The presence of moisture in industrial storage spaces threatens the interior of the structure, machinery and handling equipment, and the stored inventory. In addition to these threats, humid conditions inside manufacturing plants and working environments may have a negative effect on employee performance and overall morale. The primary contributors to increased humidity and moisture problems inside industrial facilities are cracked windows, door gaps, and any other openings where warm air might enter. Surface materials – like floors, ceilings, crates and packages, and machinery – reach their dew point at night when warm air cools and the condensation process leaves behind accumulated moisture. Common issues such as sweating on concrete surfaces, rust, and rot are the result of moisture accumulation, contributing to inventory and capital equipment losses as well as compliance issues regarding employee health and safety. Industrial dehumidifiers provide a viable solution for combating warehouse humidity, improving working conditions, and protecting your bottom line.
Controlling dew points and relative humidity in industrial storage applications from waste and freshwater treatment plants, indoor grow rooms, archive storage facilities, and a variety of other instances is made possible by using industrial dehumidifiers. They provide supplementary airflow throughout factories and storages during day time hours and mitigate condensation issues that occur overnight.
The role of HVAC systems in storage dehumidification
HVAC systems are instrumental in maintaining precise temperature and humidity conditions in storage areas. By controlling humidity levels, HVAC systems prevent excessive moisture accumulation, reduce the risk of microbial growth, and preserve product quality. Properly designed and optimized HVAC systems provide a comfortable and controlled environment for employees while ensuring the integrity and safety of food products.
Design considerations for dehumidification
Proper system sizing: Correctly sizing HVAC systems is crucial to ensure optimal dehumidification. Oversized systems may lead to inadequate dehumidification, while undersized systems can struggle to maintain desired moisture levels. Conducting a thorough analysis of the facility’s moisture load and considering factors such as ventilation rates, heat gain/loss, and process-specific requirements are essential for accurate system sizing.
Dedicated dehumidification units: In some cases, incorporating dedicated dehumidification units into the HVAC system can enhance moisture control. These units focus solely on extracting excess moisture from the air, ensuring more precise humidity regulation. Supplementing the HVAC system with dedicated dehumidifiers can be particularly beneficial in areas with high humidity levels or during specific food processing stages that require stringent moisture control.
Airflow management: Proper airflow management within the HVAC system is critical for effective dehumidification. Optimizing air distribution and circulation through well-designed ductwork, strategically placed vents, and air diffusers help control moisture levels. By ensuring consistent and balanced airflow, HVAC systems can facilitate the removal of moisture-laden air and maintain desired humidity conditions.
Advanced HVAC technologies for storage dehumidification
Desiccant dehumidification: Desiccant-based HVAC systems utilize moisture-absorbing materials to extract humidity from the air. These systems are particularly effective in high humidity environments and can achieve lower humidity levels compared to traditional refrigeration-based systems. Desiccant dehumidification technology provides precise control over moisture levels, reducing the risk of condensation and microbial growth.
Variable Refrigerant Flow (VRF) systems: VRF systems offer energy-efficient dehumidification capabilities by providing individual zone control. These systems can independently adjust cooling and dehumidification levels based on specific area requirements. VRF systems offer greater flexibility, energy savings, and precise humidity control, making them well-suited for dehumidification in the food industry.
Energy Recovery Ventilation (ERV): ERV systems allow for heat and moisture exchange between the incoming and outgoing air streams. These systems recover energy and humidity from the exhaust air, pre-conditioning the fresh air supply. By utilizing ERV technology, HVAC systems can reduce energy consumption while maintaining proper humidity levels, enhancing dehumidification efficiency.
Comparison among condensing and desiccant dehumidifiers
There are two main types of commercial dehumidifier – condensing and desiccant. They both lower humidity but do so in quite different ways, which frequently determines when you should use one instead of the other. A condensing dehumidifier operates using the basic principle of creating a cold surface upon which moisture from the air will condense. It incorporates the type of refrigeration circuit that you would find in a fridge or AC unit. Air is drawn into the dehumidifier with a fan and meets the cold coil evaporator element of the fridge circuit. Its temperature is reduced below dew point, causing condensation to form on the coil, from where it drips to drain or into a water tank for disposal. The cold air is then heated with the condenser part of the fridge circuit before being returned to the room, drier and slightly warmer than it entered the dehumidifier.
A desiccant dehumidifier operates using the adsorption properties of a rotating desiccant wheel, a bit like a sponge literally soaking up moisture directly from the air. Air is drawn into the dehumidifier and passes through a slowly revolving desiccant wheel (Fig. 1). The desiccant absorbs moisture and the dried air is returned to the room. In order to allow the desiccant wheel to indefinitely absorb moisture, the wheel passes through a regeneration area, where it is heated by a secondary hot airstream. A heater, frequently electric, heats this secondary airstream to around 120°C before passing it through the wheel. The hot air absorbs the moisture from the desiccant and is then vented externally. So, a desiccant dehumidifier has two airstreams – a process airstream and a regeneration airstream, which exhausts the moisture collected from the process airstream. As the freshly regenerated part of the wheel is hot, it carries some residual heat when it rotates back into the process airstream. Therefore, as well as drying the process airstream, the desiccant wheel also provides some heat.
As a condensing dehumidifier (Fig. 2) relies on temperature to dry the air, the technology is most efficient when the atmosphere is warm. The warmer the room, the greater the condensation effect on the dehumidifier’s cold evaporator coil. This makes this type of technology ideal for applications like swimming pools, where the air is typically very warm and moist. Especially, as some condensing dehumidifiers can incorporate heat recovery systems, which return the heat generated from the drying process to heat the pool water.
Industrial refrigerated dehumidifiers operate by using accepted refrigeration practices to lower the dew point of the facility’s incoming air. The basic dehumidification process proceeds as follows:
- Filtered air enters the dehumidifier and is passed over the cold evaporator coil.
- The moisture from the air condenses on cold evaporator coil fins into droplets as the water in the air reaches its dew point.
- The water droplets collect in the drain pan and are carried away, and the dry cool air proceeds then over the adjacent condenser (reheat) coil.
- This now warm air can be used to raise the room air temperature, if needed, or with the optional remote condenser, cool the air to maintain the desired room temperature taking a load off of the room’s primary HVAC system.
If the atmosphere requiring dehumidification is lower than around 20°C, frequently desiccant dehumidifiers start to become a more efficient solution. Their efficiency of operation is not temperature dependent, so they perform well in both warm and cold environments. However, this flexibility comes at a cost, as they do use more energy than condensing systems, due to the heating required to regenerate the desiccant wheel. In comparison, a condensing system would typically consume 0.5-1.5kW to remove one kilo of water, while a desiccant would consume 1-3kW for the same capacity. It is possible for a desiccant dehumidifier to incorporate a gas or hot water heat exchanger, which can reduce the cost of this energy consumption.
Due to the need to vent the regeneration airflow externally, to get rid of the hot wet air coming off the desiccant wheel, desiccant dehumidifiers can also be more complicated to install. A condensing dehumidifier can dry an atmosphere with only an electrical supply and a drain. A desiccant dehumidifier will always need ducting to vent the regeneration airflow away from the area being dried. So, with the higher energy costs and the more complex installation requirements involved in desiccant dehumidification, if a project’s environmental conditions suit a condensing dehumidifier, it will normally be the most cost effective solution.
However, temperature isn’t the only determining factor. Condensing dehumidifiers are very effective at maintaining an atmosphere as low as 45-50%RH. If a project calls for a humidity level below this, desiccant technology offers more powerful drying performance. A desiccant dryer can deliver extreme environmental control as low as 1%RH. This is ideal for manufacturing processes, such as lithium battery production, where very low humidity levels are needed. Effectively managing the heat generated during a drying project can also be a determining factor in technology selection. If close environmental control is needed in a project, this nearly always involves both temperature and humidity levels. Although the dehumidifier’s purpose is to control humidity, both technologies will heat the air they dry. This means they have an impact on the temperature management and will need to align alongside any associated heating and cooling equipment.
Again desiccant technology offers a more flexible solution for temperature management, as it is possible to fit pre- or post- modules to a desiccant dehumidifier that can additionally heat or cool the air. There is the possibility with some advanced condensing systems to incorporate remote condensers, which can exhaust the heat air away from the process air delivery. This can provide control over heat management but not to the precise levels offered by desiccant technology.
So in summary, for projects that need humidity control at 45% RH or above and at around 20°C or warmer, condensing dehumidifiers can be the most cost effective solution. Whilst applications that drop below this temperature level, even for short periods of time, or that need less than 45%RH, or advanced temperature management, desiccant dryers offer a much wider performance range.
Maintenance and monitoring
Regular maintenance: Proactive maintenance is crucial for ensuring optimal HVAC system performance. Routine inspections, cleaning of air filters and coils, and checking drainage systems are essential to prevent moisture-related issues, such as clogged drains or microbial growth. Regular maintenance ensures that the HVAC system operates efficiently and effectively in controlling humidity levels.
Moisture monitoring and control: Integrating moisture sensors and automated controls within the HVAC system allows for real-time monitoring of humidity levels. By continuously monitoring and adjusting moisture control parameters, HVAC systems can respond promptly to fluctuations, maintaining optimal conditions for dehumidification.
Conclusion
HVAC systems play a vital role in dehumidification within the storage by controlling humidity levels and preserving product quality and safety. By considering design considerations such as system sizing, dedicated dehumidification units, and airflow management, and incorporating advanced technologies like desiccant dehumidification, VRF systems, and ERV, food manufacturers can optimize their HVAC systems for effective moisture control. Regular maintenance and moisture monitoring further ensure the long-term performance and efficiency of HVAC systems in achieving precise dehumidification, contributing to enhanced product quality and extended shelf life.
Dr. (Prof.) D.B. Jani received Ph.D. in Thermal Science (Mechanical Engineering) from Indian Institute of Technology (IIT) Roorkee. Currently he is a recognized Ph.D. Supervisor at Gujarat Technological University (GTU). He has published more than 180 Research Articles in reputed International Conferences and Journals. He has also published 5 reputed books in the area of thermal engineering. Presently, he is an Associate Professor at GEC, Dahod, Gujarat Technological University, GTU, Ahmedabad (Education Department, State of Gujarat, India). His area of research is Desiccant cooling, ANN, TRNSYS, and Exergy.
