Glasshouse Packing Shed, Propagation Nursery, Cold Room and Pesticide Mix HVAC Duct Guide — Costa, Flavorite, Boomaroo, Sundrop, Perfection Fresh

The auxiliary buildings around a glasshouse — a separate engineering discipline

If you have come from our Greenhouse and Protected Cropping HVAC Duct Guide, you already understand that the glasshouse climate envelope is its own engineering problem — a partially open thermal shell governed by the sun, glazing transmittance, plant transpiration and the daily diurnal swing. Vapour pressure deficit, climate-computer modulation of vents, pad-and-fan evaporative cooling, CO₂ enrichment, 30–60 ACH peak air movement. That envelope is a separate scope and a separate trade.

What sits around the glasshouse is something else again. The post-harvest packing shed is a sealed temperature-controlled building under AS 1668.2 mechanical ventilation and FSANZ Standard 3.2.2 food premises code. The pre-cooling room is a refrigeration-heavy short-cycle space hitting 5–10× the steady-state cooling load on every batch entry. The cold storage rooms are AS 4326 cold chain HACCP envelopes with single-digit-degree tolerances. The controlled atmosphere stores for apples and pears operate under sealed N₂/low-O₂/elevated-CO₂ conditions at AS 4254 L1 leakage class. The ripening room for bananas and avocados is sealed to hold 100–150 ppm ethylene dosing. The tissue culture micropropagation lab is an ISO 14644 Grade C cleanroom with laminar flow hoods and autoclave exhaust. The propagation house at 22–28 °C and 80–95 % RH is a different climate problem again. The pesticide mix room is an AS 1940 dangerous-goods space with dedicated MSDS-specific extract. The fertigation mix room is acid-exposed. The boiler house has combustion ventilation requirements under NFPA 86. The CO₂ generator room sits adjacent. The workshop, office and amenity buildings need their own mechanical scope under AS 1668.2 with worker exposure standards under Safe Work Australia.

Every one of those rooms is a different HVAC duct specification — material, pressure class, sealing class, filtration, leakage limit, temperature setpoint, humidity envelope and ACH. The single biggest engineering mistake we see on first-time protected cropping site builds is trying to specify all auxiliary HVAC with one boilerplate. It costs roughly three times what it should and still fails at first BRC audit. This guide walks through the auxiliary scope room by room, with the SBKJ machinery configuration for each.

Site context — the operators we work with

Australian protected cropping has consolidated into a relatively small number of scaled operators who jointly account for the bulk of the country's glasshouse-tomato, hydroponic-cucumber, capsicum, berry, mushroom and propagation production. Each runs auxiliary scope at large scale and has refined operating practice over the last 20 years. The major operators on whose builds this guide is calibrated:

• Costa Group (ASX:CGC) — the dominant ASX-listed fresh produce grower-marketer. Tomato glasshouses at Guyra NSW and Two Wells SA. Berries at Coastal Plains TAS and Atherton QLD. Mushroom production at Mernda VIC and Ravenhall VIC. Avocado at Comboyne NSW. Citrus at Riverland SA and Sunraysia VIC. Operates packing sheds, cold rooms, ripening, CA storage, tissue culture and propagation across the portfolio — the broadest auxiliary-HVAC footprint in the country.
• Sundrop Farms — Port Augusta SA. The 20-hectare integrated solar-thermal-desalination-greenhouse tomato facility. Packing shed and cold rooms run in coastal salt-spray exposure — stainless steel mandatory across the auxiliary envelope.
• Flavorite — Warragul VIC and Katunga VIC. Australia's biggest single glasshouse operator by area, producing tomato, cucumber and capsicum. Substantial packing, cold and ripening scope.
• Perfection Fresh — Tatura VIC, Mareeba QLD and Carnarvon WA. Integrated grower-marketer covering tomato, cucumber, capsicum, salad greens and strawberry. Multi-site packing and cold scope, with the Tatura site running biomass-boiler-supported heating.
• Vitor Marketing — Stanthorpe QLD. Mid-scale glasshouse vegetable operator with integrated packing.
• Two Wells Tomatoes — Two Wells SA, part of the Costa Group portfolio. Glasshouse tomato with packing and pre-cooling.
• Boomaroo Nurseries — Lara VIC. Australia's biggest commercial wholesale propagator — supplying seedlings to most vegetable and ornamentals growers. Operates tissue culture, propagation and despatch scope at industrial scale. The cleanroom HVAC scope here is the most demanding on the Australian protected cropping landscape.
• Driscoll's Australia — Sydney and Coffs Harbour. International berry brand operator with extensive packing and cold-chain scope.
• Costa Berries — the berry division of Costa Group, with substantial tunnel and packing footprint across Tasmania, Queensland and Victoria.
• Sweets Berry TAS — Tasmanian strawberry and berry producer with cold-pack despatch.
• Mountain Blue Berries — NSW Northern Rivers blueberry producer with packing and storage.
• Houston's Farm TAS — leafy greens producer with chilled-pack scope at the low end of the produce temperature range.
• One Harvest — leafy greens processor running fresh-cut and ready-meal lines.
• Salada — cucumber specialist with packing scope.
• Costa Mushrooms — the largest Australian mushroom producer; auxiliary scope is mushroom-shed HVAC plus packing.
• Bayer Garlick — Mernda VIC; ornamental and cut-flower production scope.

The industry body landscape includes Protected Cropping Australia (PCA), Hort Innovation Australia, AusVeg and Berries Australia — each maintaining best-practice publications and audit schemes that intersect with HVAC compliance. We reference PCA technical bulletins, Hort Innovation R&D outputs and AusVeg packing-shed guidelines throughout this guide.

Standards that govern auxiliary HVAC scope

The auxiliary HVAC scope sits across multiple Australian and international standards. The HVAC engineer must integrate compliance with all of them simultaneously. The key references:

• AS 1668.2 — Mechanical ventilation in buildings. The Australian mechanical ventilation standard. Applies to packing shed, amenity, office, workshop, fertigation, pesticide mix — every staffed building on the site. Specifies V_p (occupant ventilation rate in L/s/person), filtration, supply and return air management.
• AS 4254 — Ductwork for air-handling systems in buildings. The core ductwork construction standard for the auxiliary shell. Covers sheet thickness, joint configuration, hanger spacing and pressure class. Auxiliary scope typically runs Class A or Class B sealing for general supply, Class C for CA storage, ripening and tissue culture. SBKJ machinery is configured to AS 4254 tolerances as standard.
• AS 1530.4 — Methods for fire tests on building materials. Governs fire-rated duct construction where ducting penetrates fire-rated boundaries. Most relevant at boiler-house penetrations, between cold-storage envelopes and pack-out zones, and on pesticide-store boundaries.
• ASHRAE Applications Handbook Chapter 25 — Refrigeration of Fruit and Vegetables. The reference text for cold storage and ripening room engineering. Includes precooling load curves, ripening room ethylene management and CA storage gas chemistry. Cross-applied internationally and the reference most Australian consultants work from.
• ANSI/ASABE EP 406 — Heating, Ventilating and Cooling Greenhouses. The agricultural engineering reference for greenhouse heating and ventilation. Cross-applies to propagation house design where the propagation envelope is glasshouse-like rather than packing-shed-like.
• AS 1851 — Routine service of fire protection systems and equipment. Fire damper inspection and testing regime — applies to every fire damper in auxiliary HVAC ductwork.
• ISO 14644 — Cleanrooms and associated controlled environments. The cleanroom standard for tissue culture micropropagation. Grade C (ISO 7 at-rest) is typical for the tissue culture lab envelope, with Grade A (ISO 5) terminal at laminar flow hood faces.
• AS/NZS 4187 — Reprocessing of reusable medical devices and other items in health service organisations. The reference for autoclave sterilisation cycle compliance — cross-applies to tissue culture autoclave operation where sterile media reprocessing is required.
• AS 4326 — Cold chain handling of refrigerated foodstuffs (HACCP). The cold chain integrity standard for any commercial cold store handling food product. Specifies temperature record-keeping, alarm thresholds and validation.
• AS 1940 — Storage and handling of flammable and combustible liquids. Governs the pesticide storage shed where any flammable-carrier formulations are stored. Bunded floor, segregation distance, ventilation and electrical hazardous-area classification.
• AS 5149 — Refrigerating systems and heat pumps — Safety and environmental requirements. Refrigerant safety, including ammonia (R-717) machinery room ventilation and CO₂ (R-744) leak detection.
• FSANZ Standard 3.2.2 — Food Safety Practices and General Requirements. The food premises code for packing sheds handling fresh produce. Covers surface hygiene, pest exclusion, temperature control and traceability.
• FSANZ Standard 3.2.3 — Food Premises and Equipment. Covers the structural requirements for food premises — including surface finishes, drainage and HVAC.
• HACCP — Hazard Analysis and Critical Control Points. The methodology framework underpinning fresh-produce food safety management.
• DAFF and the Biosecurity Act 2015. Federal biosecurity for imported produce inputs (seed lines, propagation material, packaging) and for export-bound produce. Applies to packing sheds despatching to Asian export markets and to propagation supply chains running tissue culture and meristem-tip starter material.
• Protected Cropping Australia (PCA) technical bulletins. Industry best-practice guidance for protected cropping operations.
• Hort Innovation R&D outputs. Crop-specific applied research on storage, ripening and post-harvest practice.
• Safe Work Australia Workplace Exposure Standards. Includes pesticide-active limits per MSDS, ammonia 25 ppm (chiller machinery room), chlorine 0.5 ppm (water sanitation), ozone 0.1 ppm (UV ozone treatment), formaldehyde 1 ppm STEL (autoclave and sterilant).

Compliance is layered rather than centralised. A typical site with packing shed, cold rooms, propagation and pesticide mix will trigger AS 1668.2 across all staffed buildings, AS 4254 across all ductwork, AS 1530.4 at fire-rated penetrations, FSANZ 3.2.2 and 3.2.3 in the packing shed, AS 4326 across all cold rooms, ISO 14644 in the tissue culture lab, AS/NZS 4187 in the autoclave area, AS 1940 in the pesticide store, AS 5149 in any refrigeration machinery room and Safe Work Australia exposure standards in all worker-occupied zones. Multi-standard compliance is the everyday reality.

The post-harvest packing shed — engineering the production hub

The packing shed is where the production economics happen. Whatever the glasshouse delivers in tonnage, the packing shed must grade, sort, pack, label and despatch to FSANZ-compliant supermarket specifications. Tomato, capsicum, cucumber, strawberry, raspberry, blueberry, leafy green, banana and avocado packing sheds all run distinct envelopes — but share core HVAC requirements: temperature control, positive pressure, HEPA filtration on makeup, dust extract on grading lines, and zoned pressurisation between dirty and clean ends.

Temperature envelope

Packing shed temperature is governed by produce-specific chilling injury thresholds and FSANZ cold chain integrity:

• Tomato, capsicum, cucumber: 12–14 °C dry-bulb, 60–70 % RH. Below 8 °C induces chilling injury in tomato and capsicum, manifesting as surface pitting and post-harvest collapse. The packing envelope deliberately runs warmer than fresh produce intuition suggests.
• Strawberry, raspberry, blackberry, blueberry: 8–12 °C cold-pack envelope. Berries have shorter shelf life and benefit from earlier cold pull-down. Costa Berries, Driscoll's and Mountain Blue all run berry sorting lines in this envelope.
• Leafy greens (lettuce, baby spinach, mesclun, herbs): 4–8 °C. Houston's Farm and One Harvest both run leafy-greens packing at this temperature.
• Banana (after ripening): 14–18 °C. Ripening then despatch at this envelope.
• Avocado: 12–14 °C pre-ripening, 8–12 °C ripening, 5–7 °C post-ripening.
• Apple, pear: 4–6 °C steady-state. Bulk volume goes into CA storage; packing runs at lower temperature than tomato envelope.
• Mushroom: 2–4 °C. Costa Mushrooms runs sorting at this envelope.

The temperature uniformity requirement is tight: ±1 °C across the working envelope, with no point exceeding the FSANZ critical control point limit. This drives the HVAC duct distribution architecture — overhead supply with multiple diffuser zones, balanced return at low level, and door-cycling compensation via positive-pressure boost on doors-open signal.

Positive pressure and HEPA filtration

Every Australian commercial packing shed worth its BRC certificate runs at positive pressure relative to corridor and dock zones. Typical setpoint is 15–25 Pa above the loading-dock pressure, with cascade falls down through grading zone, sorting zone, pack-out and despatch. The cascade prevents inward migration of insects, mould spores, dust and exterior contaminants whenever doors cycle.

Incoming makeup air is HEPA H10 filtered (>85 % efficiency at MPPS per EN 1822) — the standard food-grade filtration for non-pharmaceutical environments. The HEPA stage adds about 250–350 Pa of pressure drop, so supply fan sizing must account for it. Filtration upstream is typically MERV 13 prefilter plus G4 coarse filter to extend HEPA life; total filter train pressure budget is 500–700 Pa at end-of-life.

The pressurisation flow is roughly 20–30 % above the cooling-only flow rate, because the makeup must balance both the room load and the door-cycling exfiltration. We size supply fan capacity at 1.25–1.30× the cooling flow as a working rule for new installations.

Dust extract on grading lines

Tomato, capsicum and cucumber grading machines (Maf Roda, Sorma, Greefa and Compac are the dominant grader manufacturers used by Australian operators) generate measurable airborne particulate from brushing, sizing rollers and grader chains. Fine fruit hair and bloom dust on tomato can drop below 5 µm and migrate into the air return path. Dust extract at the grader is typically 800–1,500 m³/h per grader station, captured via overhead hoods or sidewall extract slots, ducted through a fabric filter to outside.

Strawberry and raspberry sorting lines generate less dust but more humidity — bruising and juice spray. Dust extract is replaced by a wet-collection plenum that captures both particulate and juice, typically ducted in 304 stainless to a wet sump for disposal.

Pressurisation zoning

A typical packing shed is zoned as dirty-end (incoming product, washing, hydrocooling), clean-end (grading, sorting, packing) and despatch (palletisation, cold-chain truck loading). Pressure cascade falls from clean-end (highest, +20–25 Pa) to dirty-end (medium, +10–15 Pa) to despatch (lowest, +5–10 Pa above outdoor ambient). The cascade is enforced by airflow imbalance — supply exceeds return in each zone, with the imbalance migrating from clean to dirty to despatch and finally out through the loading-dock seals.

The ducting scope to support zoning is substantial. Each zone needs independent supply branches with motor-controlled dampers, individual zone pressure sensors and a building management system (BMS) modulating dampers to hold setpoint. The supply main duct runs typically 600–1,200 mm rectangular galvanised or stainless, with branch ducts dropping to each zone in 400–600 mm round spiral.

Duct material specification

Packing shed ductwork operates in a chronic 60–70 % RH environment with periodic wash-down events. Material selection:

• Galvanised G90 (275 g/m² zinc both sides): only for offices, amenities and zones with no condensation risk. Not recommended in the active packing zone above 60 % RH continuous.
• 304 stainless steel: the standard for active packing zone supply duct. Resists condensation, daily wash-down, chlorine sanitiser exposure. 25+ year service life. Mandatory in coastal sites (Sundrop, Coffs Harbour, Carnarvon).
• Polyethylene-lined galvanised: acceptable substitute where 304 stainless capital is prohibitive but condensation exposure is moderate. 15–20 year service life.
• 316 stainless: for chlorinated wash-down zones, juice extraction and any acid-exposed zone. More expensive than 304 but mandatory where 304 corrodes.

Surface cleanability matters as much as material. FSANZ 3.2.3 requires smooth-bore internal surfaces accessible for periodic sanitation. TDF flange joints with smooth-bore internal surface are preferred over Pittsburgh lock seams in the packing envelope. Spiral lockseam round duct is acceptable because the spiral seam is mechanically sealed and the internal surface is smooth.

Sizing example — a 5,000 m² mid-scale tomato packing shed

Consider a 5,000 m² packing shed handling 30 tonnes/day of glasshouse tomato — a Flavorite Warragul or Perfection Fresh Tatura mid-scale build. Key parameters:

• Building envelope: 5,000 m² floor area, 7 m clear height, 35,000 m³ volume.
• Temperature: 13 °C dry-bulb, 65 % RH.
• Sensible cooling load: 800 kW total (160 W/m² at peak).
• Pressurisation: +20 Pa relative to despatch, +25 Pa relative to outside.
• Supply flow: 75 m³/s (270,000 m³/h), at 8 ACH.
• Supply duct mains: 1,400 × 1,000 mm rectangular 304 stainless, fabricated on SBAL-V configured for stainless coil.
• Branch round: Φ600–Φ900 mm 304 stainless spiral, fabricated on SBTF-1500.
• HEPA H10 makeup unit: 12 m³/s, with MERV 13 prefilter.
• Grading line dust extract: 5 × 1,200 m³/h hoods, ducted to fabric filter on roof.

The supply duct mass for the facility is roughly 18–22 tonnes of stainless steel, plus 4–6 tonnes of insulation. Fabrication time on an SBAL-V configured for stainless is 6–8 weeks single-shift. Site installation and balance is a further 4–6 weeks.

Pre-cooling — the 5–10× spike over steady-state

Pre-cooling is the post-harvest step that drops field-warm produce from harvest temperature (typically 22–30 °C in Australian summer) to storage temperature (4–6 °C for most crops) as quickly as possible. The faster the pull-down, the longer the produce shelf life. Pre-cooling is therefore high-power refrigeration applied in bursts as truck loads arrive from the field.

Three pre-cooling technologies dominate Australian fresh produce:

Forced-air pre-cooling

Stacked palletised product is placed in a sealed plenum with high-velocity chilled air (4–6 °C, 2–5 m/s) drawn through the pallet by suction fans. The fast air movement breaks the pallet boundary layer and drops core temperature 10–15 °C in 30–90 minutes depending on product geometry and packaging. Used for tomato, capsicum, cucumber and citrus.

HVAC duct interaction: supply duct to the forced-air room is sized for very high flow (4–8 m/s velocity) at peak. A 5-tonne forced-air pre-cool room demands 30,000–50,000 m³/h supply at peak, dropping to near-zero between batches. Variable-frequency drive on supply fan is mandatory.

Hydrocooling

Field-warm produce is showered with 0.5–2 °C chilled water for 5–15 minutes. Water-cooling is far more efficient than air-cooling for surface-pulldown because water's heat capacity is roughly 4× that of air. Used for sweetcorn, broccoli, celery, leafy greens, stone fruit and certain root vegetables. Limited use for tomato and capsicum because surface wetting promotes Botrytis.

HVAC duct interaction is significant — the hydrocooler generates 30–50 kW of latent heat per cubic metre of chilled water flow, condensing onto every cold surface in the surrounding room. Supply duct in the hydrocool room must be 304 stainless or fully sealed polyethylene-lined galvanised. Exterior insulation is 50 mm closed-cell with full vapour barrier. The room itself needs dedicated dehumidification rather than relying on cooling-coil dehumidification, because latent load swings hourly with hydrocooler use.

Vacuum cooling

Produce is placed in a sealed vacuum chamber, pressure drops to roughly 6 mbar absolute, and surface water flashes off into the vacuum. Latent heat of vaporisation cools the product. The fastest pre-cooling method available, with full pull-down in 20–30 minutes. Used heavily for leafy greens (lettuce, baby spinach), strawberry and certain ornamentals.

HVAC duct interaction with vacuum cooling is minimal because the cooling happens inside a sealed chamber rather than in the room. The room HVAC is simply maintained at a comfortable working temperature (12–16 °C). The vacuum chamber's vapour-extract system is a separate scope, typically using a steam-jet ejector or a multi-stage rotary pump with a condenser.

Sizing the pre-cooling load

A 10-tonne strawberry harvest at field temperature 25 °C entering a hydrocooler and exiting at 4 °C demands:

Q = m × c_p × ΔT = 10,000 kg × 4.0 kJ/kg·K × 21 K = 840 MJ

If pull-down is over 30 minutes, average refrigeration capacity is 840 MJ / 1,800 s = 467 kW. Peak demand will run higher — perhaps 600–700 kW. Steady-state cold storage for the same tonnage runs maybe 30–50 kW. The peak-to-average ratio of 10–15× is the defining feature of pre-cooling.

Refrigeration plant sizing for the pre-cooling system is therefore peak-driven, not average-driven. Chiller plant runs ammonia (R-717) on most large Australian installations, with HVAC duct in the chiller machinery room running 304 stainless under AS 5149 ammonia-handling provisions. The machinery room ventilation is 30 ACH minimum with ammonia-detection interlock to the exhaust fan.

Cold storage 0–4 °C — the workhorse cold room

Cold storage at 0–4 °C is the primary post-precool envelope for lettuce, leafy greens, berries, cucumber and most field vegetables. The room operates at much lower ACH than packing (8–20 typically) with humidity controlled to product-specific setpoints (95–98 % for leafy greens, 85–90 % for most fruit, 75–85 % for stone fruit).

Duct layout: perimeter supply ring at ceiling level with linear slot diffusers, drawing return at low level through a return plenum that wraps the storage racks. Air movement is gentle (0.2–0.5 m/s at the product face) to avoid dehydration on exposed product. Door cycling is the dominant load swing — every door open admits warm humid corridor air, condensing onto cold ducting surfaces.

The HVAC duct insulation specification is critical. Supply duct surface temperature in a 2 °C room sits at roughly 4 °C, well below the corridor dew point of 18–20 °C. Without continuous external insulation and vapour barrier, water sheets off the duct exterior within minutes of start-up. Standard practice is 50 mm closed-cell elastomeric insulation with FRK foil vapour barrier, all joints mastic-sealed.

Material specification: 304 stainless steel for supply duct in the active product zone. Galvanised G90 is acceptable in the chiller-room return air path (dry side of the cooling coil) but not in the product zone, where 95+ % RH is chronic. Polyethylene-lined galvanised is an acceptable substitute at lower capital. For wash-down zones around hydrocoolers and case-washers, 316 stainless is preferred.

Defrost is the other distinctive feature. Most large cold rooms run 2–4 hot-gas defrost cycles per day on the evaporator coil. The defrost meltwater is captured in drain pans and routed to drain piping outside the conditioned envelope. The duct system must clear defrost runoff cleanly — drain pan slope at minimum 1:50, P-trap on every drain, heat tracing on any exterior drain line below 0 °C ambient.

Controlled atmosphere (CA) storage — apples, pears, kiwifruit at scale

CA storage extends storage life of apples and pears from 4 months under conventional cold storage to 9–12 months under controlled atmosphere conditions. Used by every major apple and pear cooperative in Australia — Montague Fresh, Costa Group's pome-fruit divisions, Tasmanian apple growers, and Adelaide Hills pear operators. The atmosphere itself is regulated to product-specific setpoints:

• Apples: 1.0–2.0 % O₂, 2.0–5.0 % CO₂, 0–1 °C, 92–95 % RH. Some cultivars run ultra-low oxygen (ULO) at 0.5–1.0 % O₂.
• Pears: 1.5–2.5 % O₂, 0.5–2.0 % CO₂, -0.5 to 0 °C, 90–95 % RH. Ethylene scrubbing is critical for some pear cultivars (Beurré Bosc) where ethylene-driven ripening must be suppressed during storage.
• Kiwifruit: 1.5–2.5 % O₂, 4.0–5.5 % CO₂, -0.5 to 0 °C, 90–95 % RH.

The duct system in CA storage is sealed to AS 4254 L1 leakage class — far tighter than normal cold-room ductwork — because the CA gas mix is expensive to maintain and any leakage to ambient drives the O₂ scrubber and N₂ generator harder. Material is 304 stainless throughout the supply duct, with TDF flange joints and full-perimeter neoprene gasket sealing.

Subsystems integrated with the duct system:

• N₂ supply line from a dedicated pressure-swing-adsorption (PSA) generator, dosing pure N₂ to displace ambient air during pull-down and to maintain low O₂ during storage.
• CO₂ scrubber — typically lime-based or carbon-based, sized to remove the CO₂ produced by stored fruit respiration. Scrubber duty cycles with fruit metabolism — higher load early in storage, declining over months as respiration rate falls.
• Ethylene scrubber — potassium permanganate or activated-alumina catalyst, optional but standard for sensitive pear cultivars and where mixed-fruit storage demands ethylene control.
• O₂ top-up bleed — paradoxically, CA storage sometimes needs to add air back as fruit respires O₂ below setpoint. Air infiltration through door seals usually provides enough, but dedicated air bleed valves are standard.

Duct sizing is dominated by the scrubber recirculation flow rather than the cooling load. The room atmosphere is recirculated continuously through the CO₂ scrubber and ethylene scrubber at 3–6 ACH. Cooling-only flow runs at 6–12 ACH. The combined flow is 9–18 ACH, with the scrubber loop typically routed through dedicated branch ducting separate from the cooling supply.

Personnel access is dangerous — CA storage at 1 % O₂ is fatal to humans within minutes. AS 5149 and WorkSafe regulations require sealed-door access protocols with full self-contained breathing apparatus, lockable atmosphere-control panel and continuous O₂/CO₂ sensor monitoring. The duct system is not entered during operation; all maintenance is during the inter-season decommissioning window.

Ripening rooms — banana and avocado ethylene gassing

Bananas are picked green and ripened under controlled ethylene exposure in dedicated ripening rooms. Avocados follow the same pattern for ripening control. Costa Group runs the bulk of the Australian banana ripening capacity, with rooms operating at 14–18 °C and gassing to 100–150 ppm ethylene exposure for 24–48 hours.

The HVAC duct specification is dominated by sealing class. Ethylene is both an OH&S exposure (Safe Work Australia WES at 250 ppm 8-hour, with explosive limits above 27,000 ppm in air) and a wasted dosing if it leaks out. Rooms are sealed to AS 4254 L1 leakage class minimum, often tighter.

Distinctive duct requirements:

• Pre-ripening pull-down: fruit arrives at the ripening room at 12–14 °C. Ripening starts when temperature rises to 18 °C under controlled gassing. The HVAC duct must support both pull-down and active ripening modes.
• Continuous CO₂ management: banana respiration during ripening produces high CO₂ (up to 3–5 %) that suppresses ripening. The room atmosphere is scrubbed continuously through a CO₂ absorber, typically lime-based or sodium-hydroxide-based.
• Ethylene injection: ethylene is dosed from a pressurised cylinder or generated from ethephon in catalytic units. The duct system must support a dedicated injection point with metered control.
• End-of-cycle ventilation: after ripening, the room is purged with fresh air to clear residual ethylene before personnel entry. Purge ventilation runs at 30 ACH for 30–60 minutes.
• Material: 304 stainless for supply duct. Ethylene is not corrosive but the high humidity (85–90 % during ripening) demands stainless. CO₂ scrubber lime-based slurry occasionally splashes onto duct surfaces, accelerating zinc corrosion if galvanised.

The ripening room HVAC scope is one of the most overlooked auxiliary specifications in Australian protected cropping — and one of the highest-consequence to get wrong. A 10-tonne batch of bananas in a leaky ripening room dosed at 150 ppm ethylene loses both the OH&S exposure margin and the ripening efficiency, and the operator ends up running 200 ppm to compensate. We see this on first-time builds repeatedly.

Tissue culture and micropropagation laboratory

Tissue culture and meristem-tip micropropagation is the foundation of Australian propagation supply — virus-free, true-to-type planting material for berries, ornamentals, fruit trees and increasingly for vegetable hybrids. Boomaroo Nurseries at Lara VIC operates the largest Australian commercial tissue culture lab; Costa Group's berry division and several specialty nurseries operate dedicated facilities.

The tissue culture HVAC scope is closer to a pharmaceutical cleanroom than to anything else in agriculture. The lab is built to ISO 14644 Grade C (equivalent ISO 7 at-rest) as the base envelope, with Grade A (ISO 5) unidirectional flow at every laminar flow hood face for sterile transfer operations.

Room envelope conditions

Standard tissue culture lab conditions:

• Temperature: 18–22 °C ±0.5 °C steady-state. Tight uniformity is essential for repeatable culture growth.
• Relative humidity: 50–55 % RH ±5 %. Higher humidity promotes contamination; lower humidity desiccates culture media.
• Pressurisation: +10–15 Pa relative to Grade D antechamber, +25 Pa relative to corridor.
• ACH: 20–30 ACH with terminal HEPA H13 ceiling supply.
• Filtration: HEPA H13 (>99.95 % efficiency at MPPS) at every ceiling supply. MERV 14 prefilter plus G4 coarse upstream.
• Particulate target: ISO 14644 Grade C at-rest, Grade B in-operation at the working zone.

Laminar flow hood integration

Laminar flow hoods are the primary sterile-transfer workstations. Each hood delivers ISO 5 (Grade A) unidirectional flow at 0.36–0.54 m/s downflow velocity at the working surface. The hood exhausts back to room or to dedicated exhaust depending on the operations conducted inside.

The room HVAC must support the cumulative hood loads. Twenty hoods running at 0.45 m/s through 0.5 m² each = 9 m² × 0.45 m/s = 4 m³/s = 14,400 m³/h of room makeup just to feed the hoods, plus the room cleanroom 20–30 ACH. Total supply load for a 200 m² tissue culture suite with 20 hoods runs 20,000–25,000 m³/h.

Autoclave area

Sterile media preparation requires autoclaves running 121 °C saturated steam cycles to sterilise media flasks. Autoclave area is segregated from the main cleanroom envelope — typically a Grade D buffer zone with dedicated steam exhaust at 50–80 m³/min capture velocity. The autoclave exhaust contains steam, residual sterilant and trace media volatiles; ducted to outside via 316 stainless flue with weatherproof terminal.

AS/NZS 4187 governs reprocessing — sterile holding time, sterilisation cycle parameters, and validation. The autoclave HVAC interaction is the steam exhaust capture and discharge.

Sterilant exposure

Periodic room decontamination uses either formaldehyde fogging (declining use; Safe Work WES 1 ppm STEL) or vapour-phase hydrogen peroxide (VHP — preferred for new builds, 1 ppm WES). Both demand sealed-tight ductwork in 304L stainless with no organic gaskets in the airflow path. EPDM and silicone gaskets are acceptable; nitrile and natural rubber are not. The duct system must withstand the periodic decontamination cycle and return to clean-room operating parameters within 2–4 hours.

Material specification

Tissue culture duct is 304L stainless throughout, with smooth-bore interior surfaces, TDF flange joints and full-perimeter EPDM or silicone gaskets. Internal surfaces are passivated. External insulation is 50 mm closed-cell elastomeric with FRK foil vapour barrier. The full duct system is leak-tested to AS 4254 L1 class minimum, often tighter.

SBKJ machinery for tissue culture duct fabrication

Tissue culture duct demands 304L stainless coil running through the SBAL-V auto duct line. The line is configurable for stainless feed — the same tooling as galvanised operation, but with the coil feed mechanism re-tensioned for stainless's lower friction and the cut-to-length shear regulated for the thinner stainless gauge typically specified (0.8–1.2 mm rather than 1.0–1.5 mm for galvanised). Spiral round branch duct in stainless runs through SBTF-1500 with the stainless-coil feed configuration. Stitch-welded longitudinal seams on heavy stainless duct (where TDF lockseam is impractical) use the SB-ZF1500 Automatic Stitchwelder.

Propagation house — seedling and cutting production

The propagation house is where the seedling and cuttings production happens. Boomaroo Nurseries at Lara, Costa Group's nursery division, several Driscoll's berry propagation sites and dozens of smaller specialty nurseries all run dedicated propagation envelopes.

The propagation envelope is glasshouse-like rather than packing-shed-like:

• Temperature: 22–28 °C dry-bulb. Warm enough for fast germination and rooting; not so warm as to stress new transplants.
• Relative humidity: 80–95 % controlled. Cuttings root better under high humidity until callus formation; seedlings need less.
• Air movement: gentle. 0.2–0.4 m/s at the propagation tray surface to avoid desiccation.
• Light: supplemental LED at 200–300 µmol/m²/s on a programmable photoperiod, with shade-cloth modulation during direct-sun hours.
• Root-zone heat: bottom heat at 24–28 °C from heat mats or under-bench piping, accelerating rooting.
• Mist or fog systems: overhead misters fire on demand to maintain RH during early rooting; some operations run continuous fogging.
• Pest exclusion: 80-mesh insect screen on all intakes; double-door entry vestibule; positive pressure of 5–10 Pa relative to corridor.

The HVAC duct material in a chronic 85–95 % RH propagation house is 304 stainless or polyethylene-lined galvanised. Pure galvanised duct degrades visibly within 18–36 months at this humidity. Mother plant nurseries (where cuttings sources are maintained as virus-free reservoirs) run the same envelope conditions with tighter pest exclusion (60–80 mesh insect screen, double-door access with sticky mat).

Distinctive ducting features

• Mist boom integration: overhead mist systems run from a stainless steel manifold; the HVAC supply duct must coordinate with the mist boom to avoid spray contact and to handle the elevated humidity downstream.
• Bottom-heat coordination: under-bench heat piping runs at 24–28 °C — close to dew point at typical propagation temperatures. Insulation on pipes prevents condensation onto propagation trays below.
• Variable supply: propagation cycles change conditions over 4–12 weeks from initial transplant to root-out. HVAC must support seasonal setpoint changes.
• Flexible duct sections: small-diameter (Φ80–Φ300) insulated flexible duct is common for short connection runs to propagation benches. Fabricated on the SBLR-600 flexible duct forming machine.

Pesticide mix and spray-prep room

The pesticide mix room is where formulated pesticide product is diluted, decanted into spray tank, and prepared for application. Every grower handling pesticide does this somewhere; regulated operators (Costa, Flavorite, Perfection Fresh) do it in a dedicated room under AS 1940, the Australian Pesticide Application Code and state WorkSafe regulations.

Room envelope

The pesticide mix room is dedicated extract-only with no recirculation. Standard envelope conditions:

• ACH: 20–40 continuous extract, scaling up to 60+ during active mixing operations.
• Pressurisation: negative 15–25 Pa relative to corridor. Critical — outward leakage of pesticide vapour is unacceptable.
• Temperature: ambient 18–25 °C. No conditioning needed beyond comfort range.
• Floor: bunded concrete with 100 mm minimum kerb, falling to a sealed sump. Spills capture to sump rather than to floor drain.
• Eye-wash and emergency shower: within 10 m of mixing position, plumbed to potable water with 15-minute autonomy.
• Worker amenity: by full-face PAPR respirator and Tyvek coveralls. Not by HVAC dilution.

MSDS-specific extract scrubber

The extract scrubber is tuned to the dominant pesticide active ingredients used on the site:

• Organophosphates (chlorpyrifos, malathion, diazinon — declining but still in use): activated carbon scrubber, 4–8 kg carbon per m³/s extract.
• Pyrethroids (deltamethrin, cypermethrin, lambda-cyhalothrin): activated carbon scrubber, similar sizing.
• Neonicotinoids (imidacloprid, thiamethoxam, acetamiprid): activated carbon plus solvent scrubber, because some formulations include organic co-solvents.
• Copper fungicides (copper hydroxide, copper oxychloride): wet scrubber with neutralisation, because copper is captured as soluble compound.
• Sulphur (used widely on tomato, cucumber, strawberry): wet scrubber with mildly alkaline solution.
• Biological products (Bacillus thuringiensis, baculovirus): biological filter or wet scrubber, depending on formulation.

Most operators use a multi-stage scrubber that handles the broad pesticide spectrum used on the site. The scrubber is sized to the worst-case pesticide and validated annually under MSDS-specific exposure scenarios.

Duct material

Pesticide mix room ducting is polypropylene (PP) or fibre-reinforced plastic (FRP) composite. Galvanised steel and stainless both fail rapidly: chlorinated pesticides corrode zinc and chloride-stress-corrosion-crack stainless within 18–36 months. PP is chemically resistant to virtually all agricultural pesticides; FRP composite offers higher mechanical strength for larger duct cross-sections.

Fabrication of PP and FRP duct is outside the SBKJ rectangular-duct machinery scope — those materials are typically thermoformed or wet-layup fabricated by specialist plastic duct suppliers. SBKJ machinery is involved in the upstream supply mains feeding the pesticide mix room from the building management system (galvanised G90) and in the downstream stainless flue if the scrubber discharges to a stainless stack.

Pesticide storage shed

Pesticide product is stored in a dedicated shed separate from the packing and amenity buildings, under AS 1940 dangerous-goods storage. Conditions:

• Bunded floor: 110 % of largest container capacity, sealed to prevent runoff.
• Segregation distance: 5–15 m from adjacent buildings depending on dangerous-goods classification.
• Ventilation: passive at 4–6 ACH for stable formulations, active extract if any flammable-solvent carrier product is stored (toluene-based, xylene-based formulations).
• Hazardous area classification: Zone 2 if flammable solvents present, requiring explosion-proof electrical equipment and intrinsically safe ventilation fans.
• Temperature: typically 10–30 °C ambient, with insulation to prevent extreme heat exposure (some formulations destabilise above 40 °C).
• Material: ducting is light-gauge galvanised G90 for passive vent; explosion-proof fan housing required for Zone 2 active vent.

Fertigation mix room

The fertigation mix room is where the concentrated A-tank and B-tank nutrient solutions are blended. A-tank typically contains calcium nitrate (Ca(NO₃)₂) and any other calcium-soluble fertilisers; B-tank contains potassium nitrate (KNO₃), potassium sulphate (K₂SO₄), magnesium sulphate (MgSO₄), trace micronutrients and chelated iron. Acid for pH adjustment (typically nitric or phosphoric, occasionally sulphuric) is metered in separately.

The fertigation room operates with the following HVAC envelope:

• ACH: 6–10 continuous extract, no recirculation.
• Eye-wash and shower: mandatory, due to acid handling.
• Duct material: polyethylene-lined galvanised acceptable for general extract; 316 stainless preferred if acid mist exposure is chronic.
• Pressurisation: negative relative to corridor, similar to pesticide mix room but at lower magnitude (-5 to -10 Pa).
• Temperature: ambient. No conditioning needed.

Acid mist exposure is the dominant material concern. 316 stainless resists nitric and phosphoric acid mist; 304 stainless and galvanised do not. For sulphuric acid use (rare in fertigation but seen in some specialty crop protocols), even 316 stainless suffers attack at elevated concentrations and FRP composite becomes the better material choice.

Boiler house — gas-fired greenhouse heater

The boiler house feeds hot-water heating to the glasshouse and to any other building requiring heat (propagation house, packing shed in winter, amenity in winter). Most Australian sites run condensing gas boilers fired by natural gas or LPG.

HVAC duct interaction:

• Combustion air supply: 1.6 m³ per kWh of fuel input. A 1 MW boiler demands 1,600 m³/h of combustion air, sourced from outside and ducted into the burner intake. Combustion air ducting is galvanised G90 with smooth radius bends to minimise pressure drop.
• Flue gas extraction: flue is sized for the burner manufacturer's specification. Natural-gas flue gas exits at 65–80 °C in a condensing boiler, with condensate forming inside the flue. Material is 316 stainless to handle the acidic condensate (pH 3.0–5.0 from CO₂/SO₂ dissolution).
• Room ventilation: general boiler room ventilation at 6–12 ACH, ducted to outside via galvanised duct. Heat dissipation from boiler shell and from connection pipework drives the ventilation requirement.
• NFPA 86 compliance: combustion ventilation safety, including makeup air interlocks, flame failure detection and pre-purge sequences.
• AS 1851 fire damper: at every boiler-house perimeter penetration where the ducting passes a fire-rated boundary.

Boiler types in Australian protected cropping

• Condensing gas boiler: the most common type. 90–98 % thermal efficiency, gas fuel, sized 500 kW to 10 MW for typical glasshouse operations.
• Non-condensing gas boiler: legacy installations. 75–88 % efficiency. Higher flue temperature (140–180 °C) but simpler stainless requirements (304 stainless adequate for non-condensing flue).
• LPG boiler: for sites without natural gas reticulation. Comparable thermal characteristics to natural gas with marginally higher CO₂ output per unit heat.
• Diesel boiler: backup or remote-site installations. Higher particulate output requires more aggressive scrubbing if flue gas is repurposed for CO₂.

Wood biomass boiler — the Tatura model

Wood-chip or wood-pellet biomass boilers are increasingly specified in Australian protected cropping, particularly in Victorian Goulburn Valley operations near Tatura where the local timber industry provides reliable feedstock. The biomass boiler has distinctive HVAC interactions:

• Higher combustion air demand: 1.8–2.2 m³ per kWh input, due to lower fuel calorific value vs gas.
• Higher flue particulate: 50–500 mg/Nm³ uncontrolled, requiring cyclone separator plus bag filter or electrostatic precipitator before any atmospheric discharge.
• Higher flue acidity: CO₂, SO₂ and chloride from biomass create flue condensate at pH 2.5–4.0 — more acidic than natural gas. 316L stainless mandatory for flue and condensate-handling duct.
• Ash handling: bottom ash and fly ash require ducted handling from boiler to ash bin. Refractory-lined steel duct.
• CO₂ reuse: after particulate scrubbing, the flue gas can be redirected for greenhouse CO₂ enrichment — a CHP-style integration that doubles the value of the heating fuel. The scrubbing chain is much more involved than gas (particulate cyclone + bag filter + acid scrubber + NOx scrubber + CO₂ conditioning) but the economics favour it where gas prices are high.
• NFPA 86 plus AS/NZS 3814: biomass-specific combustion ventilation safety provisions.

Material specification for biomass flue is 316L stainless throughout, with 304L acceptable only above the condensate drop-out point. Refractory-lined steel for the ash handling. Galvanised steel is not used in biomass flue applications — zinc volatilises at flue temperature and corrodes rapidly under acidic condensate.

CO₂ generator room

Some sites use a dedicated CO₂ generator — an LPG or natural-gas burner sized to produce CO₂ for greenhouse enrichment without the heating output requirement. The burner is typically 50–200 kW input, producing 8–20 kg/h of CO₂ after combustion.

HVAC duct interaction:

• Combustion air: 1.6 m³ per kWh, similar to a gas boiler.
• Flue conditioning: the combustion product is cooled, scrubbed for ethylene (potassium permanganate catalyst — phytotoxic threshold 30 ppb at sensitive species), scrubbed for NOx (soda lime — phytotoxic threshold 100 ppb), then injected into the greenhouse supply manifold. Material throughout the flue conditioning is 316L stainless.
• Spark-resistant fixturing: the CO₂ generator room handles LPG and natural gas, with potential for flammable atmosphere. Any duct welding in this room requires spark-resistant fixturing — typically using non-ferrous tooling and remote control of the welding cycle. SBKJ can configure spark-resistant variants on enquiry.
• Room ventilation: 10–15 ACH continuous, with gas leak detection interlocked to a high-rate exhaust mode.

Workshop and maintenance shed

The workshop covers grader maintenance, irrigation pump repair, vehicle servicing and general fabrication work. The HVAC duct scope is comparatively light:

• General mechanical extract: 6–10 ACH, sufficient to dilute welding fume, paint solvent and degreaser to below Safe Work Australia WES.
• Local exhaust ventilation (LEV) at fixed welding stations, paint booths and battery-charging areas. AS 1668.2 specifies capture velocity and duct sizing for each.
• Compressed air supply for pneumatic tools — not strictly HVAC but coordinated with workshop layout.
• Heating in cold climates — typically forced-air unit heaters with galvanised supply ducting.
• Material: galvanised G90 for general ducting. 304 stainless for LEV at welding stations where stainless welding is performed.

Office and admin building

The office building runs standard commercial HVAC under AS 1668.2:

• V_p: 10 L/s per person occupant ventilation rate.
• Temperature: 22–24 °C heating, 24–26 °C cooling.
• Relative humidity: 40–60 % comfort range.
• Filtration: MERV 13 (ePM1 50 %) for general office air quality.
• Material: galvanised G90, standard commercial spec.

No specialty engineering needed unless the office is integrated into a packing-shed envelope or shares a wall with a cold storage room, in which case pressurisation cascade and thermal barrier construction must be detailed.

Worker amenity and lunchroom

The amenity block (lunch room, change rooms, toilets, drying room for wet weather gear, first aid) runs AS 1668.2 with V_p 10 L/s per person occupant ventilation, plus elevated extract on shower/toilet zones (25 L/s per WC, 35 L/s per shower). The drying room for wet weather gear runs 30–35 °C with elevated humidity tolerance — moisture loading from soaked PPE is substantial.

HVAC duct scope is comparable to a small commercial facility: galvanised supply, dedicated extract on wet zones, MERV 13 filtration. Pressurisation cascade isolates amenity from production zones.

Visitor centre and retail

Some growers (Tatura strawberry farm, Boomaroo Nurseries retail, several Costa berry sites) integrate a public-facing visitor centre with retail produce sales. The HVAC scope here is comfort-cooling commercial:

• Temperature: 22–24 °C, V_p 10 L/s per person under AS 1668.2.
• Retail-grade visibility: ducting may be exposed in some architectural treatments — clean lines, painted finishes, and minimum visible joints.
• Pressurisation cascade: visitor zone isolated from production zone. Often a transition vestibule with double-door entry separates the two.
• Material: galvanised G90 for general supply; 304 stainless if exposed in an architectural treatment.

Costa Group portfolio integration — the multi-site model

Costa Group's auxiliary HVAC scope across its national portfolio illustrates how complex modern protected cropping has become. The portfolio includes:

• Tomato glasshouses at Guyra NSW and Two Wells SA, each with attached packing sheds, cold rooms, propagation and fertigation.
• Berry production across Coastal Plains TAS, Atherton QLD and multiple Victorian sites — tunnel and glasshouse production, packing, cold-pack and despatch.
• Mushroom production at Mernda VIC and Ravenhall VIC — high-humidity controlled-environment scope with packing.
• Avocado at Comboyne NSW — orchard production with attached packing, cold storage, ripening and despatch.
• Citrus at Riverland SA and Sunraysia VIC — packing and cold storage scope.
• Banana wholesale and ripening operations.

Each site runs its own auxiliary HVAC specification calibrated to crop, climate and despatch profile. Costa's engineering standard is the closest thing the Australian industry has to a national reference framework — fold-over of specifications between sites is rare because the auxiliary loads differ so much (a Tasmanian berry packer at 4 °C vs a Queensland avocado packer at 14 °C).

Flavorite and Perfection Fresh — single-site scale

Flavorite operates Australia's biggest single glasshouse footprint at Warragul VIC and Katunga VIC. The auxiliary scope includes packing sheds at 12–14 °C, cold storage at 4–6 °C (for ripening-stage product), ripening rooms for banana side-business, fertigation, pesticide mix and amenity. The Katunga site runs biomass-supported heating with flue-gas CO₂ reuse — one of the larger biomass installations in Australian protected cropping.

Perfection Fresh operates a more geographically distributed portfolio — Tatura VIC, Mareeba QLD and Carnarvon WA — with each site running its own auxiliary scope. The Carnarvon WA site is coastal salt-spray exposed and runs 316 stainless across the auxiliary HVAC envelope. The Mareeba QLD site has the highest ambient humidity exposure (chronic 75 % RH outdoor) and runs the most aggressive condensation-management protocols.

Boomaroo Nurseries — the propagation-only model

Boomaroo Nurseries at Lara VIC is Australia's biggest commercial wholesale propagator. The site has minimal cold-storage scope — propagation outputs are despatched fresh to grower customers within 1–3 days of order — but has the most demanding propagation, tissue culture and shipping-prep HVAC scope on the Australian protected cropping landscape.

The Lara site runs tissue culture at ISO 14644 Grade C, multiple propagation houses at 22–28 °C / 85–95 % RH, mother-plant nurseries with tight pest exclusion, hardening-off zones for transitioning seedlings to outdoor conditions, and a despatch zone at 8–14 °C for cold-pack truck loading. Auxiliary HVAC totals roughly 8,000–10,000 m² of conditioned space.

The Boomaroo model — propagation-only with no harvest scope — illustrates that auxiliary HVAC is the dominant scope at some operations even when there is no glasshouse climate envelope to engineer. Tissue culture and propagation alone justify a full SBAL-V plus SBTF-1500 plus SB-ZF1500 machinery package on the contractor side.

Sundrop Farms — the integrated arid-coastal case

Sundrop Farms at Port Augusta SA integrates solar-thermal desalination, 20-hectare glasshouse and packing/despatch under one operating envelope. The auxiliary scope must handle the arid-coastal exposure — 35 °C+ summer ambient, intense solar load, salt-spray from coastal proximity, and the integrated water-energy-CO₂ recovery from the solar-thermal field.

The auxiliary HVAC duct scope at Sundrop runs entirely in 304 or 316 stainless because of the salt-spray exposure. The packing shed operates at 13 °C dry-bulb under 25–30 °C ambient, with the cooling load dominated by envelope heat gain and door cycling. The site's integrated approach — desalinated water for evaporative cooling pad supply, solar-thermal heat for desalination process and for greenhouse warming, scrubbed offgas for CO₂ enrichment — places exceptional demands on duct sealing class and material selection.

Sundrop is the case study that demonstrates how the auxiliary HVAC scope scales when the operating environment is exceptional. Most Australian operators run more moderate climate envelopes; Sundrop's profile illustrates the upper-bound on materials and engineering rigour.

Mushroom auxiliaries — Costa Mushrooms and the high-humidity profile

Mushroom production is HVAC-distinct from vegetable greenhouse but shares some auxiliary scope. Costa Mushrooms at Mernda VIC and Ravenhall VIC run substantial packing, cold storage and despatch scope, alongside the mushroom-growing rooms themselves. The packing shed for mushroom runs at 2–4 °C cold-pack — much colder than tomato — and the auxiliary ducting handles 85–95 % RH continuously due to the wet product profile.

Material specification across Costa Mushroom auxiliaries is 304 stainless throughout, with TDF flange joints and full-perimeter gasket sealing. The AS 2543 mushroom shed construction standard cross-applies — hygienic surface requirements, smooth-bore duct interior, accessible for periodic sanitation. SBKJ machinery configured for stainless coil feed is the standard for fabrication.

Worked example — Houston's Farm Tasmania leafy-greens auxiliary scope

Consider a mid-scale leafy-greens packing operation similar in profile to Houston's Farm Tasmania. The auxiliary scope includes:

• Packing shed: 3,000 m² at 4–6 °C, 85–90 % RH, HEPA H10 makeup, dust extract on grading line.
• Pre-cooling room: 200 m² vacuum cooling chamber + 100 m² forced-air room.
• Cold storage: 1,500 m² at 0–2 °C, 95–98 % RH for leafy greens.
• Despatch: 500 m² at 4 °C with truck loading docks.
• Fertigation: 80 m² with acid handling.
• Pesticide mix: 40 m² with MSDS-specific extract.
• Workshop: 200 m² with welding LEV.
• Office: 250 m² commercial AS 1668.2.
• Amenity: 200 m² with shower/WC extract and drying room.

The HVAC duct material schedule:

• Galvanised G90: office, amenity, workshop (12 tonnes).
• 304 stainless: packing shed, cold storage, despatch, pre-cool (32 tonnes).
• 316 stainless: fertigation acid-exposed (3 tonnes).
• Polypropylene: pesticide mix extract (1.5 tonnes equivalent).

Total ductwork fabrication weight is roughly 50 tonnes, with stainless dominating. Fabrication on an SBAL-V configured for stainless coil at 16 m/min covers the bulk of the supply mains in 8–10 weeks single-shift. Spiral round branch on SBTF-1500 runs concurrently. Stainless plenum welding for cold-room evaporator plenums uses the SB-ZF1500. Flexible duct for small-bore propagation connections uses the SBLR-600.

SBKJ machinery recommendation — the auxiliary HVAC package

The four-machine package for fabricating the full auxiliary HVAC duct scope on a commercial glasshouse site:

SBAL-V auto duct line — the main supply duct workhorse

The Auto Duct Line SBAL-V is the workhorse for rectangular supply main duct across packing shed, cold storage, CA storage, ripening, tissue culture and propagation. Configured for stainless coil feed where 304 stainless is mandatory due to humid packing shed and cold room service.

Verbatim specification per the SBKJ catalogue:

• Model: SBAL-V-1250J or SBAL-V-1500J.
• Thickness: 0.5–1.5 mm.
• Max width: 1250 mm or 1500 mm.
• Forming speed: 16 m/min.
• Overall dimensions: 14000×2000×1800 mm or 14000×2200×1800 mm.
• Power: 87 kW.
• Machine weight: approximately 16 tons.
• Voltage: 380V / 50Hz / 3PH.
• Material capability: Galvanized steel, stainless steel, aluminium.
• Standards: SMACNA, EN 1505, EN 1506, ISO 9001:2015.
• Certifications: ISO 9001:2015, CE Marking.
• Warranty: 12 months.

For the auxiliary HVAC scope, the SBAL-V handles rectangular supply mains in 600–1,500 mm width — covering the bulk of packing-shed and cold-room main duct runs. The stainless-coil configuration is mandatory for any duct serving the packing shed envelope or cold storage rooms. View full SBAL-V product specification.

SBTF-1500 spiral tubeformer — for round branch ducts

The SBTF-1500 spiral tubeformer fabricates spiral lockseam round duct in the Φ80–Φ1500 mm diameter range — covering all the round branch ducting in the auxiliary HVAC scope (packing shed branch, cold-room return, propagation house supply, ripening room recirculation).

Verbatim specification:

• Diameter: Φ80–Φ1500 mm.
• Galvanized steel: 0.4–1.2 mm.
• Stainless steel: 0.4–0.8 mm.
• Strip width: Standard 137 mm.
• Cutting system: Saw Blade Cutting.
• Power: Mainframe 5.5 kW, Saw Blade 4 kW.
• Weight: 1700 kg.
• Dimensions: 2800×2100×1200 mm.

Spiral lockseam construction is mechanically strong and inherently sealed against air leakage at the pressure classes typical of auxiliary HVAC (250–500 Pa). The SBTF-1500 runs stainless feed with the same tooling as galvanised — the strip-width specification is unchanged.

SB-ZF1500 Automatic Stitchwelder — for stainless plenum welding

The SB-ZF1500 Automatic Stitchwelder handles longitudinal stitch welding of heavy-gauge stainless duct seams, spot welding of internal stiffeners and seam welding of round duct fittings — covering the stainless plenum welding scope for cold-room evaporator plenums, CA-storage gas-mixing chambers and tissue-culture autoclave exhaust trunks.

Verbatim specification:

• Thickness: 0.8–3 mm.
• Length: 100–1500 mm.
• Diameter: Φ150–Φ1500.
• Dimensions: 2500×1000×2350 mm.
• Voltage: 380V/50Hz/3PH.

Stitch-welded longitudinal seams on stainless duct deliver SMACNA Seal Class A leakage performance — required for CA storage at AS 4254 L1 leakage class and for tissue culture supply at ISO 14644 Grade C. The SB-ZF1500 sits adjacent to the SBAL-V on the workshop floor and handles the heavier stainless gauges (above 1.5 mm) that exceed the SBAL-V's standard envelope.

SBLR-600 flexible duct forming machine — for propagation and small-bore connections

The SBLR-600 handles small-diameter flexible ducting (Φ80–Φ600 mm) for propagation house connections, mother-plant nursery distribution, retail-side small-bore HVAC and short connection runs to grading machines.

Verbatim specification:

• Model: SBLR-600 (Double Working Stations).
• Diameter: Φ80–Φ600 mm.
• Material: Non-woven Fabric, PVC Film, Aluminum Foil.
• Foil thickness: 0.02–0.06 mm.
• Length: up to 36 m.
• Forming speed: 7.6 m/min.
• Cutting system: Fully automatic cutting.
• Power: 7 kW.
• Weight: 950 kg.
• Mainframe dimensions: 3500×1200×1810 mm.
• Voltage: 380V / 50Hz / 3PH.

Spark-resistant fixturing for CO₂ generator combustion flue

Where ducting is fabricated for the CO₂ generator room combustion flue — a Zone 2 hazardous-area classification due to LPG/natural gas exposure — SBKJ can configure spark-resistant fixturing on the SB-ZF1500 stitchwelder. The configuration uses non-ferrous tooling at all contact surfaces, intrinsically safe drive controls and remote-cycle operation. Spark-resistant fabrication is a project-specific configuration; contact SBKJ engineering for specification.

Total machinery package CapEx

The four-machine package (SBAL-V plus SBTF-1500 plus SB-ZF1500 plus SBLR-600) covers the full auxiliary HVAC duct fabrication scope for a commercial glasshouse site. Total CapEx is in the range of AUD 520K–680K depending on stainless coil configuration, voltage spec and tooling options. For HVAC contractors specialising in protected cropping auxiliary scope, this package supports 4–8 sites per year at single-shift operation, with payback in 4–7 years on contractor margin against project tender pricing.

Specifying for a glasshouse auxiliary project — working procedure

The 22-step HowTo procedure embedded in the schema above is the working specification flow we use with first-time glasshouse auxiliary customers. Compressed:

1. Inventory every auxiliary building on the site plan.
2. Define the produce profile — crops, peak harvest volume, season window, FSANZ classification.
3. Set packing shed envelope conditions per crop temperature requirement.
4. Size the packing shed cooling load — steady-state plus peak.
5. Specify pre-cooling capacity — the 5–10× spike.
6. Size cold storage envelopes at 0–4 °C and 4–8 °C as required.
7. Specify CA storage with N₂ supply and CO₂ scrubbing.
8. Specify ripening rooms with ethylene dosing and CO₂ scrubbing.
9. Plan tissue culture cleanroom per ISO 14644 Grade C.
10. Size propagation house at 22–28 °C / 80–95 % RH.
11. Specify pesticide mix and spray-prep room per AS 1940.
12. Plan pesticide storage shed per AS 1940 dangerous goods.
13. Specify fertigation room with acid handling.
14. Plan boiler house combustion air and flue.
15. Plan biomass boiler if applicable.
16. Specify CO₂ generator room with spark-resistant ducting.
17. Plan workshop and maintenance shed with LEV.
18. Specify office HVAC under AS 1668.2.
19. Plan worker amenity per V_p 10 L/s/person.
20. Plan visitor centre or retail if applicable.
21. Coordinate site-wide duct material schedule.
22. Specify SBKJ machinery and schedule fabrication.

The procedure takes 6–10 weeks of front-end engineering for a typical mid-scale build, and yields a full ducting takeoff, machinery specification and commissioning plan. SBKJ engineers support customers through this process at no charge for serious project enquiries.

Lead time and seasonal coordination

Auxiliary HVAC commissioning must align with the packing shed first-use date — the moment harvest moves from glasshouse to packing. Working backwards from that date:

• SBKJ machinery build time: 90–120 days from confirmed order.
• Sea freight to Australian ports: 35–45 days.
• Installation and commissioning at HVAC contractor's facility: 5–10 days.
• Ductwork fabrication: 8–12 weeks single-shift for a typical mid-scale site.
• Site installation and balance: 6–10 weeks coordinated with the building structure handover.
• Cold-room pull-down and validation: 2–3 weeks.
• HACCP commissioning and BRC pre-audit: 2–3 weeks.
• Pre-season trial run: minimum 1 week before first harvest.

Total elapsed time from confirmed order to packing-shed first-use is 9–12 months. Glasshouse customers planning their auxiliary build should engage SBKJ at least 12 months ahead of target first-use, with the order placed 6–8 months ahead.

Where SBKJ fits in the auxiliary supply chain

SBKJ Group is headquartered in Box Hill North, Victoria, and has supplied HVAC duct fabrication machinery into Australian protected cropping auxiliary projects through HVAC contractor partners since the early 2000s. Our position:

• We do not build packing sheds or cold rooms. Building structure is the domain of specialist construction firms — typically the same builder that builds the glasshouse but sometimes a different contractor where the auxiliary scope is large.
• We do not fabricate ductwork. Ductwork fabrication is the domain of HVAC contractors serving the protected cropping market.
• We supply the machinery that the HVAC contractor uses to fabricate the ductwork. SBAL-V auto duct line, SBTF spiral tubeformer, SB-ZF1500 stitchwelder, SBLR-600 flexible duct former, and supporting tooling.
• We provide engineering support to glasshouse owners and their HVAC contractors on duct specification, machinery sizing, materials selection and commissioning planning.

This positioning lets us work upstream with the glasshouse owner on the engineering specification, and downstream with the HVAC contractor on the machinery procurement. For Australian protected cropping auxiliary projects, the typical engagement is a five-way conversation between SBKJ engineering, the glasshouse owner, the HVAC contractor, the food-safety consultant and the cold-chain refrigeration specialist.

Frequently asked questions

What is the difference between the glasshouse climate envelope and the packing shed HVAC scope?

The glasshouse climate envelope is a partially open thermal envelope governed by the sun, glazing transmittance and plant transpiration — VPD-driven, 30–60 ACH at peak, pad-and-fan or fog cooling, CO₂ enrichment, and managed by a climate computer like Priva, Hoogendoorn or Ridder. The packing shed, by contrast, is a sealed temperature-controlled building under AS 1668.2 and FSANZ 3.2.2 with 12–18 °C dry-bulb, balanced positive pressure, HEPA H10 incoming air over grading lines, and dust extract on the grader brushing zone. The two scopes share a site but are different engineering disciplines and almost always use different mechanical contractors.

What temperature should an Australian fresh produce packing shed run at?

Packing shed temperature is governed by produce being handled and FSANZ 3.2.2 cold chain requirements. Tomato, capsicum and cucumber packing sheds run 12–14 °C dry-bulb at 60–70 % RH so that fruit core temperature does not drop below 8 °C (a chilling-injury threshold). Strawberry, raspberry and blueberry sorting lines run 8–12 °C cold-pack. Leafy greens packing runs 4–8 °C. HVAC holds room temperature within ±1 °C with sensible-only cooling load of 100–180 W/m² steady-state.

Why does the packing shed need to be positive pressure with HEPA-filtered incoming air?

Positive pressure prevents inward migration of insects, dust, mould spores and exterior contaminants every time a door opens. Most Australian fresh produce packers run at 15–25 Pa above corridor pressure under AS 1668.2, with HEPA H10 filtration on the incoming makeup. The H10 grade (>85 % efficiency at MPPS) meets BRC packed-produce surface inspection. Without positive pressure the shed becomes a Botrytis incubator within weeks.

What is a hydrocooler and how does it interact with the HVAC duct design?

A hydrocooler is a post-harvest pre-cooling device that flushes 0.5–2 °C chilled water over field-warm produce, dropping core temperature from 25–30 °C down to 4–6 °C within 5–15 minutes. The hydrocooler generates 30–50 kW of latent heat per cubic metre of chilled water flow, condensing onto every cold surface. Supply duct must be 304 stainless or fully sealed polyethylene-lined galvanised, with vapour-barrier exterior insulation 50 mm thick.

What standards apply to controlled atmosphere (CA) storage HVAC?

CA storage operates under AS 4326 cold chain HACCP and AS 5149 refrigeration safety. The atmosphere is regulated by Hort Innovation for apples and pears, with N₂ from a dedicated PSA generator reducing oxygen to 1.0–2.5 %, CO₂ elevated to 1.5–5 %, and a CO₂ scrubber holding setpoint. The HVAC duct system is sealed to L1 or L2 leakage class per AS 4254 — far tighter than normal cold-room ductwork — because the CA gas mix is expensive to maintain. Material is 304 stainless.

How is the tissue culture micropropagation lab built different from a packing shed?

Tissue culture is built to ISO 14644 Grade C (equivalent ISO 7 at-rest) — substantially tighter than packing-shed FSANZ requirements. 18–22 °C ±0.5 °C, 50–55 % RH, HEPA H13 ceiling filtration providing 20–30 ACH, terminal HEPA at every laminar flow hood face delivering ISO 5 Grade A flow, positive 10–15 Pa vs antechamber, dedicated autoclave steam exhaust at 50–80 m³/min. Stainless 304L throughout. The HVAC scope is closer to a pharmaceutical cleanroom than to anything else in agriculture.

Do I need a separate exhaust for the pesticide mix room?

Yes. The pesticide mix and spray-prep room operates under AS 1940 dangerous-goods storage, the Australian Pesticide Application Code and state WorkSafe regulations. Dedicated extract-only at 20–40 ACH continuous, MSDS-specific scrubber, polypropylene or FRP composite duct, bunded floor, eye-wash and emergency shower. Worker amenity is by full-face PAPR respirator and Tyvek coveralls; room HVAC is the secondary control.

What is the biggest HVAC mistake glasshouse owners make on their first auxiliary building?

Sharing duct material and pressure class between the packing shed and the glasshouse envelope. Glasshouse ducting is 250 Pa pressure class galvanised G90 sized for bulk air movement; packing shed ducting is 500 Pa sealed positive-pressure duct, often 304 stainless, with HEPA terminal filtration and tight leakage class. Trying to use one duct type for both ends up with a packing shed that fails BRC audit and a glasshouse that costs three times what it should.

What SBKJ machinery is recommended for fabricating glasshouse auxiliary HVAC duct?

For supply mains in 304 stainless: SBAL-V auto duct line with stainless coil configuration — 0.5–1.5 mm thickness, up to 1500 mm strip width, 16 m/min forming speed, 87 kW power, 16 tonnes machine weight, 380V/50Hz/3PH. For round spiral branch: SBTF-1500 covering Φ80–Φ1500 mm in galvanised 0.4–1.2 mm or stainless 0.4–0.8 mm. For high-pressure-class stainless plenum welding: SB-ZF1500 Automatic Stitchwelder at 0.8–3 mm thickness, 100–1500 mm length, Φ150–Φ1500 diameter. For propagation flexible duct: SBLR-600 covering Φ80–Φ600 mm. Spark-resistant fixturing available for CO₂ generator flue welding.

Get a glasshouse auxiliary HVAC machinery specification from SBKJ engineering →