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High temperature fans (120°C, 150°C)

There is a line of fans in the range of products of EDV that are suitable for industrial applications for air exhaust with a temperature of 150°C (or, as the case may be, to 120°C). The following fans are suitable: TET, TTT, CRMT, CST, CTHT, CTVT, etc.  Several rules hold true for the use of fans whose violation causes damage to fans and the loss of warranty.

The maximum temperature (120 or 150°C) indicated by the manufacturer is limiting and cannot be exceeded even for a short period. The operation of the fan over the maximum temperature leads to the degradation of the grease immediately. The operational temperature should be approximately in 20% lower than the maximum temperature.

If the fan is not in operation, hot air must not flow through the fan (in such a case, bearings are not cooled and their lubricant degrades; this holds true also for the motor and other components of the fan). A fan which is switched off must be protected with a bypass, intake of cool air, mixing flap valve, etc.

A fan can be turned off only after closing the intake of hot air and after cooling the fan and its components to a temperature of 40°C.  It may be necessary to protect the fan with a bypass, intake of cool air, mixing flap valve, etc.

The maximum ambient temperature of the fan can be 40°C.  Without ensured sufficient cooling, the fan must not be built into closed uncooled technological units and equipment, into linings of metallurgical and glass technologies, cooling channels for outlet of hot waste gases from technological processes, into unventilated channels and sumps of flue gas installations of furnaces, etc. The fan must not be insulated against temperature. The individual assessment is exclusively in the competence of the customer, designer or specialized assembly company.

Regulation equipment ensuring that the maximum air temperature will not be exceeded, must be designed by a specialized company with knowledge of the technological process (time constants of heating and cooling, temperature gradients in air ducts, etc.). Temperatures must be measured at the point of the highest temperature of air or with a net of sensors across the entire fan. Temperature sensors cannot be mounted in cooled technological sections or into the parts of the piping system with a lower flow rate due to hydraulic conditions, where the cooling is greater (shaped pieces, arcs, pockets without air flow). The flow rate grows continuously in the direction from the wall to the air duct axis in the straight section of ducts. Even for simple applications with a small diameter of the air duct and low flow rate, we do not recommend measurements with one short stem sensor. Temperature differences can be significant for diameters in the range from 500 to 800 mm. Very common reason for a damage of fan is the high error rate of the method and measurement unit. The measurement shoul be approved by oficial certification body. The operation of the fan closely to the maximum temperature leads to dificulties  (See “Ventilation and air-conditioning” /Chyský, Oppl 1973, “Ventilation and air-conditioning”, Chyský, Hemzal et al. 1993, “Heating and ventilation”/Cihelka 1975). 

If the fan is disconnected by a protection element of the motor (phase loss in the installation and disconnection by the low-voltage protection, disconnection by the high-voltage relay, etc.), the fan must be protected, for example, with a bypass, intake of cool air, mixing flap valve, etc.

Regulation of the speed of fans intended for the outlet of air with higher temperatures is not possible in principle. No kind of speed regulators can be used (frequency converters, transformer regulators, pulse width regulators, or other). Lower speeds lead to a reduced output (flow rate) of secondary internal radial-flow fans that cool bearings, winding and magnetic circuits of the motor. Further secondary fans on a joint shaft cool the fan bearings and motor housing. Fans driven by a belt use the belt for the transport of air mass in the drive-shaft tunnel and for cooling the shaft bearings of the rotor wheel. Regulation of high temperature fans always leads to damage to the fan or, as the case may be, to the motor.

Belt driven fans. The belt have to be corectly adjusted. Hig tension of the belt leads to the increase of friction forces in ball bearings and causes the reduction in  their durability.  

Periodic overhauls of fans must be carried out according to the code of operations that is prepared by the customer, designer or specialized installation company and issues from the knowledge of the technological equipment. On the basis of overhauls, it is necessary to determine the periods for replacements of bearings, replacement and tightening belts, cleaning the rotor wheel, fan housing, etc.

Infringement of these basic conditions leads to the damage of the fan and loss of any warranty.
 

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