NL2018936B1 - System for ensuring constant temperature parameters of access cabinets - Google Patents

Abstract

A system for ensuring constant temperature parameters of access cabinets, including ICT cabinets, comprising two interconnected heat exchangers, at least two fans, a compressor, an expansion valve, a compressor bypass. The system is characterised in that it has one liquid circuit within which there are the two interconnected heat exchangers. At least one fan (7) and at least one heat exchanger (9) are located in a separate and thermally insulated compartment (8), the heat exchangers (9), (13) have the same performance, and the system is provided with a four-way valve (4) and a shut-off valve (1) placed on the bypass (2) of the compressor (58).

Description

System for ensuring constant temperature parameters of access cabinets

The object of the invention is a system for ensuring constant temperature parameters intended for use in access cabinets, operating especially under conditions of emergency power supply. The system according to the invention is intended in particular for use in outdoor cabinets and in rack, ICT, power, network and server enclosures. Access cabinets are used at the so-called last mile stage before the customer, under the external ICT infrastructure; for example fibre optic or energetic infrastructures. In this kind of cabinets, electronic or electrical devices that generate heat energy during their operation are installed. Most often, signal amplifiers, electronic filters, splitters, multiplexers, access devices, power stations and accumulators, surge protectors, processors, arrays, etc. are installed in access cabinets.

External access cabinets with electronic devices installed therein are mounted outside buildings, often far from professional staff. Therefore, autonomy of operation of this type of devices and possibility to remotely control their operation, including provision of optimal temperature conditions for the electronic equipment installed therein, are desirable. Access cabinets are exposed to influence of environmental factors. Dust, water and high temperature are particularly important environmental factors affecting the operation of electronic devices installed inside the access cabinet. Therefore, tightness of the cabinet design and provision of stable temperature of hardware space located inside the cabinet are technical problems that require solutions for this type of construction. Maintaining of tightness and temperature rising beyond acceptable standards are particularly relevant and interrelated problems that require solutions.

On the one hand, in order to provide protection against dust, tightness of the interior of the access cabinet should be ensured to protect sensitive electronic equipment, and on the other hand, tightening of the structure causes a faster rise in temperature inside the cabinet due to lack of ventilation and emission of heat energy by the electronics installed in the access cabinet.

The problem of temperature control in ICT cabinets is especially important for outdoor installations. This is not only related to the performance of components installed therein, but also to the influence of variable external climatic conditions, such as temperature and humidity. These factors are susceptible to changes depending on the time of the year and the day-night cycle. Existing solutions based on the use of solutions in the form of using double walls, increasing the outer active surface for removal of heat from the interior of enclosures, using electro-mechanical ventilation and air supply systems generated a lot of problems such as: — low refrigerating capacity at extreme temperatures of outside environment, for example during the summer; — loss of cabinet hermeticity, and penetration of air carrying environmental pollutants, such as dust and water, into the hardware space; — inconvenient use of filters, requiring periodic replacement or cleaning; — loud operation of cooperating fans and noise limit specified in the standards; — lack of control over the system operation in the event of power failure; — disproportionately large size in relation to the power generated; — lack of heating function or low heating efficiency.

Prior art

Solutions consisting in the use of standard air conditioners for cooling the interior of the access cabinet are known from the prior art. At the same time, standard electric heaters are used in order to increase the temperature. The solutions used are energy-intensive and require constant access to the source of primary voltage and continuous, personal service supervision.

Solutions consisting in the use of free or forced convection are commonly known and used in server and ICT cabinets. The most commonly used solution is air circulation and ventilation of the space (compartment) of the access cabinet through air flow from the outside and ejection of air, heated by electronic devices, outside.

From US 6788535 patent specification, division of the access cabinet into two compartments one of which, the upper one, is intended for heat-generating electronics, and the other one, located from below, intended for installation of the cooling system, is known. The cooled upper compartment is connected to the cooling lower compartment by two channels one of which is intended for blowing cooled air, and the other serves to direct heated air from the upper compartment to the lower compartment for cooling it down.

From US 6834715 patent specification, the use of a cooling system for lowering the temperature of a plate in contact with batteries used to power devices located in an upper hardware compartment is known. This invention also discloses the use of heaters for heating the air from the environment in order to maintain a stable temperature inside the cabinet, and the use of a heat exchanger for cooling the heated air in the access cabinet. The solution in question also describes the use of a fan and a compressor for forcing the air circulation inside the cabinet and for its cooling. US 7974094 patent specification discloses the use of fans and filtering membranes, and shape elements for ensuring optimum circulation of purified air inside the telecommunications cabinet.

From US 20130087320 patent specification, the use of a system of fans, rotating guide vanes for changing the direction of air flow and a thermometer for ensuring an optimum temperature inside the access cabinet is known.

From DE 4330923 patent specification, a cooling device intended for control cabinets with electronic devices, having two heat exchangers one of which functions as a condenser and the other as an evaporator is known. Furthermore, this patent discloses the use, within the compressor cooling system, of an expansion valve and a sensor system detecting temperature differences and controlling, on this basis, the operation of the whole system.

From US 20150296665 patent specification, a solution is known consisting in the use, within the cabinet cooling device, of two independent, closed cooling circuits, separated in terms of flow, wherein heat exchangers are installed on both circuits. A fan is used in each of the circuits.

The difficulty to maintain the tightness of the whole access cabinet in the situation where air drawn from the environment flows through the space where electronic devices sensitive to pollutants are located, as well as the low performance of cooling and ventilation systems are disadvantages of known solutions. The problem of preventing pollutants from entering the interior of the cabinet is neutralised in known solutions by the use of various membranes and filters, which, however, increases the degree of complexity, unreliability and increases costs of production and maintenance of the entire device because of the necessity of periodical cleaning and exchange of such elements. In turn, the performance of ventilation systems is in large measure dependent on the environment temperature and is significantly reduced in the case of high environment and outside air temperatures, which occurs especially in the summer months. The third important technical problem occurring in the known solutions is high energy consumption of known heating systems which use resistance heaters to increase the temperature inside the access cabinet. The fourth important problem is obtaining both cooling and heating functions within one device. The fifth issue is to maintain the operation of the air conditioning device in case of lack of the main power supply.

Purpose of the solution

The main purpose of the system, according to the invention, is to maintain a constant, set temperature inside the ICT cabinet, while ensuring, at the same time, tightness of the hardware space of the ICT cabinet, under conditions of both normal power supply and emergency power supply or during total power failure.

Essence of the solution

The structure of the system according to the invention ensures constant set parameters of temperature in access cabinets. The invention eliminates the above-described disadvantages, allowing provision of hermeticity of the cabinet access, ensuring protection against dust and preventing other unwanted elements of the environment from entering the hardware space. Furthermore, energy efficiency of the system according to the invention represents a significant improvement over known solutions. What is more, the system is capable to operate also under emergency power supply with a lower voltage, and can even operate without any power supply by means of the method of internal energy convection to the environment temperature of the exchange medium.

The system ensures maintenance of constant temperature parameters of access cabinets. According to the invention, the device comprises two heat exchangers having the same performance parameters operating in symmetric mode. The system constitutes a double heat pump system in a system of two symmetrical heat exchangers and hydraulics of conveying medium circuit. The heat exchangers are connected by one hydraulic circuit. The system allows both cooling and heating of the interior of the access cabinet. One of the heat exchangers functions as an evaporator, and the other as a condenser, wherein the exchangers can perform these functions interchangeably. At the same time, at least one of the heat exchangers is installed in a separate, tight and thermally insulated compartment through which the air coming from the hardware space flows. In the process of passive operation, the isolated compartment acts as an insulated heat compartment for increasing the internal energy, and thereby the pressure on the evaporation side for changing the medium phase. The system also includes at least two fans one of which is located in the compartment of the first heat exchanger. The other components of the system include a compressor, as well as a set of wires, valves and sensors controlling the circulation of the thermodynamic medium in the installation. It is preferable to place the whole system according to the invention above the hardware space (cabinet), which allows the use of natural convection for directing the naturally rising warm air from the hardware space located below the system and its flow to the heat exchanger compartment located above. It is also possible to mount the system on the other walls or the floor of the cabinet. Operation of the fans controls the system parameters, being responsible for processes of gas phase change under set parameters, and venting and lowering the temperature inside the access cabinet below the environment temperature. The heat exchangers operating in the system according to the invention are characterised by the same length of hydraulic components and by lamella surface.

The whole system according to the invention is enclosed in a separate housing connected to the access cabinet by two channels one of which being an inlet channel and the other being an outlet channel. The fan installed in the thermally insulated compartment sucks the air out of the hardware space of the cabinet and draws the sucked stream of air through the heat exchanger and blows the air, having a set temperature and humidity, into the interior of the cabinet. The air stream from the hardware space is directed to the inlet channel by appropriately profiled guide vanes located in the hardware space of the access cabinet. The fan of the thermal compartment is preferably mounted behind the exchanger, sucking in the air and drawing the air stream through the heat exchanger, which is characterised, with the use of a diaphragm, by a better coefficient of utilisation of the exchanger surface. Whereas the housing of the thermal compartment is profiled in such a way that the air stream, after passing through the heat exchanger and the fan, is forced through the outlet channel into the hardware space of the access cabinet.

The solution used in the system also includes a four-way valve for controlling the flow direction of the medium and changing the function of heat exchangers from evaporator to condenser, which in turn changes the function of the system from cooling to heating. Furthermore, two-way valves as well as expansion valves connected to temperature sensors of hydraulic medium are placed before the heat exchangers, and valve expansion bellows are located in the air stream, and not on suction pipes. Such a solution provides faster response of the control system during passive operation, for faster pressure compensation in the system in case of passive (without power feed) operation of the system. The system is also provided with a solenoid valve on the compressor's bypass loop. The bypass is used to bypass the compressor, as an element with high medium flow resistance under conditions of reduced emergency power or no power at all. The solenoid shut-off valve on the bypass loop is in a closed position under operating conditions in a standard mode at nominal power, directing the medium stream to the compressor. The valve opens under the system's operating conditions in an emergency mode and with the compressor being switched off.

The system according to the invention can also operate in a passive mode, i.e. without external power supply or under conditions of transition to reduced emergency power supply. In this mode, the bypass is used in the system, which allows bypassing the compressor which is switched off in the emergency mode. Bypassing the compressor by the medium is necessary due to the high hydraulic flow resistance imposed by this element. In the emergency mode, the fans operate only to assist natural convection occurring through phase transformation of the medium occurring under the influence of temperature difference between the temperature of the air from the hardware space and the temperature of the air from the environment.

Placing the compressor followed by the second heat exchanger in the space ventilated with environment air protects this exchanger against icing in the winter time and also provides additional heat recovery from the (compressor's) power feed in the heating process in the winter time.

The system is more efficient the higher the temperature difference between the environment and the hydraulic-carrying medium condensate which depends to a large extent on the active area of specially designed exchangers.

In the cooling function, the direction of medium circulation is from the first heat exchanger placed in the thermally insulated compartment, acting as an evaporator, to the second heat exchanger serving as a condenser, located at the outlet of the housing. In the heating function, the direction of medium circulation is reversed and goes from the second heat exchanger located at the place of ejection of air outside to the first heat exchanger located in the thermally insulated compartment.

Illustrations

The system for ensuring constant temperature parameters of access cabinets according to the invention is shown in the drawing in which: Fig. 1a shows a device incorporating the system in a spatial projection with the housing of the thermal compartment removed; Fig. 1b shows the device incorporating the system in a spatial projection with the housing of the thermal compartment installed; Fig. 2 shows a diagram of the system operation in the cooling function under conditions of nominal power supply; Fig. 3 shows a diagram of the system operation in the cooling function under conditions of emergency (semi-passive) power supply; Fig. 4 shows a diagram of the system operation in the heating function under conditions of nominal power supply. Flow directions of the hydraulic medium are indicated by arrows in each of the figures representing three operating modes of the system.

Embodiment

In a standard operating mode, i.e. under conditions of electrical power supply with nominal voltage and the system operation in a cooling circuit, a solenoid shutoff valve 1 is in a closed position, preventing the medium flowthrough a bypass circuit 2. Pressure of the hydraulic medium is measured by a sensor 3A located between a fourway valve 4 and a dehumidifier tank of a compressor 5 and by a second sensor 3B located behind the compressor 5B.

Example 1

In a first embodiment, illustrated in Fig.2, the system for ensuring constant temperature parameters of access cabinets according to the invention operates in a standard mode under conditions of normal electrical power supply with a rated voltage of 230V, realising a cooling function. The system is enclosed in a tight, thermally insulated housing 6 independent of the access cabinet. The maximum temperature inside the access cabinet is dependent on the type of equipment installed therein, but, as a rule, it should not exceed 45-48°C. While the lower temperature range should be in the range of 5-10°C. The optimum temperature range of the hardware space in the access cabinet is 25-40°C. In the presented example, a stream of heated, warm air from the hardware space of the access cabinet rises up due to the convection effect and additionally, it is sucked by the operation of a first fan 7 into a thermal compartment 8. The stream of warm air is directed to the first heat exchanger 9 also thanks to appropriately profiled guide vanes placed in the hardware space of the cabinet. The air stream flows through the inlet channel 10A to a separate, tight and thermally insulated compartment 8.

The first fan 7 sucks in the stream of warm air from the interior of the cabinet, and thereby draws it through a first lamella heat exchanger 9 acting as an evaporator in the cooling circuit. The medium flowing inside the hydraulic circuit, which is constituted, for example, by Freon 44, as a result of being heated with warm air coming from the inside of the cabinet, undergoes, in the evaporator 9, a phase transition from a liquid form to a gas form. Then, the medium in a gas form flows through a ball valve 11 and, having passed through the four-way valve 4 and a dehumidifier 5A, is sucked through a suction port of the compressor 5B which increases its pressure to about 25 bars. In the normal operating mode, the solenoid shut-off valve 1 is in the closed position preventing the medium flow through the bypass circuit 2. In the form of compressed gas, the medium, having left the compressor 5, is directed first through the four-way valve 4, then through a second ball valve 12 to a second lamella heat exchanger 13 acting as a condenser in the cooling function. A stream of air sucked from the environment through a second fan 14 flows through the condenser 13. The air from the environment, having passed the condenser 13 and received the heat the carrier of which is the hydraulic medium, causes condensation and transition of the medium to a liquid phase at the outlet of the condenser 13. The stream of air heated after passing through the condenser 13 is blown by the second fan 14 outside, out of the system and the access cabinet. The medium, after giving away its heat energy in the condenser 13, flows through a check valve 15, then through a filter 16 and a sight hole 17 and a bellow thermostatic expansion valve 18A reaches the evaporator 9. Change of the medium phase from a liquid state to a volatile state (gas) occurs after the medium passes through the thermostatic expansion valve 18A provided with a temperature sensor 19. The warm air from the interior of the access cabinet, having passed through the evaporator 9 and given away its heat, is, already as cooled air, blown back through the outlet channel 10B to the hardware space.

In the given embodiment, power performance in [kW], active surface [m2] and surface reserve [%] are the same for both exchangers. The use of symmetry in the structure of these elements leads to balancing of the thermodynamic process which in the process of phase change on the expansion valves leads to a faster exchange of delivered heat and allows transfer of internal energy by convection to the condenser. Symmetry of the solution occurs in the same way for the processes of cooling and heating.

Condensation

Evaporation

For full thermodynamic symmetry, the same performance of each of the fans 7 FanC [m3] = 14 FanE [m3] is an important element at pressure resistances of 40 Pa.

Example 2

In a second embodiment, illustrated in Fig.3, the system for ensuring constant temperature parameters of access cabinets according to the invention operates in an emergency (semi-passive) mode under conditions of reduced electrical power supply coming from an uninterruptible power supply with a voltage of 48V, realising a cooling function. During operation in the emergency mode, the compressor 5B is cut off from the power supply and the solenoid shut-off valve 1. placed on the bypass 2 is opened. In turn, both fans 7 and 14 of the heat exchangers 9 and 13 remain active. Circulation of the medium in the emergency mode is as follows: due to the greater resistance imposed by the four-way valve 4, the medium in a gas phase flows through the open solenoid shut-off valve 1 and then flows through a check valve 20 and the ball valve 12 to the condenser 13. Further circulation of the medium and the course of its phase changes are the same as in the first example. Flow direction of the hydraulic medium is the same as in example 1 described above.

In the emergency mode, the cooling function can be realised even in a completely passive manner, i.e. without operation of fans. Under such operating conditions, the system can cool the air inside the cabinet down to the level of environment temperature.

Example 3

In a third embodiment, illustrated in Fig.4, the system for ensuring constant temperature parameters of access cabinets according to the invention operates under conditions of normal electrical power supply, realising a heating function. In the heating circuit, functions realised by the heat exchangers 9 and 13 are reversed. The first heat exchanger 9 being an evaporator in the cooling circuit acts as a condenser in the heating circuit, and the second heat exchanger 13 being a condenser in the cooling circuit acts as an evaporator in the heating circuit. At the same time, the medium circulation in the installation is changed to an opposite direction.

In the presented example, a stream of cold air form the hardware space of the access cabinet is sucked due to the operation of the first fan 7 to the thermal compartment 8 and is directed to the first heat exchanger 9 thanks to appropriately profiled guide vanes placed in the hardware space of the cabinet. The air stream flows through the inlet channel 10A to a separate, tight and thermally insulated compartment 8. The first fan 7 sucks in the stream of warm air from the interior of the cabinet, and thereby draws it through the first heat exchanger 9 acting as a condenser in the heating circuit. The medium flowing inside the hydraulic circuit, which is constituted, for example, by Freon 44, as a result of being cooled with cold air coming from the interior of the cabinet, undergoes, in the first lamella heat exchanger acting as a condenser 9, a phase transition from a gas form to a liquid form. Then, the medium in a liquid form flows through a ball check valve 21 and the sight hole 17, and the filter 16. Then, the medium is injected through an expansion valve 18B to the second heat exchanger 13 acting as an evaporator in the heating circuit. In the second heat exchanger 13 - an evaporator, a phase change of the medium from a liquid form to a gas form occurs. After transition to a gas phase, the medium, having left the second heat exchanger 1_3, flows through the ball valve 12, then through the four-way valve 4 and the dehumidifier tank 5A, is sucked through the suction port to the compressor 5B. Then, through the ball valve 11, the medium in a liquid form flows into the first heat exchanger 9 acting as a condenser in the heating circuit. The cold air from the interior of the cabinet, heated after passing through the condenser 9, is blown back to the access cabinet. Construction and parameters of individual devices and elements of the system are the same as in the first example described above.

Advantages of the solution

The device implementing the system according to the invention is characterised by low costs of maintenance of the power feed and significantly lower costs of servicing. Due to the possibility of performing the functions of both cooling and heating, the system is versatile and adaptable to changes of temperature inside the cabinet and changes of environment temperature. The system allows operation of the device not only under conditions of nominal power supply, but also in the case of emergency power supply and even in the absence of any power supply, using the method of changing the thermodynamic phase and switching to the mode of convection ventilation with a carrying medium. In the last situation, the system will be able to cool the interior of the cabinet to a level equal to environment temperature, which in most cases is sufficient to protect electronic devices from overheating.

The system provides the possibility to construct a device of compact size. Reduction of overall dimensions of the system extends installation capabilities by varying operating positions and modular arrangement of components. The system can be positioned both horizontally and vertically. The system guarantees, by arranging one of the heat exchangers in a thermally insulated compartment, maintenance of tightness (hermeticity) of the cabinet interior without any need to use external intermediary devices of flap and shutter type. Thanks to the tightness of the structure and the protection of the cabinet's hardware space, the system increases durability of devices installed inside the cabinet and does not require the use of filters. In turn, smooth adjustment of the compressor operation ensures fluid stability of the characteristics of temperature and humidity as a function of the speed of ventilation and the power control.

Due to the possibility of connecting the system through electronic devices to remote control systems, it is possible to remotely monitor the state of the system and to control all digital and analogue parameters, for example by ETH or GSM/GPRS networks. Connecting the system to remote systems controlling the operation of the compressor and the valves consequently allows implementation of an automated network-based system for service requests using email communications, text message with the location of the device, and also archiving and recording of all states of the device operation, and continuous measurement of temperature and humidity.

The system according to the invention provides a high coefficient of performance, COP=5, which is the ratio of the received heating energy to the input electric energy, for the energy of both heating and cooling processes. The range of cooling power for the described solution in thermodynamic construction is from 1 to 15 kW. In external conditions, it is applicable in the temperature range of: -33°C to 50°C and the humidity range of: 20% to 90%.

Claims (3)

A system for ensuring constant temperature parameters of access cabinets, comprising two interconnected heat exchangers, at least two fans, a compressor, an expansion valve, a compressor bypass, characterized in that at least one fan (7) and at least one heat exchanger (9) are placed in a separate and thermally insulated compartment (8), the heat exchangers (9), (13) having the same specification and the system is provided with a four-way valve (4) and a shut-off valve (1) which are placed in the bypass (2) of the compressor (5B). The system according to claim 1, characterized in that a thermostatic expansion valve (18A), (18B) is placed in front of each of the heat exchangers (9) and (13). The system according to claim 1, characterized in that the compressor (5B) is placed in the space for direct air input from the environment.