I. Preliminary Foundation: Prerequisites for Steel Structure Buildings (Core Factor for Ventilation Success)

The ventilation system cannot be designed separately from the steel structure enclosure. Air tightness, thermal insulation and layout of beams and columns directly determine ventilation efficiency.

Poultry House Orientation Arrange the long side of the poultry house in an east-west direction to reduce direct solar radiation on the roof and side walls in the afternoon. The prevailing wind direction should be perpendicular to the long side of the house to facilitate natural air exchange.

Air Tightness Requirements for Steel Structure Enclosure (Mandatory Condition for Negative Pressure Ventilation)

The roof and walls adopt 75/100mm polyurethane PIR / rock wool insulated sandwich panels with anti-corrosion coating on the inner surface to resist ammonia corrosion.

All purlins, lap joints of wall panels, doors, windows, fan openings and positions where pipelines penetrate walls must be sealed. Acceptance Standard: Close all air inlets, start one fan, maintain stable negative pressure of 12～18 Pa inside the house without continuous air leakage.

Large-area non-insulated steel roof is prohibited. Cold roofs easily cause condensation and water dripping, resulting in litter dampness, rising ammonia concentration and corrosion of steel components.

Reserve installation space for ventilation equipment during layout of steel beams and columns: Small side-wall windows shall avoid obstruction by C-section steel purlins; Wind-resistant columns and supports shall not block airflow at gable fan positions; Reserve maintenance access and brackets for water circulation pipelines in the evaporative cooling pad area.

Recommended Building Dimensions (Longitudinal Ventilation as Mainstream Form) Width: 12～16 m (mainstream for cage rearing); Eave clear height ≥ 2.6 m; Ridge height determined by span. Length: Optimally ≤120 m; For houses longer than 120 m, pressure loss along the airflow path must be verified and high-static-pressure fans shall be adopted. Cage houses are recommended to install simple suspended ceilings (PVC / lightweight thermal insulation boards) to eliminate ineffective large upper roof space and reduce airflow dead zones.

II. Ventilation Mode Selection (Negative Pressure Mechanical Ventilation Preferred for Sealed Steel Structure Poultry Houses)

Mode 1: Longitudinal Tunnel Negative Pressure Ventilation 【First Choice for High-Density Cage / Floor Rearing】 Layout: Air intake via cooling pads on one gable, exhaust via centralized negative pressure fans on the opposite gable. ✅ Application: High-temperature cooling in summer and maximum ventilation conditions all year round; generates air cooling effect to prevent heat stress. Design target cross-section wind speed: Broiler growing / finishing stage: 2.5～3.0 m/s Multi-layer caged laying hens: 1.8～2.5 m/s

Mode 2: Side-wall Small Window Transitional Ventilation (Minimum Ventilation in Winter / Spring & Autumn) Layout: Cooling pads closed; fresh air enters through motorized small air inlet windows on both side walls, and terminal fans perform intermittent / variable-frequency exhaust. Core Requirement: Air deflectors tilted upward by 15°～30°, so fresh air flows along the roof for mixing first to avoid cold stress caused by direct blowing on flocks.

Mode 3: Transverse Ventilation (Only for Small & Medium-Sized Open / Semi-Open Poultry Houses) Fans installed on one side and air inlets on the opposite side. Not recommended for high-density sealed poultry houses due to poor airflow uniformity.

Mode 4: Natural Ventilation (Only for Low-Density Simple Sheds; Not Recommended as Main System for Large-Scale Fully Sealed Steel Structure Poultry Houses) Combination of ridge ventilators and side-wall roller shutters. Heavily affected by weather conditions, only used as auxiliary backup.

Standard Scheme: Composite system of longitudinal ventilation (summer) + side-wall small window minimum ventilation (winter & spring), general configuration for modern steel structure poultry houses.

III. Target Environmental Control Parameters (Benchmark for Design Calculation)

Temperature & Humidity Standards

表格

Air Quality Limits Ammonia NH₃ ≤20 ppm (long-term recommended target: ＜15 ppm) CO₂ ≤3000 ppm Hydrogen sulfide H₂S ≤10 ppm

Negative Pressure Control Range Minimum ventilation in winter: 8～15 Pa Transitional ventilation in spring & autumn: 10～18 Pa Full-load longitudinal ventilation in summer: 15～22 Pa

Excessively high negative pressure leads to insufficient air intake and increased fan energy consumption; excessively low negative pressure causes airflow short-circuit and ventilation dead zones.

IV. Selection & Calculation Methods of System Components

(I) Exhaust Fans (Negative Pressure Cone Axial Fans)

Selection Key Points Specification: Model 1380/1400 (50-inch) is industry mainstream; high-static-pressure models shall be adopted for long sealed poultry houses. Drive: Belt drive; FRP / hot-dip galvanized anti-corrosion housing to adapt to high-humidity ammonia environment. Variable-frequency fans are preferred to realize stepless air volume adjustment and reduce frequent fan start-stop.

Two air volume calculation methods (adopt the larger value of the two): Method A: Based on indoor cross-section wind speed (for longitudinal ventilation calculation) Total air volume Q (m³/h) = Effective cross-sectional area of poultry house A × Target wind speed v × 3600 Effective cross-sectional area: flow area excluding obstructions such as cage racks and feed silos.

Method B: Based on maximum ventilation volume per bird Finished broilers: 6～8 m³/(bird·h) Laying hens: 4～6 m³/(bird·h)

Number of fans = Total calculated air volume ÷ Actual air volume of single fan (under corresponding static pressure) Add 10%～15% redundancy factor to cope with filter dust accumulation, fan aging and wind pressure loss.

(II) Evaporative Cooling Pad System (Air Intake for Longitudinal Ventilation in Summer)

Configuration Calculation Effective cooling pad area S = Total ventilation volume Q ÷ (air velocity through pad 1.8～2.2 m/s × 3600)

Steel Structure Installation Requirements A buffer room of 0.8～1.1 m is recommended outside the cooling pad with independent steel supports. The bottom of cooling pad shall be ≥300 mm above ground to prevent sewage backflow; supporting water circulation, filtration and drainage facilities are required. Steel supports in cooling pad area shall be treated with anti-corrosion to avoid corrosion by long-term water vapor. Dust screens shall be installed on the outer side for northern regions with frequent sandstorms.

(III) Side-Wall Motorized Small Air Inlet Windows (Air Inlets for Minimum Ventilation)

Arrangement: Uniform continuous layout along both side walls, ≥2.2 m above ground and more than 40 cm above cage top. Common single window dimension: 600mm×300mm, equipped with electric actuator and adjustable air deflector. Principle for total air inlet area: Total air inlet area ≥ cooling pad area to guarantee stable airflow during mode switching. Design Red Line: Cold air is strictly prohibited from sinking and blowing directly on poultry in winter. Upper air supply and mixing shall be realized by air deflectors.

(IV) Intelligent Environmental Control System (Brain of Ventilation System)

Mandatory sensors: Temperature, humidity, indoor & outdoor differential pressure sensors; high-end configuration includes ammonia and CO₂ sensors. Hierarchical control logic:

Minimum ventilation mode (low temperature): Timed ventilation + closed-loop negative pressure control;

Transitional ventilation: Window opening interlocked with fan frequency conversion;

Summer longitudinal ventilation: Close small windows, cooling pads interlocked with staged startup of fan groups;

High & low temperature alarm, power failure alarm. Backup generator is strongly recommended for sealed steel structure poultry houses.

V. Key Details of Ventilation Airflow Design for Steel Structure Poultry Houses

Avoid Airflow Short-Circuit No partition walls or dense steel column obstructions between fans and air inlets. Gable fans shall be arranged evenly instead of concentrated on one side.

Eliminate Roof Dead Zones Steel double-slope roofs feature large internal space. Without suspended ceilings, hot waste gas tends to accumulate at the ridge in winter. Appropriately increase negative pressure for minimum ventilation, or install a small number of auxiliary ridge vents (closed and sealed in summer).

Temperature Difference Control for Long Poultry Houses For houses longer than 100 m, natural temperature difference exists between cooling pad end and fan end. Control temperature difference between two ends ≤2～3℃; wind speed shall not be reduced blindly.

Steel Structure Anti-Corrosion Coordinated with Ventilation Design Poor ventilation, high humidity and ammonia will accelerate corrosion of steel beams and purlins. Ventilation scheme must take dehumidification into account to reduce condensation on inner roof surfaces.

VI. Four-Season Operation Strategy (Matching Control Logic for Design)

Winter (Minimum Ventilation Mode) Cooling pads closed; only side-wall small windows used; low negative pressure; fresh air enters upward for full mixing inside the house. Prioritize heat preservation while ventilating to remove ammonia.

Spring & Autumn Transitional Ventilation Small windows + partial variable-frequency fans. Due to large day-night temperature difference, adopt dual linkage of temperature control and negative pressure to avoid drastic temperature fluctuation day and night.

High-Temperature Summer (Longitudinal Tunnel Ventilation + Cooling Pads) All side windows closed; all air passes through cooling pads for temperature reduction; fans run at full load to reach target wind speed at chicken height. Use cooling pads cautiously for continuous operation when ambient humidity ＞75% to prevent stuffy house under high humidity.

Extreme High-Temperature Emergency Plan Support roof sprinkling system (only spray the outer surface of steel roof; water spraying inside poultry house is forbidden).

VII. Key Points of Construction & Acceptance

Sealant shall be fully applied around steel structures of fan openings and cooling pad openings to eliminate air leakage. Commission all motorized air inlet windows: synchronous opening with consistent angles; no local massive air leakage on single side. Negative Pressure Test: Smoke tracing test to observe air inlet trajectory. Ideal status: fresh air from both sides sinks gently near the central axis of the poultry house. Wind Speed Acceptance: Measure wind speed at cage height at multiple points along the house length; maximum deviation shall not exceed ±0.5m/s. 72-hour no-load trial operation, record stable negative pressure corresponding to different numbers of running fans.