Patent Publication Number: US-2006011193-A1

Title: Water pre-heating arrangement

Description:
CROSS REFERENCE OF RELATED APPLICATION  
      This application is a Continuation-In-Part of a non-provisional application, application Ser. No. 10/893,781, filed Jul. 16, 2004. 
    
    
     BACKGROUND OF THE PRESENT INVENTION  
      1. Field of Invention  
      The present invention relates to a water heater, and more particularly to a water pre-heating arrangement for a water heating system, wherein the water is pre-heated by the solar energy through the water pre-heating arrangement before entering into the water heater of the water heating system so as to minimize the energy consumption of the water heater.  
      2. Description of Related Arts  
      Conventional water heaters mainly utilize gas or electricity as a power source to heat up water for domestic or industrial purpose. As shown in  FIG. 1 a  conventional water heating system comprises a water heater having a water outlet and a water inlet connecting with a water source in such a manner that the water at the room temperature is heated up by the water heater to reach a preset temperature.  
      The mechanical designs and operations of the water heater have been dramatically advanced in the past several decades due to helter-skelter technology development. However, no matter how far the conventional water heaters have advanced in regard of their operation principles, most of them still rely on conventional power source—power sources ‘conventional’ in the sense that they are artificially used for industrial or domestic purposes.  
      Until more recently, water heater which utilize solar energy as their power source have been developed to resolve the general problems of potential energy crises or shortages. Those solar energy heaters no doubt meet the ever-increasing demand of environmental protection and ‘clean energy source’ from people all over the world. Yet they have several drawbacks.  
      One trivial problem is the lack of adequate sunlight. Though, in principle, the energy source of solar energy heaters is absolutely free and unlimited, in practice, it hardly can be. Conventional solar energy heaters share a problem of expensive equipment and installation which significantly and realistically prohibits the extensive use of such environmentally friendly water heaters.  
      Natural limitation should be another problem. Solar energy water heaters obviously require solar energy, which is derived from sunlight. As a matter of fact, sunlight may be rare in some seasons or geographical areas. Say, for example, in some northern areas, ‘evening’ comes at 2 or 3 o&#39;clock in the afternoon. After that, no sunlight can be obtained. Thus, in such circumstances, the solar energy water heaters cannot be used.  
      Back to some less extreme cases, the problem of cloudy or rainy whether may make the users of such solar energy water heaters frustrating. Bear in mind that, from engineering or scientific point of view, the specific heat capacity of water is one of the highest among popular or widely-used raw materials, especially liquid. Accordingly, in order to heat up a large amount of water for showering or bathing, a considerable amount of solar energy has to be utilized. Given the potential unstable whether condition, smooth operation of the solar energy water heaters may not be consistently achieved.  
      At least some better cases should be taken into account. Perhaps the above-mentioned problems in some tropical areas will be minimal, for there is substantial provision of sunlight in those places. While perhaps it can be said that there is no such problem of solar energy inadequacy in those areas, some other problems still exist.  
      Imagine if a given area has an adequate supply of solar energy, the whether, temperature in particular, in that area should be fairly, if not very, high. Therefore, though the problem of lack of adequate solar energy ceases to exist, at the same the demand of such solar energy water heaters ceases to be promising either. People may simply choose not to utilize hot water for shower, or the demand of hot water for showering etc. may be so low that the cost of installing the solar energy water heater can hardly be justified. Paradoxically, for conventional solar energy heaters, engineering problems conflict with marketing or economic problems.  
      Finally, assuming that the above mentioned problems do not exist for a given solar energy water heater, there is at least one remaining difficulty sharing among almost all solar energy water heaters, irrespective of where the heater is situated, or the method by which the heater is installed. The problem is that conventional heater of average capacity only fits for families of small size. That is to say, the conventional water heater only serves a small number of people. The underlying reason for this problem is that it is difficult to store such large amount of solar energy that it can be utilized by a lot of people, even sunlight is rich. After all, there is practical limit as to how much energy can be stored for a given solar energy collecting device.  
     SUMMARY OF THE PRESENT INVENTION  
      A main object of the present invention is to provide a water pre-heating arrangement for a water heating system, wherein the water is pre-heated by the solar energy through the water pre-heating arrangement before entering into the water heater of the water heating system so as to minimize the energy consumption of the water heater.  
      Another object of the present invention is to provide a water pre-heating arrangement for a water heating system, wherein the water heating system dose not require to alter its original structural design in order to incorporate with the water pre-heating arrangement so as to minimize the installation cost of the present invention.  
      Another object of the present invention is to provide a water pre-heating arrangement for a water heating system, which successfully provides an economic and efficient solution for pre-heating the water at a predetermined temperature by solar energy so that the water heater can effectively heat up the water into a desired water temperature by conventional power source while being energy effective.  
      Another object of the present invention is to provide a water pre-heating arrangement for a water heating system, wherein water is pre-heated by solar energy so that consumption of convention no-renewable energy source can be minimized.  
      Accordingly, in order to accomplish the above objects, the present invention provides a water pre-heating arrangement for a water heating system which comprise a water tank communicating with a water source for collecting a predetermined volume of water therefrom, and a water heater powered by a fossil fuel for heating up the water in the water tank into a predetermined temperature, comprising:  
      at least a heat exchanger having a heat exchanging unit, a water inlet adapted for connecting with the water source to guide the water to flow into the heat exchanging unit, and a water outlet adapted for connecting with the water tank to guide the water to flow from the heat exchanging unit to the water tank; and  
      a solar energy collecting device having a solar energy collecting surface mounted to the heat exchanger wherein the solar energy collecting surface is adapted for collecting and transforming solar energy into heat energy to increase a water temperature in the heat exchanging unit so as to pre-heat the water in the heat exchanging unit before entering into the water tank.  
      These and other objectives, features, and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a block diagram of a conventional water heating system.  
       FIG. 2  is a block diagram of a water pre-heating arrangement incorporated with a conventional water heating system according to a preferred embodiment of the present invention.  
       FIG. 3  is a perspective view of the water pre-heating arrangement according to the above preferred embodiment of the present invention.  
       FIG. 4  is a schematic diagram of a heat exchanger according to a second preferred embodiment of the present invention.  
       FIG. 5  is a schematic diagram of a water pre-heating arrangement according to the above second preferred embodiment of the present invention.  
       FIG. 6  is a schematic diagram of a water pre-heating arrangement according to a third preferred embodiment of the present invention.  
       FIG. 7  is a sectional view of the heat conversion tube of the water pre-heating arrangement according to the above third preferred embodiment of the present invention.  
       FIG. 8  is a block diagram of a water pre-heating arrangement of a water heating system according to the above third preferred embodiment of the present invention.  
       FIG. 9  is a schematic diagram of a heat exchanger according to the above third preferred embodiment of the present invention.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Referring to  FIG. 2  of the drawings, a water pre-heating arrangement  2  incorporates with a water heating system  1  according to a preferred embodiment of the present invention is illustrated, wherein the water heating system  1 , such as a conventional water heating system, comprises a water tank  11  communicating with a water source W for collecting a predetermined volume of water therefrom, and a water heater  12  powered by a fossil fuel for heating up the water in the water tank  11  into a predetermined temperature.  
      The water pre-heating arrangement  2  comprises at least a heat exchanger  20  connected between the water source W and the water tank  11  and a solar energy collecting device  30  for pre-heating the water in the heat exchanger  20  before entering into the water tank  11 .  
      The heat exchanger  20  has a heat exchanging unit  21 , a water inlet  22  adapted for connecting with the water source W to guide the water to flow from the water source W to the heat exchanging unit  21  via a water incoming pipe  101 , and a water outlet  23  adapted for connecting with the water tank  11  to guide the water to flow from the heat exchanging unit  21  to the water tank  11  via a water outgoing pipe  102 .  
      The solar energy collecting device  30  has a solar energy collecting surface  301  provided on the heat exchanger  20  wherein the solar energy collecting surface  301  is adapted for collecting and transforming solar energy into heat energy to increase a water temperature in the heat exchanging unit  21  so as to pre-heat the water in the heat exchanging unit  21  before entering into the water tank  11 .  
      According to the preferred embodiment, water at a room temperature is guided to flow from the water source W to the heat exchanging unit  21  through the water inlet  22  in such a manner that the heat exchange process can be performed in the heat exchanging unit  21  to pre-heat the water from the room temperature to a desired temperature by the solar energy.  
      The heat exchanging unit  21  comprises at least a heat absorbing water passage  211  extended from the water inlet  22  to the water outlet  23  for allowing the water to flow from the water source W towards the water tank  11  through the heat exchanging unit  21 . As shown in  FIG. 3 , the heat absorbing water passage  221 , having a predetermined length, recursively extended in a coiled manner to maximize a heat exchanging surface thereof. Accordingly, the heat absorbing water passage  211  is constructed in a tubular shape and made of thermally conductive material, such as metal, such that solar energy collected from the solar energy collecting device  30  can be effectively absorbed the heat absorbing water passage  211  and transferred to the water flows therethrough.  
      The heat exchanging unit  21  further comprises at least a heat transfer agent  212  encirclingly extended along the heat absorbing water passage  221  to enclose the heat exchanging surface thereof wherein the heat transfer agent  212  is adapted to absorb the heat energy collected from the solar energy collecting device  30  and release the heat energy to the heat absorbing water passage  211  for heating up the water flowing therethrough. The heat transfer agent  212 , having a predetermined heat transfer coefficient, is thermally communicated with the solar energy collecting device  30  in such a manner that the solar energy, essentially heat energy, is arranged to be transferred to the heat transfer agent  212  which eventually raises the temperature of the heat transfer agent  212 . In other words, the heat transfer agent  212  is capable of further enhancing the heat absorbing of the heat absorbing water passage  221  to pre-heat the water flowing therethrough.  
      From simple heat transfer theory, since the temperature of the water flowing through the heat absorbing water passage  211  is normally lower than the temperature of the heat transfer agent  212 , the heat energy carried by the heat transfer agent  212 , derived from the solar energy collecting device  30 , will be transferred to the water flowing through the heat absorbing water passage  211  via the heat exchanging surface thereof, such that the water flowing from the water inlet  22  is preheated to a predetermined temperature by the heat transfer agent  212  before reaching the water outlet  23 . For better heat transfer performance, the heat transfer agent  212  should be circulated within the heat exchanging unit  21  with a flowing direction opposite to the flowing direction of the water through the heat absorbing water passage  211 .  
      It is worth to mention that several factors are of crucial importance in determining the heat transfer between the heat transfer agent  212  and the water within the heat absorbing water passage  211 . In short, physical parameters such as the diameter of the heat absorbing water passage  211 , the flow rate of the water within the heat absorbing water passage  211 , the thickness of the wall of heat absorbing water passage  211 , and the thermal conductivity of the material by which the heat absorbing water passage  211  is made all determine the heat transfer effectiveness and efficiency between the heat transfer agent  212  and the water within the heat absorbing water passage  211 .  
      The solar energy collecting device  30  comprises a supporting plate  31  mounted to the heat exchanging unit  21  wherein the solar energy collecting surface  301  is provided on the supporting plate  31  for absorbing radiation as the solar energy from the sunlight. Accordingly, the solar energy collecting surface  301  is arranged for being orientated to face towards the sunlight for heat absorption. The solar energy collecting device  30  is preferred to locate on top of a house or a building so that the solar energy collecting surface  301  can substantially expose to the sunlight and is capable of collecting a large amount of solar energy. In addition, the supporting plate  31  can be selectively adjusted to maximize the exposure of the solar energy collecting surface  301  with respect to the sunlight, so that the user is able to adjustably orientate the solar energy collecting device  30  to obtain a better result of the water preheating process.  
      Alternatively, the solar energy collecting surface  301  of the solar energy collecting device  30  is directly formed on an outer surface of the heat absorbing water passage  211  of the heat exchanging unit  21  such that the heat absorbing water passage  211  can be directly absorbing the heat from the sunlight to transfer the heat to the water while the water flows through the heat absorbing water passage  211 . Accordingly, the heat absorbing water passage  211  can be, for example, an all-glassed evacuated solar collector tube, wherein the heat absorbing water passage  211  directly collects the solar energy. In other words, the heat absorbing water passage  211  also embodies as the solar energy collecting device  30  to simplify the structure of the water pre-heating arrangement, so as to minimize the manufacturing cost of the present invention.  
      It is worth to mention that the power per unit surface area of the solar energy collecting surface  301  in the sun&#39;s radiation (before the sunlight passes through the earth&#39;s atmosphere) is about 1.4 kW/m 2 . A maximum of about 1.0 kW/m 2  reaches the surface of the earth on a clear day, and the time average, over a 24-hour period, is about 0.2 kW/m 2 . Therefore, the solar energy collected by the solar energy collecting device  30  is capable of pre-heating the water to a pre-heated temperature which is higher than the room temperature.  
      As shown in  FIG. 1 , the water pre-heating arrangement  2  further comprises a water reservoir  40  arranged for storing the water pre-heated from the heat exchanger  20 , wherein the water reservoir  40  has a water entrance  41  operatively connected to the water outlet  23  of the heat exchanger  20  via a water transferring pipe  401  and a water exit  42  adapted for connecting to the water outgoing pipe  102  of the water tank  11  so as to guide the water to flow to the water tank  11 . Accordingly, the water, which is pre-heated at the heat exchanger  20 , flows out of the water outlet  23  through the water transferring pipe  401  and is temporary stored in the water reservoir  40 , wherein the water reservoir  40  has a heat insulated layer  43  for minimizing heat loss of the water in the water reservoir  40  to the surroundings. The heat insulated layer  43  can be a fiber glass insulating layer formed at an outer and/or inner side of the water reservoir  40  as an outer and/or inner casing thereof to prevent heat loss of the water stored in the water reservoir  40 .  
      The water pre-heating arrangement  2  further comprises means  50  for controlling the water out-flowing from the heat absorbing water passage  211  towards the water tank  11  through the water reservoir  40 . According to the preferred embodiment, the controlling means  50  is a one-way control valve  51  connected to the water exit  42  of the water reservoir  40  wherein the control valve  51  of the controlling means  50  is capable of determining a water level of the water tank  11  for allowing the water to flow from the water reservoir  40  to the water tank  11  so as to control the water flow from the heat absorbing water passage  211  towards the water tank  11 . Accordingly, when the water in the water tank  11  drops to a predetermined water level, the control valve  51  automatically opens for refilling the water from the water reservoir  40  to the water tank  11 . However, when the water tank  11  is full of water, the control valve  51  automatically closes to stop the water flowing to the water tank  11 . Therefore, the control valve  51  of the controlling means  50  is considered as a safety valve to retain a predetermined volume of water in the water tank  11 . It is worth mentioning that the heat absorbing water passage  211  can function as the water reservoir  40  for directly flowing the water towards water tank  11  such that the water reservoir  40  is optionally installed into the water-preheating arrangement  2 .  
      It is also worth mentioning that when both the water reservoir  40  and the water tank  11  are full of water, the control valve  51  of the controlling means  50  will be closed to stop the water to flow from the water reservoir  40  to the water tank  11  wherein the water in the water reservoir  40  will remain in its pre-heated temperature and will flow to the water tank  11  once the control valve  51  opens.  
      The pre-heating arrangement  2  further comprises a water regulating circuitry  60  which comprises a water pipeline  61  having a water inlet end  611  adapted for connecting to the water source W and a water outlet end  512  adapted for connecting to the water tank  11 , and a regulating valve  62  operatively connected to the water pipeline  61  for controlling the water to flow from the water source W to the water tank  11  through the water pipeline  61 . Accordingly, the regulating valve  62  is a temperature detecting valve for detecting the temperature of the water in the water reservoir  40  wherein when the temperature of the water in the water reservoir  40  is higher than the water at a room temperature, the regulating valve  62  is closed to block the water directly flowing from the water source W to the water tank  11  through the water pipeline  61 . Once the temperature of the water in the water reservoir  40  is lower than the water at the room temperature, the regulating valve  62  will be opened to allow the water directly flowing from the water source W to the water tank  11  through the water pipeline  61 . It is because the water heater  12  requires less energy to increase the water from the room temperature to the predetermined temperature.  
      Furthermore, the water regulating circuitry  60  is constructed as a safety circuitry wherein when no water flows into the heat exchanger  20 , i.e. no water is stored in the water reservoir  40 , the regulating valve  62  will automatically open to allow the water filling into the water tank  11  so as to ensure the water in the water tank  11  reaching the predetermined water level and the normal operation of the water heater  12  to heat up the water in the water tank  11 .  
      According to the preferred embodiment, the water heater  12  is a conventional gas water heater or electric water heater powered by gas or electricity respectively. Since the water is pre-heated at the water pre-heating arrangement  2  through the solar energy to reach the pre-heated temperature, the water heater  12  can save its energy to increase the water from the pre-heated temperature to the predetermined temperature. Even though there is insufficient sunlight at some geographical areas to efficiently heat up the water from the room temperature to the predetermined temperature, the water will pre-heat to reach the pre-heated temperature, which is higher than the room temperature, to save the energy consumption of the water heater  12 .  
      It is worth to mention that the water pre-heating arrangement  2  can be simply incorporated with the conventional water heating system  1  by connecting the water incoming pipe  101  of the water source W to the water inlet  22  of the heat exchanger  20  and the water outgoing pipe  102  of the water tank  11  to the water exit  42  of the water reservoir  40 . Therefore, the water heating system does not require altering its original structural design so as to minimize the installation cost of the water heating system incorporating with the water pre-heating arrangement  2 .  
      From the forgoing analysis, one skilled in the art can easily discover that the present invention provides a convenient and simple water heater which jointly utilize solar energy and conventional fossil fuel. The requirement of obtaining a large, if not unrealistic, amount of solar energy ceases to exist because the present invention does not simply require heating up the water solely by solar energy. At the same time, solar energy plays a vital role in the present water heating system, thereby achieving the object of saving non-renewable energy source.  
      Referring to  FIG. 4  to  FIG. 5  of the drawings, a water pre-heating arrangement  2 ′ incorporates with a water heating system  1 ′ according to a second preferred embodiment of the present invention is illustrated, wherein the water heating system  1 ′, such as a conventional water heating system, comprises a water tank  11 ′ for collecting a predetermined volume of water, and a water heater  12 ′ powered by a fossil fuel for heating up the water in the water tank  11 ′ into a predetermined temperature.  
      The water pre-heating arrangement  2 ′ comprises at least a heat exchanger  20 ′ connected between the water source W′ and the water tank  11 ′, and a solar energy collecting device  30 ′ for pre-heating the water in the heat exchanger  20 ′ before entering into the water tank  11 ′. Thus, the water tank  11 ′ communicates with the water source W through the heat exchanger  20 ′ for pre-heating.  
      The heat exchanger  20 ′ has a heat exchanging unit  21 ′ for converting solar energy to heat energy which is to be utilized for pre-heating water in the water tank  11 ′, and a water reservoir  24 ′ which comprises a water storing unit  241 ′ communictaed with the water source W though a water inlet and the water tank  11 ′, and a heater transfer module  242 ′ thermally communicated with the water storing unit  241 ′. Thus, water at room temperature from the water source W is stored in the water storing unit  241 ′ for pre-heating by the heater transfer module  242 ′ before it is drained to the water tank  11 ′ though a water outlet for normal use.  
      The heat exchanger  20 ′ further comprises a heat exchange agent  201 ′ flowing between the heat exchanging unit  21 ′ and water reservoir  24 ′. The heat exchange agent  201 ′ is embodied as having a predetermined heat conductivity so as to effectively retrieve heat energy collected by the solar energy collecting device  30 ′ and transfer it to the heater transfer module  242 ′ which in turn heats up the water stored in the water storing unit  241 ′.  
      The solar energy collecting device  30 ′ has a solar energy collecting surface  301 ′ mounted to the heat exchanger  20 ′ wherein the solar energy collecting surface  301 ′ is adapted for collecting and transforming solar energy into heat energy to increase the temperature of the heat transfer agent in the heat exchanging unit  21 ′.  
      According to the second preferred embodiment, the solar energy collecting device  30 ′ comprises a plurality of heat conversion tubes  31 ′ which are integrally mounted together in such a manner that the outer surfaces of the heat conversion tubes  31 ′ define the solar energy collecting surface  301 ′. Each of the heat conversion tubes  31 ′ comprises an outer glass evacuated tube  311 ′, and a heat transfer pipe  312 ′, which is preferably embodied as a copper pipe, embedded within the glass evacuated tube  311 ′ and extended to communicate with the heat exchanging unit  21 ′ for transferring heat collected from the heat transfer pipe  312 ′ to the heat transfer agent  201 ′ flowing through the heat exchanging unit  21 ′.  
      Specifically, the heat exchanging unit  21 ′ comprises a heat transfer housing  211 ′ and a fluid passageway  212 ′ extended therein, wherein the heat transfer agent  201 ′ is arranged to flow through the fluid passageway  212 ′ from the heater transfer module  242 ′ for retrieving energy from the heat conversion tubes  31 ′ and then transfer the heat energy received back to the heater transfer module  242 ′ where the heat is further transferred to the water storing unit  241 ′ for pre-heating the water stored therein.  
      Accordingly, the fluid passageway  212 ′ in the heat exchanging unit  21 ′ is thermally communicated with the heat conversion tubes  31 ′ inside the heat exchanging unit  21 ′ such that the solar energy collected would be transferred to the heat exchange agent through the fluid passageway  212 ′.  
      Moreover, the heat exchanging unit  21 ′ further comprises heat insulating materials  213 ′ filled within the heat transfer housing  211 ′ so as to minimize heat loss from the heat transfer agent  201 ′ to the surrounding environment, especially when water pre-heating arrangement is working in a cold environment.  
      When sunlight reaches the glass evacuated tubes  311 ′, the solar energy would be trapped within the glass evacuated tubes  311 ′ in such a manner that it is then transformed into heat energy which raises the temperature of the heat transfer pipe  312 ′. As a result, from simple heat transfer theory, heat energy in the heat transfer pipe  312 ′ would then transferred to the heat transfer agent within the heat exchanging unit  21 ′. The heat transfer agent is then transported to the heater transfer module  242 ′ wherein the water in the water reservoir  24 ′ would be heated up by the heat transfer agent having the elevated temperature.  
      The heat transfer agent is preferably embodied as non-toxic, bio-degradable propylene glycol solution which is capable of transferring heat from the heat transfer pipe  312 ′ to the heater transfer module  242 ′.  
      From the forgoing descriptions, it is anticipated that since the freezing point of the heat transfer agent can be as low as below zero, the present invention would still be effectively utilized in very cold ambient temperature for pre-heating water stored in the water storing unit  241 ′, as long as there is adequate sunlight collectable by the solar energy collecting device  30 ′.  
      Moreover, the heat exchanger  20 ′ may further comprises, as in the first preferred embodiment, an insulating layer surrounding the water storing unit  241 ′ so as to minimize heat loss stored in that water storing unit  241 ′.  
      It is worth to mention that the pre-heating arrangement is preferably used in the geographical area having a temperature of −40° C. or above wherein the cold water is pre-heated in the water reservoir  24 ′ before entering into the water tank  11 ′.  
      As shown in  FIG. 6 , a third embodiment of the water pre-heating arrangement illustrates another alternative mode of the present invention, wherein the water pre-heating arrangement, which is preferably used in the geographical area having a temperature of −5° C. or above, comprises a solar energy collecting device  30 A for collecting solar energy and transforming the solar energy into heat energy and a heat exchanger  20 A connecting with the water source W to guide the water to flow to the water tank  11 A of the water heater  12 A while the water is heated up by the solar energy collecting device  30 A.  
      According to the third embodiment, the heat exchanger  20 A comprises a heat absorbing water passage  221 A communicatively extending from the water source W to the water heater  12 A for guiding the water to flow thereto.  
      The solar energy collecting device  30 A comprises a plurality of heat conversion tubes  31 A spacedly extended from the heat absorbing water passage  221 A for heating the water passing therethrough. Accordingly, the heat conversion tubes  31 A are radially extended from the heat absorbing water passage  221 A for transferring the heat from the heat conversion tubes  31 A to the heat absorbing water passage  221 A so as to heat up the water therealong.  
      As shown in  FIG. 7 , each of the heat conversion tubes  31 A comprises an outer glass evacuated tube  311 A for collecting the solar energy and a heat transfer pipe  312 A having a lower pipe body  3121 A disposed in the glass evacuated tube  311 A and an upper heating end  3122 A extended to the heat absorbing water passage  221 A such that when the pipe body  3121 A is heated up by the glass evacuated tube  311 A, the heat is transferred at the heating end  3122 A to heat up the water when the water flows along the absorbing water passage  221 A. In other words, the heating end  3122 A of each of the heat transfer pipes  312 A is extended into the heat absorbing water passage  221 A by welding such that when the water passes through the heat absorbing water passage  221 A, the water contacts with the heating ends  3122 A of the heat transfer pipes  312 A so as to heat up the water before entering to the water heater  12 A.  
      The heat transfer pipe  312 A, which is preferably embodied as a copper pipe, is a vacuum tube which has a vacuum cavity and contains a heat transfer agent  313 A therein wherein when the heat transfer pipe  312 A is heated up by the glass evacuated tube  311 A, the heat transfer agent  313 A filled in the heat transfer pipe  312 A is vaporized to the heating end  3122 A of the heat transfer pipe  312 A for heating up the water in the heat absorbing water passage  221 A. Once the heat transfer pipe  312 A is cooled down, the heat transfer agent  313 A is liquefied and returned to the bottom of the heat transfer pipe  312 A. Accordingly, the heat transfer agent  313 A is preferably embodied as non-toxic liquid adapted to repeatedly cycling between the vaporized state and the liquefied state.  
      As shown in  FIG. 6 , the heat absorbing water passage  221 A is preferably a copper pipe that the heat from the heat transfer pipes  312 A is adapted to transfer to the water in the heat absorbing water passage  221 A. The heat exchanger  20 A further comprises a heat insulating layer  213 A enclosing the heat absorbing water passage  221 A for minimizing heat loss from the heat absorbing water passage  221 A to the surrounding environment. It is worth to mention that the heat absorbing water passage  221 A embodies as a water reservoir that the water slowly flows along the heat absorbing water passage  221 A to the water heater  12 A, as shown in  FIGS. 8 and 9 . In other words, the water is heated up and temporarily stored in the heat absorbing water passage  221 A such that when the use of water, the water flows from the heat absorbing water passage  221 A to the water heater  12 A. If the water temperature does not reach the preset temperature, the water heater  12 A heats up the water therein while the water can directly flow from the water source W to the water heater  12 A as a backup section.  
      Accordingly, there are 25 heat conversion tubes  31 A radially extended from the heat absorbing water passage  221 A having a length of 1.8 meter, wherein the diameter of each of the heat conversion tubes  31 A is 47 mm and a length of each of the heat conversion tubes  31 A is 1.5 meter. For example, within Los Angeles area, the heat transfer pipe  312 A is adapted to be heated up about 200° C. at the heating end  3122 A thereof wherein when the water flows along the heat absorbing water passage  221  through the heating ends  3122 A of the heat transfer pipes  312 A, the water can be heated up from 10° C. to 18° C. Therefore, the water is pre-heated before entering into the water heater  12 A such that the water heater  12 A requires less energy to heat up the water to a predetermined temperature.  
      One skilled in the art will understand that the embodiment of the present invention as shown in the drawings and described above is exemplary only and not intended to be limiting.  
      It will thus be seen that the objects of the present invention have been fully and effectively accomplished. It embodiments have been shown and described for the purposes of illustrating the functional and structural principles of the present invention and is subject to change without departure form such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims.