Abstract:
A system for rapid and efficient water heating is provided, with a water and heat recovery component. Using a thermal store as a heat exchanger the system mixes steam and cold water to deliver hot water at a user-controlled temperature. The high operating temperature of the thermal store and its thermal efficiency result in a compact, highly-efficient means of hot water delivery. Water and energy usage are further reduced through a means of recycling hot water through the system in operation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 61/587,692 filed on Jan. 18, 2012 and U.S. Provisional Patent Application No. 61/639,128 filed Apr. 27, 2012, both of which are incorporated herein by reference in their entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention is in the field of fluid heating, more particularly a system designed for instantaneous water heating across a range of temperatures and at variable flow rates. 
       BACKGROUND OF THE INVENTION 
       [0003]    Hot water has myriad uses such as domestic heating, washing and food preparation. Numerous solutions are available based on a variety of traditional power sources such as electricity, oil and gas as well as newer technologies such as solar, geothermal and heat pumps. Aside from the power source, there are numerous options depending on the application, such as tanked systems which heat and store water as required, to instantaneous systems which heat water on demand. Each of these options has its own characteristics and constraints such as size, power consumption, installation complexity and maintenance requirements. 
         [0004]    Several factors are driving innovation in the hot water arena, including the increasing importance of energy efficiency, cost of water supply, lower carbon emissions and the demand for compact, easily-installed, low maintenance products. 
         [0005]    Recovery of treated water is well known in the art. A typical example is “greywater”, where used water from sources such as showers, baths and hand basins is recycled, often close to the original point of use, e.g. in a household. Such greywater is usually utilised for flushing toilets or soil irrigation. There are difficulties associated with using this water in applications such as washing and bathing, including purification and filtration issues, to the extent that its use is not permitted in domestic situations in many jurisdictions. 
       SUMMARY OF THE INVENTION 
       [0006]    The invention disclosed herein provides a water heater system designed to deliver hot water at a constant, user-selectable temperature with a variable flow rate. In addition, it incorporates a heat and water recovery component designed to capture the waste hot water after its initial application (for example, a domestic shower) and reuse both the water itself and the heat energy contained therein, feeding both back into the main system, thus reducing overall water and energy usage. 
         [0007]    The system is composed of a thermal store used as a heat exchanger and a cold water-to-steam mixer element. A cold water supply is heated as it enters the heat exchanger within the thermal store. Since the thermal store operates at high temperatures, this flow of water is turned into steam as it goes through it. The steam is then mixed with cold water. The set temperature is achieved by varying the mix ratio of steam and cold water. 
         [0008]    The recovery component of the system incorporates an inlet feed to take the used water. This water will need purification and reheating before it can be reused and this is achieved by passing the water through the thermal store. The amount of heat energy that can be reused is dependent on a number of factors, including the desired output temperature and temperature drop during use. 
         [0009]    The thermal store operates typically between 450-900 degrees Celsius. Due to this high operating temperature and the consequent amount of thermal energy held, large volumes of hot water can be provided while reducing the size of the thermal store compared to traditional, tank-based stores. Another benefit of this implementation is that operating at over 850 degrees Celsius prevents water scaling as limescale cannot form at this temperature. Additionally, the high temperature serves to purify the waste water being fed back into the system to ensure its suitability for re-use. The heat contained within this recycled water reduces the overall energy needed for the thermal store to provide hot water at the required temperature. 
         [0010]    Even though the temperature of the thermal store is higher than tank-based stores, the heat losses will be minimized because the thermal store is a lot smaller than normal stores thus reducing the overall surface area of the system and insulation can be applied more efficiently. 
         [0011]    The thermal store is a metallic item heated up to a high temperature. The upper limit of the temperature is dependent on the material used. The volumetric heat capacity of the material used will define the overall volume of the system. High thermal conductivity is a desirable feature of the material used for the thermal store to optimize the heat transfer from the store to the water. Very favorable results are achieved with a material that has a high volumetric heat capacity and a high thermal conductivity such as iron and steel. 
         [0012]    The thermal store can also include any phase change of the material that will give even more energy stored for the same volume such as molten metals or salts. If this method is used, the material to which the phase change occurs will be encapsulated in a high thermal conductivity metallic casing. 
         [0013]    The thermal store has holes through which water can enter and be turned into steam before exiting the heat exchanger. The space between the holes is defined by the thermal conductivity of the material used. The higher the thermal conductivity of the material, the larger the space between the holes. 
         [0014]    The volumetric size of the thermal store is defined by the type of material used such as steel and the quantity of hot water and its supplied temperature that the device has been designed to provide and the amount of used, hot water that can be recycled and its heat energy when it enters the thermal store after initial use. 
         [0015]    The metallic thermal store can be heated to its selected operating temperature in a number of different ways. The most common way is to use resistive elements such as cartridge heaters. It can also be heated up by electromagnetic induction. In addition fuels such as gas or oil can be used to heat the thermal store due to its construction and operation. 
         [0016]    The water output of the heater is non-pressurized where input and output water pressures are required to remain the same or pressurized in a containment vessel where a controlled output water pressure is required. 
         [0017]    To achieve the required water temperature, the steam is mixed with cold water. This can be done in different ways; for example using a sparger, injecting the steam into a tank of cold water, using a heat exchanger or with a mixing valve. 
         [0018]    Advantages of the system according to the disclosure include, system material requirements and weight are significantly less than a tanked system delivering comparable water volumes, and the surface area of the thermal store relative to that of a tank necessary to store water at a desired temperature is substantially lower leading to greatly reduced thermal losses. Further, the energy in the thermal store rapidly heats the cold water input thus reducing waiting time for uses requiring large volumes of hot water delivered over a short timeframe, and the high operating temperature of the system means that lime scale cannot build up in the heat exchanger, thus enhancing system life cycle even when utilised in hard water environments. Still further, no solid to liquid phase change needs to be employed hence there is no risk of the escape of high temperature fluid or any possibility of changes to the reversibility of the charge, discharge cycle. The high operating temperature of the system means that any harmful bacteria present in the waste water being recycled or run through the system are eliminated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    For a more complete understanding of the present disclosure, reference is now made to the following description taken in conjunction with the accompanying drawings. 
           [0020]      FIG. 1  is a perspective view of a heat exchanger core of a system according to the disclosure, partially in phantom, with attached manifold plates and associated pipework; 
           [0021]      FIG. 2  is a cutaway drawing of the steel core of the heat exchanger; 
           [0022]      FIG. 3  is a perspective view of the manifold plates of the heat exchanger; 
           [0023]      FIG. 4  is a view of the heat exchanger fitted with cartridge heaters and thermocouple; 
           [0024]      FIG. 5  is a schematic diagram of the system; 
           [0025]      FIG. 6  is an assembly view of the system; and 
           [0026]      FIG. 7  is a view of the sparger used in mixing the steam and cold water. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    In accordance with one embodiment of the present invention illustrated in  FIGS. 1 and 2 , a heat exchanger  10  is provided. As described, the embodiment is illustrative and the dimensions indicated are approximate and may differ in alternative embodiments. At its center is a steel core  100 . The steel core is, for example, of medium carbon steel EN8 and is 135 mm wide, 135 mm deep and 100 mm tall. Within the steel core are a number of cylindrical holes as illustrated in  FIG. 2 . In this illustrative embodiment, there are eight holes  103  in a 4-4 pattern running horizontally through the core from side to side and eight holes  104  in a 3-2-3 pattern running vertically from top to bottom through the core. The horizontal holes are 12.7 mm in diameter and arranged in two rows. The upper row has the hole centers 27.5 mm from the core&#39;s top and at 22.5 mm, 52.5 mm, 82.5 mm and 112.5 mm on the side face. The lower row has the hole centers 72.5 mm from the core&#39;s top and the same as the upper row with respect to the side face. 
         [0028]    Positioned adjacent to one of the horizontal holes is a hole  105  which is 1.5 mm in diameter and 60 mm deep, with its hole center at 82.5 mm from the side and 35.6 mm from the top intended to hold a thermocouple  110 . The thermocouple may be a K-Type, model XQ-182-RS supplied by Radionics Limited, part of Electrocomponents plc of Oxford, United Kingdom. The three columns of vertical holes in the core are arranged as follows: Columns 1 and 3 each comprise three holes with their centers at 32.5 mm, 67.5 mm and 102.5 mm from the side face. Column 2 has two holes, with their centers at 50 mm and 85 mm from the side face. All holes are 13 mm in diameter. 
         [0029]    Welded to the top and bottom of the core are two manifold plates  101 ,  102 . These plates are centered on the top and bottom of the steel core, thus substantially completely covering the eight vertical holes  104  running through the core. The plates, as illustrated in  FIG. 3 , are of stainless steel grade  304  and are 97 mm in width and depth and 20 mm tall. There is a recess  115  inside the plates which is 80 mm square and 18 mm deep, leaving a border  120  of 5 mm around the edge. It is this border which is welded to the steel core. At the center of each manifold plate is a hole  125  of 15 mm diameter. Welded to the hole in each manifold plate is a grade  304  stainless steel pipe  130 ,  135  which act as the water inlet (on the bottom of the steel core) and steam outlet (on the top of the steel core). They are 15 mm in diameter, 2 mm thick and 60 mm in length. The end of each pipe is equipped with a threaded boss  140 ,  145  for connection to inlet and outlet pipework. 
         [0030]    As shown in  FIG. 4 , each of the eight horizontal holes in the steel core is fitted with a cartridge heater  150 . These are, for example, supplied by Watlow, of St. Louis, Mo., USA, model HT Firerod, which have a maximum operating temperature of 982 degrees Celsius. 
         [0031]    Each of the cartridge heaters is connected to a controller  155 . In this embodiment a Series 122 Bare Board controller from Zytron Control Products of Trenton, N.J., USA is utilised to manage the operating temperature of the system. Power for the system is fed through the controller, in this case a typical 240V mains supply. This board is also connected to the thermocouple  110  located within the steel core as part of the control mechanism. A schematic diagram of the system is provided in  FIG. 5 . Once switched on, the heat exchanger is initially heated to a temperature of 850 degrees Celsius. The controller then shuts off the cartridge heaters and monitors the temperature of the system. When the temperature of the heat exchanger (either as a result of standing losses over time or from water being passed through) drops below a preset threshold, for example 95% of its initial temperature, the controller switches on the cartridge heaters until the system is restored to full temperature. 
         [0032]    Ultimately, the output water temperature of the system is dictated by the ratio of steam to cold water. In this embodiment two proportional flow gate valves  160 ,  165  as shown in  FIGS. 5 and 6  are used to manage this ratio. These are manually controlled but could equally be electronic and linked to a user-controlled output temperature setting to automatically adjust the output temperature. By controlling the flow of water to the heating block, the amount of steam produced can be controlled and consequently the output water temperature of the system. When a user wishes to operate the system, they press the switch  164 . 
         [0033]    Connected to the system through pipe  135  is a source of cold water, for example a main water supply. This water supply is subsequently split into two paths  170 ,  175  as shown in  FIGS. 5 and 6 . A first flow  170  is directed into the heat exchanger  10 . It flows into the manifold plate  102  and up through the eight vertical channels  104  in the heat exchanger. The 850 degree temperature of the heat exchanger converts the water to steam which passes out of the exchanger through the manifold plate  103  and pipe  140 . It then passes through a check valve  190  (to prevent the cold water in the mixer from entering the heat exchanger) and enters the mixer  180 . A second flow  175  is directed through a standard ½ inch pipe through gate valve  165  into the mixer. 
         [0034]    The mixer essentially consists of a mixing junction for steam from the heat exchanger and cold water from the second water flow  175 . Contained within it is a sparger  200  to provide for an efficient mix of the steam and water. The sparger is illustrated in  FIG. 7 . In this illustrative embodiment it is 71 mm long and cylindrical in shape over 51 mm of its length with a diameter of 6 mm, with a shoulder over its remaining 20 mm. The shoulder has a threaded end to allow it to be connected inside the mixer in conjunction with a reducer sleeve. Beginning 8 mm from the shoulder and situated along the cylindrical section are 6 rows of 8 holes, spaced 4.53 mm apart, giving a total of 48 holes, each of diameter 1.5 mm. Two solenoid valves  161 ,  162  are fitted in the system and electrically linked to the push button switch  164  shown in  FIG. 5 . Also installed is a pipe  167  which feeds the hot waste water which was originally discharged through the solenoid valve  162  back to the system at a point after the cold water supply  135  but before the proportional flow gate valve  160 , with a check valve fitted as necessary to prevent this water flowing back into the second water flow  175 . This water may be collected from a standard waste system installed for collection and disposal of the hot water originally discharged through the valve  162 . Given that the water entering the system through inlet  167  will be hotter than that entering through the supply pipe  135  the overall energy necessary to heat the water flowing through the heat exchanger  10  is reduced relative to a system where only the cold water from supply  135  is utilised. Electronic controls incorporating necessary temperature sensors for the proportional flow gate valves  160 ,  165 , while not shown in this illustrative embodiment, are well known in the art and could be readily incorporated. 
         [0035]    Once the steam and water have mixed, the resulting hot water flows into a reservoir tank  210  through a ½ inch copper pipe. The tank is constructed from  304  gauge stainless steel and is 205 mm high, 100 mm wide and 50 mm deep. It is provided with fittings to take the output from the mixer, installation of an air bleed valve  163  and an output through the second solenoid valve  162 . In an alternative embodiment, the tank may not be incorporated and the hot water may be drawn off directly from the mixer. 
         [0036]    The heat exchanger  10 , exposed pipework and the tank  210  are all covered in high-performance insulation, in this embodiment Promalight  320  by Promat UK of Bracknell, United Kingdom. 
         [0037]    Pumps are well known in the art, used for a variety of reasons including poor mains pressure, plumbing constraints where a water tank is below the desired delivery point, specific application requirements such as power showers, and so on. In a further illustrative embodiment, the system, when equipped with the tank  210  can also provide pressurised hot water, thus eliminating the need for a separate pump. A pressure gauge incorporated into the system in the tank  210  permits user-controlled delivery pressure by varying the amount of steam in the tank thus causing a pressure build-up. Standard mixing valves and aperture control allow for the user to select the desired pressure at the delivery point, the upper limit bounded by choice of materials and consequent operating parameters. 
         [0038]    While the invention has been described with reference to illustrative embodiments, it will be understood by those skilled in the art that various other changes, omissions, and/or additions may be made and substantial equivalents may be substituted for elements thereof with departing from the spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teaching of the invention without departing from the scope thereof. Depending on particular regulations or requirements, it may be desirable for all water-contacting surfaces to be made from copper or stainless steel, for example. The temperature range available to the user and the volume of hot water supplied by the system may be varied. The power source used to heat the thermal store is not limited to any one type. Further, while a metallic thermal store is described, those skilled in the art should appreciate that other materials that withstand extreme temperature could be implemented, such as any of various composite materials. The system may be utilised in a variety of situations where instant, clean, efficiently-delivered hot water is desirable, such as personal showering, hand washing, and the like. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed for carrying out this invention, but that the invention will include all embodiments, falling within the scope of the appended claims.