Centrifugal compact fan for NoFrost system means no need for manual defrosting

Refrig­er­a­tors have long become an estab­lished fixture in the kitchen. They make it easier to keep supplies and ensure that many foods stay fresh longer. Unfor­tu­nately, conven­tional refrig­er­a­tors also have disad­van­tages, and thus compro­mises must often be made for the cooling temper­a­ture of various food­stuffs such as meat and vegeta­bles. Ice forma­tion on the evap­o­rator in the freezer compart­ment must be removed by manual defrosting, and the contents of the refrig­er­ator and freezer stored else­where during this process. A new concept for refrigerator/freezer combi­na­tions with inte­grated fan provides help here. It allows better temper­a­ture distri­b­u­tion and prevents ice forma­tion on the food­stuffs stored in the freezer compart­ment. An auto­matic defrost feature also makes the previous main­te­nance effort unnec­es­sary.

Food­stuffs age, meaning that they decom­pose chem­i­cally into other compo­nents. A rule of thumb of organic chem­istry is that for each 10 °C temper­a­ture increase, the reac­tion speed doubles. Thus many food­stuffs stay fresh longer at a lower temper­a­ture. Because foods such as fruit or vegeta­bles are still “alive”, however, the temper­a­ture must not become too low. We all know that pota­toes taste “sweet” when they have been subjected to frost. There­fore, the objec­tive is to provide optimum temper­a­ture control for each food­stuff cooled. Siemens, the specialist for white goods, has come out with a new series of built-in refrigerator/freezers that address precisely this problem. The new appli­ances cool exactly to the setpoint and prevent the forma­tion of unwanted ice with the auto­matic NoFrost feature. A specially adapted fan (Figure 1) provides ideal air circu­la­tion. To adapt these compo­nents opti­mally to the condi­tions, the devel­opers brought the motor and fan experts of ebm-papst Land­shut on board with them. This resulted in a new NoFrost blower design that keeps the freezer compart­ment reli­ably free of ice.

Customised cooling

New centrifugal compact fan from ebm-papst Land­shut for NoFrost system

Saving energy is fore­most on everyone’s mind. There­fore, the new cooling units work in class A++. Despite this, improved insu­la­tion, in conjunc­tion with a new cooling concept, provide plenty of useful space for the food­stuffs (Figure 2). The refrig­er­a­tion chamber can be flex­ibly adapted to the quan­ti­ties of each food, and contin­u­ously adjustable easyLift glass plates and flex­ible door compart­ments fit the food and beverage items stored. Sensor-controlled cooling auto­mat­i­cally adjusts the output of the state-of-the-art cooling system. Thus when new food­stuffs are stored, they are quickly brought to the neces­sary storage temper­a­ture and prod­ucts that are already deep-frozen are prevented from defrosting. A modern LED lighting system prevents unnec­es­sary heat in the refrig­er­a­tion chamber and thus saves addi­tional energy costs.

However, even the best inno­va­tion cannot change the laws of physics. Warm air always contains more water vapour than cold air. In nature, this means fog or rain when the air cools; in the refrig­er­ator, this means conden­sa­tion. Partic­u­larly in the freezer compart­ment, the condensed water accu­mu­lates on all cold surfaces as a layer of ice. This effect cannot be prevented entirely, but it can be controlled! Thus the cooling experts at Siemens, together with ebm-papst Land­shut, devel­oped an optimum combi­na­tion of air conduc­tion and NoFrost blower in the inte­rior of the freezer compart­ment. This ensures that the warm air that enters is guided quickly towards the extra-cold condenser surface designed for this purpose. There, it sheds its excess water through conden­sa­tion. Thus the food­stuffs and the rest of the surfaces of the appli­ance remain free of conden­sate and ice.

Fan ensures dynamic cooling

Fans at the specific loca­tion draw moist, warm air over the cold evap­o­rator to be dehu­mid­i­fied

The inte­rior of the freezer compart­ment contains a fan that is specially opti­mised for this appli­ca­tion. It draws the moist, warm air in across the cold evap­o­rator surface, thus gener­ating a circu­lating air flow (Figure 3). There, the water vapour condenses and solid­i­fies imme­di­ately into ice. The dried air then escapes in a targeted manner in certain areas of the refrig­er­ator to attain perfect temper­a­ture strat­i­fi­ca­tion. When it contacts the food­stuffs, it heats up slightly and absorbs minimal quan­ti­ties of mois­ture during the normal refrig­er­a­tion process, then deposits it at the evap­o­rator. Result: the inte­rior remains constantly free of conden­sate and ice. If the evap­o­rator then ices up, it is defrosted auto­mat­i­cally, the conden­sate is removed and the cycle begins again.

The new size 15 motor plat­form features outstand­ingly compact instal­la­tion dimen­sions and works with minimal power consump­tion at low temper­a­tures

Of course, such an appli­ca­tion places strin­gent demands on the fan used. An optimum aero­dy­namic design and whisper-quiet drive are required. In addi­tion, a long service life, which for modern appli­ances is signif­i­cantly over 10 years, and extremely effi­cient use of energy are required, as after all, the drive motor is in the cold area. Waste heat that is not created there does not have to be removed by cooling. The fan experts solved the problem of aero­dy­namics in numerous test bench trials. So that the drive could also be ideally matched, they use a new motor design, the size 15. The drive is specially opti­mised for the require­ments for oper­a­tion at low temper­a­tures and for minimum power consump­tion, while simul­ta­ne­ously featuring espe­cially small instal­la­tion dimen­sions (Figure 4). Thus the entire centrifugal compact fan measures only approx. 135 mm x 64 mm (diam­eter x height), which makes it possible to gain extra useful space in the freezer compart­ment.

New size 15 motor plat­form

The new size 15 motor plat­form is a brush­less direct current motor. It is designed for a variety of volt­ages. In the present case, the fan is oper­ated at 9 VDC. Other voltage versions (12 VDC or 24 VDC) are like­wise possible. The avail­ability in various overall motor heights covers a wide power range, making the motor series highly versa­tile in use (even beyond the domestic refrigerator/freezer area). The motor elec­tronics can be adapted to a wide variety of customer requests. The speed of the drives, for example, can be easily regu­lated for different cooling concepts. The internal closed-loop speed control means that the motor main­tains the set speed constantly. Various closed-loop speed control concepts can be offered. The bearing and lubri­ca­tion of the shaft is specially matched to the low temper­a­tures and long service life. At the same time, the special bearing and an opti­mally matched elec­trical config­u­ra­tion reduce the power require­ment of the motor, which improves the effi­ciency of the refrigerator/freezer.

Its special design and extremely small dimen­sions allow the motor to be inte­grated into the specific fan design in a space-saving manner

Its special design and extremely small dimen­sions allow the motor to be inte­grated into the specific fan design in a space-saving manner. All impor­tant para­me­ters are veri­fied during devel­op­ment and tested later under real-world condi­tions during quality control in the ebm-papst group’s in-house test lab. Thus the perfor­mance data for service life, power input or air volume and pres­sure increase are not just theo­ret­ical values, but spec­i­fi­ca­tions that can be veri­fied in real-world appli­ca­tions. The user can there­fore be assured that values will be attain­able in his or her product as well.

Summary

Improve­ments in refrig­er­a­tion require new methods and solu­tions. For uniform or stepped temper­a­ture distri­b­u­tion, an internal air circu­la­tion is espe­cially suit­able. In addi­tion, this prevents the problem of unwanted conden­sate and ice forma­tion in the freezer. Fan solu­tions adapted to the special condi­tions in the low temper­a­ture range and the oper­ating noise stan­dards for house­hold appli­ances are the ideal means to this end.