Dehydrator Sizing Calculator

This calculator estimates required moisture removal by combining ventilation drying demand with internal and extra moisture loads. It uses common psychrometric approximations for humidity ratio.

• Ventilation airflow: Q = Volume × ACH (or user-entered Q).
• Humidity ratio: w = 0.62198 × Pv / (P − Pv), where Pv = RH × Psat(T).
• Moisture removal rate: ṁw = ṁdry × (w_in − w_target) (kg/h), negative values treated as zero.
• Ventilation load per day: L_vent = ṁw × hours/day (L/day).
• Total load: L_base = L_vent + L_internal + L_extra.
• Required capacity: L_req = L_base × (1 + safety%).
• Unit count: N = ceil(L_req / unit_capacity).
• Energy estimate: kWh/day ≈ L_req / (L/kWh).

1. Enter the space volume and expected air changes per hour, or switch on known airflow.
2. Provide inlet air temperature and humidity, then set your target conditions.
3. Add internal sources and any extra daily water removal expected from wet works.
4. Select operating hours, safety factor, and unit rated capacity.
5. Press calculate to view capacity, unit count, and export options.

Construction drying is rarely limited by one factor. Moisture enters from ventilation, fresh concrete curing, wash-down activities, groundwater intrusion, and even the people working inside an enclosure. A properly sized dehydrator removes water at a steady rate while maintaining a safe humidity setpoint for coatings, flooring systems, and finishes. Undersizing leads to schedule slips, extended cure times, and recurring condensation. Oversizing can waste energy and cause short cycling, which reduces real-world performance.

This calculator estimates daily water removal by combining three loads: ventilation drying demand, internal sources, and extra removal for wet works. The ventilation component uses humidity ratio, which expresses how much water vapor is carried per kilogram of dry air. When inlet humidity is higher than the target, the difference (Δw) determines how much moisture must be removed as air exchanges occur. If Δw is small, ventilation contributes little drying demand, and the project is dominated by internal or material moisture.

Unit ratings can differ across test standards and operating conditions. To keep sizing practical, enter the rated liters per day per unit that matches your procurement data, then apply a safety factor to cover distribution losses, door openings, and imperfect mixing. On large projects, consider deploying multiple smaller units to improve coverage, simplify power distribution, and allow staged commissioning as zones are completed.

Example (from the table below): A 450 m³ basement slab area with 1.5 ACH, inlet 25°C at 75% RH, and target 22°C at 55% RH, plus 8 L/day internal moisture and 20 L/day extra load, results in roughly 90 L/day required capacity after a 20% safety allowance. With 50 L/day units, the recommended quantity is two units. If operating hours are reduced, the required daily capacity stays similar, but average power demand increases because removal must occur in fewer hours.

Use the results as a planning baseline. Confirm airflow paths, verify that each zone has adequate circulation, and validate moisture conditions with calibrated sensors. Adjust inputs as site conditions change, especially after rain events, changes to ventilation strategy, or new wet trades entering the workspace.

1) What does “liters per day” capacity represent?

A dehumidification rating estimates how many liters of water the unit can remove in 24 hours under stated test conditions. Real removal varies with temperature, humidity, airflow, and how well air circulates through the space.

2) Should I use ACH or a known airflow?

Use known airflow when you have measured or designed ventilation in m³/h. Use ACH when you only know enclosure size and an expected air-change rate. Known airflow typically produces a more reliable ventilation moisture estimate.

3) Why is a safety factor recommended?

Safety covers imperfect mixing, door openings, wet materials, and performance losses compared to nameplate ratings. It also protects schedules when conditions worsen. Many sites start with 15–30% and refine after monitoring.

4) What if my inlet humidity is already below the target?

If inlet air is drier than the target, the ventilation drying component becomes near zero. You may still need capacity for internal moisture sources or wet works. In such cases, focus on internal and extra removal inputs.

5) How do temperature setpoints affect sizing?

Warmer air can hold more moisture, which can increase removal potential and change Δw. Lower temperatures may reduce unit performance. Keep temperature and humidity targets aligned with product requirements and equipment capability.

6) Is the energy estimate a guarantee?

No. It is a planning estimate based on your L/kWh input and the required liters per day. Actual energy use depends on unit efficiency at site conditions, cycling, defrost behavior, airflow restrictions, and heat gains.

7) How many units should I deploy for large enclosures?

Multiple units are often better than one large unit because they improve coverage and redundancy. Place units to avoid dead zones and route condensate safely. Verify with humidity sensors at multiple locations within the enclosure.