Why is Air Humidity so Critical in HVAC Systems?
Relative Humidity (Rh) directly impacts user comfort, the condition of building partitions, and the durability of equipment. For most applications, the optimal range is considered to be 30–60%.
Maintaining this range:
- Stabilizes the indoor microclimate.
- Reduces the risk of condensation and mold growth.
- Improves the efficiency of both people and equipment.
- Reduces operating costs resulting from uncontrolled dehumidification or excessive moisture.
What are the consequences of excessive humidity?
Humidity levels above 60% lead to:
- Condensation on cold surfaces (fogged windows, wet doorframes).
- Moisture penetration into building partitions and materials.
- Growth of mold and fungi.
- Deterioration of Indoor Air Quality (IAQ) and increased energy demand.
What are the consequences of low humidity?
Humidity levels below 30% cause:
- Dryness of mucous membranes and skin.
- Increased susceptibility to respiratory infections and irritation.
- Static electricity buildup and issues with technological processes (e.g., printing, electronics).
Which Facilities Require Strict Humidity Control?
- Offices, Schools, and Hotels: To ensure comfort and reduce complaints about "dry" or "stuffy" air.
- Museums, Archives, and Printing Plants: To maintain microclimate stability and protect hygroscopic materials (paper, canvas, wood).
- Swimming Pools and Laundries: To avoid condensation, corrosion, and degradation of the building structure.
How do Air Handling Units (AHUs) Manage Dehumidification and Humidification?
Modern HVAC units utilize integrated cooling, heating, and sorption systems, controlled by automation based on humidity sensor signals. Control algorithms take into account the dew point, supply air temperature, and priorities such as comfort and energy security.
Main Methods of Air Dehumidification:
- Cooling Coil Dehumidification (Condensation):
Air is cooled below the dew point, causing moisture to condense.
Commonly used in offices, hotels, and commercial buildings.
- Sorption Dehumidification (Adsorption):
A sorption rotor or cassette absorbs water vapor from the airflow.
Used in industrial processes, controlled-climate warehouses, and where low humidity is required at low temperatures.
Main Methods of Air Humidification:
- Steam Humidification (Isothermal):
The most precise and hygienic solution.
Does not change the air temperature in the stream.
Recommended for rooms requiring precise control (e.g., laboratories, archives, server rooms).
- Evaporative or Spray Humidification (Adiabatic):
A process combined with partial air cooling.
Requires high water quality and strict cleaning procedures to avoid microbiological risks.
The Role of Automation and BMS in Humidity Control
An effective HVAC control system should:
- Measure humidity at representative points in the rooms.
- Maintain a balance between dehumidification and reheating.
- Protect the installation from condensation on exchangers and ducts (anti-condensation algorithms).
- Integrate with the BMS regarding priorities: comfort, hygiene, and energy efficiency.
- Hygiene and Safety in Ventilation Systems
Regardless of the technology used:
- Condensate drainage must be effective (drain pans, siphons, and cleaning access).
- Water quality in humidification systems must be maintained through regular service and disinfection.
- Filters and exchangers must be inspected regularly, as contamination affects both hygiene and energy efficiency.
