Axial fans in evaporators have a lot to contend with. The cold side of a cooling circuit is not exactly a technology-friendly working environment. The formation of ice and its removal, often involving the forceful use of tools, demands solutions which are robust but at the same time energy-efficient and which function reliably under tough ambient conditions. The fans also have to be able to withstand mandatory regular cleaning with a steam jet cleaner.
It was with precisely these requirements in mind that the motor and fan specialists from ebm-papst in Mulfingen set about developing their AxiCool product range. With these fans it is now possible to cover the entire spectrum of evaporators and air coolers used in trade and industry. Whereas sizes up to 450 are particularly suitable for commercial applications and small store rooms on sales premises, the new sizes 500, 630 and 800 are intended for larger-scale applications, for instance in large cold stores or warehouses and production facilities used in the food processing and foodstuffs industries. This means that practical and, what’s more, highly energy-efficient axial fans are now available for high-performance evaporators in industrial and commercial cooling systems (Figure 1).
Fans used in evaporators (Figure 2) can be described as follows: Every fan is a system comprising a motor, control electronics and a flow machine. This has to be considered in its entirety, particularly when judging energy efficiency, air performance and noise characteristics. The new AxiCool fans are based on just this philosophy. All the components are perfectly matched, right down to the peripheral parts such as the guard grille and patented fan housing system, the HyBlade® fan impeller, the motor and the control electronics. This adds up to a ready-to-install, energy-efficient, quiet-running plug & play unit. It also creates an ideal basis for better classification in the context of voluntary ErP labeling, which is increasingly becoming a standard feature of evaporators and air coolers.
Integrated diffuser for better air performance and lower noise level
Consideration must always be given to the high back pressures involved when looking for ways to improve the energy efficiency of fans in evaporators. Bearing this in mind, the fans were fitted with a so-called diffuser in combination with guide vanes (Figure 3). This integrated guide vane system minimizes flow turbulence to achieve maximum efficiency and minimum noise. In this way, air performance can be increased by up to 12% and the noise level lowered by as much as 3 dB (A).
Optimization of defrosting cycles
Further design details help to counteract ice formation and optimize the defrosting cycles: For example, the fan housing and blades are made of tough plastic, a material which in itself is less prone to ice formation than metal. The metal guard grille is designed to withstand rough treatment. The need for this is obvious, given that mechanical means are usually employed to remove the ice forming on the grille. It is also flat rather than being curved to make it easier to clean.
In addition, a heating tape can be inserted directly in the fan housing system with the fan cover. The advantage of fitting the heating tape directly in the fan housing system is that the cavity acts like an insulator, thus preventing the unnecessary transfer of heat to the surrounding area. Heat is generated where it is needed. This reliably stops ice forming between the axial blade and the cover, which could block the fan. An air bag can easily be fitted to seal off the air discharge duct during defrosting and when the fan is switched off (Figure 4). An appropriate bead with a contact surface for securing is already integrated into the fan cover. The air bag causes heat to accumulate during the defrosting process and be retained in the cooler. This cuts the defrosting time by about 50% and makes for a low final defrosting temperature, thus saving a considerable amount of energy.
The more stringent the hygiene requirements, the more important the fan housing cover becomes.
Drainage channels on the inside of the fan housing route the melt water occurring on routine defrosting towards the drip pan provided at the condenser. There is no danger of the blades freezing up or water being sprayed onto the items in storage when the fan starts running again. The more stringent the hygiene requirements, the more important this feature becomes. The contamination of open foodstuffs with splash water must always be avoided for example.
Standard and High-End versions of AC and EC fans
With an air performance of up to 24,600 m³/h, the AxiCool series of axial fans is suitable for a variety of typical evaporator applications. All fans can be supplied as either a high-end version with integrated discharge vanes, fan housing cover and terminal box or as a standard version. This also has integrated discharge vanes; the terminal box and/or fan housing cover is/are optionally available with the high-end version. Where high hygiene standards are required, the extra advantage of the fan housing cover is that it is easy to remove the small amount of dirt likely to form on the smooth surface (Figure 5). It also reduces heat transfer to the cold store during the defrosting cycles.
Thanks to the special bearings and greases used, all versions can withstand temperatures down to -40 °C and, with their external rotor design, are extremely compact. This in turn means that the entire evaporator unit requires less space. As standard, the fans satisfy the requirements of degree of protection IP55, can be used for either suction or blowing and are available in the same size with AC or energy-efficient GreenTech EC motors. Being far superior to AC motors in terms of efficiency, EC motors produce less waste heat, which is of course a great advantage for cooling applications. At the same time energy consumption is reduced. For a size 500 fan for example it is around 46% lower than with standard AC fans with short nozzle (Figure 6).
Control and networking: “IoT” (Internet of Things) and remote access
As a further advantage, the EC version enables users to choose between conventional On/Off (two-step) control or demand-based control by way of a 0-10 V signal. This facilitates individual adaptation to particular cooling requirements. Typical examples include the maturing of cheese and the ripening of sensitive fruit and vegetables in storage. EC motors also retain their high efficiency level in part load operation. Demand-based control makes it possible to achieve further energy savings, for example the fan speed can be reduced when the shop doors are closed at night and the temperature tends to remain constant.
Using a serial MODBUS interface, the fans can simply be interconnected and incorporated into the higher-ranking building automation system for refrigeration circuit monitoring for instance. It is then also easier to access the refrigeration system by way of remote monitoring – a function which is certain to gain in significance in the future. The efficient, compact, tailor-made “Plug & Play” concept is sure to open up a wide range of potential industrial and commercial cooling applications for the “large” models in the AxiCool product range as well.