AU2021398580A1 - Cooling device and control method for cooling device - Google Patents
Cooling device and control method for cooling device Download PDFInfo
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- AU2021398580A1 AU2021398580A1 AU2021398580A AU2021398580A AU2021398580A1 AU 2021398580 A1 AU2021398580 A1 AU 2021398580A1 AU 2021398580 A AU2021398580 A AU 2021398580A AU 2021398580 A AU2021398580 A AU 2021398580A AU 2021398580 A1 AU2021398580 A1 AU 2021398580A1
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- pump
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- 238000000034 method Methods 0.000 title claims description 29
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Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B43/00—Arrangements for separating or purifying gases or liquids; Arrangements for vaporising the residuum of liquid refrigerant, e.g. by heat
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B49/00—Arrangement or mounting of control or safety devices
- F25B49/02—Arrangement or mounting of control or safety devices for compression type machines, plants or systems
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B49/00—Arrangement or mounting of control or safety devices
- F25B49/02—Arrangement or mounting of control or safety devices for compression type machines, plants or systems
- F25B49/022—Compressor control arrangements
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
- F25B2400/23—Separators
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B2600/00—Control issues
- F25B2600/02—Compressor control
- F25B2600/025—Compressor control by controlling speed
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B2600/00—Control issues
- F25B2600/11—Fan speed control
- F25B2600/111—Fan speed control of condenser fans
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- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Mechanical Engineering (AREA)
- Thermal Sciences (AREA)
- General Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Power Engineering (AREA)
- Control Of Positive-Displacement Pumps (AREA)
- Other Air-Conditioning Systems (AREA)
- Air Conditioning Control Device (AREA)
Abstract
An object of the present invention is to prevent cavitation in a refrigerant pump
from occurring due to a decrease in a net positive suction head in a cooling device.
A cooling device of the present invention is a cooling device using a
refrigeration cycle in which a refrigerant is circulated through a heat receiver (1), a
compressor (2), a heat radiator (3), and an expander (4), and includes a tank (5) that
separates the refrigerant supplied from the expander (4) into a gas phase refrigerant and a
liquid phase refrigerant, a pump (6) that sends the liquid phase refrigerant separated in
the tank (5) to the heat receiver (1), and a control unit (7) that controls the amount of
increase in pressure of the compressor 2 in the refrigeration cycle, and the control unit (7)
increases the pressure of the compressor (2) in a limited range in which the value of the
net positive suction head of the pump (6) does not fall below a predetermined value.
Description
[0001]
The present invention relates to a cooling device and a control method therefor.
In particular, the present invention relates to a cooling device using a refrigeration cycle
suitable for air conditioning equipment in a data center and a control method therefor.
[0002]
A cooling device using a refrigeration cycle for radiating heat to an atmosphere
via a refrigerant that has received heat from heat generation sources through steps of
heat-receiving, compressing, heat-radiating, and expanding a refrigerant is used to cool a
space in which a large number of the heat generation sources such as electronic devices
are housed, such as a server room in a data center.
In this refrigeration cycle, because the refrigerant repeats the phase change
between a liquid phase and a gas phase in each step of the cycle, it is necessary to
achieve an efficient operation of the refrigeration cycle by appropriately maintaining a
phase state of the refrigerant in pipelines between the respective steps.
[0003]
For example, in the refrigerant circulation system, because a compressor that
sucks a refrigerant in a gas-liquid mixed phase state of which heat has been received by a heat receiver and increases the pressure at a predetermined compression ratio has a structure on the basis of compression of a gas-phase refrigerant, it is not possible to compress a liquid-phase refrigerant. Therefore, before the refrigerant is sucked into the compressor, it is necessary to separate the refrigerant in the mixed phase state into gas and liquid phase refrigerants by temporarily storing the refrigerant in a gas-liquid separation tank (generally, also serving as a tank that separates a gas phase refrigerant from a gas-liquid mixed phase refrigerant directed to the heat receiver and stores a liquid phase refrigerant at a predetermined level).
On the other hand, switching from conventional high-pressure hydro fluoro
carbons (HFCs: high-pressure HFCs) having a difference between an evaporating
pressure and a condensing pressure on the order of 1000 kPa to low-pressure hydro
fluoro olefins (low-pressure HFOs) having a difference between an evaporating pressure
and a condensing pressure of about 100 kPa and a maximum vapor pressure of 1000 kPa
or less, as a refrigerant that is used in the refrigeration cycle, has been expected in
consideration of an environmental load in recent years.
[0004]
In the refrigeration cycle using the low-pressure refrigerant, because it is
necessary to appropriately perform gas-liquid separation in each step of the heat
reception side and the heat radiation side of the refrigerant circulation system, for
example, a tank (gas-liquid separator) having a predetermined capacity is provided for
the purpose of gas-liquid separation on the inlet side of the compressor and gas-liquid
separation on the suction side of a pump that sends the refrigerant to the heat receiver.
[Prior Art Documents]
[Patent Documents]
[0005]
[Patent Document 1] International Publication No. 2018/056201
[Patent Document 2] Japanese Unexamined Patent Application, First Publication No.
2019-174001
[Patent Document 3] Japanese Unexamined Patent Application, First Publication No.
2021-076364
Problem to be Solved by the Invention
[0006]
However, in a case in which the tank is connected to a suction side of the
compressor, when the pressure inside the tank decreases with the suction of the
compressor, the pressure decreases below a saturated vapor pressure of a low-pressure
refrigerant stored in the tank, and cavitation may occur in the liquid phase refrigerant
sucked into a pump for sending the liquid phase refrigerant from the tank to the heat
receiver.
When cavitation occurs due to such a cause, a decrease in flow rate of the
refrigerant to be sent from the pump is caused, the liquid phase refrigerant having a
sufficient flow rate cannot be supplied to the heat receiver, and it becomes difficult to
maintain cooling air supplied from the cooling device to a cooling target below a
predetermined temperature.
[0007]
Because this cavitation is a phenomenon that occurs with an operation of
increasing pressure of the compressor, it is necessary to pay close attention to control of a
compression operation in order to prevent the cavitation from occurring.
Further, because this phenomenon is significant when a low-pressure refrigerant is used, it is required to operate the pump stably while preventing the cavitation from occurring in order to maintain the temperature of the server appropriately.
[0008]
Patent Document 1 related to the present application describes a pump provided
in a refrigeration cycle to supply a refrigerant, but does not disclose a technology for
preventing cavitation of the refrigerant supplied to the pump from occurring due to an
influence of the compressor of the refrigerant.
Patent Document 2 related to the present application relates to a technology for
adjusting a degree of opening of an expansion valve according to a change in rotation
speed of a compressor in a refrigeration cycle, and does not disclose a technology for
preventing cavitation of a refrigerant from occurring in a pump.
Patent Document 3 related to the present application describes a technology for
preventing cavitation from occurring in a pump to which a refrigerant is supplied from a
liquid receiver, but does not disclose a technology for preventing cavitation from
occurring due to an influence of suction of a refrigerant by a compressor on the liquid
receiver.
[0009]
An object of the present invention is to prevent cavitation from occurring in a
pump that is used for pumping of a liquid phase refrigerant in a refrigeration cycle in
which cooling is performed through circulation of the refrigerant.
Means for Solving the Problem
[0010]
In order to solve the above problem, a first example aspect of the present
invention proposes the following means.
A cooling device according to the first example aspect of the present invention is
a cooling device using a refrigeration cycle in which a refrigerant is circulated through a
heat receiver, a compressor, a heat radiator, and an expander, the cooling device
including: a gas-liquid separator configured to separate the refrigerant supplied from the
expander into a gas phase refrigerant and a liquid phase refrigerant; a pump configured to
send the liquid phase refrigerant separated by the gas-liquid separator to the heat
receiver; and a control unit configured to control the amount of increase in pressure of
the compressor in the refrigeration cycle, wherein the control unit limits the value of a
net positive suction head of the pump to a range in which the value does not fall below a
predetermined value and increases the pressure of the compressor.
[0011]
Furthermore, a second example aspect of the present invention proposes the
following means.
A control method for a cooling device according to the second example aspect of
the present invention is a control method for a cooling device using a refrigeration cycle
in which a refrigerant is circulated through a heat receiver, a compressor, a heat radiator,
and an expander, the control method including: controlling, by a control unit, an increase
in the pressure of the compressor to a range in which a value of a net positive suction
head of the pump does not fall below a predetermined value, the pump being configured
to suck a liquid phase refrigerant from a gas-liquid separator configured to separate the
refrigerant supplied from the expander into a gas phase refrigerant and the liquid phase
refrigerant.
Effect of the Invention
[0012]
In the present invention, it is possible to allow the refrigerant to have an
appropriate phase of a gas phase and a liquid phase at various places constituting the
refrigeration cycle.
[0013]
Fig. 1 is a piping system diagram of a cooling device according to a minimum
configuration example of the present invention.
Fig. 2 is a process diagram of a control method for a cooling device according to
the minimum configuration example of the present invention.
Fig. 3 is a chart illustrating a change in pressure in a comparative example of a
first embodiment of the present invention.
Fig. 4 is a chart illustrating a change in pressure in the first embodiment of the
present invention.
Fig. 5 is a flowchart of the operation of a control unit of a cooling device
according to the first embodiment of the present invention.
Fig. 6 is a piping system diagram illustrating an overall configuration of the
cooling device according to the first embodiment of the present invention.
Fig. 7 is a piping system diagram illustrating an overall configuration of a
cooling device according to a second embodiment of the present invention.
Fig. 8 is a flowchart of the operation of a control unit of a cooling device
according to a third embodiment of the present invention.
Fig. 9 is a piping system diagram illustrating an overall configuration of the
cooling device according to the third embodiment of the present invention.
Fig. 10 is an illustrative diagram of a pressure measurement position in the piping system diagram of Fig. 9.
Fig. 11 is a chart illustrating an example of measurement data in each unit of Fig.
10.
Fig. 12 is a flowchart of the operation of a control unit of a cooling device
according to a fourth embodiment of the present invention.
Fig. 13 is a piping system diagram illustrating an overall configuration of the
cooling device according to the fourth embodiment of the present invention.
Fig. 14 is a flowchart of the operation of a control unit of a cooling device
according to a fifth embodiment of the present invention.
Fig. 15 is a piping system diagram illustrating an overall configuration of the
cooling device according to the fifth embodiment of the present invention.
Fig. 16 is a flowchart of the operation of a control unit of a cooling device
according to a sixth embodiment of the present invention.
Fig. 17 is a piping system diagram illustrating an overall configuration of the
cooling device according to the sixth embodiment of the present invention.
Fig. 18 is a flowchart of the operation of a control unit of a cooling device
according to a seventh embodiment of the present invention.
Fig. 19 is a piping system diagram illustrating an overall configuration of the
cooling device according to the seventh embodiment of the present invention.
[0014]
The configuration of a cooling device according to a minimum configuration of
the present invention will be described with reference to Fig. 1.
This cooling device is a cooling device using a refrigeration cycle in which a refrigerant is circulated through a heat receiver 1, a compressor 2, a heat radiator 3, and an expander 4, and includes a tank 5 that separates the refrigerant supplied from the expander 4 into a gas phase refrigerant and a liquid phase refrigerant, a pump 6 that sends the liquid phase refrigerant separated in the tank 5 to the heat receiver 1, and a control unit 7 that controls the amount of increase in pressure of the compressor 2 in the refrigeration cycle, and the control unit 7 is configured to limit the value of a net positive suction head of the pump 6 to a range in which the value does not fall below a predetermined value and increase the pressure of the compressor 2.
[0015]
According to the above configuration, the control unit 7 controls an increase in
the pressure (compression operation) of the compressor 2 so that the pressure determined
according to the net positive suction head of the refrigerant sucked into the pump 6, that
is, the pressure measurement value of a refrigerant liquid (a liquid phase refrigerant)
separated in the tank 5 and sucked into the pump 6, a head difference from a liquid level
in the tank 5 to the pump 6 (the pressure generated by the density of the refrigerant liquid
at the temperature at that point in time and gravity due to a difference in height), and a
saturated vapor pressure of the refrigerant in the tank 5 is maintained to be equal to or
higher than a predetermined pressure, by controlling the amount of increase in pressure
of the compressor 2.
[0016]
More specifically, when the net positive suction head of the pump 6 is low and
concern that cavitation may occur in the liquid phase refrigerant is high, the amount of
increase in pressure of the compressor 2 is curbed, and when the net positive suction
head increases and the concern that cavitation may occur in the refrigerant liquid is low,
the amount of increase in pressure of the compressor 2 is increased, thereby making it is possible to prevent cavitation from occurring in the pump 6.
An example of a calculation equation using parameters actually measured in the
control of the control unit 7 includes Equation (1) below.
Net positive suction head = (pump inlet pressure - saturated vapor
pressure)/(density of refrigerant liquid x gravitational acceleration) -- Equation (1)
In a temperature range in which the present invention is implemented, because
change in the density of the refrigerant liquid is negligibly small, the density can be
treated as a constant in terms of control.
[0017]
A control method for a cooling device according to the minimum configuration
of the present invention will be described with reference to Fig. 2.
This control method for a cooling device is a control method for a cooling
device using a refrigeration cycle in which a refrigerant is circulated through the heat
receiver 1, the compressor 2, the heat radiator 3, and the expander 4, and the control unit
7 is configured to limit the value of the net positive suction head of the pump 6 that sucks
the liquid phase refrigerant from the gas-liquid separator 5 that separates the refrigerant
supplied from the expander into a gas phase refrigerant and a liquid phase refrigerant to a
range in which the value does not fall below a predetermined value, and control increase
in the pressure of the compressor 2.
[0018]
More specific examples of control steps are as follows.
SP1
A net positive suction head is detected through calculation based on Equation (1)
above on the basis of an inlet pressure of the pump 6, a detection value of the
temperature, and a physical characteristic value of the refrigerant.
SP2
The detected net positive suction head is compared with a management value
(predetermined value) of the net positive suction head obtained in advance.
SP3
When the net positive suction head is smaller than the predetermined value, for
example, the rotation speed of a drive motor (not illustrated) of the compressor 2 is
decreased in order to curb the increase in the pressure of the compressor 2, and when the
net positive suction head is greater than the predetermined value, the increase in the
pressure of the compressor 2 is maintained.
[0019]
According to the above configuration, because the pressure of the refrigerant
liquid sucked into the pump 6 is maintained to be equal to or higher than a predetermined
value according to the saturated vapor pressure at that time, it is possible to prevent
cavitation from occurring on the suction side of the pump 6.
[0020]
(First Embodiment)
Hereinafter, a first embodiment of the present invention will be described with
reference to Figs. 3 to 6. In Fig. 6, the same components as those in Fig. 1 are denoted
by the same reference signs, and a description thereof will be simplified.
The heat receiver 1 is provided in, for example, a ceiling-mounted unit disposed
above a heat generation source such as an internal server of a server room or the like, and
includes, for example, a pipe through which a refrigerant flows, and fins having a
predetermined contact area to promote heat exchange. Further, the heat receiver 1
receives heat from the air that absorbs heat of an internal heat generation source by
passing through the inside of the server, is discharged to a hot aisle side of the server room (a passage in the server room on the side from which cooling air having an increased temperature is discharged), and has become an updraft to be brought into contact with the fins, and the refrigerant flowing inside evaporates according to the amount of received heat, and most of the refrigerant flows out in a liquid phase when the amount of received heat is small.
A pipe 8a connects the heat receiver 1 to a gas-liquid separator (specifically, a
closed tank, which is hereinafter referred to as a tank) 5, and a pipe 8b connects the gas
phase portion (an upper portion) of the tank 5 to the suction side of the compressor 2.
[0021]
A pipe 8c connects a discharge side of the compressor 2 to the heat radiator 3.
The heat radiator 3 is installed, for example, outside in a building including the server
room, and radiates heat by heat-exchanging the refrigerant compressed by the
compressor 2 with, for example, an atmosphere, so that the refrigerant is below a boiling
point and becomes a liquid phase refrigerant.
A pipe 8d connects the heat radiator 3 to the expansion valve 4. Therefrigerant
that has radiated the heat in the heat radiator 3 and become a liquid phase refrigerant
expands in the expansion valve 4 as an expander.
A pipe 8e supplies the refrigerant that has expanded by the expansion valve 4
and entered a gas-liquid mixed phase state to the tank 5.
[0022]
A pipe 8f connects a portion below a liquid level L of the tank 5 to the suction
side of the pump 6, and a pipe 8g connects a discharge side of the pump 6 to the heat
receiver 1.
The liquid phase refrigerant obtained by the gas and liquid separation in the tank
is sucked into the pump 6 via the pipe 8f and supplied to the heat receiver 1 via the pipe
8g. Then, in the heat receiver 1, heat is received from a heat source such as an exhaust
gas of the server, the refrigerant flows into the tank 5 again and circulates in the
refrigeration cycle.
[0023]
A temperature sensor T measures the temperature of the refrigerant at a position
immediately before the refrigerant is sucked into the pump 6 in the middle of the pipe 8f,
and a pressure sensor P similarly measures the pressure of the refrigerant at the position
immediately before the refrigerant is sucked into the pump 6.
[0024]
The control unit 7 calculates the required amount of increase in pressure of the
compressor 2 from data of the temperature and the pressure input from the temperature
sensor T and the pressure sensor P, a calculation equation for a required amount of
increase in pressure stored in a database DB1, and a calculation equation for the required
suction head stored in a database DB2, and controls the compressor 2. Details of the
control of the control unit 7 will be described below with reference to Fig. 5 together
with the operation of the cooling device.
[0025]
Control content of the control unit 7 will be described together with the
operation of the cooling device of the first embodiment having the configuration of Fig. 6
with reference to a flowchart of Fig. 5.
SP11
Control is executed on condition that the compressor 2 is operated and the
refrigerant is circulated in the refrigeration cycle.
SP12
The temperature of the refrigerant increases by the refrigerant receiving heat in the heat receiver 1 with an increase in the outside air temperature (the temperature inside the server room).
SP13
The control unit 7 refers to the database DB1 to acquire the amount of increase
in pressure required for the compressor 2. Specifically, the required amount of increase
in pressure obtained by using Equation (2) in which the amount of increase At of a
refrigerant liquid temperature is multiplied by the predetermined constant K is acquired.
The databases DB1 and DB2 to be described below are mounted in a memory as a
control program or storage data in the control unit 7, or are stored in a server physically
separate from the control unit 7 and send and receive data via a communication line.
Required amount of increase in pressure = K x At -- Equation (2)
SP14
The control unit 7 acquires measurement values required for calculation,
specifically, data of the refrigerant temperature of a suction port of the pump 6 from the
temperature sensor T, and data of a refrigerant pressure of the suction port of the pump 6
from the pressure sensor P.
SP15
The control unit 7 refers to the database DB2 to acquire data of the amount of
increase in pressure required for the compressor 2. The database DB2 calculates the
saturated vapor pressure and the refrigerant liquid density of the refrigerant from the
refrigerant liquid temperature T (or acquires the saturated vapor pressure and the
refrigerant liquid density from an existing data table stored in the database DB2),
calculates the net positive suction head from a gravitational acceleration of 9.8 kg/s2
using Equation (1), and calculates the amount by which the pressure of the compressor 2
can be increased by using Equation (3) below.
Amount by which pressure can be increased = f x (net positive suction head
required suction head) --- Equation (3)
Here, f is a constant that is set in consideration of a safety factor in which the
operational fluctuation in the amount by which the pressure of the compressor 2 can be
increased, which is determined on the basis of a head difference, is anticipated.
SP16
The control unit 7 limits the increase in the pressure of the compressor 2 to the
amount by which the pressure can be increased and increases the pressure of the
compressor 2. Specifically, rotation of the compressor 2 is controlled. Here, the pump
inlet pressure in Equation (1) above is decreased due to the increase in the pressure of the
compressor 2, but the net positive suction head can be maintained to be a predetermined
value or more due to the decrease in the refrigerant temperature and the decrease in the
saturated vapor pressure due to the increase in the pressure and heat radiation.
SP17
The control unit 7 determines whether or not the compressor 2 has reached a
predetermined amount of increase in pressure, returns to SP14 according to a
determination result to repeat control of the amount of increase in pressure, and proceeds
to the next step on condition that the compressor 2 has reached the predetermined amount
of increase in pressure.
SP18
The increase in pressure ends when the compressor 2 has reached the
predetermined amount of increase in pressure (then, a steady operation according to the
predetermined amount of increase in pressure is continued).
Although the net positive suction head decreases when the compressor 2 reaches
the predetermined amount of increase in pressure, it is possible to maintain the predetermined net positive suction head by decreasing the temperature as the refrigerant is compressed and dissipated.
[0026]
In the calculation of the net positive suction head based on Equation (1) above,
the pump inlet pressure P, a refrigerant temperature T decreases with the increase in
pressure of the refrigerant by the compressor 2, and the saturated vapor pressure
decreases with the decrease in the refrigerant temperature. In this embodiment, it is
assumed that the density of the refrigerant is constant regardless of the change in the
refrigerant temperature T.
[0027]
By the control unit 7 executing the above control to limit the increase in the
pressure of the compressor 2 and curb the decrease in the pressure inside the tank 5, it is
possible to maintain the pressure of the refrigerant sucked into the pump 6 below the net
positive suction head and prevent cavitation of the refrigerant in the pump 6.
[0028]
The operation and effects of the first embodiment will be further described with
reference to Figs. 3 and 4.
Fig. 3 illustrates a comparative example in a case in which restriction of the
increase in the pressure of the compressor 2 is not performed. In the figure, the
horizontal axis indicates the passage of time, but the vertical axis does not indicate
changes in absolute values of temperature, pressure, and the like, but is an index merely
indicating relative changes in the values over time.
Here, in the figure, a dashed line a indicates change in the amount of increase in
pressure due to the drive of the compressor 2, an alternating chain line b indicates change
in the pressure inside the tank 5, a dashed linec indicates change in the refrigerant temperature due to the increase in the pressure of the compressor 2, a chain line d indicates change in the saturated vapor pressure of the refrigerant, a thick line e indicates a change in the net positive suction head, and a thin line f indicates a required suction head with less concern of causing cavitation.
Specifically, in the vertical axis of Figs. 3 and 4, the dashed line a indicates the
rotation speed (of the drive motor) of the compressor 2, the chain line b indicates the
pressure inside the tank 5, the dashed line c indicates the temperature of the refrigerant,
the chain line d indicates the saturated vapor pressure of the refrigerant, and the solid
lines e and f indicate a net positive suction head (NPSH) and pressure of the required
suction head.
[0029]
The compressor 2 is activated, an increase in the pressure (compression) of the
refrigerant is started, a degree of increase in the pressure of the compressor 2 increases as
indicated by the dashed line a (more specifically, the rotation speed of the drive motor of
the compressor 2 increases), and the refrigerant is compressed. Further, the pressure
inside the tank 5 decreases with a time delay as indicated by the chain line b due to the
suction of the compressor 2. By the compressed refrigerant circulating in the
refrigeration cycle, the temperature of the refrigerant, which was initially room
temperature, decreases further after the pressure decrease, as indicated by the dashed line
c. The saturated vapor pressure of the refrigerant indicated by the chain line d decreases
with the decrease in the temperature (which depends on physical characteristics of the
refrigerant having a predetermined composition). Further, as indicated by a solid line e,
the net positive suction head of the pump 6 decreases due to suction pressure (negative
pressure) with the increase in pressure indicated by the dashed line a and the changes
indicated by the chain lines b and d.
[0030]
The net positive suction head falls below the required suction head, which is a
lower limit of the pressure that does not cause cavitation in the pump 6, during a period
from time tl to t2 due to this decrease in the net positive suction head. That is, because
a required refrigerant cannot be supplied from the pump 6 to the heat receiver 1 due to
the occurrence of the cavitation, it is inevitable that a cooling capacity becomes
insufficient. Thereafter, when the pressure of the compressor 2 continuously increases,
the refrigerant flows into the tank 5 via the heat radiator 3 and the expansion valve 4, and
the refrigerant is stored until the liquid level L reaches a predetermined height or higher,
the net positive suction head increases as indicated by the solid line e, and the state in
which the pump 6 can normally supply the refrigerant to the heat receiver 1 when the net
positive suction head exceeds the required suction head at time t2 is obtained.
Thus, a predetermined time elapses since the pressure of the compressor 2 is
increased, the amount of refrigerant sent by the pump 6 is stable, the refrigerant
temperature, the pressure in the gas-liquid separator, and the saturated vapor pressure are
all stable, and refrigerant is circulated in the refrigeration cycle.
[0031]
On the other hand, according to the control by the operation of the first
embodiment illustrated in Fig. 4, when the net positive suction head decreases to such an
extent that the net positive suction head indicated by the solid line e approaches the
required suction head indicated by a solid line f due to the control of the net positive
suction head in the control unit 7, the control unit 7 curbs an increase in the amount of
increase in pressure of the compressor 2. That is, the increase in the pressure of the
compressor 2 is curbed each time a net positive suction head e decreases to the extent
that the net positive suction head e approaches a required suction head f, to achieve recovery of the net positive suction head e, thereby making it possible to prevent cavitation from occurring in the pump 6 and stably supply the refrigerant to the heat receiver 1.
[0032]
Further, because the refrigerant can circulate in the refrigeration cycle while the
occurrence of cavitation is curbed, the pressure inside the tank 5 gradually decreases
linearly as indicated by the chain line b in Fig. 4, the temperature of the refrigerant also
decreases linearly as indicated by the chain line d, and a stable state is obtained.
[0033]
In order to curb the increase in the pressure of the compressor 2, it is possible to
use a means such as rotation speed control of the drive motor of the compressor 2 and a
temporary unloading operation.
[0034]
In the first embodiment, because the net positive suction head of the pump 6 can
be maintained above the required suction head, it is possible to stably supply the
refrigerant from the pump 6 to the heat receiver 1 without causing cavitation immediately
after the start of the operation of the refrigeration cycle.
[0035]
(Second Embodiment)
A second embodiment of the present invention will be described with reference
to Fig. 7. In Fig. 7, the same components as those in Figs. 1 and 6 are denoted by the
same reference signs and a description thereof will be simplified.
In the second embodiment, a suction side and a discharge side of a pump 6 are
connected by a bypass pipe 8h, a bypass valve 9a is provided in the middle of the bypass
pipe 8h, and a degree of opening of the bypass valve 9a is controlled by the control unit
7.
[0036]
Even in the second embodiment, the control unit 7 performs control according to
the same processing as the flowchart illustrated in Fig. 5 that is executed in the first
embodiment.
That is,
SP11
Control is executed on condition that the compressor 2 is operated and the
refrigerant is circulated in the refrigeration cycle.
SP12
The temperature of the refrigerant increases by the refrigerant receiving heat in
the heat receiver 1 with an increase in the outside air temperature (the temperature inside
the server room).
SP13
The control unit 7 refers to the database DB1 to acquire the amount of increase
in pressure required for the compressor 2. Specifically, the control unit 7 acquires the
required amount of increase in pressure obtained by using Equation (2) above in which
the amount of increase At of the refrigerant liquid temperature is multiplied by the
predetermined constant K.
SP14
The control unit 7 acquires measurement values required for calculation,
specifically, data of the refrigerant temperature from the temperature sensor T, and data
of a refrigerant pressure from the pressure sensor P. In the second embodiment, the
control unit 7 acquires data of the temperature and the pressure of the refrigerant that is
sucked into the pump 6 again from the bypass pipe 8h on the suction side of the pump 6.
SP15
The control unit 7 refers to the database DB2 to acquire data of the amount of
increase in pressure required for the compressor 2. The database DB2 calculates the
saturated vapor pressure and the refrigerant liquid density of the refrigerant from the
refrigerant liquid temperature T (or acquires the saturated vapor pressure and the
refrigerant liquid density of the refrigerant from the table stored in the database DB2),
calculates the net positive suction head from a gravitational acceleration 9.8 kg/s2 using
Equation (1), and calculates the amount by which the pressure of the compressor 2 can be
increased using Equation (3) above.
SP16
The control unit 7 limits the amount by which the pressure can be increased and
increases the pressure of the compressor 2. Specifically, rotation of the compressor 2 is
controlled.
SP17
The control unit 7 determines whether or not the compressor 7 has reached a
predetermined amount of increase in pressure, returns to SP14 according to a
determination result to repeat control of the amount of increase in pressure, and proceeds
to the next step on condition that the compressor 2 has reached the predetermined amount
of increase in pressure.
SP18
The increase in pressure ends when the compressor 2 has reached the
predetermined amount of increase in pressure (then, a steady operation according to the
predetermined amount of increase in pressure is continued).
Respective steps thereof are executed.
[0037]
Further, in the second embodiment, when the flow rate of the refrigerant
becomes extremely small as a result of curbing the amount of increase in pressure of the
compressor 2 in order to maintain the net positive suction head when steps SP11 to SP18
above are executed, the bypass valve 9a is opened to return the refrigerant from the
discharge side of the pump 6 to the suction side via the bypass pipe 8h so that the
refrigerant is sucked into the pump 6 again.
Thus, by circulating a part of the refrigerant to be supplied to the heat receiver 1,
it is possible to secure the minimum refrigerant flow rate for continuity of the operation
(sending of the refrigerant) of the pump 6 and to prevent cavitation from occurring due to
a reduction of the suction flow rate.
Also in the second embodiment, it is possible to secure the net positive suction
head sucked into the pump 6 and stably send the refrigerant using the pump 6.
[0038]
(Third Embodiment)
A third embodiment of the present invention will be described with reference to
Figs. 8 to 11. In Figs. 8, 9, and 10, the same components as those in Figs. 1 and 6 are
denoted by the same reference signs and a description thereof will be simplified.
In the third embodiment, a regulation valve 9b is included in a pipe 8b on the
suction side of a compressor 2. The regulation valve 9b adjusts a flow rate of a gas
phase refrigerant sucked into the compressor 2, and it is possible to prevent pressure
inside the tank 5 from excessively decreasing and thus maintain a net positive suction
head, by decreasing a degree of opening of the regulation valve 9b to curb the amount of
the refrigerant sucked from a tank 5.
Further, a DB3 for calculating a required amount of increase in pressure that is
obtained by using Equation 2 in which the amount of increase At of the refrigerant liquid temperature is multiplied by the predetermined constant K, and also calculating the degree of opening of the regulation valve 9b from the amount of increase in pressure of the compressor, and a DB4 for calculating the saturated vapor pressure and the refrigerant liquid density from the refrigerant liquid temperature, and calculating the net positive suction head are mounted in the control unit 7.
[0039]
The operation of the cooling device of the third embodiment having the
configuration of Fig. 9 and control content of the control unit 7 will be described with
reference to a flowchart of Fig. 8.
SP1l
Control is executed on condition that the compressor 2 is operated and the
refrigerant is circulated in the refrigeration cycle.
SP12
The temperature of the refrigerant increases by the refrigerant receiving heat in
the heat receiver 1 with an increase in the outside air temperature (the temperature inside
the server room).
SP33
The control unit 7 refers to the database DB3 to acquire the amount of increase
in pressure required for the compressor 2. Specifically, the required amount of increase
in pressure that is obtained by using Equation (2) in which the amount of increase At of
the refrigerant liquid temperature is multiplied by the predetermined constant K is
calculated.
The required amount of increase in pressure calculated from amount of increase
in refrigerant liquid temperature = K x At --- Equation (2)
K is a constant for conversion of the amount of temperature increase into the amount of increase in pressure.
Degree of opening of regulation valve 9b at compressor inlet = Kv x required
amount of increase in pressure --- Equation (4)
Kv is a constant for converting the degree of opening of the regulation valve 9b
required to obtain the amount of increase in pressure from the required amount of
increase in pressure in anticipation of a predetermined safety factor.
SP34
The control unit 7 controls rotation of the compressor 2 to obtain a
predetermined required amount of increase in pressure based on Equation (2) above, and
adjusts the degree of opening of the regulation valve 9b to a predetermined degree of
opening based on Equation (4) above.
SP35
The control unit 7 acquires data of refrigerant temperature at a suction port of
the pump 6 from a temperature sensor T and data of refrigerant pressure at the suction
port of the pump 6 from a pressure sensor P.
[0040]
SP36
The control unit 7 refers to the database DB4 to calculate the saturated vapor
pressure and the refrigerant liquid density from the refrigerant liquid temperature. The
gravitational acceleration is 9.8 m/sec 2, and the required suction head is a value
determined according to a specification of the pump 6. The required suction head is
calculated by using Equation (1) above, and a changeable amount of the degree of
opening of the regulation valve 9b is calculated from the required suction head by using
Equation (5) below.
Changeable amount of degree of opening = fl x (net positive suction head - required suction head) --- Equation (5) fl in Equation (5) is a coefficient for converting the amount by which the pressure can be increased from a head difference in anticipation of a safety factor, and is, in this case, a constant that is determined by a specification (a flow rate according to the degree of opening) of the regulation valve 9b.
SP37
The control unit 7 limits the changeable amount of the degree of opening
calculated in SP36 above and opens the regulation valve 9b. More specifically, a
command according to the degree of opening is output to a circuit that drives an actuator
(not illustrated) that operates the regulation valve 9b. The amount of refrigerant
according to the degree of opening of the regulation valve 9b according to this command
is sucked into the compressor 2, the pressure of the refrigerant is increased, and the
refrigerant is circulated in a refrigeration cycle.
SP38
The control unit 7 determines whether the regulation valve 9b reaches a
predetermined degree of opening, repeats SP35 to SP37 above until the regulation valve
9b reaches a predetermined degree of opening, and proceeds to SP18 to complete the
increase in the pressure when the regulation valve 9b reaches the predetermined degree
of opening (thereafter, a steady operation according to a predetermined amount of
increase in pressure is continued).
Here, because the amount of suction into the compressor 2 is limited by the
regulation valve 9b, a phenomenon that the pressure inside the tank 5 decreases below
the required suction head is curbed, and therefore, it is possible to prevent cavitation in
the pump 6 from occurring.
[0041]
An example of an effect of curbing the decrease in the net positive suction head
regardless of the amount of increase in pressure of the compressor 2 according to control
for adjusting the degree of opening of the regulation valve 9b will be described in detail
with reference to Figs. 10 and 11.
A relationship between the degree of opening of the regulation valve 9b and
change in the amount of increase in pressure (a compression ratio of the compressor 2) is
arranged as a relationship illustrated in a chart of Fig. 11, in which pressure on the
upstream side of the regulation valve 9b provided at the inlet of the compressor 2 is A,
pressure on the suction side of the compressor 2 on the downstream side is B, and
pressure on the outlet side of the compressor 2 on the downstream side is C, as illustrated
in Fig. 10.
[0042]
In a case in which the degree of opening of the regulation valve 9b is 100%, that
is, a case in which the regulation valve 9b is not provided as a comparative example, for
example, the pressures A and B are 100 kPa (kilopascal) and the pressure C at the outlet
of the compressor 2 is 150 kPa, and the amount of increase in the pressure (the
compression ratio) is 1.5 times.
Further, the pressure at the outlet of the compressor 2 is determined by the
amount of heat radiation based on the difference between the heat radiator 3 on the
downstream side and the outside temperature when the degree of opening of the
regulation valve 9b is set to 100% and the degree of opening is not controlled, and
therefore, when the pressure at the outlet of the compressor 2 is, for example, 150 kPa,
the pressures on the upstream and downstream sides of the regulation valve 9b become
kPa, which is half of the pressure at the outlet of the compressor 2, in order to obtain a
double compression ratio. As a result, because the pressure inside the tank 5 decreases, the net positive suction head of the pump 6 may be equal to or smaller than the required suction head.
[0043]
On the other hand, in a case in which the degree of opening of the regulation
valve 9b is controlled by the control unit 7 so that the degree of opening is 60%, even
when the pressure B on the downstream side of the regulation valve 9b is 75 kPa, the
pressure C at the outlet of the compressor 2 is 150 kPa, and the compression ratio is
doubled, it is possible to set the pressure A on the upstream side of the regulation valve
9b to about 95 kPa, curb a decrease in pressure inside the tank 5, and maintain the net
positive suction head of the pump 6 to be equal to or greater than the required suction
head.
[0044]
(Fourth Embodiment)
A fourth embodiment of the present invention will be described with reference
to Figs. 12 and 13. In Fig. 13, the same components as those in Figs. 1, 6, 7, and 9 are
denoted by the same reference signs, and a description thereof will be simplified.
In the fourth embodiment, a heat radiator 3 that radiates heat of a refrigerant
compressed by a compressor 2 into atmosphere is provided with a fan 3a that supplies
cooling air to the heat radiator 3. Further, databases DBla and DB4a in which an
equation for calculating a net positive suction head as in the third embodiment and
calculating the amount by which the rotation speed of the fan 3a can be increased is
stored are mounted on a control unit 7.
[0045]
In the fourth embodiment, it is possible to adjust the temperature of a refrigerant
supplied to a tank 5 by controlling the amount of air of the fan 3a provided in the heat radiator 3 using the heat radiator 3, and to adjust the net positive suction head calculated by using Equation (1) through the adjustment of the refrigerant temperature.
[0046]
Control content of the control unit 7 will be described together with the
operation of the cooling device of the fourth embodiment with reference to a flowchart of
Fig. 12.
SP11
Control is executed on condition that the compressor 2 is operated and the
refrigerant is circulated in the refrigeration cycle.
SP12
The temperature of the refrigerant increases by the refrigerant receiving heat in
the heat receiver 1 with an increase in the outside air temperature (the temperature inside
the server room).
SP43
The control unit 7 determines whether or not an upper limit of increase in the
pressure (an upper limit of a discharge capacity) of the compressor 2 has been reached,
and proceeds to the next step 44 on condition that the upper limit has been reached.
When the upper limit has not been reached, for example, the rotation speed of a drive
motor is increased in order to further increase the pressure in the compressor 2.
[0047]
SP44
The control unit 7 refers to the database DBla to calculate the amount of
increase in rotation speed required for the fan 3a to blow the amount of air required for
heat radiation, from the amount of temperature increase of the liquid phase refrigerant.
Here, a required amount of increase in the rotation speed of the fan 3a is
Required amount of increase = K1 x increase value of refrigerant temperature
--- Equation (6)
KI is a constant that is determined by performance of the fan 3a and heat
radiation capacity of the heat radiator 3.
SP45
The control unit 7 acquires data of refrigerant temperature at a suction port of
the pump 6 from a temperature sensor T and data of refrigerant pressure at the suction
port of the pump 6 from a pressure sensor P.
[0048]
SP46
The control unit 7 refers to a database DB4a to calculate the saturated vapor
pressure and the refrigerant liquid density from the refrigerant liquid temperature. The
gravitational acceleration is 9.8 m/sec 2, and the required suction head is a value
determined according to a specification of the pump 6. The required suction head is
calculated by using Equation (1) above, and the amount by which the rotation speed of
the fan can be increased is calculated by using Equation (7) below.
Amount by which rotation speed of fan can be increased = f2 x (net positive
suction head - required suction head)
---- Equation (7)
f2 is a coefficient for conversion of the amount by which the power can be
increased from the head difference in anticipation of a safety factor, and is, in this case, a
constant determined by a specification of the fan 3a (the amount of blown air according
to the rotation speed).
SP47
The control unit 7 limits the rotation speed to the amount by which the rotation speed can be increased, which is calculated in SP46 above, and increases the rotation speed of the fan 3a. More specifically, a control signal is output to a drive circuit of a motor (not illustrated) that drives the fan 3a in order to obtain rotation at a predetermined rotation speed. Accordingly, the amount of heat radiation of the heat radiator 3 is limited, and the liquid phase refrigerant is limited to a predetermined temperature.
SP48
The control unit 7 determines whether the fan 3a has reached a predetermined
rotation speed, repeats SP45 to SP47 above until the fan 3a has reached the
predetermined speed, and proceeds to SP49 to end the control of the rotation speed of the
fan 3a when the fan 3a has reached the predetermined speed (thereafter, a steady
operation according to a predetermined amount of increase in pressure and amount of
heat radiation is continued).
[0049]
According to the curbing of the rotation speed of the heat radiation fan 3a, for
example, when the rotation speed of the fan 3a of the heat radiator 3 increases in order to
decrease the refrigerant temperature with an operation of increasing the pressure of the
compressor 2 to near an upper limit of a rated capacity thereof, it is possible to maintain
the net positive suction head of the refrigerant temperature by curbing the increase in the
rotation speed of the fan 3a when the pump inlet temperature decreases due to the
increased in pressure of the compressor 2 and the saturated vapor pressure decreases due
to the decrease in the refrigerant temperature in Equation (1).
The curbing of heat radiation according to curbing of the amount of air of the
fan 3a is suitably adopted for free cooling in which a heat medium is moved between the
heat receiver 1 and the heat radiator 3 without using a compressor (including a case in
which the refrigerant is caused to pass through with the compressor stopped or the compressor bypassed, in addition to a case in which the compressor is not provided in the first place), such as a case in which the outside air temperature is sufficiently low or when the refrigeration cycle is started.
As a modification example of the fan 3a that adjusts the amount of heat radiation
of the heat radiator 3, a mechanism (so-called louver) for adjusting an angle of a cooling
air adjustment plate 3b that adjusts the amount of outside air passing through the heat
radiator 3 as indicated by a dashed line in Fig. 13 is provided, the amount of outside air
flowing into the heat radiator 3 can be limited by adjusting an angle of the cooling air
adjustment plate 3b, or this can also be applied to a case in which a scheme of adjusting
the flow rate and temperature of cooling water coming into contact with a pipe through
which the refrigerant flows when the heat radiator 3 is a water-cooled type is adopted.
[0050]
(Fifth Embodiment)
A fifth embodiment of the present invention will be described with reference to
Figs. 14 and 15. In Fig. 15, the same components as those in Figs. 1, 6, 7, 9, and 13 are
denoted by the same reference signs and a description thereof will be simplified.
In the fifth embodiment, a heat radiator 3 that radiates heat of a refrigerant
compressed by a compressor 2 into atmosphere is provided with a fan 3a that supplies
cooling air to the heat radiator 3. Further, a database DB5 that calculates a net positive
suction head in consideration of the amount by which the pressure of the compressor 2
can be increased and the changeable amount of air amount of the fan 3a, in addition to
the database DB1, is mounted on a control unit 7.
The database DB5 calculates the saturated vapor pressure and the refrigerant
liquid density of the refrigerant from the refrigerant liquid temperature T (or acquires the
saturated vapor pressure and the refrigerant liquid density of the refrigerant from an existing data table stored in the database DB1), and calculates the net positive suction head from the gravitational acceleration 9.8 kg/s2 using Equation (1).
[0051]
Control content of the control unit 7 will be described together with the
operation of the cooling device of the fifth embodiment with reference to a flowchart of
Fig. 14.
SP11
Control is executed on condition that the compressor 2 is operated and the
refrigerant is circulated in the refrigeration cycle.
SP12
The temperature of the refrigerant increases by the refrigerant receiving heat in
the heat receiver 1 with an increase in the outside air temperature (the temperature inside
the server room).
SP13
The control unit 7 refers to the database DB1 to acquire the amount of increase
in pressure required for the compressor 2. Specifically, the required amount of increase
in pressure obtained by using Equation (2) in which the amount of increase At of the
refrigerant liquid temperature is multiplied by the predetermined constant K is acquired.
SP54
The control unit 7 acquires data of a pump inlet pressure from the pressure
sensor P and the data of refrigerant temperature from the temperature sensor T.
SP55
The control unit 7 obtains the net positive suction head from the database DB5
by using Equation (1), calculates the amount by which the pressure of the compressor 2
can be increased by using Equation (3) in which the difference between this net positive suction head and the required suction head is multiplied by the constant f, and multiplies the amount by which the pressure can be increased by a constant K2 to calculate the changeable amount of rotation speed of the fan 3a.
Changeable amount of rotation speed = K2 x amount by which pressure of
compressor can be increased --- Equation (8)
SP56
The control unit 7 limits the amount by which the pressure of the compressor 2
can be increased and then increases the rotation speed.
SP57
The control unit 7 decreases the rotation speed of the fan 3a within a range of
the calculated changeable amount, and curbs the amount of heat radiation of the heat
radiator 3.
SP17
The control unit 7 repeats SP54 to 57 above until the compressor 2 reaches the
predetermined amount of increase in pressure, and proceeds to the next step on condition
that the compressor 2 has reached the predetermined amount of increase in pressure.
SP18
The increase in pressure ends on the condition that the compressor 2 has reached
the predetermined amount of increase in pressure (then, a steady operation according to
the predetermined amount of increase in pressure is continued). Control for adjusting
the degree of opening of the regulation valve provided at the inlet of the compressor 2
adopted in the third embodiment may be adopted instead of the control of the increase in
the pressure of the compressor 2 that is performed in steps SP56 and SP57.
[0052]
In the fifth embodiment, it is possible to compensate for the pressure decrease of the tank 5 due to the increase in pressure of the compressor 2 through the decrease in the refrigerant temperature to curb a decrease in the net positive suction head and prevent cavitation from occurring in the pump 6 by decreasing the rotation speed of the fan 3a to increase the temperature of the refrigerant.
According to curbing of the rotation of the fan 3a, for example, it is possible to
curb excessive heat radiation of the heat radiator 3 immediately after the increase in the
pressure of the compressor 2 starts due to the an increase in the temperature of the server
room from a free cooling state in which the compressor 2 is not operated because the
temperature of the server room is low and the amount of heat received by the heat
receiver 1 is small, and to stabilize the operation of the pump 6.
[0053]
(Sixth Embodiment)
A sixth embodiment of the present invention will be described with reference to
Figs. 16 and 17. In Fig. 17, the same components as those in Figs. 1, 6, 7, 9, 13, and 15
are denoted by the same reference signs and a description thereof will be simplified.
In the sixth embodiment, a control unit 7 controls an inverter 6a that drives a
motor (not illustrated) that rotates a rotor of a pump 6, in addition to control of the
amount of increase in pressure of the compressor 2. Further, the control unit 7 receives
data from the pressure sensor P in the gas-liquid separator, the refrigerant temperature
sensor T in the gas-liquid separator, and a liquid level height sensor L in the gas-liquid
separator.
Further, the control unit 7 includes a database DB5a, and the database DB5a
calculates a net positive suction head by using Equation (') below.
Net positive suction head = liquid level height in gas-liquid separator + (pressure inside
gas-liquid separator - pipe pressure loss - saturated vapor pressure)/(refrigerant liquid density x gravitational acceleration) ---- Equation (1')
The pipe pressure loss can be calculated by multiplying the flow rate of the
refrigerant (determined by a flow velocity and a pipe diameter) by a predetermined
pressure loss coefficient a.
[0054]
Control content of the control unit 7 will be described together with the
operation of the cooling device of the sixth embodiment with reference to a flowchart of
Fig. 16.
SP11
Control is executed on condition that the compressor 2 is operated and the
refrigerant is circulated in the refrigeration cycle.
SP12
The temperature of the refrigerant increases by the refrigerant receiving heat in
the heat receiver 1 with an increase in the outside air temperature (the temperature inside
the server room).
SP13
The control unit 7 refers to the database DB1 to acquire the amount of increase
in pressure required for the compressor 2. Specifically, the required amount of increase
in pressure obtained by using Equation (2) in which the amount of increase At of the
refrigerant liquid temperature is multiplied by the predetermined constant K is acquired.
SP64
The control unit 7 acquires data of the pressure inside the tank 5 from the
pressure sensor P, the temperature of the refrigerant in the tank 5 from the temperature
sensor T, and the height of the liquid level L in the gas-liquid separation tank 5 from the
liquid level sensor L.
SP65
The control unit 7 obtains the net positive suction head from the database DB5a
by using Equation ('), and calculates the amount by which the pressure of the
compressor 2 can be increased by using Equation (3) in which the difference between
this net positive suction head and the required suction head is multiplied by the constant f.
Here, a pressure L in the tank decreases due to the increase in the pressure of the
compressor 2, a pressure loss occurs due to a flow path resistance of the pipe to the
suction port of the pump 6, and a net positive suction head corresponding to the pressure
of the suction port of the pump 6, which has reflected an influence of the decrease in the
saturated vapor pressure due to the decrease in the refrigerant temperature with the
increase in pressure of the compressor 2, is calculated. The constant f is a constant that
is set in consideration of a safety factor in which the operational fluctuation in the
amount by which the pressure of the compressor 2 can be increased, which is determined
on the basis of a head difference, is anticipated.
SP66
The control unit 7 limits the amount by which the pressure of the compressor 2
can be increased and then increases the pressure.
SP17
The control unit 7 repeats SP64 to 66 above until the compressor 2 reaches the
predetermined amount of increase in pressure, and proceeds to the next step on condition
that the compressor 2 has reached the predetermined amount of increase in pressure.
SP18
The increase in pressure ends on condition that the compressor 2 has reached the
predetermined amount of increase in pressure (then, a steady operation according to the
predetermined amount of increase in pressure is continued).
[0055]
According to the above configuration, it is possible to calculate the required
suction head that can prevent the occurrence of cavitation of the pump 6, on the basis of
the data acquired by the sensors provided in order to measure the pressure, the
temperature, and the liquid level in the tank 5 using the sensors without separately
providing sensors in the pipe 8f of the suction portion of the pump 6.
[0056]
(Seventh Embodiment)
A seventh embodiment of the present invention will be described with reference
to Figs. 18 and 19. In Fig. 19, the same components as those in Figs. 1, 6, 7, 9, 13, 15,
and 17 are denoted by the same reference signs and a description thereof will be
simplified.
In the seventh embodiment, a control unit 7 performs control according to the
number of pressure increase steps stored in a database DB6 and a waiting time until an
increase in pressure by the compressor 2 starts.
For the number of pressure increase steps, for example, data of pressure increase
steps of the compressor 2 that can maintain the net positive suction head without causing
cavitation in the pump 6 on the basis of operation record data of the refrigeration cycle
for each outside air temperature is collected and stored in advance. Further, the waiting
time is calculated by using Equation (9) below.
Waiting time = KT x amount of increase in pressure of compressor/total
refrigerant flow rate of heat receiver -- Equation (9)
KT is a time sufficient for the refrigerant temperature to begin to decrease with
an increase in the pressure, and is an constant that is determined on the basis of operation
record data for a degree of increase in pressure of the refrigeration cycle and occurrence or non-occurrence of the cavitation (the operation situation of the pump), and used to convert the flow rate into a waiting time.
The measurement of the amount of increase in pressure of the compressor and
the refrigerant flow rate is not limited to actual measurement values using sensors such as
a pressure sensor and a flow rate sensor, and the amounts may be obtained through
conversion from a load current of the drive motor of the compressor 2 and a load current
of a drive motor of the pump 6, that is, current values obtained from ammeters of the
respective motors.
[0057]
Control content of the control unit 7 will be described together with the
operation of the cooling device of the seventh embodiment with reference to a flowchart
of Fig. 18.
SP11
Control is executed on condition that the compressor 2 is operated and the
refrigerant is circulated in the refrigeration cycle.
SP12
The temperature of the refrigerant increases by the refrigerant receiving heat in
the heat receiver 1 with an increase in the outside air temperature (the temperature inside
the server room).
SP73
The control unit 7 acquires data of the amount of increase in pressure in each
predetermined step and a predetermined time to wait until the increase in pressure is
completed, from the database DB6.
SP74
The control unit 7 gradually increases the rotation speed of the compressor 2 to obtain the amount of increase in pressure in each step acquired from the database DB7.
Also, the temperature of the refrigerant begins to drop with the increase in pressure.
SP75
The control unit 7 compares a predetermined waiting time with an elapsed time
of the increase in pressure, and proceeds to the next step on condition that the waiting
time is exceeded.
SP76
The control unit 7 repeats SP74 to SP76 above until the temperature of the
refrigerant reaches a target value, and proceeds to the next step on condition that the
temperature of the refrigerant has reached a predetermined target value.
SP18
The increase in pressure of the compressor 2 ends when the refrigerant
temperature has reached the predetermined target value (then, a steady operation
according to the predetermined amount of increase in pressure is continued).
[0058]
According to the above configuration, it is possible to prevent the cavitation
from occurring in the pump 6 by gradually increasing the pressure using the compressor
2 over a predetermined time when the pressure of the refrigerant is expected to reach the
net positive suction head of the pump 6. Further, because the above control is executed
according to preset pressure increase steps, it is not necessary to provide sensors at
various places in the refrigeration cycle to measure the pressure, temperature, and the like,
and it is possible to simplify the configuration of a refrigeration device. This control is
suitable for shift from a so-called free cooling state in which the increase in pressure is
not performed by the compressor 2 and the heat is simply transferred from the heat
receiver 1 to the heat radiator 3 by the refrigerant, for example, when the temperature of the server room is not so high, to a state in which it is necessary to increase the pressure of the refrigerant using the compressor 2 due to temperature increase in the server room.
[0059]
Specific configurations of the heat receiver, the compressor, the heat radiator,
the gas-liquid separator, the expander, the pump, and the control unit that constitute the
refrigeration cycle are not limited to the embodiments and, of course, may be changed
without departing from the gist of the present invention. For example, the expander has
a function of depressurizing and expanding a refrigerant in a flow path of the liquid phase
refrigerant by applying a throttle to the flow path, and an orifice (simply, a throttle) or a
capillary (which is a thin tube having a predetermined length formed in a coil shape, and
gives resistance to a fluid by flowing through a flow path having a small cross-sectional
area) can be adopted, in addition to the valve in the embodiment.
[0060]
Further, control of the compressor, the heat radiator, and the valve that is
performed in the first to seventh embodiments is not limited to a single implementation,
and a plurality of controls may be implemented in combination. Further, when the
plurality of controls may be implemented in combination, any one of the controls may be
preferentially executed in consideration of conditions such as, for example, the response
speed to an increase or decrease of the net positive suction head, and the influence on
loads of refrigeration cycles of other systems.
[0061]
Some or all of the above embodiments may also be described as in the following
supplementary notes, but the present inventions is not limited thereto: In supplementary
notes 1 to 32, the compressor constituting the refrigeration cycle is not necessarily
limited to a device having a function of positively compressing a refrigerant, such as a compressor, and is assumed to include a component having an operation of substantially compressing a refrigerant without using special power, such as a pipe between the heat receiver and the heat radiator, according to so-called free cooling.
(Supplementary note 1)
A cooling device using a refrigeration cycle in which a refrigerant is circulated
through a heat receiver, a compressor, a heat radiator, and an expander, the cooling
device including: a gas-liquid separator configured to separate the refrigerant supplied
from the expander into a gas phase refrigerant and a liquid phase refrigerant; a pump
configured to send the liquid phase refrigerant separated by the gas-liquid separator to the
heat receiver; and a control unit configured to control the amount of increase in pressure
of the compressor in the refrigeration cycle, wherein the control unit limits a value of a
net positive suction head of the pump to a range in which the value does not fall below a
predetermined value and increases the pressure of the compressor.
(Supplementary note 2)
The cooling device according to supplementary note 1, wherein the control unit
calculates the net positive suction head from an inlet pressure of the pump, a saturated
vapor pressure of the refrigerant, and a density of the refrigerant.
(Supplementary note 3)
The cooling device according to supplementary note 1, wherein the control unit
calculates the net positive suction head from detection data of a pressure sensor and a
temperature sensor, the pressure sensor being configured to measure an inlet pressure of
the pump, the temperature sensor configured to measure the temperature of a liquid phase
portion of an inlet of the pump.
(Supplementary note 4)
The cooling device according to supplementary note 1, wherein the control unit calculates the net positive suction head from detection data of a pressure sensor and a temperature sensor, the pressure sensor being configured to measure the pressure of the refrigerant inside a bypass pipe configured to connect a discharge side to a suction side of the pump, the temperature sensor configured to measure the temperature of the refrigerant.
(Supplementary note 5)
The cooling device according to supplementary note 1, wherein the control unit
calculates the net positive suction head from the pressure, the temperature, and a liquid
level height of the refrigerant inside the gas-liquid separator.
(Supplementary note 6)
The cooling device according to supplementary note 1, wherein the control unit
increases the pressure of the compressor in a plurality of stages.
(Supplementary note 7)
The cooling device according to any one of supplementary notes 1 to 6, wherein
the control unit controls the amount of heat radiated from the heat radiator together with
the increase in pressure of the compressor.
(Supplementary note 8)
A control method for a cooling device using a refrigeration cycle in which a
refrigerant is circulated through a heat receiver, a compressor, a heat radiator, and an
expander, the control method including: limiting, by a control unit, a value of a net
positive suction head of a pump to a range in which the value does not fall below a
predetermined value, the pump being configured to suck a liquid phase refrigerant from a
gas-liquid separator and send the liquid phase refrigerant to the heat receiver, the
gas-liquid separator being configured to separate the refrigerant supplied from the
expander into a gas phase refrigerant and the liquid phase refrigerant; and controlling, by the control unit, an increase in the pressure of the compressor.
[0062]
(Supplementary note 9)
A control device for a cooling device using a refrigeration cycle in which a
refrigerant is circulated through a heat receiver, a compressor, a heat radiator, and an
expander, wherein the control device limits the amount of increase in the pressure of the
compressor to a range in which a value of a net positive suction head of a pump does not
fall below a predetermined value, the pump being configured to send a liquid phase
refrigerant separated by a gas-liquid separator to the heat receiver, the gas-liquid
separator being configured to separate the refrigerant supplied from the expander into a
gas phase refrigerant and the liquid phase refrigerant.
(Supplementary note 10)
A program for causing a computer to execute limitation of the amount of
increase in pressure in the control device according to supplementary note 9.
[0063]
(Supplementary note 11)
A cooling device using a refrigeration cycle in which a refrigerant is circulated
through a heat receiver, a compressor, a heat radiator, and an expander, the cooling
device including: a gas-liquid separator configured to separate the refrigerant supplied
from the expander into a gas phase refrigerant and a liquid phase refrigerant; a pump
configured to send the liquid phase refrigerant separated by the gas-liquid separator to the
heat receiver; and a control unit configured to control the amount of increase in pressure
of the compressor in the refrigeration cycle, wherein the control unit limits a value of a
net positive suction head of the pump to a range in which the value does not fall below a
predetermined value and controls a flow rate of the refrigerant sucked by the compressor.
(Supplementary note 12)
The cooling device according to supplementary note 11, wherein the control unit
controls a suction flow rate of the compressor according to a degree of opening of a
regulation valve provided in a pipe configured to supply a refrigerant from the gas-liquid
separator to the compressor.
(Supplementary note 13)
A control method for a cooling device using a refrigeration cycle in which a
refrigerant is circulated through a heat receiver, a compressor, a heat radiator, and an
expander, the control method including: limiting, by a control unit, a value of a net
positive suction head of the pump to a range in which the value does not fall below a
predetermined value, the pump being configured to suck a liquid phase refrigerant from a
gas-liquid separator configured to separate the refrigerant supplied from the expander
into a gas phase refrigerant and the liquid phase refrigerant; and adjusting, by the control
unit, the amount of suction of the refrigerant of the compressor.
(Supplementary note 14)
A control device for a cooling device using a refrigeration cycle in which a
refrigerant is circulated through a heat receiver, a compressor, a heat radiator, and an
expander, wherein the control device limits a value of a net positive suction head of a
pump to a range in which the value does not fall below a predetermined value , the pump
being configured to send a liquid phase refrigerant separated by a gas-liquid separator to
the heat receiver, the gas-liquid separator being configured to separate the refrigerant
supplied from the expander into a gas phase refrigerant and the liquid phase refrigerant,
and controls a flow rate of the refrigerant sucked by the compressor.
(Supplementary note 15)
A program for causing a computer to execute limitation of a flow rate of the refrigerant in the control device according to supplementary note 14.
[0064]
(Supplementary note 16)
A cooling device using a refrigeration cycle in which a refrigerant is circulated
through a heat receiver, a compressor, a heat radiator, and an expander, the cooling
device including: a gas-liquid separator configured to separate the refrigerant supplied
from the expander into a gas phase refrigerant and a liquid phase refrigerant; a pump
configured to send the liquid phase refrigerant separated by the gas-liquid separator to the
heat receiver; and a control unit configured to control the amount of increase in pressure
of the compressor in the refrigeration cycle, wherein the control unit limits a value of a
net positive suction head of the pump to a range in which the value does not fall below a
predetermined value and limits the amount of heat radiated from the heat radiator.
(Supplementary note 17)
The cooling device according to supplementary note 16, wherein the control unit
controls the amount of air sent by a fan configured to supply cooling air to the heat
radiator.
(Supplementary note 18)
A control method for a cooling device using a refrigeration cycle in which a
refrigerant is circulated through a heat receiver, a compressor, a heat radiator, and an
expander, the control method including: limiting, by a control unit, a value of a net
positive suction head of the pump to a range in which the value does not fall below a
predetermined value, the pump being configured to suck a liquid phase refrigerant from a
gas-liquid separator configured to separate the refrigerant supplied from the expander
into a gas phase refrigerant and the liquid phase refrigerant; and controlling, by the
control unit, the amount of heat radiated from the heat radiator.
(Supplementary note 19)
A control device for a cooling device using a refrigeration cycle in which a
refrigerant is circulated through a heat receiver, a compressor, a heat radiator, and an
expander, wherein the control device limits a value of a net positive suction head of a
pump to a range in which the value does not fall below a predetermined value, the pump
being configured to send a liquid phase refrigerant separated by a gas-liquid separator to
the heat receiver, the gas-liquid separator being configured to separate the refrigerant
supplied from the expander into a gas phase refrigerant and the liquid phase refrigerant,
and controls the amount of heat radiated from the heat radiator.
(Supplementary note 20)
A program for causing a computer to execute control of the amount of heat
radiated from the refrigerant in the control device according to supplementary note 19.
[0065]
(Supplementary note 21)
A cooling device using a refrigeration cycle in which a refrigerant is circulated
through a heat receiver, a compressor, a heat radiator, and an expander, the cooling
device including: a gas-liquid separator configured to separate the refrigerant supplied
from the expander into a gas phase refrigerant and a liquid phase refrigerant; a pump
configured to send the liquid phase refrigerant separated by the gas-liquid separator to the
heat receiver; and a control unit configured to control the amount of increase in pressure
of the compressor in the refrigeration cycle, wherein the control unit gradually increases
the pressure of the compressor over a predetermined time.
(Supplementary note 22)
A control method for a cooling device using a refrigeration cycle in which a
refrigerant is circulated through a heat receiver, a compressor, a heat radiator, and an expander, the control method including: gradually increasing, by a control unit, the pressure of the compressor over a predetermined time.
(Supplementary note 23)
A control device for a cooling device using a refrigeration cycle in which a
refrigerant is circulated through a heat receiver, a compressor, a heat radiator, and an
expander, wherein the control device gradually increases the pressure of a compressor
over a predetermined time, the compressor being configured to compress a liquid phase
refrigerant separated by a gas-liquid separator configured to separate the refrigerant
supplied from the expander into a gas phase refrigerant and the liquid phase refrigerant.
(Supplementary note 24)
A program for causing a computer to execute a stepwise increase in pressure
using the control device according to supplementary note 23.
[0066]
(Supplementary note 25)
A cooling device for controlling the net positive suction head in combination of
a plurality of controls executed by the respective control units according to
supplementary notes 1, 11, 16, and 21.
(Supplementary note 26)
The cooling device according to supplementary note 25, wherein, in the control
in which a plurality of controls executed by the control unit of the cooling device
according to supplementary notes 1, 11, 16 and 21 are combined, any one of the controls
is executed in preference to the other controls.
(Supplementary note 27)
A control method for controlling the net positive suction head in combination of
a plurality of controls executed by using the respective control methods according to supplementary notes 8, 13, 18, and 22.
(Supplementary note 28)
The cooling device according to supplementary note 27, wherein, in the control
in which a plurality of controls executed by using the respective control methods
according to supplementary notes 8, 13, 18, and 22 are combined, any one of the controls
is executed in preference to the other controls.
(Supplementary note 29)
A control device for controlling the net positive suction head in combination of a
plurality of controls executed by the respective control devices according to
supplementary notes 9, 14, 19, and 23.
(Supplementary note 30)
The control device according to supplementary note 29, wherein, in the control
in which a plurality of controls executed by the respective control device according to
supplementary notes 9, 14, 19, and 23 are combined, any one of the controls is executed
in preference to the other controls.
(Supplementary note 31)
A program for controlling the net positive suction head in combination of a
plurality of the processes that the respective programs according to supplementary notes
, 15, 20, and 24 cause a computer to execute.
(Supplementary note 32)
The program according to supplementary note 31, wherein, in the processes that
the respective programs according to supplementary notes 10, 15, 20, and 24 cause a
computer to execute, any one of the processes is executed in preference to the other
processes.
[0067]
The cooling device and cooling method of the present invention can be used for
air conditioning applications of a data center or the like.
Reference Symbols
[0068]
1 Heat receiver
2 Compressor
3 Heat radiator
3a Fan
3b Cooling air adjustment plate
4 Expander
5 Gas-liquid separator (tank)
6 Pump
7 Control unit
8a, 8b, 8c, 8d, 8e, 8f, 8g, 8h Pipe
9a Bypass valve
9b Regulation valve
DB1, DB1', DB2, DB3, DB3a Database
DB4, DB4a, DB5, DB5a Database
T Temperature sensor
P Pressure sensor
L Liquid level sensor
Claims (8)
1. A cooling device using a refrigeration cycle in which a refrigerant is circulated
through a heat receiver, a compressor, a heat radiator, and an expander, the cooling
device comprising:
a gas-liquid separator configured to separate the refrigerant supplied from the
expander into a gas phase refrigerant and a liquid phase refrigerant;
a pump configured to send the liquid phase refrigerant separated by the
gas-liquid separator to the heat receiver; and
a control unit configured to control an amount of increase in pressure of the
compressor in the refrigeration cycle,
wherein the control unit limits a value of a net positive suction head of the pump
to a range in which the value does not fall below a predetermined value and increases the
pressure of the compressor.
2. The cooling device according to claim 1, wherein the control unit calculates the
net positive suction head from an inlet pressure of the pump, a saturated vapor pressure
of the refrigerant, and a density of the refrigerant.
3. The cooling device according to claim 1, wherein the control unit calculates the
net positive suction head from detection data of a pressure sensor and a temperature
sensor, the pressure sensor being configured to measure an inlet pressure of the pump, the
temperature sensor configured to measure a temperature of a liquid phase portion of an
inlet of the pump.
4. The cooling device according to claim 1, wherein the control unit calculates the
net positive suction head from detection data of a pressure sensor and a temperature
sensor, the pressure sensor being configured to measure a pressure of the refrigerant
inside a bypass pipe configured to connect a discharge side to a suction side of the pump,
the temperature sensor configured to measure a temperature of the refrigerant.
5. The cooling device according to claim 1, wherein the control unit calculates the
net positive suction head from a pressure, a temperature, and a liquid level height of the
refrigerant inside the gas-liquid separator.
6. The cooling device according to claim 1, wherein the control unit increases the
pressure of the compressor in a plurality of stages.
7. The cooling device according to any one of claims 1 to 6, wherein the control
unit controls an amount of heat radiated from the heat radiator together with the increase
in pressure of the compressor.
8. A control method for a cooling device using a refrigeration cycle in which a
refrigerant is circulated through a heat receiver, a compressor, a heat radiator, and an
expander, the control method comprising:
limiting, by a control unit, a value of a net positive suction head of a pump to a
range in which the value does not fall below a predetermined value, the pump being
configured to suck a liquid-phase refrigerant from a gas-liquid separator and send the
liquid phase refrigerant to the heat receiver, the gas-liquid separator being configured to
separate the refrigerant supplied from the expander into a gas phase refrigerant and the liquid phase refrigerant; and controlling, by the control unit, an increase in the pressure of the compressor.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| PCT/JP2021/030413 WO2023021660A1 (en) | 2021-08-19 | 2021-08-19 | Cooling device and method for conrolling cooling device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| AU2021398580A1 true AU2021398580A1 (en) | 2023-03-09 |
Family
ID=81926018
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| AU2021398580A Abandoned AU2021398580A1 (en) | 2021-08-19 | 2021-08-19 | Cooling device and control method for cooling device |
Country Status (3)
| Country | Link |
|---|---|
| JP (2) | JP7081731B1 (en) |
| AU (1) | AU2021398580A1 (en) |
| WO (1) | WO2023021660A1 (en) |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR101168945B1 (en) * | 2003-11-21 | 2012-08-02 | 마에카와 매뉴팩쳐링 캄파니 리미티드 | Ammonia/co2 refrigeration system, co2 brine production system for use therein, and ammonia cooing unit incorporating that production system |
| JP2011196607A (en) * | 2010-03-19 | 2011-10-06 | Toyo Eng Works Ltd | Cooling system |
| JP2017020687A (en) * | 2015-07-09 | 2017-01-26 | パナソニックＩｐマネジメント株式会社 | Refrigeration cycle apparatus |
| JP6927229B2 (en) | 2016-09-21 | 2021-08-25 | 日本電気株式会社 | Phase change cooling device and phase change cooling method |
| JP6978363B2 (en) | 2018-03-27 | 2021-12-08 | 株式会社コロナ | Heat pump heat source machine |
-
2021
- 2021-08-19 AU AU2021398580A patent/AU2021398580A1/en not_active Abandoned
- 2021-08-19 JP JP2022510105A patent/JP7081731B1/en active Active
- 2021-08-19 WO PCT/JP2021/030413 patent/WO2023021660A1/en unknown
-
2022
- 2022-05-23 JP JP2022083923A patent/JP2023029214A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| JPWO2023021660A1 (en) | 2023-02-23 |
| EP4160115A1 (en) | 2023-04-05 |
| JP7081731B1 (en) | 2022-06-07 |
| WO2023021660A1 (en) | 2023-02-23 |
| JP2023029214A (en) | 2023-03-03 |
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