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Particularly for Outdoor applications extreme environmental influences such as sand, dust, insects, rodents, vandalism and vibration always have to be taken into account. Equally important factors are cold, heat and sun radiation. Therefore suitable climate control (Picture 1) is imperative. In order to keep the noise pollution at the installation site as low as possible, the noise level of such Outdoor cabinets generated by different climate control measures and the installed components has to be kept as low as possible.
Picture 1. Thermal simulation of an Outdoor cabinet with assembled cooling unit
Two versions...
For these applications Schroff has two standardised versions of Outdoor cabinets: “Modular” and “Unibody”. The Modular version is based on an extruded aluminium frame with high flexibility with regard to the cabinet dimensions and at the same time allows good accessibility from all sides. The more affordable Unibody version is based on a one-part aluminium inner housing, which is particularly suited for smaller dimensions for wall, pole and ground mounting. Both cabinet versions protect the assembled components from wind, rain, heat, cold etc. They have flexible assembly possibilities for 19”, ETSI or other, non-standard accessories. The cover parts are coated with a weather resistant powder finish. Furthermore there are no visible screws and assembly parts, thus preventing unauthorised access. The hinged top construction enables easy installation and the cable entry is protected against rodents and insects from the bottom. The cabinets, whose standardised components are based on IEC 61 969, fulfil the guide lines and standards for shock and vibration stability tested to IEC 68-2-6 and -27, earth quake stability and offer a climate protection tested to IEC 68-2-1, -2, -14.
...one climate control concept
The subject climate control is particularly important for outside installation, as here not only the performance loss of the assembled components has to be taken into account, but also the influence of the outside temperatures (summer/winter and time of day). The double wall concept of the Outdoor cabinets from Schroff guarantees a natural air flow between the outer and inner wall, so that considerably fewer measures are required for additional cooling. 85 % of the heat generation through direct and reflective sun rays is kept out.
Additional cooling and heating components
If this and the natural convection are not suffcient, additional cooling components are installed as neede: Filter fans, air/air heat exchangers (LLWT) or a cooling unit. Depending on the framework conditions the concrete cooling requirement is established (Table 1). Speed regulated filter fans represent an economical and effective form of cabinet climatisation. The filter mats used for these fans correspond to class EU5 and protect the cabinet interior reliably from dust. The internal assembly of the cabinet has to ensure the air circulation over the components by a filter fan. Therefore as a rule air inlets and outlets should be arranged diagnoally over the entire height of the cabinet. If filter fans are used in very low outside temperatures, an additional small heating element is installed in the cabinet.
For these applications Schroff has two standardised versions of Outdoor cabinets: “Modular” and “Unibody”. The Modular version is based on an extruded aluminium frame with high flexibility with regard to the cabinet dimensions and at the same time allows good accessibility from all sides. The more affordable Unibody version is based on a one-part aluminium inner housing, which is particularly suited for smaller dimensions for wall, pole and ground mounting. Both cabinet versions protect the assembled components from wind, rain, heat, cold etc. They have flexible assembly possibilities for 19”, ETSI or other, non-standard accessories. The cover parts are coated with a weather resistant powder finish. Furthermore there are no visible screws and assembly parts, thus preventing unauthorised access. The hinged top construction enables easy installation and the cable entry is protected against rodents and insects from the bottom. The cabinets, whose standardised components are based on IEC 61 969, fulfil the guide lines and standards for shock and vibration stability tested to IEC 68-2-6 and -27, earth quake stability and offer a climate protection tested to IEC 68-2-1, -2, -14.
...one climate control concept
The subject climate control is particularly important for outside installation, as here not only the performance loss of the assembled components has to be taken into account, but also the influence of the outside temperatures (summer/winter and time of day). The double wall concept of the Outdoor cabinets from Schroff guarantees a natural air flow between the outer and inner wall, so that considerably fewer measures are required for additional cooling. 85 % of the heat generation through direct and reflective sun rays is kept out.
Additional cooling and heating components
If this and the natural convection are not suffcient, additional cooling components are installed as neede: Filter fans, air/air heat exchangers (LLWT) or a cooling unit. Depending on the framework conditions the concrete cooling requirement is established (Table 1). Speed regulated filter fans represent an economical and effective form of cabinet climatisation. The filter mats used for these fans correspond to class EU5 and protect the cabinet interior reliably from dust. The internal assembly of the cabinet has to ensure the air circulation over the components by a filter fan. Therefore as a rule air inlets and outlets should be arranged diagnoally over the entire height of the cabinet. If filter fans are used in very low outside temperatures, an additional small heating element is installed in the cabinet.
Example 1: A heat exchanger is used with a cooling performance of 55 W/K (830 W : 15 K = 55 W/K) ;
Example 2: A cooling unit is used with a cooling performance of 1500 W at Tu = Ti = 35 °C (corresponds to L35L35, in accordance with DIN 3168)
Example 2: A cooling unit is used with a cooling performance of 1500 W at Tu = Ti = 35 °C (corresponds to L35L35, in accordance with DIN 3168)
The operating principle of an air/air heat exchanger (LLWT) is based on two independent air cycles, which each carry heat energy. The inner air cycle circulates the air inside the cabinet and transports the heat which is taken up internally to the heat exchanger. The outer air cycle transports the ambient air past the heat exhanger and takes away the heat energy. Precondition for the use of filter fans or an LLWT is that the ambient temperature is at least 5 K below the maximum possible internal cabinet temperature.
If this is not the case, a cooling unit especially configured for Outdoor applications has to be developed. Such a cooling unit consists of a compressor that transports the heat from the cabinet via a cooling medium to the outside and thereby keeps the internal cabinet temperature at the required level. The fan responsible for the internal cycle circulates the cabinet air permanantly.
Cooling unit and heat exchanger are equipped with a heating element as standard and with the Schroff concept they are always assembled on the cabinet door inside the cabinet. Thus the cooling unit is protected and the user is not restricted when selecting the installation site.
Limitation of noise level
Not to be underestimated is the possible noise pollution which people who live in the vicinity of the installation site are exposed to. Therefore Schroff makes particular efforts to observe the international noise pollution laws, such as ETS 300 753 (European Telecommunication Standard) (Table 2).
If this is not the case, a cooling unit especially configured for Outdoor applications has to be developed. Such a cooling unit consists of a compressor that transports the heat from the cabinet via a cooling medium to the outside and thereby keeps the internal cabinet temperature at the required level. The fan responsible for the internal cycle circulates the cabinet air permanantly.
Cooling unit and heat exchanger are equipped with a heating element as standard and with the Schroff concept they are always assembled on the cabinet door inside the cabinet. Thus the cooling unit is protected and the user is not restricted when selecting the installation site.
Limitation of noise level
Not to be underestimated is the possible noise pollution which people who live in the vicinity of the installation site are exposed to. Therefore Schroff makes particular efforts to observe the international noise pollution laws, such as ETS 300 753 (European Telecommunication Standard) (Table 2).
Limits for the acoustic pressure level L in accordance with ETS 300 753
A suitable measure to adhere to these laws, in the case of active air cooling with filter fans, is the control of the speed with an intelligent algorithm, so that the noise limits for day and night operation can be observed. Furthermore, fans in the Schroff concept are always configured below their capacity, so that they do not have to run at full speed in order to reach the maximum required air volume, thus keeping the noise level low (Picture 2). When LLWTs and cooling units are used, they are mechanically removed from the cabinet as far as possible by suitable isolation of the oscillation. If need be, additional strengthening is installed inside the cabinet, in order to move oscillation into a less disturbing frequency area.
Picture 2. Fan parameter depending of temperature and acoustic power level
Despite the fact that the standard defines limits for the noise level, the noise perception of people is very subjective. Therefore it is more and more the case that Outdoor cabinets have to be attenuated above the set limits. Here the lining of the air channels with special noise minimising mats and the fixing of noise reducing materials in cabinet areas where the air flows at high speed, show good results.
Each Outdoor cabinet is tested in Schroff’s own laboratory before being shipped to make sure the defined limits for climate control and noise levels are met. Tests in an independent institute confirm the correct and professional working methods of the Schroff laboratory.
Each Outdoor cabinet is tested in Schroff’s own laboratory before being shipped to make sure the defined limits for climate control and noise levels are met. Tests in an independent institute confirm the correct and professional working methods of the Schroff laboratory.
