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Pool Ventilation Guide: VDI 2089 & ASHRAE Dehumidification Design (2025)

Master indoor pool ventilation with interactive calculator. Evaporation rates, dehumidifier sizing, condensation prevention per VDI 2089 & ASHRAE standards.

Enginist Technical Team
The Enginist Technical Team comprises licensed Mechanical Engineers (P.E.) and ASHRAE-certified HVAC professionals with 15+ years of experience in natatorium and aquatic facility design. Our team has designed ventilation and dehumidification systems for residential pools, commercial fitness centers, and Olympic-standard competition facilities across Europe and North America.
Reviewed by P.E.-Licensed Mechanical Engineers with ASHRAE HBDP Certification
Published: October 23, 2025
Updated: November 27, 2025
Related Calculators:HRV SizingFresh Air FlowPsychrometric Calculator

Table of Contents

Pool Ventilation and Dehumidification Guide (2025)

Quick AnswerHow do you calculate pool evaporation rate?
Calculate pool evaporation using W=nW = n × A × ΔP × (1 + v) per VDI 2089, where n is activity factor (0.5-2.0), A is pool area (m²), ΔP is vapor pressure difference (Pa). Size dehumidifier at 1.2 times the evaporation rate.
Example

50m² residential pool at 28°C, 30°C/60% air = 0.5 × 50 × 1234/100000 × 1.01 = 31 kg/h.

Introduction

Walk into a poorly ventilated indoor pool, and you'll feel it immediately: the oppressive humidity, the foggy windows, the unmistakable sting of chloramines in the air. Now walk into a well-designed natatorium—the air feels fresh, the glass is clear, and the environment is genuinely pleasant. The difference? A properly engineered ventilation and dehumidification system.

Indoor pools are humidity factories. A typical residential pool (32 m²) evaporates 20-30 kg of water per hour—that's roughly a bathtub full of water entering the air every 60 minutes. Without intervention, this moisture wreaks havoc: condensation corrodes structural steel in 5-10 years, mold colonizes walls and ceilings, and chloramine concentrations can exceed safe limits, causing respiratory irritation for swimmers and staff.

Why Pool Ventilation is Different

Unlike standard HVAC focused on thermal comfort, pool ventilation has a singular mission: moisture control. The physics are unforgiving—warm water constantly evaporates, and that moisture must go somewhere. You have two choices:

  1. Ventilation-only approach: Exhaust humid air and replace with dry outdoor air. Requires 25-30 ACH and massive heating loads—economically impractical.
  2. Dehumidification approach: Use refrigerant or desiccant systems to condense moisture from recirculated air. Requires only 6-8 ACH with 70-80% energy savings.

This guide follows the VDI 2089 [1] standard (the gold standard for pool ventilation) and ASHRAE [2] guidelines to help you design systems that keep pools comfortable, safe, and energy-efficient.

What You'll Learn

  • Evaporation calculation using the VDI 2089 formula
  • Dehumidifier sizing for 70-80% moisture removal
  • Ventilation rates (6-12 ACH) for air quality
  • Condensation prevention strategies for the building envelope
  • Energy optimization through heat recovery systems

Quick Answer: How to Calculate Pool Ventilation and Dehumidification?

Pool ventilation and dehumidification are calculated using evaporation rates and moisture removal requirements per VDI 2089 [1] standards.

Core Evaporation Formula (VDI 2089)

W=n×A×ΔP×(1+v)W = n \times A \times \Delta P \times (1 + v)

Where:

  • WW = Evaporation rate (kg/h)
  • nn = Activity factor (0.5 residential to 2.0 competition)
  • AA = Pool surface area (m²)
  • ΔP\Delta P = Vapor pressure difference (Pa)
  • vv = Air velocity factor

Vapor Pressure Difference

ΔP=Psat(Tw)−Psat(Ta)×ϕ\Delta P = P_{\text{sat}}(T_w) - P_{\text{sat}}(T_a) \times \phi

Where:

  • Psat(Tw)P_{\text{sat}}(T_w) = Saturation vapor pressure at water temperature
  • Psat(Ta)P_{\text{sat}}(T_a) = Saturation vapor pressure at air temperature
  • ϕ\phi = Relative humidity (decimal)

Dehumidifier Capacity

Mremoval=W×(1−ηvent)M_{\text{removal}} = W \times (1 - \eta_{\text{vent}})

Where:

  • MremovalM_{\text{removal}} = Required dehumidifier capacity (kg/h)
  • ηvent\eta_{\text{vent}} = Fraction removed by ventilation (typically 0.2-0.3)

Reference Table

ParameterTypical RangeStandard
ACH (Residential Pool)6-8VDI 2089
ACH (Public Pool)8-12ASHRAE
ACH (Competition Pool)12-15ASHRAE
Air Temperature Above Water2-3°CVDI 2089
Relative Humidity (Maximum)50-60%VDI 2089
Evaporation (Residential)15-30 kg/hTypical
Evaporation (Public)80-150 kg/hTypical
Outdoor Air (Per Person)30-50 m³/hVDI 2089

Key Standards

Worked Example: Residential Pool Design

This example demonstrates the complete design process for a typical residential indoor pool using the VDI 2089 methodology.

Residential Indoor Pool: 32 m² Design

Scenario: Design a ventilation and dehumidification system for a private indoor pool in a residential home.

Design Inputs:

ParameterValueNotes
Pool Dimensions8 m × 4 m = 32 m²Standard residential size
Water Temperature (TwT_w)28°CTypical comfort temperature
Air Temperature (TaT_a)30°CMaintained 2K above water per VDI 2089
Target Relative Humidity (ϕ\phi)60%Maximum per VDI 2089
Activity Factor (nn)0.5Residential, covered when not in use
Air Velocity< 0.1 m/sLow velocity over pool surface
Hall Volume~200 m³Pool area + deck + 3m ceiling

Step 1: Calculate Vapor Pressure Difference (ΔP\Delta P)

The vapor pressure difference drives evaporation. First, find saturation vapor pressures using the Psychrometric Calculator or steam tables:

  • At water temperature: Psat(28°C)=3780 PaP_{\text{sat}}(28°\text{C}) = 3780 \text{ Pa}
  • At air temperature: Psat(30°C)=4243 PaP_{\text{sat}}(30°\text{C}) = 4243 \text{ Pa}

Now calculate the driving pressure difference: ΔP=Psat(Tw)−Psat(Ta)×ϕ=3780−(4243×0.60)=3780−2546=1234 Pa\Delta P = P_{\text{sat}}(T_w) - P_{\text{sat}}(T_a) \times \phi = 3780 - (4243 \times 0.60) = 3780 - 2546 = \textbf{1234 Pa}

  • ✔ Positive ΔP means evaporation will occur (water vapor pressure exceeds air vapor pressure)
  • ✔ The 2K air-water temperature difference reduces ΔP significantly—without it, ΔP would be ~1500 Pa (22% higher evaporation)

Step 2: Calculate Evaporation Rate (WW)

Apply the VDI 2089 evaporation formula: W=n×A×ΔP×(1+v)W = n \times A \times \Delta P \times (1 + v)

Where vv is the air velocity factor (for < 0.1 m/s, use v=0.01v = 0.01): W=0.5×32 m2×1234100,000×(1+0.01)≈20 kg/hW = 0.5 \times 32 \text{ m}^2 \times \frac{1234}{100{,}000} \times (1 + 0.01) \approx \textbf{20 kg/h}

Note: The coefficient 0.5 is the activity factor for residential pools with covers. During active swimming, this increases to 1.0-1.5.

Step 3: Size the Dehumidifier

The dehumidifier is the primary moisture removal system. Size it to handle 100% of evaporation (with safety margin):

CalculationValue
Base evaporation rate20 kg/h
Safety factor (1.2×)24 kg/h
Required dehumidifier capacity24 kg/h (576 kg/day)
  • ⚠️ Select a pool-specific dehumidifier with heat recovery to warm pool water
  • ⚠️ Refrigerant type (COP 2.5-3.5) is most efficient for 15-35°C air temperatures

Step 4: Calculate Ventilation Rate (ACH)

Ventilation provides fresh air for chloramine dilution and air quality—not primary moisture removal:

Q=V×ACH=200 m3×6 h−1=1200 m3/hQ = V \times \text{ACH} = 200 \text{ m}^3 \times 6 \text{ h}^{-1} = \textbf{1200 m}^3\textbf{/h}

ParameterValueStandard
Room Volume200 m³Pool + deck + ceiling
Required ACH6VDI 2089 (Residential)
Ventilation Airflow1200 m³/hBase requirement
Outdoor Air per Person30-50 m³/hVDI 2089 Section 5.2

Final Design Summary:

ComponentSpecificationPurpose
Dehumidifier24 kg/h capacity with heat recoveryPrimary moisture removal
Ventilation Unit1200 m³/h (6 ACH) with heat recoveryAir quality & chloramine dilution
Air Temperature30°C (2K above water)Minimize evaporation
Target Humidity50-60% RHPrevent condensation

How do you calculate the energy costs of pool ventilation and dehumidification?

Energy costs for pool ventilation come from two main sources: heating the ventilation air and running the dehumidifier. Here's how to calculate each.

Energy Cost Calculation: 50 m² Pool

Given:

  • Pool area: 50 m²
  • Hall volume: 150 m³
  • Ventilation rate: 6 ACH (900 m³/h)
  • Evaporation rate: 31.2 kg/h
  • Climate: 20°C average outdoor, 30°C indoor
  • Operating hours: 8,760 h/year (continuous)

1. Ventilation Heating Energy

Heating outdoor air from 20°C to 30°C:

Qvent=V˙×ρ×cp×ΔT×HQ_{\text{vent}} = \dot{V} \times \rho \times c_p \times \Delta T \times H

ParameterValue
Airflow (V˙\dot{V})0.25 m³/s
Air density (ρ\rho)1.204 kg/m³
Specific heat (cpc_p)1.005 kJ/kg·K
Temperature difference (ΔT\Delta T)10 K
Hours per year (HH)8,760 h

Qvent=0.25×1.204×1.005×10×8760=26,500 kWh/yearQ_{\text{vent}} = 0.25 \times 1.204 \times 1.005 \times 10 \times 8760 = \textbf{26,500 kWh/year}

2. Dehumidifier Energy

Refrigerant dehumidifier power consumption:

P=W×hfg3600×COPP = \frac{W \times h_{fg}}{3600 \times \text{COP}}

ParameterValue
Evaporation rate (WW)31.2 kg/h
Latent heat (hfgh_{fg})2,500 kJ/kg
COP (typical)3.0

P=31.2×25003600×3.0=7.2 kWP = \frac{31.2 \times 2500}{3600 \times 3.0} = \textbf{7.2 kW}

Annual consumption: 7.2 kW×8760 h=63,100 kWh/year7.2 \text{ kW} \times 8760 \text{ h} = \textbf{63,100 kWh/year}

3. Heat Recovery Savings

The dehumidifier recovers latent heat to warm pool water:

Qrecovery=W×hfg3600=31.2×25003600=21.7 kWQ_{\text{recovery}} = \frac{W \times h_{fg}}{3600} = \frac{31.2 \times 2500}{3600} = \textbf{21.7 kW}

This offsets pool heating by approximately 50,000 kWh/year.

4. System Comparison

System TypeAnnual EnergySavings
Ventilation-only (29 ACH required)128,000 kWh/year—
Dehumidification + Ventilation89,600 kWh/year30%
Dehumidification + Heat Recovery39,600 kWh/year69%

Use our free pool ventilation air supply calculator for instant calculations.

Related tools:

Conclusion

Proper ventilation and dehumidification are essential for indoor pool environments. By calculating evaporation rates and heat loads accurately, engineers can design efficient systems that maintain comfort while minimizing energy consumption.

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Key Takeaways

RuleRequirementWhy It Matters
Evaporation CalculationUse W=n×A×ΔP×(1+v)W = n \times A \times \Delta P \times (1 + v) per VDI 2089Determines dehumidification capacity and ventilation requirements
Air-Water TemperatureMaintain air 2-3°C above water temperatureReduces evaporation rate by 20-30% and prevents condensation
Ventilation RateProvide 6-12 ACH with dehumidificationVentilation-only requires 25-30 ACH (energy-prohibitive)
Dehumidifier SizingSize for 70-80% of total evaporationVentilation handles 20-30%; dehumidifier removes the rest
Humidity ControlMaintain 50-60% RH maximumPrevents condensation while limiting evaporation
Heat RecoveryRecover latent heat from dehumidifierSaves 70-80% of energy (15-30 kW) by warming pool water

Further Learning

References & Standards

Primary Standards

[1] VDI 2089 German standard for indoor pool air conditioning. Requires air temperature 2-3°C above water temperature, relative humidity 50-60% maximum, 6-12 ACH ventilation, and dehumidification for pools >25 m². Specifies evaporation calculation methods and condensation prevention requirements.

[2] ASHRAE Handbook - HVAC Applications Chapter 5: Natatoriums and Indoor Aquatic Facilities. Provides comprehensive guidance on pool ventilation design, evaporation rates, dehumidification systems, and energy efficiency strategies.

Supporting Standards & Guidelines

[3] ASHRAE Standard 62.1 Ventilation and acceptable indoor air quality in commercial buildings. Provides outdoor air requirements for pool facilities.

Further Reading

Note: Standards and codes are regularly updated. Always verify you're using the current adopted edition applicable to your project's location. Consult with local authorities having jurisdiction (AHJ) for specific requirements.

Disclaimer: This guide provides general technical information based on international ventilation standards. Always verify calculations with applicable local codes and consult licensed professionals for actual installations. Ventilation system design should only be performed by qualified professionals. Component ratings and specifications may vary by manufacturer.

Frequently Asked Questions

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