Patent Publication Number: US-6983723-B2

Title: Method and apparatus for providing on-demand hot water

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims priority from U.S. Provisional Patent Application No. 60/578,299 filed Jun. 10, 2004 entitled On-Demand Water Heater. 

   FIELD OF THE INVENTION 
   This invention relates to steam driven hot water heaters and more specifically very compact low-pressure (I 5 psi to 300 psi) steam driven hot water-on-demand heat exchangers for use primarily in light industrial and commercial applications such as dry cleaners having continuously operational boilers which are not continuously in use to their full capacity. 
   BACKGROUND OF THE INVENTION 
   It is known that on heating, water-on-demand can be more efficient than heating and storing a tank of water as in a domestic hot water tank. To date most on-demand hot water heaters are powered by either electricity or gas (natural gas or propane). It is also known that heat exchangers have been used in industrial applications where high pressure steam is used to provide on-demand heating of water using primarily large U-tube or straight-through tube-type heat exchangers as in the Flo-Rite Steam Instantaneous Water heater made by Armstrong of Three Rivers, Mich., and the Instantrol Steam/Fluid Heater Package made by Robertshaw of Knoxville, Tenn. The heated water temperature is generally maintained by a thermally responsive valve that controls the inlet steam. 
   Another on-demand water heater is the MicroMix II produced by the Graham of Batavia, N.Y., in which water heated in a steam fed helical-coil heat exchanger is mixed with cold feed water using a thermally controlled mixing valve to achieve the desired output water temperature. 
   Applicant is also aware of patents regarding such on-demand heaters and variants such as: 
   U.S. Pat. No. 6,739,288 which issued to Kumamoto on May 25, 2004, teaches a method of regulating temperature between a heat exchanger and a condensate recovering unit by means of a steam ejector valve. 
   U.S. Pat. No. 4,278,069 which issued to Clark, Jr. on Jul. 14, 1981, teaches a water heater using an elongated vessel having a heat exchanger at one end leaving a volume storage and blending zone at the other end of the vessel. 
   U.S. Pat. No. 5,233,970 which issued to Harris on Aug. 10, 1993, teaches a helical coil heat exchanger in between two cylindrical metal sheets immersed in a tank of water to be heated. 
   U.S. Pat. No. 6,275,655 which issued to Rixen on Aug. 14, 2001, teaches a supplemental heating system configured for recreational vehicle use where hot engine coolant is circulated through a heat exchanger to heat potable domestic water using a compact heat exchanger and in some cases either thermal control of the feed valve, or mixing of hot and cold water to achieve desired water temperatures. 
   Many light industrial or commercial applications such as dry cleaners, hotels, etc presently use boilers for supply of steam and hot water. Typically the boilers will be run continuously during business hours, if not longer. In the use of boilers producing hot water, once the water is heated it may be stored for later use. In the case of boilers producing steam, the steam may not be usefully stored as it will return to condensate. Consequently, in the case of steam producing boilers, herein referred to as steam boilers, there exists a thermal inefficiency in producing steam which goes un-used and so is lost to condensate as it cools, only to be returned to the boiler to be re-heated. One object of the present invention is, in one embodiment, to recapture such wasted heat in an on-demand water heater by the use of a steam-to-water heat exchanger. Another object is to further recapture waste heat from the steam boiler by using the return steam condensate to pre-heat cold water entering the steam-to-water heat exchanger. 
   SUMMARY OF THE INVENTION 
   A first aspect of the present invention is therefore utilizing waste heat from a steam cycle employing a steam boiler in an industrial or commercial facility so as to heat water, on an on-demand basis, in a steam-to-water heat exchanger wherein the supply of steam into the heat exchanger is regulated so as to maintain the temperature of the heated water exiting the heat exchanger at a relatively constant pre-set temperature for end use in the industrial or commercial facility. In one embodiment this is accomplished by a temperature sensor sensing the outlet temperature of the heated water exiting the heat exchanger, and the sensed temperature being used to trigger opening or closing of a steam regulator regulating the in-flow of steam into the heat exchanger. Thus the steam regulator is opened to allow pressurized steam to flow into and through the heat exchanger when the outlet water temperature falls before a desired pre-set hot water temperature, and the steam regulator is closed once the pre-set hot water temperature is attained. 
   A second aspect of the present invention is further recapturing waste heat from the steam boiler steam cycle by pre-heating the incoming cold water being fed into the steam-to-water heat exchanger in the on-demand water heater using the still-hot condensate from the condensation of the steam which is typically recycled directly to a condensate tank cooperating with the steam boiler. Thus a further heat exchanger, a condensate-to-water heat exchanger, may be employed to pre-heat the cold water infeed to the steam-to-water heat exchanger thereby possibly boosting the efficiency or productivity (maximum available flow rate) and reducing the delay in the on-demand water heater in producing hot water at the desired temperature. For example, if the desired temperature is one hundred forty degrees Fahrenheit and the cold water infeed is pre-heated in the condensate-to-water heat exchanger to one hundred ten degrees Fahrenheit (that is, to approximately the temperature of the steam condensate), then the steam-to-water heat exchanger in the on-demand water heater only has to further heat the cold water infeed a further thirty degrees Fahrenheit. For a given maximum heat transfer rate in the steam-to-water heat exchanger, reducing the required increase in water temperature to go from the cold water infeed temperature to the desired outlet temperature may increase the attainable maximum flow rate through the on-demand water heater and reduces the time delay from the time the demand is made for hot water to the time it is delivered at the desired temperature, for example, to less than three seconds. 
   In one example, the present invention serves to heat water on demand using low pressure (15 psi to 300 psi) steam as a energy source, as commonly found in commercial dry-cleaning and laundering facilities, collectively referred to as cleaning facilities. Cleaning facilities commonly employ steam, for example in steam pressing of clothes. This source of steam is thus available for other uses, which is particularly efficient because steam, if not used, is quickly lost as condensate. Thus using steam that may not otherwise be used in cleaning facilities creates a re-capture efficiency. In the present invention, the recapture efficiency allows the use of steam to generate on-demand hot water in facilities such as cleaning facilities that use large quantities of hot water and can often ill-afford the space and expense of commercial boilers and the like. The present invention in one embodiment controls the inflow of steam by a self-modulating temperature control valve driven by the output water temperature of the on-demand water heater. The steam passes through a compact brazed-plate heat exchanger in which heat is transferred from the steam to domestic feed-water to an adjustably desired temperature, advantageously 140° F. in cleaning facilities. 
   In summary, the present invention may be characterized in one aspect as a device and a method for providing on-demand hot water including:
         a) providing an on-demand water heater which itself includes:
           i) a steam infeed conduit,   ii) a steam flow regulator cooperating with the steam infeed conduit to regulate the flow of steam through the steam infeed conduit according to a trigger signal governed by a hot water outlet temperature from a steam-to-water heat exchanger,   iii) the steam-to-water heat exchanger operatively connected in fluid communication with the steam feed conduit and having a steam infeed and a steam outlet downstream of the steam infeed for channelling steam from the steam feed conduit through the steam-to-water heat exchanger, the steam-to-water heat exchanger having a cold water infeed and a hot water outlet downstream of the cold water infeed for channelling water to be heated through the steam-to-water heat exchanger,   iv) a hot water conduit operatively connected in fluid communication with the hot water outlet,   v) a temperature sensor cooperating with the hot water conduit for sensing the temperature of hot water leaving the steam-to-water heat exchanger and for sending corresponding temperature information to a means for controlling the steam flow regulator,   vi) a means for generating the trigger signal when the temperature of the hot water leaving the steam-to-water heat exchanger falls below a threshold temperature, the means for generating the trigger signal cooperating with the means for controlling the steam flow regulator;   
           b) providing pressurized steam, by a means for providing pressurized steam, to the steam infeed conduit from a steam boiler so as to re-capture waste heat in a steam circuit of the steam boiler wherein the pressurized steam is otherwise not in demand in the steam circuit within a facility containing the steam boiler wherein the steam circuit may not be otherwise using the steam from the steam boiler;   c) causing, by a hot water demand device, hot water to flow to an end use from the hot water outlet upon demand by the hot water demand device from the end use so as to draw water through the steam-to-water heat exchanger from the cold water infeed;   d) causing the steam flow regulator to open the flow of steam upon the trigger signal to allow flow of steam from the boiler through the steam-to-water heat exchanger upon detection by the temperature sensor of a hot water temperature below the threshold temperature;   e) causing the steam flow regulator to close off the flow of steam to the steam-to-water heat exchanger upon detection by the temperature sensor of a hot water temperature at or above the threshold temperature.       

   A water-to-water pre-heating heat exchanger may be provided wherein a hot water infeed of the pre-heating heat exchanger is in fluid communication with the steam outlet from the steam-to-water heat exchanger, and wherein a cold water outlet of the pre-heating heat exchanger is in fluid communication with the cold water infeed of the steam-to-water heat exchanger so as to pre-heat cold water fed into the steam-to-water heat exchanger. 
   The pre-heating heat exchanger may advantageously be mounted in fluid communication between the steam outlet and a condensate tank of the steam boiler, wherein steam condensate flows from the steam outlet through the pre-heating heat exchanger and thence into the condensate tank. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is, a schematic view of one embodiment of the present invention showing an on-demand steam driven water heater having a steam condensate driven infeed water pre-heater. 
       FIG. 2  is, in perspective view, the on-demand water heater according to one aspect of the present invention. 
       FIG. 3  is in front elevation view, the on-demand water heater of  FIG. 2 . 
       FIG. 4  is, in left side perspective view, the on-demand water heater of  FIG. 2  with the cabinet removed. 
       FIG. 5  is, in right side perspective view, the on-demand water heater of  FIG. 4 . 
       FIG. 6  is, in right side perspective view, the steam-to-water heat exchanger of  FIG. 5 . 
       FIG. 7  is, in partially cut away partially exploded view, the steam-to-water heat exchanger of  FIG. 6 . 
   

   DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
   The present invention includes a small-footprint steam-driven on-demand water heater  10  that uses a steam-to-heat heat exchanger  12  to transfer heat from steam, at for example 15 psi to 300 psi pressure, to water, thereby heating the water. The steam supply is modulated using a self-modulating temperature control valve  14  in order to effect demand based temperature control of the output water temperature. 
   The water to be heated is supplied to cabinet  16  through water feed pipe  18 , which then passes through strainer  20 , which removes debris from the water flow. From the strainer the water flows into heat exchanger  12  which may be a vertically oriented brazed plate heat exchanger such as supplied by the SEC company of Belfast, Prince Edward Island, Canada, for example a model M14 20 plate (approximately 12 gallons per minute hot water supply) or 30 plate (approximately 20 gallons per minute hot water supply) brazed plate heat exchanger. Heat exchanger  12  is supplied cold (or pre-heated) water through heat exchanger water inlet port  22 , collecting beat from the plates  12   a  in heat exchanger  12  as the water passes through the heat exchanger and eventually exiting from the heat exchanger at hot water outlet  24 . The heat exchanger is supported vertically so as to dispose the internal plates  12   a  vertically, The hot water temperature is measured at the hot water outlet  24  of heat exchanger by temperature sensor  26  controlling operation of a steam modulating valve  15  which includes control valve  14 . Depending on the temperature set point set on the modulating steam valve, and the measured temperature of the outflow water at outlet  24 , the control valve  14  will open if the measured temperature is below the set point (including hysteresis), or close if the measured temperature is at or above the set point. The temperature of the outflow water is also measured and displayed by temperature gauge  28  for a visual indication of the water temperature. 
   The heated water flows from hot water outlet  24  and out through cabinet hot water outlet  30 . The heated water circuit is protected by a hot water temperature and pressure relief valve  32 , which opens when the pressure or temperature exceeds the specified values of the valve, resulting in the hot water being vented through hot water over pressure/temperature outlet  34 . Heat exchanger  12  is supported in its vertical orientation in cabinet  16 . 
   Steam is supplied to water heater  10  through cabinet steam inlet  36  from boiler  38 . The steam flows through modulating steam valve  14  when it is open, and into heat exchanger  12  through the heat exchanger steam inlet port  40 . When the steam enters heat exchanger  10  it contacts internal plates  12   a  and transfers heat to the plates. The heat is thermally conducted to the water in the cooler water conduits of the heat exchanger. Eventually enough heat is extracted from the steam so that the steam condenses and flows out of the heat exchanger steam outlet  42  to the steam trap  44 , and out of the cabinet steam condensate outlet  46 . 
   In the embodiment of  FIG. 1  steam condensate exiting from condensate outlet  46  flows into a pre-heating heat exchanger  48  so as to flow through helical coil conduit  50 . Helical coil conduit  50  is immersed in cold water entering heat exchanger  48  through cold water infeed  52 . The steam condensate may flow counter-current to the direction of flow of cold water entering heat exchanger  48  through cold water infeed  52  and exiting from heat exchanger  48  through pre-warmed water outlet  54 . The pre-warmed water leaving water outlet  54  is fed into water infeed pipe  18  so as to pass through strainer  20  and enter heat exchanger  12  through cold water inlet port  22 . Steam condensate leaving helical coil conduit  50  flows into condensate tank  56  for return to steam boiler  38 . 
   When no water is being demanded from the water heater the water temperature at the heat exchanger water outlet  24  will rise in temperature until the set point temperature of the modulating steam valve is met, at which point the control valve  14  will substantially close, effectively shutting off steam to the heat exchanger  12  with the exception that valve  14  is always slightly open, assisting in regulating the water temperature to approximately ±1–2 degrees of 140° F. in the one preferred embodiment. When water is again demanded of the water heater from cabinet hot water outlet  30 , the water will begin to flow and cool water will enter heat exchanger  12 , and the water temperature at the heat exchanger water outlet  24  will drop until the temperature reaches the set point (plus hysteresis) at which point the control valve  14  will open and allow steam to flow to heat exchanger  12 . In this way water may be heated on demand using steam from boiler  38  as a heat source. 
   As better seen in  FIGS. 6 and 7 , heat exchanger  12  in one preferred embodiment is a brazed plate heat exchanger, comprised of a sandwich of metal plates  12   a , for example twenty or thirty plates, so as to interleave layers of water and steam The modulating steam valve in one preferred embodiment may be a Model 150F steam valve supplied by Sterlco of Milwaukee, Wis., USA. 
   
     
       
         
             
          
             
                 
             
             
               List of items shown in figures 
             
          
         
         
             
             
          
             
               Item 
               Description 
             
             
                 
             
             
               12 
               SEC Brazed Plate Heat Exchanger (M14a (20 or 30 Plate)). 
             
             
               40 
               Heat Exchanger Steam Inlet 
             
             
               42 
               Heat Exchanger Steam Outlet 
             
             
               22 
               Heat Exchanger Water Inlet 
             
             
               24 
               Heat Exchanger Water Outlet 
             
             
               15 
               Steam Modulating, Water Temperature Driven one inch Valve. 
             
             
                 
               (Sterlco Model 150F Modulating Steam Valve, 110F. to 190F. 
             
             
                 
               Range) 
             
             
               14 
               Valve part of Steam Modulating Valve 
             
             
               26 
               Temperature sensor part of Steam Modulating Valve 
             
             
               44 
               Steam Trap (Sterlco Self Cleaning one inch Brass Angle Steam 
             
             
                 
               Trap.) 
             
             
               32 
               Hot Water Pressure Relief Valve (¾ inch Watts #100 XL 
             
             
                 
               Temperature Pressure Blow-off Valve.) 
             
             
               20 
               Strainer (one inch I.P. Red &amp; White Bronze Y Strainer 380/15) 
             
             
               28 
               Temperature Gauge (¼ inch NPT triticator 2½ inch gauge 0 to 
             
             
                 
               75 PSI.) 
             
             
               16 
               Cabinet (20 inch by 20 inch by 8 inches deep). 
             
             
               18 
               Cabinet Water Inlet 
             
             
               30 
               Cabinet Hot Water Outlet 
             
             
               36 
               Cabinet Steam Inlet 
             
             
               34 
               Hot Water Over Pressure/Temperature Outlet. 
             
             
               46 
               Cabinet Steam Condensate Outlet 
             
             
               38 
               Steam Boiler 
             
             
               56 
               Condensate Tank 
             
             
               48 
               Pre-heater 
             
             
                 
             
             
               @ 
             
          
         
       
     
   
   As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.