Patent Publication Number: US-2021172622-A1

Title: Humidifying unit for a hvac system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. application Ser. No. 14/897,550 filed on Dec. 10, 2015, which is a National Phase Application of PCT/IL2014/050532 filed on Jun. 12, 2014 claiming priority to U.S. Provisional Application Ser. No. 61/834,475 filed Jun. 13, 2013, U.S. Provisional Application Ser. No. 61/938,601 filed Feb. 11, 2014 and U.S. Provisional Application Ser. No. 61/969,159 filed Mar. 23, 2014. The disclosure of U.S. application Ser. No. 14/897,550 and the PCT Application are hereby incorporated by reference into the present application. 
    
    
     TECHNOLOGICAL FIELD 
     The presently disclosed subject matter, relates to a humidifying unit in general and in particular to a humidifying unit for a Heating Ventilation and Air Conditioning (hereinafter HVAC). 
     BACKGROUND 
     The presently disclosed subject matter, in some examples thereof, relates to a humidifying unit for a Heating Ventilation and Air Conditioning (HVAC) system and, more particularly, but not exclusively, to a humidifying unit that is operable to be retrofit on existing HVAC systems. 
     Various humidifiers have been used in the connection with home or commercial heating systems to increase the humidity level of a discharged, heated air stream. A proper humidity level in the air can enhance the comfort level of an occupant in a heated room as the moisture in the air is known to inhibit discomfort associated with undesirable drying of the nasal passages. Furthermore, the increase in air moisture enables the occupant to feel more comfortable at a lower temperature level and thereby can be used to reduce costs associated with heating. 
     Evaporative cooling systems that humidify circulated air are also known to be used to augment cooling provided by traditional air circulators. Some known evaporative cooling systems operate with a fluid source in combination with a powered propeller to draw an airstream through a water-soaked filter. Optionally, a separate, stand-alone pumping system is used to supply fluid to augment the cooling provided by a separate air circulator. 
     U.S. Pat. No. 3,855,371 entitled “Humidifying Apparatus for Warm Air Ducts and the Like,” the content of which is incorporated herein by reference describes an atomizing or spray type humidifier assembly that can be removably mounted in an air conveying duct, such as a main trunk horizontal duct, of a hot air heating system. The humidifier assembly includes a solenoid-controlled spray nozzle and a multi-layer screen supported in an elongated tunnel structure of rectangular cross-section having opposite open ends to be removably positioned wholly within the air conveying duct. 
     U.S. Pat. No. 4,006,674 entitled “Humidifiers for forced air systems,” the content of which is incorporated by reference herein describes a humidifier for use in forced air heating systems. The humidifier includes a housing having a water reservoir adapted to be positioned adjacent an air register, outlet, or diffuser. A duct in communication with the air register is provided within the housing for delivery of air to the water reservoir, and a flexible curtain or baffle is positioned within the housing across said duct and extending into the water of said reservoir. The arrangement requires the forced air entering the duct to flex, balloon or bow out the curtain to raise it above the water surface in order to escape to the outside. The device is adaptable to forced air floor, wall or overhead registers, outlets, or diffusers. 
     U.S. Pat. No. 4,741,871 entitled “Free flow humidifier,” the content of which is incorporated by reference herein describes a humidifier for use in combination with a hot air forced heating system. The humidifier consists of a main housing (water box) which maintains a constant water level from an existing water source and controlled by a float control valve. The water is heated by a hot water heating coil. Hot air is directed into, though, and back into the main hot air stream. During this process, the hot dry air picks up moisture, becoming saturated, which is returned and mixed in the hot air supply duct, providing humidity throughout the entire system. The amount of air and humidity can be controlled by the inlet dampers, which regulates the amount of air flowing through the humidifier. 
     U.S. Pat. No. 4,986,937 entitled “Central air duct scooper humidifier,” the content of which is incorporated herein by reference describes an ultrasonic humidifier system which is mounted to an air duct of a heating system. A vibrator excites water within a reservoir so as to create a fog within a fog chamber. A panel directs air flow from an upstream furnace into the fog chamber for interaction of the air flow with the fog. This interaction increases the moisture content of the air flow so as to increase the humidity level thereof. Reed switches are provided to preclude vibration if the level within the reservoir is low and/or if no air stream is delivered from the furnace. 
     U.S. Pat. No. 6,850,698 entitled “Humidifier for use with source of heated air,” the content of which is incorporated herein by reference describes a free-standing humidifier that is suitable for placement near a source of heated air. Optionally, the humidifier is placed over a floor register in a home. The humidifier has a main reservoir for holding water, a rod having a length sufficient to extend across the reservoir, and panels that support the rod. A disposable paper towel is draped over the rod and one end of the paper towel is inserted through an opening in the top of the reservoir into water in the reservoir. Air flowing from the source impinges upon the paper towel and picks up moisture from it. A supplemental reservoir can be used to automatically supply additional water to the main reservoir from a water line that has a valve controlled by a float which turns the valve on and off. 
     GENERAL DESCRIPTION 
     According to one aspect of the presently disclose subject matter there is provided a humidifying unit for a heating ventilation air conditioning (HVAC) system comprising a tray disposed at the airways of the HVAC system configured to hold water therein and for humidifying the air stream in the airways. The humidifying unit can be provided as a stand-alone apparatus for integrating in the airways of a HVAC or can be integrally formed in the airways of an HVAC system. 
     The humidifying unit can be configured to be integrated or installed in a ductwork of a central HVAC system or in the airways of a single room unit such as ductless system, a split-system, window air conditioner or a portable system. 
     The humidifying unit can be provided with a humidity level by controlling the exposure of airstream to the water in the tray control which according to an example can be in the form of a moving lid disposed over the tray. 
     The humidifying unit allows a passive operation of introducing humidity into the air steam of the HVAC system by utilizing the kinetics of the air stream flowing in the airways thereof. 
     According to an example of the presently disclosed subject matter, the humidifying unit is integrated into an air handler of a ductless HVAC unit proximal to a vent through which air stream is pushed out. The humidifying unit can include a tray, channel and/or box for holding water. The tray can be integral to a frame of the vent in the air handler through which air stream is blown out. The frame of the air handler can provide a dedicated space and/or base for positioning the humidifying unit. Optionally, frames of existing air handlers are modified to provide the dedicated space and/or base. The tray can further include one or more water inlets and/or outlets. 
     The humidifying unit can be operable to increase a humidity level of air stream outflow from the HVAC system during heating, ventilation and also during cooling. During heating, the hot air stream blown out of the HVAC system passes over the tray filled with water leading to evaporation. The inventor has found that since both the velocity of air flow and the temperature of the air stream is relatively high as it exits the vent, a relatively high rate of evaporation can be achieved by pacing the humidifying unit near the vent. 
     Optionally, while the HVAC system is operated in a cooling mode, e.g., air conditioning mode, water that is condensed during cooling is directed toward the tray and used to humidify the air stream outflow of the HVAC system. Although, the rate of evaporation is typically lower during cooling, the inventors have found that some water will be absorbed in the air stream. Optionally, while the HVAC system is operated in ventilation mode and the ventilated air is relatively warm and dry, HVAC system together with the humidifying unit can be operated as an evaporated cooling system to both cool and humidify the ventilated air. 
     According to another example of the presently disclosed subject matter, the humidifying unit is integrated into a grille and/or ductwork connector of a mini-duct or duct HVAC unit. The humidifying unit can include a tray for holding water that is integral to the grille or ductwork connector. As used herein the term ductwork connector refers to a part that used to connect duct tubing to a grille. The tray can include one or more water inlets and/or outlets through which tubing can be connected. 
     According to further examples of the presently disclosed subject matter, the humidifying unit is integrated into a main airflow duct channel of a central HVAC system and is operable to humidify the air stream outflow prior to splitting the air stream outflow to a plurality of different ducts. 
     According to a further aspect of the presently disclose subject matter there is provided a HVAC system having airways configured to direct airflow towards a confined area, the system comprising a humidifying unit having a tray disposed in the airways and configured to hold water therein, the tray is so disposed in said airways such that the water humidifies the airflow in said airways controlling thereby the humidity level in the confined area. 
     The water tray can be integrally formed with a wall portion of the airways. The airways can include a duct channel having a grille and wherein the water tray is integrally formed with said grille. The airways can include a ductwork connector and wherein the water tray is integrated therein. 
     The HVAC system can be a central air system having a central duct and the water tray can disposed in said duct. 
     The humidifying unit can include an adjusting mechanism for adjusting the surface area of the water exposed to the airflow in the airway. The adjusting mechanism can include a lid configured to be selectively disposed with respect to the tray determining thereby the surface area of the water exposed to the air in the airway. 
     The HVAC system can further include a controller for controlling the disposition of the lid in accordance with the desired humidity level. The HVAC system can include a water inlet line connected to the water tray via a water inlet port. The HVAC system can include a condensation drainer being configured to direct water from a condensation drain towards the tray. The controller can be operative to initiate filling of water in response to turning on of the HVAC system. 
     The tray can be provided with a drain line configured to drain the water inside the water tray. A controller can be provided and can be operative to initiate draining of water in the water tray in response to turning off the HVAC system. 
     The adjusting mechanism can include a water level regulator configured to control the water level in the water tray thereby adjusting the surface area of the water exposed to the airflow in the airway. 
     The HVAC system can further comprise a heating element disposed in the water tray and configured to heat the water therein thereby accelerating humidification of the air in the airways. The heating element is a heated gas line of the HVAC system directed to the water tray for heating water in the water tray. 
     The HVAC system can further comprise a cleaning mechanism for removing calcification accumulating therefrom. The cleaning mechanism can include a brush for breaking up calcification accumulating in the water tray. The cleaning mechanism comprising a high-pressure sprinkling rod operative to direct high-pressure water toward in surface of the water tray for breaking up calcification accumulating in the water tray. The HVAC system can further comprise a wall portion disposed inside the airways, having a surface configured to allow water flow thereon to form said tray. The wall portion can be a sloped wall and the tray can be at a top portion thereof, such that water from the tray can flow downwardly under gravitational forces towards a low portion of the wall. 
     The humidifying unit may be configured to have any of the following features:
         a removable cover that can be partially and fully opened and/or closed to vary the exposure of water to the air stream and thereby alter the humidity level achieved with the humidity unit;   a mechanism for tilting the tray by varying degrees, thereby controlling the surface area of the water that comes into contact with the airstream;   A humidity sensor for sensing the humidity level in a room, the sensor being coupled to the humidifying unit which determines the exposure area of the water inside the airways;   A manual or automatic mechanism for halting of the humidifying unit when the HVAC unit is on the cooling mode thereof;   An adjusting mechanism for adjusting the exposure area of the water, thereby adjusting the humidity level in the air;   A filling mechanism for filling the tray in response to a water level therein below a predetermined threshold; the filing mechanism can be in configured to collect condensed water formed during cooling mode;   A draining mechanism for draining the tray in response to a water level therein above a predetermined threshold;   An auxiliary reservoir being in fluid communication with the tray and configured for despising thereto cleaning liquid;   The cleaning liquid can be configured to prevent bacteria accumulation or can be a scale cleaning liquid or can include an odor elimination material.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, examples will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: 
         FIGS. 1A and 1B  are simplified schematic drawings respectively of a known air handler for a ductless HVAC unit and the air handler with a humidifying unit in accordance with some examples of the presently disclosed subject matter; 
         FIG. 2  is a simplified schematic drawing of optional water supply and drainage features of a humidifying unit in an air handler of a ductless HVAC system in accordance with an example of the presently disclosed subject matter; 
         FIG. 3  is a simplified schematic drawing of a humidifying unit integrated into a grille extending from duct channel of an HVAC system in accordance with some examples of the presently disclosed subject matter; 
         FIG. 4  is a simplified schematic drawing of a humidifying unit integrated into a connector between a duct channel and grille of an HVAC system in accordance with some examples of the presently disclosed subject matter; 
         FIG. 5  is a simplified schematic drawing of a humidifying unit integrated with a central air HVAC system in accordance with some examples of the presently disclosed subject matter; 
         FIG. 6A  is a simplified schematic drawing of a HVAC system having a humidifying unit in accordance with another example of the presently disclosed subject matter; 
         FIG. 6B  is an exploded view of the HVAC system of  FIG. 6A ; 
         FIG. 6C  is a side sectional view of the HVAC system of  FIG. 6A ; 
         FIG. 7A  is a front perspective view of the humidifying unit of  FIG. 6A ; 
         FIG. 7B  is an exploded view of the humidifying unit of  FIG. 7A ; 
         FIG. 7C  is an enlarged view of the pumping mechanism of the humidifying unit of  FIG. 7A ; 
         FIG. 7D  is an enlarged view of the adjusting mechanism of the humidifying unit of  FIG. 7A ; 
         FIG. 8  is a simplified schematic drawing of a humidifying unit with an optional tilting feature in accordance with some examples of the presently disclosed subject matter; 
         FIG. 9A  is a side sectional view a folded cardboard in accordance with one example of the presently disclosed subject matter, disposed in a tray of a humidifying unit; 
         FIG. 9B  is a side sectional view of cardboard of  FIG. 9A ; 
         FIG. 9C  is a side perspective view of the tray of  FIG. 9A ; 
         FIG. 10A  is a top view of a cardboard in accordance with another example of the presently disclosed subject matter; 
         FIG. 10B  is a perspective view of a cardboard in accordance with another example of the presently disclosed subject matter; 
         FIG. 11A  is a side sectional view of an AC unit having a humidifying unit in accordance with another example of the presently disclosed subject matter; and, 
         FIG. 11B  is an enlarged view of the humidifying unit of  FIG. 11A . 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLES 
     Reference is now made to  FIGS. 1A and 1B  showing simplified schematic drawings respectively of a known air handler for a ductless HVAC system and the air handler with a humidifying unit in accordance with some examples of the presently disclosed subject matter. A known air handler and/or evaporator unit  101  of a split ductless HVAC system typically includes a vent  110  through which conditioned air, e.g., heated, cooled, or ventilated air is expelled and/or blown out. Typically, vent  110  is encompassed and/or defined by a frame  112  that is formed as part of a cover of air handler  101 . Typically, an array of directional blades  115  can be controlled to direct the air expelled through vent  110  in a desired direction, e.g., left, or right. The vent  110  can be covered by a flap  120  that can be rotated to control the direction of air flow in a vertical direction, e.g., up, and down. The flap  120  can be closed while air handler  101  is not in an operational mode, e.g., while air handler  101  is switched off. 
     According to some examples of the presently disclosed subject matter, there is provided a humidifying unit  150  that is integrated into an air handler  105  of an HVAC system. According to some examples of the presently disclosed subject matter, humidifying unit  150  is positioned in a vent  111 . Typically, frame  113  defining an extent of the vent  111  is enlarged as compared to frame  112  ( FIG. 1A ) to accommodate humidifying unit  150 . In some examples, humidifying unit  150  is positioned below directional blades  115  and within frame  113 . 
     According to some examples of the presently disclosed subject matter, humidifying unit  150  includes a tray and/or water box  160  for collecting and/or holding water. Optionally, tray  160  includes one or more inlet and/or outlet ports through which water and/or other fluids can be introduced and/or drained from tray  160 . According to some examples of the presently disclosed subject matter, tray  160  is formed as part of frame  113 . Optionally, frame  113  is formed from with a polymer material by a molding process and tray  160  is molded as part of frame  113 . Alternatively tray  160  is a part distinct from frame  113  and is inserted into frame  113 . According to some examples of the presently disclosed subject matter, as air outflow  180  is expelled from air handler  105 , it skims the surface of water contained in tray  160  and becomes humidified, e.g., saturated with water vapor. In some examples, water supply for humidifying unit  150  is provided by a water supply tube  170  that optionally connects to a main water line or other water source, e.g., a tank. Optionally, water supply tube  170  is fitted with a safety valve  175  for cutting off water supply to tray  160 . Optionally, safety valve  175  is fitted within the housing of air handler  105 . Optionally, a filter is fitted in tube  170  for filtering water supply to tray  160 . Optionally, tray  160  is manually filled with water. 
     The tray  160  can be sized to extend over a substantially entire length of vent  111  so that air outflow  180  has adequate interface with water contained in tray  160 . The height of tray  160  can span between 1-5 cm and the depth of tray  160  can span between 1-5 cm, depending on dimensions of air handler  105 . The tray  160  can be sized to hold approximately 100-400 ml of water. Reference is now made to  FIGS. 2A and 2B , water supply tube  170  can be provided and configured to supply water to tray  160  to maintain a desired level and/or volume of water within tray  160 . The water supply tube  170  can be associated with a valve  172  that can be controlled by controller  200  of humidifying unit  150  or a float valve in tray  160 . The valve  172  and safety valve  175  can be integrated in a single module integral. In some examples of  FIG. 2 b   , water from condensate drain tube  177  drains water via and/or to tray  160  so that condensate drain tube  177  can supply water to the tray  160  while the HVAC system is in a cooling mode. Optionally, a gas pipe in a condenser portion of the HVAC system is extended into tray  160  and used to warm the collected water. 
     The humidifying unit  150  can include a drain  175  for draining water out of tray  160 . Optionally, two drains  175  on opposite sides of tray  160  are used to avoid drainage problems due to an angle in tray  160 . The drain  175  can be connected with tubing  176  that typically directs condensed water formed during cooling to outside a building or home so as to allow evacuation of water from the tray. Alternatively, humidifying unit uses dedicated tubing to drain water out of tray  160  to a sewage line and/or outside a building or home. Typically drain  175  is associated with a valve  179  for controlling water flow out of drain  175  that can be operated by a controller  200  of humidifying unit  150 . The humidifying unit  150  can additionally include an overflow drain (not shown) which drains into condensate drain line  176 . It is appreciated that in case the HVAC system is not configured with a cooling mode, and thus does not provide condensed water, the system can be provided with a condensation apparatus, for example, from the outside ambient, so as to provide water into the tray. 
     It is noted that although humidifying unit  150  has been described in  FIGS. 1, 2A and 2B  as being integrated into a split ductless HVAC system typically including an air handler inside of a room and a compressor positioned outside, a similar construction can be used for example in a single unit air conditioner, e.g., an air conditioning window unit. 
     Reference is now made to  FIG. 3 , a humidifying unit can be integrated into a grille extending from duct channel of an HVAC system. According to some examples, the humidifying unit is integrated into ductwork of the HVAC system. A tray  260  of a humidifying unit  250  can be positioned and/or integrated onto a grille and/or register  210  positioned on a wall of a room, e.g., a wall of a dropped ceiling. As air outflow  280  blowing out from grille  210 , e.g., in a generally horizontal direction it skims the surface of water contained in a tray  260  of humidifying unit  250  and becomes humidified, e.g., saturated with water vapor. In some examples, tray  260  is integral to grille  210  and includes one or more water outlet and/or inlet ports for receiving and/or draining water into tray  260 . Optionally, grille  210  is molded with a cavity defining tray  260 . Optionally, a depth of grille  210 , e.g., its dimension going into the wall is increased relative to known dimensions of grilles to accommodate tray  260 . Optionally, tray  260  is a separate part that is fastened onto grille  210  during manufacturing. Typically tray  260  extends over a length of a vent opening of grille  210  and is typically interior to direction blades of grille  210  so that it is concealed. In some examples, both height depth of tray  260  ranges between 0.5-3 cm, although dimensions of tray  260  typically vary with size of grille  210 . Optionally, for ceiling grilles, tray  160  is integrated into the direction blades of the grille. 
     The water supply to tray  260  can be provided by a water line  270 . Optionally water line  270  connects to a water source, e.g., a main water line and water line  270  that extends through duct tubing  220  to tray  260 . Alternatively, water line  270  can be positioned outside of duct tubing  220  and is connected to tray  260  via a port in tray  260  (not shown). The water can be filled by manually filing tray  260 . According to some examples of the presently disclosed subject matter, a drain  275  with drain line  282  connects to tray  260  for draining water from the tray when required. Typically, drain  275  with drain line  282  is associated with a valve for controlling draining. Optionally, drain line  282  is directed toward a sewage line of the premises or is otherwise drained outdoors. Optional features of humidifying unit  250  are described in more details herein in reference to  FIGS. 6-8 . 
     Reference is now made to  FIG. 4  showing a humidifying unit  350  integrated into a connector between a duct channel and grille of an HVAC system in accordance with some examples of the presently disclosed subject matter. The tray  360  of a humidifying unit  350  is positioned and/or integrated into a ductwork connector  310  between a duct channel  320  and grille  310  of an HVAC system, where at least a portion of the ductwork connector is positioned horizontally, e.g., parallel to a dropped ceiling. Optionally, grille  310  is a wall grilled. Alternatively, a ceiling grille that directs air flow from a generally horizontal duct channel  320  downwards in a generally vertical direction is used. 
     Typically, tray  360  is positioned so that walls of the tray do not obstruct air flow  380  blowing through connector  310 . Optionally, walls of tray  360  are insulated to avoid condensation on outer walls. As air outflow  380  blows out through grille  310  in a horizontal direction it skims the surface of water contained in tray  360  of a humidifying unit  350  and becomes humidified, e.g., saturated with water vapor. The tray  360  can be integral to connector  310  and includes water outlet and/or inlet ports for receiving and draining water into tray  360 . Optionally, connector  310  is molded with a cavity defining tray  360 . Optionally, tray  360  is a separate part that is fastened onto connector  310  during manufacturing and/or assembly. Optionally, tray  360  is sized to substantially extend over a diameter of duct tubing  320 . Optionally, tray  360  is sized to substantially extend over a length of connector  310 . Optionally, the depth of tray ranges between 1-5 cm although its depth will typically vary with different sizes of duct connectors and/or duct tubing and can be deeper than 5 cm. 
     The water supply to tray  360  can be provided by a water line  370 . Optionally water line  370  connects to a water source, e.g., a main water line and water line  370  extends through duct tubing  320  to tray  360 . Alternatively, water line  370  is positioned outside of duct tubing  320  and is connected to tray  360  via a port in tray  360  (not shown). in addition, a drain  375  can be provided and can include drain line  382  connected to tray  360  for draining water from the tray when required. Typically, drain  375  with drain line  382  is associated with a valve for controlling draining. Optionally, drain line  382  is directed toward a sewage line of the premises or is otherwise drained outdoors. Optional features of humidifying unit  350  are described in more details herein in reference to  FIGS. 6-8 . 
     Reference is now made to  FIG. 5  showing a simplified schematic drawing of a humidifying unit  450  integrated with a central air HVAC system in accordance with some examples of the presently disclosed subject matter. A tray  460  of a humidifying unit  450  is positioned and/or integrated onto a main duct line  420  of the central HAVC system prior to the air flow splitting into plurality of duct lines  421 ,  422 ,  423  and  424 . Optionally, tray  460  is sized to substantially extend over a diameter of main duct tubing  420 . A water supply to tray  460  can be provided by a water line  470  and is drained with a drain line  482 . Optional features of humidifying unit  450  are described in more details herein in reference to  FIGS. 6-8 . 
     Reference is now made to  FIG. 6 , a humidifying unit  550  can be integrated in a wall mounted AC unit  500  having a cooling unit  510  and a cover  512  defining an air outlet aperture  514 . As sown in  FIGS. 7A and 7B , the humidifying unit  550  includes a tray  560  and a pumping mechanism  570  for supplying the tray  560  with water. The pumping mechanism  570  can be configured to pump water from a reservoir  555  coupled to the AC unit  500 . 
     As shown in  FIG. 7C  the pumping mechanism  570  can include a pump  572  which is configured to pump liquid, such as water, form the reservoir  555 . According to the illustrated example the pump  572  is coupled to an auxiliary reservoir  574  via a pipe  575 , which can include a cleaning liquid, and which is coupled to the reservoir  555 . This way, the pump draws water from the reservoir  555  as well as cleaning liquid from the auxiliary reservoir  574 . The cleaning liquid can be any known liquid configured to prevent bacteria accumulation inside the tray  560 , or can be a scale cleaning liquid, or odor elimination material. In addition, the cleaning liquid can include other additives for purifying the air in the room, smell additives, or other chemicals which it is desired to spray in the room. 
     It is appreciated that the tray can be provided with a sensor for sensing the quality of the water therein, such that the pump can be activated to draw cleaning liquid from the auxiliary reservoir  574  in response to low quality water in the tray. 
     According to an example the tray can be removable tray such that it can be periodically removed and cleaned. 
     According to an example, the tray can be formed form a scale resistant material. It is appreciated that according to an example the tray can be disposed with respect to the airflow, such that dust in the air can be collected by the water surface, such that the water facilitates in cleaning the air. 
     According to an example the pump is coupled to an electric valve  578  which is configured to provide water to a dripper element  580 . The dripper element  580  is configured to release a small stream of water, or drips of water into the tray  560 . The electric valve  578  can be configured to control the operation of the pump and to dictate the amount of cleaning liquid which is released. The pumping mechanism  570  can be encased in a housing  582  provided with a door  584 . 
     According to an example, the pumping mechanism  570  further includes a draining pump  576 , coupled to the tray  560  via a pipe  562 . The draining pump is configured to draining the water in the tray, and it can be coupled to a sewage system, or can be coupled to a pipe which can be used to direct the drained fluid into a bowl upon the need. The draining pump can be activated to drain water from the tray, when the temperature of the water rises above a predetermined threshold, for example to a level which does not allow proper humidification of the airstream. In the latter case the pumping mechanism  570  can be configured to provide fresh water to the tray so as to allow continuous humidification of the airstream. 
     The tray  560  can be provided with an adjusting mechanism for adjusting the exposure area of the water, thereby adjusting the humidity level in the air. The adjusting mechanism can include removable lid  505  configured to selectively open and close in response to the humidity level in the room. The removable lid can be provided with an actuating mechanism  530 . 
     Reference is now made to  FIG. 7D , the actuating mechanism  530  can include a motor  531  having a cogwheel  532  mounted thereon configured to engage a corresponding cogwheel  524  on which the lid  505  is mounted. When the motor  531  is activated the cogwheel  532  is rotated in one direction causing the corresponding cogwheel  524  and the lid  505  to turn in the opposite direction. The lid  505  according to this example is configured as a semi-circular cover, such that in response to rotation of corresponding cogwheel  524  the lid  505  rotated about the tray  560 . This way, the disposition of the lid  505  with reference to the tray  560  can be determined and so does the surface area of the water which is exposed to the air in the airway of the AC unit. 
     It is appreciated that the corresponding cogwheel  524  can defined teeth  526  only about a portion of the circumference thereof. This way when the motor  531  is rotated and the teeth of the cogwheel  532  engage teeth  526 , the corresponding cogwheel  524  and the lid  505  are rotated as well. As the teeth of the cogwheel  532  reach the area on the circumference of the corresponding cogwheel  524  which does not include teeth the rotation of the corresponding cogwheel  524  and the lid  505  stops. Thus, the amount of teeth on the corresponding cogwheel  524  determines the maximum rotation of the lid  505 , and precludes damage thereto, when fully closed or fully opened. 
     In some examples, a heating element (not shown) is introduced into tray  560  for heating and/or sterilizing water in the tray. Optionally, the heating element can be operated to boost evaporation of water in tray  560 . The tray  560  can be fitted with a removable lid  505 . The humidity level provided by the humidifying unit can be controlled by controlling position of removable lid  505 . The controller can be configured to partially close removable lid  505  to reduce the humidity level provided by humidifier  550 . Optionally the controller can fully close the removable lid  505  while the AC unit  500  is not operated, e.g., is turned OFF so that the water and/or tray remains clean while not being used. Optionally, a humidity sensor (not shown), e.g., a hygrometer is used to detect a humidity level in room and to provide input to controller for controlling a humidity level provided by humidifying unit  550 . The humidity sensor can be positioned in an air handler, near a thermostat of the AC unit  500  and/or anywhere in a room that is being heated or cooled. 
     According to another example the adjusting mechanism can include a water level regulator configured to sense and control the water level in the water tray thereby adjusting the surface area of the water exposed to the airflow in the airway. 
     The tray  560  can be installed with one or more mechanisms for breaking up calcification that can accumulate on inner surfaces of tray  560 . Optionally, a brush (not shown) can be provided for removing scale from the tray and can be disposed in the tray such that it touches the floor thereof. The brush can be operated with a piezoelectric element that vibrates and/or motor that moves brush so that it breaks up accumulated calcification. Alternatively, a high-pressure sprinkling rod can be fluidly connected to a water supply line and high pressurized water expelled from a sprinkling rod provides for breaking up accumulated calcification, on walls and floor of tray  560 . The tray  560  is installed with a basket (not shown) that is operable to hold a tablet for softening, disinfecting and/or adding fragrance to the water in tank  560 . Optionally, the basket can include a removable cover that can be used controllably expose the basket to water in tank  560 . 
     The tray can further be provided with means for stirring the water, for example a small turbine coupled to a motor, a flow generator inside the tray, or a pump, this way the top surface of the water is constantly stirred, and the heating of the water surface is mitigated. It is appreciated that maintaining the temperature of the water surface below a certain threshold can help the humidifying process of the airstream. The turbine can be activated only in response to a rise in the temperature of the water surface in the tray. According to another example the turbine can be activated so as to reduce the evaporation of the water in the tray. 
     A draining pump  576  can be provided and can be operable to initiate draining of tray  560  in response to sensing that theca unit has been turned off. Optionally, the controller is operable to initiate cleaning of tray  560  with the brush and/or sprinkler rod in response to sensing that the AC unit  500  has been turned off. Optionally, controller is operable to initiate filling of tray  560  with water in response to detecting that the systemic unit has been turned on and/or in response to input from a humidity sensor. Optionally, the tray is slanted so that calcification is localized near drain. 
     According to some examples of the presently disclosed subject matter, the cover can be rounded and can be formed from one or more blades that can be collapsed to open cover to varying extents, e.g., partially, or fully. 
     Reference is now made to  FIG. 8  showing a tray  560  in accordance with another example. The tray  560  is supported with by an axle  513  that can be rotated to tile tray  560  to a desired angle. Optionally, a motor communicates with axle  513  for rotating the axle. Optionally, different tilt angles are used to control the humidity level provided by humidifying unit  550 . Optionally, tilting tray  560  provides for changing the surface area of the water in tray  560  and thereby changing humidity level provided by humidifying unit  550 . Typically, a larger surface area provides increased humidity while a smaller surface area provides decreased humidity. Optionally, tilting tray  560  away from air flow reduces the humidity level provided or stops the humidifying action while tilting tray  560  toward the air flow increases the humidity level provided by humidifying unit  550 . Optionally, the tilting feature is used in place of the lid. In the previous examples the humidifying systems is configured to provide a contact between the passing air and a surface of water disposed inside the ventilation system thereby humidifying the air. It will be appreciated however, that the amount of moisture transferred from the water to the air is proportional to the area of contact surface between the air and the water. Accordingly, in order to achieve sufficient air humidity in the room, the contact area can be increased, beyond the dimensions of the tray of the humidifying systems. 
     According to an example increasing the surface area can be carried out by utilizing a porous hydrophilic material, such as a cardboard, for significant increase of the contact area of passing air with water. 
     Reference is now made to  FIG. 9A , a tray  605  can be configured to hold water  606  therein, together with a folded cardboard  600 . The cardboard  600  is configured to absorb water  606  therein, and due to the folding thereof it can define a large surface area, thus increasing the surface area of water particles with the air. It is appreciated that folding of the cardboard  600  is configured such that on one hand water can be absorbed therein and on the other hand air form the HVAC system can flow through the gaps  607  formed between the folds. The cardboard  600  can be disposed inside the tray  605  such that the folds are perpendicular to the direction of the airflow in the HVAC system, such that the air flows through the gaps  607  formed therebetween. 
     To improve water transfer, a variety of cardboard can be selected having wetting ability and at the same time maintaining rigidity in wet condition. It is also possible to add a certain detergent to the water, which would increase the wetting and improve the transfer of moisture. 
     As shown in  FIG. 9B , the cardboard  600  can includes an inner layer  602 , and outer layer  604  and a corrugated layer  603  disposed therebetween configured to provide capillary water transfer therethrough. 
     According to another example, as shown in  FIG. 10A , the cardboard  630  can be provided with a plurality of apertures  635 , such that air can flow therein contacting thereby more surfaces of cardboard and accumulating humidity thereby. 
     According to a further example, as shown in  FIG. 10B , the cardboard  640  can be provided with a plurality of apertures  642 , provided at the top portioned of each fold such that air can flow through the top portion of the cardboard  640 , contacting thereby more surfaces of cardboard and accumulating humidity thereby. 
     It is appreciated that other techniques form improving humidifying of the water can be utilized such as heating and evaporating portion of water or applying ultrasound waves for forming water particles. 
     The tray according to other examples can be filled with ice powder or pulverized or powder-like ice can also cool air. 
     As shown in  FIGS. 11A and 11B , according with a further example an AC unit  670  can be provided with a humidifying unit  680  configured to provide fluids flow, such as water, along a wall  682  disposed inside the air duct. The wall  682 , here illustrated as sloped wall can alternatively be a vertical or a, such that water provided on a top portion thereof, flow downwardly under gravitational forces towards a low portion thereof. It is appreciated that the wall  682  can be one of the inner walls of the airway of the AC unit. 
     The water can be provided on the wall  682  by forming a water channel  681  at the top portion of the wall  682 . The channel  681  is configured such that when water therein overflow, the water spill onto the wall downwardly. This way, the exposure area of the air to the water is not only the area of the tray, rather it is the area of the wall  682  on which water are provided. 
     Thus, the channel  681  can be defined along the entire length of a wall portion which in the airway of the AC unit, such that all the air flowing inside the AC unit is exposed to the water on the wall and humidity is accumulated in the air. The level in the water tray can be maintained such that water overflow towards the wall when the humidity level of the room falls below the desired level. This can be carried out for example by providing a tray  685  having water  675  therein, and a pump  690  providing fluid communication between the tray  685  and the channel  681  by means of pipe segments  692   a  and  692   b . The pump  690  can be configured to pump water onto the channel  681  when the humidity level drops below the desired level. 
     The humidifying unit  680  can further be provided with a draining mechanism for draining any redundant water at the bottom of the wall portion  682 . According to the illustrated example the draining mechanism is a slit  695  defined along the length of the wall, underneath which the tray  685  is disposed. 
     According to an example, the humidifying unit can be a slit  695  provided with water therein, for example by disposing a water tray underneath. The slit  695  can be disposed along the entire width of the airway, and the can disposed at the bottom of the wall portion  682 , or along nay other point of the wall portion, which is illustrated here as a sloped wall portion. It is appreciated that according to this example, the wall portion  682  is not configured to allow water flow thereon, rather the inventor has found that defining a slit  695 , or a similar channel on the sloped wall or at the bottom thereof, enhances the humidification process. 
     It is appreciated that the humidifying unit of the presently disclosed subject matter substantially does not consume energy however merely operate by utilizing the kinetics of the air stream flowing in the airways thereof. The humidifying unit can be provided with an energy source for operating the adjusting mechanism and such that the disposition of the cover is manipulated, or for operating the pump providing the water into the tray. 
     It is appreciated that in addition, to the above, utilizing the humidifying unit substantially eliminate the need to open the window so as to adjust the humidity level in the room, thus the presently disclosed humidifying unit reduces the energy consumption of the HVAC system. 
     When hot air flows through the air duct, the water along the wall raise the humidity level of the air. 
     It is appreciated that the dimensions of the wall, such as the length and the width thereof determine the exposure of the air inside the air duct to the water, and the humidity formed thereby. 
     According to an example the wall can be a horizontal wall, the water can be provided on one side thereof by sprinklers, the airflow urges the water to flow along the wall. 
     According to other examples, the water can be provided by means of sprinkles configured to sprinkle water on the top of the wall, thereby causing the water to flow downwardly. 
     It is noted that although most of the examples of the presently disclosed subject matter have been discussed in reference to home and/or building HVAC systems, the humidifying units described herein can also be used and/or adapted for use in HVAC systems in vehicles, such as cars, trains, busses, and aircrafts. 
     In addition, the humidifying units can be integrated in any A/C system such as air curtains, air conditionings, evaporative Cooling Units, and humidifiers. Etc. The terms: “comprises”, “comprising”, “includes”, “including”, “having” and their conjugates mean “including but not limited to.” 
     As used herein, the singular form “a”, “an” and “the” include plural references unless the context clearly dictates otherwise. For example, the term “a compound” or “at least one compound” may include a plurality of compounds, including mixtures thereof. 
     It is appreciated that certain features of the subject matter, which are, for clarity, described in the context of separate examples, may also be provided in combination in a single embodiment. Conversely, various features of the subject matter, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination or as suitable in any other described embodiment of the subject matter. Certain features described in the context of various examples are not to be considered essential features of those examples unless the embodiment is inoperative without those elements.