WO1996016485A1

WO1996016485A1 - Method of emergency cooling of an equipment room in which existing cooling equipment is out of service

Info

Publication number: WO1996016485A1
Application number: PCT/SE1995/001309
Authority: WO
Inventors: Rolf Ulfvengren; Anders Johansson
Original assignee: Skövde Climator Ab
Priority date: 1994-11-21
Filing date: 1995-10-26
Publication date: 1996-05-30
Also published as: SE9404056L; SE9404056D0; EP0820660A1

Abstract

This application describes a way of providing emergency cooling of a room containing heat-emitting equipment. Emergency cooling is required in the event of a power failure in the room containing heat-emitting equipment even during a break in the power supply, when battery operation often comes into force. Then problems occur in that the battery capacity does not permit operation of the cooling equipment. This invention shows a way of obtaining emergency cooling of material with a high thermal capacity, thanks to phase changes. In this way the heat-emitting equipment can work without interruption in the event of a power failure without the equipment's maximum working temperature being reached, which would be the case without emergency cooling.

Description

Method of emergency cooling of an equipment room in which existing cooling equipment is out of service.

Earth-bound versions of mobile telecommunications systems require a large number of transmission/reception stations. These stations are often placed in containers or small buildings. The working equipment emits a large amount of energy as a result of it being used. To avoid the risk of overheating, which is a great problem with this type of station, the units are equipped with cooling devices, often in the form of air conditioning. In countries with hot climates - desert areas, for example - a power failure can have serious consequences. A container holding heat-emitting equipment whose cooling is suddenly out of operation can result in the performance of the equipment stopping or being seriously impaired. There is therefore a need for emergency cooling. This emergency cooling must work without outside energy and also be effective over the time during which a power failure could be imagined.

The possibility of using phase-changing material (PCM) for temporary energy storage has been earlier demonstrated. A common material capable of providing these energy-storage facilities is Glauber's salt, i.e. sodium sulphate decahydrate. Glauber's salt has a change point at a temperature of about 30°C, when a part of the water of crystallization is lost. At the same time the sodium sulphate can dissolve in the water released. During 'melting' both the heat of crystallization and heat of transformation are absorbed. In the reverse case, energy is given off. By adding salts, such as common salt, the temperature at which this phase change takes place can be reduced. These are facts known in the literature. This is called a passive system, in contrast to air conditioning, which is called an active system.

The problem with passive systems, despite the simple theoretical explanation, is that they are rather large. One problem is how in a practical way does one re-cool a charged passive system. If emergency cooling for period has been necessary, the passive phase-change system will be charged, i.e. melt and a solution will be formed. The duration of such emergency cooling is so limited in time that the total capacity can only just be used. When the normal cooling system has restarted, it is a matter of restoring the phase-changing material back to the state in which it can store energy. It has even been found that this re-cooling sequence is difficult to achieve, specially taking into account air currents and the design of the containers for the phase- changing material.

This invention describes a way of designing a station of limited volume containing electronic components, preferably in the field of telecommunications, in such a way that an emergency cooling capacity of passive type can be used. This way consists of packing phase-changing material in material that permits a high rate of heat transfer and, at the same time, possesses sufficient impermeability so as to assure the vapour tightness of the components. The packaging units shall be of a size adapted to fast absorption of surplus heat, but also for quickly giving off heat during re-transformation to the heat-absorbing state. It has been found in practice that it is advantageous to use aluminium as the packaging material. The form of the unit shall be such that the volume/area ratio (square centimetres: cubic centimetres) should be between 1 and 2. A specially advantageous results have been obtained with the ratio 1.5. In addition, it has been found that the contents of the units should weigh less than 500 grams.

Another important detail is the location of the units in relation to the heat- generating equipment and to the equipment used for re-cooling the material.

The heat absorbing units with the correct volume/area ratio shall preferably be placed above the heat generating equipment. Cold outside air, which is normally available at night, is used for re-cooling. It is therefore a matter of monitoring the outside temperature and allowing outdoor air to flow through system of heat-absorbing units. It has been found advantageous to use a small (smaller than 100 W) fan for transporting the cooling air past the units.

Figure 1 shows a general arrangement. The outside walls (1) are well insulated. The upper part of the room is fitted with shelves (2) on which the units containing the phase-changing material are placed. The shelves are placed so as to create a duct connected to the electrically operated fan (4) for admitting the outdoor air. In the duct is also placed a fan (5) that provides an air flow through the duct. The outdoor air admitted is then transported down to the vicinity of the heat-generating equipment, where a slave valve has been opened to permit the air admitted as described above to flow out.

In the room there is an air conditioning installation. Under normal conditions this provides the necessary cooling of equipment to such a temperature that the equipment performs in accordance with stipulated requirements. A temporary power failure can occur at an unfavourable time of day, i.e. when the solar radiation is strong. To function satisfactorily, telecommunications stations of this type are equipped with a back-up system using batteries as the source of energy. Cooling, on the other hand, requires so much power that it is not used as the possible operating time for the back-up unit would be far too short. In such a case, the phase-changing material comes into force and stores the heat generated by the equipment. The energy stored in the batteries can be used to drive the equipment. When the power comes on again, the cooling unit starts again. This can then be run sufficiently hard to restore the phase-changing material. Alternatively, below a certain given ambient temperature in the surroundings of the station, the valve mentioned above can open to admit cooler air. This can suitably be controlled by a PLC.

Claims

Patent claim

Method of emergency cooling of an equipment room in which existing cooling equipment is out of service, by using phase-changing material for absorbing energy characterized in that the phase-changing material is packed in a vapour- tight material in units weighing less than one kilogram, where the enclosing area in square centimetres is larger than the volume in cubic centimetres, and which is placed in the upper part of the apparatus room in at least two layers with air circulation, free or forced, between the layers and the units containing phase-changing material.