JP2018175728A - Hair dryer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hair dryer more suppressing damage of hair.SOLUTION: A hair dryer includes: a blowing part blowing warm air; a hair temperature detection part detecting the temperature of hair heated by the warm air blown from the blowing part; a heating amount calculation part integrating the variation per unit time of the hair temperature detected by the temperature detection part to heating time, and calculating a heating amount applied to the hair by warm air on the basis of the result of the integration; a moisture amount determination part estimating an amount of moisture included in the whole hair on the basis of the heating amount calculated by the heating amount calculation part, and determining whether or not the moisture amount reaches to at least one of preliminarily set moisture amount reference values; and a warm air control part controlling at least one of the temperature or wind speed of the warm air blown from the blowing part on the basis of the result determined by the moisture amount determination part.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a hair dryer having a function of controlling the temperature or wind speed of warm air.

  Conventionally, as a hair dryer of this type, for example, one described in Patent Document 1 is known. In Patent Document 1, the temperature of the hair to which the warm air is applied is detected, and when the detected temperature of the hair reaches a predetermined temperature, control is simultaneously performed to weaken the temperature (heating power) of the warm air and the wind speed. The hair dryer configured is described.

Unexamined-Japanese-Patent No. 7-289347 gazette

  However, the hair dryer of Patent Document 1 still has room for improvement from the viewpoint of further suppressing damage to the hair.

  Accordingly, it is an object of the present invention to solve the above-mentioned problems and to provide a hair dryer capable of further suppressing damage to hair.

In order to achieve the above object, the hair dryer according to the present invention is
A blower for blowing warm air,
A hair temperature detection unit that detects the temperature of hair heated by warm air blown from the blower unit;
The amount of change per unit time of the temperature of the hair detected by the temperature detection unit is integrated with respect to the heating time, and the heating amount for calculating the amount of heating given to the hair by the warm air based on the integration result A calculation unit,
The amount of water contained in the entire hair is estimated based on the amount of heating calculated by the heating amount calculation unit, and it is determined whether the amount of water reaches at least one predetermined water amount reference value set in advance. Water content determination unit,
A warm air control unit that controls at least one of the temperature of the warm air blown by the blower and the wind speed based on the result determined by the water content determination unit;
Are configured to provide.

  According to the hair dryer of the present invention, damage to hair can be further suppressed.

It is a perspective view of a hair dryer concerning an embodiment of the present invention. It is a longitudinal cross-sectional view which shows the internal structure of the hair dryer of FIG. It is a block diagram regarding the control part of the hair dryer of FIG. It is a graph which shows an example of the temperature change of the hair at the time of heating by warm air. It is a graph for demonstrating the principle which integrates the heating amount given to hair. It is a graph which shows the relationship between the amount of heat given to hair, and the moisture content of hair. It is a graph which shows the relationship between the amount of heat given to hair, and the moisture content of hair. It is a graph which shows the relationship between the moisture content of hair, and the temperature of hair.

(Findings that formed the basis of this disclosure)
The present inventors earnestly studied to further reduce hair damage and as a result, they obtained the following new findings.

  When heating the hair with warm air, in the initial stage of heating, the moisture contained in the hair functions to shield the heat and the damage to the hair is suppressed. On the other hand, as the heating of the hair by warm air proceeds, the amount of water contained in the hair decreases. For this reason, the function of shielding heat due to the amount of water contained in the hair is weakened, and the hair is easily damaged. Therefore, the conventional hair dryer is configured to detect the temperature of the hair to which the warm air is applied, and to perform control to simultaneously reduce the temperature of the warm air and the wind speed when the detected temperature of the hair reaches a predetermined temperature. It is done. However, the amount of water contained in the hair is not proportional to the temperature of the hair.

  For example, in the case of hair to which warm air is applied, it is assumed that the water content (water content) contained in the hair is 35% and the temperature of the hair is 30 degrees at the start of heating. Further, at the end of heating, it is assumed that the optimum amount of water contained in the hair is 10%, and the temperature of the hair required to obtain the optimum amount of water is 60 degrees. In this case, when heating is started by the hair dryer, as shown in FIG. 8, the temperature of the hair rises rapidly, and the temperature change of the hair becomes small when it becomes about 50 degrees or more. When the temperature of the hair reaches about 60 degrees, the amount of water continues to decrease while maintaining the temperature nearly constant. More specifically, when the amount of water contained in the hair is 10% to 20%, the temperature of the hair is maintained at about 60 degrees.

  For this reason, in the conventional configuration in which the temperature of the hot air and the wind speed are simultaneously reduced when the temperature of the hair reaches a predetermined temperature (for example, 60 degrees), the amount of water contained in the hair is the optimum amount of water. Before reaching a certain 10%, the temperature of the warm air and the wind speed will be reduced simultaneously. For this reason, the user erroneously recognizes that the drying of the portion of the hair to which the hot air is applied has ended, and changes the portion to which the hot air is applied to another portion of the hair or stops the operation of the hair dryer. In this case, the overall dry condition of the hair may be insufficient, which may cause damage to the hair.

  Also, usually, the user changes the part of the hair to which the warm air is applied in order to dry the whole hair more uniformly. At this time, the temperature of the portion of the hair which has been heated by the warm air and has reached the optimum amount of water decreases while the warm air is not applied. In this state, when warm air is again applied to the portion of the hair, warm air of high temperature and strong wind speed is blown until the temperature of the portion of the hair reaches 60 ° C., and the entire hair is overheated. Can happen. In this case, the hair will be damaged.

  On the other hand, the inventors found that there is a correlation between the amount of water contained in the entire hair and the amount of heat given to the hair. Furthermore, the present inventors calculate the amount of heating based on the temperature of the hair, estimate the amount of water contained in the entire hair based on the amount of heating, and the temperature or wind speed of the warm air according to the amount of water concerned It has been found that controlling hair loss can reduce hair damage. Based on these novel findings, the present inventors arrived at the following invention.

According to the first aspect of the present invention, a blower for blowing warm air,
A hair temperature detection unit that detects the temperature of hair heated by warm air blown from the blower unit;
The amount of change per unit time of the temperature of the hair detected by the temperature detection unit is integrated with respect to the heating time, and the heating amount for calculating the amount of heating given to the hair by the warm air based on the integration result A calculation unit,
The amount of water contained in the entire hair is estimated based on the amount of heating calculated by the heating amount calculation unit, and it is determined whether the amount of water reaches at least one predetermined water amount reference value set in advance. Water content determination unit,
A warm air control unit that controls at least one of the temperature of the warm air blown by the blower and the wind speed based on the result determined by the water content determination unit;
Provide a hair dryer.

According to a second aspect of the invention, it further comprises a length input unit for inputting the hair length,
The water content determination unit corrects the water content estimated based on the heating amount calculated by the heating amount calculation unit according to the length of the hair input by the length input unit, and the correction The hair dryer according to the first aspect is provided that determines whether the amount of water that has been reached has reached at least one preset water amount reference value.

According to the third aspect of the present invention, it further comprises a hair amount input unit for inputting the hair amount of hair;
The water content determination unit corrects the water content estimated based on the heating amount calculated by the heating amount calculation unit according to the hair amount of the hair input by the hair amount input unit, and the correction is performed There is provided the hair dryer according to the first or second aspect, which determines whether the amount of water has reached at least one preset water amount reference value.

According to the fourth aspect of the present invention, it further comprises an environmental temperature detection unit for detecting an environmental temperature around hair.
The water content determination unit corrects the water content estimated based on the heating amount calculated by the heating amount calculation unit according to the environmental temperature detected by the environmental temperature detection unit, and the correction is performed The hair dryer according to any one of the first to third aspects, which determines whether the amount of water has reached at least one preset water amount reference value.

According to a fifth aspect of the present invention, the apparatus further comprises an environmental humidity detector for detecting environmental humidity around the hair,
The water content determination unit corrects the water content estimated based on the heating amount calculated by the heating amount calculation unit according to the environmental humidity detected by the environmental humidity detection unit, and the correction is performed The hair drier according to any one of the first to fourth aspects, which determines whether the amount of water has reached at least one preset water amount reference value.

According to a sixth aspect of the present invention, the apparatus further comprises a heating time detection unit that detects an elapsed time from the start of heating of the hair heated by the warm air,
The water content determination unit corrects the water content estimated based on the heating amount calculated by the heating amount calculation unit according to the elapsed time detected by the heating time detection unit, and the correction is performed The hair dryer according to any one of the first to fifth aspects, which determines whether the amount of water has reached at least one preset water amount reference value.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited by this embodiment.

  Also, in the following, for convenience of explanation, it is assumed that the normal use state is assumed, but the term indicating the direction such as "upper", "lower", "front", "rear", etc. is used, but the use of the hair dryer of the present invention It does not mean to limit the state or the like.

<< Embodiment >>
The entire structure of the hair dryer according to the embodiment of the present invention will be described.

  FIG. 1 is a perspective view of a hair dryer according to an embodiment of the present invention. FIG. 2 is a longitudinal sectional view showing an internal configuration of the hair dryer of FIG.

  As shown in FIG. 1, the hair dryer 1 according to the present embodiment includes a main body 10 and a handle 20.

  As shown in FIG. 2, a blower unit 11 for blowing warm air is provided inside the main body unit 10. The blower unit 11 includes a fan 12, a motor 13 which is an example of a drive source, and a heater 14 which is an example of a heating unit. The fan 12 is rotationally driven by the motor 13 to take in external air into the main body 10 through the suction port 10 a provided at the rear end of the main body 10, and is provided at the front of the main body 10 The air is blown to the outside through the air outlet 10b. The heater 14 heats the air blown from the fan 12 to generate warm air higher than the ambient temperature (for example, room temperature) around the hair. The detailed configuration in the vicinity of the air outlet 10b is the same as that of the conventional hand drier and thus will not be described.

  Further, a room temperature sensor 15, which is an example of an environmental temperature detection unit that detects an environmental temperature around hair, and a humidity, which is an example of an environmental humidity detection unit that detects an environmental humidity around hair, A sensor 16 is provided.

  As shown in FIGS. 1 and 2, an infrared sensor 17, which is an example of a hair temperature sensor for detecting the temperature of hair, is provided at the front of the main body 10. The infrared sensor 17 detects the temperature of the hair by detecting the infrared light emitted from the hair.

  At the upper part of the main body 10, a length input unit 18 for inputting the length of the hair and a hair amount input unit 19 for inputting the hair amount of the hair are provided. The length input unit 18 is configured to be able to input the hair length in three stages of, for example, “short”, “normal”, and “long”. The hair amount input unit 19 is configured to be able to input the hair amount of hair in three stages of, for example, "more", "normal", and "less".

  The handle portion 20 is formed in a substantially cylindrical shape. An upper end portion 20 a of the handle portion 20 is rotatably attached to a rear lower end portion 10 c of the main body portion 10. The power cord 21 is connected to the lower end portion 20 b of the handle portion 20. The power cord 21 is connected to an external power supply to supply power for driving the hair dryer 1.

  On the front side surface of the handle portion 20, a switch 23 which is an example of an input unit is provided. The user can operate the switch 23 to switch on / off the power supply, switch between warm air and cold air, switch air volume, and the like.

  Inside the handle portion 20, a control unit 22 that controls the operation of each unit and each device is provided.

  FIG. 3 is a block diagram of the control unit 22 of the hair dryer 1 according to the present embodiment.

  As shown in FIG. 3, the control unit 22 includes a blower 11, a room temperature sensor 15, a humidity sensor 16, an infrared sensor 17, a length input unit 18, a hair amount input unit 19, and a switch 23. It is electrically connected. The control unit 22 controls the driving of the blower unit 11 based on input information input through the switch 23, detection information of the room temperature sensor 15, the humidity sensor 16, and the infrared sensor 17. The control unit 22 includes a heating time detection unit 24, a heating amount calculation unit 25, a water content determination unit 26, and a hot air control unit 27.

  The heating time detection unit 24 detects an elapsed time from the start of heating of the hair heated by the warm air.

  The heating amount calculation unit 25 integrates the variation per unit time of the temperature of the hair detected by the infrared sensor 17 with respect to the heating time, and based on the result of the integration, the heating amount given to the hair by the warm air Calculate

  FIG. 4 is a graph showing an example of the temperature change of hair when heated (dried) by warm air. As shown in FIG. 4, as the heating time increases, the temperature of the hair gradually increases while largely fluctuating up and down on the basis of room temperature (for example, 25 ° C.). In FIG. 4, the dashed-dotted line has shown the substantially average of the temperature of hair.

  FIG. 5 is a graph for explaining the principle of integrating the amount of heat given to hair. As shown in FIG. 5, the heating amount calculation unit 25 integrates the amount of change of the temperature of the hair per unit time tm with respect to the heating time. That is, the heating amount calculation unit 25 calculates the area of the region (hatched portion in FIG. 5) sandwiched by the temperature change curve of the hair and the straight line indicating room temperature. The area is the amount of heat given to the hair.

  In addition, it is based on room temperature because it can be assumed that the temperature of the hair when not applying hot air (when not heating) is the same as or substantially the same as room temperature (environmental temperature). In the present embodiment, the room temperature is detected by the room temperature sensor 15, but may be detected by the infrared sensor 17. That is, the infrared sensor 17 may be configured to detect the temperature of the hair and to detect the room temperature. Further, the heating amount calculating unit 25 may store in advance a temperature assumed to be room temperature. In this case, the need to provide the room temperature sensor 15 can be eliminated.

  In addition, after the power supply of the hair dryer 1 is once turned off by the user during heating, it may happen that it is turned on again. In this case, for example, if the period during which the power is off is within a preset time, the hair dryer 1 may be regarded as being substantially continuously used, and the heating amount may be integrated.

  The water content determination unit 26 estimates the water content included in the entire hair based on the heating amount calculated by the heating amount calculation unit 25, and the water content reaches at least one preset water content reference value. It is determined whether the

  FIG. 6 is a graph showing the relationship between the amount of heat given to the hair and the amount of water in the hair. As shown in FIG. 6, it is assumed that the water content (water content) contained in the hair at the start of heating is 35%, and the optimum water content contained in the hair at the end of the heating is 10%. In this case, the amount of heat given to the hair increases in proportion to the reduction of the water content of the hair. That is, the amount of heat given to the hair and the amount of water in the hair are in a proportional relationship. Therefore, the water content determination unit 26 can estimate the total water content of the hair based on the heating amount given to the hair. The water content determination unit 26 stores in advance a water content determination formula based on a proportional relationship between the amount of heat applied to the hair and the water content of the hair.

  The water content determination unit 26 determines whether the estimated water content has reached at least one water content reference value set in advance. For example, when the estimated water content is 25% and the water content reference value is 20%, the water content determination unit 26 determines that the estimated water content has not reached the water content reference value. Also, for example, when the estimated water content is 15% and the water content reference value is 20%, the water content determination unit 26 determines that the estimated water content has reached the water content reference value. .

  The warm air control unit 27 controls at least one of the temperature and the wind speed of the warm air blown by the blower unit 11 based on the result determined by the water content determination unit 26. That is, the warm air control unit 27 controls the driving of the fan 12, the motor 13, and the heater 14 based on the result determined by the water content determination unit 26. For example, when the result determined by the water content determination unit 26 does not reach the water content reference value, the warm air control unit 27 controls the blower unit 11 to maintain the temperature and the wind speed of the warm air. Also, for example, when the result determined by the water content determination unit 26 reaches the water content reference value, the warm air control unit 27 controls the blower unit 11 so as to weaken at least one of the temperature of warm air and the wind speed. Do. As a result, when the amount of water contained in the entire hair is small, at least one of the temperature of the warm air and the wind speed is weakened, and thus the damage to the hair can be further suppressed.

  The hair dryer 1 according to the present embodiment calculates the amount of heating based on the temperature of the hair, estimates the amount of water contained in the entire hair based on the amount of heating, and the temperature of the warm air according to the amount of water And at least one of the wind speed is controlled. Thereby, damage to hair can be further suppressed.

  In addition, the hair dryer of patent document 1 is comprised so that the temperature and the wind speed of warm air may be weakened, when the temperature of the part to which warm air is applied reaches predetermined | prescribed temperature. For this reason, the user needs to change the part to which the warm air is applied to another part whenever the temperature and the wind speed of the warm air are weakened. That is, while the entire hair is heated by the warm air, the temperature of the warm air and the strength of the wind speed are frequently switched. Also, as described above, the amount of water contained in the hair is not proportional to the temperature of the hair. For this reason, it may happen that the temperature and the wind speed of the warm air are weakened despite the insufficient drying state of the hair. In this case, the comfort of the user is lost.

  On the other hand, according to the hair dryer 1 according to the present embodiment, at least one of the temperature of the warm air and the wind speed is controlled based on the amount of water contained in the entire hair, not a part of the hair. It is done. According to this configuration, for example, when the amount of water contained in the entire hair approaches the optimum amount of water, at least one of the temperature of the warm air and the wind speed is automatically reduced, and the amount of water contained in the entire hair is When the optimum amount of water is reached, the hot air can be stopped. At this time, the user only needs to consciously use so that the warm air is evenly applied to the entire hair, and the air flow of the warm air is automatically stopped, whereby the amount of water contained in the entire hair is increased. It can be known that the optimum amount of water has been reached. In addition, since at least one of the temperature and the wind speed of the warm air is controlled based on the amount of water contained in the entire hair, it is possible to suppress that the temperature and the wind speed of the warm air are weakened when the dry condition of the hair is insufficient. Can. Therefore, the comfort of the user can be improved.

  Next, the case where the hair length is input to the length input unit 18 will be described.

  If the hair lengths are different, the amount of heating required to achieve an optimal moisture content for the entire hair also varies. For example, if the length of the hair is long, the amount of heating required to make the total amount of water in the hair optimal will be more than if the length of the hair is short or normal. For this reason, the amount of heat given to the hair and the amount of moisture of the hair have a relationship as shown in FIG. 7 according to the length of the hair. In FIG. 7, the dashed-dotted line shows the relationship between the amount of heating given to the hair and the amount of moisture in the hair when the length of the hair is long. The solid line shows the relationship between the amount of heat given to the hair and the amount of moisture in the hair when the length of the hair is normal. Moreover, the dashed-two dotted line has shown the relationship of the heating amount and the moisture content of hair which were given to hair in the case where the length of hair is short.

  Therefore, the water content determination unit 26 corrects the water content estimated based on the heating amount calculated by the heating amount calculation unit 25 according to the length of the hair input by the length input unit 18; It is preferable to determine whether the corrected water content has reached the water content reference value. Thus, the amount of water contained in the entire hair can be more appropriately determined in consideration of the length of the hair, and at least one of the temperature of the warm air and the wind speed is controlled based on the determination result. , Can further reduce hair damage.

  Next, the case where the hair amount of the hair is input to the hair amount input unit 19 will be described.

  As in the case of the different lengths of hair described above, when the amount of hair of the hair is different, the amount of heating required to make the total amount of moisture in the hair different is also different. For example, if the hair has a large amount of hair, the amount of heating required to make the total amount of moisture in the hair optimal will be less than normal or more than a small amount of hair. Therefore, the amount of heat given to the hair and the amount of moisture of the hair have the same relationship as that shown in FIG. 7 according to the amount of hair of the hair.

  In this case, the water content determination unit 26 corrects the water content estimated based on the heating amount calculated by the heating amount calculation unit 25 in accordance with the hair amount of the hair input by the hair amount input unit 19 It is preferable to determine whether the corrected water content has reached the water content reference value. Thereby, the amount of water contained in the entire hair can be determined more appropriately in consideration of the amount of hair of the hair, and by controlling at least one of the temperature of the warm air and the speed of the wind based on the determination result, Damage to the hair can be further suppressed.

  Also, depending on the user, the hair dryer 1 may be used to completely dry the hair on one side and then to dry the hair on the other side. In such a case, while heating the hair on one side, the hair on the other side is naturally dried under the influence of the ambient temperature (room temperature) or the environmental humidity, and the total moisture of the hair is optimized. The amount of heating required for the

  For this reason, the water content determination unit 26 corrects the water content estimated based on the heating amount calculated by the heating amount calculation unit 25 according to the room temperature detected by the room temperature sensor 15, and the corrected water It is preferable to determine whether the amount has reached the water content reference value. Thus, the amount of water contained in the entire hair can be more appropriately determined in consideration of the room temperature, and at least one of the temperature of the warm air and the wind speed is controlled based on the determination result. Damage can be further suppressed.

  Further, the water content determination unit 26 corrects the water content estimated based on the heating amount calculated by the heating amount calculation unit 25 in accordance with the humidity detected by the humidity sensor 16, and the corrected water amount It is preferable to determine whether the water content has reached the water content reference value. Thus, the amount of water contained in the entire hair can be determined more appropriately in consideration of the humidity, and at least one of the temperature of the warm air and the wind speed is controlled based on the determination result. Damage can be further suppressed.

  Further, the water content determination unit 26 corrects the water content estimated based on the heating amount calculated by the heating amount calculation unit 25 in accordance with the elapsed time detected by the heating time detection unit 24, and the correction is performed. It is preferable to determine whether the amount of water has reached the water amount reference value. Thus, the amount of water contained in the entire hair can be more appropriately determined in consideration of the elapsed time from the start of heating, and at least one of the temperature of warm air and the speed of wind is controlled based on the determination result. Thus, the damage to the hair can be further suppressed.

  In addition, the effect which each has can be exhibited by combining suitably the arbitrary embodiment of the said various embodiment.

  While the invention has been fully described in connection with the preferred embodiments with reference to the accompanying drawings, various changes and modifications will be apparent to those skilled in the art. Such variations and modifications are to be understood as included within the scope of the present invention as long as they do not depart from the scope of the present invention according to the appended claims.

  The present invention is useful for professional and household hair dryers, because it can further reduce hair damage.

DESCRIPTION OF SYMBOLS 1 Hair-dryer 10 Body part 10a Suction port 10b Air vent 10c Rear lower end part 11 Fan part 12 Fan 13 Motor 14 Heater 15 Room temperature sensor 16 Humidity sensor 17 Infrared sensor 18 Length input part 19 Hair quantity input part 20 Handle part 20a upper end 20b lower end portion 21 power supply cord 22 control unit 23 switch 24 heating time detection unit 25 heating amount calculation unit 26 water content determination unit 27 hot air control unit

Claims (6)

A blower for blowing warm air,
A hair temperature detection unit that detects the temperature of hair heated by warm air blown from the blower unit;
The amount of change per unit time of the temperature of the hair detected by the hair temperature detection unit is integrated with the heating time, and the heating amount given to the hair by the warm air is calculated based on the result of the integration. A quantity calculation unit,
The amount of water contained in the entire hair is estimated based on the amount of heating calculated by the heating amount calculation unit, and it is determined whether the amount of water reaches at least one predetermined water amount reference value set in advance. Water content determination unit,
A warm air control unit that controls at least one of the temperature of the warm air blown by the blower and the wind speed based on the result determined by the water content determination unit;
, Hair dryer. It further comprises a length input unit for inputting the hair length,
The water content determination unit corrects the water content estimated based on the heating amount calculated by the heating amount calculation unit according to the length of the hair input by the length input unit, and the correction The hair dryer according to claim 1, wherein it is determined whether the amount of water that has been reached has reached at least one preset water amount reference value. It further comprises a hair amount input unit for inputting hair amount of hair,
The water content determination unit corrects the water content estimated based on the heating amount calculated by the heating amount calculation unit according to the hair amount of the hair input by the hair amount input unit, and the correction is performed The hair dryer according to claim 1 or 2, wherein it is determined whether the amount of moisture has reached at least one preset moisture amount reference value. It further comprises an environmental temperature detection unit that detects the environmental temperature around the hair,
The water content determination unit corrects the water content estimated based on the heating amount calculated by the heating amount calculation unit according to the environmental temperature detected by the environmental temperature detection unit, and the correction is performed The hair dryer according to any one of claims 1 to 3, wherein it is determined whether the amount of moisture has reached at least one preset amount of moisture reference value. It further comprises an environmental humidity detector that detects the environmental humidity around the hair,
The water content determination unit corrects the water content estimated based on the heating amount calculated by the heating amount calculation unit according to the environmental humidity detected by the environmental humidity detection unit, and the correction is performed The hair dryer according to any one of claims 1 to 4, wherein it is determined whether the amount of water has reached at least one predetermined water amount reference value. The heating apparatus further comprises a heating time detection unit that detects an elapsed time from the start of heating of the hair heated by the warm air.
The water content determination unit corrects the water content estimated based on the heating amount calculated by the heating amount calculation unit according to the elapsed time detected by the heating time detection unit, and the correction is performed The hair dryer according to any one of claims 1 to 5, wherein it is determined whether the amount of water has reached at least one predetermined water amount reference value.

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