Greenhouse and Protected Cropping HVAC Duct Guide — Sundrop Farms, Costa Group, Tomato/Cucumber, VPD Control

Why greenhouse HVAC is its own engineering discipline

If you have specified HVAC for a vertical farm, an indoor cannabis grow, a poultry shed or a commercial kitchen, none of those frameworks transfer cleanly to a greenhouse. Protected cropping is not a sealed building with controlled internals — it is a partially open thermal envelope governed by the sun, the structure's solar transmittance, plant transpiration, and the daily diurnal swing. The HVAC engineer's job is not to recreate a refrigerator; it is to take a structure that wants to overheat by 15–20 °C above ambient at midday and bleed that heat off cheaply, while protecting the canopy zone from VPD excursions that crash yield.

The first rule of greenhouse climate engineering is that natural light is the primary energy input, not lighting. Even high-tech facilities running supplemental LED at 200+ µmol/m²/s rely on the sun for the bulk of their daily light integral. This drives every downstream HVAC choice. You are not designing for a steady-state heat load like an office building or a vertical farm; you are designing for a sinusoidal load curve that peaks at noon, troughs at 4 a.m., and shifts seasonally from a winter heat-deficit problem to a summer heat-surge problem. The same facility that needs 100 W/m² of supplemental heat at 4 a.m. in July needs 600 W/m² of cooling capacity at 1 p.m. in January.

The second rule is that the greenhouse glazing is part of the HVAC system. Glass, polycarbonate twin-wall and double poly-film all transmit short-wave solar radiation and trap long-wave thermal re-radiation — the greenhouse effect. A clear glass Venlo at midday in Mildura concentrates 700–900 W/m² of solar load on the canopy, with the air gap between glazing and crop acting as a thermal accumulator. When ambient air is 35 °C, the unventilated greenhouse can hit 50 °C in fifteen minutes. The HVAC strategy must continuously dump that heat at the same rate the sun is delivering it, or the plants close their stomata and yield collapses.

The third rule is that the plants themselves are an active heat-mass-and-moisture transfer element. A mature tomato canopy in production transpires roughly 4–6 litres per square metre per day in summer, releasing 9–14 MJ/m²/day of latent heat. That latent load is doing free evaporative cooling in the canopy zone — but it is also raising humidity to fungal-disease territory. The HVAC engineer is not just moving heat; they are moving moisture, balancing transpiration against ventilation against fogging, and holding VPD inside the 0.4–1.0 kPa target band that separates a productive crop from a Botrytis outbreak.

This guide walks through the engineering choices for a protected cropping HVAC ductwork system: climate zoning, ACH calculation, cooling and heating strategies, CO2 enrichment, materials, pest exclusion, and the SBKJ machinery used to fabricate the supply mains, branch ducts and CO2 distribution headers. Costa Group, Sundrop Farms, Perfection Fresh, d'Vine Ripe, Flavorite and Sweeter Banana operate at this level of engineering specificity every day. So should your facility.

How greenhouse HVAC differs from vertical farming and indoor CEA

The most common engineering mistake we see in first-time protected cropping projects is treating the greenhouse like an indoor controlled-environment-agriculture (CEA) facility. They are not the same building physics problem. A side-by-side comparison clarifies why:

• Primary light source. Greenhouse: natural sunlight (with optional LED top-up). Vertical farm: 100% artificial. This drives the heat-load profile from sinusoidal-diurnal (greenhouse) to constant-flat (vertical farm).
• Heat surge profile. Greenhouse: sun-driven, peaking at noon, requiring 30–60 ACH peak cooling. Vertical farm: lighting-driven, constant when lights are on, typically 6–12 ACH.
• Evaporative cooling viability. Greenhouse: strong (open structure allows pad-and-fan to draw makeup air across wet pad). Vertical farm: weak (sealed envelope makes evaporative humidity uncontrollable, dehumidification load explodes).
• CO2 enrichment economics. Greenhouse: viable but leaky — enrichment ramps down when vents open. Vertical farm: highly viable, sealed envelope holds enrichment at 1,200+ ppm continuously.
• Pest exclusion difficulty. Greenhouse: hard, vents and openings are the entire ventilation strategy, requires fine insect mesh at every intake. Vertical farm: easy, sealed envelope and HEPA filtration.
• Climate computer scope. Greenhouse: must simultaneously modulate vents, screens, fogging, heating, CO2 and lighting against a moving solar target. Vertical farm: tighter setpoint band, simpler control loops.
• Energy intensity. Greenhouse: 8–12 kWh/m²/year electricity and 200–400 kWh/m²/year thermal in temperate climates. Vertical farm: 200–400 kWh/m²/year electricity and zero thermal (lighting waste heat covers heating load).
• CapEx per square metre. Greenhouse high-tech: AUD 600–1,200/m² for structure plus HVAC. Vertical farm: AUD 8,000–15,000/m² with full lighting and racking.

The implication is that greenhouse HVAC ductwork is generally larger in cross-section, lower in pressure class, and much more focused on bulk air movement than indoor CEA. Where a vertical farm might run 600 mm rectangular supply duct at 250 Pa pressure class, a 4-hectare tomato glasshouse routinely runs 1,200–1,600 mm round galvanised supply mains at 250–500 Pa, with vast extraction louvres at the far end of each bay rather than recirculating return ducts.

Greenhouse structure types — how the shell drives the duct design

The structural envelope determines solar transmittance, infiltration rate, openable vent fraction and thermal mass — all of which feed directly into HVAC sizing. Five structures dominate Australian protected cropping:

Dutch Venlo glass-house

The reference structure for high-tech production. Single or double-pane horticultural glass on a steel-and-aluminium frame, gutter-connected, with continuous roof vents on alternating bays and side-wall vents. Solar transmittance is high (88–92% PAR for single glass, 78–82% for double) and the structure supports heavy loads — climate computers, thermal screens, supplemental LED, irrigation pipework. Costa Group's high-tech facilities, d'Vine Ripe's premium tomato operations, and most large Sundrop-style integrated projects use Venlo construction. HVAC supply duct is typically routed along the gutter trusses, with branch take-offs into each bay.

Polycarbonate twin-wall

Multi-wall polycarbonate (10 mm or 16 mm twin-wall) on aluminium framing. Lower solar transmittance than glass (60–70% PAR) but higher thermal resistance (R-1.6 to R-2.5 vs glass R-0.9), making it more energy-efficient in cold-temperate climates. Common in Tasmania, Victorian high-country and southern New South Wales for berry and capsicum production. HVAC sizing reduces somewhat because the heat-surge is less severe under lower-transmittance glazing, but the heating load increases proportionally in winter.

Single-poly tunnel

The lowest-cost protected cropping structure. Polyethylene film stretched over hooped steel frames, anchored at the ground line. Single-layer film offers minimal thermal resistance, so heat loss at night is high. Common for berry crops (raspberry, blackberry), seasonal vegetables and ornamentals. HVAC is typically passive — roll-up side curtains and end-wall fans — with limited ducting. Costa Group operates extensive berry tunnels across regional Australia.

Double-poly tunnel

Two layers of polyethylene film with a 10–15 cm air gap maintained by a low-pressure inflation fan. The inflated air gap doubles the thermal resistance of single-poly. Common for capsicum, eggplant and warm-season crops in transitional climates. HVAC is more substantial than single-poly but typically still relies on natural ventilation supplemented by extraction fans rather than full ducted air distribution.

Gutter-connected high-tech

The most sophisticated configuration. Multiple Venlo or polycarbonate bays connected at gutter level into a single climate volume of 1–10 hectares. Allows uniform climate control across a large footprint and amortises the climate computer and thermal screen across a bigger area. Requires the most extensive HVAC ductwork — supply mains spanning hundreds of metres along the gutter line, branch take-offs into each bay, and integrated CO2 and fogging headers. This is where SBKJ machinery is most heavily specified: long runs of large-diameter galvanised supply main, fabricated on auto duct line, supplemented with spiral round branch lines.

The Australian protected cropping market — where this guide applies

Australia hosts the world's third-largest protected cropping industry by output value, after the Netherlands and Spain. Industry analyst estimates put the sector at roughly USD 4 billion annually, with strong concentration in tomato, cucumber, capsicum, leafy greens, berries and ornamentals. The sector has roughly tripled in scale over the last 15 years, driven by water efficiency advantages over field cropping (greenhouse hydroponic uses 90% less water per kilogram of produce), domestic supermarket demand for premium produce, and the closure of cheaper international supply chains during the pandemic.

The major Australian operators we encounter on protected cropping HVAC projects include:

• Costa Group — ASX-listed dominant producer of berries (raspberries, blackberries, strawberries, blueberries), tomatoes, mushrooms and avocados. Operates substantial protected cropping footprints in Victoria, Queensland and New South Wales, including large-scale glasshouse tomato facilities and extensive berry tunnel operations. The largest single private-sector consumer of protected cropping HVAC in Australia.
• Sundrop Farms — Port Augusta, South Australia. The 20-hectare integrated solar-thermal-desalination-greenhouse facility is one of the most engineering-distinctive protected cropping projects globally. Detailed case study below.
• Perfection Fresh Australia — major integrated grower-marketer producing tomato, cucumber, capsicum and salad greens for domestic supermarkets. Operates several high-tech glasshouse facilities including premium truss tomato operations.
• Flavorite — Victorian high-tech glasshouse operator, producing hydroponic tomatoes (cocktail, truss, gourmet), capsicum and mushrooms. Notable for early adoption of climate computer integration and CO2 enrichment.
• d'Vine Ripe — premium hydroponic truss tomato producer, known for tight VPD control and sophisticated CO2 dosing strategy. Their facilities are reference projects for high-grade ducting and climate-tight construction.
• Nature Fresh Farms Australia — North-American-linked operator producing premium tomato and pepper varieties under Dutch Venlo glasshouses. Brings North American operational practice into the Australian market.
• Sweeter Banana — Carnarvon, Western Australia. Banana production under polycarbonate and tunnel protection, exploiting the desert subtropical climate. HVAC is dominated by extraction cooling and fogging.
• Nu-Flora — Adelaide-based ornamentals producer, gerbera and cut-flower production under high-tech glass. Different VPD targets (tighter humidity control for cut-flower vase life) and lighter heat loads than fruit-vegetable production.

The geographical spread is broad — South Australia (Sundrop, Adelaide region), Victorian Goulburn and Mornington valleys (Flavorite, multiple Costa sites, Costa berry farms), Queensland Lockyer and Granite Belt (Perfection Fresh, several mid-scale operators), New South Wales central coast and Hunter Valley, Western Australia Carnarvon and Manjimup, and Tasmania Huon Valley. Each climate zone drives different cooling and heating priorities, but the engineering principles below apply across all of them.

Standards that apply to greenhouse HVAC

Australian protected cropping HVAC sits at the intersection of building services, agricultural process, and food-safety regulation. The standards that matter:

• AS/NZS 4254 — HVAC ductwork. The core ductwork construction standard for the project shell. Covers sheet thickness, joint configuration, hanger spacing and pressure class. SBKJ machinery is specified to AS/NZS 4254 tolerances as standard for Australian projects.
• AS 2543 — Mushroom shed construction. Mushroom-specific but extensively cross-applicable to high-humidity vegetable operations and pesticide-handling zones. Specifies hygienic surface requirements and cleanability.
• AHRI 880 — Air terminal units (fan coils). Covers fan coil unit performance certification used for under-bench heating and air distribution in many protected cropping facilities.
• ASHRAE 62.1 — Ventilation for acceptable indoor air quality. Applies to the staff-occupied portions of the facility — packing rooms, control rooms, amenity blocks. Does not apply to the growing zone, which is governed by horticultural climate-control practice.
• Australian Pesticide Application Code. Spray exhaust and chemical handling areas have specific ducting material and isolation requirements. Polypropylene or FRP composite duct is standard for spray-room exhaust.
• NCC (National Construction Code) Section J. Energy efficiency provisions apply to glazed structures above a certain footprint where they include conditioned non-growing zones.
• State WorkSafe regulations. Cover occupational exposure to pesticides, CO2 (asphyxiation risk in enriched zones), and confined space entry for inspection and maintenance.

Compliance is layered, not centralised. A high-tech glasshouse with a packing facility, spray room, CO2 enrichment and fogging system will trigger AS/NZS 4254 in the supply ducting, AS 2543 if it includes mushroom or high-humidity rooms, AHRI 880 in the fan coil performance, ASHRAE 62.1 in the packing area, the Pesticide Application Code in the spray exhaust, and WorkSafe rules in the CO2-enriched zone. The HVAC engineer must navigate all of them together.

The four climate zones inside a greenhouse

Climate computer manufacturers (Priva, Hoogendoorn, Ridder) all model the greenhouse as four functionally distinct zones, each with its own temperature, humidity and air-velocity targets. Understanding these zones is the foundation of HVAC duct layout.

Canopy zone (the leaves)

Where photosynthesis happens. The HVAC engineer's primary target. Temperature targets are crop-specific — tomato 22–26 °C day, 16–18 °C night; cucumber 24–28 °C day, 18–20 °C night; capsicum similar to tomato but slightly warmer; leafy greens 18–22 °C day, 14–16 °C night. VPD held at 0.4–1.0 kPa with crop-stage-specific tightening. Air velocity at canopy level should be 0.3–0.7 m/s — too still and you starve transpiration, too fast and you induce stress and mechanical damage. Most HVAC supply diffusers terminate above the canopy, with downward throw configured to bring fresh air to leaf level.

Root zone (the rockwool, coir or NFT channel)

Where water and nutrient uptake happens. Temperature targets are tighter than canopy — typically 18–22 °C year-round for hydroponic tomato, 20–24 °C for cucumber. Root zone temperature is governed primarily by irrigation water temperature and any heating mat or under-bench piping rather than by air HVAC, but air infiltration into the root volume can dehydrate substrate and stress roots. Some facilities run dedicated under-bench heating duct at low velocity to lift root-zone air temperature in winter without disturbing canopy.

Ambient air zone (the bulk volume)

The thermal accumulator. The greenhouse air mass acts as a thermal flywheel, smoothing the rate at which the canopy and root zones see external temperature swings. HVAC sizing must move enough air to keep ambient zone within the heat-rejection capacity of the cooling system at peak solar load. This is where the 30–60 ACH peak cooling number comes from.

Vent zone (the upper roof and side openings)

The interface with the outside. Roof and side-wall vents provide the bulk of passive ventilation and the entire forced-extraction path in mechanical systems. Pest exclusion is critical here — every vent and intake needs insect mesh sized to the target pest profile. The vent zone is also where heat rejected from cooling exits the structure, which means inadequate vent area caps the maximum cooling capacity of the system regardless of fan or pad sizing.

Cooling strategies — five tiers from passive to mechanical

Greenhouse cooling is a hierarchy of strategies, applied in combination based on climate, crop value and energy budget. Each tier delivers different ACH performance and below-ambient capability.

Tier 1 — Passive roof and side ventilation only

The cheapest cooling strategy. Continuous roof vents on alternating bays, opened by climate-computer-controlled rack-and-pinion drives. Side-wall louvres or roll-up curtains supplement at low level. Effective ACH is roughly 5–10 with full vent opening and a 2 m/s wind drive. No below-ambient capability — best case the greenhouse runs at outdoor wet-bulb on a still hot day, which is often above 30 °C in Australian summer. Suitable for low-value seasonal crops in moderate climates. Most single-poly tunnels operate this way.

Tier 2 — Forced mechanical extraction

Powered exhaust fans at one end-wall draw outside air through inlet louvres at the far end-wall. Air flows axially along the bay length. Achievable ACH is 20–40 depending on fan sizing. No below-ambient capability — temperature inside the bay tracks ambient closely, but uniformity is much better than passive ventilation alone. Common in mid-tier polycarbonate and double-poly facilities for capsicum, eggplant and warm-season vegetables. Duct integration is light — extraction fans typically eject through end-wall louvres directly to outside, with no real return-air ducting.

Tier 3 — Pad-and-fan evaporative cooling

The workhorse cooling strategy for high-value crops in dry climates. Wetted pads at one end-wall (typically corrugated cellulose, 100–150 mm thick), exhaust fans at the opposite end-wall draw air through the pad. The water evaporating off the pad surface depresses incoming air temperature by 2–5 °C below ambient, with the magnitude depending on outdoor relative humidity. ACH is typically 30–60. Highly effective in arid Australian climates (Mildura, Carnarvon, Port Augusta). Less effective in coastal humid climates (Brisbane summer, North Queensland) where wet-bulb depression is small. Sundrop Farms, Sweeter Banana and most premium tomato operations use pad-and-fan as the primary summer cooling.

Tier 4 — High-pressure fog/mist

Atomised water droplets injected into the canopy zone from overhead nozzles at 70 bar pressure (or higher). Droplet size is 5–15 µm, small enough to evaporate completely before settling on leaves. Performs evaporative cooling within the canopy itself rather than at the inlet. Achievable temperature depression is similar to pad-and-fan (2–5 °C below ambient) but is delivered uniformly across the entire bay rather than declining along the air path. Higher CapEx and more complex water-quality management (RO filtration mandatory to prevent nozzle clogging) but more uniform cooling. Used in d'Vine Ripe and several premium tomato operations.

Tier 5 — Mechanical refrigeration with fan-coil distribution

Full chiller plant feeding fan-coil units distributing chilled air to the canopy zone. Below-ambient cooling capacity unlimited by climate. Energy-intensive — typically 3–5x the energy cost of pad-and-fan. Reserved for the highest-value crops (some cannabis cultivation, premium ornamentals, seedstock production) or for facilities where wet-bulb cooling is inadequate due to humid climate. Fan-coil ducting is the most extensive HVAC fabrication scope on a greenhouse project — large-diameter insulated supply mains, branch ducts to each fan-coil, condensate drain piping, and return air collection.

Sizing the cooling load — a worked example

Consider a 1-hectare (10,000 m²) high-tech glasshouse in the Goulburn Valley, Victoria, growing truss tomato. Peak solar heat load through clear glass at midday in mid-January is 800 W/m² × 10,000 m² = 8 MW thermal. Plant transpiration handles roughly 25% of that latent load (free evaporative cooling at the canopy), leaving 6 MW sensible load to be removed by the HVAC system.

If the climate strategy is pad-and-fan at 5 °C wet-bulb depression delivering air at 25 °C against 30 °C target ambient inside the bay, the air mass flow required is:

m_dot = Q / (cp × ΔT) = 6,000,000 W / (1,005 J/kg·K × 5 K) = 1,194 kg/s

At standard air density (1.2 kg/m³), volumetric flow is 1,194 / 1.2 = 995 m³/s, equivalent to roughly 60 ACH at a 60,000 m³ structure volume (1 ha × 6 m mean height). This validates the 30–60 ACH peak number for high-tech pad-and-fan facilities.

The supply ducting carrying this air mass must move 995 m³/s. At a typical supply velocity of 8 m/s, the required cross-section is 124 m². Distributed across, say, 20 supply mains running gutter-line, that is 6.2 m² per main — translating to a 2,800 mm round equivalent or a 2,500 × 2,500 mm rectangular trunk. That is large duct, fabricated on an auto duct line capable of high panel widths and continuous coil feed. SBAL-V is the standard SBKJ tool here.

Heating strategies — winter is the other half of the problem

Australian protected cropping is dominated by cooling-driven design in summer, but winter heating in Tasmania, Victorian high-country, southern NSW and southern WA is a meaningful HVAC scope. The four heating approaches we encounter:

Hot-water under-bench piping

The reference heating method for high-tech production. 70 °C flow water circulates through smooth steel piping mounted under crop benches or in-row at canopy level. Direct radiative and convective heat transfer to the canopy and root zone. Typical capacity is 70–120 W/m² peak, sized for the coldest design night. Boiler is gas, biomass or electric (heat pump) depending on energy costs and decarbonisation strategy. No HVAC ductwork involved in the heat distribution itself, but the boiler plant typically requires combustion air and flue ducting.

Forced warm-air via fan-coil units

Fan-coil units with hot-water or electric resistance coils blow warm air through ducted supply to the canopy. Faster temperature recovery than under-bench piping (minutes vs hours) but less energy-efficient because warm air rises away from the canopy. Common as supplementary heating in shoulder seasons and in cooler operations like ornamentals and seedstock production. Fan-coil ducting is standard galvanised G90 supply duct with insulated lining.

Infrared overhead radiant

Gas-fired or electric radiant tubes hung above the canopy. Heat is delivered as long-wave infrared directly to leaf surfaces, bypassing the bulk air mass. Energy-efficient at low ambient temperatures because no air heating losses, but creates strong vertical temperature gradient in the bay. Less common in Australian protected cropping than in northern-hemisphere European operations.

Biomass boiler integration

Wood-chip or wood-pellet biomass boilers feeding hot-water distribution. Capital-intensive but low operating cost where biomass feedstock is local. Boiler plant requires substantial combustion-air ducting (typically 2–3 m³/s at boiler full load) and flue gas extraction. Common in Tasmanian and southern Victorian operations where local timber industry supplies biomass economically. The flue gas, after particulate scrubbing, can be redirected for CO2 enrichment supply — a CHP-equivalent integration that doubles the value of the heating fuel.

CO2 enrichment — the photosynthesis multiplier

Atmospheric CO2 averages around 420 ppm globally. C3 plants — including tomato, cucumber, capsicum, leafy greens and most berries — are CO2-limited at this level under high-light conditions. Enriching the canopy zone to 800–1,200 ppm during photosynthesis hours typically yields a 20–35% productivity gain, depending on crop and lighting conditions. CO2 enrichment is therefore standard in high-tech protected cropping economics.

Three CO2 supply approaches are standard:

Liquid CO2 vaporiser

Bulk liquid CO2 stored on site in a vacuum-insulated tank (typically 30–50 tonnes capacity for a 4-ha facility), vaporised through a heated heat exchanger and metered into the canopy zone. The simplest integration — no combustion engineering, no offgas scrubbing — but expensive at AUD 350–500 per tonne delivered. Used by virtually every high-tech facility under 5 hectares.

CHP burner offgas (combined heat and power)

Natural-gas-fired internal combustion engine driving a generator, with waste heat captured for greenhouse heating and offgas captured for CO2 enrichment. Offgas is roughly 8–10% CO2 by volume after combustion of natural gas. Requires NOx scrubbing (typically a wet scrubber with soda lime catalyst) and ethylene removal (potassium permanganate scrubber) before injection — ethylene at even low ppm levels causes severe damage to flowering crops. CapEx is high but operating cost is low because the same gas fuel produces electricity (sold to grid), heat (greenhouse heating) and CO2 (enrichment) — three revenue streams from one fuel input. Common in Dutch operations and increasingly adopted by larger Australian facilities.

Scrubbed flue gas from biomass boiler

Where a biomass boiler is already installed for heating, the flue gas can be scrubbed and redirected for CO2 enrichment. Wood combustion produces lower NOx than gas combustion but higher particulate, requiring more aggressive scrubbing. Common in Tasmanian and southern Victorian biomass-heated operations.

CO2 distribution ductwork

Two distribution methods: (1) Dedicated CO2 distribution line — a 100–150 mm polyethylene tube routed along each crop row at canopy level, with metered injection points every 5–10 m. Delivers CO2 directly into the canopy zone with minimal mixing losses. (2) Injection into the main HVAC supply duct upstream of diffusers — simpler installation but mixing losses are higher and bulk-air enrichment is less precise.

For approach (2), the supply duct must hold pressure tightly enough that CO2 leakage to outside is minimal. Standard practice is to spec the CO2-zone ducting at one pressure class above the rest of the supply system — typically 500 Pa where the rest of the system runs at 250 Pa. TDF flange with full-perimeter neoprene gasket is the industry-standard sealing method, fabricated on an SBKJ TDF flange line as part of the auto duct line build. Cross-leakage testing at 1.5x design pressure is standard commissioning practice.

Supplemental lighting and its heat impact

Supplemental lighting extends the daily light integral (DLI) in winter and on overcast days, lifting yield in seasons when natural light is limiting. Two technologies dominate:

High-pressure sodium (HPS) — legacy

1,000 W HPS fixtures emit roughly 500–600 W of usable photosynthetic light and 400–500 W of waste heat. Heat output is concentrated in long-wave infrared, much of which radiates downward to the canopy and is absorbed as direct sensible heat. A 200 µmol/m²/s HPS installation adds roughly 100 W/m² heat load to the cooling system, which is significant — it can shift the peak cooling load from January-only to a 9-month problem. HPS is being phased out in new high-tech operations.

LED — modern

Horticultural LED at 2.7+ µmol/J efficacy emits much less waste heat per photon delivered. A 200 µmol/m²/s LED installation typically adds 60–90 W/m² to the heat load — still meaningful, but 30–40% lower than equivalent HPS. LED also concentrates heat at the fixture body rather than radiating to the canopy, allowing some of the waste heat to be captured by water-cooled heat exchangers and redirected to root-zone or under-bench heating. Costa Group, d'Vine Ripe and most new-build high-tech facilities are LED-only.

Lighting heat is constant during operating hours, unlike solar heat which is sinusoidal. The HVAC system must handle solar peak plus lighting load on bright days when supplemental lighting is still running for early-morning DLI extension, and this combined peak typically governs the cooling sizing in dual-light facilities.

Materials selection — what to specify and why

Greenhouse HVAC ductwork operates in some of the more demanding service environments in commercial HVAC. Daily condensation cycles, periodic pesticide spray exposure, occasional CO2 enrichment, and 20+ year design lives all push material selection harder than office-building HVAC. The standard hierarchy:

• Galvanised G90 (275 g/m² zinc both sides) sheet steel — the workhorse for general supply duct in dry zones. Feeds directly into SBAL-V auto duct line tooling without modification. 20-year service life in sheltered greenhouse conditions. Acceptable for canopy supply where condensation is intermittent.
• Galvanised with polyethylene-lined interior — for high-humidity zones (above 80% RH for prolonged periods, common in cucumber and leafy greens). The polyethylene liner protects the zinc layer from chronic moisture exposure. Service life extends to 25+ years. Slightly higher fabrication cost but justified in chronic high-humidity service.
• Stainless steel grade 304 — for severe service: chronic 90%+ RH (mushroom rooms), pesticide spray zones, salt-air coastal facilities (Sundrop, Carnarvon). 30+ year service life. Higher capital cost but no chronic corrosion concern. Specified on a case-by-case basis where galvanised will not survive.
• Polypropylene (PP) — for pesticide spray exhaust ducts. Chemically resistant to most agricultural pesticides and fungicides. Lighter than steel and easy to clean. Limited to spray-room exhaust and chemical handling — not used for primary supply ducting because of fire-rating limitations.
• FRP composite (fibre-reinforced plastic) — for some chemical-resistant applications and for very long service lives in coastal or industrial-adjacent environments. Higher CapEx than galvanised, but can be specified for irreplaceable underground or buried sections where material longevity dominates economics.
• Aluminium — limited use in greenhouse HVAC. Soft and dent-prone for primary supply duct, but used for some ornamental and climate-screen integration where weight matters more than mechanical durability.

Material choice is also driven by surface cleanability. AS 2543 (mushroom shed) requires smooth-bore interior surfaces accessible for periodic sanitation. Galvanised duct meets this where grooved-seam construction is avoided in favour of TDF flange joints with smooth-bore internal surface. Pillow-edge longitudinal seams are preferred over lock-form seams for cleanability.

Pest exclusion — the underrated HVAC requirement

Insect intrusion is the single biggest disease vector in Australian protected cropping. Whitefly, thrips, aphids, spider mites and various lepidopteran pests can collapse a tomato or capsicum crop in two weeks if they breach the structure. Pest exclusion is therefore a primary HVAC design constraint, not an afterthought.

Insect screening at all intakes

Every air intake — pad-and-fan inlet, side-wall vent, roof vent gap, packing-room makeup air intake — needs insect mesh sized to the target pest profile. Mesh sizes:

• 0.6 mm (16 mesh) — coarse — excludes large insects, butterflies, moths, but allows whitefly and thrips passage. Suitable only as outer protection layer.
• 0.4 mm (40 mesh) — medium — excludes whitefly, most aphids and large thrips. Standard mesh for general protected cropping.
• 0.2 mm (60 mesh) — fine — excludes western flower thrips and most disease-vector insects. Required for high-value tomato, cucumber and ornamental operations.
• 0.15 mm (80 mesh) — very fine — excludes virtually all flying insect pests. High pressure drop requires upsized fan capacity. Used for premium operations and seed-stock production.

Crop Defenders and Phytotronics are the two specialist mesh suppliers most commonly specified on Australian projects. The mesh installation method matters as much as the mesh choice — a 60-mesh insect screen with a 5 mm gap at the top corner is a 5 mm gap, not a 60-mesh screen. Inspection and integrity testing on commissioning is essential.

Positive pressure at sensitive zones

Seed-stock zones, propagation rooms and clean propagation tunnels are typically held at 50–100 Pa above ambient via dedicated supply fans. Air leaks outward through any gap, preventing inward pest migration. The HVAC ducting feeding these zones must be sized for the pressurisation overflow plus normal supply, typically 20–30% above the climate-only requirement.

Double-door entry vestibule

Personnel and material entry is the single largest pest ingress path. A double-door vestibule with interlocked doors (only one door open at any time) and air shower or sticky-mat treatment between doors reduces ingress by 80–90%. The vestibule must be conditioned by its own small HVAC supply, ideally HEPA-filtered, with the supply ducted from the main greenhouse system or from a dedicated air-handling unit.

Tomato and cucumber high-tech case — the 4-hectare reference facility

The reference design we walk customers through is a 4-hectare (40,000 m²) gutter-connected high-tech glasshouse for hydroponic truss tomato, sited in temperate Australian conditions (Goulburn Valley or comparable). Key parameters:

• Crop: Truss tomato, hydroponic rockwool, single-truss training, 2.5 plants/m² density.
• Structure: Dutch Venlo glass, 6.4 m gutter height, 9.6 m ridge height, gutter-connected across 8 bays of 50 m × 100 m each.
• Annual yield target: 75 kg/m²/year (300 tonnes/ha/year) — premium production benchmark.
• VPD targets: 0.6–0.9 kPa daytime, 0.3–0.5 kPa overnight, with crop-stage adjustment.
• Air movement: Peak 30–50 m³/s total facility flow at maximum cooling demand. Supply mains running gutter-line.
• Cooling: Pad-and-fan primary at 30,000 m³/h per bay, fog supplementary.
• Heating: Hot-water under-bench piping, gas-fired condensing boiler, 100 W/m² peak capacity.
• CO2 enrichment: Liquid CO2 vaporiser, 35-tonne onsite tank, dosed to 900 ppm during photosynthesis hours.
• Lighting: Supplemental LED at 180 µmol/m²/s, top-light only, 16-hour photoperiod in winter.
• Climate computer: Priva or Hoogendoorn integration with sensor placements at canopy, root zone, ambient and outside.
• Thermal energy curtain: Aluminised polyester drawn closed at night, opened during photosynthesis hours.

The HVAC ducting scope for this facility includes:

• Eight gutter-line supply mains, 1,400–1,600 mm round equivalent, fabricated on SBAL-V auto duct line.
• Branch supply from each main into bay distribution headers, 800–1,000 mm round, fabricated on SBTF spiral tubeformer.
• Canopy-level distribution diffusers, sized for 0.5 m/s canopy velocity.
• End-wall extraction louvres with 60-mesh insect screening.
• Pad-and-fan supply distribution from inlet pads to the bay length.
• CO2 distribution headers — 100 mm polyethylene tube along each crop row, fed from the central vaporiser through a stainless-steel manifold.
• Fog distribution headers — 12 mm stainless steel tube at canopy level, with high-pressure nozzles every 4 m.
• Boiler combustion-air supply and flue extraction ducting.
• Packing-room and amenities HVAC — separate ASHRAE 62.1 compliant supply with conditioned makeup.

Total ductwork fabrication weight for the facility is roughly 60–80 tonnes of galvanised steel, plus 8–12 tonnes of insulation and lining. SBKJ machinery typical for the project includes one SBAL-V Auto Duct Line for the bulk of supply main fabrication, one SBTF spiral tubeformer for round branch ducting, and a TDF flange line for high-pressure-class joint preparation on CO2-enriched zones.

Berry production — Costa Group's tunnel-based operation

Berry production differs structurally and HVAC-wise from glasshouse vegetable production. Costa Group operates extensive blueberry, blackberry, raspberry and strawberry operations across regional Australia — much of it under polythene tunnel rather than glass.

Tunnel-based berry HVAC is typically passive — roll-up side curtains, end-wall fans, occasional fogging — with relatively limited ducting. The exceptions are premium hydroponic blueberry and raspberry operations under polycarbonate or glass, where the climate management approaches that of vegetable greenhouses. Key differences from tomato/cucumber:

• Lower VPD targets (0.4–0.7 kPa) — berries are more sensitive to humidity-driven fungal disease.
• Cooler temperature setpoints — blueberry production targets 20–24 °C day, 14–16 °C night.
• Chilling hour requirement for many berry varieties — winter cooling rather than heating, sometimes via mechanical refrigeration.
• Lower stocking density — typically 1–1.5 plants/m² versus 2.5 for tomato — meaning lower transpiration heat removal and greater reliance on mechanical cooling.
• Pollinator integration — bumblebee or honeybee pollinator hives inside the structure require pesticide-free zones and careful air-velocity control to avoid disturbing pollinator activity.

HVAC duct scope for premium hydroponic berry under polycarbonate is similar in principle to tomato glasshouse but at smaller scale per facility — typically 0.5–2 hectares versus 4–10 hectares for vegetable.

Cannabis cultivation in glasshouse — the Australian medical regulatory context

Australian medical cannabis cultivation operates under licence from the Office of Drug Control. A meaningful share of licensed production is conducted in glasshouses rather than indoor vertical farms — exploiting natural light to reduce energy cost while maintaining the security and traceability requirements of licensed cultivation.

Cannabis glasshouse HVAC differs from vegetable production in several specific ways:

• Light deprivation capability. Cannabis flowering requires a strict 12-hour dark period. Glasshouse operations install full blackout curtains drawn at sunset and opened at sunrise during flowering. The HVAC system must operate efficiently with no natural light input during flowering dark hours, including avoiding stratification and condensation under closed blackout.
• Tighter VPD control. Cannabis flowers are highly susceptible to powdery mildew and Botrytis, both VPD-sensitive. Targets are 1.0–1.4 kPa during flower (drier than vegetable production) and 0.6–0.8 kPa during vegetative growth.
• Higher CO2 enrichment levels. 1,200–1,400 ppm during photosynthesis is typical for cannabis, versus 800–1,000 ppm for tomato. Stronger ducting pressure-class spec follows.
• Ozone or UVC integration for odour and pathogen control. Some operators add ozone generation or UVC sterilisation to the HVAC return-air path. Material selection in those zones must be ozone-resistant — stainless steel preferred over galvanised.
• Activated-carbon exhaust scrubbing. Cannabis odour management is mandatory under most state environmental licences. End-of-line exhaust through carbon scrubber adds pressure drop and requires upsized extraction fans.
• Strict pest exclusion. Cannabis growers cannot use most conventional pesticides under therapeutic cultivation licences, making pest exclusion entirely physical. 80-mesh insect screening and double-door vestibules are standard.

The HVAC ducting for licensed cannabis glasshouse is typically a tighter spec — 500 Pa pressure class, full-perimeter gasket sealing, ozone-compatible materials in scrubbing zones — and lends itself to the higher-grade SBKJ machinery configurations: TDF flange standard, stainless-fed auto duct line where corrosive zones are present.

Sundrop Farms case study — solar-thermal-desalination integration

The Sundrop Farms facility at Port Augusta, South Australia, is the most engineering-distinctive protected cropping project we know of, globally. Commissioned in 2016, the 20-hectare integrated facility produces hydroponic tomato (originally for a long-term Coca-Cola Amatil truss tomato offtake contract) using a fully integrated renewable-energy and seawater-desalination system.

The integration architecture:

• Solar thermal field — 23,000 heliostats focusing on a 127 m central receiver tower, generating high-temperature thermal energy.
• Seawater desalination — solar-thermal heat drives multi-effect distillation, producing fresh water for irrigation, humidification and pad-and-fan cooling. Eliminates dependence on local groundwater.
• Greenhouse heating — recovered low-grade heat from desalination warms the greenhouse on cold nights and during winter.
• Pad-and-fan cooling — desalinated water feeds the evaporative cooling pads, depressing supply air temperature 4–5 °C below ambient on hot days. Port Augusta's arid climate makes pad-and-fan highly effective.
• CO2 enrichment — liquid CO2 supplemented by scrubbed offgas from the boiler when running on backup gas.
• Controlled-environment integration — climate computer modulates vents, screens, fogging, heating, CO2 and water dosing simultaneously against the facility's solar input and crop demand.

The HVAC ductwork scope at Sundrop is substantial. Twenty hectares of gutter-connected high-tech glasshouse requires kilometres of supply main, branch and CO2 distribution. The arid coastal location demands stainless-steel materials in the salt-spray zones and high-grade galvanised elsewhere. Pad-and-fan inlet and forced extraction at scale requires industrial-scale ducting fabricated on auto duct line — this is the kind of project profile where SBAL-V configuration to the buyer's coil specification is critical.

The Coca-Cola Amatil offtake contract anchored the project economics by providing a 10-year guaranteed offtake at a defined price, which in turn made the unprecedented capital investment in solar-thermal-desalination feasible. The facility is widely cited as a demonstration that solar-thermal water and energy integration can support large-scale protected cropping in arid coastal locations — a model relevant to many Australian regional sites including the Pilbara, Carnarvon, Pinnaroo, Robinvale and similar inland and coastal arid zones.

Mushroom production — separate engineering, related materials

Mushroom production is HVAC-distinct from vegetable greenhouse but shares some material and ducting fabrication overlap. Costa Group operates substantial mushroom production in Victoria, and several mid-scale operators serve regional markets. The defining characteristics:

• Extreme humidity. Mushroom growing rooms operate at 85–95% RH continuously. Galvanised duct degrades rapidly at this humidity; stainless steel grade 304 or polyethylene-lined construction is mandatory.
• CO2 management. Mushrooms produce CO2 through respiration. Mature flushes can push room CO2 to 5,000+ ppm if ventilation is inadequate, suppressing yield. The HVAC system runs continuous fresh-air injection and CO2-scrubbing extraction. Air change rates run 6–12 ACH continuously, much higher than vegetable greenhouse off-peak.
• Temperature uniformity. Mushroom mycelial growth requires 18–22 °C with very tight uniformity (±0.5 °C across the growing room). HVAC sizing oversizes the air movement to achieve this uniformity.
• AS 2543 compliance. Australian mushroom shed construction is governed by AS 2543, which specifies hygienic surface requirements and cleanability. Smooth-bore stainless duct with TDF flange joints (no internal protrusions) is standard.
• Pasteurisation cycle. Some mushroom rooms pasteurise the substrate in-situ at 60+ °C for 6–12 hours, then cool back to growing temperature. The HVAC system must withstand the pasteurisation temperature and rapid cool-down without damage.

The HVAC machinery profile for mushroom production tends toward stainless-fed auto duct line and stainless TDF flange. SBKJ configures stainless variants of SBAL-V and SBTF for mushroom and other corrosive-service applications.

Aquaponics — niche but growing

Integrated aquaponics — fish cultivation tank water recirculated to hydroponic vegetable beds, creating a closed-loop nutrient cycle — is a niche but expanding category in Australian protected cropping. Yarra Valley, Tasmanian and Western Australian operators run aquaponics at small-to-mid scale (typically 0.1–1 hectare).

HVAC implications:

• Higher humidity due to fish-tank evaporation. 70–85% RH continuously is typical, requiring upgraded duct material spec (polyethylene-lined or stainless).
• Ammonia management. Fish-tank ammonia requires careful ventilation to avoid stress on either the fish or the plants. HVAC integration must handle the ammonia-laden air at fish-tank zone separately from the canopy zone.
• Fish-tank temperature stability. Tilapia, barramundi and trout each have specific temperature preferences (24–28 °C, 26–30 °C, 12–18 °C respectively). HVAC must coordinate fish-tank water heating with greenhouse climate.

Aquaponics is small in absolute scale but a useful proving ground for closed-loop greenhouse engineering and growing rapidly as a high-value local-food category.

Energy efficiency — where the savings come from

Energy is the largest operating cost in protected cropping after labour. A well-designed HVAC system unlocks meaningful efficiency gains:

Combined heat and power (CHP)

Discussed above for CO2 supply. CHP integration reduces total facility energy intensity 25–40% versus a baseline of separate gas heating, grid electricity and liquid CO2. Capital-intensive — typical CHP unit for a 4-ha facility is AUD 800K–1.2M — but payback periods are 4–7 years at Australian gas and electricity prices.

Thermal energy curtain (energy screen)

Aluminised polyester thermal screens drawn closed at night reduce radiative heat loss from glazing by 40–60%. Reflective aluminium layer faces inward, reducing canopy radiative cooling to the night sky. CapEx is moderate (AUD 8–15/m² installed) and energy savings are 25–35% of heating energy in temperate climates. Standard installation in any high-tech facility.

Heat recovery from forced extraction

Air-to-air heat exchangers (typically aluminium plate or counterflow) recover 50–70% of the sensible heat in extracted air, preheating incoming makeup. Effective in winter when the bay is heated and the extracted air is warmer than incoming makeup. Less effective in summer when extracted air is colder than incoming makeup. Capital cost moderate, payback 5–8 years in temperate-climate facilities with significant winter heating loads.

Solar PV integration

Roof-mounted PV on adjacent shed structures offsets electricity demand from the grid. Greenhouse glazing itself is typically not PV-overlaid (the natural-light requirement is too high), but auxiliary buildings, packing rooms and parking shade structures often carry significant PV capacity.

Heat pump heating versus gas boiler

Air-source heat pumps with COP of 3.5–4.5 in temperate climates can replace gas boilers at 30–50% lower operating cost where electricity is renewable-sourced. CapEx is higher than gas boiler equivalent. Heat pump integration is rapidly growing in Australian protected cropping as electricity decarbonises and gas prices rise.

Demand-controlled CO2 dosing

Climate computer integration with CO2 sensing and ventilation modulation cuts CO2 wastage by 20–35% versus open-loop dosing. The control loop dampens dosing when vents open (CO2 would just leak out) and increases dosing when vents close (the enrichment is held).

SBKJ machinery for greenhouse projects

SBKJ machinery scope on protected cropping HVAC projects typically covers three tools:

SBAL-V auto duct line — for supply mains

The SBAL-V auto duct production line fabricates rectangular galvanised supply main duct in the 600–2,500 mm dimension range typical of large greenhouse projects. Continuous coil feed, automatic length cutting, integrated TDF flange forming, and seam closure yield duct ready for installation in single-pass production. For a 4-hectare reference facility, SBAL-V output of 1,500 m/shift is sufficient to fabricate the full supply-main scope in 4–6 weeks of single-shift operation. Stainless-fed variants are available for mushroom and corrosive-service zones. Read more about SBKJ auto duct lines.

SBTF spiral tubeformer — for round branch ducts

Round duct dominates branch supply and return-air ducting in greenhouse projects. The SBTF spiral tubeformer fabricates spiral lockseam round duct in the 100–1,500 mm diameter range, in galvanised G90, stainless 304 or aluminium. Continuous coil feed yields any-length duct without joint interruption. Spiral lockseam construction is mechanically strong and inherently sealed against air leakage at the lower pressure classes typical of greenhouse supply (250–500 Pa). Read more about SBKJ spiral tubeformer machinery.

TDF flange line — for tight pressure class

TDF (Transverse Duct Flange) is the industry-standard joint method for high-pressure-class supply duct, including CO2-enriched zones at 500 Pa. The TDF flange line forms the integrated flange directly at the duct ends during the auto duct line cycle, eliminating separate flange-bolting operations and yielding consistent gasket-faced joints. SBKJ TDF lines are configured to the project pressure class and gasket spec.

The full machinery package for a 4-hectare greenhouse HVAC fabrication scope, fabricated on-site by the buyer's HVAC contractor, is typically one SBAL-V auto duct line, one SBTF spiral tubeformer, and one TDF flange line — total CapEx in the range of AUD 480K–620K depending on configuration. For HVAC contractors serving the Australian protected cropping market, this is a 6–10 year payback set against project-by-project ductwork tender pricing.

Specifying for a greenhouse project — a working procedure

The 18–22-step HowTo procedure embedded in the schema above is the working specification flow we use with first-time greenhouse customers. The compressed version:

1. Define crop and growth-stage VPD targets.
2. Choose greenhouse structure type and confirm solar transmittance.
3. Map the four climate zones with temperature, humidity and velocity targets.
4. Calculate peak heat load (solar plus lighting plus process).
5. Calculate target ACH for each zone.
6. Size the cooling system — pad-and-fan, fog, mechanical or hybrid.
7. Size the heating system — under-bench piping, fan-coil, infrared or biomass.
8. Specify CO2 enrichment supply method and distribution.
9. Select duct materials by zone — galvanised, polyethylene-lined, stainless, polypropylene or FRP.
10. Specify pest exclusion mesh and entry vestibules.
11. Size main supply ducts and branch ducts.
12. Lay out branch ducts and diffuser placements.
13. Specify pressure class and sealing method (TDF flange standard).
14. Plan thermal energy curtain integration.
15. Specify climate computer (Priva, Hoogendoorn or Ridder).
16. Plan packing room and amenities HVAC distinct from growing zone.
17. Specify SBKJ machinery for the buyer's HVAC contractor.
18. Run CFD simulation of the canopy zone with all duct in place.
19. Plan installation sequence with greenhouse structure erection.
20. Schedule pre-season commissioning at least 4 weeks before crop transplant.

This sequence takes 6–10 weeks of front-end engineering for a 4-hectare reference project, 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 delivery — planning to commissioning

Greenhouse projects have non-negotiable seasonal commissioning windows. A facility planned to transplant tomato in late August needs HVAC commissioned by early August at the latest, which means installation complete by mid-July, machinery delivered by early-to-mid June, and machinery built and shipped by April-May. Working backwards from the crop calendar dictates the procurement timeline.

• SBKJ machinery build time — 90–120 days from confirmed order, for SBAL-V and SBTF configurations to project specification.
• Sea freight to Melbourne, Sydney or Brisbane — 35–45 days.
• Installation and commissioning at HVAC contractor's facility — 5–10 days.
• Ductwork fabrication for the project — 4–8 weeks single-shift, depending on project size.
• Site installation and air balance — 4–6 weeks, coordinated with greenhouse structure erection.
• Climate computer programming and calibration — 2–3 weeks.
• Pre-crop trial run — minimum 1 week of full diurnal cycle operation before transplant.

Total elapsed time from order to crop transplant is 8–10 months. Greenhouse customers planning their first protected cropping facility should engage SBKJ at least 12 months before the target transplant date to allow for engineering refinement, machinery configuration and procurement of supporting climate-control equipment.

Where SBKJ fits in the Australian protected cropping value chain

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

• We do not build greenhouses. Greenhouse structure erection is the domain of specialist horticultural contractors — most projects use Dutch, Spanish or Australian greenhouse-construction firms.
• 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. Auto duct line, spiral tubeformer, TDF flange line, and supporting tooling.
• We provide engineering support to greenhouse owners and their HVAC contractors on duct specification, machinery sizing, materials selection and commissioning planning.

This positioning lets us work upstream with the greenhouse owner on the engineering specification, and downstream with the HVAC contractor on the machinery procurement. For Australian protected cropping projects, the typical engagement is a four-way conversation between SBKJ engineering, the greenhouse owner, the HVAC contractor and the climate-computer integrator.

Frequently asked questions

What VPD range should a tomato or cucumber greenhouse target?

Vapour Pressure Deficit (VPD) targets vary by crop and growth stage. For tomato in production, target 0.6–1.0 kPa during the day and 0.3–0.5 kPa overnight. For cucumber, target 0.4–0.8 kPa during the day. Leafy greens and seedlings sit at the lower end (0.4–0.6 kPa). VPD outside these ranges either restricts transpiration (too low, fungal risk) or causes stomatal closure and yield loss (too high). Climate computers like Priva, Hoogendoorn or Ridder modulate ventilation, fogging and heating to hold VPD within the target band.

What air change rate is typical for a high-tech greenhouse?

Air change rates (ACH) for greenhouses depend on the cooling strategy. Passive ventilation (roof and side vents) delivers roughly 5–10 ACH effective, which is insufficient on hot summer days in most Australian climate zones. Forced extraction with mechanical fans achieves 20–40 ACH. Pad-and-fan evaporative cooling typically runs at 30–60 ACH to keep wet-bulb depression effective along the air path. CO2-enriched zones run at the lower end (10–20 ACH) to retain enrichment cost-effectively, with bypass dampers for emergency overheat conditions.

What duct material should I specify for a high-humidity greenhouse zone?

For general supply duct in dry zones, galvanised G90 sheet steel (275 g/m² zinc both sides) is the standard choice and feeds directly into SBAL-V auto duct line tooling. For high-humidity zones (above 80% RH for prolonged periods), polyethylene-lined galvanised duct or stainless steel grade 304 is the durable choice. Pesticide spray exhaust ducts should be polypropylene or FRP composite. Pure galvanised duct in chronic 90%+ RH conditions corrodes within 5–8 years; spec the right material upfront and you gain a 20-year service life.

How do you handle CO2 enrichment in greenhouse HVAC?

Two common approaches: dedicated CO2 distribution line (4–6 inch polyethylene tube along each crop row) tapping from a liquid CO2 vaporiser; or injection into the main HVAC supply duct upstream of the diffusers. For combined heat and power (CHP) installations, scrubbed burner offgas can supplement liquid CO2 — but offgas requires NOx and ethylene removal before injection. Target enrichment is 800–1,200 ppm during photosynthesis hours, dropped to ambient (~420 ppm) when vents open. Pressure class on CO2-enriched supply duct should be one class above standard for tight sealing — TDF flange with full-perimeter gasket is standard.

What standards apply to Australian protected cropping HVAC?

AS/NZS 4254 governs general HVAC ductwork construction for the project shell. AS 2543 covers mushroom shed construction (relevant for mushroom growers and cross-applicable to high-humidity vegetable rooms). AHRI 880 applies to fan coil units used for heating and air distribution. ASHRAE 62.1 ventilation standards apply where greenhouses include staff workspaces or packing rooms. Pesticide application and spray exhaust are governed by the Australian Pesticide Application Code and state-level WorkSafe regulations. SBKJ machinery is specified to meet AS/NZS 4254 tolerance and pressure class requirements as standard.

Did Sundrop Farms really use desalination for a greenhouse cooling system?

Yes. The Sundrop Farms facility at Port Augusta, South Australia integrates solar-thermal seawater desalination with a 20-hectare greenhouse for hydroponic tomato production. The solar thermal field heats seawater for distillation, supplying fresh water for irrigation and humidification, while the recovered low-grade heat warms the greenhouse on cold nights. Desalinated water also feeds the evaporative cooling pad system. Coca-Cola Amatil signed a long-term offtake contract for the truss tomato output at facility commissioning. The project demonstrated that solar-thermal water and energy integration can support large-scale protected cropping in arid coastal locations.

What is the typical lead time for a greenhouse HVAC duct production line?

From a confirmed SBKJ order, build time is 90–120 days depending on configuration. Add 35–45 days sea freight to most Australian east-coast ports (Melbourne, Sydney, Brisbane), and 5–10 days for installation and commissioning. Total elapsed time from purchase order to first production duct is typically 4.5–6 months. For greenhouse projects with seasonal commissioning windows (commission before late-spring heat surge), plan to place the order at least 8 months before crop transplant date.

How energy-efficient can a modern greenhouse HVAC system be?

Combined-heat-and-power (CHP) integration with a thermal energy curtain (energy screen) and heat-recovery from forced extraction can reduce greenhouse heating energy by 30–50% versus a baseline gas-heated facility. CHP supplies electricity to grid (or to supplemental LED lighting) while waste heat preheats the climate zone and CO2-rich offgas (after scrubbing) supplements enrichment. The thermal screen (typically aluminised polyester, drawn closed at night) reduces radiative heat loss by 40–60%. Modern Dutch Venlo glass-houses operating in cool-temperate climates achieve 8–12 kWh/m²/year electricity and 200–400 kWh/m²/year thermal — well below indoor vertical farms.

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