In industrial facilities, temperature and humidity control have long gone beyond the realm of “comfort” and directly impact product yield, equipment lifespan, warehouse safety, and even process stability. However, in actual projects, we often encounter two extremes: either the equipment runs at full capacity yet fails to “fully dehumidify,” or the units cycle on and off frequently, resulting in high energy consumption while temperature and humidity levels still fluctuate wildly. At the root of the problem, the vast majority of issues stem from the initial selection process—by bypassing the core logic of thermal and humidity load calculations and relying solely on area estimates or experience, potential problems are inevitably set in motion for subsequent operations.

Step 1: Define Core Target Parameters and Boundary Conditions

Equipment selection calculations do not begin with formulas, but rather with “defining the problem.” First, the temperature and humidity control targets for the facility must be clearly defined:

• Process requirements: For example, precision assembly areas must be maintained at 22±1°C and 45±5% relative humidity year-round;

• Storage requirements: For example, raw material warehouses only need to prevent condensation and mold growth, so a maximum humidity of 60% is sufficient;

• Transitional requirements: In staff work areas, parameters may be moderately relaxed during high-temperature summer conditions.

At the same time, it is essential to record the extreme outdoor meteorological parameters at the facility’s location (summer dry-bulb/wet-bulb temperatures, winter humidity levels), as well as the facility’s annual operating patterns (whether it operates on a three-shift system, whether operations are suspended on weekends, and whether there are periods of locally high humidity). These boundary conditions determine whether design conditions or annual average conditions should be used for calculations—misapplication of the latter is often a direct cause of undersizing equipment.

Step 2: Quantify the Five Core Heat and Moisture Sources

The moisture and heat loads of large facilities cannot be estimated broadly but must be broken down into independent components and calculated individually:

Heat Transfer and Infiltration Through Envelope Structures

Calculate the heat transfer from the outdoors based on the surface areas of walls, roofs, and floors, along with their heat transfer coefficients. At the same time, assess the uncontrolled fresh air infiltration caused by gaps in doors and windows, as well as the frequency of openings in logistics passageways. This component is often underestimated in older facilities but may actually account for 20% to 35% of the cooling load.

Moisture and Heat Dissipation from Occupants

Determine the sensible and latent heat dissipation rates based on the number of workers per workstation and the level of labor intensity. Note: Moisture emission in areas with heavy physical labor is significantly higher than in office areas; therefore, values cannot be uniformly applied based on standards for sedentary workers.

Heat Generation from Process Equipment and Lighting

This presents a unique challenge in large-scale industrial facilities. Equipment such as motors, electric furnaces, drying lines, and compressors not only release sensible heat, but certain process operations (e.g., washing, steaming, and spraying) also directly emit large amounts of water vapor into the environment, creating process-related sources of moisture. It is essential to collect data on equipment rated power, simultaneous operation rates, and moisture discharge methods, rather than simply applying the “power per unit area method.”

Internal Moisture Accumulation and Re-evaporation

Standing water on the floor, undried materials, and floors after cleaning can create a “moisture buffer” effect that releases moisture slowly, which is particularly noticeable during the restart phase after a shutdown. If the facility has periodic flushing processes, this component should be included in the verification as a peak load.

Step 3: Calculate Nominal Dehumidification Capacity and Cooling Capacity Separately

After aggregating all components, the total moisture load (kg/h) and total heat load (kW) are obtained. However, these values cannot be directly compared with equipment catalog specifications at this stage, as catalog data is typically measured under standard conditions (e.g., 27°C/60% RH), whereas the actual return air conditions in the facility may differ significantly.

The correct approach is as follows:

• Dehumidification Capacity Selection: Base the selection on the peak moisture load under the most unfavorable operating conditions, applying a safety factor of 1.1 to 1.15. Additionally, the dry-bulb temperature and relative humidity of the return air corresponding to this dehumidification capacity must be specified to allow the equipment supplier to perform operating condition adjustments.

• Cooling Capacity Selection: Distinguish between sensible heat load and latent heat load. In large industrial facilities, the sensible heat ratio (sensible heat / total cooling capacity) may reach as high as 0.7–0.9. If conventional comfort air conditioning systems (with a sensible heat ratio of approximately 0.6) are selected, the latent heat capacity will be excessive while the sensible heat capacity is insufficient. This results in temperatures meeting standards but humidity levels being too low, which in turn wastes energy. Therefore, industrial-grade units with an adjustable sensible heat ratio should be prioritized, and the required cooling capacity should be determined based on the actual sensible heat load.

The key formula logic can be simplified as follows:

• Required nominal dehumidification capacity = (moisture from occupants + moisture from processes + moisture carried by fresh air + moisture from building envelope leakage + other moisture sources) / (operating condition correction factor)

• Required cooling capacity = (heat transfer through building envelope + heat generated by equipment + heat generated by lighting + sensible heat from fresh air + sensible heat from occupants) / (safety margin)

Step 4: Final Verification by Integrating Operating Strategies with Intelligent Control

The calculated theoretical capacity must be further verified in conjunction with the facility’s actual operating conditions. For example:

If intermittent operation is adopted (production only during the day), the “cooling and dehumidification” time during the startup phase must be verified to avoid a transition period lasting several hours that could disrupt production;

If variable fresh air control is used, consideration should be given to switching to all-fresh-air operation during seasons with low outdoor humidity. In this case, the required mechanical cooling capacity can be significantly reduced, but the dehumidifier must be equipped with bypass or variable-frequency regulation capabilities;

If the facility has multiple independent temperature and humidity zones, consider using multiple small units instead of a single large unit to increase redundancy and control flexibility.

The final selection recommendation should follow the principle of “determining capacity based on peak conditions and energy efficiency based on average conditions”: that is, use data from the most adverse day to determine the equipment’s maximum output, and then use hourly simulation data for the entire year to verify the partial load performance coefficient (IPLV). Only a solution that simultaneously meets the requirements of peak dehumidification capacity and energy-efficient daily operation is a truly suitable industrial dehumidification solution.

Conclusion

Selecting a refrigeration dehumidifier for a large-scale factory is, at its core, a rigorous thermodynamic engineering decision—not a simple equipment procurement process. From on-site surveys and data mapping to item-by-item load breakdown, operating condition adjustments, and the adaptation of operating strategies, every step influences the final outcome. Only by making “thermal and humidity load calculations” the starting point and central focus of the selection process can you avoid common pitfalls such as oversizing or undersizing the equipment, ensuring a stable production environment while optimizing total life-cycle costs. Remember: the best equipment isn’t the one with the highest specifications, but the one that “breathes in sync” with your facility.