WO2020084790A1

WO2020084790A1 - Cooling system, control device therefor, method of cooling, and program

Info

Publication number: WO2020084790A1
Application number: PCT/JP2018/040786
Authority: WO
Inventors: Nirmal Singh RAJPUT; Yoshinori Miyamoto; Takafumi Natsumeda; Masaki Chiba; Koichi Todoroki
Original assignee: Nec Corporation
Priority date: 2018-10-26
Filing date: 2018-10-26
Publication date: 2020-04-30
Also published as: JP7259950B2; JP2022512819A

Abstract

The present disclosure provides, a control device for a cooling system including a heat exchanger, measurement sensors, and a cooling cycle unit configured to provide compressor cooling and free cooling to the heat exchanger, the control device including: a processing unit; and an I/O unit configured to receive from the measurement sensors: a refrigerant inlet pressure to the heat exchanger measurement; a refrigerant outlet pressure; a refrigerant inlet temperature; a refrigerant outlet temperature; an outdoor environment temperature; and a refrigerant flow rate; wherein the processing unit is configured to output a command to the cooling cycle unit to switch between a compressor cooling cycle and a free cooling cycle based on the refrigerant inlet pressure to the heat exchanger; the refrigerant outlet pressure; the refrigerant inlet temperature; the refrigerant outlet temperature; the outdoor environment temperature; and the refrigerant flow rate.

Description

[DESCRIPTION]

[Title of Invention]

COOLING SYSTEM, CONTROL DEVICE THEREFOR, METHOD OF COOLING,

AND PROGRAM

[Technical field]

[0001]

The. present invention relates to a cooling system, a cooling system controller, method of cooling, and program which allow for energy consumption reduction. More specifically, the present invention relates to system for reducing data center cooling system power consumption while maintaining a desired environmental temperature.

[Background Art]

[0002]

Energy conservation in data center cooling systems has a high impact on overall data center energy consumption savings. Energy conservation in such cooling systems can be achieved by operating free cooling cycle using local level cooling systems. However, free cooling cycle has cooling capacity limitations, and therefore, whenever required, the cooling cycle is switched to compression cooling. Appropriate cooling cycle switching methods/algorithms should be used for maximizing energy conservation and safe cooling system operation in data centers.

[0003]

Data center cooling systems typically employ two kinds of cooling cycles, compression cooling and free cooling. Compression cooling can provide year-round cooling irrespective of the outside temperature, but consumes high electrical energy. On the other hand, free cooling consumes relatively lower electrical energy, but can only provide a required cooling capacity when the outside environment temperature is sufficiently low. Therefore, to save energy, free cooling cycle should be operated as much as possible but at the same time, sufficient cooling must be ensured for safe data center operation.

[0004]

FMACS-V hybrid is one example of room level cooling system, i.e. placed at the end of rack rows and provides cooling to all racks in a designated rack row, utilizing compressor and free cooling cycles. To reduce the excess electrical power consumption due to excess cooling characteristics of a room level cooling system, local level cooling systems for data centers are being employed.

[0005]

A local level cooling system is placed near a designated rack and provides cooling to the rack and eliminates the need for excess cooling. To further reduce energy consumption, these local level cooling systems can also use an appropriate cooling cycle switching method to switch between compressor and free cooling cycles.

Several techniques have attempted to solve one or more of the above problems such as those taught in Patent Citations 1-3 (specified below), but have shortcomings in their considerations and/or solutions as compared with the present invention, and are unable to achieve the technical effects of the present invention alone or in combination.

[0006]

Generally, an appropriate cooling cycle switching method, such as that disclosed in Non Patent Citation 1, utilizes the outside environment temperature and the exhausted heat load to decide the appropriate cooling cycle. However, switching between the compressor cooling cycle and the free cooling cycle should not merely focus on energy conservation and must satisfy the cooling needs of the heat load. Otherwise, insufficient data center cooling could result and may lead to data center failure.

[Citation List]

[Patent Literature]

[PTL 1]

WO2015/004742; Komatsu et. al.; Thermal Load Predicting Device, Distribution System, Thermal Load Predicting Method, and Program

[PTL 2]

Japanese Published Application 2011-247433; Miyajima et al; Facility and Method of Producing Cold Water

[PTL 3]

Japanese Published Application 2009-252056; Kato et al; Method and Device for Operation Management of Information-Processing System

[Non Patent Literature]

[NPL 1]

N. Futawatari et. al.; Packaged air conditioner incorporating free cooling cycle for data centers

[Summary of Invention]

[Technical Problem]

[0007] An exemplary object of the present disclosure is to provide a cooling system for a server rack which can efficiently switch between modes of cooling, i.e., free cooling cycle and compressor cooling cycle, depending on environmental and system measurements taken by various sensors, in order to reduce the power consumed by the cooling system and to appropriately cool electronic equipment contained in the server rack.

[Solution to Problem]

[0008]

An appropriate cooling cycle should be determined on the basis of the outside environment temperature, the exhausted heat load, and the refrigerant inlet temperature to the heat exchanger near rack outlet.

[0009]

As a first exemplary aspect of the present disclosure, a cooling system is provided including a server rack; a heat exchanger configured to produce cooled air; a first pressure sensor configured to measure refrigerant inlet pressure to the heat exchanger; a second pressure sensor configured to measure refrigerant outlet pressure of the heat exchanger; a first temperature sensor configured to measure refrigerant inlet temperature to the heat exchanger; a second temperature sensor configured to measure refrigerant outlet temperature of the heat exchanger; a third temperature sensor configured to measure outdoor environment temperature; a flow rate sensor configured to measure a refrigerant flow rate to the heat exchanger; and a controller configured to switch between a compressor cooling cycle and a free cooling cycle based on measurement data received by the first, second, and third temperature sensors, the flow rate sensor and the first and second pressure sensors, wherein the compressor cooling cycle utilizes the compressor for cooling server rack exhaust air, and the free cooling cycle utilizes outside environment air for cooling the server rack exhaust air..

[0010]

As a second exemplary aspect of the present disclosure, a control device is provided for a cooling system of a server rack. The cooling system includes a heat exchanger, measurement sensors, and a cooling cycle unit configured to provide compressor cooling and free cooling to the heat exchanger. The control device includes: a processing unit; and an I/O unit configured to receive from the measurement sensors: a refrigerant inlet pressure to the heat exchanger measurement; a refrigerant outlet pressure measurement; a refrigerant inlet temperature measurement; a refrigerant outlet temperature measurement; an outdoor environment temperature measurement; and a refrigerant flow rate measurement; wherein the processing unit is configured to output a command to the cooling cycle unit to switch between a compressor cooling cycle and a free cooling cycle based on the refrigerant inlet pressure to the heat exchanger measurement; the refrigerant outlet pressure measurement; the refrigerant inlet temperature measurement; the refrigerant outlet temperature measurement; the outdoor environment temperature measurement; and the refrigerant flow rate measurement.

[0011]

As a third exemplary aspect of the present disclosure, a cooling method is provided for a server rack. The cooling method includes: measuring a refrigerant inlet pressure to a heat exchanger; measuring a refrigerant outlet pressure of the heat exchanger; measuring a refrigerant inlet temperature to the heat exchanger; measuring a refrigerant outlet temperature of the heat exchanger; measuring outdoor environment temperature; measuring a refrigerant flow rate to the heat exchanger; and determining whether to operate a compressor cooling cycle or a free cooling cycle based on a relationship between the refrigerant inlet pressure; the refrigerant outlet pressure; the refrigerant inlet temperature; the refrigerant outlet temperature; the outdoor environment temperature; and the refrigerant flow rate.

[0012]

As a fourth exemplary aspect of the present invention, a program is provided which causes a computer to execute: measuring a refrigerant inlet pressure to a heat exchanger; measuring a refrigerant outlet pressure of the heat exchanger; measuring a refrigerant inlet temperature to the heat exchanger; measuring a refrigerant outlet temperature of the heat exchanger; measuring outdoor environment temperature; measuring a refrigerant flow rate to the heat exchanger; and determining whether to operate a compressor cooling cycle or a free cooling cycle based on a relationship between the refrigerant inlet pressure; the refrigerant outlet pressure; the refrigerant inlet temperature; the refrigerant outlet temperature; the outdoor environment temperature; and the refrigerant flow rate.

[Advantageous Effects]

The present disclosure provides a cooling system, control device, method, and program which are able to provide necessary cooling to a server rack while reducing the power consumption.

[Brief Description of Drawings]

[0013] [Fig- l]

Fig.l shows an exemplary embodiment of a cooling system containing racks dissipating a heat load.

[Fig- 2]

Fig. 2 shows racks with servers, heat exchangers and air flow.

[Fig- 3]

Fig. 3 shows a functional diagram of compressor/free cooling cycle unit of an exemplary embodiment of the present invention.

[Fig- 4]

Fig. 4 shows an activity diagram illustrating the workflow of a temperature controller of an exemplary embodiment of the present invention.

[Fig. 5]

Fig. 5 shows an activity diagram illustrating workflow of a switching controller of an exemplary embodiment of the present invention.

[Fig, 6A]

Fig. 6A shows an example of a predetermined table showing a relationship between heat exchanger refrigerant inlet temperature (°C), outdoor environment temperature (°C) and exhausted heat load (kW).

[Fig. 6B]

Fig. 6B shows another example of a predetermined table showing a relationship between heat exchanger refrigerant inlet temperature (°C), outdoor environment temperature (°C) and exhausted heat load (kW).

[Fig- 7]

Fig. 7 shows another example of a predetermined table showing a relationship between heat exchanger refrigerant inlet temperature (°C), outdoor environment temperature (°C) and exhausted heat load (kW).

[Fig. 8]

Fig. 8 is a functional diagram of an exemplary embodiment of a control device for a server rack of the present invention.

[Description of Embodiments]

[0014]

Exemplary embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same elements are denoted by the same reference numerals, and thus redundant descriptions are omitted as needed.

[0015]

Reference throughout this specification to“one embodiment”,“an embodiment”, “one example” or“an example” means that a particular feature, structure or characteristic described in connection with the embodiment or example is included in at least one embodiment of the present embodiments. Thus, appearances of the phrases“in one embodiment”,“in an embodiment”,“one example” or“an example” in various places throughout this specification are not necessarily all referring to the same embodiment or example. Furthermore, the particular features, structures or characteristics may be combined in any suitable combinations and/or sub-combinations in one or more embodiments or examples.

[0016]

For a room level cooling system, an appropriate cooling cycle selection can be performed on the basis of the outside environment temperature and the total exhausted heat load. In the case of a local level cooling system, the actual local cooling requirement may exceed the average value of cooling requirement, depending on local exhausted heat load variation. Therefore, local level cooling systems must consider exhausted heat load variation as well as the total exhausted heat load. Hence, the appropriate cooling cycle switching algorithm of a room level cooling system can fail if applied to a local level cooling system.

[0017]

For room level cooling systems, all hot exhausted air from the rack outlet is well mixed before it reaches the cooling system inlet, due to large free space availability between the rack outlet and the cooling system inlet. Hence, the cooling system treats the total heat load, not the individual heat load of each rack. Therefore, the room level cooling system is limited by the maximum total heat load it can extract, not by the maximum heat load of individual rack.

[0018]

For local level cooling systems, the cooling system is distributed in the vicinity of rack dissipating heat load. Local level cooling system may contain multiple local cooling equipment such as a heat exchanger, wherein the individual cooling equipment cools individual heat loads.

[0019]

In such a local level cooling system, the exhausted heat load from the rack outlet is directly taken by the cooling system inlet without any mixing with nearby exhausted heat loads from other racks. Individual distributed cooling units such as heat exchangers near individual heat loads should satisfy their respective cooling requirements. Therefore, the cooling system is limited by the maximum local heat load, not the total heat load of all racks.

[0020]

Therefore, an appropriate cooling cycle switching algorithm for a room level cooling system will fail when applied to a local level cooling system, if maximum heat load of any rack is greater than average heat load of all racks.

[0021]

This failure occurs because cooling cycle parameters for the average load determined for a room level cooling system will extract only the average heat load from individual local level cooling systems. Therefore, if any local heat load is higher than the average heat load, the remaining load, i.e. (maximum heat load - average heat load), is not extracted by the cooling system and can result in data center failure.

[0022]

Fig. 1 shows the overall system containing server racks 110 and 111, heat exchangers 112 and 113, a cooling inlet pipe 119, a cooling outlet pipe 120, an outlet pressure sensor 121, an inlet pressure sensor 124, temperature sensors 122, 123 and 126, flow rate sensor 125, compressor/free cooling cycle unit 114, switching controller 115 and power source 127. Fig. 1 shows the overall cooling system which is used to cool the cooling racks 110 and 111.

[0023]

The server racks 110 and 111 may store electronic equipment 212 such as computing servers, networking devices, etc. as shown in Fig. 2. Electronic equipment 212 consumes electrical power for their operation and dissipates thermal energy of an equivalent amount. This thermal energy is transferred to cold air which can be pulled into the equipment body by fans 213 attached to the electronic equipment, as shown in Fig.2. The fans 213 also exhausts hot air out of the equipment body as shown in Fig. 2 by the rack exhaust airflow direction 214.

[0024]

The exhausted hot air from the electronic equipment 212 outlet flows towards the cooling units 112 and 113. The cooling units 112 and 113 extract thermal energy from hot air until it reaches a predefined temperature and air flows out of the cooling units 112 and 113 as shown by the heat exchanger exhaust direction 215 in Fig. 2. The airflow between cooling and rack is shown by arrows 215 in Fig. 2. One example of such a cooling unit is a heat exchanger.

[0025]

The heat exchanger 112 and 113 may also contain an auxiliary fan to assist air flow around server racks 110 and 111, if needed.

[0026]

Also, the heat exchanger 112 and 113 is shown in horizontal position. Depending on the cooling system design, the heat exchangers 112 and 113 can have any orientation.

[0027]

The server racks 110 and 111 consumes electrical energy from power source 127 which is dissipated as thermal energy.

[0028]

The dissipated thermal energy is extracted by refrigerant flowing inside the heat exchangers 112 and 113. The liquid refrigerant reaches the heat exchanger from a heat exchanger inlet pipe 119. The liquid refrigerant absorbs thermal energy to cool down the rack exhaust air temperature. By absorbing the thermal energy, liquid refrigerant turns into vapor refrigerant. The vapor refrigerant is carried away from the heat exchangers by a heat exchanger outlet pipe 120.

[0029]

Fig. 3 shows an example of the compressor/free cooling cycle unit 114, comprising basic equipment to perform either a compressor cooling cycle or a free cooling cycle at a given moment in time. The compressor/free cooling cycle unit 114 comprises a compressor 310, a pump 315, an expansion valve 316, a cycle switching valve 312, an outdoor unit 326 and a temperature controller 317.

[0030]

During the compressor cycle operation, the compressor 310 operates to compress vapor refrigerant coming from the heat exchanger outlet pipe 120. Then, vapor refrigerant is passed to the outdoor unit 326 via the pipe 313, which returns liquid refrigerant by removing thermal energy from the vapor refrigerant to the outdoor environment. The liquid refrigerant returned by the outdoor unit 326 via the pipe 314 is expanded using the expansion valve 316. Then, liquid refrigerant returns to the heat exchangers 112 and 113 via the heat exchanger inlet pipe 119. The switching valve 312 remains closed and the pump 315 remains off.

[0031]

During the free cooling cycle operation, vapor refrigerant coming from the heat exchanger outlet pipe 120 bypasses the compressor 310 through the compressor bypass 311 and directly goes to the outdoor unit 326 via the pipe 313, which returns liquid refrigerant by removing the thermal energy from the vapor refrigerant to the outdoor environment. The liquid refrigerant received by the outdoor unit 326 via the pipe 314 passes through the pump 315 and returns to the heat exchanger via the heat exchanger inlet pipe 119. The compressor 310 remains off and the expansion valve remains closed.

[0032]

The pump 315 only assists the refrigerant flow. Depending on system design, the pump 315 may be removed.

[0033]

The outdoor unit 326 is used to remove heat from vapor refrigerant to the outside environment. The refrigerant inlet pipe 313 carries the vapor refrigerant to a single or multiple heat exchangers 321. A fan 323 may be used to move outside environment air over the heat exchanger as shown by the airflow direction 322. The vapor refrigerant loses thermal energy to the outside air and transform into liquid refrigerant. The liquid refrigerant then passes back to refrigerant outlet pipe 314.

[0034]

The compressor/free cooling cycle unit 114 may contain a temperature controller 317. The temperature controller 317 controls and maintains the heat exchanger outlet cold air temperature. The temperature controller 314 may contain 3 functions: a‘receive the heat exchanger outlet air temperature’ function 318 which receives the heat exchanger outlet cold air temperature data, a‘decide actuator target’ function 319 which decides the action of an actuator; and an‘actuator operator’ function 320 which actuates the actuator. These functions will be explained in detail later in Fig. 4.

[0035]

In Fig. 1, the inlet pressure sensor 124 at the heat exchanger inlet pipe 119 is used to measure refrigerant pressure at the heat exchanger inlet pipe 119. The outlet pressure sensor 121 at the heat exchanger outlet pipe 120 is used to measure refrigerant pressure at the heat exchanger outlet pipe 120. The inlet temperature sensor 123 at the heat exchanger inlet pipe 119 is used to measure refrigerant temperature at the heat exchanger inlet pipe 119. The outlet temperature sensor 122 at the heat exchanger outlet pipe 120 is used to measure refrigerant temperature at the heat exchanger outlet pipe 120. The temperature sensor 126 located outdoors is used to measure the outdoor environment temperature of the outdoor environment. The flow rate sensor 125 is used to measure the liquid refrigerant flow rate at the heat exchanger inlet pipe 119.

[0036]

A power source 127 is used to supply electrical energy required by various equipment such as the server racks 110 and 111, the compressor/free cooling cycle unit 114, and the switching controller 115. The electrical energy requirement of a sensor can be fulfilled by hardware used for a‘fetch data’ function 118. If required, the power source 127 can also supply electrical energy to various sensors.

[0037]

The switching controller 115 controls and maintains the appropriate cooling cycle operation. The switching controller 115 may contain, for example, 3 functions: the‘fetch data’ function 118 which fetches the data from various sensors, a‘cycle selection’ function 116 which selects appropriate cycle from compressor/free cooling cycle and an‘actuator operator’ function 117 which actuates the actuator required to operate the appropriate cooling cycle. The details of the switching controller 115 are shown in Fig. 5.

[0038]

The‘fetch data’ function 118 communicates with the respective sensors 121, 122, 123, 124, 125, 126 and receives the measured values thereof. Then, received values are sent to the‘cycle selection’ function 116. The‘cycle selection’ function 116 processes the received data from the‘fetch data’ function 118 and decides the appropriate cooling cycle. The appropriate cooling cycle decision is transmitted to the‘actuator operator’ function 117. Based on the appropriate cooling cycle decision, the‘actuator operator’ function 117 communicates with the compressor/free cooling cycle unit 114. Based on the command received from the‘actuator operator’ function 137, the compressor/free cooling cycle unit 114 operates the appropriate actuators.

[0039]

Fig. 1 shows only shows 2 server racks 110 and 111 with their respective local cooling systems, i.e. the heat exchangers 112 and 113. It should be noted that the number of racks is not particularly limited and may be extended to any number of racks.

[0040]

Hereinafter, the work flow of temperature controller 317 will be described.

(1) Step 411

First, a target temperature value for the heat exchanger outlet cold air temperature is set as per data center condition requirements.

[0041]

(2) Step 412

The heat exchanger outlet cold air temperature is measured using a temperature sensor via the‘receive heat exchanger outlet air temperature’ function 318. Multiple sensors may be used to measure multiple heat exchangers respective outlets cold air temperature. Depending upon the rack power distribution, the heat exchanger outlet cold air temperature may vary.

[0042] In one of the exemplary embodiments, both server racks 110 and 111 in Fig. 1 consume equal power and therefore the rack exhaust outlet air temperature is equal for both racks. As heat exchanger refrigerant inlet pipe 119 is common to the heat exchangers 112 and 113, the liquid refrigerant inlet thermo-physical condition is the same at both heat exchangers. Hence, for the same rack exhaust temperature and the same liquid refrigerant inlet condition, the heat exchanger outlet cold air temperature is also equal.

[0043]

In an another exemplary embodiment, the server rack 110 consumes higher power than the rack 111, under the condition that the total rack power of the server racks 110 and 111 is equal to that of the previous case. In this case, the server rack 110 exhaust temperature is higher than the rack 111. Therefore, the heat exchanger outlet cold air temperature of heat exchanger in the vicinity of the server rack 110 is higher than the heat exchanger in the vicinity of rack 111 because the liquid refrigerant inlet thermo-physical condition is the same for both heat exchangers.

[0044]

Therefore, even for equal total rack power consumption in different embodiments, the heat exchanger outlet cold air temperature may be different and it depends upon rack power distribution.

Again, the number of racks is not particularly limited for the above explanation and may be extended to any number of racks.

[0045]

All measured temperature sensor values that are used are forwarded to the next step. (3) Step 413

The ‘decide actuator target’ function 319 calculates the maximum heat exchanger outlet cold air temperature from all measured temperature sensor values. The calculated maximum heat exchanger outlet cold air temperature from is compared to the set point for heat exchanger outlet cold air temperature from step 410.

[0046]

(4) Step 414

If maximum temperature value of the heat exchanger outlet cold air temperature is higher than the set point for the heat exchanger outlet cold air temperature, then an increase in the heat exchange amount of the heat exchangers 112 and 113 is sent to the ‘actuator operator’ function 320 by the‘decide actuator target’ function 319. One example for increasing heat exchanging amount is to decrease heat exchanger inlet refrigerant temperature.

[0047]

(5) Step 415

In response to an increase in heat exchange amount, the‘actuator operator’ function 320 operates the minimum set of actuators appropriate for operating the cooling cycle. As per example in step 414, there are several ways to decrease heat exchanger refrigerant inlet temperature, one example uses compressor 310 to reduce heat exchanger pressure.

[0048]

(6) Step 416

If the maximum temperature value of the outlet cold air temperature of the heat exchangers 112 and 113 is lower than the set point for the outlet cold air temperature, then decrease heat exchange amount of heat exchanger 112 and 113 is send to‘actuator operator’ function 320 by the‘decide actuator target’ function 319. One example for decreasing the heat exchanging amount is to increase the heat exchanger inlet refrigerant temperature.

[0049]

(7) Step 417

In response to a decrease of heat exchange amount, the‘actuator operator’ function 320 operates the minimum set of actuators appropriate for operating the cooling cycle. As per the example in step 416, there are several ways to increase the heat exchanger refrigerant inlet temperature. One example is using the compressor 310 to increase the heat exchanger pressure.

[0050]

(8) Step 418

The temperature controller 317 waits for M minutes, which is a preset value and can be modified as required.

[0051]

The effect of rack power distribution can be quantified using a set a variables such as (total rack power consumption and heat exchanger refrigerant inlet temperature). As discussed in above, the heat exchanger outlet cold air temperature depends on rack the power distribution. Also, temperature controller maintains heat exchanger outlet cold air temperature by controlling heat exchanger refrigerant inlet temperature. Therefore, a variable set of (total rack power consumption and heat exchanger refrigerant inlet temperature) can be utilized to quantify rack power distribution affect.

[0052] Work flow of switching controller 115

(1) Step 511

The current values of the heat exchanger inlet liquid refrigerant pressure is fetched from the inlet pressure sensor 124 at the heat exchanger inlet pipe 119, the heat exchanger outlet vapor refrigerant pressure is fetched from the outlet pressure sensor 121 at heat exchanger outlet pipe 120, the heat exchanger inlet liquid refrigerant temperature is fetched from the inlet temperature sensor 123 at heat exchanger inlet pipe 119, the heat exchanger outlet vapor refrigerant temperature is fetched from the outlet temperature sensor 122 at the heat exchanger outlet pipe 120, the heat exchanger inlet liquid refrigerant flow rate is fetched from flow rate sensor 125 at heat exchanger inlet pipe 119, and the data center outside environment temperature is fetched from temperature sensor 126 at the outside environment.

[0053]

(2) Step 512

Using the heat exchanger inlet liquid refrigerant pressure and the heat exchanger inlet liquid refrigerant temperature, the enthalpy of the heat exchanger inlet liquid refrigerant can be calculated using a property table of the refrigerant. The property table of the refrigerant is available from manufactures as well as in standard databases of refrigerant properties such as REFPROP by NIST.

[0054]

Using the heat exchanger outlet liquid refrigerant pressure and the heat exchanger outlet liquid refrigerant temperature, the enthalpy of heat exchanger outlet vapor refrigerant can be calculated using the property table of the refrigerant. Using the heat exchanger inlet liquid refrigerant pressure and the heat exchanger inlet liquid refrigerant temperature, the density of the heat exchanger inlet liquid refrigerant can be calculated using the property table of the refrigerant.

[0055]

Using the formula below in Math 1, the current exhausted heat load can be calculated.

[Math 1]

Wherein Heatjoad is the current exhausted heat load, p is the density of the heat exchanger inlet liquid refrigerant, q is the heat exchanger inlet liquid refrigerant flow rate as obtained from the flow rate sensor, h_vapor is the enthalpy of the heat exchanger outlet vapor refrigerant and h _quid is the enthalpy of the heat exchanger inlet liquid refrigerant.

[0056]

(3) Step 513

For the current heat exchanger refrigerant inlet temperature, a predetermined table is selected. In the selected predetermined table, the intersection cell of the current outdoor environment temperature row and the current exhausted heat load column is selected. These predefined tables define the relationship between the outdoor environment temperature, the total exhausted heat load, and the refrigerant inlet temperature to the heat exchanger as shown in Fig. 6A and Fig. 6B.

[0057]

This predetermined table defines the relationship in terms of whether or not it is possible to extract the current heat load by the free-cooling cycle under the provided outdoor temperature for the required heat exchanger liquid refrigerant inlet temperature and total heat load. The possibility can be represented as a 1 or a 0, wherein a 1 means that it is possible to extract the current heat load by the free-cooling cycle under the provided outdoor temperature for the required heat exchanger liquid refrigerant inlet temperature and a 0 means that it is not possible to extract the current heat load by the free-cooling cycle under the provided outdoor temperature for the required heat exchanger liquid refrigerant inlet temperature.

[0058]

In one of the exemplary embodiments, wherein the current heat exchanger refrigerant inlet temperature is 20 °C, the exhausted heat load is 30kW and the outdoor environment temperature is 6 °C; Table 1 is selected on the basis of the current heat exchanger refrigerant inlet temperature of 20 °C. In Table 1, based on values of exhausted heat load =30kW and outdoor environment temperature=6 °C; and an appropriate table cell is selected as shown in Fig. 7.

[0059]

(4) Step 514

Based on Step 513, a cell value is received.

As per one exemplary embodiment defined in step 513 and Fig., 7, the received cell value is 1.

[0060]

(5) Step 515

If the cell value is 1 , then the switching controller 115 selects the free cooling cycle for operation.

[0061]

(6) Step 516 If the cell value is 0, then the switching controller 115 selects the compressor cooling cycle for operation.

[0062]

(7) Step 517

The decision of step 515 or step 516 is provided to the‘actuator operator’ function 117, which appropriately operates the actuator.

[0063]

As per the exemplary embodiment of step 514, i.e., the case of free cooling cycle, the‘actuator operator’ function 117 sets the switching valve 312 to an open position and starts the pump 315. Also, the ‘actuator operator’ function 117 shuts down the compressor 310 and sets the expansion valve 316 to a close position

[0064]

In the case of the compressor cooling cycle, as shown in Fig. 3, the‘actuator operator’ function 117 sets the expansion valve 316 to the open position and turns on the compressor 310. Also, the‘actuator operator’ function 117 sets the switching valve 312 to the closed position and shuts down the pump 315.

[0065]

(8) Step 518

After operating the actuator, the switching controller 115 waits for N minutes, which is a preset value and can be modified as required.

[0066]

Step 511 of Fig. 5 is performed by the‘data fetch’ function 118, Step 512 to Step 516 are performed by the‘cycle selection’ function 116, and Step 517 is performed by ‘actuator operation’ function 117. (Other Exemplary Embodiments)

[0067]

In another exemplary embodiment, the heat exchangers 112 and 113 are placed on rack inlet air side instead of the rack outlet air side of the first exemplary embodiment.

[0068]

In another exemplary embodiment, instead of a refrigeration cycle, a constant temperature coolant is supplied to the heat exchangers 112 and 113. In this exemplary embodiment, the current exhaust heat load, the outdoor environment temperature and the heat exchanger inlet coolant mass flow rate are utilized to determine appropriate cooling cycle.

[0069]

In another exemplary embodiment, the current exhausted heat load is determined from the total rack power.

[0070]

In another exemplary embodiment, for incompressible single phase refrigerant systems, only temperature and flow rate sensors are utilized to determine the current exhaust heat load, the outdoor environment temperature, and the heat exchanger inlet refrigerant temperature.

[0071]

In another exemplary embodiment, a single rack may contain multiple heat exchanger units for removing the rack heat load.

[0072]

In another exemplary embodiment, a single heat exchanger is used to remove exhausted heat load of multiple racks.

In another exemplary embodiment, the predetermined table uses values other than 0 and 1 to define the relationship.

[0073]

In another exemplary embodiment, the values of the predetermined table are compared against some set/variable value. The comparison can utilize functions such as greater than, lesser than, equal to, or any combination thereof.

[0074]

It should be noted that in the above description“a heat exchanger” may be a plurality of heat exchangers operating independently or in combination. Likewise, other components may also be included as a plurality of the respective other components in accordance with design specifications.

[0075]

Furthermore, exemplary embodiments in accordance with the present exemplary embodiments may be implemented as an apparatus, a device, a method, or a computer program product. Accordingly, the present exemplary embodiments may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.), or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “module” or“system.” Furthermore, the present exemplary embodiments may take the form of a computer program product embodied in any tangible medium of expression having computer-usable program code embodied in the medium.

[0076]

Additionally, any examples or illustrations given herein are not to be regarded in any way as restrictions on, limits to, or express definitions of any term or terms with which they are utilized. Instead, these examples or illustrations are to be regarded as being described with respect to one particular embodiment and as being illustrative only. Those of ordinary skill in the art will appreciate that any term or terms with which these examples or illustrations are utilized will encompass other embodiments which may or may not be given therewith or elsewhere in the specification and all such embodiments are intended to be included within the scope of that term or terms. Language designating such nonlimiting examples and illustrations includes, but is not limited to:“for example,” “for instance,”“e.g.,” and“in one embodiment.”

[Industrial Applicability]

[0077]

The present disclosure is applicable to a cooling system, which are able to provide necessary cooling to a server rack while reducing the power consumption.

[Reference Signs List]

110 Server Rack

111 Server Rack

112 Heat Exchanger

113 Heat Exchanger

114 Compressor/Free Cooling Cycle Unit

115 Switching Controller

116 Cycle Selection Function

117 Actuator Operation Function F etch Data Function

Cooling Inlet Pipe

Cooling Outlet Pipe

Outlet Pressure Sensor

Outlet Temperature Sensor Inlet Temperature Sensor

Inlet Pressure Sensor

Flow Rate Sensor

Outside Temperature Sensor Power Source

CPU

Memory Unit

I/O Unit

Electronic Equipment

Fan

Rack Exhaust Airflow Direction Heat Exchanger Exhaust Direction Compressor

Compressor Bypass

Switching Valve

Refrigerant Inlet Pipe

Refrigerant Outlet Pipe

Pump

Expansion Valve Temperature Controller

Receive Outlet Temperature Function

Decide Actuator Target Function

Actuator Operator Function

Heat Exchanger

Airflow Direction

Fan

Outdoor Unit

Claims

[Claims]

1. A cooling system comprising:

a server rack;

a heat exchanger configured to produce cooled air;

a first pressure sensor configured to measure refrigerant inlet pressure to the heat exchanger;

a second pressure sensor configured to measure refrigerant outlet pressure of the heat exchanger;

a first temperature sensor configured to measure refrigerant inlet temperature to the heat exchanger;

a second temperature sensor configured to measure refrigerant outlet temperature of the heat exchanger;

a third temperature sensor configured to measure outdoor environment temperature;

a flow rate sensor configured to measure a refrigerant flow rate to the heat exchanger; and

a controller configured to switch between a compressor cooling cycle and a free cooling cycle based on measurement data received by the first, second, and third temperature sensors and the first and second pressure sensors, wherein

the compressor cooling cycle utilizes the compressor for cooling server rack exhaust air, and

the free cooling cycle utilizes outside environment air for cooling the server rack exhaust air.

2. The cooling system of Claim 1, wherein

the controller determines a heat load of the cooling system based on a difference between the refrigerant outlet and the refrigerant inlet using the measurement data in order to determine whether or not to switch between the compressor cooling cycle and the free cooling cycle.

3. The cooling system of Claim 2, wherein

the heat load and an outdoor environment temperature value are compared to a predetermined table in order to determine whether or not to switch between the compressor cooling cycle and the free cooling cycle.

4. The cooling system of Claim 3, wherein

the predetermined table contains data regarding whether or not the free cooling cycle can remove an exhausted heat load for the outdoor environment temperature value and a heat exchanger refrigerant inlet temperature.

5. A control device for a cooling system of a server rack, the cooling system including a heat exchanger, measurement sensors, and a cooling cycle unit configured to provide compressor cooling and free cooling to the heat exchanger, the control device comprising:

a memory unit;

a processing unit; and

an I/O unit configured to receive from the measurement sensors: a refrigerant inlet pressure to the heat exchanger measurement; a refrigerant outlet pressure measurement; a refrigerant inlet temperature measurement; a refrigerant outlet temperature measurement; an outdoor environment temperature measurement; and a refrigerant flow rate measurement; wherein

the processing unit is configured to output a command to the cooling cycle unit to switch between a compressor cooling cycle and a free cooling cycle based on the refrigerant inlet pressure to the heat exchanger measurement; the refrigerant outlet pressure measurement; the refrigerant inlet temperature measurement; the refrigerant outlet temperature measurement; the outdoor environment temperature measurement; and the refrigerant flow rate measurement.

6. A cooling method for a server rack, comprising:

measuring a refrigerant inlet pressure to a heat exchanger;

measuring a refrigerant outlet pressure of the heat exchanger;

measuring a refrigerant inlet temperature to the heat exchanger;

measuring a refrigerant outlet temperature of the heat exchanger;

measuring outdoor environment temperature;

measuring a refrigerant flow rate to the heat exchanger; and

determining whether to operate a compressor cooling cycle or a free cooling cycle based on a relationship between the refrigerant inlet pressure; the refrigerant outlet pressure; the refrigerant inlet temperature; the refrigerant outlet temperature; the outdoor environment temperature; and the refrigerant flow rate.

7. A program causing a computer to execute:

measuring a refrigerant inlet pressure to a heat exchanger; measuring a refrigerant outlet pressure of the heat exchanger;

measuring a refrigerant inlet temperature to the heat exchanger;

measuring a refrigerant outlet temperature of the heat exchanger;

measuring outdoor environment temperature;

measuring a refrigerant flow rate to the heat exchanger; and