Chocolate, cake, confectionery, and biscuit production involves manufacturing processes that rely on precise temperature and humidity control. To ensure the aesthetic appearance of chocolate and consumer satisfaction, the humidity level in chocolate cooling tunnels is kept low enough to prevent indoor condensation. High humidity levels can cause unwanted condensation on the chocolate surface, leading to spots and dulling on the product surface. Since the crystallization process of chocolate is very sensitive, keeping the humidity level under control ensures proper hardening of the chocolate.
The situation is no different for sugar and confectionery products. Preventing these products from becoming sticky and moist makes a difference in production and packaging processes. High humidity can also cause unwanted crystallization in the structure of sugars, which negatively affects the texture and taste quality of the product. For this reason, cooling tunnels that preserve product quality and ensure flavor excellence play an important role in production processes. In cooling tunnels, which are an integral part of sugar, chocolate, cake, and biscuit manufacturing, the use of dehumidifiers becomes necessary when the cold air used for product cooling is below the dew point of the external environment, which would cause condensation inside the tunnel. To prevent product stability from deteriorating due to seasonal effects at the tunnel exit, dehumidifiers must be integrated into cooling tunnels with proper engineering infrastructure.
For proper air conditioning in the system, in addition to outdoor reference temperature and humidity values, the following factors are important: tunnel internal operating temperatures, product identity, belt speed, tunnel internal dimensions, tunnel entrance and exit openings, number of tunnel levels, and the number of evaporators used in the design. Effective operation of cooling tunnels is closely related to proper dehumidifier selection and airflow management. Products that need to be brought to appropriate temperature conditions before packaging enter the cooling tunnel via a conveyor at a constant temperature or with zone-based gradual temperature conditioning.
First, a dehumidifier of appropriate capacity should be selected considering the tunnel size, operating temperature, and moisture load. The unit should be positioned in harmony with the airflow inside the tunnel, and the airflow should be adjusted with dampers when necessary to ensure homogeneous distribution. Determining the appropriate airflow rate according to the system requirements, with proper fan selection, ensures that dry air is distributed equally to every section of the tunnel. Maximum efficiency is obtained from the dehumidifier through proper placement of the unit and correct direction of airflow into the unit. Humid air should be directed properly into the unit, and dry air should be distributed equally to other sections of the tunnel. Particularly when the output from the dehumidifier is taken from the suction side of the cooling tunnel's high-pressure fans, healthy airflow cannot be provided to the dehumidifier, and the dehumidifier will not be able to produce dry air efficiently.
The airflow must be compatible with the temperature control of the cooling tunnel, and the temperature difference that will be transferred inside the tunnel due to the discharge of latent heat (absolute humidity) in the air must be communicated to the tunnel designer before evaporator selection. As products enter the tunnel through the entrance opening, they also drag the air outside the tunnel into the interior. Therefore, the operating speed (m/s) of the conveyor belt running inside the tunnel must be taken into account in dehumidifier capacity calculations.
For the moisture load from entrance and exit openings in dehumidifier capacity selection, the following must be known:
- Conveyor speed,
- Absolute humidity inside the tunnel,
- Absolute humidity outside the tunnel,
- Surface area of tunnel entrance and exit openings.
Based on these values, the moisture load coming from tunnel openings can be calculated through the infiltration channel to the dehumidifier.
The dehumidifier must operate in harmony with the cooling tunnel's temperature and humidity levels, supported by a proper drainage system. Proper drainage of the condensation formed by the cooling system inside the tunnel is important for indoor humidity values to reach the set values. Liquid swept by the tunnel's fan can cause humidity fluctuations in the indoor environment. It is very important that the moisture condensed by the high-flow evaporators inside the tunnel is discharged as liquid through a proper siphon system and drainage channel. Otherwise, when the evaporator fans activate, the condensed water will disperse as droplets inside the tunnel. Even if the dehumidifier is operating, liquid that does not leave the environment without proper siphon drainage will cause erratic readings on the dehumidifier's inlet sensor.
For indoor stabilization of the cooling tunnel, the dehumidifier capacity and the cooling system integrated into the tunnel form a unified structure. In horizontally long cooling tunnels, while indoor temperature balance is maintained with multiple evaporators, dry air can be distributed through branches from a single dehumidifier, or multiple dehumidifiers can provide regional dry air supply to evaporators. When determining the number and position of units, maintenance and accessibility of the units should also be considered. Regular maintenance and inspections of the airflow and distribution system are essential for efficient system operation. If the cooling tunnel is divided into graduated cooling zones, the lowest temperature zone is selected as the reference when determining the dehumidifier capacity. The capacity of desiccant rotor industrial dehumidifiers also decreases at low temperatures. Therefore, the unit configuration is designed using the lowest temperature stage inside the tunnel as a reference for the dehumidification capacity calculation.
The product type being processed in cooling tunnels with dehumidifier integration, the moisture content of the product, and the moisture characteristics of the product are additional parameters in tunnel indoor humidity stabilization. The moisture load from the product, moisture characteristic curve, and conveyor speed must be included in dehumidifier capacity calculations.
The designer decides on the integration method of the dehumidifier into the cooling tunnel by considering all parameters. Below is a brief overview of the integration methods of a dehumidifier into a cooling tunnel.
Semi-Open System:
This is a design where the dehumidifier positively conditions the interior of the cooling tunnel, and the return air from the cooling tunnel along with outside air enters the dehumidifier together, delivering dry air to the suction line of the cooling tunnel evaporator. In this system, not only does no air enter the cooling tunnel interior from the conveyor openings, but air actually exits. The tunnel interior is under positive pressure. Factors such as the air volume, temperature, and absolute humidity drawn from the outside must be carefully considered.
Closed System:
This is a system design where the dehumidifier takes air from inside the tunnel and sends it back into the tunnel. In this design, moisture entering the cooling tunnel interior from the outside environment cannot be prevented. Therefore, the designer must also consider other parameters when selecting the dehumidifier capacity.
In both systems, the dehumidifier must be in communication with the cooling tunnel, and the automation infrastructure must be designed to operate in coordination. Incorrect designs can lead to problems such as insufficient airflow and temperature imbalances. Additionally, using a dehumidifier of the wrong size or capacity can result in increased energy consumption, product quality defects, and even damage to other system components, causing malfunctions.
NKT – Humidity Control Technologies, with our expert engineering team, provides our customers with the most suitable industrial dehumidifier solutions, offering energy-efficient, high-performance recommendations for cooling tunnel dehumidifier integrations.
