EP2857761A1

EP2857761A1 - Water heater

Info

Publication number: EP2857761A1
Application number: EP14162197.9A
Authority: EP
Inventors: Nobuki Sato; Yuuji Tarumi; Tomoyoshi Oobayashi; Yoshio Yamano; Katsunori Horiuchi
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2013-10-03
Filing date: 2014-03-28
Publication date: 2015-04-08
Anticipated expiration: 2034-03-28
Also published as: EP2857761B1; JP6304996B2; JP2015072102A

Abstract

[Object] To obtain a water heater that is capable of delivering hot water at a higher temperature, while suppressing an increase in the condensing pressure of a refrigerant.

[Solution] A refrigerant circuit includes a compressor 2 that compresses a refrigerant, the capacity of the compressor 2 being variable; a refrigerant/water heat exchanger 12 that exchanges heat between the refrigerant and water; a decompression device 4 that decompresses the refrigerant by opening degree adjustment; and an evaporator 5 that evaporates the refrigerant by heat exchange, and the compressor 2, the refrigerant/water heat exchanger 12, the decompression device 4, and the evaporator 5 are connected by pipes. A refrigerant circuit further includes a water supply pump 7 that forms a flow of water passing through the refrigerant/water heat exchanger 12, the water flow rate of the water supply pump 7 being variable; water inlet temperature detection means 8 for detecting a water inlet temperature of the water flowing into the refrigerant/water heat exchanger 12; water outlet temperature detection means 10 for detecting the water outlet temperature of the water flowing out of the refrigerant/water heat exchanger 12; and a controller 15 that performs fixed control for the capacity of the compressor 2 when the water inlet temperature is determined to have reached a preset first temperature, and that performs variable control for the water flow rate of the water supply pump 7 so that the water outlet temperature is made equal to a second temperature, are provided.

Description

[Technical Field]

The present invention relates to a water heater that heats fluid using a heat pump.

[Background Art]

As a conventional water heater, a water heater including a heat pump apparatus that heats fluid such as water (hereinafter, water will be described as a typical fluid) which circulates in a water circuit or the like using a heat pump (refrigeration cycle) as a heat source of the water heater is known.
In such water heaters, there are ones which include, for example, a capacity control unit that controls the capacity of a compressor so that the capacity is variable, and a flow rate control unit that controls the flow rate of water flowing in the water circuit by driving of a water supply pump (hereinafter, will be referred to as the water flow rate of a water supply pump) so that the flow rate is variable (see, for example, Patent Literature 1). Thus, for example, when the water temperature of the water inlet side of a device which exchanges heat between the refrigerant and water, that is, a refrigerant/water heat exchanger, is at or below a specific temperature, the flow rate control unit causes the water flow rate of the water supply pump to be fixed, and the capacity control unit controls the capacity of the compressor so that the capacity is variable. Meanwhile, when the water temperature of the water inlet side of the refrigerant/water heat exchanger is above the specific temperature, the capacity control unit causes the capacity of the compressor to be fixed, and the flow control unit controls the flow rate of the pump so that the flow rate is variable.

[Citation List]

[Patent Literature]

[Patent Literature 1] Japanese Unexamined Patent Application Publication No. 2002-228276 (Fig. 1)

[Summary of Invention]

[Technical Problem]

However, with the above-mentioned heat pump apparatus of the water heater such as of Patent Literature 1, the saturation temperature obtained at the same saturation pressure (condensing pressure) differs depending on the refrigerant used in the heat pump. Therefore, in the case of a refrigerant where the saturation pressure needs to be increased in order to obtain a specific saturation temperature, there were some cases where changes in refrigerant pipe(s) or the like took place.
An example will be given for the case of killing Legionella bacteria. In order to suppress the growth of Legionella bacteria in a hot water storage tank, the hot water delivery temperature needs to be kept at 65 degrees Celsius. That is, because sterilizing effect from heat cannot be expected when the water temperature is below 55 degrees Celsius. Here, with the water heater, when comparing the case where R407C is used as a refrigerant and the case where R410A is used as a refrigerant for the heat pump apparatus in order to ensure the hot water delivery temperature, for example, at 65 degrees Celsius, R410A has a higher condensing pressure.
With the above-mentioned water heater of Patent Literature 1, fixed control for either one of the capacity of the compressor and the flow rate of the pump is performed based on the water temperature of the water inlet side of the refrigerant/water heat exchanger. Therefore, the water temperature of the water inlet side of the refrigerant/water heat exchanger and the water temperature of the water outlet side of the refrigerant/water heat exchanger are not controlled simultaneously (controlled in conjunction with each other). Thus, it has been unable to control an increase in the condensing pressure of the refrigerant.
The present invention has been made in order to solve the above-mentioned problems. An object of the present invention is to obtain a water heater which can deliver hot water at a higher temperature, while suppressing an increase in the condensing pressure of a refrigerant.

[Solution to Problem]

A water heater according to the present invention including a refrigerant circuit including a compressor that compresses a refrigerant, a capacity of the compressor being variable, a refrigerant/water heat exchanger that exchanges heat between the refrigerant and water, a decompression device that decompresses the refrigerant by opening degree adjustment, and an evaporator that evaporates the refrigerant by heat exchange, the compressor, the refrigerant/water heat exchanger, the decompression device, and the evaporator being connected by pipes, includes a water supply pump that forms a flow of water passing through the refrigerant/water heat exchanger, a water flow rate of the water supply pump being variable; water inlet temperature detection means for detecting a water inlet temperature of the water flowing into the refrigerant/water heat exchanger; water outlet temperature detection means for detecting a water outlet temperature of the water flowing out of the refrigerant/water heat exchanger; and a controller that performs fixed control for the capacity of the compressor when the water inlet temperature is determined to have reached a preset first temperature, and that performs variable control for the water flow rate of the water supply pump so that the water outlet temperature is made equal to a preset second temperature.

[Advantageous Effects of Invention]

According to a water heater of the present invention, for example, for a change in local hot water supply load, it is possible to heat water up to a higher hot water delivery temperature and maintain the higher hot water delivery temperature without changing the condensing pressure of a refrigerant,.

[Brief Description of Drawings]

[Fig. 1] Fig. 1 is a diagram illustrating a configuration of a hot water storage system which includes a heat pump apparatus according to Embodiment of the present invention.
[Fig. 2] Fig. 2 is a diagram illustrating a configuration of devices of a control system according to Embodiment of the present invention.
[Fig. 3] Fig. 3 includes schematic diagrams illustrating the relationship between the water temperature, the capacity of a compressor, and the capacity of a water supply pump when the hot water usage load from a hot water storage tank is decreased.
[Fig. 4] Fig. 4 is a T/s chart illustrating a temperature change in a refrigerant and water flowing through a refrigerant/water heat exchanger according to Embodiment of the present invention.
[Fig. 5] Fig. 5 is a flowchart illustrating a processing procedure by a controller 15 according to Embodiment of the present invention.

[Description of Embodiments]

Embodiment.

In Embodiment, a water heater including a hot water storage tank will be described as a water heater according to an aspect of the present invention. Here, including Fig. 1, in the illustrations which will be explained below, the same reference signs are intended to refer to the same or corresponding components, and are assumed to be common throughout the full text of Embodiment described below. Furthermore, the form of components represented throughout the description is merely an example. Therefore, the form of the components is not limited to that mentioned in the description. Moreover, the relationship between the sizes of the components in the illustrations may differ from the actual relationship. In addition, regarding the degree or the like of temperature, pressure, or the like, for example, how high or low is not particularly determined in relation to an absolute value, but is determined relative to a state, operation, or the like, of an apparatus or the like.
Fig. 1 is a diagram illustrating a configuration of a hot water storage system which includes a heat pump apparatus according to Embodiment of the present invention. In Fig. 1, the flow direction of a refrigerant is illustrated by solid arrows, and the flow direction of water is illustrated by dashed arrows. As illustrated in Fig. 1, the hot water storage system of Embodiment includes a heat pump apparatus 1 and a water circuit 6. Furthermore, heat is transferred via a refrigerant/water heat exchanger 12 which is of a plate type, a double pipe type, or the like, between the heat pump apparatus 1 and the water circuit 6. Here, the refrigerant/water heat exchanger 12 of Embodiment is a convection heat exchanger, which enables the flow direction of the refrigerant and the flow direction of the water to be opposite to achieve convection.
The heat pump apparatus 1 includes a heat pump circuit through which the refrigerant circulates (refrigerant circuit), which includes a compressor 2, a condenser 3, a decompression device 4, and an evaporator 5 that are connected by pipes. Furthermore, the heat pump apparatus 1 serves as a heat source to heat the water that flows through the water circuit 6, by heat exchange, by allowing the condenser 3 to cause the refrigerant to reject heat.
The compressor 2 sucks, compresses, and discharges the refrigerant. Under the control of capacity control means 13 which will be described later, for example, by changing the driving frequency in a desired manner, the capacity (feed rate per unit time) may be changed. The refrigerant side flow passage of the refrigerant/water heat exchanger 12 serves as the condenser (radiator) 3. The condenser 3 causes the refrigerant to reject heat, and heats the water that flows through a water heat exchanger 9 which serves as a water side flow passage of the refrigerant/water heat exchanger 12. For example, the decompression device 4 which includes an expansion valve or the like, decompresses the refrigerant that flows through the refrigerant circuit. The evaporator (cooler) 5, for example, exchanges heat between the air and the refrigerant to evaporate the refrigerant.
The water circuit 6 includes a water supply pump 7, the water heat exchanger 9, and a hot water storage tank 11. The water supply pump 7 pressurizes and circulates the water within the water circuit 6. Under the control of water flow rate control means 14 which will be described later, for example, by changing the driving frequency in a desired manner, the flow rate of the water that flows through the water circuit 6 may be changed. Furthermore, the water side flow passage of the refrigerant/water heat exchanger 12 serves as the water heat exchanger 9. The water heat exchanger 9 exchanges heat between the refrigerant that flows through the condenser 3 and the water. By exchanging heat, the water heats up, and the refrigerant cools down. The hot water storage tank 11 stores water (hot water) that has been heated. Moreover, water inlet temperature detection means 8 and water outlet temperature detection means 10, which are temperature sensors that detect the temperature of the water (water temperature) which flows in and out of the water heat exchanger 9, are attached to the water circuit 6.
Here, operation of each component unit of the water heater will be explained. Firstly, operation and the like of each component unit of the heat pump apparatus 1 side will be explained, based on the flow of the refrigerant that circulates through the refrigerant circuit. The compressor 2 compresses the sucked refrigerant into a high-temperature, high-pressure vapor state, and discharges the refrigerant. The discharged refrigerant flows into the condenser 3. Within the condenser 3, the refrigerant is condensed and liquefied by heat exchange of the water flowing through the water heat exchanger 9 (water circuit 6). The condensed and liquefied refrigerant passes through the decompression device 4. The decompression device 4 decompresses the condensed and liquefied refrigerant. The decompressed refrigerant flows into the evaporator 5. The evaporator 5 evaporates and gasifies the refrigerant by heat exchange with, for example, the outdoor air (outside air). The compressor 2 sucks the evaporated and gasified refrigerant.
Next, operation and the like of each component unit of the water circuit 6 side will be explained, based on the flow of the water. The water supply pump 7 is driven, and a water flow is generated within the water circuit 6. The water stored in the hot water storage tank 11 flows into the water heat exchanger 9. The water that has flowed into the water heat exchanger 9 is heated by heat exchange with the refrigerant that passes through the condenser 3 of the heat pump apparatus 1. The heated water flows out of the water heat exchanger 9 and returns to the hot water storage tank 11.
Fig. 2 is a diagram illustrating a configuration of devices of a control system according to Embodiment of the present invention. The capacity control means 13 includes, for example, an inverter circuit or the like, and adjusts the capacity (driving frequency) of the compressor 2. The water flow rate control means 14 includes, for example, an inverter circuit or the like, adjusts the driving rotation speed (driving frequency) of the water supply pump 7, and adjusts the water flow rate of the water supply pump 7.
Furthermore, in Embodiment, a controller 15 which controls the entire water heater is provided. A signal which contains information on the water inlet temperature detected by the water inlet temperature detection means 8 is input to the controller 15 of Embodiment. Meanwhile, a signal which contains information on the water outlet temperature detected by the water outlet temperature detection means 10 is also input to the controller 15. Then, an instruction signal regarding the capacity of the compressor 2 is sent to the capacity control means 13. Furthermore, an instruction signal regarding the water flow rate (driving rotation speed) of the water supply pump 7 is sent to the water flow rate control means 14.
When determining that the water inlet temperature according to the detection by the water inlet temperature detection means 8 is below a preset first temperature (for example, 55 degrees Celsius), the controller 15 sends to the capacity control means 13 an instruction signal to perform variable control for the capacity of the compressor 2. Furthermore, the controller 15 performs fixed control for the water flow rate of the water supply pump 7, sends to the water flow rate control means 14 an instruction signal to maintain the flow rate of the water that circulates through the water circuit 6, and controls the water outlet temperature according to the detection by the water outlet temperature detection means 10 to be at a specific temperature (for example, 60 degrees Celsius).
In the case where it is determined that the water inlet temperature according to the detection by the water inlet temperature detection means 8 has reached the first temperature (for example, 55 degrees Celsius), a signal of an instruction to perform fixed control for the capacity of the compressor 2 is sent to the capacity control means 13. Furthermore, by sending to the water flow rate control means 14 an instruction signal to perform variable control for the water flow rate of the water supply pump 7, the water outlet temperature according to the detection by the water outlet temperature detection means 10 is controlled to be at a second temperature (for example, 65 degrees Celsius).
Furthermore, when determining that the temperature according to the detection by the water inlet temperature detection means 8 has exceeded a preset third temperature (for example, 57 degrees Celsius), the controller 15 sends to the capacity control means 13 an instruction to perform variable control for the capacity of the compressor 2, performs control to lower the condensing temperature, and controls the water inlet temperature according to the detection by the water inlet temperature detection means 8 to be at the first temperature (for example, 55 degrees Celsius). Meanwhile, the controller 15 sends to the water flow rate control means 14 an instruction to perform variable control for the water flow rate of the water supply pump 7, and controls the water outlet temperature according to the detection by the water outlet temperature detection means 10 to be at the second temperature (for example, 65 degrees Celsius) by causing the compressor 2 and the water supply pump 7 to perform the control in conjunction with each other. Now, it is preferable that the third temperature is the same as the first temperature, however here, in consideration of the stability of the control, a temperature error, and the like, the third temperature is set to a temperature slightly higher than the first temperature.
Fig. 3 includes schematic diagrams illustrating the relationship between the water temperature, the capacity of the compressor, and the capacity of the water supply pump when the hot water usage load from the hot water storage tank is decreased. Here, Fig. 3(a) is a diagram illustrating the relationship in the water heater according to Embodiment. Fig. 3(b) is a diagram illustrating the relationship in a conventional water heater.
For example, as in the conventional water heater such as in Fig. 3(b), in the case where the control of the compressor 2 and the control of the water supply pump 7 are performed separately (not performed in conjunction with each other), firstly, in order to maintain the water outlet temperature at a specific temperature, the capacity of the compressor 2 is decreased. Then, in the case where the hot water usage load decreases and the capacity of the compressor 2 reaches a minimum level, control is performed to maintain the water outlet temperature at a specific temperature by making the water supply pump 7 increase its flow rate.
However, during this time, the water inlet temperature will rise. Furthermore, as the water inlet temperature further rises, the temperature difference between the temperature of the refrigerant passing through the condenser 3 and the water inlet temperature becomes smaller, and the condensing temperature rises while the condensing pressure increases.
Therefore, in the water heater according to Embodiment, by controlling to decrease the capacity of the compressor 2 so that the water inlet temperature is made equal to the first temperature, in conjunction with controlling to decrease the flow rate of the water supply pump 7 so that the water outlet temperature is made equal to the second temperature, while suppressing the rise in the condensing temperature, both the water outlet temperature and the water inlet temperature are maintained at a desired temperature, and the pressure increase of the refrigerant passing through the condenser 3 is suppressed.
Fig. 4 is a T/s chart illustrating the temperature change of the refrigerant and the water flowing through the refrigerant/water heat exchanger according to Embodiment of the present invention. The controller 15 sends to the capacity control means 13 an instruction signal to fix the capacity of the compressor 2 when the water inlet temperature according to the detection by the water inlet temperature detection means 8 has reached the first temperature (for example, 55 degrees Celsius). Furthermore, the controller 15 sends to the water flow rate control means 14 an instruction signal to decrease the water flow rate of the water supply pump 7, and decreases the water flow rate. By increasing the length of the time for the heat exchange and by performing heat exchange of the water that passes through the water heat exchanger 9 up to the superheated vapor region of the refrigerant, the controller 15 makes the water outlet temperature according to the detection by the water outlet temperature detection means 10 rise to the second temperature (for example, 65 degrees Celsius) without raising the condensing temperature of the refrigerant in the condenser 3.
Fig. 5 is a flowchart illustrating a processing procedure by the controller 15 according to Embodiment of the present invention. The operation of the water heater according to Embodiment will be explained with reference to Fig. 5. Firstly, in step S1, the operation of the water heater starts by driving the compressor 2 and the water supply pump 7 (step S1). In step S2, an instruction signal is sent to the water flow rate control means 14, and based on a preset water flow rate, a fixed control is performed for the water flow rate of the water supply pump 7 (step S2). At this time, the flow rate of the water flowing through the water circuit 6 (the flow rate of the water which flows in and out of the water heat exchanger 9) is also fixed. In step S3, an instruction signal is sent to the capacity control means 13, and variable control is performed for the capacity (driving) of the compressor 2 so that the water outlet temperature according to the detection by the water outlet temperature detection means 10 is fixed at a specific temperature (for example, 60 degrees Celsius)(step S3).
Next, in step S4, it is determined whether the water inlet temperature according to the detection by the water inlet temperature detection means 8 is below the first temperature (for example, 55 degrees Celsius) or not (step S4). When the temperature is determined to be below the first temperature, the procedure returns to step S3, and similar control processing continues until the water inlet temperature is determined to be at or above the first temperature.
Meanwhile, in step S4, when the water inlet temperature according to the detection by the water inlet temperature detection means 8 is determined to be at or above the first temperature, in step S5, an instruction signal is sent to the capacity control means 13 to perform fixed control for the capacity of the compressor 2 (step S5). Furthermore, in step S6, the flow rate of water flowing through the water circuit 6 is controlled by sending an instruction signal to the water flow rate control means 14 to perform variable control for the water flow rate of the water supply pump 7, so that the water outlet temperature according to the detection by the water outlet temperature detection means 10 is fixed at the second temperature (for example, 65 degrees Celsius).
While variable control is being performed for the flow rate of the water supply pump 7 in step S6, in step S7, it is determined whether the water inlet temperature detected by the water inlet temperature detection means 8 has exceeded the third temperature (for example, 57 degrees Celsius) or not (step S7). When the temperature is determined not to have exceeded the third temperature, the procedure returns to step S6, and variable control is performed for the water flow rate of the water supply pump 7, so that the water outlet temperature is fixed at the second temperature.
An example will be given for a case where it is assumed that the hot water usage load decreases, and the temperature of the water (hot water) stored within the hot water storage tank 11 rises. When the temperature is determined to have exceeded the third temperature, in step S8, an instruction signal is sent to the capacity control means 13, to perform variable control for the capacity of the compressor 2 so that the water inlet temperature according to the detection by the water inlet temperature detection means 8 is fixed at the first temperature (for example, 55 degrees Celsius) (step S8). At this time, variable control is continuously performed for the water supply pump 7, so that the water outlet temperature according to the detection by the water outlet temperature detection means 10 is fixed at the second temperature (for example, 65 degrees Celsius).
Next, in step S9, it is determined whether the water inlet temperature according to the detection by the water inlet temperature detection means 8 is below the first temperature (for example, 55 degrees Celsius) or not (step S9). When the temperature is determined not to be below the first temperature, the procedure returns to step S6, and similar control processing continues until the temperature is determined to be below the first temperature.
Meanwhile in step S9, when the water inlet temperature according to the detection by the water inlet temperature detection means 8 is determined to be below the first temperature, the procedure returns to step S4, a signal of an instruction to perform fixed control for the capacity of the compressor 2 is sent to the capacity control means 13, and the control processing continues.
As described above, according to the water heater of Embodiment, by controlling the flow rate of the water supply pump 7, it is possible to raise the temperature of the water flowing out of the water heat exchanger 9, close to the superheated vapor temperature of the refrigerant flowing into the condenser 3. At this time, by controlling the compressor 2 in conjunction with the water supply pump 7, such as lowering the condensing temperature detected by performing variable control for the compressor 2, when the water inlet temperature rises, it is possible to control both the temperature of the water flowing into and the temperature of the water flowing out of the water heat exchanger 9.

[Reference Signs List]

1: heat pump apparatus, 2: compressor, 3: condenser, 4: decompression device, 5: evaporator, 6: water circuit, 7: water supply pump, 8: water inlet temperature detection means, 9: water heat exchanger, 10: water outlet temperature detection means, 11: hot water storage tank, 12: refrigerant/water heat exchanger, 13: capacity control means, 14: water flow rate control means, 15: controller

Claims

A water heater including a refrigerant circuit including a compressor (2) that compresses a refrigerant, a capacity of the compressor (2) being variable, a refrigerant/water heat exchanger (12) that exchanges heat between the refrigerant and water, a decompression device (4) that decompresses the refrigerant by opening degree adjustment, and an evaporator (5) that evaporates the refrigerant by heat exchange, the compressor (2), the refrigerant/water heat exchanger (12), the decompression device (4), and the evaporator (5) being connected by pipes, the water heater comprising:
a water supply pump (7) configured to form a flow of water passing through the refrigerant/water heat exchanger (12), a water flow rate of the water supply pump (7) being variable;

water inlet temperature detection means (8) for detecting a water inlet temperature of the water flowing into the refrigerant/water heat exchanger (12);

water outlet temperature detection means (10) for detecting a water outlet temperature of the water flowing out of the refrigerant/water heat exchanger (12); and

a controller (15) configured to perform fixed control for the capacity of the compressor (2) when the water inlet temperature is determined to have reached a preset first temperature, and perform variable control for the water flow rate of the water supply pump (7) so that the water outlet temperature is made equal to a preset second temperature.
The water heater of claim 1,
wherein, when the temperature according to the detection by the water inlet temperature detection means (8) is determined to have exceeded a third temperature which is set at or above the first temperature, the controller (15) performs
control to decrease the capacity of the compressor (2), and
variable control for the water flow rate of the water supply pump (7) so that the water outlet temperature is made equal to the second temperature.
The water heater of claim 1 or 2, wherein the controller (15) performs variable control for the water flow rate of the water supply pump (7) so that the temperature according to the detection by the water outlet temperature detection means (10) is made equal to the second temperature.
The water heater of claim 2, wherein the controller (15) controls the compressor (2) so that the water inlet temperature is made equal to the first temperature, and performs control for the water flow rate of the water supply pump (7) so that the temperature according to the detection by the water outlet temperature detection means (10) is made equal to the second temperature.
The water heater of any one of claims 1 to 4, wherein the controller (15) performs fixed control for the water supply pump (7) during a period from start of an operation to a time when the water inlet temperature is determined to have reached the first temperature.