Abstract:
Air humidification system using microwave energy to heat water to produce steam. The system may include an automatic controller.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to an apparatus and method for humidifying air, and more specifically to an apparatus and method that use microwave energy to generate steam for humidifying air. 
     BACKGROUND OF THE INVENTION 
     When using a heating system to provide ambient air at a comfortable temperature indoors, it is often desirable to increase the humidity of the heated air. If the air to be heated is initially very cold, such as outdoor air in winter, the heated air will contain very little moisture. Indeed, indoor air may have a humidity, or moisture content, as low as 10 to 15 percent, which is significantly drier than even desert air. Such dry air can cause skin and mucous membranes to dry out, making people uncomfortable and perhaps increasing their susceptibility to infection by air-borne viruses and bacteria. Dry air can also lead to drying of wood structures, such as flooring and furniture, and it can lead to increased static electricity that may damage electronic equipment, such as computers. Thus, indoor air is often humidified, using one of several types of humidification systems that are currently available for residential and commercial use. 
     In a bypass type of humidification system, air passes over or through a pad or sheet of wet material that has a large surface area. As the air passes the wet surface, it picks up water that evaporates from the surface. Other systems use nozzles to spray small water droplets into the air. If the droplet size is small enough, the droplets evaporate quickly in the air, thereby preventing significant fogging. These types of systems generally require significant maintenance to prevent scale buildup on the pads or sheets or in the nozzles. 
     Steam humidifiers use heat to boil water in a reservoir or tank, most commonly with a heating coil located inside the tank. This type of humidifier generally uses tap water, which may contain significant quantities of dissolved minerals. As the water in the tank evaporates, the mineral content of the remaining water increases, and eventually minerals precipitate from the water to form scale deposits on the walls of the tank and the heating coil. Over time, the tank volume decreases, and the scale layer on the heating coil acts as a thermal insulator. As a result, the humidifier becomes increasingly inefficient. Although frequently flushing clean water through the tank can slow down the rate of scale buildup, there is no simple way to remove the scale deposits once they form in the tanks and in associated plumbing, and the tanks must be replaced periodically. 
     Thus, there is a need for a steam humidifier that operates more reliably over long periods of time and that can be easily maintained, rather than routinely replacing major system components, such as holding tanks, heating elements, and solenoid valves. 
     SUMMARY OF THE INVENTION 
     In accordance with the purpose of the present invention broadly described herein, one embodiment of this invention comprises an air humidifier system. The system comprises a water reservoir and means for heating water in the reservoir using microwave energy. The reservoir may comprise a cavity that can contain microwave energy therewithin, and the means for heating water may be a magnetron positioned near the reservoir. Alternatively, the means for heating water may comprise a cavity surrounding the water reservoir, with the cavity able to contain microwave energy therewithin. The reservoir may be easily removable from and replaceable into the system, thereby facilitating cleaning. 
     The air humidifier system also includes means for providing water to the reservoir, means for releasing steam from the reservoir, and means for draining water from the reservoir. The means for providing water may comprise an inlet conduit connected to the reservoir and an inflow control valve for controlling flow of water through the inlet conduit. The means for releasing steam may be a conduit connected to an air duct in a forced air heating system or an air handling mechanism for dispersing steam directly into a room. The means for draining water from the reservoir may comprise an outlet conduit connected to the reservoir and an outflow control valve for controlling flow of water through the outlet conduit. Alternatively, the reservoir may comprises a single water inlet and outlet, and the means for providing water and the means for draining water may comprise a 3-way valve. 
     Further, the air humidifier system includes means for controlling water flow into and out of the reservoir. The means for controlling water flow may comprise a device responsive to the water level in the reservoir. 
     The humidifier system also may further comprise means for controlling operation of the system, and the control means may operate automatically. The means for controlling water flow into and out of the system may comprise at least one solenoid valve. The solenoid valve or valves may be in signal communication with the control means, with the control means operative to open and close each of the solenoid valves. In addition, the humidifier system may comprise a humidity sensor and an air proving switch. The system may include an overflow conduit. An overflow alarm may be in signal communication with the control means. In addition, the system may include an overflow drain. The control means may be in signal communication with the means for heating water and the means for water fill, and it may be operative to switch the means for heating water on and off. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description, appended claims, and accompanying drawings, where: 
         FIG. 1  is a schematic drawing of one embodiment of a humidifier system in accordance with the present invention; 
         FIG. 2  is a schematic drawing of another embodiment of a humidifier system in accordance with the present invention; 
         FIG. 3  is a schematic drawing showing water filling of the embodiment of  FIG. 2 ; 
         FIG. 4  is a schematic drawing showing operation of the embodiment of  FIG. 2  to provide humidity; and 
         FIG. 5  is a schematic drawing showing flushing of the embodiment of  FIG. 2 . 
     
    
    
     DESCRIPTION OF THE INVENTION 
     In accordance with the present invention, microwave energy can be used to evaporate water inside a reservoir and supply humidity to air. 
     One embodiment of a microwave humidifier system  100  in accordance with the present invention in shown in  FIG. 1 . A magnetron or other microwave source  102  is adjacent microwave cavity/reservoir  104 , similar to a conventional microwave oven. Preferably, cavity/reservoir  104  has walls  106  that are appropriately shielded to prevent leakage of microwaves outside of cavity  104 . Cavity/reservoir  104  has a water inlet  110 , equipped with inlet valve  112  in inlet conduit  114 , and a drain  116 , equipped with drain valve  118  in outlet conduit  120 . A steam outlet  122  is provided generally near the top of reservoir  108  for escape of steam from the reservoir and into an air duct  124  in a forced air heating system, delivering air from furnace  126  to a room. Alternatively, the steam can be released directly into a room. If the steam is released directly into a room, it is desirable to use a fan or other air handling mechanism (not shown) to disperse the steam. 
     In use, initially, water outlet valve  118  is closed, and water inlet valve  112  is then opened to supply water to cavity/reservoir  104 . When reservoir  104  is filled with water to a desired level, inlet valve  112  is closed. Microwave energy is supplied by source  102  to heat the water in the reservoir  104  sufficiently to provide steam, which exits the reservoir via steam outlet  122 , either into the air duct  124  of a heating system, or directly into a room which is to be humidified (not shown). The microwave source  102  may be turned off when the desired humidity level is reached and restarted when the humidity drops below a desired level. When the water level in reservoir  104  becomes low, the inlet valve  112  may be opened to refill reservoir  104 . If it is desired to drain the reservoir  108 , drain valve  118  is opened. 
     Preferably, at least periodically during the operation of the humidifier, mineral-rich water is drained from cavity/reservoir  104 , and the reservoir is flushed by refilling it with water and subsequently draining it again. The flushing operation may be conducted by successively closing drain valve  118 , opening inlet valve  112 , allowing the reservoir  104  to fill, closing inlet valve  112 , and opening drain valve  118 . After the reservoir is flushed, drain valve  118  is closed, and inlet valve  112  is opened to refill the reservoir. 
     It is desirable to include a control system for a humidifier in accordance with the present invention, so that the humidifier operates with minimal human involvement. Preferably, the system is designed to receive and operate with standard 110V power, which is advantageous when compared with steam humidifiers currently in use that operate with 220V power. 
       FIGS. 2-5  show another embodiment  200  of a humidifier that includes one such control system. Reservoir  208  is formed from plastic or another microwave-transparent material and is positioned within a microwave cavity  204  having suitable shielding  206 . A microwave source  202  is positioned to transmit microwaves into cavity  204 . At the top of reservoir  208  is a steam outlet  222 . It should be noted that the steam outlet could also be positioned on the side wall  230  of reservoir  208 , above the maximum liquid water level expected in reservoir  208 . At or near the bottom of reservoir  208  is an electrically activated 3-way fill/drain valve  232 , leading to drain conduit  220  and inlet conduit  214 . A 3-way drain solenoid  234  operates fill/drain valve  232 . Inlet conduit  214  is in fluid communication with chamber  236  and reservoir  208  via fill solenoid  242  and fill valve  212 , float valve  238  in chamber  236 , and 3-way drain/fill valve  232 . A branch from inlet conduit  214  extends above the height of float valve  238  and past an overflow alarm  240  to a drain outlet  216 . Overflow alarm  240  includes an overflow sensor at least partly within the branch of conduit  214 . 
     System  200  is controlled by controller  244 , which is in electrical contact with a humidistat  246 , an air proving switch  248 , overflow alarm  240 , microwave source  202 , fill solenoid  242 , 3-way solenoid  234 , and a 110 V power source  250  via electrical lines  252 ,  254 ,  256 ,  258 ,  260 ,  262 , and  264 , respectively. As shown, controller  244  and a portion of the inlet system are enclosed in a housing  266 , which provides protection for the system components and may make the system more attractive. However, the housing  266  does not affect the functions of system  200 , and the system would operate without it. Also, overflow alarm  240  may only provide an audible or visible alarm signal indicating that the system needs attention, although it is preferable that the alarm  240  is in communication with the controller  244 , as shown. 
     The operation of humidifier system  200  can be understood with reference to  FIGS. 3-5 . Once the system is connected via lines  264  to a source of electricity, such as a standard 110 volt line, and microwave source  202  is enabled, controller  244  receives a signal from humidistat  246  indicating the humidity of the room air is too low. If air proving switch  248  indicates that the blower fan is operating and the humidistat  246  signals that more humidity is required, controller  244  sends a signal to fill solenoid  242  to open fill valve  212  and another signal to 3-way solenoid  234  to position 3-way valve  232  such that water can flow into reservoir  208  and not through drain conduit  220 , thus allowing water  270  to flow through inlet conduit  214  past float valve  238  and into reservoir  208 , as indicated by the arrows in  FIG. 3 . When reservoir  208  is filled to a sufficiently high level, float valve  238  shuts off the flow of water through conduit  214 . 
     Referring to  FIG. 4 , controller  244  then sends a signal to microwave source  202  to generate microwaves for transmission into cavity  204  to heat the water in reservoir  208 , rapidly creating steam. The steam  272  escapes through steam outlet for release into an air duct or directly into a room. As the water evaporates in reservoir  208 , the water level decreases, and float valve  238  allows additional water to flow through inlet conduit  214  and into reservoir  208 . If the humidistat still indicates that the humidity is too low, the cycle continues. If the humidistat  246  indicates that the humidity level is acceptable, the controller  244  shuts off power to the system  200 , except that the microwave source  202  remains enabled. The system  200  is ready to repeat the cycle as needed when the humidity drops below an acceptable level. It should be noted that air proving switch  248  prevents the system from providing steam when the heating system fan is not operating, thereby preventing water from condensing and accumulating in the air ducts. An accumulation of water in the ducts may cause the ducts to rust. 
     If the water level reaches a level higher than the upper level allowed by float valve  238 , overflow alarm  240  is triggered and provides an alarm signal to controller  244 , which then closes inlet valve  212  via fill solenoid  242 . Alarm  240  preferably also provides an audible or visible signal that the system needs attention due to an overflow. Alternatively, the audible or visible alarm could alert a person to shut the system down manually. 
     The humidifier system plumbing, including inlet conduit  214 , reservoir  208 , and drain conduit  220 , may be flushed to prevent accumulation of scale inside the reservoir and conduits. Preferably, the system is flushed at selected time intervals, such as every twenty-four hours. Alternatively, the system could be flushed after a pre-selected number of cycles, but this is less desirable because the system might run continuously under some circumstances, such as in a large building, 
     The flushing process can be understood with reference to  FIG. 5 . After a predetermined period of operation, Controller  244  sends a signal to 3-way solenoid  234  to position 3-way valve  232  so as to open drain conduit  216  and close inlet conduit  214 , thus allowing mineral-rich water to drain from reservoir  208 . After a predetermined amount of time that is sufficient for reservoir  208  to drain completely, 3-way valve opens the inlet conduit  214  and closes drain conduit  220 , and reservoir  208  is refilled with water. 
     Preferably, the water reservoir in accordance with the present invention is easily removed from the system for cleaning and removal of any scale that accumulates inside reservoir. Also preferably, the reservoir is easily replaceable if it is damaged or, possibly, if it is desired to use a different size reservoir. The humidifier of the present invention can be installed with a new forced air heating system, or it can be added onto an existing forced air heating system with only minor modifications to the heating system, such as providing a connection between the steam outlet and an air duct. 
     As illustrated in  FIGS. 2-5 , a controller suitable for use in accordance with the present invention may operate via electrical connections between all of the system components it controls. Alternatively, one or more of the electrical connections could be replaced by another communication method known in the art, including but not limited to sound, radio frequency, or visible light waves transmitted and received between the system components. 
     The foregoing description is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and process shown and described above. Accordingly, all suitable modifications and equivalents may be resorted to falling within the scope of the invention.