JP2009243798A - Heater for water for hot-water supply system, and hot-water supply system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heater for water for a hot-water supply system and the hot-water supply system using the heater for water, for enhancing efficiency of work for removing scale within a water side heat-transfer pipe of the heater for water and simplifying the work. <P>SOLUTION: The heater 3 for water includes the water side heat-transfer pipe 29 wound and formed to have a coil shape and a water outlet header 25 to which a tip of a water outlet part 29E of the water side heat-transfer pipe 29 is connected. The water outlet part 29E of the water side heat-transfer pipe 29 is formed as a straight pipe part 36. In the water outlet header 25, an insertion hole for a cleaning tool is formed on an opposing wall face in a position facing, within the pipe, a wall face to which the straight pipe part 36 of the water side heat-transfer pipe 29 is connected, and a stopper member detachably fitted to the insertion hole for the cleaning tool is provided. The heater 3 for water is suitably used for the hot-water supply system K comprising a heat pump refrigerant circuit 1 and a water channel 2 for hot water supply. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a water heater for a water heater having a structure capable of physically cleaning and removing scale attached to the inner surface of a water-side heat transfer tube, and a water heater using the same.

Conventionally, heat pump type hot water heaters that heat water using atmospheric heat or the like as a heat source of a heat pump refrigerant circuit using condensation heat of the refrigerant or the like are known. The water used for this water heater is tap water or groundwater. In general, tap water, groundwater, and the like contain hardness components such as calcium and magnesium, but depending on the region, they may contain a very large amount of hardness components. Therefore, when water containing a relatively large hardness component is heated to a high temperature for a long time with a water heater of a heat pump type hot water heater, the hardness component is scaled around the vicinity of the water outlet of the water channel that becomes the highest temperature (for example, , Often as calcium carbonate). When such a scale adheres to and accumulates on the heat transfer surface in the water flow path of the water heater, it becomes water flow path resistance and pressure loss increases. In addition, the heat resistance of the heat transfer surface when the refrigerant and water exchange heat, and in order to significantly reduce the heat transfer rate, the operation of circulating the scale remover or increasing the water flow rate (Patent Document 1 below) The scale is washed by passing water under pressure by an operation for increasing the amount of water circulation (Patent Document 2 below). However, the scale once deposited and stuck is very hard, and it is extremely impractical to peel it off simply by passing water under pressure as in the heat pump type water heater described in Patent Documents 1 and 2.

JP 2006-125654 A JP 2005-308235 A

By the way, when water containing hardness components such as calcium and magnesium is heated to a high temperature by a water heater, calcium carbonate dissolved in water is supersaturated and precipitated, and the calcium carbonate is a water heater. It crystallizes and accumulates in the water-side heat transfer tube.

Scale adhesion due to precipitation of calcium carbonate or the like becomes significant when the water temperature exceeds around 80 ° C. However, until now, heat pump water heaters using HFC refrigerants have been remarkably reduced in efficiency when 90 ° C. hot water is used, so the maximum hot water temperature is generally up to 70 ° C. On the other hand, a heat pump water heater using carbon dioxide (hereinafter referred to as CO2) refrigerant that can ensure high efficiency even at high temperature hot water and can hot water at 90 ° C. is likely to precipitate calcium carbonate that causes scale. .

Further, in a conventional heat pump type water heater using an HFC refrigerant, a circulating heating method has been adopted as a temperature raising method because a heat retaining operation is possible and a defrosting time can be shortened. That is, as shown in FIG. 15 (A), since the temperature is gradually raised while circulating water several times between the heat pump type hot water heater K1 and the hot water tank 60, a scale is locally formed in the heat exchanger. It was not easy to adhere. However, the CO2 refrigerant heat pump type hot water heater is not suitable for the circulation type because it cannot efficiently raise the temperature of hot water exceeding 45 ° C. In addition, a one-time heating method is employed with the aim of increasing the heating capacity by using the condensation heat up to the feed water temperature and increasing the COP by reducing the pump power by reducing the flow rate. As shown in FIG. 15 (B), the water at the outlet side of the water heater is supplied to the hot water tank 60 by raising the temperature from the water supply temperature to 90 ° C. at a stretch in the water flow path of the water heater of the water heater K2. Scale easily adheres locally in the side heat transfer tubes.

Therefore, when scale adheres to the water-side heat transfer tube of the water heater of the water heater due to precipitation of calcium carbonate or the like, the piping is clogged or the heat transfer coefficient is reduced, so that the scale needs to be removed.

However, in a conventional method using a scale remover such as an acidic solution, the heat exchanger base material may be corroded depending on the combination of the scale remover or cleaning agent used and the heat exchanger material. There was a problem. In general, neutralization cleaning is used to prevent corrosion caused by acid as a scale remover. However, if the acid is not completely cleaned, corrosion occurs in the base material. To do. Furthermore, since there are many substances using organic acids in the water treatment after the washing treatment, there is a problem that a large drainage treatment is required.
Further, when the scale is accumulated over a long period of time, the scale removal ability is limited only by circulation of the scale remover, and finally physical cleaning with a brush or the like is required.

Also, if the heat transfer length of the heat exchanger is increased, the pressure loss of the water-side heat transfer tube and the refrigerant-side heat transfer tube increases. Therefore, when increasing the heat exchanger in order to increase the hot water supply capacity, there are multiple heat transfer tubes. Divided into paths. However, with regard to removal by pressurized water flow, which is one of the conventional methods, in a heat exchanger branched internally into several passes, when scale is removed in a certain pass, water flows in that pass. Concentration causes a problem that the flow rate is not evenly distributed, and there is a possibility that a path where the scale cannot be removed may occur.

Further, although cleaning with a brush or the like is effective in a straight tubular heat exchanger, there is a problem that it is difficult to clean the bent portion and the subsequent portions in a wound heat exchanger.

The present invention has been made to solve the above-described problems, and improves the efficiency and simplification of work in removing the scale in the water-side heat transfer tube of the water heater without disassembling the water heater and the water heater. It is an object of the present invention to provide a water heater for a water heater that can be converted into a water heater, and a water heater using the same.

The water heater of the present invention is a water heater having a water side heat transfer tube formed by being wound in a coil shape, and a water outlet header to which the tip of the water outlet portion of the water side heat transfer tube is connected. The water outlet part of the water-side heat transfer tube is formed as a straight pipe part, and the cleaning tool is inserted into the opposite wall surface of the water outlet header facing the wall surface where the straight pipe part of the water-side heat transfer pipe is connected. A hole is formed, and a sealing plug member that is detachably attached to the cleaning tool insertion hole is provided. The water heater includes a heat pump refrigerant circuit formed by connecting a compressor, a refrigerant side heat transfer tube, an expansion valve, and a heat source side heat exchanger, and a water pump and a refrigerant in the refrigerant side heat transfer tube. It is suitably applied to a water heater having a hot water supply channel formed by connecting water-side heat transfer tubes of a water heater that performs heat exchange.

A water heater for a water heater according to the present invention includes a water outlet portion of a water side heat transfer tube formed as a straight tube portion, and a wall surface and a pipe connected to the straight tube portion of the water side heat transfer tube in a water outlet header. Since the cleaning tool insertion hole is formed on the opposite wall surface at the facing position, and the sealing tool insertion hole is detachably attached to the cleaning tool insertion hole, the cleaning tool insertion hole is usually sealed with a sealing plug member. Have been used. And when scale deposits on the water outlet part of the water side heat transfer tube with the highest temperature, the water outlet part is formed as a straight pipe part, so without removing the water heater from the water heater body, the sealing plug member It is possible to physically easily remove the scale by inserting a cleaning tool such as a brush into the straight pipe portion from the cleaning tool insertion hole opened by removing the. That is, according to the present invention, even with a coil-wound heat exchanger, the provision of the predetermined straight pipe portion enables physical cleaning of most of the attached scale. Thereby, the efficiency and simplification of the operation | work in scale removal in the water side heat exchanger tube of the heater for water can be achieved.

Embodiment 1 FIG.
FIG. 1 is a circuit configuration diagram of a water heater in Embodiment 1 of the present invention.
In the figure, a water heater K according to the first embodiment includes a heat pump refrigerant circuit 1 and a hot water supply channel 2. In the heat pump refrigerant circuit 1, a compressor 4, a refrigerant side heat transfer tube 30 of a heat transfer tube coil 24 of a water heater 3, an expansion valve 6, a heat source side heat exchanger 7, and a muffler 8 are annularly connected by a refrigerant pipe 9. It is configured. In the heat pump refrigerant circuit 1, carbon dioxide (CO2) is used as a refrigerant. The hot water supply channel 2 includes a water pump 22, a water flow rate adjusting valve 12, and a water side heat transfer tube 29 of a heat transfer tube coil 24 of the water heater 3 connected in series via a water pipe 14. In the water heater 3, heat exchange is performed between the water in the water flow path 13 of the water side heat transfer tube 29 and the refrigerant in the refrigerant flow path 5 of the refrigerant side heat transfer tube 30. Then, outdoor air is blown to the heat source side heat exchanger 7 by a fan 10 driven by a motor 11. This hot water heater K employs a one-time temperature raising method capable of high temperature hot water.

Next, the outer structure of the water heater K is shown in FIGS. The front panel 42, the fingered 43, and the upper panel 44 are disposed in the front part of the base 41, the side panel 45 and the side panel 46 are provided on both sides of the base 41, and the rear panel 49 and the rear upper part are disposed on the back of the base 41. A panel 47 is provided. A fan guard 48 is installed in an upper surface opening surrounded by the upper panel 44, the side panel 45, the side panel 46, and the rear upper panel 47. The heat source side heat exchanger 7 is disposed so as to cross the air passage formed by the side panels 45, 46, the bell mouth 50, and the machine room partition plate 51, and the fan 10 and the heat source side heat exchanger 7 are disposed above the heat source side heat exchanger 7. A motor 11 is arranged. Further, in the machine room partitioned from the outside environment by the machine room partition plate 51, the front panel 42, and the rear panel 49 at the lower part of the casing, there are a compressor 4, a muffler 8, a water heater 3, a water pump 22, a water flow rate. A regulating valve 12, a piping group 52 such as a refrigerant piping regret and water piping, a control box 23, and others are provided.

On the other hand, since the compressor 4, the expansion valve 6, the control box 23, and the water pump 22 are frequently serviced, they are arranged in the front part of the base 41, and work such as repair and replacement is performed on the front panel at the bottom of the unit. 42 is performed. On the other hand, the water heater 3 having a large volume and a relatively low service frequency cannot be disposed at the front portion, and is disposed at the rear portion of the base 41.

Service work such as repair or replacement of the water heater 3 is difficult from the front because the compressor 4, the control box 23, the piping group 52, etc. are obstructed, and the work space from the rear panel 49 is difficult. The work is not possible due to the small size. Moreover, since the side panels 45 and 46 are structural members that support the weight of the fan 10 and other panels, it is difficult to remove them. Moreover, since the heat source side heat exchanger 7 is also arranged in the upper part of the water heater 3, the operation becomes difficult.

And in the machine room of the water heater K, the water heater 3 is arranged so that the cleaning tool insertion hole 37 of the water side heat transfer tube 29 faces the side panel 46 as shown in FIG. And the opening part 38 for implementing the washing | cleaning operation | work of the water heater 3 as shown in FIG.5 and FIG.6 is formed in the side panel 46. FIG. The opening 38 is formed in such a size that all the cleaning tool insertion holes 37, 37, 37, 37, 37 formed in the water outlet header 25 are exposed. The opening 38 is covered with a cover plate 39 so as to be opened and closed.

As shown in FIG. 7, the water heater 3 includes five-path heat transfer tube coils 24, 24, 24, 24, 24 and water-side heat transfer tubes 29 to the heat transfer tube coils 24, 24, 24, 24, 24. , 29, 29, 29, 29, the water inlet header 26 connected to the water inlet side, and the water side heat transfer tubes 29, 29, 29, 29, 29 from the heat transfer tube coils 24, 24, 24, 24, 24. A water outlet header 25 to which the outlet side is connected, and a refrigerant inlet header 27 to which the refrigerant inlet side of the refrigerant side heat transfer tubes 30, 30, 30, 30, 30 to the heat transfer tube coils 24, 24, 24, 24, 24 is connected The refrigerant outlet header 28 is connected to the refrigerant outlet side of the refrigerant side heat transfer tubes 30, 30, 30, 30, 30 from the heat transfer tube coils 24, 24, 24, 24, 24. These heat transfer tube coil 24, water inlet header 26, water outlet header 25, refrigerant inlet header 27, and refrigerant outlet header 28 are connected by brazing or the like. By the way, it is necessary to enlarge the water heater 3 in order to increase the hot water supply capacity. However, when the heat transfer tube length of the water heater 3 is increased, the pressure loss on the water flow path 13 side and the refrigerant flow path 5 side is increased. Therefore, when increasing the hot water supply capacity, the heat transfer tube coils 24 are arranged in parallel in a plurality of paths as shown in FIG. In addition, since this water heater K has the capacity | capacitance equivalent to the maximum capacity | capacitance of 20 horsepower, the heat transfer tube coil 24 (n = 1-5) of 5 paths | paths (5) is mounted. The length of the one-pass heat transfer tube coil 24 is about 10 m.

FIG. 8A shows an example of a cross-sectional view of the heat transfer tube coil 24 of the water heater 3 of FIG. The heat transfer tube coil 24 has a double tube structure in which a water side heat transfer tube 29 is accommodated in a refrigerant side heat transfer tube 30. In this case, heat is exchanged with water in the water flow path 13 by using water and a refrigerant as opposed flows and flowing the refrigerant through the refrigerant flow path 5A around the water-side heat transfer tube 29.

The heat transfer tube coil used in the present invention is not limited to the heat transfer tube coil 24 described above, and may be a heat transfer tube coil 24A as shown in FIG. This heat transfer tube coil 24A has three heat transfer tubes 30A, 30A, 30A (each with an outer diameter of about 4 mmφ) wound around the water side heat transfer tube 29A (with an outer diameter of about 15 mmφ) and fixed by twisting. The heat exchange is performed by making the water in the water flow path 13A and the refrigerant in the refrigerant flow path 5A counter flow. This heat transfer tube coil 24A can reduce the size of the heat exchanger by improving the heat transfer efficiency. On the other hand, the scale tends to accumulate in a recessed portion such as a groove in the water flow path 13, and the heat transfer coil 24A can be washed with pressurized water. There is a drawback that it is difficult.

Then, in this water heater K, as shown in FIG. 7, in the heat transfer tube coil 24 (FIG. 9) which is wound to accommodate the water heater 3 in the machine room, the water outlet to which scale easily adheres. A straight pipe portion 36 having a predetermined length is formed linearly on the portion 29E. Further, as shown in FIG. 10, in the water outlet header 25, the cleaning tool insertion hole 37 is formed on the opposing wall surface 25 </ b> B at a position facing the wall surface 25 </ b> A to which the straight pipe portion 36 of the water-side heat transfer tube 29 is connected. , 37, 37, 37, 37 are formed. In this case, each cleaning tool insertion hole 37 is arranged on the opposing wall surface 25 </ b> B at a position substantially coaxial with the tube axis of each straight pipe portion 36. The cleaning tool insertion hole 37 is formed to have a hole diameter enough to accommodate a cleaning tool such as a brush. The cleaning tool insertion hole 37 is detachably mounted with a sealing member 40 which is sealed with water when the water heater is in operation and opened during cleaning.

As shown in FIGS. 11A and 11B, the sealing member 40 for opening and closing the cleaning tool insertion hole 37 is easily opened and closed by a connection structure using a commercially available quick fastener 55, and water leaks. Used in a highly credible manner. A header side pipe 53 whose pipe end is processed as shown in FIG. 11 is connected to the cleaning tool insertion hole 37 of the water outlet header 25, and the sealing member 40 is attached and water sealed. Watertightness is ensured in the gap between the header side pipe 53 and the sealing plug member 40 by the O-ring 54. And the peripheral flange part 53A provided in the outer peripheral surface of the header side piping 53 over the perimeter, and the peripheral flange part 40A provided in the outer peripheral surface of the sealing plug member 40 over the entire periphery are clamped by the quick fastener 55. Thus, the movement of the sealing plug member 40 in the tube axis direction is regulated so as not to be detached from the header side piping 53.

Fig. 12 shows the water temperature and scale film thickness in water heaters with scales attached using water heaters of water heaters with scales in various parts of Japan sampled for scale film thicknesses in A and B districts. Shows the relationship. As can be seen from the curve in the figure, although there is a slight difference in the tendency, there is a tendency that the adhesion of the scale becomes remarkable from the portion where the water temperature is 80 ° C. or higher. Although there is a difference in the amount of hardness components such as calcium and magnesium depending on the region, a difference occurs in the scale film pressure at the time of melting, but the film thickness is equivalent at 90 ° C. or higher. That is, it can be seen that even if there is a difference in the amount of hardness component, there is no difference in the amount of scale attached at 90 ° C. or higher. It can be said that as the temperature increases, the amount of air that can be dissolved decreases, bubbles are generated, accumulate on the inner surface of the water-side heat transfer tube 29, and the flow rate resistance increases, thereby increasing the scale generation rate.

FIG. 13 shows the relationship between the distance from the water outlet end in the water-side heat transfer tube of the water heater to which the scale is attached and the scale film thickness. As can be seen from the curve in the figure, the portion where the scale easily adheres is 4 to 8% of the entire heat exchanger, and the scale easily adheres in this range. This water heater K is a 20 horsepower class, and the water heater 3 is divided into five-path heat transfer tube coils 24, 24, 24, 24, 24, and the total length of one heat transfer tube coil is about 10 m. . In that case, the length of the water-side heat transfer tube 29 that is easily attached to the scale and needs to be cleaned is about 80 cm. Therefore, a portion (water outlet portion 29E) having a length L that is longer than this length, that is, about 10% of the total length retroactively from the water outlet end portion (that is, a predetermined ratio, in this case, about 1 m) is connected to the straight pipe portion 36. By making the cleaning work easy with a cleaning tool such as a brush, almost all scales can be removed.

Accordingly, the cleaning of the scale inside the water-side heat transfer tube 29 by the hot water heater K will be described. First, the operation of the hot water heater is stopped and the water in the unit is drained from the water inlet of the unit, and then the water heater The cover plate 39 is removed from the nearby side panel 46 to open the working opening 38, then the sealing plug member 40 is removed from the water outlet header 25 to open the cleaning tool insertion hole 37, and the brush is inserted into the cleaning tool insertion hole. 37 to the farthest end of the straight pipe portion 36 of the water-side heat transfer tube 29, and the scale attached to the inner wall of the straight pipe portion 36 is scraped off. The scale remaining in the water-side heat transfer tube 29 without being scraped by the brush is poured by pouring water in the reverse direction with the hose from the cleaning tool insertion hole 37, and the drainage structure at the lowest position of the water supply channel 2 and Drain from the water inlet of the unit. Water injection was stopped when it was confirmed that the scale did not come out from the water inlet of the unit, the cleaning tool insertion hole 37 of the water outlet header 25 was closed with the sealing member 40, and the working opening 38 of the side panel 46 was closed. The cover is stopped by the cover plate 39 and the operation is completed.

The brush used for cleaning radially has a bristle length that easily reaches the bottom of the groove portion of the water flow path 13 on the outer periphery of a rod having a diameter that can easily enter the straight pipe portion 36 of the water-side heat transfer tube 29. A planted one having a length that can reach the entire length of the straight pipe portion 36 provided in the water outlet portion 29E is used. As the bristle material of the brush, fibers made of a material that hardly damages the piping base material are used.

As described above, according to the water heater K of the first embodiment, the water outlet portion 29E of the water-side heat transfer tube 29 is formed as the straight tube portion 36, so that the casing can be disassembled or the water heater 3 It is possible to physically remove the scale of the straight pipe portion 36 by inserting a cleaning tool such as a brush from the cleaning tool insertion hole 37 which is opened by removing the sealing plug member 40 without removing the base 41 from the base 41. it can.

Embodiment 2. FIG.
In Embodiment 1 described above, the cleaning tool insertion hole 37 is provided in the water outlet header 25 in order to physically clean the inside of the straight pipe portion 36 of the water heater 3 with a brush or the like. Is not limited to this.
For example, as shown in FIG. 14, you may employ | adopt the structure which divides | segments easily the water outlet header 25, the heat exchanger tube coil 24 of the heater 3 for water, and the water piping 14 after the water outlet header 25. FIG. For example, the water outlet portion 29 </ b> E of the water side heat transfer tube 29 is formed as the straight tube portion 36, and the water receiving pipe 56 that receives water from the water side heat transfer tube 29 is connected to the water outlet header 25. And the front-end | tip of the water receiving pipe 56 and the front-end | tip of the straight pipe part 36 are connected through the connection means 63 so that removal is possible. In this case, for example, a flange portion 61 provided at the tip of the straight pipe portion 36, a flange portion 62 provided at the tip of the water receiving pipe 56, and bolts and nuts (not shown) that connect these flange portions 61 and 62. Thus, the connecting means 63 is configured. On the other hand, the upper end of the water outlet header 25 and the lower end of the water pipe 14 are detachably connected via a connecting means 66. In this case, for example, a flange portion 64 provided at the upper end of the water outlet header 25, a flange portion 65 provided at the lower end of the water pipe 14, and bolts and nuts (not shown) connecting these flange portions 64 and 65, Thus, the connecting means 66 is configured.

As described above, by adopting a structure in which the removal unit 67 including the water outlet header 25 can be integrally removed, the scale can be removed by washing the inside of the straight pipe portion 36 with a brush or the like.

Embodiment 3 FIG.
In each of the above-described embodiments, the example in which the water heater 3 is disposed in the vicinity of the side panel 46 and the working opening 38 is provided in the side panel 46 has been described. If there is room, the water heater 3 is arranged in the vicinity of the service panel such as the front panel 42, and the cleaning tool insertion hole 37 of the water heater 3 is directed toward the service panel so that a wide working space is obtained. The scale removal work can be performed from the front side of the water heater that can be easily serviced.

  As the refrigerant used in the heat pump refrigerant circuit of the water heater, the carbon dioxide mentioned above is most suitable, but other than that, it is also possible to use a refrigerant that makes the hot water temperature 70 ° C. or higher.

It is a circuit block diagram of the water heater in Embodiment 1 of this invention. It is an external view of the water heater in Embodiment 1 of this invention. It is a disassembled perspective view of the water heater in Embodiment 1 of this invention. It is a top view in the machine room of the water heater in Embodiment 1 of this invention. It is a left view of the water heater in Embodiment 1 of this invention. FIG. 6 is a partially enlarged side view showing a state in which the work opening is opened in FIG. 5. It is a perspective view of the water heater of the water heater in Embodiment 1 of this invention. (A) is sectional drawing of the heat exchanger tube coil of the said water heater, (B) is sectional drawing which shows another example of the said heat exchanger tube coil. (A) is a front view of the heat transfer tube coil, (B) is a plan view of the heat transfer tube coil, and (C) is a side view of the heat transfer tube coil. It is a front view which shows the said heat exchanger tube coil, a water outlet header, a water inlet header, and a sealing plug member. (A) is a partial rear view showing the header side piping, sealing plug member and quick fastener of the water outlet header, and (B) is a perspective view showing the header side piping, sealing plug member and quick fastener of the water outlet header. It is a figure which shows the relationship between the water temperature and the scale film thickness in the water heater of the water heater used in a different area and having a scale attached. It is a figure which shows the relationship between the distance from the water exit end in the water side heat exchanger tube of the water heater to which the scale adhered, and a scale film thickness. It is a front view which shows the connection structure of the heat exchanger tube coil and water outlet header of the water heater in Embodiment 1 of this invention. It is a figure which shows schematic structure figure of a general heat pump water heater and a hot water storage tank, Comprising: (A) is a figure which shows the thing of the circulation-type temperature rising system which circulates hot water, (B) is a transient type which produces | generates hot water from water It is a figure which shows the thing of a temperature rising system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heat pump refrigerant circuit, 2 hot water supply channel, 3 water heater, 4 compressor, 6 expansion valve, 7 heat source side heat exchanger, 22 water pump, 25 water outlet header, 25A wall surface, 25B opposing wall surface, 29, 29A water Side heat transfer pipe, 29E Water outlet, 30, 30A Refrigerant side heat transfer pipe, 36 Straight pipe, 37 Cleaning tool insertion hole, 38 Work opening, 40 Seal plug member, 63 Connection means, 66 Connection means, K Water heater , L Length.

Claims (4)

A water heater having a water-side heat transfer tube formed in a coil shape and a water outlet header to which a tip of a water outlet portion of the water-side heat transfer tube is connected, the water-side heat transfer tube A water outlet portion is formed as a straight pipe portion, and a cleaning tool insertion hole is formed on the opposite wall surface of the water outlet header at a position facing the wall surface to which the straight pipe portion of the water-side heat transfer tube is connected, A water heater for a water heater, comprising a sealing plug member detachably attached to the cleaning tool insertion hole. A water heater having a water-side heat transfer tube formed in a coil shape and a water outlet header to which a tip of a water outlet portion of the water-side heat transfer tube is connected, the water-side heat transfer tube A water heater for a water heater, wherein the water outlet portion is formed as a straight pipe portion, and the water outlet header and the tip of the straight pipe portion are detachably connected via a connecting means. Heating water for heat exchange between a heat pump refrigerant circuit formed by connecting a compressor, a refrigerant side heat transfer tube, an expansion valve, and a heat source side heat exchanger, a water pump, and a refrigerant in the refrigerant side heat transfer tube A water heater having a hot water supply channel formed by connecting water-side heat transfer tubes of a water heater, wherein the water heater is constituted by the water heater according to claim 1 or 2, and the water-side heat transfer tube The water heater is characterized in that the water heater is disposed in the water heater casing such that the front end of the straight pipe portion faces the working opening of the water heater casing. Carbon dioxide is used as the refrigerant, and the length of the straight pipe portion of the water-side heat transfer tube is set to a predetermined ratio to the total length of the water-side heat transfer tube, and water is allowed to flow through the hot water supply channel temporarily. The hot water heater according to claim 3, wherein the hot water generator is configured to generate hot water.

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