design elements of ventilation system for farrowing house

As the core facility linking upstream and downstream operations on a swine farm, the farrowing house ventilation system must be designed to meet the environmental needs of sows while also accommodating the requirements of piglets.

In practice the farrowing house ventilation system is a mutually constraining environment: sows are heat sensitive while piglets are cold sensitive. Coordinating this production environment is crucial for sow lactation, postpartum estrus, subsequent piglet growth and condition, postweaning piglet survival, and even overall annual herd performance. Based on the mutual constraints between sows and piglets, the following introduces and analyzes the design elements of farrowing house ventilation systems.

Ventilation modes:

1. Farrowing house ventilation can be organized as positive pressure, negative pressure, equal pressure (or slight positive pressure), or natural ventilation. Positive and equal (or slight positive) pressure modes are suitable for filtered systems; there are also negative pressure modes used with filtration. Natural ventilation applies to traditional independent buildings and is now less common in modern farms. This article mainly introduces the common non‑filtered negative pressure farrowing house ventilation system.
2. Under non‑filtered negative pressure, intake methods differ: roof inlet, evaporative pad cooled roof inlet, and a combined roof plus pad longitudinal (tunnel) inlet mode. In northern cold regions of our country where summer outdoor high temperatures do not exceed or only slightly exceed 30°C, roof inlet or pad cooled roof inlet modes can be used. In other hot summer regions, a combined roof plus pad longitudinal inlet (or pad cooled roof inlet) is advisable. This mode requires thermal insulation materials for both roof and suspended ceiling and must ensure sufficient ventilation volume according to the local area.

Building structure and stall layout:

1. Venting design for farrowing houses cannot be separated from building structure and stall layout. These must consider farm scale, terrain, investment cost, production rhythm, pig turnover and other factors. Modern farms commonly use connected building designs with a “large building, small units, all in all out” workflow. Barn spans are usually within 30 m. For larger sow farms, to save space two barns with spans over 20 m may be combined into a single 50 m large span farrowing house, with farrowing units arranged symmetrically along a central aisle.
2. For stall layout, when using evaporative pad longitudinal (tunnel) ventilation during hot summers, it is recommended that each row not exceed 12 or 13 stalls, because temperature differences between the exhaust and intake ends affect lactation of sows at the row end and the next estrus. This difference arises because farrowing house exhaust volume and wind speed should not be too large, avoiding cold stress to suckling piglets, while still accommodating lactating sows. Therefore, spans for tunnel ventilation are relatively short. When each row exceeds 14 stalls, the pad cooled roof inlet mode is recommended, because in that mode intake openings are evenly distributed on the suspended ceiling between farrowing units, ensuring no dead zones and improving fresh air contact with the herd.
3. Regardless of building structure or stall layout, the house must be well sealed, and insulated building materials with good thermal performance should be used where conditions allow.

Climate temperature and air quality:

1. After selecting ventilation mode, building structure, and stall layout according to production processes and investment conditions, ventilation design must follow local climate and the environmental requirements inside the farrowing house. Latitude, elevation, precipitation and other factors determine local climate conditions, which in turn influence internal barn conditions. Although mechanical ventilation and human intervention can control the internal environment, whether ventilation meets the intended goals or the herd’s environmental needs is constrained by multiple factors.
2. When designing farrowing house ventilation, use appropriate temperature, humidity, and air quality parameters. Typical target temperatures are: lactating sows 16°C to 18°C, newborn piglets 35°C to 37°C, and nursing piglets 30°C to 34°C. Relative humidity is generally 60°C to 80%, applicable to most pig barns. In hot summers, high humidity reduces evaporative pad cooling effectiveness and worsens heat stress; in cold winters, high humidity increases animal heat loss, affecting thermoregulation and worsening cold stress. High humidity also raises concentrations of harmful airborne substances, encourages microbial growth, and promotes feed spoilage, negatively affecting herd health. Low humidity is less harmful than high humidity, but when relative humidity falls below 40% it can cause skin cracking and increased airborne particulates, leading to skin or respiratory problems. When temperature is appropriate, humidity extremes are less critical; raising temperature or increasing ventilation can mitigate high humidity. Excessive humidity control may interfere with temperature control and fresh air intake and could reduce overall air quality, so relative humidity values should be used as a reference.
3. In addition, harmful gases, volatile manure and urine compounds, feed and organic dust, and animal activity produce odors, microbes and particulates that affect herd health and barn conditions. Generally requested limits are CO2 up to 3000 mg/m3, NH3 15 mg/m3, and H2S 5 mg/m3. These limits are slightly stricter than for other pig houses because piglets are more vulnerable. In hot summer conditions, the farrowing house should achieve at least 80 air changes per hour; in cold winter conditions, ventilation per sow with piglets should be at least 45 m3/h to ensure adequate fresh air and good air quality.

Supporting equipment:

1. Exhaust:
   To ensure the exhausted indoor air volume exceeds fresh air intake, create negative pressure inside the house, and meet large ventilation with modest negative pressure for good performance, axial fans are recommended. Fan housings on the market are mainly galvanized steel or fiberglass; fiberglass housings are more corrosion resistant and durable but costlier. Typical models are 18″, 24″, and 36″ direct‑drive fans; farrowing units rarely use 50″ to 54″ belt‑driven fans because fans over 50″ have large exhaust volumes and the sudden airflow at startup can cause cold stress in piglets. Farrowing units are usually small, so medium and small fans are preferred. When calculating exhaust volume, use fan curves at static pressures of 12.5 Pa or 25 Pa; higher static pressure yields lower airflow and higher power consumption. Considering barn airtightness, manufacturer fan data accuracy, and interior structure, using the airflow corresponding to 25 Pa static pressure is safer and more accurate.
   Also, during winter low‑ventilation operation, using gutter (manure pit) exhaust is effective at suppressing harmful vapors from the pit that affect piglets. In summer, with increased ventilation and exchange frequency, the relative impact of gutter exhaust is reduced.
2. Inlet:
   After exhausting stale air, fresh air must be supplied via two intake modes: through the suspended ceiling or through end walls. In the ceiling inlet mode, small ceiling inlet windows are driven to open downward. At low ventilation rates the louver opens slightly and the airflow hugs the ceiling and mixes slowly with indoor air before descending to the pens. At higher ventilation rates the louver angle increases and the airflow enters the pen area obliquely. To avoid direct vertical drafts that can harm piglets or stir up harmful gases from manure pits, limit and control the louver angle. Ceiling inlets should be evenly distributed to increase fresh air coverage and avoid dead zones, and should not conflict with feeders, power cables, or lights.
   The end‑wall inlet mode is used for summer tunnel ventilation. The section wind speed in farrowing houses generally does not exceed 1 m/s; tunnel inlet area is calculated using inlet wind speeds of 3 m/s to 4 m/s. Inlet openings can be adjusted with driven PVC panels or automatically based on fan exhaust volume.
3. Cooling:
   Evaporative pad cooling based on the evaporation principle is a proven reliable cooling method. Water wets the pad media from above; hot air drawn through the pad under negative pressure contacts the wet pad and is cooled by evaporation while increasing indoor humidity. Tunnel ventilation wind speed adds wind‑cooling effect to achieve desired temperatures. However, pad cooling effectiveness decreases as ambient relative humidity increases.
   Typically use pad media 15 cm thick with a corrugation angle (e.g., 45/15 degrees) to ensure smooth air entry and prolonged air‑pad contact time. Calculate pad area using a through‑pad velocity of 1.7m/s to 1.9 m/s; higher through velocities increase pressure loss and reduce fan airflow. Because farrowing houses avoid excessive air speeds and often have limited fan counts, it is practical to increase pad area and choose a lower through‑pad velocity.
4. Heating:
   Besides local heating of piglet rest areas with creep heat lamps, farrowing houses require additional heat sources in cold seasons to offset ventilation heat loss and reach target temperatures. Heating options are generally hot‑water systems and gas heaters. Hot‑water heating has lower operating cost but slower response; gas heating costs more but can raise barn temperature instantly. In larger sow farms, gas heaters can shorten post‑disinfection drying times and improve farrowing room turnover.
5. Automation control:
   The ventilation objective is to maintain suitable nursing temperatures for sows and piglets, so operation of inlet, exhaust, cooling and heating equipment requires high‑precision automated control rather than manual intervention. Choose precision environmental controllers to avoid large ventilation swings that cause temperature fluctuations harmful to piglets and to achieve good energy efficiency. In negative pressure control systems, alarm functions are indispensable, especially temperature‑abnormality alarms in farrowing houses.