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COOL FOR CABS
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Myriad yellowish lamps glare down. making a light as intense as that from the glaciers in the summer. In addition, a hot and humid wind sweeps over the trucks standing in tightly staggered formation in the Vienna Climatic WindTunnel.
It is 35 .0 and the solar panels on the wall have been heating the cabs from the side for two hours. They may not be able to simulate everything the sun can manage, but with 700 Watts per square metre, bright evening sunshine in high summer is certainly possible.
Curious gazes are directed towards the large monitor in the control room on which the measurements from the sensors in the cab interiors appear.The temperature charts have been climbing upwards, sometimes more, sometimes less steeply — depending on the truck —during the past two hours.
Solar radiation victim
The most outlying curves are provided by the two Scandinavians: the Volvo FH heated up the most and it is now almost 470 inthe interior of the Globetrotter XL cab, which easily falls victim to solar radiation with its sloping windscreen and the darkest paintwork in the whole field. It finishes almost five degrees cooler in the top-of-the-line Scania, which shrugs off this procedure with its doublelayered side windows.
Similarly, the Mercedes with Megaspace cab and the hew Stralis get away relatively lightly In both cabs the temperature remains under 43'. Lying in the middle of the range, at about 44', are the Daf with Super Spacecab and the XXL-MAN from the TG A range.The generously proportioned window areas naturally present difficulties for this cab.
All in all then. this is the ideal opportunity for the air conditioners to prove their worth under extreme conditions. Equipped with dark glasses, the test crew enter the tropical environment of the climatic tunnel to start the engines and air conditioners Maximum cooling is required —still in the face of solar radiation stimulation from the side and 35' outside temperature, as well as a tough 50% relative humidity: in recirculating mode too,so that it goes faster. And generally at 1,200rpm, so that the air conditioners are on top form.
Again the eyes in the control room are all glued to the monitor, which shows quite astonishing curves during the next 60 minutes. The air conditioning on the Volvo, which heated up so fast, expels the heat just as quickly.The temperature in the Volvo falls below the 300 mark within 10 minutes, and after another 50 minutes, the sensor at driver head height indicates less than 200.
The middle field of Mercedes, Iveco,Scania and Daf settles down at values between 23.5° and 25°,while the MAN cools similarly briskly at the start, but contents itself with around 29' in the end. Compared to the initial temperature of just under 45°, that is still a quite a feat.
Point two of the test programme consists of: first set point at 24', then at 20°— this time without sun and without manually switching on recirculation,but still with an exacting 35° external temperature as well as a relative humidity of 50 %.These values are also the starting conditions inside the drivers' cabs.
The multicoloured curves on the monitor in the control room again take on extremely different forms. The Iveco, the Volvo and the Mercedes put themselves at the forefront of the action and cool down rapidly, to exactly 24.5' during the first 20 minutes.
The Iveco subsequently homes in on the 23.5° mark and also stops, while the Volvo keeps on going down to 23.5°. In the Megaspace Mercedes the air conditioning rests on its laurels a little and, with 24.5°, misses the target by exactly half a degree.
Daf. Scania and MAN take a more relaxed attitude to this exercise. After four minutes the temperature in the Daf has fallen to just under 26°, the MAN remains two degrees above that, and the Scania has followed sedately down to the 29° mark.
Rol lercoaster rides
But there is a rationale behind this. It is not good for people, says Scania, if the temperature sinks too quickly. MAN also considers the scale on the temperature control mainly as an approximate guiding value and has deliberately designed the system this way so that the driver does not experience any thermal rollercoaster rides.
But on switching to set point at 20°,it is revealed beyond doubt that the MAN system is barely able to cope with the particularly large volume of the XXL cab: it now cools down from just below 28' to 25.5 ° within 40 minutes, while the Scania pushes its temperature down from 29° to 25° over the same period. Only the Iveco and the Volvo get right down to the desired 20".The Mercedes acquits itself quite passably with a final value of 21.5°, while the Daf misses the class target rather more widely with 23' as its final value.
But what happens if the sun is added to these conditions? Another experiment brings it to light. First back to set point at 24', then after half an hour climatic tunnel sunshine at a strength of 700 Watts per square metre is turned on. None of the subjects achieves the desired 24° in the course of half an hour: The Volvo works its way up to 22.3° and the Iveco to 23, while the Mercedes climbs to 25.5°, the Daf to 25.7°, the MAN to 26.5° and the Scania to 27.7°.
As soon as the sun comes into play, the temperature in all the trucks climbs briskly upwards.The Iveco traces out the flattest curve and settles down at 3.4' above the starting temperature. The Mercedes occupies second place with 4° over the starting point. Scania, Daf and Volvo each allow themselves a value of about 4.5° above the base temperature. while the MAN rushes off up to around 6' above the starting value.
'the best control accuracy, even under these circumstances, is offered by the Iveco, closely followed by the Mercedes.The Volvo, however, suffers noticeably under the handicap of its sloping windscreen.The MAN has to struggle with both a high cab volume and a large window area.The now familiar inertia dominated in the cases of the Daf and Scania — but this time in a positive sense.
The systems are spared no abuse because there is a little acid test to finish off. Engine speed is reduced to SOOrpm, the sun continues to blaze,the set point is still 24'', but the external temperature is raised to 45". The good news first: none of the systems throws in the towel, but the candidates are beginning to flag.
The highest toll for such barbaric conditions is exacted on the Daf, with almost three degrees of additional warming. It is nearly two degrees for the MAN.This little heat inferno wrests another 1.3' each from the Iveco and Scania, while the Mercedes just about gains a degree, and the Volvo resists most valiantly with only 0.7° of warming.
On the whole, the Iveco acquits itself best in this comparison of air conditioners. Close on its heels comes the Mercedes Actros, with similarly well-balanced qua lities.That the Volvo — in spite of its excellent air conditioning — is able to achieve only third place is a consequence of its susceptibility to solar radiation resulting from its construction (that sloping windscreen).
Daf and Scania share the midfield: the Dutch truck doesn't have too much to offer, but it doesn't stand out as being especially unpleasant.The Swede benefits particularly from its double-layered side windows—available only as an option though —but suffers from the phlegmatic constitution of its air conditioner.
The MAN,in turn, labours under the burden of a three-fold handicap: the giant cab is difficult to cool: it heats up fairly rapidly and strongly because of its large window areas: and the air conditioner does seem a little undersized for circumstances such as these.
However, while the test was still under way, Scania announced that a new solution with a faster reaction time can be expected as early as this autumn. For MAN, the big model upgrading is just around the corner; one might presume the air conditioner will also benefit strongly from this. • If the air is too dry, one's nose soon starts to smart. if it is too humid, then people find this unpleasant, particularly at higher temperatures. A spot check during the hot phase of the test gave the following snapshot: only the Volvo and Daf regulate the humidity to a level that lies within the official recommendation. In the Iveco, MAN and Mercedes, the air is a bit too dry in each case; in the Scania, on the other hand, it is a touch too humid.