Abstract:
Today vaporizing humidifier must achieve their desired function and operate with conflicting requirements such as cost of ownership (CoO) and regulatory guidelines. Low CoO requires high injection efficiency, low water consumption, and high energy efficiency to reduce energy consumption and running costs. All of this is sought with variable humidification and low exhaust gas temperatures from safety/regulatory viewpoints as well as ducting material selection and venting of the exhaust gases and high efficiency. To date vaporizing humidifiers have been partially successful utilizing a single stage heat exchanger that could not extract latent energy from exhaust gases because the secondary fluid is boiling water. High exhaust temperature requires high temperature stainless steel exhaust venting. Embodiments of the invention provide dual-stage humidification systems with an effective design for achieving the conflicting objectives under variable humidification operation as well as addressing the control loop design of such dual-stage humidification systems.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application claims the benefit of U.S. Provisional Patent Application 62/349,237 filed on Jun. 13, 2016 entitled “Dual-Stage Humidifier Methods and Systems”, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to humidifiers and more particularly to the design of high efficiency two-stage heat exchangers within humidifiers and their control. 
       BACKGROUND OF THE INVENTION 
       [0003]    A humidifier is a device that increases humidity (moisture) in a single room or an entire building. Point-of-use humidifiers are commonly used to humidify a single room, while whole-house or furnace humidifiers, which connect to a building&#39;s home&#39;s heating, ventilation and air conditioning (HVAC) system, provide humidity to the building. Large humidifiers are used in commercial, institutional, or industrial contexts, often as part of a large HVAC system. 
         [0004]    The need for humidifiers arises in low humidity environments which may occur in hot, dry desert climates, or indoors in artificially heated spaces. In winter, especially when cold outside air is heated indoors, the humidity may drop as low as 10-20%. This low humidity can cause adverse health effects for humans and animals within these environments either as workers, visitors, or residents. Industrial humidifiers may also be used when a specific humidity level must be maintained to achieve specific requirements such as preventing static electricity buildup or preserving material properties (e.g. art galleries, museums, libraries, and their 
         [0005]    Whilst evaporative humidifiers, natural humidifiers, 
         [0006]    Whilst evaporative humidifiers, natural humidifiers, vaporizing humidifiers, impeller humidifiers and ultrasonic humidifiers are all common types, it is the vaporizing humidifier (or vaporizer, steam humidifier, warm mist humidifier) that dominates the industry for most commercial humidification systems. These operate by heating or boiling water, releasing steam and thereby moisture into the air. However, today the vaporizing humidifier must achieve its desired function and operate with what are quite often conflicting requirements arising from different factors such as cost of ownership (CoO) and regulatory guidelines. From the CoO perspective owners seek high injection efficiency (so that the desired humidity within the air flow is achieved with minimal steam losses to condensate) together with low water consumption, and high energy efficiency to reduce energy consumption and running costs. Further, for low CoO the vaporizing humidifier should be high reliability, low maintenance, and simple to repair. Further, all of this is sought with variable humidification as the humidity level in an air flow unless it is dried first will vary throughout the day and through the year such that the humidity demand may range from nothing to all the desired level. Finally, the humidifier when exploiting a heat exchanger between a combusted material (e.g. natural gas, oil, etc.) should have low exhaust gas temperatures both from a safety/regulatory viewpoint but also from the desire to use reducing installation cost by using low temperature plastics for ducting/venting of the exhaust gases and high efficiency. 
         [0007]    To date vaporizing humidifiers have been partially successful at achieving these requirements because they have utilized only a single stage heat exchanger that could not extract latent energy from exhaust gases because the secondary fluid is boiling water. The high temperature of the exhaust required use of high temperature stainless steel exhaust venting and resulted in potentially useful energy being simply exhausted into the atmosphere. 
         [0008]    Accordingly, it would be beneficial to provide designs of dual-stage humidification systems with an effective design for achieving the conflicting objectives under variable humidification operation as well as addressing the control loop design of such dual-stage humidification systems. 
         [0009]    Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures. 
       SUMMARY OF THE INVENTION 
       [0010]    It is an object of the present invention to mitigate limitations within the prior art relating to humidifiers and more particularly to the design of high efficiency two-stage heat exchangers within humidifiers and their control. 
         [0011]    In accordance with an embodiment of the invention there is provided a humidifier comprising:
   a burner for burning a fuel within a water tank for generating steam in response to a demand;   a primary heat exchanger within the water tank for transferring heat from products of combustion of the fuel to the water within the water tank;   a secondary heat exchanger comprising a combusted gas section coupled to primary heat exchanger for receiving the cooled products of combustion from the primary heat exchanger and a water section for transferring additional heat from the cooled products of combustion at an output of the primary heat exchanger to water flowing within the secondary heat exchanger from a fill box to the water tank;   the fill box comprising:
       a first water tank chamber coupled to a primary water fill from an external water source via a primary water fill valve in order to maintain cool water in the chamber;   a first outlet coupled from the first water tank chamber to the secondary heat exchanger via a micropump;   a second outlet coupled to a drain via a drain valve, wherein the drain also coupled the bottom of the water tank;   a second water tank chamber coupled to the bottom section of the water tank that contains floats which are used to control water level in the water tank; and   a third outlet coupled to the upper section of the water tank to maintain pressure balance between the water tank and first water tank chamber.   
       
 
         [0021]    In accordance with an embodiment of the invention there is provided a humidifier comprising:
   a burner for burning a fuel within a water tank for generating steam in response to a demand;   a primary heat exchanger within the water tank for transferring heat from products of combustion of the fuel to the water within the water tank;   a secondary heat exchanger comprising a combusted gas section coupled to primary heat exchanger for receiving the cooled products of combustion from the primary heat exchanger and a water section for transferring additional heat from the cooled products of combustion to water flowing within the secondary heat exchanger from a fill box to the water tank; and   a secondary fill valve connected to the secondary heat exchanger which is pulsed to provide cool water for transferring additional heat from the cooled products of combustion to water flowing within the secondary heat exchanger; wherein   the fill box comprises:
       a first water tank chamber coupled to a primary water fill from an external water source via a valve;   a first outlet coupled to a drain via a drain valve, the drain also coupled the bottom of the water tank;   a first inlet to the first water tank chamber coupled to the outlet of the secondary heat exchanger;   a second water tank chamber coupled to the bottom section of the water tank;   a plurality of floats which are used to control water level in the water tank;   a second outlet coupled to the upper section of the water tank to maintain pressure balance between the water tank and first water tank chamber.   
       
 
         [0033]    In accordance with an embodiment of the invention there is provided a humidifier comprising:
   a burner for burning a fuel within a water tank for generating steam in response to a demand;   a primary heat exchanger within the water tank for transferring heat from products of combustion of the fuel to the water within the water tank;   a secondary heat exchanger comprising a combusted gas section coupled to primary heat exchanger for receiving the cooled products of combustion from the primary heat exchanger and a water section for transferring additional heat from the cooled products of combustion to water flowing within the secondary heat exchanger from a fill box to the water tank; and   a secondary fill valve connected to the secondary heat exchanger which is pulsed to provide cool water for transferring additional heat from the cooled products of combustion to water flowing within the secondary heat exchanger; wherein   the water from a primary fill valve is fed directly into the tank; and   an outlet of the secondary heat exchanger is fed directly into the tank.   
 
         [0040]    Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0041]    Embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein: 
           [0042]      FIG. 1  depicts an example of a range of compact humidifiers; 
           [0043]      FIG. 2  depicts schematically from two viewpoints a compact high efficiency humidifier exploiting embodiments of the invention; 
           [0044]      FIG. 3  depicts the external connections of a compact high efficiency humidifier exploiting embodiments of the invention; 
           [0045]      FIG. 4A  depicts a schematic of a compact high efficiency humidifier exploiting embodiments of the invention; 
           [0046]      FIGS. 4B and 4C  schematics of humidifier variants according to embodiments of the invention comprising a condensing humidifier with micropump and a condensing humidifier without micropump respectively; 
           [0047]      FIG. 5  depicts a schematic of a fill box for a compact high efficiency humidifier exploiting embodiments of the invention; 
           [0048]      FIG. 6  depict exemplary display screens of a control interface for a compact high efficiency humidifier exploiting embodiments of the invention; and 
           [0049]      FIG. 7  depicts the float assembly within a fill box of a compact high efficiency humidifier exploiting embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0050]    The present invention is directed to humidifiers and more particularly to the design of high efficiency two-stage heat exchangers within humidifiers and their control. 
         [0051]    The ensuing description provides representative embodiment(s) only, and is not intended to limit the scope, applicability or configuration of the disclosure. Rather, the ensuing description of the embodiment(s) will provide those skilled in the art with an enabling description for implementing an embodiment or embodiments of the invention. It being understood that various changes can be made in the function and arrangement of elements without departing from the spirit and scope as set forth in the appended claims. Accordingly, an embodiment is an example or implementation of the inventions and not the sole implementation. Various appearances of “one embodiment,” “an embodiment” or “some embodiments” do not necessarily all refer to the same embodiments. Although various features of the invention may be described in the context of a single embodiment, the features may also be provided separately or in any suitable combination. Conversely, although the invention may be described herein in the context of separate embodiments for clarity, the invention can also be implemented in a single embodiment or any combination of embodiments. 
         [0052]    Reference in the specification to “one embodiment”, “an embodiment”, “some embodiments” or “other embodiments” means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least one embodiment, but not necessarily all embodiments, of the inventions. The phraseology and terminology employed herein is not to be construed as limiting but is for descriptive purpose only. It is to be understood that where the claims or specification refer to “a” or “an” element, such reference is not to be construed as there being only one of that element. It is to be understood that where the specification states that a component feature, structure, or characteristic “may”, “might”, “can” or “could” be included, that particular component, feature, structure, or characteristic is not required to be included. 
         [0053]    Reference to terms such as “left”, “right”, “top”, “bottom”, “front” and “back” are intended for use in respect to the orientation of the particular feature, structure, or element within the figures depicting embodiments of the invention. It would be evident that such directional terminology with respect to the actual use of a device has no specific meaning as the device can be employed in a multiplicity of orientations by the user or users. Reference to terms “including”, “comprising”, “consisting” and grammatical variants thereof do not preclude the addition of one or more components, features, steps, integers or groups thereof and that the terms are not to be construed as specifying components, features, steps or integers. Likewise, the phrase “consisting essentially of”, and grammatical variants thereof, when used herein is not to be construed as excluding additional components, steps, features integers or groups thereof but rather that the additional features, integers, steps, components or groups thereof do not materially alter the basic and novel characteristics of the claimed composition, device or method. If the specification or claims refer to “an additional” element, that does not preclude there being more than one of the additional element. 
         [0054]    An example of a range of commercial gas-fired humidifiers providing clean steam humidification with an economical operating cost is depicted in  FIG. 1 . Offered in condensing high-efficiency (CS), ultra-low NOX condensing (NX) and standard-efficiency models humidifiers with capacities ranging from 50 lb/h (23 kg/h) to 600 lb/h (270 kg/h). Standard efficiency units exploit just a primary heat exchanger whilst CS and NX variants employ a secondary heat exchanger to achieve the desired overall system performance. First to fifth humidifier models  110  to  150  respectively supporting:
       First model  110 : maximum capacities of 50 lb/h (˜23 kg/h) or 1001b/h (˜45 kg/h);   Second model  120 : maximum capacity of 150 lb/h (˜65 kg/h);   Third model  130 : maximum capacities of 200 lb/h (˜90 kg/h) or 3001 b/h (˜130 kg/h);   Fourth model  140 : maximum capacity of 450 lb/h (˜195 kg/h); and   Fifth model  150 : maximum capacity of 600 lb/h (˜260 kg/h).       
 
         [0060]    These humidifiers are designed for humidification through the ducts in an air handling unit using a steam distributor or alternatively a steam distribution manifold as well as directly into a space with one or more blowers. Such humidifiers typically have an integrated controller board which not only controls the humidifier, but also allows the humidifier to be connected to a building automation system (e.g. BACnet, Lonworks, or Modbus) or the Internet so it can be controlled and monitored remotely. Further, humidifier designs allow multiple humidifiers to be combined using master-slave or main-extension configurations using linking/communications between the humidifiers directly or indirectly through building automation systems and/or Internet. 
         [0061]    Referring to Table 1 there is listed a summary of the major components in each of first to fifth models  110  to  150  respectively to facilitate the range of humidification outputs from 50 lb/h (23 kg/h) to 600 lb/h (270 kg/h) respectively. Evident from Table 1 is that the design methodology of the steam based humidifier systems exploits multiple heat exchangers to provide higher steam output whilst reducing operating costs and meeting statutory requirements. However, other variants are possible such as a single primary heat exchanger with secondary heat exchangers of different size options for each, multiple primary heat exchangers with a single secondary heat exchanger, single primary heat exchanger with multiple secondary heat exchangers etc. The modular design concepts discussed and presented are not a requirement but one variant design methodology of many that may exploit embodiments of the invention. 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Components by Depicted Humidifier Model 
               
             
          
           
               
                   
                 Quantity 
               
             
          
           
               
                   
                 First 
                 Second 
                 Third 
                 Fourth 
                 Fifth 
               
               
                   
                 Model  
                 Model  
                 Model  
                 Model  
                 Model  
               
               
                 Component 
                 110 
                 120 
                 130 
                 140 
                 150 
               
               
                   
               
             
          
           
               
                 Steam Capacity (lb/h) 
                 50/100 
                 150 
                 300 
                 450 
                 600 
               
               
                 Primary Heat Exchanger 
                 1 
                 1 
                 2 
                 3 
                 4 
               
               
                 Secondary Heat Exchanger 
                 1 
                 1 
                 2 
                 3 
                 4 
               
               
                 Water Tank 
                 1 
                 1 
                 1 
                 1 
                 1 
               
               
                 Burner 
                 1 
                 2 
                 2 
                 3 
                 4 
               
               
                 Blower 
                 1 
                 2 
                 2 
                 3 
                 4 
               
               
                 Gas Valve 
                 1 
                 2 
                 2 
                 3 
                 4 
               
               
                 Ignition Control 
                 1 
                 2 
                 2 
                 3 
                 4 
               
               
                 Fill Box 
                 1 
                 1 
                 1 
                 2 
                 2 
               
               
                 Dual Fill Valve 
                 1 
                 1 
                 1 
                 2 
                 2 
               
               
                 Micropump 
                 1 
                 1 
                 2 
                 3 
                 4 
               
               
                   
               
             
          
         
       
     
         [0062]    Now referring to  FIG. 2  there are depicted first and second views  200  and  250  of a humidifier according to an embodiments of the invention, e.g. second model  120  depicted in  FIG. 1 , are provided without the exterior panels allowing the major components to be identified which are listed in Table 2 below. 
         [0000]    
       
         
               
             
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Main Components of Humidifier System according to  
               
               
                 an Embodiment of the Invention 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 201 
                 Vent, exhaust 
               
               
                 202 
                 Hose, dual fill valve to fill box 
               
               
                 203 
                 Inlet, gas 
               
               
                 204 
                 Label, specification 
               
               
                 205 
                 Micropump 
               
               
                 206 
                 Inlet, dual fill valve 
               
               
                 207 
                 Switch, over-temperature 
               
               
                 208 
                 Heat-exchanger, secondary (CS/NX) 
               
               
                 209 
                 Port, drain 
               
               
                 210 
                 Port, condensate (CS/NX) 
               
               
                 211 
                 Trap, condensate (CS/NX) 
               
               
                 212 
                 Valve, manual drain 
               
               
                 213 
                 Panel, front 
               
               
                 214 
                 Hose, fill box to drain pump 
               
               
                 215 
                 Hose, fill box to water tank 
               
               
                 216 
                 Hose, float chamber to water tank 
               
               
                 217 
                 Fill box and float chamber 
               
               
                 218 
                 Switch, On/Off 
               
               
                 219 
                 Display, touchscreen 
               
               
                 220 
                 Hose, fill box overflow 
               
               
                 221 
                 Pump, drain 
               
               
                 222 
                 Cover, water tank 
               
               
                 223 
                 Tank, water 
               
               
                 224 
                 Spark-igniter and flame sensor 
               
               
                 225 
                 Combustion chamber and primary heat-exchanger 
               
               
                 226 
                 Module, ignition control 
               
               
                 227 
                 Assembly, blower 
               
               
                 228 
                 Inlet, air intake 
               
               
                 229 
                 Outlet, steam 
               
               
                 230 
                 Valve, gas 
               
               
                 231 
                 Terminal strip, low voltage 
               
               
                 232 
                 Board, integrated controller 
               
               
                 233 
                 Board, driver 
               
               
                   
               
               
                 (Note: 
               
               
                 (CS/NX) = CS and NX versions only) 
               
             
          
         
       
     
         [0063]    Combustion: Within a high efficiency humidifier, the combustion system may consist of a fully modulating forced-draft combustion air blower(s), a negative pressure regulated gas valve(s), and a premix burner(s). On a call for humidity, the blower is energized to purge the system. During this time the control software performs diagnostic checks of the safety systems, such as the air proving switch (not shown) and the over-temperature switch, as well as the blowers. When the functions of the safety systems have been verified successfully, the gas valve(s) opens and the gas-air mixture is pushed through the burner ports into the combustion chamber(s). The spark-igniter(s) is simultaneously activated to ignite the gas-air mixture. If a flame is not sensed by the flame sensor(s) after a predetermined number of attempts, then the ignition control module(s) locks out and a fault message “Ignition Fail” generated. If a flame is sensed by the flame sensor(s), the gas valve(s) remains open and combustion continues. The gas valve(s) continues to maintain a constant air-to-gas ratio independent of the blower speed or external conditions. Within as discussed and depicted within this specification a standard efficiency humidifier the hot flue gases pass through the primary, in fact only, heat exchanger, and out to atmosphere. On the high efficiency CS and NX models, the hot flue gases pass through the primary heat-exchanger and then into a secondary heat-exchanger, wherein the flue gases are cooled further before exiting through the exhaust vent. The heat recovered by the secondary heat-exchanger is used to warm up the feed water. Optionally, another variant may be where the secondary heat exchanger and primary heat exchanger are essentially combined 
         [0064]    Water Management: Referring to  FIG. 3  there is depicted a schematic of a humidifier such as depicted in  FIG. 2  with the external water management aspects depicted. These are identified below in Table 3. 
         [0000]    
       
         
               
             
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                 Water Management Components of a Humidifier System according to  
               
               
                 an Embodiment of the Invention 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 301 
                 Vent, air intake—connected to exterior (optional connection) 
               
               
                 302 
                 Steam line (rigid pipe) 
               
               
                 303 
                 Vent, exhaust 
               
               
                 304 
                 Valve, manual gas shutoff 
               
               
                 305 
                 Supply line, gas 
               
               
                 306 
                 Adaptor, breakout 
               
               
                 307 
                 Hose, steam 
               
               
                 308 
                 Distributor, steam (or absorption manifold) 
               
               
                 309 
                 Duct 
               
               
                 310 
                 Drain line, condensate (with trap) 
               
               
                 311 
                 Funnel (with trap) 
               
               
                 312 
                 Filter, Water (optional) 
               
               
                 313 
                 Valve, water shutoff 
               
               
                 314 
                 Supply line, water 
               
               
                 315 
                 Cables, power and control signal  
               
               
                 316 
                 Drain line 
               
               
                 317 
                 Drain line, condensate (CS and NX models only) 
               
               
                   
               
               
                 (Note: 
               
               
                 (CS/NX) = CS and NX versions only) 
               
             
          
         
       
     
         [0065]    According to an embodiment of the invention a humidifier is equipped with a combination fill box, float chamber, and water trap for connection to the train line. This combination fill box, float chamber and water trap is depicted as fill box and float chamber  217  (hereinafter fill box  217 ) in second view  250  of  FIG. 2  and exploits innovative float chamber water level monitoring devices. The water trap is connected to a drain pump which is used to empty the main tank and perform drains to control mineral build up. All three components, namely fill box, float chamber, and water trap are essentially independent except the water trap and the float chamber share a common pressure balancing line to the top of the tank. 
         [0066]    The innovative float chamber water level monitoring devices employ a pair of magnetic floats, main and backup, in order to measure multiple, for example five (5), water levels in the humidifier for proper operation. This float chamber and its control board are located away from the primary and secondary heat exchangers and any burners in order to increase reading accuracy and reduce mineral build-up within the fill box  217 . The fill box  217  is connected to the water tank, e.g. water tank  223  (hereinafter tank  223 ) in first view  200  of  FIG. 2 , through four hoses. One hose connects to the bottom of the tank, and is used as the primary means to fill the tank  223 . A second hose routes water through the secondary heat-exchanger, depicted as secondary heat-exchanger  208  (hereinafter SEC-HEX  208 ) in second view  250  of  FIG. 2  into the tank (on CS and NX models only). A third hose runs from the float chamber to the tank allowing the water level within the tank  223  to be monitor using the magnetic floats. The final, fourth hose, connection is above water level in order to ensure equalization of pressure between the tank and float chamber. 
         [0067]    The fill box  217  also includes an internal barrier structure to isolate the water within the tank from the water supply, as well as a vacuum breaker on top of the water trap. The vacuum breaker prevents siphoning when the drain pump is stopped. For example, this internal barrier structure is a 1″ (25 mm) air gap although other structures may be employed with departing from the scope of the invention. As noted supra the float chamber provides monitoring of multiple levels for the control software of controller within the humidifier, e.g. integrated board  232  depicted in first view  200  of  FIG. 2 . Externally on the integrated display, e.g. touchscreen display  219  in second view  250  of  FIG. 2 , or a separate display these may be depicted through simple visual colour combinations of an LED array, discrete LEDs etc. or as a bar chart, visual image, etc. Considering the example of five (5) levels with three LEDs (red, green, yellow) then these would provide level indications as presented in Table 4 below. 

 
         [0068]    On initial start-up, dual fill valves fill the tank as well as the float chamber. The water level reaches the backup float first, then the main float. As water fills the float chamber and reaches the L1 level, the control software performs a series of tests to verify that the dual fill valves and drain pump function properly. During these tests, the dual fill valves continue to fill the tank until the water level reaches the L5 level in order to verify that all levels are detected correctly. Once the L5 level has been reached during start-up then the drain pump energizes in order to lower the water level to just below the L1 level. As the water level in the tank rises, if the float readings are inconsistent, a warning message “Float Inconsistent” is triggered and escalates to a subsequent fault message “Float Inconsistent Fault” if three consecutive inconsistencies occur. As the tests continue, if the water level does not rise to the L5 level, a fault message “Fill Check Fault” appears. Likewise, if the level does not drop just below the L1 level, the fault message “Drain Check” appears. When the tests are completed successfully, the dual fill valves energize again to fill the float chamber to either the L3 level or L4 level according to the controller software. 
         [0069]    If a demand signal is present, indicating a need for steam (humidification) then the humidifier then begins the combustion sequence. A first fill valve has a high flow rate and is used to fill the tank quickly. The second fill valve has a low flow rate and is used to match steam production. Within some embodiments of the invention the second fill valve would be a modulating fill valve but in other embodiments may be a pulsed valve. 
         [0070]    The low flow fill valve maintains the water level between L3 and L5. In normal operation the low flow valve is pulsed or modulated at a rate that will result in the water level increasing to L5. It must be pulsed/modulated to keep water in the fill box cool so that cool water is fed to the secondary from the fill box. If the water heats up then it will not cool the exhaust sufficiently to achieve condensing of exhaust gases. If the water level ever drops below L3 then the high flow valve is activated. When the pulsing/modulation results in water level reaching L5 then a drain is performed to remove minerals from the tank. On dual stage heat exchanger designs (e.g. CS and NX models) one or more micropumps are triggered periodically to cycle water through the SEC-HEX (s) into the tank. 
         [0071]    During steam production, the control software activates a drain sequence, e.g. every 24 hours which itself adjustable as is the time of day it executes, in order to verify that the floats and drain pump are still functioning properly. 
         [0072]    Accordingly, referring to  FIG. 4A  a schematic of a dual-stage humidifier according to an embodiment of the invention is depicted such as the humidifiers of CS/NX series depicted in  FIGS. 1 to 3  respectively. Accordingly, as depicted there are a first fluidic circuit relating to the combustion of an energy source, e.g. gas, and a second fluidic circuit relating to the humidification via the primary heat exchanger (PRI-HEX)  435 , exhaust gas cooling via the secondary heat exchanger (SEC-HEX)  450 , and associated fill, drain and blowdown functions. Accordingly, the first fluidic circuit relating to the combustion begins with an Air Inlet  415  and Gas Inlet  410  which are coupled to a blower  490 . The Gas Inlet  410  via a Mix Control  485  to ensure consistent air-gas ratio for high efficiency consumption with low soot etc. The output of the Blower  490  is coupled to the Burner  440  within the PRI-HEX  435  wherein combustion occurs and the hot combusted gases are coupled from the PRI-HEX  435  to the Primary Exhaust  445  via Heat Exchanger Tubes (HEX-Tubes)  495 . From the Primary Exhaust  445  the partially cooled combustion gases due to conduction heat transfer to the water within the Main Tank  405  surrounding the PRI-HEX  435 , HEX-Tubes  495 , and Primary Exhaust  445  exit the humidifier in a standard efficiency humidifier. 
         [0073]    The Primary Exhaust  445  is coupled to the Secondary Heat Exchanger (SEC-HEX)  450  where further heat exchange occurs, but now to water that is fed from the Water Tank  470  through the SEC-HEX  450  to the Main Tank  405  surrounding the PRI-HEX  435 , HEX-Tubes  495 , and Primary Exhaust  445 . The now cooler exhaust is released to atmosphere (the environment) at Exhaust Outlet  455 . 
         [0074]    The second fluidic circuit begins essentially with the Water Tank  470  which is filled via a Water Inlet  460  and a Pulsed Water Inlet  465 . As will be discussed below the Water Inlet  460  is employed for “coarse” water actions such as initial fill, blowdown etc. whereas the Pulsed Water Inlet  465  is employed during “fine” water actions of the humidifier when a demand is present, e.g. a demand for steam. The Water Tank  470  is coupled directly to the Main Tank  405  for “coarse” filling such as the initial fill operation. This connection is also coupled to the Drain  480  and Blowdown Outlet  475 . The former Drain  480  allows the Water Tank  470  and Main Tank  405  to be drained directly to a municipal sewer, another tank, etc. The Blowdown Outlet  475  is employed during a blowdown sequence within the humidifier wherein the Main Tank  405  is drained through a pumping sequence rather than simple gravity drain via the action of Blowdown Pump  420  which pumps the water from the Main Tank  405  to the Blowdown Outlet  475 . A blowdown processes allows for excess dissolved minerals accumulated inside the Main Tank  405  to be removed and extracted from the water to prevent excessive fouling of heat exchange surfaces due to mineral buildup. 
         [0075]    The Water Tank  470  is also connected to the upper region of the Main Tank  405  which is open to atmospheric pressure via the air conditioning system attached to the Steam Output  430 . In this manner the Water Tank  470  is maintained at equal pressure to the Main Tank  405 . As depicted in  FIG. 5  the Water Tank  470  is partitioned into Partition A  4100  and Partition B  4200  with Barrier  4300  disposed between them. The connection from Partition A  4100  to SEC-HEX  450  is via a Micropump  4400 . As depicted in FIG. 5 Partition A is open to atmosphere to allow an air gap between the fill lines and the water in the tank. The air gap is maintained in all cases by an overflow line which goes to drain in case the water level reaches its level. Partition B  4200  is sealed and connected to the top of the main tank with one connection at the top and to the bottom with another. Within other embodiments of the invention the Barrier  4300  may, for example, be a wall to each partition with a 1″ (25 mm) air gap between them although other structures may be employed with departing from the scope of the invention. 
         [0076]    Now referring to  FIGS. 4B and 4C  respectively there are depicted condensing humidifier designs with and without micropump  4400 . In  FIG. 4B  as with  FIG. 4A  the water tank is coupled to Water Inlet  460  and Pulsed Water Inlet  465  and the condenser on the second stage heat exchanger is coupled to the Water Tank  470  via Micropump  4400 . However, in  FIG. 4C  the Micropump  4400  is omitted and whilst Water Inlet  460  still couples directly to the Water Tank  470  the Pulsed Water Inlet  465  is now coupled to the Water Tank  470  via the secondary heat exchanger. Optionally, in each instance rather than a Pulsed Water Inlet  465  the pump and/or valve on that inlet may be modulated rather than pulsed in order to adjust the overall flow rate. 
         [0077]    The control software through a graphical user interface forming part of the humidifier provides access to a range of control parameters for the dual stage humidifier but it also allows access to a Service menu which provides a user with access to aspects such as Humidifier Service, General Service, Fault Service History, and Diagnostics. Through the Diagnostics sub-menus accessed through the Service Menu option the user can access diagnostics relating to the blowers within the humidifier. As such these are presented to the user as first to fifth Input Diagnostics Blower Sub-Menu (INDI-SUB)  610  to  650  respectively, wherein
       First INDI-SUB  610  relating to Blower 1 rpm, Blower 2 rpm, Blower 3 rpm, and Blower 4 rpm;   Second INDI-SUB  620  relating to Primary Valve  1 , Primary Valve  2 , Secondary Valve  1 , and Secondary Valve  2 ;   Third INDI-SUB  630  relating to Micropump  1 , Micropump  2 , Micropump  3 , and Micropump  4 ;   Fourth INDI-SUB  640  relating to Pulse Time On  1 , Pulse Time On  2 , Micropump Time On  2 B, and Micropump Time On  1 B; and   Fifth INDI-SUB  650  relating to Micropump Time On  2 A, and Micropump Time On  1 A.       
 
         [0083]    Accordingly, the control software executed upon an integrated controller in addition to providing a user access to many conventional control aspects of the humidifier the control software also supports fine tuning of 1) pulse rate of the low flow inlet valve; 2) pulse rate of the micropump; and 3) flow rate of the micropump in order to ensure proper cooling of the exhaust gases from the dual stage humidifier is achieved. 
         [0084]    Accordingly, through the control software and the diagnostics sub-menus a user is able to adjust the settings of the valves and pumps associated with Water Tank  470  and its 4 connections to the humidifier overall both inlets and outlets. However, normally a humidifier according to an embodiment of the invention would operate using the factory installed settings for these different controls which may be constant or vary according to the demand placed on the humidifier. These arise when seeking to ensure high efficiency operation as during operation at different demand levels of steam from the humidifier different effects within the humidifier must be factored into the control settings to ensure that not only is the overall efficiency maintained but that all other aspects of the humidifier specification are maintained. 
         [0085]    For example, at low demand the overall control system must account for an increasing water temperature within the Water Tank  470  which accordingly reduces the efficiency of the SEC-HEX and hence the exhaust outlet temperature would increase but this cannot exceed the maximum rated exhaust and accordingly at low demand the control system must ensure that the temperature of the water not increase too much which means increasing cold water inlet flow and flow but this cannot be arbitrarily increased at low demand as the temperature of the water within the main tank will reduce thereby reducing its efficiency. In contrast, at high demand with both increased energy to be absorbed from the exhaust gases and generated steam to be replaced the initial response is to increase the flow rate from the Water Tank  470  to the main tank through the SEC-HEX. However, again increasing the water flow too far results in cooler water flowing into the main tank reducing its efficiency. 
         [0086]    Accordingly, the inventors have established an advanced control algorithm to address the different conflicting demands of high efficiency steam generation at varying demand and exhaust gas upper temperature limit. The inventors have employed micropumps with variable pulse rates and pulse width modulation to provide the required control levels at the lowest flow rates. 
         [0087]    An example of this is presented below in Table 5 with respect to fill water management based upon the float board inputs as presented above and in respect of Table 4. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 Fill Water Management 
               
             
          
           
               
                   
                   
                 All Units 
                   
                   
               
             
          
           
               
                   
                   
                 Primary  
                 Secondary  
                 CS/NX  
                   
               
               
                 Float  
                 Software 
                 Fill 
                 Fill 
                 Units 
                 Burner/ 
               
               
                 Board 
                 Water 
                 Valve(s) 
                 Valve(s) 
                 Modulating 
                 Blower 
               
               
                 Input 
                 Level 
                 Response 
                 Response 
                 Pump(s) 
                 Operation 
               
               
                   
               
             
          
           
               
                 None 
                 0 
                 ON— 
                 OFF 
                 OFF 
                 Not  
               
               
                   
                   
                 continuous 
                   
                   
                 Permitted 
               
               
                 Low Only 
                 1 
                 ON— 
                 OFF 
                 OFF 
                 Not  
               
               
                   
                   
                 continuous 
                   
                   
                 Permitted 
               
               
                 Low +  
                 2 
                 ON— 
                 OFF 
                 On—Pulsed  
                 Permitted 
               
               
                 Mid 
                   
                 continuous 
                   
                 Mode (1) 
                   
               
               
                 Mid Only 
                 3 
                 OFF 
                 On—Pulsed  
                 On—Pulsed  
                 Permitted 
               
               
                   
                   
                   
                 Mode (1) 
                 Mode (1) 
                   
               
               
                 Mid +  
                 4 
                 OFF 
                 On—Pulsed  
                 On—Pulsed  
                 Permitted 
               
               
                 High 
                   
                   
                 Mode (1) 
                 Mode (1) 
                   
               
               
                 High Only 
                 5 
                 OFF 
                 On—Pulsed  
                 On—Pulsed  
                 Permitted 
               
               
                   
                   
                   
                 Mode (1) 
                 Mode (1) 
               
               
                   
               
               
                 Note 1: 
               
               
                 If blowers active, based on number of burners required 
               
             
          
         
       
     
         [0088]    Pulse filling is controlled by an off time (SVT OFF (X), X=1,2) and an on time (SVT ON (X), X=1,2). Within an embodiment of the invention the off time is a constant whilst the on time is calculated based upon demand, blowdown, burner capacity, number of active burners and fill correction values. An example of the calculation for SVT ON (X) is given by Equation (1) below. 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       SVT 
                       ON 
                     
                      
                     
                       ( 
                       X 
                       ) 
                     
                   
                   = 
                   
                     ( 
                     
                       
                         
                           FILL 
                           CORR 
                         
                          
                         
                           ( 
                           X 
                           ) 
                         
                       
                       × 
                       
                         
                           
                             SVT 
                             OFF 
                           
                            
                           
                             ( 
                             X 
                             ) 
                           
                         
                         
                           
                             ( 
                             
                               
                                 
                                   SV 
                                   RATE 
                                 
                                  
                                 
                                   ( 
                                   X 
                                   ) 
                                 
                               
                               
                                 
                                   REQ 
                                   RATE 
                                 
                                  
                                 
                                   ( 
                                   X 
                                   ) 
                                 
                               
                             
                             ) 
                           
                           - 
                           1 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       REQ 
                       RATE 
                     
                      
                     
                       ( 
                       X 
                       ) 
                     
                   
                   = 
                   
                     
                       ( 
                       
                         
                           
                             BL 
                             CAPACITY 
                           
                           × 
                           
                             N 
                             BURNERS 
                           
                           × 
                           Demand 
                         
                         100 
                       
                       ) 
                     
                     × 
                     
                       ( 
                       
                         1 
                         + 
                         
                           
                             BD 
                             RATE 
                           
                           100 
                         
                       
                       ) 
                     
                     × 
                     
                       ( 
                       
                         
                           
                             Burn 
                             1 
                           
                           + 
                           
                             Burn 
                             2 
                           
                         
                         
                           REQ 
                           
                             BURN 
                             - 
                             ON 
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0089]    The micropumps are activated according to the number of burners so MicroPump(X)=ON when Burner(X)=ACTIVE for 1≦X≦4. Each pump is cycled on and off with, for example, a fixed off time MicroPump−Time OFF  and a calculated on time MicroPump−Time ON  which changes based upon demand, blowdown, burner capacity and number of active burners. Each micropump is controlled through a pulse width modulated (PWM) control signal when on and PWM=0 during off time. The micropump timing is given by Equation (3). 
         [0000]    
       
         
           
             
               
                 
                   
                     MicroPump 
                     - 
                     
                       Time 
                       ON 
                     
                   
                   = 
                   
                     
                       MicroPump 
                       - 
                       
                         Time 
                         OFF 
                       
                     
                     
                       
                         ( 
                         
                           MicroPump_Rate 
                           
                             
                               REQ 
                               RATE 
                             
                              
                             
                               ( 
                               MicroPump 
                               ) 
                             
                           
                         
                         ) 
                       
                       - 
                       1 
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       REQ 
                       RATE 
                     
                      
                     
                       ( 
                       MicroPump 
                       ) 
                     
                   
                   = 
                   
                     
                       ( 
                       
                         
                           
                             BL 
                             CAPACITY 
                           
                           × 
                           
                             N 
                             BURNERS 
                           
                           × 
                           Demand 
                         
                         100 
                       
                       ) 
                     
                     × 
                     
                       ( 
                       
                         1 
                         + 
                         
                           
                             BD 
                             RATE 
                           
                           100 
                         
                       
                       ) 
                     
                     × 
                     
                       ( 
                       
                         1 
                         
                           REQ 
                           
                             BURN 
                             - 
                             ON 
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
         [0090]    Now referring to  FIG. 7  there is depicted a schematic of a Fill Box  217  as depicted in  FIG. 2  according to an embodiment of the invention within a Humidifier  300 . Accordingly, the Fill Box  217  comprises a Fill Box Body  706  into which is inserted a Float Sleeve  702  via Screws  701 . Within each tube of the Float Sleeve  702  a Magnetic Float  703  is disposed and the tube ends capped with Cap End  704 . A Gasket  705  provides a seal between the upper portion of the Float Sleeve  702  and the Fill Box Body  706 . As depicted the Float Sleeve  702  is disposed within Partition B  4200  of the Fill Box  217 . 
         [0091]    According to an embodiment of the invention a call for humidity when the humidifier changes from an idle to humidifying state then the primary fill valves are energized for a predetermined duration in order to flush and cool off the Fill Box  217 . At a predetermined point after starting the primary fill valves the micropumps are actuated to flush the SEC-HEX. After this the normal water management process takes over. 
         [0092]    Within a humidifier according to an embodiment of the invention when the drain pump is activated, the fill valve may also be activated to cool the drain water to an acceptable temperature to meet local plumbing requirements. Optionally, a humidifier design may allow for the drain cooling to be undertaken using a water source that is separate from the humidifier water supply. 
         [0093]    According to an embodiment of the invention then a humidifier may be implemented with the following design guidelines. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
             
           
               
                   
               
             
             
               
                 Gas Inlet 
                 132 kBTU/h 
                   
                   
               
               
                 Air Inlet 
                 28.6 cfm 
                   
                   
               
             
          
           
               
                 Steam 
                 100 lb/h 
                 Q = 97,000  
                 BTU/h 
                 212 F. 
               
               
                 Combustion  
                 ΔT = 2550 F. 
                 Q = xx  
                 BTU/h 
                   
               
             
          
           
               
                 Gases 
                 (2900-350) 
                   
                   
               
             
          
           
               
                 Main Tank 
                 125 lb/h  
                 Q = 6,250  
                 BTU/h 
                 ΔT = 50 F. 
               
             
          
           
               
                 Exhaust  
                 170 F. 
                 30 cfm 
                 (212-162) 
               
               
                 Outlet 
                   
                   
                   
               
               
                 Flue  
                 170 F. 
                 6 lb/h 
                   
               
               
                 Condensate 
                   
                   
                   
               
               
                 SEC-HEX 
                 Stages 1 &amp; 2 
                 Water 
                 Q = 14,000  
               
               
                   
                   
                 ΔT = 120 F. 
                 BTU/h 
               
               
                   
                   
                 (170-50)  
                   
               
               
                   
                   
                 Flue Gas 
                   
               
               
                   
                   
                 ΔT = 180 F. 
                   
               
               
                   
                   
                 (350-170) 
               
               
                   
               
             
          
         
       
     
         [0094]    Specific details are given in the above description to provide a thorough understanding of the embodiments. However, it is understood that the embodiments may be practiced without these specific details. For example, circuits may be shown in block diagrams in order not to obscure the embodiments in unnecessary detail. In other instances, well-known circuits, processes, algorithms, structures, and techniques may be shown without unnecessary detail in order to avoid obscuring the embodiments. 
         [0095]    Implementation of the techniques, blocks, steps and means described above may be done in various ways. For example, these techniques, blocks, steps and means may be implemented in hardware, software, or a combination thereof. For a hardware implementation, the processing units may be implemented within one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described above and/or a combination thereof. 
         [0096]    Also, it is noted that the embodiments may be described as a process which is depicted as a flowchart, a flow diagram, a data flow diagram, a structure diagram, or a block diagram. Although a flowchart may describe the operations as a sequential process, many of the operations can be performed in parallel or concurrently. In addition, the order of the operations may be rearranged. A process is terminated when its operations are completed, but could have additional steps not included in the figure. A process may correspond to a method, a function, a procedure, a subroutine, a subprogram, etc. When a process corresponds to a function, its termination corresponds to a return of the function to the calling function or the main function. 
         [0097]    Furthermore, embodiments may be implemented by hardware, software, scripting languages, firmware, middleware, microcode, hardware description languages and/or any combination thereof. When implemented in software, firmware, middleware, scripting language and/or microcode, the program code or code segments to perform the necessary tasks may be stored in a machine readable medium, such as a storage medium. A code segment or machine-executable instruction may represent a procedure, a function, a subprogram, a program, a routine, a subroutine, a module, a software package, a script, a class, or any combination of instructions, data structures and/or program statements. A code segment may be coupled to another code segment or a hardware circuit by passing and/or receiving information, data, arguments, parameters and/or memory content. Information, arguments, parameters, data, etc. may be passed, forwarded, or transmitted via any suitable means including memory sharing, message passing, token passing, network transmission, etc. 
         [0098]    For a firmware and/or software implementation, the methodologies may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. Any machine-readable medium tangibly embodying instructions may be used in implementing the methodologies described herein. For example, software codes may be stored in a memory. Memory may be implemented within the processor or external to the processor and may vary in implementation where the memory is employed in storing software codes for subsequent execution to that when the memory is employed in executing the software codes. As used herein the term “memory” refers to any type of long term, short term, volatile, nonvolatile, or other storage medium and is not to be limited to any particular type of memory or number of memories, or type of media upon which memory is stored. 
         [0099]    Moreover, as disclosed herein, the term “storage medium” may represent one or more devices for storing data, including read only memory (ROM), random access memory (RAM), magnetic RAM, core memory, magnetic disk storage mediums, optical storage mediums, flash memory devices and/or other machine readable mediums for storing information. The term “machine-readable medium” includes, but is not limited to portable or fixed storage devices, optical storage devices, wireless channels and/or various other mediums capable of storing, containing or carrying instruction(s) and/or data. 
         [0100]    The methodologies described herein are, in one or more embodiments, performable by a machine which includes one or more processors that accept code segments containing instructions. For any of the methods described herein, when the instructions are executed by the machine, the machine performs the method. Any machine capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken by that machine are included. Thus, a typical machine may be exemplified by a typical processing system that includes one or more processors. Each processor may include one or more of a CPU, a graphics-processing unit, and a programmable DSP unit. The processing system further may include a memory subsystem including main RAM and/or a static RAM, and/or ROM. A bus subsystem may be included for communicating between the components. If the processing system requires a display, such a display may be included, e.g., a liquid crystal display (LCD). If manual data entry is required, the processing system also includes an input device such as one or more of an alphanumeric input unit such as a keyboard, a pointing control device such as a mouse, and so forth. 
         [0101]    The memory includes machine-readable code segments (e.g. software or software code) including instructions for performing, when executed by the processing system, one of more of the methods described herein. The software may reside entirely in the memory, or may also reside, completely or at least partially, within the RAM and/or within the processor during execution thereof by the computer system. Thus, the memory and the processor also constitute a system comprising machine-readable code. 
         [0102]    In alternative embodiments, the machine operates as a standalone device or may be connected, e.g., networked to other machines, in a networked deployment, the machine may operate in the capacity of a server or a client machine in server-client network environment, or as a peer machine in a peer-to-peer or distributed network environment. The machine may be, for example, a computer, a server, a cluster of servers, a cluster of computers, a web appliance, a distributed computing environment, a cloud computing environment, or any machine capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken by that machine. The term “machine” may also be taken to include any collection of machines that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein. 
         [0103]    The foregoing disclosure of the exemplary embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many variations and modifications of the embodiments described herein will be apparent to one of ordinary skill in the art in light of the above disclosure. The scope of the invention is to be defined only by the claims appended hereto, and by their equivalents. 
         [0104]    Further, in describing representative embodiments of the present invention, the specification may have presented the method and/or process of the present invention as a particular sequence of steps. However, to the extent that the method or process does not rely on the particular order of steps set forth herein, the method or process should not be limited to the particular sequence of steps described. As one of ordinary skill in the art would appreciate, other sequences of steps may be possible. Therefore, the particular order of the steps set forth in the specification should not be construed as limitations on the claims. In addition, the claims directed to the method and/or process of the present invention should not be limited to the performance of their steps in the order written, and one skilled in the art can readily appreciate that the sequences may be varied and still remain within the spirit and scope of the present invention.