Technical Field
[0001] The present invention relates to a heat medium cycle system including a refrigeration
cycle circuit and a heat medium cycle circuit.
Background Art
[0002] Examples of known heat medium cycle systems, such as a water cycle air-conditioning
system, include an air-conditioning system including a chilling unit, serving as a
heat source. Such an air-conditioning system is used in, for example, a building or
a large commercial facility. The air-conditioning system circulates water, serving
as a heat medium, through a structure in such a manner that heat from the water is
used for cooling or heating through a fan coil unit or an air handling unit, serving
as a load-side device.
[0003] A plurality of chilling units are typically installed parallel to each other in a
single water cycle circuit. Water through the water cycle circuit is circulated through
the plurality of chilling units via header pipes.
[0004] In this air-conditioning system, the use of an inverter-driven compressor and an
inverter-driven water circulating pump is effective in saving power. To control inverters
for the compressor and the water circulating pump, the temperature of the water is
measured and the optimum control for a load is performed on the basis of the measured
water temperature.
[0005] In the air-conditioning system including the plurality of chilling units, not only
the inverters but also the number of chilling units that are being operated are controlled
to achieve power saving.
[0006] An effective manner to save power includes adjusting the flow rate of the water through
the chilling units on the basis of a load. For example, reducing the water flow rate
is effective when the load is small, to reduce water sending power. However, when
the water flowing through the chilling units is cold, a reduction in water flow rate
may cause a water heat exchanger to freeze and break.
[0007] A known technique for protecting the water heat exchanger includes measuring the
difference in water pressure between an inlet and an outlet of the water heat exchanger
by using two water pressure sensors each provided at a corresponding one of the inlet
and the outlet of the water heat exchanger, converting the pressure difference into
a water flow rate, and keeping the compressor from being activated when the water
flow rate has not reached a predetermined value (refer to Patent Literature 1, for
example).
Citation List
Patent Literature
[0008] Patent Literature 1: Japanese Patent No.
5622859
Summary of Invention
Technical Problem
[0009] Patent Literature 1 discloses a heat medium cycle system that uses water pressure
sensors only to inhibit a compressor from being operated when water in a water heat
exchanger is frozen. Disadvantageously, the provided water pressure sensors are not
effectively used for other purposes, and no consideration is given to preventing the
water from freezing in the water heat exchanger. Once the water is frozen in the water
heat exchanger, the heat medium cycle system inconveniently cannot be used until the
frozen water is eliminated.
[0010] The present invention aims to overcome the above-described disadvantages and to
provide a heat medium cycle system capable of being continuously operated while a
heat medium is being prevented from freezing in a heat medium heat exchanger by using
a pressure difference of the heat medium obtained from a measurement value of an inlet
pressure sensor provided at an inlet of the heat medium heat exchanger and a measurement
value of an outlet pressure sensor provided at an outlet of the heat medium heat exchanger.
Solution to Problem
[0011] A heat medium cycle system according to an embodiment of the present invention includes
a refrigeration cycle circuit, through which refrigerant is circulated, including
a compressor, a heat-source-side heat exchanger, an expansion device, and a heat medium
heat exchanger connected by pipes and a heat medium cycle circuit, through which a
heat medium is circulated, including a pump circulating the heat medium, the heat
medium heat exchanger, and a load-side heat exchanger connected by pipes. The heat
medium cycle system further includes an inlet temperature sensor configured to measure
a temperature of the heat medium at a heat medium inlet of the heat medium heat exchanger,
an inlet pressure sensor configured to measure a pressure of the heat medium at the
heat medium inlet of the heat medium heat exchanger, an outlet pressure sensor configured
to measure a pressure of the heat medium at a heat medium outlet of the heat medium
heat exchanger, an evaporating temperature sensor configured to detect an evaporating
temperature of the refrigerant in the heat medium heat exchanger, and a controller
configured to, under a first condition where the heat medium is to freeze in the heat
medium heat exchanger, obtain a minimum on-state flow rate at which the heat medium
is kept from freezing in the heat medium heat exchanger, on the basis of the temperature
of the heat medium at the heat medium inlet measured by the inlet temperature sensor
and the evaporating temperature of the refrigerant detected by the evaporating temperature
sensor, and control the pump in such a manner that the minimum on-state flow rate
is maintained to make a pressure difference of the heat medium obtained from a measurement
value of the inlet pressure sensor and a measurement value of the outlet pressure
sensor into a minimum on-state pressure difference.
Advantageous Effects of Invention
[0012] In the heat medium cycle system according to an embodiment of the present invention,
under the first condition where the heat medium is to freeze in the heat medium heat
exchanger, the controller obtains the minimum on-state flow rate at which the heat
medium is kept from freezing in the heat medium heat exchanger, on the basis of the
temperature of the heat medium at the heat medium inlet measured by the inlet temperature
sensor and the evaporating temperature of the refrigerant detected by the evaporating
temperature sensor. Then, the controller controls the pump in such a manner that the
minimum on-state flow rate is maintained to make the pressure difference of the heat
medium obtained from the measurement values of the input pressure sensor and the outlet
pressure sensor into the minimum on-state pressure difference. Consequently, the pressure
difference of the heat medium obtained from the measurement values of the inlet pressure
sensor placed at the inlet of the heat medium heat exchanger and the outlet pressure
sensor placed at the outlet of the heat medium heat exchanger is used to prevent the
heat medium from freezing in the heat medium heat exchanger, thus preventing the heat
medium cycle system from being stopped.
Brief Description of Drawings
[0013]
Fig. 1 is a schematic diagram illustrating an exemplary configuration of a water cycle
air-conditioning system according to Embodiment 1 of the present invention.
Fig. 2 is a characteristic graph showing the relationship between the evaporating
temperature of refrigerant, the inlet temperature of water, and the minimum on-state
flow rate of the water in Embodiment 1 of the present invention.
Fig. 3 is a flowchart illustrating control for the water cycle air-conditioning system
according to Embodiment 1 of the present invention.
Fig. 4 is a schematic diagram illustrating an exemplary configuration of a water cycle
air-conditioning system according to Embodiment 2 of the present invention.
Description of Embodiments
[0014] Embodiments of the present invention will be described below with reference to the
drawings.
[0015] Note that components designated by the same reference signs in the figures are the
same components or equivalents. The same reference signs apply to the entire description
herein.
[0016] Furthermore, note that the forms of components described herein are intended to be
illustrative only and the forms of components are not limited to the descriptions
of the forms of components.
Embodiment 1
[0017] Fig. 1 is a schematic diagram illustrating an exemplary configuration of a water
cycle air-conditioning system 100 according to Embodiment 1 of the present invention.
In Embodiment 1, the water cycle air-conditioning system 100 will be described as
an example of a heat medium cycle system according to the present invention.
[0018] The water cycle air-conditioning system 100 includes a chilling unit 1 and a water
circuit 2 including the chilling unit 1. The water circuit 2 corresponds to a heat
medium cycle circuit in the present invention. Water circulated through the water
circuit 2 corresponds to a heat medium in the present invention.
[0019] The chilling unit 1 includes a refrigeration cycle circuit 10, a water circulating
pump 3, and a controller 20, and constitutes part of the water circuit 2.
[0020] In the chilling unit 1, the refrigeration cycle circuit 10 includes a compressor
11, a heat-source-side heat exchanger 12, an expansion device 13, and a water heat
exchanger 14 connected by pipes in such a manner that refrigerant is circulated through
the refrigeration cycle circuit 10.
[0021] The compressor 11 compresses the refrigerant, serving as heat-source-side refrigerant,
such as chlorofluorocarbon. The compressor 11 is inverter-controlled by the controller
20. The heat-source-side heat exchanger 12 exchanges heat between the refrigerant
and air, such as outside air. An air-sending fan 15 sending the air to the heat-source-side
heat exchanger 12 is disposed next to the heat-source-side heat exchanger 12. The
air-sending fan 15 is inverter-controlled by the controller 20. The expansion device
13 adjusts the pressure of the refrigerant. Opening and closing of the expansion device
13 is controlled by the controller 20. For the expansion device 13, a valve whose
opening degree is adjustable, for example, a linear expansion valve (LEV), can be
used. Other usable examples of the expansion device 13 include a capillary tube whose
opening degree is fixed. The water heat exchanger 14 exchanges heat between the refrigerant
and water different from the refrigerant. The water heat exchanger 14 cools the water
circulated through the water circuit 2 to a target temperature by using heat from
the refrigerant. The water heat exchanger 14 corresponds to a heat medium heat exchanger
in the present invention.
[0022] The water circuit 2 includes the chilling unit 1, a load-side heat exchanger 4, and
a control valve 5 connected by pipes in such a manner that the water is circulated
through the water circuit 2.
[0023] The water circulating pump 3 of the chilling unit 1 circulates the water for heat
exchange in the water heat exchanger 14 through the water circuit 2. The water circulating
pump 3 is inverter-controlled by the controller 20.
[0024] For the load-side heat exchanger 4, for example, a heat exchanger that cools indoor
air in a structure by using the water circulated through the water circuit 2 is used.
[0025] The control valve 5 adjusts the flow rate of the water flowing through the load-side
heat exchanger 4. The opening degree of the control valve 5 is adjusted toward an
open position or a closed position by the controller 20.
[0026] The controller 20 includes a microcomputer including a central processing unit (CPU),
a read-only memory (ROM), a random access memory (RAM), and an input-output (I/O)
port.
[0027] The controller 20 is connected to various sensors by wired or wireless control signal
lines 21 in such a manner that the controller can receive measurement values from
the sensors. The sensors include an inlet temperature sensor 22, an outlet temperature
sensor 23, an inlet pressure sensor 24, an outlet pressure sensor 25, and a refrigerant
temperature sensor 26.
[0028] The controller 20 is connected to the compressor 11, the air-sending fan 15, the
expansion device 13, and the water circulating pump 3 by wired or wireless control
signal lines 21 in such a manner that the controller can transmit operation instructions
to these components.
[0029] The controller 20 stores a table from which a minimum on-state flow rate is obtained
on the basis of the temperature of the water at a water inlet measured by the inlet
temperature sensor 22 and the evaporating temperature of the refrigerant detected
by the refrigerant temperature sensor 26.
[0030] The inlet temperature sensor 22 measures the temperature of the water at the water
inlet of the water heat exchanger 14. The outlet temperature sensor 23 measures the
temperature of the water at a water outlet of the water heat exchanger 14. The inlet
pressure sensor 24 measures the pressure of the water at the water inlet of the water
heat exchanger 14. The outlet pressure sensor 25 measures the pressure of the water
at the water outlet of the water heat exchanger 14. The refrigerant temperature sensor
26 detects the evaporating temperature of the refrigerant in the water heat exchanger
14.
[0031] The refrigerant temperature sensor 26 corresponds to an evaporating temperature sensor
in the present invention. For the evaporating temperature sensor, a refrigerant pressure
sensor that measures the pressure of the refrigerant at a refrigerant outlet of the
water heat exchanger 14 may be used.
[0032] The controller 20 calculates optimum operating conditions on the basis of measurement
values of the inlet temperature sensor 22, the outlet temperature sensor 23, the inlet
pressure sensor 24, and the outlet pressure sensor 25, and a detection value of the
refrigerant temperature sensor 26. Furthermore, the controller 20 outputs operation
instructions for the calculated optimum operating conditions to the compressor 11,
the air-sending fan 15, the expansion device 13, and the water circulating pump 3,
and controls these components.
[0033] The controller 20 is connected in communication with a remote control 6 by a wireless
control signal line 27. The controller 20 changes condition settings of the operating
conditions in response to a user operation on the remote control 6, and enables the
changed condition settings to be displayed on the remote control 6.
[0034] An operation of the water cycle air-conditioning system 100 will be described below.
[0035] In the water cycle air-conditioning system 100, the controller 20 measures temperatures,
which vary depending on the amount of heat required for the load-side heat exchanger
4, of the water circulated through the water circuit 2 by using the inlet temperature
sensor 22 placed at the water inlet of the water heat exchanger 14 and the outlet
temperature sensor 23 placed at the water outlet of the water heat exchanger 14. Then,
the controller 20 calculates, on the basis of the measurement values of the inlet
temperature sensor 22 and the outlet temperature sensor 23, the rotation frequency
of the compressor 11, the rotation frequency of the air-sending fan 15, the opening
degree of the expansion device 13, and the rotation frequency of the water circulating
pump 3 for an optimum operating efficiency. The controller 20 transmits operation
instructions based on the calculation results to the compressor 11, the air-sending
fan 15, the expansion device 13, and the water circulating pump 3. The controller
20 controls the compressor 11, the air-sending fan 15, the expansion device 13, and
the water circulating pump 3 so that the measurement value of the outlet temperature
sensor 23 reaches a target water temperature.
[0036] A reduction in load during operation of the water cycle air-conditioning system 100
leads to a reduction in difference between the temperature of the water at the water
outlet and that at the water inlet of the water heat exchanger 14. For this reason,
the rotation frequency of the compressor 11, the rotation frequency of the air-sending
fan 15, and the rotation frequency of the water circulating pump 3 are reduced.
[0037] In a cooling operation of the water cycle air-conditioning system 100 illustrated
in Fig. 1, a reduction in rotation frequency of the water circulating pump 3 results
in a reduction in flow rate of the water through the water heat exchanger 14. At this
time, under operating conditions where the temperature of the refrigerant is below
freezing, that is, the water is to freeze in the water heat exchanger 14 of the water
circuit 2, the water freezes in the water heat exchanger 14, possibly causing the
water heat exchanger 14 to be broken.
[0038] However, reducing the rotation frequency of the water circulating pump 3 to reduce
the flow rate of the water is effective in reducing the water sending power. This
operation is effective in reducing power consumption. Furthermore, output power can
be easily increased again because the water cycle air-conditioning system 100 is not
stopped.
[0039] The controller 20 can estimate the flow rate of the water through the water circuit
2 on the basis of a water pressure difference obtained from the measurement values
of the inlet pressure sensor 24 and the outlet pressure sensor 25 by using Bernoulli's
theorem. Consequently, under operating conditions where the temperature of the refrigerant
is below freezing, that is, the water is to freeze in the water heat exchanger 14
of the chilling unit 1 in the water circuit 2, the controller 20 adjusts the rotation
frequency of the water circulating pump 3 to maintain the minimum on-state flow rate
of the water at which the water is kept from freezing in the water heat exchanger
14.
[0040] Specifically, under operating conditions where the water is to freeze in the water
heat exchanger 14, the controller 20 calculates the minimum on-state flow rate at
which the water is kept from freezing in the water heat exchanger 14. Then, the controller
20 adjusts the rotation frequency of the water circulating pump 3 to maintain the
minimum on-state flow rate in such a manner that the water pressure difference obtained
from the measurement values of the inlet pressure sensor 24 and the outlet pressure
sensor 25 is at a minimum on-state pressure difference.
[0041] The minimum on-state flow rate of the water at which the water is kept from freezing
in the water heat exchanger 14 varies depending on the relationship between the evaporating
temperature of the refrigerant and the temperature of the water at the water inlet
of the water heat exchanger 14.
[0042] Fig. 2 is a characteristic graph showing the relationship between the refrigerant
evaporating temperature, the inlet water temperature, and the minimum on-state flow
rate of the water in Embodiment 1 of the present invention. The controller 20 stores
the table representing the relationship in the characteristic graph of Fig. 2.
[0043] The controller 20 receives an inlet water temperature that is a measurement value
of the inlet temperature sensor 22 and a refrigerant temperature that is a measurement
value of the refrigerant temperature sensor 26, and applies the temperatures to the
table in Fig. 2, thus automatically calculating the minimum on-state flow rate. At
high inlet water temperatures, therefore, the minimum on-state flow rate can be reduced,
thus reducing the power consumption.
[0044] The minimum on-state flow rate obtained from the table in Fig. 2 is the flow rate
maintained to keep the water from freezing in the water heat exchanger 14 even when
the rotation frequency of the water circulating pump 3 can be further reduced under
conditions where the load decreases and the opening degree of the control valve 5
adjusting the flow rate of the water flowing through the load-side heat exchanger
4 is adjusted toward the closed position.
[0045] As described above, the inlet temperature sensor 22 and the inlet pressure sensor
24 are arranged in the pipe adjacent to the water inlet of the water heat exchanger
14. The outlet temperature sensor 23 and the outlet pressure sensor 25 are arranged
in the pipe adjacent to the water outlet of the water heat exchanger 14. The refrigerant
temperature sensor 26 is disposed adjacent to a refrigerant passage in the water heat
exchanger 14. The controller 20 calculates optimum operating conditions from the measurement
values of the inlet temperature sensor 22, the outlet temperature sensor 23, the inlet
pressure sensor 24, and the outlet pressure sensor 25, and the detection value of
the refrigerant temperature sensor 26 connected by the control signal lines 21. The
controller 20 transmits operation instructions based on the calculated optimum operating
conditions to the compressor 11, the air-sending fan 15, the expansion device 13,
and the water circulating pump 3. Then, the controller 20 controls the compressor
11, the air-sending fan 15, the expansion device 13, and the water circulating pump
3 so that the measurement value of the outlet temperature sensor 23 reaches the target
water temperature.
[0046] Under conditions where the water is to freeze in the water heat exchanger 14, the
controller 20 calculates the minimum on-state flow rate at which the water is kept
from freezing in the water heat exchanger 14. Then, the controller 20 adjusts the
rotation frequency of the water circulating pump 3 to maintain the minimum on-state
flow rate in such a manner that the water pressure difference obtained from the measurement
values of the inlet pressure sensor 24 and the outlet pressure sensor 25 is at the
minimum on-state pressure difference. Consequently, the minimum on-state flow rate
at which the water is kept from freezing in the water heat exchanger 14 can be maintained,
thus achieving high efficiency of the water cycle air-conditioning system 100. Furthermore,
the water is prevented from freezing in the water heat exchanger 14. This operation
enables the water cycle air-conditioning system 100 to be continuously operated, thus
enhancing convenience.
[0047] Control for maintaining the minimum on-state flow rate by using the water circulating
pump 3 will be described below.
[0048] Fig. 3 is a flowchart illustrating control for the water cycle air-conditioning system
100 according to Embodiment 1 of the present invention.
[0049] At the beginning of the process, in step S1, the controller 20 measures an outlet
water temperature of the water heat exchanger 14 by using the outlet temperature sensor
23.
[0050] In step S2, the controller 20 determines whether the measured outlet water temperature
of the water heat exchanger 14 has reached a target water temperature. When the outlet
water temperature has reached the target water temperature, the process proceeds to
step S3. When the outlet water temperature has not reached the target water temperature,
the process proceeds to step S4.
[0051] In step S4, the controller 20 increases the rotation frequency of the compressor
11 and the rotation frequency of the air-sending fan 15. After step S4, the process
returns to step S1.
[0052] In step S3, the controller 20 determines whether the rotation frequency of the water
circulating pump 3 can be reduced. Whether the rotation frequency of the water circulating
pump 3 can be reduced is determined on the basis of, for example, determination on
whether the difference between the outlet water temperature and an inlet water temperature
of the water heat exchanger 14 is less than a set value. When the rotation frequency
of the water circulating pump 3 can be reduced, the process proceeds to step S5. When
the rotation frequency of the water circulating pump 3 cannot be reduced, the process
returns to step S1.
[0053] In step S5, the controller 20 reduces the rotation frequency of the water circulating
pump 3. At this time, step 5 may be taken under operating conditions where the temperature
of the refrigerant is below freezing, that is, the water is to freeze in the water
heat exchanger 14 of the water circuit 2. Furthermore, the rotation frequency of the
compressor 11 and that of the air-sending fan 15 can be reduced in addition to the
rotation frequency of the water circulating pump 3. The rotation frequency of the
water circulating pump 3 is adjusted to maintain the minimum on-state flow rate. The
minimum on-state flow rate is automatically calculated by applying the inlet water
temperature that is the measurement value of the inlet temperature sensor 22 and the
refrigerant temperature that is the measurement value of the refrigerant temperature
sensor 26 to the table in Fig. 2. For example, when the process proceeds to step S5
after step S9, the rotation frequency of the water circulating pump 3 is adjusted
to maintain a flow rate slightly greater than the minimum on-state flow rate. After
step S5, the process proceeds step S6.
[0054] In step S6, the controller 20 determines a water pressure difference between the
pressure of the water inlet and that of the water outlet of the water heat exchanger
14. This step, in which the water pressure difference is obtained from the measurement
values of the inlet pressure sensor 24 and the outlet pressure sensor 25, is taken
to estimate the actual flow rate of the water through the water circuit 2 on the basis
of the obtained water pressure difference by using Bernoulli's theorem. The water
pressure difference obtained in this step is the minimum on-state pressure difference
at which the flow rate of the water through the water circulating pump 3 is at the
minimum on-state flow rate. After step S6, the process proceeds to step S7.
[0055] In step S7, the controller 20 determines whether the water flow rate estimated in
step S6 meets the minimum on-state flow rate. The minimum on-state flow rate is automatically
calculated by applying the inlet water temperature that is the measurement value of
the inlet temperature sensor 22 and the refrigerant temperature that is the measurement
value of the refrigerant temperature sensor 26 to the table in Fig. 2. The controller
20 determines whether the water flow rate estimated in step S6 is greater than or
equal to the calculated minimum on-state flow rate. When the water flow rate meets
the minimum on-state flow rate, the process proceeds to step S8. When the water flow
rate does not meet the minimum on-state flow rate, the process proceeds to step S9.
[0056] In step S9, the controller 20 increases the rotation frequency of the water circulating
pump 3, thus allowing the water flow rate to meet the minimum on-state flow rate.
After step S9, the process returns to step S3.
[0057] In step S8, the controller 20 maintains a state in which the water flow rate estimated
in step S6 meets the minimum on-state flow rate. Consequently, even under conditions
where the rotation frequency of the water circulating pump 3 is reduced and the water
is to freeze in the water heat exchanger 14, the controller 20 adjusts the rotation
frequency of the water circulating pump 3 to maintain the minimum on-state flow rate
in such a manner that the water pressure difference is at the minimum on-state pressure
difference. After step S8, the process terminates.
[0058] Advantages offered by the water cycle air-conditioning system 100 according to Embodiment
1 will be described below.
[0059] The water cycle air-conditioning system 100 according to Embodiment 1 includes the
refrigeration cycle circuit 10, through which the refrigerant is circulated, including
the compressor 11, the heat-source-side heat exchanger 12, the expansion device 13,
and the water heat exchanger 14 connected by the pipes. The water cycle air-conditioning
system 100 includes the water circuit 2, through which the water is circulated, including
the water circulating pump 3 circulating the water, the water heat exchanger 14, and
the load-side heat exchanger 4 connected by the pipes. The water cycle air-conditioning
system 100 includes the inlet temperature sensor 22 measuring the temperature of the
water at the water inlet of the water heat exchanger 14. The water cycle air-conditioning
system 100 includes the inlet pressure sensor 24 measuring the pressure of the water
at the water inlet of the water heat exchanger 14. The water cycle air-conditioning
system 100 includes the outlet pressure sensor 25 measuring the pressure of the water
at the water outlet of the water heat exchanger 14. The water cycle air-conditioning
system 100 includes the refrigerant temperature sensor 26 detecting the evaporating
temperature of the refrigerant in the water heat exchanger 14. The water cycle air-conditioning
system 100 includes the controller 20, which obtains the minimum on-state flow rate
at which the water is kept from freezing in the water heat exchanger 14, on the basis
of the water temperature at the water inlet measured by the inlet temperature sensor
22 and the refrigerant evaporating temperature detected by the refrigerant temperature
sensor 26 under conditions where the water is to freeze in the water heat exchanger
14. The controller 20 controls the water circulating pump 3 in such a manner that
the minimum on-state flow rate is maintained to make the water pressure difference
obtained from the measurement values of the inlet pressure sensor 24 and the outlet
pressure sensor 25 into the minimum on-state pressure difference.
[0060] The above-described configuration prevents the water from freezing in the water heat
exchanger 14 by using the water pressure difference obtained from the measurement
values of the inlet pressure sensor 24 placed at the water inlet of the water heat
exchanger 14 and the outlet pressure sensor 25 placed at the water outlet of the water
heat exchanger 14, thus preventing the water cycle air-conditioning system 100 from
being stopped. Furthermore, the water heat exchanger 14 can be prevented from being
broken by freezing of the water in the water heat exchanger 14.
[0061] Under operating conditions where the water is to freeze in the water heat exchanger
14, the controller 20 controls the water circulating pump 3 in such a manner that
the minimum on-state flow rate is maintained. Consequently, an excess of power for
driving the water circulating pump 3 can be reduced, thus reducing the power consumption.
This operation achieves high efficiency of the water cycle air-conditioning system
100.
[0062] In Embodiment 1, in the case where the load decreases and the opening degree of
the control valve 5 adjusting the flow rate of the water flowing through the load-side
heat exchanger 4 is adjusted toward the closed position, the controller 20 controls
the water circulating pump 3 in such a manner that the minimum on-state flow rate
is maintained.
[0063] Such a configuration keeps the water from freezing in the water heat exchanger 14.
An excess of power for driving the water circulating pump 3 can be reduced, thus reducing
the power consumption. This operation achieves high efficiency of the water cycle
air-conditioning system 100.
[0064] In Embodiment 1, the controller 20 has the table from which the minimum on-state
flow rate is obtained on the basis of the water temperature at the water inlet measured
by the inlet temperature sensor 22 and the refrigerant evaporating temperature detected
by the refrigerant temperature sensor 26. The controller 20 obtains the minimum on-state
flow rate by using the table.
[0065] Such a configuration enables the controller 20 to automatically obtain the minimum
on-state flow rate from the table in Fig. 2 on the basis of the inlet water temperature
at the water inlet measured by the inlet temperature sensor 22 and the refrigerant
evaporating temperature detected by the refrigerant temperature sensor 26, thus achieving
high efficiency of the water cycle air-conditioning system 100.
Embodiment 2
[0066] Fig. 4 is a schematic diagram illustrating an exemplary configuration of a water
cycle air-conditioning system 200 according to Embodiment 2 of the present invention.
In Embodiment 2, a description of the same components as those in Embodiment 1 is
omitted. The following description will focus on differences between Embodiment 1
and Embodiment 2.
[0067] As illustrated in Fig. 4, the water circuit 2 of the water cycle air-conditioning
system 200 includes a plurality of chilling units 1, each including the refrigeration
cycle circuit 10 and the water circulating pump 3, arranged in parallel to the load-side
heat exchanger 4. The plurality of chilling units 1 each have the configuration described
in Embodiment 1. Specifically, each chilling unit 1 includes the refrigeration cycle
circuit 10 and the water circulating pump 3 and constitutes part of the water circuit
2. In the water circuit 2, a water outlet pipe extending from the chilling unit 1
has no check valve.
[0068] An operation of the water cycle air-conditioning system 200 will be described below.
[0069] In the water cycle air-conditioning system 200 including the plurality of chilling
units 1 arranged parallel to each other, the number of chilling units 1 is controlled
on the basis of the amount of heat required for the load-side heat exchanger 4 in
such a manner that one or more chilling units 1 can be stopped.
[0070] At this time, power generated by the water circulating pump 3 in the chilling unit
1 that is being operated causes the water through the water circuit 2 to flow toward
the chilling unit 1 in which the water circulating pump 3 is stopped in a direction
opposite to a water sending direction in which the water circulating pump 3 sends
the water. In a traditional configuration, a check valve is disposed in the water
outlet pipe extending from the chilling unit 1 to prevent a short cycle phenomenon
caused by the water flowing in the opposite direction.
[0071] In contrast, according to Embodiment 2, in a case where the compressor 11 is stopped
in a corresponding one or more chilling units 1 of the plurality of chilling units
1, under conditions where the water is to flow in the direction opposite to the water
sending direction, that is, the measurement value of the outlet pressure sensor 25
is greater than the measurement value of the inlet pressure sensor 24, the controller
20 of each of the corresponding one or more chilling units 1 calculates a minimum
off-state flow rate at which the water is kept from flowing in the opposite direction,
on the basis of a water pressure difference obtained from measurement values of the
inlet pressure sensor 24 and the outlet pressure sensor 25. Then, the controller 20
of each of the corresponding one or more chilling units 1, in each of which the compressor
11 is stopped, adjusts the rotation frequency of the water circulating pump 3 to maintain
the minimum off-state flow rate in such a manner that the water pressure difference
obtained from the measurement values of the inlet pressure sensor 24 and the outlet
pressure sensor 25 is at a minimum off-state pressure difference.
[0072] Specifically, each chilling unit 1 in which the compressor 11 is stopped would also
be stopped in a traditional configuration. However, in such a chilling unit 1 in which
the compressor 11 is stopped, the water circulating pump 3 is slightly operated to
maintain the minimum off-state flow rate at which the water is kept from flowing in
the opposite direction. This configuration enables omission of a check valve that
prevents the water from flowing in the opposite direction. Furthermore, as the water
circulating pump 3 is slightly operated, the minimum off-state flow rate ensures that
the water is kept from freezing in the water heat exchanger 14, similar to the minimum
on-state flow rate in Embodiment 1.
[0073] At this time, the minimum off-state flow rate is a flow rate of greater than 0 at
which only heat generated by operating the water circulating pump 3 is rejected.
[0074] Advantages offered by the water cycle air-conditioning system 200 according to Embodiment
2 will be described below.
[0075] According to Embodiment 2, the water circuit 2 includes the plurality of chilling
units 1, each including the refrigeration cycle circuit 10 and the water circulating
pump 3, arranged in parallel to the load-side heat exchanger 4. In the case where
the compressor 11 is stopped in a corresponding one or more chilling units 1 of the
plurality of chilling units 1, under conditions where the water is to flow in the
direction opposite to the water sending direction in which the water circulating pump
3 sends the water, the controller 20 of each of the corresponding one or more chilling
units 1 obtains the minimum off-state flow rate at which the water is kept from flowing
in the opposite direction, on the basis of the water pressure difference obtained
from the measurement values of the inlet pressure sensor 24 and the outlet pressure
sensor 25. Then, the controller 20 of each of the corresponding one or more chilling
units 1, in each of which the compressor 11 is stopped, controls the water circulating
pump 3 in such a manner that the minimum off-state flow rate is maintained.
[0076] Such a configuration prevents the water through the water circuit 2 from flowing
in the opposite direction and thus enables omission of check valves. As the water
circulating pump 3 is slightly operated, the minimum off-state flow rate ensures that
the water is kept from freezing in the water heat exchanger 14, similar to the minimum
on-state flow rate. This operation prevents the water from freezing in the water heat
exchanger 14, thus preventing the water cycle air-conditioning system 200 from being
stopped. Furthermore, the water heat exchanger 14 can be prevented from being broken
by freezing of the water in the water heat exchanger 14.
[0077] In Embodiment 2, the minimum off-state flow rate is a flow rate of greater than 0
at which only heat generated by operating the water circulating pump 3 is rejected.
[0078] With this definition, the minimum off-state flow rate at which the water is kept
from flowing in the opposite direction can be calculated, and the water circulating
pump 3 can be slightly operated in such a manner that the water does not flow in the
direction opposite to the water sending direction in which the water circulating pump
3 sends the water, thus reducing the power consumption. In addition, heat generated
by the water circulating pump 3 that is being operated can be cooled.
[0079] In Embodiments 1 and 2 described above, the water cycle air-conditioning systems
100 and 200 have been described as examples. The water cycle air-conditioning systems
100 and 200 include one or more chilling units 1 of an air heat source type that includes
the water heat exchanger 14 for cooling the water to a target temperature by using
heat from the heat-source-side refrigerant, such as chlorofluorocarbon. Other applications
include a water cycle air-conditioning system including, as a heat source, a chilling
unit of a water heat source type in which a heat-source-side heat exchanger exchanges
heat between water and heat-source-side refrigerant. The water cycle air-conditioning
system may include a four-way valve provided in the refrigeration cycle circuit so
that heat from the heat-source-side refrigerant, such as chlorofluorocarbon, can be
used not only to cool the water to a target temperature but also to heat the water
to a target temperature. For the heat medium, brine may be used instead of the water
circulated through the water circuit. Applications of the heat medium cycle system
according to the present invention include systems through which the heat medium is
circulated, including water cycle air-conditioning systems.
Reference Signs List
[0080] 1 chilling unit 2 water circuit 3 water circulating pump 4 load-side heat exchanger
5 control valve 6 remote control 10 refrigeration cycle circuit 11 compressor 12 heat-source-side
heat exchanger 13 expansion device 14 water heat exchanger 15 air-sending fan 20 controller
21 control signal line 22 inlet temperature sensor 23 outlet temperature sensor 24
inlet pressure sensor 25 outlet pressure sensor 26 refrigerant temperature sensor
27 control signal line 100 water cycle air-conditioning system 200 water cycle air-conditioning
system