What would you like today? roast with sauce, fish and chips or assorted vegetables instead? In canteen kitchens guests are now spoilt for choice. The selection is large – as are frequently the portions as well. Putting 300 meals or more on the table in timely fashion is an everyday event as well as a challenge for the cooks. After all, the timing isn’t all that’s important; quality is also in demand in the canteen kitchens of the world. Chefs are supported in this by the RATIONAl selfCookingCenter® whiteefficiency®. The combi steam oven prepares food quickly and easily using hot air and steam. Whether meat, vegetables or baked goods, it cooks everything to just the right point – at the touch of a button. The cook enters the desired results and then the device controls itself. sensors make sure that nothing gets burned: They detect the size of the food being cooked and the amount of steam added. They check the cooking process up to 60 times per minute and adjust the temperature, cooking time and cooking chamber atmosphere. Moreover, this has the positive effect of enabling the chef to use 95 percent less fat when preparing.
Alternating running direction
Since 2004, motors from ebm-papst have been providing optimum air distribution in the cooking chamber. “Previously we used an asynchronous motor with frequency inverter,” reports Michael schmidt of strategic Purchasing at rational. “Today we work with GreenTech EC technology. This is qualitatively better; in addition, it also saves costs by means of its high efficiency.” A corporate restaurant uses 60 percent less energy by using the combi steam oven. The Mulfingen-based developer met the special customer requirements for the new series by completely redeveloping the existing motor. Gerhard Gauß, Department Manager for project engineers Germany at ebm-papst, remembers, “In principle, we modified everything except for the ball bearings – and those we are replacing now as well,” he says with a laugh. The most important innovation: Previously the impeller in the cooking chamber always rotated in one direction only, meaning that optimum air distribution was attainable only with mechanical flow aids. “Now we use an impeller that moves air in both directions,” explains Gauß. “The motor changes its direction of rotation every minute; consequently, we achieve better air turbulence without additional flow aids and attain a more uniform cooking result.”
Motor with brains
The service life of the components was particularly important to RATIONAl. “After all, here we are talking about 30,000 to 40,000 hours in ten years,” says Schmidt. The EC motor withstands ambient temperatures of 75 °C and even runs smoothly while withstanding grease and chemical cleaning agents. “That is important above all for the shaft, since it comes into contact with the cooking chamber,” continues schmidt. Additionally, the motor does not require much space: It supplies the same output despite its reduced size due to its better efficiency. “The energy efficiency of the EC motors helped us make it even more compact,” says Gauß.
The technology presents advantages for control options as well. If things get too hot for the motor due to extreme ambient temperatures in the kitchen, it does not simply switch off. Instead it reduces speed and power. It does not stop completely unless the heat is not abated by this approach. “By means of this ‘power derating’, the device remains usable even under extreme conditions,” emphasises Gauß. And while the previously used asynchronous motor required 16 voltage versions, the EC motor from Mulfingen does the job with only two. This is made possible by a wide voltage input of 100 to 240 volts. Different power frequencies are no longer a problem; one device for normal applications with single-phase current and a second for three-phase AC suffice.
Gas or electricity?
In canteen kitchens round the globe, many cooks prefer working with gas instead of electricity. Therefore the SelfCookingCenter® whiteefficiency® can be selected with one of the two connections. Appliances heated with gas operate with two gas blowers from ebm-papst Landshut. They generate the correct gas-air mixture for optimum combustion with low emission values. “Depending on the size of the selfCookingCenter® whiteefficiency® the gas blowers are used in various sizes and performance classes,” reports Gerhard Gauß.
“Annually we produce approximately 35,000 units of the selfCookingCenter® whiteefficiency® and another 10,000 units of our CombiMaster® Plus,” reveals schmidt. RATIONAl produces six unit sizes, beginning with six fan trays and a connected load of ten kilowatts and going up to steam ovens with 20 double plates and a connected load of 64 kilowatts. “some of the large combi steam
ovens have two motors installed,” says Gauß.
In all of the appliances a diagonal fan from ebm-papst st. Georgen provides cooling of the standard electronic devices in the installation space. Moreover, the work environment of the kitchen also places particular demands on the cooling units. Grease particles from frying pans and deep fryers accumulate in the ambient air. Therefore a filter in the rear panel of the combi steam oven protects the electronics from grease deposits. “However, the filter results in a higher pressure,” explains Gauß. ”With convection alone ventilation would not be possible; we have to actively suck in the air through the installation space. This is why we have used a fan.” The compact devices from st. Georgen have been tried and tested in real-world use for this task with their high power density and a 230-volt direct connection.
As far as the inner processes of the combi steam oven are concerned, the cook notices nothing, but the result, in turn, is all the more evident – not just in the cooking itself. The device requires little space, is energy-efficient and, since it is easy to work with, employees can operate it without special training, which saves on personnel costs. And perfectly prepared meals are all that make it to the plates, even by the hundreds.