Broiler House Ventilation Upgrade in Georgia, USA

Case Study 1: Broiler House Ventilation Upgrade in Georgia, USA

Scenario A commercial broiler operation in rural Georgia (humid subtropical climate) retrofitted a 12,000-bird tunnel-ventilated house built in 2008. The existing axial fans were undersized and failing to maintain target indoor temperature (<27°C) during summer peaks (outdoor temps up to 35°C). Key constraints included limited electrical panel capacity (max 15 kW total fan load), retrofit-only budget (no structural modifications), and strict ammonia compliance (<25 ppm), requiring precise moisture and CO₂ control.

Given data

• Mass of birds: 1,200 kg (average live weight = 120 g × 10,000 birds; note: input adjusted for actual flock density — 10,000 birds at 120 g avg = 1,200 kg)
• Indoor temperature: 26.5°C
• Outdoor temperature: 32.0°C
• Evaporation rate: 0.018 kg/s (measured via pen-scale moisture balance during peak production week)
• Latent heat of vaporization: 2,440,000 J/kg (standard value for water at ~25°C)
• Number of birds: 10,000
• CO₂ generation rate per bird: 12.5 g/bird·h → converted to 0.00347 g/s/bird = 34.7 g/s total
• Static pressure difference: 25 Pa (measured across new 12" inlet curtains + 30-m tunnel length)
• Fan efficiency: 68% (field-tested value for aging units; used for baseline comparison)

Calculation The Ventilation Fan Capacity Calculator uses two parallel load-based airflow determinants — sensible heat removal, latent heat removal, and CO₂ dilution — then selects the maximum required airflow rate:

1. Latent load airflow: Q_latent = (evaporation_rate × latent_heat) / (ρ_air × c_p × ΔT_sensible) is not used directly. Instead, the tool prioritizes moisture-driven ventilation where evaporation rate is provided as a direct mass flux. The calculator internally computes minimum airflow to carry away evaporated moisture:
   Q_moisture = evaporation_rate / (ρ_air × (w_in − w_out)), but per spec, it uses a simplified hybrid model. Given inputs, the tool computes:
   • Moisture removal demand → drives ~1.85 m³/s
   • CO₂ dilution demand: Q_CO2 = (total_CO2_gen_rate) / (CO2_allowable_conc − CO2_outdoor) ≈ (34.7 g/s) / (1,500 ppm − 400 ppm) × (1 m³ air ≈ 1.2 g × 0.0004 g CO₂/g air) → yields ~2.14 m³/s
   • Sensible heat load not explicitly input, but implied via ΔT and mass; tool defaults to dominant moisture/CO₂ drivers.

Using the calculator with above inputs:

• Required airflow rate = 2.38 m³/s (governed by CO₂ + moisture co-constraints)
• Fan power = (Q × ΔP) / η = (2.38 × 25) / 0.68 ≈ 87.9 W per fan — but scaled for system: total power = 2.38 m³/s × 25 Pa / 0.68 = 87.9 W (for single-fan equivalent); actual design used 3 × high-efficiency 0.85 kW fans (2.55 kW total) to achieve redundancy and turndown.

Result and decision Selected three 800 mm backward-curved centrifugal fans (each rated 0.85 kW, η = 78%, max airflow 1.1 m³/s @ 25 Pa), replacing six aging axial units. System achieved stable 26.2°C indoor temp (±0.3°C) and <18 ppm NH₃ during 35°C outdoor events. Electrical load remained within 15 kW limit (peak draw: 13.2 kW).

Lesson Moisture and CO₂ loads—not just temperature—dictate minimum ventilation in dense broiler houses; relying solely on sensible heat calculations risks ammonia accumulation and wet litter. Always validate evaporation rate with on-farm pen-scale measurements during peak production.