WO1998010629A2

WO1998010629A2 - An equipment cabinet and a method for controlling the temperature and relative humidity of internal air in such an equipment space

Info

Publication number: WO1998010629A2
Application number: PCT/FI1997/000511
Authority: WO
Inventors: Jorma Manninen
Original assignee: Nokia Telecommunications Oy
Priority date: 1996-09-06
Filing date: 1997-09-02
Publication date: 1998-03-12
Also published as: FI104131B1; AU722793B2; WO1998010629A3; FI104131B; NZ334499A; DE19782002T1; FI963492A0; FI963492A; CN1229570A; DE19782002B4; AU4119797A; CN1113591C

Abstract

The invention is related to the control of temperature and relative humidity of the internal air in an equipment space (10), especially in a space for electric or telecommunications equipment. The temperature is controlled by changing the cooling power directed to the equipment space by the cooling equipment (13) included in the equipment space in such a way that the temperature of the internal air remains within the allowed temperature range defined by the requirements of the equipment located in the equipment space. The relative humidity of the internal air in the equipment space is controlled by using the same cooling equipment and by additionally keeping the temperature at such a level that the relative humidity of the internal air remains within the allowed value range defined by the humidity requirements of the equipment located in the equipment space. In order to implement the control by using as simple equipment as possible, the environmental conditions of the geographical location of the equipment space are used as a basis for selecting the value range for the absolute humidity, the value range corresponding to the said conditions, the selected value range and the humidity requirements of the equipement are used as a basis for defining the first temperature range allowed for the internal air in the equipment space, the defined first temperature range and the temperature requirements of the equipment are used as a basis for selecting the minimum and maximum temperature values allowed for the internal air in the equipment space, and both the temperature and the relative humidity are controlled solely on the basis of a control message given by a sensor measuring the temperature, by keeping the temperature between the minimum and maximum values selected.

Description

AN EQUIPMENT CABINET AND A METHOD FOR CONTROLLING THE TEMPERATURE AND RELATIVE HUMIDITY OF INTERNAL AIR IN SUCH AN EQUIP MENT SPACE

Field of the invention

The invention is related in general to the control of the quality of the air inside an equipment space, and in particular to the control of temperature and relative humidity in spaces which contain electric and telecommunications equipment, are located in a damp environment and require cooling equipment in order to ensure reliable operation.

Background of the invention

In order to ensure normal operation of equipment, it is important that the relative humidity of the air in spaces containing electric and telecommunications equipment (from now on referred to by the more general term 'equipment space'), such as cabinets installed outdoors, remain within the allowed limits. Too high/low relative humidity of the internal air shortens the lifespan of the equipment and may cause operating errors.

Electric devices generate heat during operation. However, large amounts of heat cannot be removed from closed spaces without mechanical devices, such as an air-to-air heat exchanger, an air-to-liquid heat exchanger or a so-called heat-pipe heat exchanger (which are all referred to as heat exchangers from now on). If the temperature and humidity of the environment fluctuate heavily as happens, for example, in tropical conditions, the equipment space and its heat exchanger are exposed to condensation/condensing of the internal air into water. Condensation usually takes place as the temperature of the environment changes rapidly. This may endanger the operation of the electric equipment.

Previously, the problem of condensation in the equipment spaces of electric or telecommunications equipment has been solved, for example, by sealing off the equipment space from the environment, so that water vapour cannot get into the equipment space. This solution is expensive and, in the long run, it may not be reliable.

Another known solution for solving the problem of humidity is to install various chemical dehumidifiers in the equipment space. The operating time of these chemical dehumidifiers is rather limited and they may require regeneration/refreshing often, depending on the environment. The humidity has also been controlled with various mechanical devices, such as cooling devices, which are used to create a so-called cold spot in a certain part of the equipment space. In this spot the water vapour condenses into water which is removed in a controlled manner. The disadvantage common to the above-mentioned known solutions is that they are additional devices, as regards the cooling equipment of the equipment space, they make the equipment more complicated, require additional investment, increase the total energy consumption and/or increase the need for servicing of the equipment. The need for additional equipment has been decreased in the method presented in the DE publication DE-A1-3811189. In this method the relative humidity of the internal air in an equipment cabinet is controlled by using the same cooling equipment which is used for controlling the temperature of the internal air. The temperature is controlled by using the measure- ment acquired from a temperature sensor and the relative humidity by using the measurement acquired from a humidity sensor. The equipment is still rather complicated and several setting values must be defined in order to carry out the control. This means that the manufacturing and servicing of the equipment requires expertise. For these reasons, the manufacturing, installation and servicing of the equipment cabinets is still relatively expensive, especially as the number of cabinets is increased. Thus, for applications where exact humidity control is not necessary, the solutions described above are oversized.

Summary of the invention The objective of the invention is to remove the above-mentioned disadvantages and to solve the humidity problem in such a way that the temperature and the relative humidity of the internal air in an equipment space can be controlled by using as simple equipment as possible and by utilising the technology existing in the equipment space as efficiently as possible. This objective can be obtained by using the solution defined in the independent patent claims.

The solution in accordance with the invention is also based on the above-mentioned idea of controlling the relative humidity of the internal air by using the same cooling equipment that is used for adjusting the temperature of the equipment space. The idea of the invention is to define, by using the environmental conditions of the equipment space installation site and, for example, the known Mollier diagram, a temperature range which makes it possible to adjust both the temperature and the relative humidity by using only the measurement acquired from the temperature sensor.

The advantages of the solution in accordance with the invention are its beneficial features in the economical sense and the security of the operation. The beneficial features are based on the more efficient utilisation of the existing equipment and on the minimal number of required additional components. The solution in accordance with the invention is also advantageous from the point of view of service. This is not only due to the fact that no addi- tional components are required but also due to the fact that the logic circuit required for the control is typically reliable in operation and service-free.

Due to the solution in accordance with the invention, there is no need to seal off the equipment space from the environment in order to have it vaporproof. This in turn enables considerable economic savings. The solution in accordance with the invention also has the additional advantage that the lifespan and reliability of the equipment or the components installed in the equipment space are very likely to increase. This is due to the fact that the temperature adjustment required by the relative humidity decreases the temperature fluctuations present in the equipment space as a function of time (for example, the difference between the highest and the lowest temperatures during a day decreases).

The solution in accordance with the invention also has the additional advantage that it is easy to add the control of relative humidity to equipment cabinets that have already been installed. This can even be done re- motely by setting the new temperature limits required by the humidity control.

Brief description of the figures

In the following, the invention and its embodiments are described more closely with reference to the examples in accordance with the accompa- nying drawings, in which

Figure 1 shows the equipment space equipped with a control mechanism in accordance with the invention, Figure 2 is a simplified Mollier diagram which illustrates the selection of the temperature limits in order to control the temperature and the rela- tive humidity of the equipment cabinet by using only a temperature sensor, and Figure 3 is a flow chart illustrating the adjustment in accordance with the invention.

Detailed description of the invention

In the following, the invention is described in further detail with reference to an exemplary case in which the space for telecommunications or electronic equipment, for example, has been equipped with some known heat exchanger which takes care of the cooling required by the said equipment.

Normally the relative humidity of the air in the equipment space rises to the condensation level (100% RH) when the outside temperature drops low enough. Then the heat exchanger is too powerful as regards the conditions and the air in the equipment space cools too much. In an equipment space in accordance with the invention, the control of the relative humidity of the internal air is based on decreasing the heat transfer rate of the heat exchanger as the relative humidity increases. As the heat transfer rate decreases, the temperature of the internal air rises and its relative humidity decreases (because the same amount of water vapour causes a higher relative humidity in a lower temperature than in a higher temperature). Thus, by adjusting the heat transfer rate of the heat exchanger, both adequate cooling of the electronic equipment and an acceptable relative humidity of the internal air can be achieved.

Figure 1 illustrates the principle in accordance with the invention by showing a diagram of an equipment cabinet 10, in accordance with the invention, equipped with a typical heat exchanger 13. The internal air circulation of the heat exchanger is handled by a fan (or a pump, if a liquid circulation is involved) 14a and the external air circulation by a fan (or a pump) 14b. The actual exchanger core 15 (cells, disk pack, etc.), which reserves heat and trans- fers it from the internal circulation to the external circulation, is located between the internal and external circulations.

A sensor 11 metering the temperature of the internal air in the equipment space has been installed in the equipment space. The sensor may be located, for example, in the location within the space where the tempera- ture is the highest (in the upper part of the equipment space or near the hottest devices). This selection of location is based on adjusting the temperature of the equipment space primarily on the basis of the temperature criteria of the equipment. However, especially in situations in which the maximum and minimum temperatures of the equipment are defined on the basis of the humidity criteria of the equipment, the temperature sensor may be located in some other place.

Even though the relative humidity is also adjusted, there is no need for a separate humidity sensor in the equipment. The reason for this is that it is possible to control the relative humidity by using only the control message given by the temperature sensor, when the environmental conditions of the equipment space are known. On the basis of the geographical location of the equipment space, it is possible to define a required value for the absolute air humidity, for example, a value which is not exceeded in any circumstances (excluding peaks caused by rain; the equipment is protected against splashing water). In tropical conditions, for example, the typical maximum value for the absolute humidity is 0.025 (kg H₂O/kg of dry air, that is, kilograms of water vapour per kilogram of dry air). A certain temperature value corresponds to the selected absolute humidity and the highest relative humidity allowed in the equipment space (the temperature value can be determined by using, for example, the Mollier diagram for humid and wet air). In controlling the relative humidity (the upper limit), it is enough to take this temperature value into consideration when adjusting the temperature so that the temperature of the internal air does not go below this value. Correspondingly, in controlling the lower limit of the relative humidity, it is enough to consider, when adjusting the temperature, a certain highest allowed temperature, defined by the environmental conditions, which the temperature of the internal air in the equipment space must not exceed. Thus, we know that the relative humidity of the internal air in the equipment space remains within the allowed limits.

So we let the absolute humidity of the internal air in the equipment space follow the absolute humidity of the air outside. In other words, the equipment space is not sealed off from the environment to be vaporproof. In this respect it is enough to prevent water entering the equipment space from outside and to prevent any significant mixing of internal air with the air outside (additional cooling).

The signal from the temperature sensor 11 is connected to the control logic circuit 16 which is used to adjust the cooling power of the heat exchanger. This can be done, for example, by adjusting the ratio of the air flows/mass flows of the internal and external circulations of the heat exchanger (the ratio of the flows) or the heat transfer area. In practice it is probably simplest and most economical to adjust the ratio of the air flows/mass flows (although the adjustment can be made also in such a way that the ratio of the flows remains the same).

The adjustment of the ratio of the air flows in the internal and external circulations of the heat exchanger can be implemented, for example, by adjusting the rotation speed of the external circulation fan 14b of the heat exchanger. In this way the circulation of the air inside the equipment space works on a constant speed and realises the air flow conditions required for the cooling of the electronic equipment. When the temperature inside the equipment space drops and the relative humidity of the internal air rises to a certain predefined maximum value (for example, 60% RH), the control logic 16 decreases the cooling of the equipment space by decreasing the rotation speed of the external circulation fan 14b of the heat exchanger. Information on the change in the relative humidity is obtained from the temperature sensor 11 which sends a signal showing that the temperature has dropped and is now at the value which corresponds, at the maximum, to the said predefined maximum value for the relative humidity (when the maximum value of the absolute hu- midity is a certain constant).

The rotation speed can be decreased until the signal from the temperature sensor shows that the temperature has risen to a value which corresponds, at the minimum, to the predefined minimum value for the relative humidity (or the temperature of the air inside the equipment space reaches the maximum value allowed as regards the temperature criteria).

In the following, the selection of the upper and lower limits of the temperature range allowed for the air inside the equipment space in order to also control the relative humidity by using only the temperature sensor is described in more detail with reference to Figure 2. Figure 2 shows the known Mollier diagram in a simplified form. The slant vertical axis illustrates temperatures. Temperatures are marked in the diagram in 10 degree steps on a scale of 0°C to 60°C.

In order to use the Mollier diagram, the temperature and humidity values of the geographical installation location of the equipment space must be established. This can be done either by using one's own measuring equip- ment or by using public statistical data offered by, for example, universities, departments of meteorology or commercial information services.

When using one's own measuring equipment, the temperature and humidity sensors are installed outdoors at the installation site. The humidity to be measured can be either relative or absolute humidity. The longer the measuring period, the more accurate and reliable the control is. Of course, one's own measuring results can be complemented by using statistical data offered by public institutes or information services. Because the (possible) measurement of temperature and humidity values is known as such, it is not described in more detail here.

The temperature and humidity information offered by public institutes are typically given as the minimum, maximum and average temperatures for a month and as the minimum, maximum and average values of the relative humidity for a month. The minimum and maximum values of the temperature of the environment and the minimum and maximum values of the relative humidity of the environment are marked on the Mollier diagram. In this way, an area defined by the environment can be marked on the Mollier diagram and this area shows the range of variation of relative humidity in the environment around the equipment space. Let us assume that the temperature at the installation site varies between T^δ and T₂=25°C and the relative humidity between RH,=90% and RH₂=80%. When these two ranges are marked on the Mollier diagram, the minimum value of the absolute humidity Xmin can be obtained from the intersection (P2) of the curve RH₂ and the temperature T₂ and the maximum value of the absolute humidity Xmax can be obtained from the intersection (P1) of the curve R^ and the temperature T- (extreme values of the section). In this example Xmin«0.016 kg H₂O/kg of dry air and Xmax«0.033 kg H₂O/kg of dry air.

After this, the minimum and maximum values for the temperature and the relative humidity, defined on the basis of the requirements set for the equipment, are marked on the Mollier diagram. In the example shown in the figure it is assumed that the maximum and minimum temperatures allowed for the equipment are T₃=55°C and T₄=10°C and the maximum and minimum values for the relative humidity required by the equipment are RH_mιn=20% and RH_max=60%. After this the Mollier diagram can be used to define the initial values for the maximum and minimum temperatures (T_max and T_mιn) of the internal air in the equipment space. The initial maximum value can be obtained from the intersection (P3) of the straight line corresponding to the minimum value of the absolute humidity (Xmin) and the minimum curve of the relative humidity (RH_mrn). The initial minimum value can be obtained from the intersection (P5) of the straight line corresponding to the maximum value of the absolute humidity (Xmax) and the maximum curve of the relative humidity (RH_max). In this example, the values obtained are T_max=49°C and T_mιn=42°C. These initial values are compared to the temperature requirements of the equipment and the final temperature limits are selected in such a manner that both the temperature and the relative humidity remain continuously within the allowed range. In the example presented above, the humidity requirements of the equipment define the temperature limits in practice, that is, the temperature requirements of the equipment are not as strict as the humidity requirements. Thus, the selected final limits in this example are the values T_max=49°C and T_mjn=42°C.

If the daily cycle of variations in the temperature and the relative humidity at the installation site are well known, the minimum value T_mn does not necessarily need to be selected from the above-mentioned intersection (P5), but some other temperature value from the curve RH_max can be used as long as the absolute humidity corresponding to that value is between the values Xmin and Xmax (including these values). In this example, this means that the minimum temperature of the equipment space can be between T_mιn=42°C and T_mn=30°C (the temperature corresponding to the point P4).

In the example presented above, the relatively low maximum value (60%) of the relative humidity of the equipment (as compared to the environmental conditions) limited the minimum temperature to a relatively high value. If the maximum value allowed by the equipment is, for example, 90%, the minimum temperature defined using the method described above is T_rnιn=35°C. It may further be possible to lower this minimum temperature, on the basis of the daily cycle of variation of the temperature and the relative humidity, to a value that is between 23°C and 35°C.

The flow chart in Figure 3 illustrates the control carried out by the control logic when only the measurement of temperature is used. The phases described above are marked in the figure by using reference numbers 20 and 21. These phases take place before the installation of the equipment cabinet or before adding the humidity adjustment to existing equipment.

For the control, the minimum and maximum values for the absolute humidity are defined for the environmental conditions of the equipment cabinet installation site (phase 20). This can be done by using statistics or one's own measurements and the Mollier diagram as described above. It is also possible to obtain the minimum and maximum values of the absolute humidity directly from the statistics. The minimum and maximum values (T_max and T_mn) for the air temperature in the equipment space are defined on the basis of the value range of the absolute humidity and the temperature and humidity requirements of the equipment.

In this way it is possible to set the upper and lower limits of the allowed temperature range in the control logic (phase 30). After this there is a transfer to the continuous operation, which begins with the control logic circuit reading the equipment space temperature (T) coming from the sensor 11 (phase 31). The value obtained is compared to the set upper limit (phase 32). If the equipment space temperature is higher than the maximum value allowed, the cooling power is increased (phase 33). If this is not the case, the next step is to see whether the equipment space temperature is lower than the minimum value allowed (phase 34). If this is the case, the cooling power is decreased (phase 31). In the opposite case, the next step is to read a new value for the equipment space temperature. Using the method described above, a constant effort is made to keep the temperature in the allowed range.

Equipment equipped with just a temperature sensor and an adjust- ment algorithm in accordance with Figure 3 is naturally a more economic solution than equipment equipped with both a temperature sensor and a humidity sensor. Regardless of the more robust adjustment, it is an adequate solution in most cases, because few applications require exact adjustment of relative humidity. Additionally, the solution has other advantages which have been de- scribed above.

There are various different options for implementing the principle in accordance with the invention. These are described briefly below.

For example, the increasing/decreasing of the cooling power can be handled in many different ways. As these methods are known and are not re- lated to the actual idea of the invention, they are not described in more detail here. The adjustment of the external circulation fan can be implemented, for example, using two or more steps. For example, using two speeds can be an adequate option in practice. The adjustment can also be stepless.

The adjustment of the ratio of the air or mass flows can be imple- mented by affecting both or just one of the flows. The adjustment can also be made, for example, by choking the air flows by using adjustment plates or affecting the amount of flow coming into the exchanger (cells, disk pack, etc.) by channelling.

The idea in accordance with the invention can also be utilised in connection with compressor cooling. In this case the adjustment can be implemented, for example, by limiting the amount of air in the equipment space going through the vaporiser, in which case the cooling of the equipment space is decreased, or by adjusting the amount of cold matter coming into the vaporiser. Also the temperature measurement can be done in very many different ways, for example, based on the thermal expansion of liquid, the thermal expansion of solid matter, the capillary effect, the thermoelectric effect, the electric resistance of material or the thermal radiation emitted from matter. Because the actual implementation of the measurement is not related to the in- vention, it is not described in more detail. The essential aspect as regards the measurement is that it can be implemented with known methods and known and commercially available sensors can be selected for the measuring. One possible, commercially available temperature sensor is the Vaisala DTS12A.

Although normally the temperature is increased when the relative temperature exceeds the allowed limit, the adjustment can also be made in an opposite direction (that is, the temperature is lowered, if the relative humidity decreases too much). In principle, the idea in accordance with the invention can be used in any equipment space or other space in which the air must meet similar requirements as the air inside a space for electric or telecommunica- tions equipment, so the term 'equipment space' is to be understood as a term which is not necessarily limited to mean only space for electric or telecommunications equipment.

Even though the invention has been described in relation to examples referring to the accompanying figures, it is clear that the invention is not limited to these, but that it can be varied in many ways within the limits of the idea of the invention presented in the accompanying claims.

Claims

1. A method for controlling the temperature and relative humidity of internal air in an equipment space (10) according to which

- the temperature of the internal air in the equipment space is con- trolled by changing the cooling power directed to the equipment space by the cooling equipment (13) included in the equipment space in such a way that the temperature of the internal air remains within the allowed temperature range defined by the requirements of the equipment located in the equipment space, and - the relative humidity of the internal air in the equipment space is controlled by using the same cooling equipment and by additionally keeping the temperature at such a level that the relative humidity of the internal air remains within the allowed value range defined by the humidity requirements of the equipment located in the equipment space, ch a racterized in that

- minimum and maximum values for the temperature of the internal air in the equipment space are selected on the basis of the absolute humidity in the geographical location of the equipment space and on the basis of the temperature and humidity requirements of the equipment, and - both the temperature and the relative humidity are controlled on the basis of a control message given solely by a temperature sensor, by keeping the temperature between the minimum and maximum values selected.

2. A method according to claim ^characterized in that the value range for the absolute humidity is selected by using the known Mollier diagram.

3. A method according to claim 1, characterized in that the equipment space (10) is equipped with a heat exchanger and the controlling is done by changing the heat transfer rate of the heat exchanger in response to the temperature indicated by said sensor.

4. A method according to claim 3, characterized in that the heat transfer rate of the heat exchanger is controlled by changing the ratio of its internal and external circulation flows.

5. A method according to claim 4, c h a r a c t e r i z e d in that the heat transfer rate of the heat exchanger is controlled by changing only the external circulation flow.

6. An equipment cabinet which comprises

- cooling equipment (13) for controlling the temperature of internal air in the cabinet,

- first means for measuring a quantity indicating the relative humid- ity of the internal air, and

- second means (15, 16) for controlling the relative humidity of the internal air by changing the temperature of the internal air as a response to said quantity indicating that the relative humidity has reached a certain limit value, characterized in that the first means consist only of a tempera- ture sensor (11) and that the information about the temperature value corresponding to the said limit value has been stored in the second means.

7. An equipment cabinet according to claim 6 in which the cooling equipment comprises a heat exchanger, characterized in that the second means comprise a fan (14b) maintaining the external circulation of the heat exchanger and a control logic circuit (16) controlling the speed of the fan.