The Golden Ratio of Swimming Pool Ventilation and Dehumidification Systems: The Balancing Act of Airflow, Humidity and Energy Consumption

       In the design and operation and maintenance of indoor swimming pools, the performance of ventilation and dehumidification systems directly affects the comfort, safety and operating costs of the pool environment. How to find the "golden ratio" between airflow, humidity and energy consumption is the core challenge for engineers, designers and operation and maintenance teams. Based on the ASHRAE standard and actual measurement data, this paper analyzes the dynamic balance strategy among the three, providing a scientific basis for swimming pool system optimization.

‌I. Theoretical Model: Basic Calculation of Air Volume and Humidity‌

1. ‌ASHRAE airflow calculation framework‌
   According to ASHRAE 62.1, there are two conditions that need to be met for the minimum amount of fresh air for indoor pools:

   • ‌human respiratory requirements: Calculated at 10 L/s of fresh air per capita (based on maximum occupancy).
   • ‌Humidity control requirements: Calculate the amount of dehumidification required by using the evaporation formula, and then invert the ventilation airflow.

   Eq. simplifies the expression to:Q=ACH×V/60

   1. Among them.$Q$is the fresh air volume (m³/h).$ACH$is the number of air changes per hour.$V$is the volume of the pool space (m³).ASHRAE recommends that the number of air changes for indoor pools be controlled at 4-6 times/hour, which needs to be adjusted in conjunction with the humidity load.

   2. ‌Thresholds for humidity control: Dew point temperature vs. evaporation‌
      Pool surface evaporation ($W$) is calculated by the Dalton formula:

      W=(Pw​-Pa​)×A×F

      • Pw​: Saturated vapor pressure (kPa) at the water surface, positively correlated with water temperature;
      • Pa​: Actual vapor pressure of air (kPa);
      • $A$: Pool water surface area (m²);
      • $F$: Evaporation coefficient (usually taken as 0.1-0.2, influenced by wind speed and intensity of activity).

      When the ventilation airflow is insufficientPaPa​Elevated, resulting in evaporation$W$The humidity will drop, but too much humidity will cause condensation problems; on the other hand, excessive ventilation can reduce humidity, but it will cause heat loss and energy consumption to rise.

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   ‌Second, dynamic equilibrium: air volume, humidity and energy consumption of the game‌

   1. ‌"The Three Core Principles of the Golden Ratio‌

      • ‌Principle 1: Prioritize humidity--Control air humidity at 50%-60% (dew point temperature ≤14℃) to avoid structural corrosion and mold growth.
      • ‌Principle 2: Minimum airflow--Select the minimum number of air changes (e.g., 4/hour) to minimize heat loss while meeting humidity requirements.
      • ‌Principle 3: Energy recovery--Compensate for energy loss due to ventilation by recovering latent heat of evaporation through heat pump dehumidifiers.

   2. ‌Energy saving optimization path‌

      • ‌Path 1: air volume hierarchical control‌
        Dynamically adjust the airflow according to the intensity of pool use (e.g. opening hours, number of visitors). Example:
        • Peak hours: 6 air changes/hour enabled;
        • Low hours: drop to 4 times/hour in conjunction with a dehumidifier to maintain humidity.
      • ‌Path 2: Heat pump system integration‌
        With dehumidifiers with heat recovery (such as the Dantherm CDP series), the heat recovered during dehumidification is used for pool water or air heating, saving energy up to 60%-70%.
      • ‌Path 3: Intelligent Predictive Control‌
        Through the humidity sensor + AI algorithm to pre-determine changes in evaporation (e.g., sudden weather changes or event bookings), the ventilation and dehumidification modes are adjusted in advance to avoid overloading or redundant operation of the system.

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   ‌III. Practical verification: comparison of measured data and cases‌

   An international hotel swimming pool renovation project as an example, the original system uses a fixed 6 times / hour air exchange + traditional dehumidifier, after the renovation upgraded to variable frequency ventilation + heat pump dehumidification linkage system, data comparison is as follows:

   norm	pre-remodeling	after remodeling	degree of reduction (in prices, numbers etc)
   Average annual energy consumption (kWh/m²)	320	180	43.8%
   Humidity compliance (%)	75% (highly volatile)	95% (stabilized)	–
   Equipment failure rate (times/year)	8	2	75%

   ‌Key improvement points::

   • Frequency-controlled fans adjust airflow according to real-time humidity, reducing ineffective ventilation;
   • Heat pump dehumidifiers recover heat for pool water thermostat and reduce boiler load;
   • Intelligent control system reduces manual intervention errors.

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   ‌IV. Design recommendations: 4 steps to realize the "golden ratio"‌

   1. ‌Accurate load calculation‌
      Use specialized software (e.g. Carrier HAP or IESVE) to simulate pool evaporation, ventilation requirements and heat loss to avoid equipment selection errors due to empiricism.

   2. ‌Selection of highly integrated devices‌
      Prioritize the use of 3-in-1 systems for ventilation, dehumidification, and heat recovery (e.g., Calorex Varipac) to reduce plumbing complexity and space occupation.

   3. ‌Allow for redundancy in regulation‌
      Adding 10%-15% of regulation margin to the airflow design value to cope with unexpected high load scenarios (e.g. pool parties or tournament events).

   4. ‌Long-term monitoring and iteration‌
      Installation of IoT sensors to monitor humidity, airflow and energy consumption data, quarterly analysis of the system's energy efficiency ratio (COP), and continuous optimization of operation strategies.

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   ‌concluding remarks‌

           The essence of the "golden ratio" of swimming pool ventilation and dehumidification system is to find the optimal solution between environmental safety and energy efficiency through scientific modeling and technological innovation. With the advancement of heat pump technology and intelligent control algorithms, this balance will be more refined and dynamic, providing a solid guarantee for the sustainable development of indoor swimming pools.

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