Besides efficiency, especially important requirements for fans used in evaporators today are service life and ruggedness as well as compact dimensions permitting the production of space-saving evaporation units. Moreover, convenient service access is important for activities such as cleaning and de-icing the devices. The air throw also plays an important role in distributing cold air to a cold store’s remotest corners. Fans designed especially to meet such requirements provide a variety of benefits. Not only do they improve ease of use, they also help to protect valuable chilled goods as well as contributing to reduced energy costs. In this respect, designs with GreenTech EC technology deliver particularly impressive results.
Axial fans in evaporators have to withstand difficult conditions. Work on the cold side of the cooling circuit is very demanding. Ice formation and removal, which often require crude tools, call for rugged solutions that also work reliably in harsh conditions. While developing the AxiCool series, motor and fan specialist ebm-papst Mulfingen gave special consideration to such requirements. Thanks to their many practical design details, the new axial fans are ideally adapted to their field of application, simplifying compliance with hygiene regulations (Fig. 2).
Ice formation less worrisome; defrosting cycles optimised
Unfortunately it will never be possible to avoid ice formation on heat exchangers and fans completely, but it can be minimised with an attendant extension of maintenance intervals. This wish, expressed by many users, was realised by the developers of the new series with a variety of measures. For example, the wall ring and fan blades are made of rugged plastic, a material for which ice formation is less of a worry than it is for metal-based designs to begin with. By contrast, the fans’ safety grilles are still made of metal. The reason is clear enough when one considers that in practice, ice is also removed from the grille by mechanical means. In addition, the metal safety grille is not curved, making cleaning easier. This hybrid design makes the overall system robust and specially designed for this application.
The wall ring’s two-part construction is a further practical design detail that counteracts ice formation and optimises defrosting cycles by making it possible to retrofit a heating tape when needed. Installing the heating tape directly in the wall ring has the benefit of avoiding unnecessary heat transfer into the cold store because the hollow space acts as insulation (Fig. 3). Heat originates where it is needed, reliably preventing ice formation between the fan blades and the wall ring where it could block the fan.
Melt water, hygiene and cleaning
Drainage channels on the inside of the wall ring ensure that melt water, such as that formed during regular de-icing, can drain in the direction of the drip pan that is normally installed on the evaporator (Fig. 4). This also keeps the fan blades from freezing up when cooling is resumed and averts the danger of water being sprayed into the cold store when the fan restarts. This feature gains in significance as hygiene requirements become more stringent. For example, contamination by splash water must be prevented for foodstuffs in open storage.
Convenient cleaning also plays an important role, especially in connection with hygiene requirements, and the fans’ surface design allows for this. Flat, smooth surfaces keep the rate of contamination build-up low to begin with. The motor is protected from splash water for additional protection during cleaning with a water jet. Fan designs with a swivel joint in the integrated mounting flange also simplify required servicing such as cleaning the heat exchanger. The technician simply loosens the attachment screws and can then swing the fan to the side (Fig. 5).
Air-guiding system for increased air throw
Fans used in cold stores face further requirements. For instance, the distribution of cold air needs to be as uniform as possible, so their air throw becomes a key criterion. The AxiCool series thus includes an optional air-guiding system (Fig. 6) that nearly doubles the fan’s air throw while increasing the flow resistance only minimally so that the air volume and with it the refrigeration capacity stay nearly constant (Figs. 7a, 7b). It can be said to “replace” the safety grille; it is easily installed and can also be retrofitted without difficulty at any time. Problem-free removal facilitates easy cleaning, e.g. with a dishwasher.
The axial fans in the AxiCool series are available in sizes of 300, 350 and 450 mm. With their air performance ranging from 800 to 6,200 m³/h, they are suited to a wide variety of typical evaporator applications (Fig. 8).
Both directions of air flow are possible for the designs with safety grilles. The AxiCool series is available for operating temperatures to -40 °C; its external-rotor design allows for very compact dimensions. The complete evaporator unit thus requires little space. The fans already exceed the 2015 ErP requirements today and are available in identical dimensions with both AC and energy-efficient GreenTech EC motors.
Designs with EC motors for especially high efficiency
EC motors produce less waste heat than AC motors because of their significantly higher efficiency – a major advantage for refrigeration applications. At the same time, their energy consumption is lower. For example, for a size 350 fan it is 25% lower than for the same design with an AC motor. That pays off in practice: at an air volume of 2,500 m³/h the EC fan consumes 42 W less than the AC version. In addition to the direct energy savings resulting from the fan’s reduced power consumption, the waste heat it transfers into the cold store also needs to be considered. The refrigeration process has to use electrical power to remove this waste heat. All told, in the overall refrigeration process savings of approximately 55 W can be achieved with the EC fan. Given an electricity price of 0.13 euro/kWh and a working time of 6,000 h/year, the savings per fan add up to 43 euros per year.
As an additional advantage, the user can choose between a two-step motor design or a demand-based control system using a 0-10 V signal that simplifies customised adaptations for special refrigeration requirements. Typical example applications include maturing processes for cheese storage, or the storage of sensitive fruits and vegetables. In addition, the aeroacoustically optimised design of the fans with HyBlade® plastic impellers allows for noise reduction of up to 4 dB(A) in comparison with typically available solutions using sheet metal blades. As a compact, efficient plug-and-play solution perfectly tailored to its application, the AxiCool series has a wide variety of uses.