Introduction:
When designing cold storage facilities—especially for fruits, vegetables, and other biologically active perishables—respiration rate heat load plays a critical role. Often overlooked by general HVAC designers, this hidden heat source can significantly affect energy efficiency, temperature stability, and product shelf life. In this post, we explore what respiration heat load is, why it matters in cold room applications, and how to account for it in HVAC design.
What Is Respiration Rate Heat Load?
Respiration rate heat load refers to the thermal energy released by biological products (like fruits and vegetables) as they continue to respire post-harvest. Respiration is a biochemical process where oxygen is consumed and carbon dioxide is produced—along with latent and sensible heat.
Biochemical Basis of Respiration Heat
- Carbohydrates + O₂ → CO₂ + H₂O + Heat
- The heat generated depends on:
- Type of product (e.g., bananas respire more than apples)
- Storage temperature and humidity
- Duration of storage
Why Respiration Load Is Critical in Cold Room Design
1. Impacts Cooling Load Calculations
Respiration heat adds to the total internal load, along with:
- Product load (initial cooling)
- Lighting
- Equipment
- Personnel
Neglecting respiration heat can result in undersized refrigeration systems, leading to temperature drift, overworked compressors, and product spoilage.
2. Affects Temperature and Humidity Control
High respiration rates elevate room temperature and relative humidity, making it harder to:
- Maintain optimal storage conditions
- Prevent microbial growth
- Extend shelf life
This is especially relevant for produce stored near the climacteric peak, such as avocados and mangoes.
3. Determines Airflow and Ventilation Needs
Respiring products emit CO₂ and moisture. Without proper ventilation, this can lead to:
- Anaerobic conditions (bad for product quality)
- Condensation issues
- Ethylene buildup (speeds ripening)
How to Account for Respiration Rate Heat in Design
1. Use Published Respiration Data
Refer to USDA and ASHRAE tables for respiration rates by product type (e.g., kcal/ton/hour). For instance:
- Apples (0°C): ~2 kcal/ton/hr
- Bananas (13°C): ~45 kcal/ton/hr
2. Adjust for Temperature Sensitivity
Respiration rate is temperature-dependent, often doubling with every 10°C rise. Designing with modulating refrigeration systems can help manage these fluctuations efficiently.
3. Include in Load Calculation Software
Modern HVAC software like CoolPack, HVAC Load Explorer, or Carrier HAP allows inclusion of custom internal loads, including respiration.
Common Cold Room Applications Where Respiration Heat Load Is Crucial
- Banana Ripening Chambers
- Mango and Avocado Storage
- Leafy Greens Cold Storage
- Packhouses and Distribution Centers
These facilities require precise climate control, making respiration heat a major factor in system sizing and airflow planning.
FAQ: Respiration Rate Heat Load in Cold Room Design
Q1: What is respiration rate in cold storage design?
A1: It refers to the heat produced by biological activity in stored products, affecting cooling load and storage conditions.
Q2: Which products generate the highest respiration heat?
A2: Fruits like bananas, mangoes, and tomatoes have high respiration rates, especially during ripening.
Q3: Can respiration rate be ignored in cold room design?
A3: No. Ignoring it can cause system underperformance, temperature instability, and product spoilage.
Q4: How is respiration heat managed in design?
A4: By including it in heat load calculations and using variable capacity refrigeration systems and controlled ventilation.
Q5: Does respiration rate change over time?
A5: Yes, it generally decreases as the product cools but can spike during ripening or spoilage.