratory problems. The dry air will also exacerbate the generation of static electricity and give a feeling of general discomfort.

The symptoms of very low indoor relative humidity can be relieved by the introduction of moisture into the air. There are many methods introducing moisture to the air which are well known, including ultrasonic misting, release of steam and direct evaporation from wetted surfaces. While known humidification systems are effective at introducing moisture to the air, they are subject to problems in operation. Misting systems are known to result in the deposition of salt from the water supply onto

surfaces in the home, and steaming systems are relatively expensive to make and operate. Direct evaporations systems overcome most of these problems. However, the continuous re-circulation of interior air through a direct evaporative humidifier can result in bacteria, fungi, mites and other microscopic particles accumulating on the evaporative pad and washed into the reservoir of the humidifier. Accumulation of these microbes in the reservoir is undesirable, requiring frequent cleaning of the reservoir to keep the humidifier in good working condition.

Direct evaporation humidifiers can be constructed in a similar manner to direct evaporative air coolers. Such devices are disclosed in US 4, 615, 844 issued to Dickison and US 4,338, 264 issued to Seeley. Humidifiers constructed by this means typically include: * A base or reservoir used to contain the water supply for the humidifier.

A housing to contain the internal components, generally mounted on the base.

An evaporative media which readily allows evaporation of water from its surfaces when kept moist and air is drawn through it.

A pump and water distribution means to keep the evaporative media continuously moist.

A fan to draw air through the evaporative media and deliver to the room space.

A motor to drive the fan and pump, if the pump does not have an independent power source.

In operation, water is added to the reservoir, the motor causes rotation of the fan which causes air to be drawn through the evaporative media and delivered to the room space. Simultaneously, the motor causes rotation of a pump means which draws water from the reservoir and delivers it to the evaporative media via the water distribution means. As air is drawn through the wetted evaporative media, intensive evaporation of the water occurs thereby increasing the moisture content of the air passing through the humidifier, and simultaneously reducing the temperature of the air.

It will be apparent to those skilled in the art that any microscopic matter in the air drawn through the evaporative media of such a humidifier is likely to be caught on the wetted surfaces within the media while the air passes through the media. Repeated recirculation of air through the humidifier will therefore continuously increase the

quantity of such contaminants within the evaporative media, which is then washed into the water reservoir by the continuous flow of water through the evaporative media. It will also be apparent that if the humidifier is used continuously within an indoor environment of human habitation with recirculated air, that much of the contaminant entrapped within the evaporative media is likely to be biological in nature, in the form of bacteria, fungi, mites etc. Such an accumulation of material within the evaporative media is undesirable and likely to lead to proliferation of the biological material in the moist environment of the appliance. It is desirable to prevent contact between any biological material and the wet surfaces of the appliance as much as possible, and to allow for the ready removal of such material while it is still dry.

There are air filtration materials available which are capable of removing extremely small particles from the air while presenting little resistance to air flow through them. These filtration materials rely on fibres within the filter matrix retaining an electrostatic charge imparted to them during the manufacturing process.

Contaminants in the air passing through the filter are attracted and retained by the electrostatically charged fibres without the need for fine opening sizes in the filter to trap the particles.

Disclosure of Invention The inclusion of a filter adapted to remove microscopic biological particles in an airstream passing through a humidifier is provided by the present invention. A preferred form of filter comprises an electrostatically charged filter material within an evaporative humidifier which functions to entrap and contain airborne contaminants down to extremely small sizes. Such a filter is kept separate from the wet surfaces within the humidifier. When the material of the filter is filled with contaminants to its capacity, the filter can then be removed and replaced with a fresh filter without the contaminants ever reaching the wet areas of the humidifier. This reduces the possibility of biological material in the airstream passing through the humidifier from reaching the wet parts of the humidifier and being able to proliferate within the humidifier.

An evaporative humidifier of this invention comprises a water reservoir, an evaporative element, pump means for delivering water from the water reservoir to the evaporative element, a fan and motor for drawing air through the evaporative media, a housing to contain the fan and motor, water reservoir and evaporative element and an opening in the housing to allow for delivery of humidified air, wherein a filter adapted

to remove microscopic biological particles is positioned in the airstream upstream of the evaporative element of the humidifier.

In a preferred embodiment, the filter is formed from an electrostatically charged polymer fibre.

Preferably, the filter is easily removable for ready replacement without dismantling of the humidifier.

Brief Description of Drawings Details of embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a known evaporative humidifier; Figure 2 is a cross section through the conventional evaporative cooler/humidifier of Figure 1; Figure 3 is a cross section through an evaporative cooler/humidifier incorporating an embodiment of the current invention; Figure 3a shows details of the included filter medium, being a magnification of the circled portion of Figure 3; and Figure 4 shows an exploded view of the components of the evaporative cooler/humidifier of Figure 3.

BestModes The prior art evaporative humidifier as depicted in Figures 1 and 2 comprises a water reservoir 10 onto which is attached a structural centre panel 20. The structural panel 20 supports a motor 30, which drives a fan 40. A decorative front panel 50 forms the front face of the humidifier. The motor 30 also drives a water pump 60 which pumps water through a conduit 65 to a water distributor 70. A rear panel 80 forms the outer rear surface of the humidifier and contains the evaporative media 90 to which water from the water distributor is delivered.

In operation, the motor 30 simultaneously drives the fan 40 and water pump 60 via belt 62 when energised. Water delivered by the pump 60 to water distributor 70 keeps the evaporative media 90 continuously wet. Fan 40 draws air through the wetted evaporative media 90. The effect of drawing air through the wetted evaporative media is to intensively evaporate water from the inner surfaces of the evaporative media.

This evaporation cools the wetted surfaces to temperatures approaching the Wet Bulb temperature of the incoming air, thereby cooling the air passing through the evaporative media. All water evaporated from the wetted evaporative media is then

present in the delivered air stream, thereby raising the moisture content, or humidity of the air leaving the evaporative humidifier.

In normal operation, any airborne contaminants present in the air stream entering the evaporative media are likely to be trapped on the internal surfaces of the evaporative media. The internal construction of the evaporative media is such that air passing through it must make many changes in direction around the internal wetted surfaces. The purpose of this construction is to maximise surface evaporation of water by forcing the air to impinge on the internal surfaces. Such a construction also ensures that any solid contaminants in the incoming air stream are likely to impinge on the internal surfaces and become trapped on the wet surfaces. Since the wetted surfaces of the evaporative media are continuously washed by flowing water, any contaminant so trapped will be flushed into the water reservoir and be re-circulated through the water system while the evaporative humidifier is running. It can be readily appreciated that if the evaporative humidifier is continuously operated in an environment where there is a constant source of contamination, such as an inhabited indoor environment, then there will be an accumulation of contaminants within the water system of the evaporative humidifier.

Figures 3 and 4 shows the evaporative humidifier with the filter system, subject of the current invention, in place. The addition of the filter medium 100 to the passage of the air stream, before the air passes through the evaporative media, provides an opportunity for any airborne contaminants to be trapped and retained before they come in contact with the water system of the evaporative humidifier. If the contaminants are so trapped, then the possibility of the contaminants entering and proliferating in the water system is reduced. To be effective, the filter medium 100 must be proficient at the removal and retention of microscopic particles in the size range of bacteria and fungi. Electrostatically charged filter media manufactured from polymer fibres of the type marketed by the 3M Corporation as"Filtrete"are known to have these characteristics. Such filter materials are described in US RE 30, 782 (Re- issue of US 3,998, 916) and US 3,644, 605 and others. Clearly, any other filter medium with a similar capability of removal and retention of particles in the size range of bacteria and fungi would be equally effective in preventing contamination of the water system of the evaporative cooler.

The filter medium 100 is mounted in a sub-frame 105 which allows easy removal of the filter medium pad and replacement with a new pad. It is not possible to

clean an electrostatically charged filter medium, which must be discarded when contaminated.

The inclusion of a filter medium, adapted to remove microscopic biological particles, in the air stream prior to the wetted evaporative media functions to prevent airborne contaminants from reaching the water system of the evaporative humidifier.