Intensive Livestock HVAC Ductwork — Poultry, Pig, Dairy and Feedlot Ventilation Guide

Why intensive livestock ductwork is its own engineering discipline

Walk into an Australian broiler shed on a 42°C summer afternoon outside Tamworth or Griffith and you will hear three things at once: the roar of forty-eight 1,250 mm tunnel fans pulling air down the length of a 150 m shed, the trickle of water across a 200 m² evaporative cooling pad, and a peculiar silence among the 40,000 birds. The silence is what you want. It means the wind-chill at bird level is keeping the flock below the lethal core temperature threshold of 43°C. The fans, pads and the ductwork between them are not a comfort system. They are the engineering control that stands between a viable production cycle and a six-figure mortality event triggered by a single ventilation failure.

Intensive livestock ventilation operates in conditions that destroy most commercial HVAC ductwork within five years. Atmospheric ammonia from urine and manure forms an acidic condensate on cold duct surfaces. Respirable dust loading saturates filters and abrades duct interiors. Pressure-washing on cycle changeover floods duct exteriors with chlorinated cleaning solutions. The duct system is simultaneously the largest single piece of plant in a livestock building, the most exposed to corrosive insult, and the single point on which animal welfare, worker safety, and operating economics all depend. This guide is the operating manual for designing ductwork systems that survive those conditions and meet the welfare, exposure and audit standards Australian intensive producers operate under.

The discipline matters because the customers matter. Australia's intensive livestock sector is dominated by integrated processors and specialist breeder-grower-finisher operations. Inghams Group — the country's largest poultry producer and ASX-listed since the 2021 IPO — runs vertically integrated broiler operations across NSW, Victoria, Queensland, South Australia and Western Australia. Baiada Poultry operates the Steggles and Lilydale Free Range brands. Hazeldenes specialises in free-range broiler production from Victoria. Pace Farm and Sunny Queen Farms dominate Australian table-egg supply. In pigs, SunPork Farms / SunPork Group operates across Queensland and NSW; Rivalea Australia (owned by JBS) runs major piggeries in NSW and Victoria. In dairy, Saputo Dairy Australia (formerly Murray Goulburn) and Bega Cheese operate processing-aligned supplier networks. In beef, Australian Country Choice, Teys Australia and JBS Australia operate large feedlots feeding integrated processing operations. Industry bodies including Australian Pork Limited (APL) and the Australian Chicken Meat Federation set the welfare and biosecurity codes that every duct specification must support.

The technical framework that runs underneath all of them is the same: a ventilation standard derived from ASABE EP 270, overlaid with an industry-specific welfare code, a Safe Work Australia exposure ceiling for workers, and a corrosion-and-cleaning environment that punishes ordinary galvanised ductwork. The producers do not need education on biology — they live it. They need education on ductwork: which materials survive ten years, which fan and duct combinations meet 6–8 m/s tunnel velocity at 40,000 birds stocked, which exhaust treatments allow them to expand without triggering an EPA odour complaint. This guide answers those questions.

The standards stack — ASABE, AVMA, industry codes, RSPCA, Safe Work Australia

A working ductwork specification in an Australian intensive livestock building is the intersection of four standards layers. Skip any one and the design is either non-compliant, fails an audit, or harms animals or workers.

ASABE EP 270 — the engineering baseline

The American Society of Agricultural and Biological Engineers Engineering Practice EP 270 (Design of Ventilation Systems for Poultry and Livestock Shelters) is the global engineering reference for sizing livestock ventilation rates, fan capacities, inlet areas and duct cross-sections. Although authored in North America, ASABE EP 270 is the standard most consultancies and equipment manufacturers worldwide build to, including the Australian-equipment suppliers who serve Inghams, Baiada, SunPork and the integrated beef feedlot operators. ASABE EP 270 provides species-specific ventilation rate tables (m³/h per kg of liveweight), guidance on cold-weather minimum ventilation for moisture control, hot-weather maximum ventilation for heat removal, and recommendations for inlet jet velocity, throw and stratification mixing. Every duct sizing calculation in this guide ultimately derives from EP 270 rate tables adjusted for Australian summer dry-bulb peaks.

Two ASABE numbers do most of the work. Winter minimum ventilation runs at 0.5–1.5 m³/h per kg of liveweight, just enough to remove moisture and keep ammonia under welfare thresholds without losing barn heat. Summer maximum ventilation runs at 8–10 m³/h per kg, the rate at which sensible heat from animals is removed fast enough to prevent core temperature rise. The ratio between winter minimum and summer maximum is roughly 1:15 — and a duct system that performs only at maximum airflow will create cold drafts on chicks or piglets in winter that cause chilling and mortality. A duct system that performs only at minimum will cook the flock in summer. Australian intensive livestock ductwork must work across this 15:1 dynamic range, every day of the year.

AVMA welfare guidelines

The American Veterinary Medical Association publishes welfare guidelines that are widely referenced in Australian veterinary and audit literature, particularly the AVMA guidance on environmental temperature, humidity and air quality thresholds for production animals. AVMA does not have direct regulatory force in Australia, but its environmental thresholds — for instance the AVMA-cited bird-level ammonia threshold of 25 ppm — are the de facto reference in supplier and welfare audits. Specifying a duct system that can hold AVMA thresholds at maximum stocking density is the practical floor of welfare compliance.

Australian Industry Codes of Practice

The Australian welfare regime for intensive livestock is delivered through species-specific Model Codes of Practice and Industry Standards. For poultry, the Australian Animal Welfare Standards and Guidelines for Poultry (developed under the auspices of state agriculture departments and supported by the Australian Chicken Meat Federation) set housing, stocking density, lighting and air quality requirements. For pigs, the Australian Pork Industry Quality Assurance Program (APIQ) — administered by Australian Pork Limited — sets equivalent benchmarks. These codes are not engineering documents — they specify outcomes such as "ammonia must not exceed welfare thresholds" — but the engineering implication is that the duct system must deliver compliant air quality across the full production cycle, including the high-summer peak when ventilation rates are highest and ammonia is hardest to control.

RSPCA Approved Farming Scheme

The RSPCA Approved Farming Scheme is a voluntary higher-welfare accreditation overlaid on the codes above. Producers selling under RSPCA Approved labelling — a marketing requirement for several major retailers and food-service buyers — submit to more stringent space, enrichment, lighting and air quality audits. From a duct engineering standpoint, RSPCA accreditation typically requires lower bird-level ammonia targets (under 20 ppm versus the 25 ppm welfare threshold), better dust control, and acoustic levels that do not stress birds. RSPCA-accredited sheds often run 10–15% more ventilation capacity than minimum-compliant sheds, and the duct system must be sized for the higher target from day one — retrofitting is rarely cost-effective.

Safe Work Australia exposure standards

The worker-protection layer is Safe Work Australia's Workplace Exposure Standards for Airborne Contaminants. Three numbers anchor every intensive livestock duct specification:

• Ammonia (NH3): 25 ppm 8-hour Time-Weighted Average; 35 ppm Short-Term Exposure Limit. Above 25 ppm sustained, the worker entering the shed for daily inspection or harvest is in breach of the exposure standard and the producer is in breach of WHS obligations.
• Hydrogen sulfide (H2S): 10 ppm STEL. H2S is the more dangerous gas — generated almost exclusively from anaerobic decomposition in deep pig manure pits and at higher concentrations potentially lethal. Pit-stirring events on a piggery can release H2S at hundreds of ppm in seconds.
• Respirable dust: 3 mg/m³ 8-hour TWA. Poultry and pig shed dust contains a mix of skin scales, dried manure, feed particles and bacterial endotoxin. Endotoxin alone is a major contributor to farmer's lung and chronic respiratory disease in livestock workers.

The exhaust duct system is the engineering control that holds workers below all three limits. No PPE-led control strategy is acceptable in modern Australian agricultural WHS practice — the duct system must do the work.

AS 4466 portable sanitary facilities

AS 4466 Portable Sanitary Conveniences applies where the producer relies on portable amenities for shed-side personnel — common on remote feedlot sites and during construction or commissioning of new sheds. Where AS 4466 facilities are within or adjacent to ventilation intake zones, the duct system must include sufficient setback and prevailing-wind orientation to prevent contamination of fresh-air supply. This is a small but frequently missed detail in greenfield feedlot construction.

Species-specific ventilation — poultry

Poultry, and broiler chickens in particular, are the most ventilation-sensitive of the major intensive livestock species. A 32-day-old broiler at 2.2 kg liveweight generates roughly 6 W of sensible heat. Multiply by 40,000 birds in a 150 m × 16 m shed and the heat load is 240 kW — the equivalent of a small office building, packed into a structure with no thermal mass. Add Australian summer ambient of 38–42°C, and the duct system has 90 seconds to fail before bird core temperature reaches the 43°C mortality threshold.

Broiler shed tunnel ventilation

The dominant Australian broiler housing strategy is tunnel ventilation. Cold air enters at one end through inlet shutters or evaporative pads; banks of large-diameter fans (typically 36-inch / 1,250 mm or 50-inch / 1,375 mm diameter) at the opposite end pull air the length of the shed at 6–8 m/s. The wind-chill effect at bird level reduces apparent temperature by 5–7°C — a 40°C dry-bulb becomes a 33–35°C apparent temperature, within the survivable range for adult broilers. The complete air change time in tunnel mode is approximately 2 seconds for a 150 m shed at 8 m/s.

The duct engineering challenge is not the tunnel run itself — that is a building-wide moving air mass with no traditional ductwork. The duct engineering challenges are at the four interface points:

1. Inlet plenum. Air drawn through the pad must distribute evenly across the full 16 m shed width without short-circuiting. The inlet plenum is typically a galvanised duct or shaped sheet-metal hood spanning the pad face, sized for 4–5 m/s face velocity to drop pressure across the pad evenly.
2. Cold-weather minimum-ventilation inlets. In winter the tunnel fans are off and a small number of sidewall inlets deliver 0.5–1.5 m³/h per kg of liveweight for moisture and ammonia control. These inlets need to throw fresh air across the shed ceiling to mix with warm air rising from birds — galvanised inlet boxes with adjustable baffles, typically fabricated from 0.6–0.8 mm galvanised sheet.
3. Stir fans and roof plenums. Some operators include roof plenum ductwork to redistribute air during minimum ventilation mode — typically lightweight aluminium or galvanised round ducting.
4. Exhaust trunks. The fans pull air directly to atmosphere in most Australian broiler designs, but where odour or particulate dispersion is regulated — particularly in newer sheds within nuisance distance of residential areas — exhaust trunks lead to a treatment train (cyclone, biofilter or scrubber). These trunks are the most aggressive corrosion environment in the building and demand 304/316 stainless or FRP construction.

Layer hen barns

Cage and barn-laid layer operations operate at higher stocking densities than broiler sheds and at lower individual heat loads. A 1.8 kg adult layer hen at the peak of lay generates approximately 4 W of sensible heat, but population densities reach 20–24 hens per square metre in multi-tier cage systems. Pace Farm, Sunny Queen Farms and Hazeldenes operate variants of this housing system across Victoria, NSW and Queensland. Ventilation strategy is similar to broiler — tunnel ventilation with pad cooling for summer heat removal, sidewall inlet minimum ventilation in winter — but with two specific duct differences. First, the manure belt and manure pit systems under multi-tier layer cages generate sustained ammonia release that loads exhaust ductwork harder than broiler litter. Stainless or FRP exhaust trunks are effectively mandatory. Second, dust loading from feed and feather material is high enough that cyclone separators upstream of the discharge stack are common — and the recovered dust is recycled as litter or fertilizer additive.

Australian climate context

The Australian summer climate puts poultry duct design at the harder end of the global spectrum. Broiler sheds at Tamworth, Griffith, Toowoomba, the Murray-Darling region of Victoria and the Perth-area broiler corridor regularly see 40°C+ days for 10–30 days per summer. Drought years compound the stress — low overnight humidity helps pad cooling, but the same dry years often coincide with extreme afternoon heat. Climate-driven mortality events at major Australian poultry operations have driven progressive upgrades in ventilation capacity over the past decade, and most new-build sheds for Inghams, Baiada and Hazeldenes commissioned since 2020 spec ventilation to 10 m³/h per kg of liveweight as standard — at the upper end of the ASABE EP 270 envelope.

Species-specific ventilation — pigs

Pig housing splits into three production phases — farrowing (sow plus piglets), grower (weaned through finisher growth), and finisher (terminal market weight) — and each has a distinct ventilation profile. SunPork Farms / SunPork Group operations across Queensland and NSW, and Rivalea Australia (owned by JBS) operations across NSW and Victoria, represent the mainstream of Australian intensive pig production. Each phase makes different demands on the duct system.

Farrowing sheds

The farrowing shed houses sows from a few days before farrowing through approximately three weeks of lactation. Sows and piglets have radically different temperature preferences — the sow is comfortable at 18–20°C, the newborn piglet needs 32°C at the heat lamp. This is solved with a creep-zone heat lamp and a piglet warming area, but it has a duct consequence: minimum ventilation must remove moisture and ammonia from the sow area without delivering cold draft to piglets. The duct strategy is typically a ceiling-distributed minimum ventilation system feeding multiple low-velocity inlets — galvanised sheet metal ductwork running the length of the shed, drilled with carefully sized supply holes that throw air against the ceiling rather than down at floor level. Tolerance on hole placement and size matters: a 5% variation translates to 20% airflow variation between rooms in a long shed.

Grower and finisher sheds

Once weaned, pigs move into grower and then finisher housing. Grower-finisher sheds in Australia typically use deep manure pit construction — pigs live on a slatted floor over a manure pit that is emptied every 6–12 months. The pit is the dominant source of ammonia and hydrogen sulfide. Pit ventilation is the duct engineering specialty here: a dedicated low-volume continuous extract from the pit headspace, ducted directly to atmosphere or to a treatment train, prevents H2S buildup. The pit-extract duct is the single most corrosive ductwork in pig housing — FRP or polypropylene construction is standard, with stainless as a heavy-duty alternative.

Above the slats, conventional tunnel or cross-flow ventilation removes sensible heat and excess moisture. Finisher pigs at 90–110 kg liveweight at densities of 0.8–1.0 m² per pig generate a substantial heat load — Australian summer ventilation rates run 8–10 m³/h per kg the same as broilers. Misting and fogging systems are common in finisher sheds because pigs do not sweat and rely on water-skin evaporation for thermoregulation. The duct integration point for misting is at the inlet end: high-pressure (50–70 bar) fogging nozzles fed from corrosion-resistant stainless lines deliver a fine mist into the inlet air stream, dropping inlet temperature 4–8°C before air enters the pig zone.

Hydrogen sulfide — the under-recognised hazard

Hydrogen sulfide in deep-pit pig housing is the lethal gas hazard in Australian intensive livestock. Routine concentrations in well-ventilated pit headspace sit at 1–5 ppm, comfortably under the 10 ppm STEL. But pit-stirring or pit-emptying events — particularly when a frozen or crusted manure surface is broken — can release H2S in concentrations of hundreds to thousands of ppm within seconds. Fatalities at pig operations globally have occurred from worker entry to a pit-vicinity during stirring without respiratory protection. The duct engineering response is twofold: continuous pit-headspace extraction sized for stirring events (typically 4–8 air changes per hour in the pit headspace), and a hardwired interlock between stirring equipment and exhaust fans so stirring cannot start without confirmed pit ventilation.

Species-specific ventilation — dairy

Dairy ventilation in Australia is dominated by two operational contexts: the dairy parlour (where cows are milked twice daily) and the cow housing or feed-pad shelter where cows rest between milkings. The Australian dairy industry is overwhelmingly grazing-pasture-based, so the cow housing intensity is lower than in North American or European confinement dairies, but the parlour is a concentrated ventilation problem. Saputo Dairy Australia (the former Murray Goulburn cooperative business) and Bega Cheese both operate processing-aligned supplier networks where higher-spec parlour ventilation correlates with milk quality and somatic cell count outcomes.

Dairy parlour

The parlour holds 12–60 cows in a confined milking pit and surrounding holding yard for the duration of milking — typically 90–180 minutes twice daily. Heat load is substantial: a 600 kg dairy cow at peak lactation generates approximately 1,200 W of sensible heat. A 40-bail rotary parlour holds 40 cows at any moment plus another 80–120 in the holding yard, for a total parlour-area heat load of 130–150 kW. Australian summer ambient regularly drives parlour temperature 8–10°C above ambient without engineered ventilation, with measurable consequences for cow throughput, kicking incidents, milk let-down and worker fatigue.

The duct engineering for a dairy parlour typically combines roof-mounted exhaust fans pulling air upward and a fresh-air inlet plenum at the holding-yard end. Misting in the holding yard reduces apparent temperature by 3–6°C. Inlet ductwork is normally aluminium or galvanised, sized for 3–4 m/s face velocity at the holding-yard inlet. The exhaust path is shorter and less corrosive than poultry or pig exhaust because cattle generate lower atmospheric ammonia (urine drops onto a concrete floor that is regularly hosed), so 304 stainless is sufficient where corrosion protection is needed.

Loose housing and freestall barns

A small but growing minority of Australian dairy operations — particularly higher-rainfall southern Victoria and parts of Tasmania — use freestall or loose-housing barns where cows rest indoors between milkings. Ventilation strategy in these barns is typically natural with assisted tunnel fans for peak summer days, or cross-ventilation with cyclic recirculation fans. The duct contribution is mostly in supply plenum and inlet box fabrication.

Species-specific ventilation — feedlots

Australian beef feedlots are a distinct ventilation problem. Major feedlot operators — Australian Country Choice, Teys Australia and JBS Australia — run open-air or roofed feedlot pens with cattle on dirt or compacted-manure flooring. The ventilation problem is not enclosed-building exchange but heat stress mitigation on extreme-heat days. The engineered response is shade-and-mist systems: fixed misting headers running along shade structures, fed from booster pumps and corrosion-resistant stainless distribution lines, delivering low-pressure or medium-pressure mist directly over cattle in pens. The duct contribution is the air-handling envelope around shaded loafing and processing areas, where conditioned air may be supplied for worker comfort during processing.

The misting and ventilation systems at processing facilities adjacent to feedlots — including the integrated abattoirs operated by Teys Australia, JBS Australia and Australian Country Choice — are full industrial HVAC builds with extensive stainless and aluminium ductwork.

Pad cooling — the dominant Australian summer strategy

Evaporative pad cooling is the single most important cooling technology in Australian intensive livestock production. The principle is straightforward: outside air is pulled through a wetted cellulose or paper pad (the dominant brand is CELdek 7090, but several equivalents exist). As the air passes through the pad, water evaporates from the pad surface, absorbing latent heat from the air. The air leaving the pad is cooler than the air entering it by 6–12°C depending on dry-bulb temperature and relative humidity. The drier the inlet air, the bigger the temperature drop; this is why pad cooling performs spectacularly well in inland Australian conditions and less well in coastal humid climates.

A typical Australian broiler pad system uses a 7090 (180 mm thick × 600 mm tall) cellulose pad sized for 2.0 m/s face velocity. At 38°C ambient and 25% relative humidity (typical Tamworth or Griffith summer afternoon), pad-leaving air sits at 26–28°C — a 10–12°C drop. The fans then pull this cooled air along the shed at 6–8 m/s tunnel velocity, where wind-chill at bird level shaves another 5–7°C off apparent temperature. The net result is that birds in a 38°C ambient experience an apparent temperature of 21–23°C — a survivable, productive thermal environment.

The duct engineering implications of pad cooling are:

• Inlet plenum. The duct or hood across the pad face must distribute air evenly across the full pad area. Uneven face velocity causes uneven pad wetting and channeling, dropping average performance.
• Inlet humidity. The air entering the shed from the pad is humidity-saturated. Cold ductwork downstream of the pad in early-morning conditions can condense water out of the air stream and back onto duct interior surfaces. Stainless or aluminium inlet plenums tolerate this; galvanised plenums corrode rapidly.
• Drift and overspray. Pad systems generate fine droplet drift in some operating conditions. Drift onto galvanised exterior surfaces accelerates corrosion.
• Water management. The recirculation tank, pump, header and distribution piping feeding the pad are all corrosion-exposed water systems. PVC or stainless distribution is standard; brass and bronze fittings fail in chlorinated bore water.

Misting and fogging — finisher pigs and feedlot cattle

For pig finishers and feedlot cattle, misting and fogging are the dominant cooling supplement to ventilation. The principle is the same as pad cooling — evaporative cooling — but the delivery is direct droplet injection rather than airflow through a wetted pad. Two pressure classes dominate:

• Low-pressure misting (5–10 bar). Larger droplets, partial evaporation, wetting of the animal directly. Used in feedlots and outdoor cattle pens where the goal is to wet the hide for evaporative cooling at the animal-skin interface.
• High-pressure fogging (50–70 bar). Very fine droplets (5–10 micrometre nozzle output) that flash-evaporate in the air stream without wetting surfaces. Used in finisher pig houses and dairy parlours where wet floor management is undesirable.

Both systems integrate with the duct system at the inlet end. The duct's job is to draw in mist-cooled air and distribute it without re-heating before it reaches the animals. Distribution duct material selection follows the pad-cooling logic — aluminium or stainless for the wetted-air zone, galvanised acceptable for the downstream dry zones.

Ammonia, hydrogen sulfide and dust — the corrosive and health load

Atmospheric ammonia and hydrogen sulfide are the primary chemical exposure hazards in intensive livestock housing. Respirable dust is the primary particulate hazard. All three load the exhaust duct system, all three have Safe Work Australia exposure limits, and all three are managed by the duct system rather than by PPE.

Ammonia — generation, control and exhaust treatment

Atmospheric ammonia is generated by urease enzymatic conversion of urea (in poultry and pig urine) and uric acid (in poultry droppings) to NH3. The conversion is moisture- and temperature-driven: dry litter releases less ammonia than wet litter, and ammonia release rises 2–3 fold for every 10°C of litter temperature increase. Ammonia release in a 40,000-bird broiler shed at end of cycle can exceed 500 g/hour, in a 1,000-sow gestation shed can exceed 800 g/hour. Ventilation must move this ammonia load out of the shed faster than birds and workers are exposed to it.

The two-stage control strategy is: (1) maintain dry litter and good litter chemistry to suppress release at source; (2) ventilate at a rate that dilutes residual ammonia below 20–25 ppm at bird level. Ductwork is the dilution and removal pathway. Where the diluted ammonia in the exhaust would still trigger an odour or air-quality complaint at the boundary fence — particularly within nuisance distance of residential development — exhaust treatment is added:

• Acid scrubber. Exhaust air is pulled through a column wetted with dilute sulfuric or phosphoric acid. Ammonia reacts with the acid to form ammonium sulfate or phosphate, which is captured as a liquid fertiliser by-product. Removal efficiency 80–95%. Stainless or FRP ductwork mandatory throughout.
• Biofilter. Exhaust air is pulled through a wood-chip and compost bed where microbial communities oxidise ammonia. Capital cost lower than scrubber, footprint larger. FRP, polypropylene or stainless ductwork upstream of the bed.
• Dilution and dispersal stack. Where regulation permits, exhaust is vented through a tall stack that disperses ammonia to atmospheric dilution. Cheapest option, lowest treatment efficiency. Stainless stack standard.

Hydrogen sulfide

H2S in pig housing has been discussed above. The duct engineering response — continuous pit-headspace extraction, interlocks on stirring events, FRP or polypropylene duct material — is the single most important worker-safety control in pig finishing.

Respirable dust

Poultry and pig shed dust is a mix of dried manure, skin and feather material, feed particles, and bacterial endotoxin. The Safe Work Australia respirable dust limit of 3 mg/m³ is routinely exceeded in inadequately ventilated sheds, particularly during dry summer minimum-ventilation periods. Exhaust treatment for dust is straightforward — cyclone separators for the coarse fraction, baghouse filtration for the fine fraction — and the captured material can be recycled as litter additive in poultry or fertiliser feedstock in pigs. The duct path through cyclone and baghouse is moderately corrosive (dust + condensed moisture + ammonia) and 304 stainless or coated mild steel is standard.

Duct material selection — why galvanised fails and what works

The single most common procurement mistake in Australian intensive livestock duct projects is over-reliance on standard galvanised steel ductwork. Galvanised duct is the workhorse of commercial HVAC and survives decades in office building installations. In a poultry or pig shed it fails catastrophically within 5 years — sometimes within 2 years on the most aggressive runs. Understanding the failure mode drives the material selection.

The galvanised failure mechanism

Galvanised steel is mild steel coated with metallic zinc, typically applied by hot-dip immersion (Z275 — 275 g/m² total coating across both faces — is standard for HVAC sheet stock). The zinc coating protects the underlying steel by two mechanisms: barrier (physical separation of steel from atmosphere) and sacrificial (zinc oxidises preferentially to iron, sacrificing itself). Both mechanisms have a finite lifespan that depends on environmental aggression.

In a livestock building, three factors accelerate zinc loss. First, atmospheric ammonia reacts directly with zinc to form zinc-ammonia complexes, particularly in the presence of condensed moisture. Second, the diurnal temperature swing between bird-body-warmed air and cool overnight duct walls causes repeated condensation cycles that wash dissolved corrosion products off duct interiors and present fresh zinc surface for attack. Third, pressure-washing on cycle changeover floods duct exteriors with chlorinated cleaning solutions that strip zinc by chloride pitting attack. The net result is that Z275 galvanised duct in a broiler exhaust runs typically loses 50–80% of zinc coating within 3 years and develops through-thickness pinholes within 5 years.

Recommended materials by zone

• Inlet plenum and supply ductwork (dry-air zone, low ammonia). Galvanised Z275 or aluminium. Service life 15+ years. Aluminium is preferred where occasional wet-cleaning is anticipated.
• Roof plenum and recirculation ducts. Galvanised Z275 acceptable, aluminium preferred. Service life 10–15 years.
• Exhaust trunks (ammonia + moisture). 304 stainless steel as default; 316 stainless where chlorides are present (proximity to coast or chlorinated wash water). Service life 25+ years.
• Scrubber-side exhaust (high ammonia, acid wetting). FRP (fibreglass-reinforced plastic) or polypropylene. Stainless not recommended downstream of acid scrubbers — chloride and acid combination causes stress corrosion cracking.
• Pit-extract ductwork (H2S exposure). Polypropylene or FRP as default. 316 stainless acceptable where wall thickness is upgraded.
• Misting and fogging air distribution. Aluminium or 304 stainless — repeated humidity cycling destroys galvanised quickly.

Tunnel and cross-flow ventilation — duct sizing rules of thumb

The two dominant ventilation patterns in Australian intensive livestock buildings are tunnel ventilation (air moves length-wise through the building) and cross-flow ventilation (air moves cross-wise through the narrow dimension). Each has duct sizing rules.

Tunnel ventilation

The whole shed is the duct. Air enters at one end, accelerates as the cross-section narrows or as fans pull harder, and exits at the other end. Sizing rules:

• Target tunnel air velocity: 6–8 m/s at bird/animal level on the hottest design day.
• Total exhaust airflow = target velocity × cross-sectional area available to the air (typically 70–80% of nominal cross-section, allowing for cage racks, water lines, perches and other obstructions).
• Inlet area: airflow ÷ inlet face velocity. For pad-cooled inlets the face velocity target is 2.0 m/s on the pad — much lower than the tunnel-mode velocity inside the shed.
• Fan count: total airflow ÷ per-fan capacity, plus one redundant fan. A 40,000 m³/h tunnel design with 1,250 mm 12,000 m³/h fans needs 4 working fans + 1 spare.
• Air change time: shed volume ÷ total airflow. Target ≤ 2 seconds for broiler tunnel mode.

Cross-flow with pad cooling and tunnel fans

Cross-flow ventilation is common in older or shorter sheds and in some pig housing. Air enters through a pad along one long sidewall and exhausts through fans along the opposite long sidewall. The duct contribution is mostly the inlet plenum across the pad face and the exhaust fan plenum on the opposite wall. Sizing rules are similar but velocities are typically lower (3–5 m/s rather than 6–8 m/s) because cross-flow distance is shorter.

Minimum ventilation

Winter minimum ventilation is the harder duct-engineering case. The 0.5–1.5 m³/h per kg of liveweight rate must be delivered through sidewall inlets that throw fresh air across the ceiling to mix with shed air before reaching bird/animal level. Without ceiling-throw, cold inlet air drops as a curtain along the sidewall, chilling birds in that zone and causing mortality. The inlet baffle geometry, throw angle and shutter control are all duct engineering, even though the volumes are small. Galvanised or aluminium inlet boxes typically suffice — these are dry-air items not exposed to ammonia exhaust.

Acoustic design — NC-50 in animal housing

The acoustic environment in an intensive livestock building affects animal welfare directly. Continuous high-frequency fan noise, intermittent banging from poorly mounted ductwork, and resonance from fan-blade pass tones all stress animals — and stressed animals eat less, grow slower and have higher mortality. RSPCA Approved Farming Scheme audits include acoustic checks; routine welfare practice now targets NC-50 (Noise Criterion 50) or quieter in animal housing zones.

The duct design contribution to acoustic compliance is in three areas:

• Fan mounting. Fans must be vibration-isolated from the building structure. Flexible duct connections, anti-vibration mounts, and avoidance of structural resonance frequencies are standard.
• Duct turbulence. Sharp duct transitions, abrupt expansions and contractions, and high-velocity entries to fan inlets all generate noise. Smooth transitions and gradual area changes reduce turbulent noise generation.
• Velocity selection. Doubling air velocity in a duct multiplies generated noise by approximately 9 dB. Designing inlet plenums for 4–5 m/s rather than 8–10 m/s reduces inlet noise by 6–9 dB at the cost of slightly larger duct cross-section.

Energy and solar integration — SunFarm Australia precedent

The single largest operating cost in an Australian broiler or pig shed is summer ventilation electricity. A 40,000-bird tunnel-ventilated broiler shed pulls 50–80 kW of fan electrical load during peak summer ventilation, running 24/7 through summer months. Cumulative annual electricity cost runs into six figures for a multi-shed site.

Solar-powered ventilation has become a mainstream investment for Australian intensive producers. The SunFarm Australia agribusiness solar model — large-scale rooftop or ground-mount PV directly powering ventilation load — has been adopted across Inghams, Baiada and SunPork sites and is now standard for greenfield broiler complex design. The duct system is unaffected by the energy source, but two design considerations matter: (1) the fan electrical specification (typically variable-frequency drives for staged ventilation) interfaces with the solar inverter system; (2) the rooftop PV array competes with stack and ridge vent space for roof real estate, so coordination between the duct designer and the PV designer at the design stage prevents conflicts at construction.

SBKJ machine configuration for livestock duct projects

SBKJ supplies HVAC ductwork production machinery into Australian intensive livestock projects through three core machine configurations, sized to match the duct portfolio described above.

SBAL-V auto duct line — galvanised baseline

For the inlet plenum, supply duct and dry-zone ductwork in poultry, pig and dairy projects, the SBKJ SBAL-V auto duct line produces rectangular galvanised ductwork at line speeds compatible with multi-shed construction schedules. The SBAL-V handles 0.5–1.5 mm galvanised coil and integrates coil feeding, notching, longitudinal seaming, TDF flange roll-forming and cut-off in a single line. For a typical Australian broiler complex commissioning at 40,000-bird × 6-shed scale, the SBAL-V produces the full inlet and supply duct package in 4–6 weeks of single-shift production.

SBTF-1602 spiral tubeformer — round duct for inlet and recirculation

The SBKJ SBTF-1602 spiral tubeformer produces spiral round duct from 80 mm to 1,600 mm diameter, used extensively for inlet ducts, recirculation distribution and stir-fan plumbing in livestock buildings. Spiral round duct has lower friction loss than rectangular ductwork at equivalent flow capacity, and the inherent strength of the spiral seam means lighter-gauge coil can be used — saving 10–15% on material cost per metre of duct.

Stainless option for ammonia exhaust zones

For the ammonia-exhaust and pit-extract duct runs requiring 304 or 316 stainless construction, SBKJ supplies machine configurations that handle stainless coil. The same SBAL-V and SBTF-1602 platforms, with hardened tooling and adjusted line tension, run 304 stainless at 0.6–1.0 mm equivalent gauges. Stainless duct projects typically run 30–40% of total project duct volume — sized to the high-corrosion zones — and the dual-material capability lets producers commission stainless and galvanised in parallel on the same SBKJ machine fleet.

Aluminium variant for budget-constrained projects

For projects with capital constraint where 25-year stainless service life is not required, SBKJ supplies aluminium-coil-capable machine configurations. Aluminium ductwork in livestock service typically achieves 12–15 year service life — better than galvanised, less than stainless, at intermediate material cost. The decision between aluminium and stainless usually comes down to ammonia loading and cleaning regime: low-density barns with infrequent pressure washing run well on aluminium; high-density layer or pig finisher operations justify stainless from day one.

Biosecurity, cleaning and cycle changeover

Australian intensive livestock operations run on tightly choreographed cycle changeovers. A broiler shed cycle is 35–55 days from chick placement to harvest, followed by a 7–14 day downtime for cleaning, disinfection and litter management before the next placement. A pig finisher cycle runs 14–18 weeks. In all cases the duct system is exposed to the cleaning and disinfection chemistry between cycles, and this is where many otherwise well-designed duct systems fail.

The cleaning regime typically involves high-pressure water washing of shed interior surfaces — including duct exteriors and any accessible duct interiors — followed by application of a disinfectant. Common disinfectant chemistries include peroxygen compounds (such as potassium peroxymonosulfate), glutaraldehyde-quaternary ammonium combinations, and chlorinated phenolic compounds. Several of these chemistries — particularly chloride-bearing disinfectants — accelerate corrosion of stainless steel through pitting and stress corrosion cracking if residual cleaner is not rinsed off. Operating procedures must include a thorough fresh-water rinse after disinfection, and duct material selection in heavy-cleaning zones (close to the floor, accessible to pressure washers) should favour 316 stainless over 304 where chloride exposure is likely.

Biosecurity audits under industry codes including the Australian Pork Industry Quality Assurance Program (APIQ) and broiler company biosecurity protocols typically include a duct-system inspection point. Duct interiors must be inspectable through removable access panels, drain points must be visible and functional, and the design must allow for full cleaning without dismantling. Build-in inspection access during fabrication is far cheaper than retrofitting it later. SBKJ's standard duct fabrication for livestock projects includes hinged access doors at every directional change and a drain port at every low point.

Insulation and condensation control

An underappreciated duct engineering consideration in Australian livestock buildings is condensation control on duct exterior surfaces. Cold winter overnight conditions inside an unheated broiler shed can drop duct surface temperatures below the dew point of the bird-warmed humid air inside the shed. Condensation drips from duct exteriors onto bird-level litter, creating wet patches that drive ammonia release, damage litter quality and feed back into worsened shed conditions. The fix is duct exterior insulation — typically closed-cell foam wrap or fibreglass with a vapour barrier — sized to keep duct surface temperature above the dew point under design winter conditions. The insulation also reduces fan power consumption by maintaining duct interior air temperature closer to the conditioned setpoint.

Insulation specification varies by zone. Inlet ducts feeding directly from outside need outside-face insulation to prevent condensation on the inside of the duct (humid shed air contacting cold duct interior); exhaust ducts pulling shed air to atmosphere need inside-face vapour barriers to prevent insulation saturation from inside-duct humidity. The duct material chosen — galvanised, stainless, aluminium, FRP — affects the insulation attachment method but not the overall thermal calculation.

Integration with controllers and sensors

Modern Australian intensive livestock buildings run on shed-controller platforms that integrate fan staging, inlet position, pad water flow, misting and heater operation. The major controller vendors in the Australian market — Hotraco, Munters, Skov, Big Dutchman and Inteva — each have their own electrical and sensor interface conventions. The duct designer's job is to coordinate with the controller vendor on three interfaces: (1) static pressure sensor tap locations on inlets and the shed-to-atmosphere differential, (2) airflow measurement station locations (where used) for staged-ventilation feedback, and (3) temperature and humidity probe locations to drive the controller setpoint logic. Poorly located sensors give the controller bad data; bad data drives bad ventilation outcomes regardless of how well-built the duct system is.

Variable-frequency drive (VFD) integration with the duct system is the other major coordination item. Staged ventilation — running fans in groups at different speeds rather than all-or-nothing — requires that the duct system pressure drop characteristics match the fan curves across the speed range. A duct designed for full-flow performance at the design day may stall fans at low-speed minimum-ventilation operation; conversely, a duct designed for minimum-ventilation performance may overload fans at maximum-flow operation. The duct sizing exercise needs to be checked against the fan curve at three operating points: minimum, intermediate and maximum.

Commissioning and verification

The hand-over of an intensive livestock duct system is not complete until three measurements are made and recorded against the design specification.

1. Air velocity at animal level. Anemometer traverses at multiple bird-level positions across the shed cross-section, taken in tunnel mode at design-day fan operation. Target 6–8 m/s for broiler tunnel mode; lower values for pig and dairy.
2. Air quality at worker breathing height. Electrochemical sensor readings for ammonia and (in pig housing) hydrogen sulfide, taken at multiple positions, in both minimum and maximum ventilation modes. Document that the system holds ammonia under 25 ppm at the highest expected stocking density and that H2S stays under 10 ppm STEL during routine and pit-stirring operations.
3. Acoustic level at animal level. Sound pressure level measurements across the animal housing zone, demonstrating compliance with NC-50 or local welfare audit thresholds.

How SBKJ supports Australian intensive livestock projects

SBKJ Group operates from Box Hill North in Victoria and supports Australian intensive livestock duct-machinery projects across the full procurement and commissioning cycle:

• Pre-procurement engineering. Review of the producer's housing design, ventilation calculation, and duct schedule. Materials recommendation aligned to corrosion zone. Output is an SBKJ quotation that maps each duct zone to the correct material and gauge.
• Machine supply. SBAL-V auto duct line, SBTF-1602 spiral tubeformer, or stainless-capable variant — supplied with full CE marking, ISO 9001 manufacture, Factory Acceptance Test before shipment, and ISPM-15 crating.
• Installation and commissioning. SBKJ engineers supervise installation and run operator training on Australian sites; standard scope includes 5–10 days for installation and commissioning, operator and maintenance training, and written commissioning report.
• After-sales support. One-year wear-parts kit standard, 72-hour remote response, 10-year+ parts continuity. Box Hill North office provides English-speaking after-sales for Australian operators.

Get an SBKJ quote for an intensive livestock duct project →

FAQ

What ventilation standard applies to intensive livestock buildings in Australia?

ASABE EP 270 is the engineering reference for sizing ventilation rates and duct cross-sections. Overlaid on this are the Model Code of Practice for poultry (supported by the Australian Chicken Meat Federation) and pigs (Australian Pork Limited), and where applicable the RSPCA Approved Farming Scheme. Worker exposure is governed by Safe Work Australia — 25 ppm ammonia 8-hour TWA, 10 ppm H2S STEL, 3 mg/m³ respirable dust.

Why does galvanised ductwork fail in poultry and pig sheds?

Atmospheric ammonia plus condensed moisture creates an acidic film that strips zinc coating within 2–5 years. Once the zinc is gone the underlying steel corrodes through within 12–24 months. SBKJ recommends 304/316 stainless for ammonia exhaust trunks, aluminium for budget-constrained projects, and FRP or polypropylene for acid-scrubber and H2S exhaust zones.

What air velocity is required for tunnel ventilation in Australian broiler sheds?

6–8 m/s at bird level, with complete air change every 2 seconds at peak summer stocking. Maximum airflow 8–10 m³/h per kg of liveweight on the hottest day, falling to 0.5–1.5 m³/h per kg in winter minimum ventilation. The duct system must operate across this 15:1 dynamic range.

How does pad cooling integrate with the duct system?

Air is pulled through a wetted cellulose pad (typically CELdek 7090) at 2.0 m/s face velocity. Pad-leaving air is 6–12°C cooler than ambient depending on inlet humidity. Tunnel fans then pull this cooled, humidified air the length of the shed. Inlet plenum and downstream ducting in the wetted zone should be aluminium or stainless — galvanised will corrode through within 5 years.

What ammonia and H2S exposure limits apply?

Safe Work Australia limits: ammonia 25 ppm 8-hour TWA / 35 ppm STEL; hydrogen sulfide 10 ppm STEL; respirable dust 3 mg/m³. The exhaust duct system is the engineering control that holds workers below all three limits. PPE alone is not an acceptable strategy under modern Australian WHS practice.