The Importance of Humidity Control in Commercial Buildings
Maintaining precise humidity control in commercial buildings is crucial for energy efficiency, indoor air quality (IAQ), and equipment longevity. High humidity levels can lead to mould growth, discomfort, and inefficiencies in HVAC systems. Dedicated Outdoor Air Systems (DOAS) with desiccant dehumidification provide an optimal solution, offering independent temperature and humidity control while reducing energy consumption and HVAC workload.
Benefits of DOAS Dedicated Outdoor Air Dehumidification
- Energy Efficiency: Reduces air-conditioning energy consumption and system workload.
- Improved IAQ: Controls humidity levels to prevent mould and bacterial growth.
- Independent Temperature & Humidity Control: Allows for precise climate regulation without overcooling.
- Reduced Air-Conditioning Load: Lowers required cooling capacity and ducting size.
- Chiller Capacity Gains: Improves overall system efficiency by up to 10%.
- Flexible System Options: Compatible with solar, DX, chilled water (CHW), and energy recovery ventilator (ERV) solutions.
Key Advantages of Commercial Dehumidification
1. Improved Indoor Air Quality (IAQ)
Maintaining surface humidity below 60% RH mitigates mould and bacterial growth. Relevant industry standards acknowledge the importance of humidity control:
- ASHRAE Standards: Recommends a design window between 40-60% RH and energy modelling at 65% RH (ASHRAE 62.1-2007, 5.10.1).
- Japan’s Sanitation Law: Mandates 40%-65% RH for health compliance.
- Australia’s Green Star Ratings: Awards credits for maintaining below 60% RH in spaces and 80% RH in ducts.
Many conventional buildings suffer from high humidity during “part load” hours when cooling demand is low but moisture remains a concern.
2. Better Temperature & Humidity Control
Desiccant dehumidifiers precondition fresh air to below 5°C dew point (dp) or 30% RH at 23°C, allowing for efficient moisture absorption. The system operates effectively when reactivated at 50-60°C and requires minimal preconditioning at 120°C.
Central HVAC systems often experience a sensible heat ratio (SHR) mismatch when outdoor humidity is high. DOAS mitigates this by handling the latent load separately from sensible cooling.
3. Reduced Air-Conditioning Coil Work
DOAS with desiccant dehumidification removes outdoor air humidity efficiently, preventing the need to dehumidify the entire recirculated air stream. This approach:
- Eliminates excessive cooling and reheating cycles.
- Saves energy by reducing latent loads before they enter the indoor environment.
- Utilizes ERV systems to capture and reuse exhaust air for further efficiency.
4. Reheat Avoidance
Traditionally, overcooled air is reheated to maintain room temperature, leading to wasted energy. Since 1999, this practice has been restricted in the U.S. by ASHRAE 90.1 and is banned in Australia for electric reheat elements.
5. Reduced Plant Size & Increased Coefficient of Performance (COP)
DOAS allows for the integration of chilled beams and smaller, more efficient cooling plants. Standard air-conditioning oversizes cooling equipment to handle both sensible and latent loads. With DOAS:
- Recirculated airflow can be reduced by 50%.
- Chiller efficiency improves due to higher operating temperatures.
- Oversized systems are optimized for commercial building requirements.
7-Step Dehumidification Selection Method
Step 1: Determine Building Occupancy
Local building codes define minimum outdoor air (OA) requirements per person:
- USA: 15 cfm per person.
- Australia: 7.5 L/s per person.
- Example: 400 occupants × 7.5 L/s = 3000 L/s (10,000 m³/h).
Step 2: Define Outdoor Air (OA) Design Condition
- Example: 35°C dry bulb (DB), 24°C wet bulb (WB) for chilled water capacity assessment.
Step 3: Establish Room Humidity Ratio
- Library: 50% RH at 23°C (8.8 g/kg).
- Commercial Building: 60% RH at 23°C.
- Supermarket: 50% RH at 23°C (8.8 g/kg).
- Swimming Pool: 60% RH at 28°C.
Step 4: Calculate People-Generated Humidity Load
- Humidity per person: 100 g/h.
- Example: 400 occupants × 100 g/h = 40 kg/h latent load.
Step 5: Assess Internal Infiltration Rate
- Tight Building: 0.1 cfm/ft² (8.8 cmh/m²).
- Average Building: 0.3 cfm/ft² (25 cmh/m²).
- Loose Building: 0.6 cfm/ft² (50 cmh/m²).
Example: Room 20m × 20m × 3m (400m²)
- Moisture load calculation: 23 kg/h.
Step 6: Calculate Required Humidity Ratio Change (Δg/kg)
- Formula: Δg/kg = (internal load Q4 + Q5) / (OA m³/h × air density kg/m³) × 1000
- Example: (40 + 23) / (10,000 × 1.2) = 5.25 g/kg.
Step 7: Required OA Supply Humidity Ratio (HR g/kg)
- Formula: SA HR = Room HR (Step 3) − Δg/kg (Step 6)
- Example: Supermarket: 8.8 – 3.5 = 5.3 g/kg.
- Conclusion: This requires 4.5°C dew point, achievable only with desiccant dehumidification.
Desiccant Dehumidification for Commercial Applications
Desiccant dehumidification is widely used in commercial buildings, particularly in humid climates where conventional HVAC systems struggle to control moisture. Its benefits include:
- Compliance with stringent building standards.
- Energy savings through optimal latent load management.
- Enhanced system performance by integrating with existing HVAC systems.
For expert consultation on integrating DOAS and desiccant dehumidification into your commercial building, contact Air and Aqua Tech Australia today.
📍 Location: Cromer, NSW 2099
📞 Phone: 1300 002 228
📧 Email: info@aaatec.com.au
Frequently Asked Questions (FAQ)
Q: Why is humidity control crucial in commercial buildings?
A: It prevents mould, improves indoor air quality, and enhances HVAC efficiency.
Q: How does desiccant dehumidification compare to traditional air conditioning?
A: It removes moisture without overcooling, reducing energy use and system strain.
Q: Does humidity control impact energy efficiency?
A: Yes, it reduces HVAC workload, leading to lower operational costs.
For more details, reach out to our team today!