GB2040033A

GB2040033A - Cooling arrangements

Info

Publication number: GB2040033A
Application number: GB7901241A
Authority: GB
Original assignee: Daikin Industries Ltd; Nippon Electric Co Ltd; Daikin Kogyo Co Ltd
Current assignee: Daikin Industries Ltd; NEC Corp
Priority date: 1979-01-12
Filing date: 1979-01-12
Publication date: 1980-08-20
Also published as: FR2446455A1; FR2446455B1; GB2040033B

Abstract

The invention is concerned with a cooling arrangement suitable for cooling telecommunication equipment 2 at an unattended microwave relay station located in desert or like region where there is a large difference between the maximum day-time temperature and minimum night-time temperature. The cooling arrangement includes an outdoor heat exchanger 6 disposed outside and above a shelter 3 accommodating the equipment 2, an indoor heat exchanger 7 disposed in the shelter 3 and a heat storage means 5 disposed at an intermediate level between the heat exchangers 6 and 7. A condensable refrigerant circulates naturally by gravity. When the outdoor temperature is low, most of the cooling energy absorbed by the outdoor heat exchanger 6 is stored in the heat storage means 5, while the remaining part is used for cooling the equipment 2, whereas when the outdoor temperature is high, the cooling energy is released from the heat storage means 5 effectively to cool the equipment 2. The two heat exchangers may be interconnected to form a heat pipe. <IMAGE>

Description

SPECIFICATION Cooling arrangements The invention relates to cooling arrangements for cooling a space in a room and, more particularly, but not exclusively, to cooling arrangements for cooling telecommunication equipment at a radio relay station located in desert or like region where there is a large difference between the day-time and nighttime temperatures.

There have been a remarkable growth of microwave communication systems for covering wide areas in various regions of the world. In a longdistance microwave communication system, it is necessary to construct unattended relay stations at intervals of 10 to 50 Km.

Figures 1 A and 1 B schematically show the construction of a typical conventional radio relay station, which has a steel tower 20 for supporting a parabolic antenna, and a shelter for accommodating various telecommunication equipment 2'. In this conventional relay station, the maximum power consumed is as large as about 1 Kw. To cope with this demand for electric power, in the conventional relay station, it has been necessary to generate a large electric power by means of a generator 22 driven by a diesel engine or the like. Generated electric power is supplied, through a rectifier 23 and batteries 24, to the telecommunication equipment 2', and also to a motor-driven compressor of a cooling system 4', for cooling the telecommunication equipment 2'. Thus, the conventional relay station required a frequent supply of fuel and maintenance work.

However, as a result of recent developement of semi-conductor devices, the power consumption on the part of the telecommunication equipment has been reduced to 50 to 150 W (43 to 129 Kcal/hr) which is only 1/20 to 1/6 of that consumed by the conventional one. Consequently, a power supply means of much smaller capacity suited for unattended relay stations, such as battery or solar battery, has become sufficient for the telecommunication equipment. Under the circumstances, the power consumption on the part of the motor-driven compressor of the cooling system, which amounts to 0.75 Kw or so, is impractically large.

For this reason, there is an increasing demand for a a non-powered cooling system which requires substantially no maintenance work.

According to the present invention there is provided a cooling arrangement for cooling a space in a room, the arrangement comprising: a a cooling apparatus for collecting cooling energy from outdoor air to cool said space when the outdoor temperature is lower than the temperature of said space, said cooling apparatus including a first heat exchanger disposed outside said room, a second heat exchanger disposed inside said room, conduit means connecting said first and second heat exchangers to form a circuit isolated from the atmosphere, and a condenseable refrigerant with which said circuit is charged, said second heat exchanger being disposed at a level below said first heat exchanger so that said refrigerant is naturally circulated through said circuit to cool the space when the outdoor temperature is lower than the temperature of said space; and a heat storage means for storing a portion of said cooling apparatus, said storage means releasing said cooling energy to cool the space when the temperature of said space rises beyond the temperature of the heat storage means.

Embodiments of the cooling arrangement are particularly suited for a radio relay station located in desert or like regions in Africa or Middle East where a large difference, e.g., 35 C to 50 C, occurs between day-time and night-time temperatures.

The invention will now be described by way of example with reference to the accompanying drawings, in which: Figures 1A and 7B show the layout of a conventional radio relay station; Figures 2 to 8 show a cooling arrangement for a radio relay station and constructed in accordance with the invention, in which:: Figure 2 shows partly in section a side elevation of a radio relay station; Figures 3A and 38 are front elevational view and a side elevational view, respectively, of a cooling apparatus and a heat storage disposed in the shelter of the radio relay station as shown in Figure 2; Figure 4 shows temperature variation in various structural elements shown in Figures 3A and 3B; Figure 5 shows another embodiment of the invention in which the shelter of the station is installed above the ground surface; Figure 6 shows still another embodiment of the invention in which the shelter is half buried in the ground; and Figure 7 shows a further embodiment of the invention in which the shelter in entirely buried under the ground; Figure 8 shows a further embodiment of the invention; Figures 9A, 9B and 9C show various piping suited for the embodiments of the invention; and Figure 10 shows a further embodiment of the invention.

A basic cooling arrangement in accordance with the invention will now be described with specific reference to Figures 2 and Figures 3A, 3B.

Referring to these Figures, a radio relay station 1 has a steel tower 20 for supporting a parabolic antenna and a shelter 3 for accommodating telecommunication equipment for amplifying the microwave signal. As shown in Figure 3A, the wails of the shelter 3 have a layer of heat insulating material 8 such as urethane foam or the like sandwiched between steel plates with laminated white vinyl chloride coating. The top of the shelter is covered by a sun shade 9. Thus, the shelter 3 has a heat insulating construction and is intended to be installed on the ground.

A cooling apparatus 4 used in the relay station 1 has, as shown in Figure 3A, an outdoor heat exchanger 6 mounted on a column 10 disposed on the top of the shelter 3, and an indoor heat exchanger 7 installed at a level lower than the outdoor heat exchanger 6. These heat exchangers 6 and 7 function as a condenser and an evaporator, respectively, and are connected to each other through a piping system to form a closed circuit charged with a condensable gaseous refrigerant.

The refrigerant is naturally circulated in this closed circuit by gravity.

As will be clearly seen from Figure 3A, the outdoor heat exchanger 6 is slanted so that a lower header 6b provided at the liquid refrigerant outlet of the heat exchanger 6 is placed below the level of this heat exchanger 6, while the indoor heat exchanger 7 is also slanted so that an upper header 7a provided at the gaseous refrigerant outlet of the heat exchanger 7 7 is placed above the level of this heat exchanger 7.

The exchangers 6 and 7 are communicated with each other through a single refrigerant pipe 11 interconnecting the lower header 6b of the exchanger 6 and the upper header 7a of the exchanger 7.

On the other hand, a heat storage means 5 is placed at a level lower than the outdoor heat exchanger 6 and higher than the indoor heat exchanger 7, i.e., at an intermediate level between the heat exchangers 6 and 7. As shown in Figures 3A and 3B, the heat storage means 5 has a plurality of double tube structures arrayed side by side in a horizontal plane, each of the double tube structures having an inner tube 12 and an outer tube 13. A plurality offins 14 are attached at regular intervals to the outer pheripheral surface of each innertube 12. The annular space in each double tube structure between the inner and outer tubes 12 and 13 is charged with a heat storing agent.

Gas tubes 16 and liquid tubes 17 are connected to the upper and lower sides of the inner tubes 12.

These gas and liquid tubes 16 and 17 are connected to the upper and lower sides of the upper header 7a, i.e., to the gas side and liquid side of the upper header 7a, thereby to form a closed shunt circuit.

Thus, the closed shunt circuit is connected to the aforementioned closed circuit. The arrangement is such that a closed natural circulation circuit of gravity flow type is formed between the heat storage means 5 and the outdoor heat exchanger 6 or between the heat storage means 5 and the indoor heat exchanger 7, so that the heat storage means 5 may serve as an evaporator or a condenser, depending on the outdoor temperature.

The aforementioned circuits are charged with a condensable gaseous refrigerant which makes a phase change from liquid to gas and vice versa in response to a predetermined temperature change.

Since the heat storage means 5 serves as an evaporator and also as a condenser, the amount of refrigerant in the closed circuit is so selected that the inner tubes 12 are filled to an intermediate level thereof with the refrigerant under a predetermined pressure, as shown in Figure 10. Thus, heat ex- change is effected in each double tube structure between the refrigerant flowing in the inner tube 12 and the heat storing agent 15 charged in the space between the inner and outer tubes 12 and 13, in response to the evaporation and condensation of the refrigerant in the inner tube 12. More specifically, when the refrigerant flowing through the inner tube 12 is evaporated, the heat storing agent 15 is cooled, while, when the refrigerant is condensed, the heat storing agent 15 is heated.

The aforementioned condensable gaseous refrigerant preferably has a large latent heat and a high saturation pressure. For instance, flouric refrigerants such as R-22 (CHF2CI, chlorodifluoromethane), R-12 (CCl2F2, dichlorodifluoromethane), R-1 1 (CCI3F, trichlorofluoromethane) or the like can conveniently be used as the refrigerant for this cooling system. The refrigerant R-22 having a high saturation pressure in the high temperature range is most suited for the present cooling arrangement from the view point of the cooling efficiency.

On the other hand, the material used as the heat storing agent 15 is required to have a large specific heat and a melting point comparable to the possible higher temperature of the inside of the shelter 3. At the same time, the temperature at which the material makes the phase change from liquid to solid and vice versa has to be substantially constant. Further, the material should exhibit a small supercooling effect and should be substantially non-corrosive, and non-poisonous, and reasonably cheap.

Various materials can be used as the heat storing agent 15, the typical examples of which are: fatty acids having a melting point near the room temperature in the shelter, e.g., caprylic acid (C7H15COOH, melting point 16 C), capric acid (CgH19COOH,31.5 C), undecylic acid (C10H21COOH, 28.6#), lauric acid (C11H23COOH, melting point 44 C), myristic acid (C13H27COOH, 58 C) and palmitic acid (C15H31r 63 64 C); solid paraffins having a melting point of between 37.8 to 64.6 C; dichlorobenzene (P CeH4Cl2, 52-54 C) or the like.These materials are selectively used depending on the room temperature in the shelter 3.

The annular space between the inner tube 12 and the outer tube 13 is filled up to 95% of its full volume with the heat storing agent 15 in the liquid state, while the remaining part of volume is filled with N2 gas until the internal pressure is increased up to 4 Kg/cm2. Due to this increased internal pressure, the annular space between the inner and outer tubes 12 and 13 can be maintained at a pressure higher than the atmospheric pressure, even when the cooled heat storing agent 15 is solidified to reduce its volume, so that the entry of external air is substantially avoided even if the outer tube 13 is not strictly airtight.

The outdoor and indoor heat exchangers 6 and 7 are preferably of the cross-fin type which is suitable for heat exchange with ambient air, so that the heat exchange may effectively be made between the refrigerant and the ambient air, by making positive use of the natural convection of air. However, if there is any suplus electric power available, a motordriven fan may be used for effecting a forced draught, thereby to enhance the heat exchange.

The cooling arrangement having the described construction functions in a manner explained hereinunder.

At night when the outdoor temperature is low, most of the cooling energy collected at the outdoor heat exchanger 6 is introduced into the heat storage means 5 through the natural circulation between the heat exchanger 6 and the heat storage means 5, while the remaining part of the cooling energy is transferred to the indoor heat exchanger 7 through the natural circulation between the outdoor and indoor heat exchangers 6 and 7, thereby to cool the air in the shelter 3.

On the other hand, during the day-time when the outdoor temperature is substantially higher, the outdoor heat exchanger 6 cannot function as a condenser. Under this state, the cooling energy stored in the heat storing agent 15 of the heat storage means 5 is utilized for cooling, with the heat storage means 5 used as the condenser. Thus, the refrigerant is circulated naturally by gravity between the heat storage means 5 and the indoor heat exchanger 7, thereby effectively to cool the inside of the shelter 3.

More specifically, during the night when the outdoor temperature is below 40 C, the refrigerant in the outdoor heat exchanger 6 releases latent heat and gets condensed and liquefied. The liquefied refrigerant is collected in the lower header 6b and flows down along the inner surface of the piping 11, as shown by a solid line arrow in Figure 3A. Most of this liquid refrigerant flows into the inner tubes 12 of the heat storage means 5 through the liquid pipe 17, while the remaining part is made to flow into the indoor heat exchanger 7 through the upper header 7a. In the indoor heat exchanger 7, the liquid refrigerant absorbs heat from the air inside the shelter 3 while being evaporated.

Meanwhile, in the heat storage means 5, the heat storing agent 15 is cooled and solidified by the latent heat absorbed by the refrigerant, while the latter is evaporated.

The refrigerant evaporated in the indoor heat exchanger 7 and the heat storage 5, now in the gaseous phase, is collected at the upper header 7a of the indoor heat exchanger 7, and flows into the outdoor heat exchanger 6 through the central portion of the pipe 11.

The descending flow of the liquid refrigerant and the ascending flow of the gaseous refrigerant simultaneously take place in the common pipe 11. These flows, however, do not disturb or hinder each other, when the heat generation from equipment 2 is not so large, because the ascending flow of the gaseous refrigerant has a sufficiently small flow velocity, due to a small rate of evaporation of the refrigerant, so that the liquid flows down in contact with the wall of the pipe 11, while the gas flows upward through the central portion of the same pipe 11.

As a result of the natural circulation of refrigerant involving the phase change of the refrigerant from gas to liquid and vice versa, the cooling energy is stored in the heat storing agent 15, and, at the same time, the air inside the shelter 3 is effectively cooled.

During the day-time when the outdoor temperature is raised to a level above 50 C, for example, the refrigerant which has cooled the air inside the shelter 3 and evaporated in the indoor heat exchanger 7 cannot be condensed by the outdoor heat exchanger 6. Therefore, the evaporated refrigerant does not flow upward through the pipe 11 but is introduced into the inner tubes 12 of the heat storage means 5, via the upper header 7 and the gas pipe 16.

Then, the gaseous refrigerant undergoes a heat exchange with the heat storing agent 15, in which the cooling energy has been stored, so as to be liquefied and condensed. The condensed refrigerant then flows back to the indoor heat exchanger 7, through the liquid pipe 17. As this circulation is continued, the cooling energy stored in the heat storage means 5 is taken out and conveyed by the refrigerant effectively to cool the air in the shelter 3, thereby to maintain the temperature of the telecommunication equipment 2 at a desired temperature, e.g., about 50 C or lower.

The fins 14 attached to the outer surface of the inner tube 12 enhances and promotes the heat exchange between the refrigerant and the heat storing agent 15. At the same time, the heat exchange between the air and refrigerant is performed at each of the heat exchangers 6 and 7 through the natural convection of air, even in the absence of a motor-driven fan.

Further, since the heat storage means 5 is disposed at an intermediate level between the outdoor and indoor heat exchangers 6 and 7, liquid refrigerant condensed in the outdoor heat exchanger 6 by the low outdoor temperature at night is allowed to flow smoothly into the heat storage means 5 and the indoor heat exchanger 7 solely by gravity, while the gaseous refrigerant evaporated in the indoor heat exchanger 7 and the heat storage 5 can flow smoothly upward into the outdoor heat exchanger 6.

Thus, the natural circulation of the refrigerant involving the phase change is maintained.

Similarly, during the day-time when the outdoor temperature is high, the natural circulation of the refrigerant is maintained by gravity, because the heat storage means 5 now acting as a condenser is disposed at a level higher than the indoor heat exchanger 7 acting as an evaporator.

The heat storage means 5 has to play a double role, i.e., a role.of an evaporator for night-time and a role of condenser for daytime. To cope with this demand, the heat storage means 5 is disposed horizontally, and is filled with the liquid refrigerant to an intermediate level of the inner tubes 12. When the heat storage means 5 functions as an evaporator at night, the refrigerant condensed in the outdoor heat exchanger 6 is evaporated through a heat absorption from the heat storing agent 15, thereby cooling the latter by the latent heat, while the refrigerant itself is evaporated to become gaseous refrigerant. Since a gas plenum or gaseous space is preserved at the upper portion of each inner tube 12, the evaporated refrigerant can flow back to the outdoor heat exchanger 6, via the gaseous space in each inner tube 12 and the gas pipe connected to one end of the inner pipe 12 to open in the upper gaseous space.

When the heat storage means 5 functions as a condenser during the daytime, the refrigerant which has been evaporated as a result of the heat exchange in the indoor heat exchanger 7 to cool the indoor air is introduced into the upper gaseous space of each inner tube 12, so as to be cooled and condensed by the heat storing agent 15 in which the cooling energy has been stored during the night. This condensation is performed in an efficient manner, because about a half of the whole surface area of the inner tube 12, above the level of the liquid refrigerant, serves as the heat transfer surface. It will be seen that the two-way heat exchange is made in an efficient manner, through the gaseous space of the inner tubes 12, during both day-time and night-time.

When the heat storage means 5 is not disposed in a horizontal position, the liquid refrigerant and the gaseous refrigerant are collected, respectively, at the upper and lower portions of the heat storage means 5. In such a case, the liquid refrigerant at the lower portion is evaporated to cool the heat storing agent 15 at night, whereas during day-time, the gaseous refrigerant at the upper portion is condensed by the cooling energy derived from the heat storing agent 15.

Needless to say, it is possible to enhance the evaporation and condensation of the refrigerant in the heat storage means 5 by forming on the inner surface of the inner tube 12 a wick which provides a capillary action.

In the cooling arrangement described, the heat storage means 5 has a double tube construction constituted by an inner tube charged with the refrigerant and an outer tube 13 which cooperates with the inner tube in defining therebetween an annular space charged with the heat storing agent.

Since the refrigerant is confined at a high pressure within the inner tube 12 having a small diameter, the heat storage means 5 as a whole sufficiently withstands the high internal pressure of the refrigerant.

Further, in the described embodiment, almost all of the volume in the annular space between the inner and the outer tubes is occupied with the refrigerant, while the remaining part of the volume is filled with a compressed gas. Therefore, the pressure in the heat storage means 5 does not come down to a value below the atmospheric pressure, even when the volume of the heat storing agent 15 is reduced as a result of cooling and solidification of the same.

Therefore even if the air-tightness of the outer tube 13 is not perfect, the ambient air is prevented from entering the heat storage means 5, contributing to the maintenance of the quality of the heat storing agent 15.

The use of fatty acids as the heat storing agent 15 offers the following advantages. Namely, this heat storing agent has a high solidifying point, and the required superheating is as small as several degrees when the solidifying point at the commencement of solidification is different from the melting point to require some super-cooling. Therefore, the refrigerant need not be at a low temperature to solidify the heat storing agent. A rather high night-time outdoor temperature around 30 C is adequate for the achievement of the solidification.

In addition, the fatty acids have a relatively stable performance, and are generally not very poisonous.

Particularly, the fatty acids having a large number of carbon exhibits superior properties such as low poisonousness.

Hereinunder, experimental results obtained with a cooling arrangement according to the invention will be described with specific reference to Figure 4.

In this experiment, the size of the shelter 3, the size and construction of the heat insulating structure and the heat output from the equipment in the shelter 3 were selected to be equal to those of the actual radio relay station, so as to simulate the actual operating condition as much as possible. The shelter was situated in a room whose temperature was changed to simulate the large temperature change experienced in the desert or like regions in Africa orthe Middle East. The state of cooling in the shelter 3, and the operation of the heat storage means 5 were observed employing a cooling arrangement as shown in Figures 3A and 3B, the result of which is shown in Figure 4.

More specifically, a rectangular parallelopiped shelter of 2.3 m in width, 2.3 m in depth and 3.1 m in height was used. In order to reduce the overall heat transmission coefficient, a heat insulating material lining 8 of urethane foam of 150 mm in thickness was used. The urethane foam lining 8 was sandwiched by a pair of 1.6 mm thick steel sheets which in turn were coated with laminated white vinyl chloride coating. Consequently, the overall heat transmission coefficient was reduced to K = 0.2 Kcal/m2 h C, while the reflection factor of the wall surface was increased to E = 0.6 or higher. Incandescent lamps or the like for producing a total heat output of 150 W were placed at a position where the telecommunication equipment 2 is to be placed, so as to simulate the latter.

As means for changing the temperature of the inside of the shelter 3, an electric heater of 0.5 kW and a motor-driven fan were placed above the shelter. The temperature in the shelter 3 was changed between 50 C and 35 C by suitably operting this heater and fan, to simulate the ambient temperature change. The simulated temperature of 45 C is for 19 to 20 o'clock; 40 C, for 21 to 23 o'clock; 35 C, for 24 to 7 o'clock; 40 C, for 8 to 10 o'clock; 45 C, for 11 to 12 o'clock; and SOC, for 13 to 18 o'clock, as shown in Figure 4.

Cross-fin type heat exchangers were used as the outdoor heat exchanger 6 and the indoor heat exchanger 7 of the cooling apparatus, while refrigerant R-22 was used as the refrigerant. Also, five units of heat storage means 5 were arranged side by side, in which a fatty acid was used as the heat storing agent 15.

As will be seen from Figure 4, it was confirmed from the experimental results that the inside temper- ature of the shelter 3 can be maintained below 50 C even when the outdoor temperature is kept at its maximum.

The heat storing agent 15 in the heat storage means 5 was solidified during the night-time, i.e., from 21 o'clock to 5 o'clock, when the outdoor temperature was between 40 C and 35 C, and was supercooled in the early morning hours till 7 o'clock when the outdoor temperature was 35 C. Then, as the outdoor temperature was elevated, the heat storing agent 15 began to melt at about 10 o'clock (outdoor temp. 450C). The melting was continued throughout the daytime when the outdoor temperature is maintained at its maximum, i.e., C, the daytime lasting until 20 o'clock when the outdoor temperature was lowered to 45 C.

The cooling arrangement of this embodiment is suitable for use with a microwave relay station having a telecommunication equipment of comparatively small heat output of about 150 W. If the heat output is larger, the amount of refrigerant evaporated in the indoor heat exchanger 7 and in the heat storage means 5 must be much larger.

In such a case, it will become necessary to smooth the gravity-induced natural circulation of the refrigerant through various measures. For instance, as will be detailed in the description of other embodiments, two separate pipes interconnecting the lower header 6b of the outdoor heat exchanger 6 and the upper header 7a of the indoor heat exchanger 7 may be employed. In this case, one of these pipes is used for the gaseous refrigerant coming up from the indoor heat exchanger 7, while the other pipe is used for the liquid refrigerant coming down from the outdoor heat exchanger 6.

Alternatively, the outdoor heat exchanger 6 and the indoor heat exchanger 7 may be additionally provided with an upper header and a lower header, respectively. In this case, a smooth flow of the refrigerant can be obtained by connecting a gas pipe and a liquid pipe, respectively, between the upper header of the outdoor heat exchanger 6 and the upper header 7a of the indoor heat exchanger 7, and between the lower header 6b of the outdoor heat exchanger 6 and the lower header of the indoor heat exchanger 7.

In the described embodiment, the heat storage means 5 is disposed at an intermediate level between the outdoor and indoor heat exchangers 6 and 7, and connected to these heat exchangers 6 and 7 through refrigerant pipes, so that the refrigerant may flow naturally by gravity, thereby to store cooling energy in the heat storage means 5. This arrangement, however, permits further modifications. For instance, instead of connecting the heat storage means 5 to the cooling apparatus 4 through refrigerant pipes, the arrangement may be such that the heat storing agent 15 of the heat storage means 5 is air-cooled within the shelter 3, which in turn is cooled by the indoor heat exchanger 7 of the cooling apparatus 4.

Further, it is possible to install the shelter 3 on the steel tower 20 at a certain level from the ground surface, as shown in Figure 5. It is also possible partly to or entirely bury the shelter 3 under the ground, as shown in Figure 6 or 7. In such a case, the portion of the walls of the shelter 3 lying under the ground surface is constituted by a material having a good heat conductivity such as iron or stainless steel, so that the soil around the shelter 3 may be utilized for heat storage. Needless to say, it is possible to use a heat storage means 5' installed in the shelter 3, simultaneously with a heat storage constituted by the soil, as shown in Figure 7. In the latter case, it is possible to reduce the capacity of the indoor heat storage means 5'.

Figure 8 shows still another embodiment of the invention in which a heat pipe 18 provided at both ends with fins and having no wick is used as the cooling apparatus 4. In this case, the upper portion of the heat pipe 18 located above the shelter 3 constitutes the outdoor heat exchanger 6', while the lower portion located in the shelter 3 constitutes the indoor heat exchanger 7'. At the same time, the heat storage means 5 is installed to surround the indoor heat exchanger 7' in close contact with the latter. The heat pipe 18 is charged with the refrigerant. In this embodiment, as in the foregoing embodiments, the refrigerant in the outdoor heat exchanger 6' is cooled and solidified due to the lower temperature at night, and comes down into the indoor heat exchanger 7' to cool the heat storage means 5.In the day-time when the outdoor temperature is high, the cooling energy is released from the heat storage means 5, so as effectively to cool the air in the shelter 3 and, accordingly, the telecommunication equipment 2 disposed in the shelter 3.

Figures 9A to 9C show a modification of the embodiment shown in Figure 3. In this embodiment, a gas pipe 1 is and a liquid pipe 1 ib are used as shown in Figure 9A for connecting the lower header 6b of the outdoor heat exchanger 6 and the upper header 7a of the indoor heat exchanger 7. More particularly, the gas pipe 1 1a connects the upper header 7a to the gaseous upper space of the lower header 6b, as shown in Figure 9B, while the liquid pipe 1 1b connects the lower portion of the lower header 6b to a portion of the upper header 7a other than the portion to which the gas pipe 1 is is connected, as shown in Figure 9C.

This arrangement affords an enhanced natural circulation of the refrigerant by gravity, so that the cooling arrangement can effectively cool electric appliances having a larger heat output than those of Figure 3. Namely, the liquid refrigerant condensed in the outdoor heat exchanger 6 flows down along the liquid pipe 1 1b connected to the lower side of the lower header 6b, while the gaseous refrigerant evaporated in the indoor heat exchanger 7 and in the heat storage means 5 can flow upward through the gas pipe 11b which opens in the upper gaseous space in the lower header 6b, so that the ascending flow of the gaseous refrigerant and the descending flow of the liquid refrigerant do not hinder each other, thereby to smooth the natural circulation of the refrigerant.

The cooling arrangements as shown in Figures 3 and 9A to 9C are suitable for use for cooling a communication equipment of comparatively small heat output. When a larger heat is generated by the communication equipment, the evaporation of the refrigerant in the indoor heat exchanger 7 and the heat storage means 5 may be enhanced correspondingly.

Consequently, the flow velocity of the gaseous refrigerant is increased. In such a case, the ascending flow of gaseous refrigerant and the descending flow of the liquid refrigerant will hinder each other, when the outdoor heat exchanger 6 and the indoor heat exchanger 7 are provided with single headers, respectively, resulting in a less efficient natural circulation of the refrigerant.

To avoid this, each of the outdoor and indoor heat exchangers 6 and 7 can have two headers, as shown in Figure 10. More specifically, a gas pipe 11a is connected between the upper header 7a of the indoor heat exchanger 7 and an upper header 6a which is provided at the upper gas inlet side of the inclined outdoor heat exchanger 6, while a liquid pipe 1 1b is used to connect the lower header 6b of the outdoor heat exchanger 6 and a lower header 7b provided at the lower liquid inlet side of the inclined indoor heat exchanger 7, so that a closed circulation circuit is formed by the outdoor heat exchanger 6, liquid pipe 11 b, indoor heat exchanger 7 and the gas pipe 11a.Further, gas pipes 16 and liquid pipes 17 shunting from these gas pipe 1 lea and liquid pipe 1 ib connect these pipes 11a and 1 1b to the heat storage means 5. Other structural elements are all identical to those of the embodiments as shown in Figures 3 and 9A to 9C.

In operation, the gaseous refrigerant coming from the indoor heat exchanger 7 acting as an evaporator and the gaseous refrigerant coming from the heat storage means 5 flow upwardly into the upper header 6a of the outdoor heat exchanger 6, through the upper header 7a and the gas pipes 16 leading from the upper side of the inner tube 12, respectively, and then flows into the outdoor heat exchanger 6.

The gaseous refrigerant in the outdoor heat exchanger 6 is cooled and condensed as a result of a heat exchange with the low temperature ambient air, and the liquefied refrigerant flows down through the lower header 6b and the liquid pipe 1 it, due to gravity. A part of liquid refrigerant then flows back to the heat storage means 5 through the liquid pipe 17, while the remaining part is returned to the indoor heat exchanger 7 via the lower header 7b. It will be seen that, since the ascending flow of gaseous refrigerant and the descending flow of the liquid refrigerant pass through separate pipes, the circulation of the refrigerant due to gravity is performed in an efficient manner.

In the foregoing embodiments, the heat exchange in the outdoor and indoor heat exchangers 6 and 7 is performed by making use of natural convection of air around these heat exchangers 6 and 7, without employing any forced draught by a motor-driven fan. However, if electric power is available, motordriven fans may be provided for a forced draught to achieve a higher efficiency of heat exchange.

As has been described, there is provided a cooling arrangement having a cooling apparatus including outdoor and indoor heat exchangers 6 and 7 constituting a natural circulation circuit for refrigerant, and a heat storage means 5. During the night-time when the outdoor temperature is low, the cooling energy is stored in the heat storage means 5, through a natural circulation of the refrigerant between the heat exchangers 6 and 7 and the heat storage means 5, while the remaining part of the cooling energy is delivered to the indoor heat exchanger 7 effectively to cool the air in the shelter 3, whereas during day-time when the outdoor temperature is high, the cooling energy released from the heat storage means 5 is delivered to the indoor heat exchanger 7, through a natural circulation of the refrigerant between the heat storage means 5 and the indoor heat exchanger 7, so as effectively to cool the air inside the shelter and, accordingly, the various telecommunication equipment in the shelter 3.

Consequently, no power source nor combustion source is required for the circulation of the refrigerant. Particularly, the power and the combustion are not required at all, when the heat exchange at the heat exchangers is made solely by the natural convection of air. Even if motor-driven fans are used for forced draught around the heat exchangers, the power consumption by these fans is negligibly small.

It is remarkable that the cooling arrangement which consumes no or extremely small power can effectively cool the object in the shelter. The described arrangements are particularly effective in improving the circumstance of unattended communication stations such as microwave relay stations installed in desert or like regions where the difference is very large between the day-time and night-time temperatures.

Claims

1. A cooling arrangement for cooling a space in a room, the arrangement comprising: a cooling apparatus for collecting cooling energy from outdoor air to cool said space when the outdoor temperature is lower than the temperature of said space, said cooling apparatus including a first heat exchanger disposed outside said room, a second heat exchanger disposed inside said room, conduit means connecting said first and second heat exchangers to form a circuit isolated from the atmosphere and a condenseable refrigerant with which said circuit is charged, said second heat exchanger being disposed at a level below said first heat exchanger so that said refrigerant is naturally circulated through said circuit to cool the space when the outdoor temperature is lower than the temperature of said space; and a heat storage means for storing a portion of said cooling energy collected from the outdoor air through said cooling apparatus, said storage means releasing said cooling energy to cool the space when the temperature of said space rises beyond the temperature of the heat storage means.

2. A cooling arrangement as claimed in claim 1, wherein said heat storage means is cooled by said refrigerant in said cooling apparatus to store cooling energy.

3. A cooling arrangement as claimed in claim 1, wherein said cooling apparatus further includes a third heat exchanger fluidically connected to said circuit for performing a heat exchange between said refrigerant and said heat storage means, said third heat exchanger being disposed at a level below said first heat exchanger and above said second heat exchanger, whereby natural circulation of the refrigerant is established between the first and third heat exchangers to cool the heat storage means by the outdoor air when the outdoor temperature is lower than the temperature of said heat storage means, and between the second and third heat exchangers to cool the space by the heat storage means when the temperature of said sapce is higher than that of said heat storage means.

4. A cooling arrangement as claimed in claim 1, wherein said heat storage means is cooled through the air in said room, said air being cooled by said cooling apparatus.

5. A cooling arrangement as claimed in anyone of claims 1 to 4, wherein said room is defined by a shelter for accommodating a telecommunication equipment of a radio relay station.

6. A cooling arrangement as claimed in anyone of claims 1 to 4, wherein said room is defined by a shelter for accommodating a telecommunication equipment of each of a plurality of radio relay stations which are situated at substantially constant intervals.

7. A cooling arrangement as claimed in claim 1 or 4, wherein said room is defined by a shelter accommodating a telecommunication equipment of a radio relay station, said shelter being at least partly buried under the ground surface, the underground portions of the wall of said shelter having a portion constituted by a material having a good heat conductivity, so that the ambient soil constitutes said heat storage means.

8. A cooling arrangement as claimed in claim 1 or 4, wherein said room is defined by a shelter accommodating a telecommunication equipment of each of a plurality of radio relay station which are situated at, substantially constant intervals, said shelter being at least partly buried under the ground surface, the underground portions of the wall of said shelter having a portion formed of a material having a good heat conductivity, so that the ambient soil forms said heat storage means.

9. A cooling arrangement as claimed in claim 3, wherein said third heat exchanger has a double pipe construction formed by an inner pipe and an outer pipe, said inner pipe being in communication with said conduit means of said cooling apparatus, while the space between said inner and outer tubes being charged with a heat storing material.

10. A cooling as claimed in claim 9, wherein heat exchanges at said first and second heat exchangers between said refrigerant and air are performed by natural convection of air around said first and second heat exchangers.

11. A cooling as claimed in claim 9, wherein said first and second heat exchangers are disposed in inclined postures, and wherein said conduit means have a first header connected to the lower end or its vicinity of said first heat exchanger and a second header connected to the upper end or its vicinity of said second heat exchanger.

12. A cooling arrangement as claimed in claim 11, wherein said third heat exchanger is disposed substantially horizontally, and wherein said inner tube of said third heat exchanger is connected at its upper portion to the upper portion of said second header through a gas pipe, and, at its lower portion, to the lower portion of said second header through a liquid pipe.

13. A cooling arrangement as claimed in claim 11 or 12, wherein said first and second headers are connected to each other by a single pipe.

14. A cooling arrangement as claimed in claim 11 or 12, wherein said first and second headers are connected to each other by at least two pipes, one of said two pipes communicating with a liquid space in said first header, while the other of said two pipes communicating with a gaseous space of said first header.

15. A cooling arrangement as claimed in claim 9, wherein said third heat exchanger is disposed substantially horizontally.

16. A cooling arrangement as claimed in claim 12 or 15, wherein said circuit is filled with said refrigerant by such an amount that the level of the liquid refrigerant in said innertube of said third heat exchanger is located substantially at the mid-point of the height of said inner tube.

17. A cooling arrangement as claimed in claim 13, wherein said circuit is filled with said refrigerant by such an amount that the level of the liquid refrigerant in said inner tube of said third heat exchanger is located substantially at the mid-point of the height of said inner tube.

18. A cooling arrangement as claimed in claim 14, wherein said circuit is filled with said refrigerant by such an amount that the level of the liquid refrigerant in said inner tube of said third heat exchanger is located substantially at the mid-point of the height of said inner tube.

19. A cooling arrangement as claimed in anyone of claims 9, 10, 11, 12 and 15, wherein said heat storing material is a fatty acid.

20. A cooling arrangement as claimed in claim 13, wherein said heat storing material is a fatty acid.

21. A cooling arrangement as claimed in claim 14, wherein said heat storing material is a fatty acid.

22. A cooling arrangement as claimed in claim 19, wherein a plurality of fins are provided on the outer surface of said inner tube of said third heat exchanger.

23. A cooling arrangement as claimed in claim 9 or 15, wherein said first and second heat exchangers are connected to form a closed loop.

24. A cooling arrangement as claimed in claim 23, wherein said first and second heat exchangers are disposed in inclined postures, and wherein the upper ends or their vicinities of said first and second heat exchangers are connected to each other, while the lower ends or their vicinities of said first and second heat exchangers are connected to each other.

25. A cooling for cooling a finite space defined by a building structure for accommodating a heatgenerating body, said building structure being arranged to be located in a geographical region where a large difference is observed between maximum day-time and minimum night-time temperatures, said cooling arrangement comprising; a first heat exchanger disposed outside said space; a second heat exchanger disposed inside said space at a level lower than said first heat exchanger; a heat storage means disposed inside said space at a level intermediate between said first and second heat exchangers; a conduit means forming a closed fluid path linking and extending into said first and second heat exchangers and said heat storage means;; a condensable refrigerant filling and flowing through said fluid path depending on the temperature difference between said space and outside thereof, said refrigerant being capable of evaporating through heat absorption at a temperature higher than a value preset for said space, and of being liquefied through heat discharge at a temperature lower than said maximum daytime temperature; and a heat storing agent charged in said heat storage means in contact with said fluid path, said heat storing agent being capable of being solidified through heat discharge when cooled during nighttime by said refrigerant flowing thereinto after being cooled at said first heat exchanger, and of being liquified through heat absorption when heated during day-time by said refrigerant heated due to said heat generating body.

26. A cooling arrangement substantially as hereinbefore described with reference to Figures 2, 3A and 3B of the accompanying drawings.

27. A cooling arrangement substantially as hereinbefore described with reference to Figures 2, 3A and 3B as modified by Figure 5 of the accompanying drawings.

28. A cooling arrangement substantially as hereinbefore described with reference to Figures 2, 3A and 3B as modified by Figure 6 of the accompanying drawings.

29. A cooling arrangement substantially as hereinbefore described with reference to Figures 2, 3A and 3B as modified by Figure 7 of the accompanying drawings.

30. A cooling arrangement substantially as hereinbefore described with reference to Figures 2, 3A and 3B as modified by Figure 8 of the accompanying drawings.

31. A cooling arrangement substantially as hereinbefore described with reference to Figures 2, 3A and 3B as modified by Figure 10 of the accompanying drawings.