Utility-Scale Solar Farm, BESS & Inverter Station HVAC Ductwork — An Australian Renewables Build Guide

1. The Scale of the Australian Renewables Build, and Why Ductwork Matters

By the middle of this decade Australia is on track to commission more utility-scale renewable generation and storage than any comparable economy on a per-capita basis. The Australian Energy Market Operator's Integrated System Plan calls for roughly 28 gigawatts of large-scale variable renewable energy and 22 gigawatts of dispatchable storage by 2030. To put that into mechanical contractor terms: every gigawatt of solar PV adds 200 to 250 inverter stations of various sizes; every gigawatt-hour of battery storage adds a compound of 20 to 80 BESS containers plus control, switching and transformer buildings; and every connection point requires an MV substation building with its own ventilation envelope. Across the National Electricity Market this is somewhere between four and eight million square metres of new ancillary building floor area between now and the end of the decade — most of it air-conditioned, almost all of it mechanically ventilated, every cubic metre of supply and return air moving through formed sheet duct.

The HVAC industry tends to underweight this segment because the buildings are small relative to commercial towers. A typical 100 MW solar inverter building is 120 to 200 square metres. A BESS control building might be 40 to 60 square metres. A switchroom is often a kit-of-parts modular unit no bigger than two shipping containers stitched together. But the count is enormous. A single 720 MW solar farm such as New England Solar will land with 160 to 200 inverter buildings on a site that spans several thousand hectares. A 2.5 GWh battery like the Waratah Super Battery has dozens of MV switchrooms and a handful of larger control buildings sprinkled across a precinct. Multiply that across the projects under construction or in late-stage planning — Western Downs, Wallerawang, Liddell, Eraring, Bungala, Hornsdale, Victorian Big Battery, Capital Wind Farm storage and the hundreds of smaller hybrid plants approaching financial close — and the ductwork demand becomes visible.

The catch is that this is not commercial HVAC. The buildings are unmanned for 95 percent of their operating life, sited in some of the hottest inland conditions on the continent, exposed to dust, smoke from bushfires, salt at coastal sites, and high humidity in northern projects. The mechanical scope is dominated by equipment heat rejection rather than human comfort. And the operating consequence of HVAC failure is not occupant discomfort — it is generator derate, missed dispatch, NEM frequency events and, in the worst case, AEMO non-conformance under the Generator Performance Standard. The cost of a hot inverter day is measurable in dollars per megawatt-hour and reported on a five-minute settlement cycle. There is no other sector where HVAC underperformance has such a clear and direct line to revenue.

This is why SBKJ Group treats the renewables segment as a distinct vertical with its own ductwork specification. The material grades, pressure classes, joint details, support arrangements, fire compartmentation and electrical interfaces all differ from a commercial office or shopping centre fit-out — and they differ for good engineering reasons that we will work through in the sections below.

2. The Regulatory and Standards Landscape

A renewables project in Australia sits at the intersection of the National Electricity Rules, the Building Code of Australia (now the National Construction Code), the relevant state planning and EPA frameworks, and an increasingly international set of OEM and insurer-driven standards. For HVAC ductwork the load-bearing standards are the ones below.

2.1 AEMO Generator Performance Standard

The AEMO GPS is the connection contract for any generator above 5 MW on the National Electricity Market. It does not specify ductwork directly — but it specifies the operating envelope the plant must demonstrate. Schedule 5.2 of the National Electricity Rules sets minimum access standards for active and reactive power capability, voltage and frequency ride-through, fault response and power quality. Every one of those obligations is a thermal obligation in disguise. Inverters that derate above 40 degrees Celsius cannot meet active power capability at 45 degree Celsius ambient unless the building envelope holds them below their derate threshold. Battery management systems that throttle above their cell temperature window cannot demonstrate the GPS dispatch requirements unless the cooling system works through summer peaks. AEMO's R0 to R2 commissioning hold points test all of this. Mechanical contractors who think their scope ends at "the building is air-conditioned" rapidly discover that the AEMO connection engineers think otherwise.

2.2 AS/NZS 3000 Wiring Rules

The Wiring Rules govern every electrical interface in the building — the supply to fans and air handlers, the bonding of metal duct to the building's equipotential earth reference, the segregation of HVAC cabling from MV power and protection wiring. Of particular relevance for ductwork is Section 5 (earthing arrangements) and Section 7 (special electrical installations). Metal ductwork in an MV switchroom must be bonded at intervals no greater than 6 metres and cross-bonded at every flexible coupling. Failure to do this creates a step-touch potential hazard during fault events and shows up in the energisation safety case.

2.3 AS 60079 — Hazardous Areas

The AS 60079 series adopts IEC 60079 for explosive atmospheres. On modern lithium-ion BESS sites it has limited application because integrated containers are factory-classified by the OEM and the gas-rich envelope is contained inside the container shell. However, legacy lead-acid battery rooms — still present in older substations being retained as part of grid-forming hybrid projects, and in some operator amenity blocks — must be treated as Zone 1 or Zone 2 hazardous areas during charging. Ductwork penetrations into those rooms require purged enclosures or explosion-proof fittings, and exhaust ductwork must be electrostatically bonded along its length. SBKJ supplies AS 60079-compliant duct fittings where the project envelope requires them; in practice for new-build lithium projects the requirement is rarely triggered.

2.4 NFPA 855 — Stationary Energy Storage Systems

NFPA 855 is a North American consensus standard for stationary energy storage systems, but it is increasingly referenced in Australian BESS projects because international insurers, OEM warranty terms and some state planning conditions cite it. The mechanical implications are significant: minimum separation distances between BESS units, requirements for deflagration venting, mechanical ventilation rates for indoor storage and fire-rated separations between BESS rooms and adjacent spaces. Where NFPA 855 applies, ductwork crossing the BESS room boundary must be rated for the relevant fire compartmentation, fire dampers must be provided at the boundary, and the BMS must integrate with the fire indicator panel to shut HVAC down on an off-gas detection signal. NFPA 855 also drives a particular detail: exhaust ductwork from BESS spaces must be sized to handle the deflagration vent flow without imposing back-pressure that would inhibit venting — this is a calculation few mechanical contractors are used to.

2.5 AS 1668.1 and AS 1668.2 — Mechanical Ventilation

AS 1668.1 (fire and smoke control in buildings) sets the requirements for smoke control systems, fire dampers and the integration of HVAC with the building's fire safety strategy. For unmanned solar and BESS ancillary structures the AS 1668.1 obligations are usually limited to fire-rated penetration sealing at compartment boundaries and fire dampers in any duct crossing a fire-rated wall. AS 1668.2 (mechanical ventilation) is the workhorse standard for outside-air provision, exhaust rates, contaminant control and toilet and amenity ventilation in any portion of the project where staff are present — the operations and maintenance building, the security gatehouse, the control room.

2.6 AS/NZS 4254 — Ductwork Construction

AS/NZS 4254 Part 1 (low pressure) and Part 2 (medium and high pressure) are the construction standards SBKJ ductwork must satisfy. Part 1 covers duct material thickness selection, reinforcement spacing, joint type, sealant class, hanger and support arrangements for systems operating at or below 500 Pa static pressure. Part 2 extends the requirements for systems above 500 Pa, with stricter sealing class and reinforcement requirements. Most ancillary structure ductwork on a renewables project sits in the low-pressure category, but the supply runs from rooftop or skid-mounted DX units to inverter rooms often need to be rated for medium pressure due to the long external runs and the high airflow velocities required to limit duct cross-section in compact buildings.

2.7 AS 60529 — IP Rating

External duct terminations, weather louvres, intake hoods and exhaust cowls must satisfy AS 60529 ingress protection ratings appropriate to their location. Typical specifications are IP44 for sheltered roof-mounted equipment, IP55 for ground-level external louvres exposed to dust, IP65 or IP66 for terminations exposed to direct hose-down or coastal salt spray.

2.8 AS 5034 — Lead-Acid Battery Installations

For the legacy lead-acid sites that remain in service alongside lithium-ion replacements, AS 5034 governs ventilation of stationary battery rooms. The standard requires sufficient hydrogen exhaust to maintain hydrogen concentration below 1 percent by volume — typically 2 to 4 air changes per hour during equalisation charging. The exhaust ductwork must be non-sparking, terminate above the building roofline and be electrostatically bonded.

2.9 NFPA 850 — Utility Electrical Generating Plants

NFPA 850 is a recommended practice for fire protection at electrical generating plants. For oil-filled transformer compounds the standard guides ventilation rates, oil containment integration, and the separation of transformer ventilation from adjacent occupied space ventilation. While not mandatory in Australia, AEMO-connected projects under international insurance often adopt NFPA 850 alongside the AS standards.

3. Solar Inverter Rooms — The Workhorse of Utility-Scale PV

The inverter is where DC photovoltaic current becomes AC grid current, and it is where the largest single concentration of heat on a solar farm appears. Modern central inverters in the 3 to 5 MW class — SMA Sunny Central UP, Sungrow SG3600UD, Power Electronics FS3500K, Hitachi Energy PVS980 — operate at peak conversion efficiencies of 98.5 to 99.0 percent. At full rated output this means 1.0 to 1.5 percent of throughput is rejected as heat. For a 4.4 MW inverter that is 44 to 66 kW of continuous heat dissipation, all of it leaving the inverter chassis through forced-air outlets.

3.1 Heat Load and Air Change Rate

An inverter station building housing two 4.4 MW central inverters faces a continuous equipment heat load of approximately 90 to 130 kW. Solar gain through the building fabric adds another 10 to 20 kW in the worst-case afternoon hour. Lighting and ancillary equipment contribute a few kW. The total cooling load is dominated almost entirely by the inverter heat rejection, and the cooling strategy must remove this heat while maintaining the air at the inverter intake below the manufacturer derate threshold — typically 40 to 45 degrees Celsius.

The fundamental design choice is between full air-conditioning of the building (DX or chilled water) and a ventilation-only strategy that simply moves outside air through the building fast enough to limit internal rise. The economics generally favour ventilation-dominated designs because the inverters are tolerant of high ambient as long as the rise above outside air is controlled. SBKJ typical practice for inland Australian inverter stations is direct evaporative cooling for projects sited above 35 degrees latitude south where summer wet-bulb temperatures permit, or DX make-up cooling for coastal and humid sites where evaporative is ineffective.

Air change rates are sized to maintain a 5 to 8 Kelvin rise from outside air to building return. At 6 to 8 ACH the duct cross-section becomes substantial — for a 200 square metre inverter building with a 5 metre ceiling, 8 ACH is 8000 cubic metres per hour, which at typical low-velocity duct sizing requires a 900 by 600 mm supply trunk feeding four to six branch take-offs. This is where the SBAL-V auto duct production line earns its keep: the long straight runs of rectangular galvanized supply duct are the highest-volume single item in the inverter station bill of quantities.

3.2 Cooling Equipment Selection

For coastal and humid sites the standard package is rooftop or skid-mounted DX cooling — typically 30 to 80 kW units in N+1 redundant configuration. The supply duct runs from the rooftop unit down through a roof penetration into the building, distributes along a central spine, and returns to the unit via a parallel return path. For inland sites with low summer wet-bulb temperatures (below 22 degrees Celsius wet-bulb at the 1 percent exceedance level), direct evaporative coolers deliver substantially lower energy consumption and simpler maintenance. Indirect evaporative systems sit between the two — they avoid adding moisture to the supply air but extract less heat per cubic metre.

A common detail SBKJ engineers in collaboration with EPC mechanical leads is the "summer-winter" damper arrangement, where evaporative cooling is bypassed in winter and the building is simply ventilated with cooler outside air. The bypass duct shares the same SBAL-V galvanized trunk but routes through a motorised damper assembly that closes the evaporative path on a building automation controller signal. This is a small detail in capital cost terms but pays back substantial water savings on inland sites where water is not free.

3.3 Inverter Room Pressurisation

Slight positive pressurisation of the inverter room — typically 5 to 15 Pascals above outside air — keeps dust out. Australian utility-scale solar sites accumulate enormous quantities of fine red dust during summer, and inverter air filters that have to deal with infiltration through every door seal and cable penetration choke much faster than filters in a slightly positive building. The supply system is sized to deliver 5 to 10 percent more air than the extract system, with the differential exhausted through automatic relief dampers at the door head. This is a detail that affects filter change frequency and therefore operational maintenance cost over the asset life.

3.4 Material Grade and Joint Detail

Inverter rooms have benign internal atmospheres — they are dry, dust-controlled and free of corrosive contaminants. Z275 galvanized sheet to AS/NZS 4254 in 0.6 to 1.0 mm thickness is the cost-effective specification for the bulk of the supply and return runs. Joints are TDF (transverse duct flange) for the larger sections and Pittsburgh seam for the smaller branch take-offs, sealed to AS/NZS 4254 Class C. The duct sits on threaded rod hangers from the building purlins, with proprietary trapeze brackets at every 2.4 metres. Penetrations through the building envelope are fitted with weatherproof flashings and weather louvres rated to IP55.

3.5 Acoustic Considerations

Inverter stations are unmanned, so internal acoustic comfort is not a driver. The driver is the external noise emission to the project boundary. Australian state EPA conditions typically set environmental noise limits at the nearest residential receiver of 35 to 45 dBA at night, 40 to 50 dBA during the day. Inverter cooling fans, exhaust louvres and rooftop DX units all radiate. SBKJ ductwork specifications include in-duct acoustic attenuators at the supply discharge and at the exhaust intake, sized to deliver insertion loss of 10 to 15 dB across the 250 to 2000 Hz octave bands. The internal acoustic absorption is typically lined with non-friable mineral wool to AS/NZS 4254 erosion class A, faced with perforated metal to prevent fibre release into the airstream.

4. BESS Containers, Control Buildings and Ancillary Structures

Battery energy storage at utility scale is dominated by integrated container products from a handful of suppliers — Tesla Megapack, Wartsila GridSolv Quantum, Sungrow PowerTitan, BYD MC Cube, CATL EnerC, Fluence Cube, Hitachi Energy e-mesh PowerStore. Every one of these products ships with sealed factory-integrated liquid cooling, redundant pumps, factory-balanced glycol loops and self-contained ducted air management within the container envelope. From a ductwork contractor's point of view the cells themselves are not in scope. The work is in the structures around the containers.

4.1 The Container Itself — What Is and Is Not in Scope

The integrated BESS container is supplied as a turnkey enclosure. The OEM is responsible for thermal management of the cells under their warranty, the fire detection and suppression integrated into the container, the deflagration vents on the roof or end walls, and the secondary glycol heat exchanger that rejects waste heat to outside air. The mechanical contractor's interface ends at the building services connection: cooling water (if liquid cooling rejects to a site loop), power, control signals, and any deflagration vent exclusion zones around the container that affect siting of adjacent buildings.

However, a few projects opt for "walk-in" BESS architecture rather than integrated containers — a purpose-built MV battery building with racks of cells installed inside a conventional structure. Walk-in designs are less common at utility scale because integrated containers are faster to commission and easier to warranty, but they appear on some EPC scopes (particularly older designs and a few specialist applications). For walk-in BESS the ductwork scope is similar to the integrated container's internal ducting — multiple zones, redundant supply and return, deflagration venting, fire compartmentation between zones. SBKJ engineers walk-in BESS ductwork only where the project's electrical OEM specifies it, because the design constraints are tight and the standards interpretation is complex.

4.2 The BESS Control Building

Every BESS compound has a control building housing the SCADA gateway, the battery management system control hardware, the protection relays, the operator interface workstation and the communications equipment. This is a small building — typically 40 to 80 square metres — but it is the brain of the storage asset and must be air-conditioned to maintain electronics within their operating window through summer peaks.

Cooling load is dominated by equipment heat dissipation (typically 8 to 20 kW) and solar gain through the envelope (4 to 12 kW depending on roof construction). The cooling strategy is invariably DX, often with a small skid-mounted or split unit serving the building. The ductwork is short, simple and low-pressure — a rectangular supply trunk along the ceiling spine with grilles into each zone, a return air plenum, and a small outside-air make-up duct to satisfy AS 1668.2 occupant ventilation rates when staff are present for maintenance. The building is normally unmanned and operates on lower outside-air settings, ramping up automatically when occupancy is detected.

4.3 The MV Switchroom

The MV switchroom houses the medium-voltage switchgear that interconnects the BESS containers, the inverter blocks, the auxiliary transformer and the high-voltage substation. Switchgear is typically air-insulated 11 to 33 kV in metal-clad cubicles, with arc-resistant construction to AS/NZS 62271. The room is sized for the OEM switchgear envelope plus maintenance access, typically 100 to 250 square metres.

The HVAC requirements for an MV switchroom are: maintain ambient within the switchgear thermal envelope (usually 5 to 40 degrees Celsius), control humidity to below 70 percent relative humidity to prevent condensation on busbar insulators, and maintain slight positive pressurisation to keep dust out. Air change rate is typically 4 to 6 ACH, with DX cooling sized to handle equipment heat dissipation (3 to 8 kW depending on switchgear count and rating) plus solar gain.

The two engineering details that matter most in switchroom ductwork are EMC segregation and arc-flash containment. Metal ductwork running parallel to MV busbars can couple capacitively to the busbars during faults, creating step-touch potential issues for maintenance personnel. SBKJ practice is to maintain a minimum 600 mm clearance between any metal duct and the busbar zone, bond the duct to the equipotential earth at every 6 metre interval, and use flexible non-metallic transitions where ducting crosses a busbar chamber. For arc-flash containment, ductwork penetrations into the switchroom must be fitted with intumescent seals rated to the same time-current curve as the building fire compartmentation, and any return air paths must avoid direct line-of-sight from a switchgear arc-vent location.

4.4 The Auxiliary Transformer Compound

Every BESS site has at least one auxiliary transformer that supplies station service — the power to fans, pumps, lighting, control systems and BESS thermal management. Most utility-scale BESS sites also have one or more grid-interface transformers that step up the inverter output to transmission voltage. These transformers are typically oil-filled units between 5 and 250 MVA, located in outdoor compounds rather than buildings.

Strictly speaking outdoor transformer compounds do not have HVAC ductwork. But the adjacent buildings — the control building, the switchroom, the substation building — frequently have ducting that exits into the compound airspace, and the materials and detailing of that ducting are affected by the transformer environment. Mineral oil vapour from breathers, ozone from corona discharge at the MV bushings, and at coastal sites airborne salt all accelerate galvanized degradation. SBKJ practice within a 10 metre radius of any oil-filled transformer breather, or at coastal sites within 5 kilometres of surf, is to specify 304 stainless steel duct for any external ductwork, with 316 stainless reserved for marine-exposed locations.

For indoor dry-type transformer installations — common in modular substation buildings — the ductwork scope is more conventional. Dry transformers reject heat as forced convection, the rooms are sized for natural or assisted ventilation, and air change rates are calculated from the transformer heat dissipation curve. NFPA 850 provides guidance on the segregation of transformer airflow from occupied spaces, and AS/NZS 4254 sets the duct construction standard.

4.5 The Fire Panel and Communications Rooms

A typical BESS site has a small but critical room housing the fire indicator panel, the gas detection master controller, the BESS off-gas detection aggregator, and the communications equipment for AEMO SCADA. This is a sub-10 square metre room that is air-conditioned to a tight setpoint (20 to 24 degrees Celsius) on N+1 redundant DX. The ductwork is short, low-pressure, and engineered for reliability rather than capacity — every joint sealed to Class D, every penetration through the building envelope fitted with intumescent collars, every duct support designed for seismic restraint in the relevant Australian seismic zone.

5. Switchroom Ventilation in Detail

The MV switchroom deserves its own section because the engineering decisions are subtle and the consequences of getting them wrong are operational. Switchrooms house assets that are simultaneously expensive (a 33 kV switchgear lineup can run to several million dollars), critical (loss of switchgear means the entire BESS or inverter block is offline), and intolerant of environmental excursion (a single cycle of condensation on a busbar insulator can trigger a flash-over).

5.1 Dust Control

Australian utility-scale renewables sites are dusty. The combination of cleared paddock, summer wind, construction traffic and seasonal bushfire smoke means that infiltrated air carries substantial fine particulate. Particulate settling on switchgear insulators forms a conductive layer that, when combined with humidity, can track and flash over. The ventilation system must therefore deliver filtered, slightly positive-pressure supply air. SBKJ specification is G4 panel pre-filter followed by F7 bag or pleated filter on the supply path, with differential pressure transmitters across each filter bank feeding back to the BMS so maintenance crews can change filters before they choke.

5.2 Humidity Control

Tropical and subtropical project sites in Queensland and northern New South Wales operate in high-humidity envelopes. Switchgear that sees morning condensation on insulator skirts develops surface tracking over time. The HVAC specification therefore includes reheat or dehumidification capacity on the supply DX unit to maintain the room below 70 percent relative humidity year-round, with the room temperature held in a band that prevents the dewpoint approaching the busbar surface temperature.

5.3 EMC and EMI Segregation

Medium-voltage switchgear generates substantial electromagnetic interference during normal operation and very large EMI transients during fault clearing. Ductwork acts as a conductor and an antenna. Two design choices keep this manageable. First, route metal ductwork at least 600 mm from any MV busbar chamber and 300 mm from any MV cable tray. Second, bond the duct to the equipotential earth at intervals no greater than 6 metres, and cross-bond every flexible coupling. AS/NZS 3000 Section 5 sets the bonding requirements. Where the duct must cross an MV chamber boundary, use a non-metallic flexible transition rated for the building's fire compartmentation.

5.4 Arc-Flash and Fire

Modern MV switchgear is arc-resistant to AS/NZS 62271, which means an internal arc fault is vented through designated pressure-relief paths — typically into the ceiling void above the switchgear cubicles or through chimneys to outside. The HVAC ductwork must not interfere with these arc-vent paths. SBKJ practice is to coordinate the duct routing with the switchgear OEM's arc-vent plan during shop drawing review, before fabrication starts. Any duct penetration through a fire-rated wall is fitted with a listed fire damper to AS 1668.1, the damper actuator wired through the fire indicator panel, with access panels each side of the damper for periodic inspection.

6. Transformer Rooms — Oil-Filled and Dry-Type

Transformers convert between voltage levels, dissipate heat in the process, and present a specific set of ventilation challenges that depend on whether the unit is oil-filled or dry-type, indoor or outdoor.

6.1 Oil-Filled Transformer Compounds

Utility-scale grid-interface transformers — typically 33/132 kV or 33/220 kV step-up units rated 50 to 250 MVA — are virtually always oil-filled, sited outdoors on bunded concrete pads. The ventilation envelope is the atmosphere. There is no HVAC ductwork for the transformer itself. However, the compound is enclosed by walls or fences to maintain electrical clearances, and adjacent buildings open into the compound airspace. The relevant ductwork engineering decision is material selection for any duct that terminates in or near the compound.

Mineral oil breather vents emit small quantities of oil vapour. Over years this vapour deposits a microscopic oil film on surrounding surfaces. Galvanized steel ductwork exposed to this environment shows degradation at decade-15 to decade-20 inspection points — pitting at fold lines, accelerated corrosion at supports. SBKJ practice within a 10 metre radius of any oil-filled transformer breather is 304 stainless steel ductwork, with 316 stainless for coastal sites within 5 kilometres of surf where chloride accelerates pitting.

6.2 Dry-Type Transformer Rooms

Auxiliary transformers in the 500 kVA to 5 MVA range are increasingly specified as dry-type cast-resin units, located indoors in modular substation buildings or skid-mounted enclosures. Dry transformers reject heat as forced convection and require directly-ventilated rooms. Air change rate is calculated from the transformer heat dissipation curve at full load, with a temperature rise from inlet to outlet of 10 to 15 Kelvin. The supply air enters at low level, the exhaust leaves at high level, and the room is sized for natural convection augmented by relief fans on a thermostat trigger.

Ductwork is conventional rectangular galvanized to AS/NZS 4254, with stainless steel reserved for the discharge ductwork where ozone from any corona is concentrated. NFPA 850 guidance is to keep transformer airflow segregated from any adjacent occupied space, with fire-rated separations between the transformer compartment and any control room.

6.3 Fire Protection Integration

Both oil-filled and dry-type transformers can fail with a fire. Oil-filled transformer fires are particularly dramatic — burning mineral oil under pressure. NFPA 850 and the project insurer's standard typically require fire walls between transformer pads, separation distances to adjacent buildings, and integration of any HVAC ducting with the fire indicator panel. Where ducting from an adjacent building exits into the transformer compound airspace, SBKJ practice is to fit motorised dampers that close on a fire signal, sealing the building from the transformer fire plume.

7. Legacy Lead-Acid Battery Rooms and the Hydrogen Question

Most new-build utility-scale BESS uses lithium-ion chemistry in integrated containers. But many AEMO-connected sites are not greenfield. The major brownfield BESS projects — Liddell, Eraring, Wallerawang — sit on or adjacent to former coal generation sites that still operate substantial legacy infrastructure. Substations connected to those sites often retain lead-acid station batteries for protection and control DC supplies. AS 5034 governs the ventilation of those rooms.

The fundamental hazard is hydrogen gas evolved during overcharge or equalisation charging of vented lead-acid cells. Hydrogen reaches the lower explosive limit at 4 percent concentration by volume, and AS 5034 sets the design limit at 1 percent — providing a four-times safety margin. The ventilation rate to maintain 1 percent under worst-case charging is calculated from the cell ampere-hour rating, the charge current and the room volume. Typical design produces 2 to 4 air changes per hour during charging, with continuous low-rate ventilation between charge cycles.

The ductwork requirements are specific. Exhaust ducting must be non-sparking — typically aluminium or stainless steel rather than galvanized — and electrostatically bonded along its full length to dissipate static charge. The exhaust must terminate above the building roofline and clear of any building intake by at least 6 metres. Ductwork penetrations into the battery room must be sealed with intumescent collars rated to the fire compartmentation. If the room is classified as Zone 2 hazardous area to AS 60079 during charging, all fan motors and switchgear in the airstream must be rated Ex e or Ex d to suit.

Sealed valve-regulated lead-acid (VRLA) cells generate substantially less hydrogen than flooded cells but the AS 5034 ventilation requirements still apply. Lithium-ion station batteries — increasingly specified as replacements for legacy lead-acid — do not generate hydrogen in normal operation and the AS 5034 obligations fall away. However, lithium-ion off-gassing during a thermal runaway event is hazardous in a different way (hydrocarbons, hydrogen fluoride, hydrogen cyanide), which is why the BMS integrates off-gas detection with the fire indicator panel and the HVAC system shuts down on a positive detection signal.

8. Australian Projects Setting the Specification Benchmark

The HVAC specifications that SBKJ Group works to are not abstract — they emerge from the actual mechanical scopes on the major Australian utility-scale projects under construction or in late-stage planning. The sections below summarise the publicly disclosed scope and the ductwork implications.

8.1 Waratah Super Battery (New South Wales)

The Waratah Super Battery, located near the former Munmorah power station on the New South Wales Central Coast, is targeting roughly 2.5 GWh of storage capacity once fully commissioned. The site combines integrated BESS containers from multiple OEM suppliers with control buildings, MV switchrooms and a substantial grid-interface substation that ties into the existing 330 kV transmission network. The site's coastal location — within 5 kilometres of the Tasman surf — drives a stainless steel specification for any external ductwork at the transformer compound and a careful filter strategy at the switchrooms to handle salt-laden air. The control building cooling load is dominated by the SCADA gateway and the AEMO communications hardware, with N+1 redundancy on all DX units feeding from the station service bus with automatic transfer to the BESS-backed essential services supply on grid loss.

8.2 Wallerawang BESS (New South Wales)

The Wallerawang BESS, sited on the former Wallerawang coal station footprint in the Lithgow region, brings approximately 500 MW of storage onto the network. The brownfield nature of the site means the project inherits legacy substation infrastructure including some lead-acid station batteries that remain in service for protection DC supply. The HVAC scope therefore spans the modern integrated lithium-ion BESS compound (no internal ductwork to the cells, substantial ductwork in adjacent buildings) and the legacy substation buildings where AS 5034 hydrogen exhaust ducting is still in service.

8.3 Western Downs Solar + Battery (Queensland)

The Western Downs Solar + Battery project, west of Dalby in southern Queensland, combines roughly 460 MW of solar PV with 180 MW of co-located battery storage — a hybrid generation profile. The inverter station count is substantial: a 460 MW solar block at typical inverter block sizing translates to 100 to 130 separate inverter buildings, each with its own HVAC scope. The inland Queensland climate brings design dry-bulb temperatures into the 45 to 48 degree Celsius range, which makes inverter derate a major operational consideration. Evaporative cooling is the dominant strategy for the inverter buildings; the BESS control and switchrooms run on DX. Total ductwork on a project of this scope runs to 6000 to 9000 square metres of formed sheet.

8.4 New England Solar (New South Wales)

The New England Solar project near Uralla in northern New South Wales is one of the largest single-site solar farms on the National Electricity Market at roughly 720 MW. The inverter building count exceeds 160, with associated MV switchrooms and a substantial substation that ties into the 132 kV network. The site sits at relatively high elevation (around 1000 metres above sea level) which moderates summer peaks but introduces a winter design consideration: morning condensation on switchgear insulators during inversion conditions. The HVAC specification therefore includes humidity control on the switchrooms with reheat capacity to manage dewpoint excursions.

8.5 Bungala Solar (South Australia)

The Bungala Solar project near Port Augusta in South Australia represents the established generation that newer projects are benchmarking against. Approximately 370 MW of solar PV with associated inverter blocks. South Australian summer peaks are among the hottest in the National Electricity Market, regularly exceeding 47 degrees Celsius dry-bulb in the Spencer Gulf region. The inverter building HVAC therefore prioritises summer thermal management over winter heating — direct evaporative is the standard approach, with DX make-up cooling on the worst-case afternoon hour.

8.6 Liddell BESS (Hunter Valley, New South Wales)

The Liddell BESS sits on the former Liddell coal station footprint, replacing decommissioned coal with grid-forming storage. Like Wallerawang the site inherits legacy substation buildings alongside the new integrated lithium-ion compound, so the HVAC scope spans new-build for BESS control and switchgear plus retrofit ductwork in the repurposed legacy buildings.

8.7 Eraring BESS (New South Wales)

Origin Energy's Eraring BESS is co-located with the Eraring coal generator on the New South Wales Central Coast, providing storage capacity that supports the eventual coal retirement transition. The project's coastal location and salt exposure mirror the Waratah considerations — stainless external ducting, salt-tolerant filtration on switchroom supplies, careful corrosion management at the transformer compound.

8.8 Capital Wind Farm BESS, Hornsdale and Victorian Big Battery

Capital Wind Farm BESS near Bungendore integrates utility-scale storage with an existing wind asset, with the HVAC scope concentrated in the new control compound and the substation tying into the existing 132 kV network. The Hornsdale Power Reserve near Jamestown (Neoen, Tesla Megapack and earlier Powerpack hardware) put grid-scale lithium-ion storage on the global map and has expanded multiple times since 2017; summer peaks in the Mid North regularly exceed 45 degrees Celsius dry-bulb. The Victorian Big Battery near Geelong (also Neoen) was one of the world's largest single batteries at commissioning; like Hornsdale the integrated Megapack architecture concentrates in-scope ductwork in the ancillary buildings, with coastal exposure and the Geelong industrial corridor driving salt and particulate considerations.

8.9 The Broader Pipeline

Beyond the named projects the AEMO connection queue contains dozens at various development stages. Neoen, AGL, Origin Energy, EnergyAustralia, Snowy Hydro, Edify Energy, Lightsource bp, Acen Australia, Genex, BayWa r.e., Iberdrola and Squadron Energy lead the development side; UGL, Downer, John Holland and Worley dominate the EPC market. SBKJ Group's ductwork machinery installed base across the EPC supply chain serves projects from earthworks through commissioning, with the SBAL-V and SBTF-1602 supplying the bulk of rectangular and round duct demand.

9. Cooling Strategy by Climate Zone

Australia's continental scale means that a single HVAC specification cannot serve every project. The cooling strategy is properly informed by the local climate envelope, and SBKJ engineers typically segment specifications into four climate zones.

9.1 Inland Hot Arid — Queensland, Western Riverina, Mid-North South Australia

Design dry-bulb temperatures of 45 to 48 degrees Celsius, design wet-bulb of 20 to 22 degrees Celsius. The low wet-bulb is the key — it enables direct or indirect evaporative cooling at a fraction of the energy consumption of DX. SBKJ specification for inverter buildings in this zone is direct evaporative cooling with bypass dampers for winter ventilation. Control buildings and switchrooms remain on DX because they require humidity control. Material grade is standard galvanized Z275, with stainless reserved for transformer-adjacent ducting.

9.2 Coastal Subtropical — Central and Northern New South Wales, Southern Queensland

Design dry-bulb 35 to 42 degrees Celsius, design wet-bulb 24 to 26 degrees Celsius. Evaporative is ineffective above 22 degrees Celsius wet-bulb. DX is the default for all spaces. Material grade is galvanized for internal, with 304 stainless for any external ducting within 5 kilometres of surf.

9.3 Coastal Temperate — Victoria, Tasmania, Southern New South Wales

Design dry-bulb 30 to 38 degrees Celsius, design wet-bulb 18 to 22 degrees Celsius. Evaporative becomes viable for inverter buildings on the hot inland edge of the zone but not for coastal sites. The temperate climate means HVAC sizing is more relaxed than in the hot zones, but winter heating capacity becomes a consideration for control buildings during minimum-occupancy site visits. Material grade is standard galvanized for internal, stainless for transformer-adjacent and coastal.

9.4 Tropical North — Far North Queensland, Northern Territory

Design dry-bulb 33 to 38 degrees Celsius, design wet-bulb 26 to 28 degrees Celsius. The high wet-bulb makes evaporative cooling unviable. DX with reheat for humidity control is the default. Material grade is the most demanding of any zone — 316 stainless for any external ducting due to combined salt and high-humidity corrosion, careful coating specifications on internal galvanized to prevent condensation under-deposit attack.

10. Acoustic Design and Planning Compliance

Renewable energy projects sit in rural and peri-urban landscapes where the nearest residential receivers can be anywhere from a few hundred metres to several kilometres from the site boundary. State EPA environmental noise conditions are project-specific but typically set night-time limits of 35 to 40 dBA at the nearest receiver, with daytime limits 5 to 10 dB higher. The dominant noise sources on the site are inverter cooling fans, BESS container heat rejection fans, transformer hum and any rooftop HVAC units on control and switchroom buildings.

SBKJ ductwork specifications for acoustic-sensitive locations include in-duct silencers at the supply discharge and the exhaust intake, sized to deliver insertion loss of 10 to 15 dB across the 250 to 2000 Hz octave bands. The silencers are typically rectangular splitter attenuators with non-friable mineral wool absorber lined with perforated metal facing. The duct cross-section through the silencer is sized for maximum 7 metres per second face velocity to avoid regenerated noise. Where the planning condition is particularly tight, SBKJ engineers in cylindrical silencers on round duct from the SBTF-1602 — these deliver better attenuation per metre of duct length and fit neatly into the long external trunks that connect rooftop equipment to building intake points.

Internally, control buildings target NC-50 background level so that operators can use voice communication during occasional site visits. Switchrooms and inverter buildings are unmanned and have no internal acoustic target — but reverberation control matters because hard surfaces and high fan output combine to push fabric-borne sound transmission to adjacent rooms.

11. Prefabrication, Logistics and Remote Site Delivery

Australian utility-scale renewables sites are typically 200 to 1000 kilometres from the nearest major fabrication base. Western Downs Solar is 250 kilometres west of Brisbane. New England Solar is 450 kilometres north of Sydney. Bungala Solar is 300 kilometres north of Adelaide. The site logistics make on-site fabrication impractical — there is no power supply for an SBAL-V auto duct line on a greenfield earthworks compound, there is no skilled labour pool, and the construction schedule does not allow time for slow on-site fabrication.

The standard EPC mechanical model is therefore to prefabricate all ductwork in a fabrication shop, palletise the components on Euro pallets with bagged consumables, transport by curtain-side B-double truck to site, and install with a small site crew. SBKJ machinery is configured for exactly this model: the SBAL-V auto duct line in a fabrication shop produces several hundred metres of rectangular duct per shift, sized and labelled by section to match the site shop drawings; the SBTF-1602 spiral tubeformer produces round duct in long continuous sections that can be transported as 6 to 12 metre lengths on standard flatbed trailers.

The packaging and transport detail matters. Bare galvanized sheet exposed to ocean transport — or even to a 1000 kilometre overland haul in winter — accumulates surface oxidation that requires reworking before installation. SBKJ specification is to wrap every duct section in protective film at the fabrication shop, pallet-wrap the assemblies in moisture-resistant shrink wrap, and include desiccant in any sealed container shipment. For the largest projects this packaging discipline alone has eliminated weeks of on-site rework time.

On-site crane access is a constraint at most remote sites. The main building cores are typically erected by the structural contractor before the mechanical trade is on-site. Once the steel and roof deck are up, crane access to high-level duct runs becomes a coordinated activity around other trades — electrical, instrumentation, fire. SBKJ duct prefabrication breaks the runs into 2.4 to 6 metre sections that can be lifted by scissor lift or boom lift rather than requiring a mobile crane, which removes one significant coordination dependency from the install plan.

12. Commissioning, Balancing and AEMO Hold Points

HVAC commissioning on a utility-scale renewables project is not a sign-off-and-leave activity. It is a sequenced set of demonstrations that has to integrate with the AEMO connection commissioning plan, which itself is a sequence of Hold Points (R0, R1, R2) at which the connection conditions are demonstrated to AEMO and the relevant transmission network service provider.

The HVAC system must be operational, balanced and stable before the inverter station can be energised for the first time. Once the inverters are energised the building heat load steps up immediately, and the HVAC has to maintain the inverter intake temperature within the OEM derate envelope through the full output ramp. Mechanical contractors who treat HVAC commissioning as a tail-end activity discover that the AEMO commissioning team will not accept a Hold Point demonstration if the inverters are derating because of HVAC underperformance.

SBKJ ductwork specifications include a full commissioning and balancing package: pre-fabrication FAT records, on-site installation inspection records, pressure leakage test records to AS/NZS 4254 sealing class, balancing reports to AS 1668.2 outside air rates, acoustic verification at the worst-case receiver, and an as-built drawing set in AEMO-compliant project documentation format. The package becomes part of the asset owner's lifecycle file and is referenced in subsequent maintenance, retrofit and decommissioning decisions over the 25 to 30 year asset life.

13. Operational Redundancy and the Essential Services Bus

The single most important operational consideration for HVAC on a utility-scale renewables project is what happens when the grid trips. If the site loses its 33 kV or 132 kV grid connection, the station service supply powering HVAC fans, pumps and DX disappears. Inverter rooms heat up. Switchrooms climb. BESS containers eventually derate once their internal thermal management has drawn down the cell-cooling buffer.

The standard utility-scale BESS architecture provides an essential services bus — a portion of BESS capacity that automatically transfers to feed station service on grid loss. HVAC is a top-priority load on that bus. SBKJ designs HVAC supply panels with two incoming feeds, an automatic transfer switch, and a load-shedding sequence that drops non-essential loads (lighting, amenity heating, water heaters) before inverter and switchroom cooling on long outages. The duct itself doesn't change for this, but the building-services interface with the BESS controller is a coordination point that catches inexperienced contractors out.

Operational redundancy on air-moving plant is N+1 across all critical buildings. SBKJ practice is to design the supply trunk so loss of one DX unit still delivers airflow to every zone through cross-connected branch take-offs, with motorised dampers reconfiguring airflow on a control signal.

14. The SBKJ Machine Configuration for Australian Renewables

Across the EPC contractors and mechanical fabrication shops serving Australian utility-scale renewables, the SBKJ configuration that consistently matches the bill of quantities is the SBAL-V auto duct production line for rectangular galvanized supply and return duct, paired with the SBTF-1602 spiral tubeformer for round duct on long horizontal exhaust trunks and extract risers.

The SBAL-V handles coil widths up to 1500 mm and thickness from 0.6 to 1.5 mm, covering the entire range of duct sizes used in renewables ancillary buildings. The machine integrates coil feeding, levelling, notching, Pittsburgh seam locking, TDF flange forming and shear-to-length in a single line, producing duct at 12 to 18 metres per minute. For a project requiring 4000 to 8000 square metres of formed duct, the SBAL-V delivers the entire scope in 2 to 4 weeks of single-shift production; a second shift doubles throughput for the largest jobs.

The SBTF-1602 spiral tubeformer produces round duct from 80 to 1600 mm diameter. Round duct is standard for long horizontal exhaust trunks because of its strength-to-weight ratio and low pressure drop. On a renewables project the SBTF-1602 forms the supply and return trunks between rooftop DX units and the building interior, the relief discharge runs from inverter rooms, and the exhaust risers from BESS or switchroom relief paths — with continuous lengths up to 12 metres minimising field joints and field leakage.

Beyond the two main lines, SBKJ supplies the supporting shop equipment — TDF flange machines, plasma cutters for branch fittings, finger-edge benders for radius fittings, and roll-formers for accessories. The complete shop-fit allows a single mechanical fabrication contractor to handle the entire ductwork scope of a 500 MW solar farm or 1 GWh BESS project from one fabrication base, with prefabricated ductwork transported to site by curtain-side B-double. Both lines accommodate stainless coil with tooling adjustments, typically at 15 to 25 percent reduced throughput.

15. Cross-References and Related Reading

The renewable energy verticals share substantial engineering DNA but diverge on specific details. Readers working on related projects should consult the following companion guides from the SBKJ insights library:

• EV Charging and BESS HVAC Duct Guide — for distributed EV charging stations and smaller-scale battery storage, including the differences in regulatory framework (focus on Network Connection Standards rather than AEMO GPS).
• Battery Gigafactory HVAC Duct Guide — for cell and pack manufacturing facilities, including dry-room ventilation, electrode coating exhaust and the substantially more complex hazardous area classification that applies during cell formation.
• Hydrogen Production HVAC Duct Guide — for electrolyser halls, ammonia synthesis plants and the substantially higher-stakes hazardous area regime that applies to facilities handling pure hydrogen and ammonia gas streams.
• AS 1668.2 Australian Ventilation Code Reference — the engineering reference for outside-air rates, exhaust requirements and the contaminant control matrix that drives AS 1668.2 calculation for any occupied space.
• SBAL-V vs SBAL-III Comparison — for fabrication shops weighing the choice between the SBAL-V auto line and the higher-throughput SBAL-III for renewables project bid pipelines above 1 GW per year of project flow.

16. Talking to SBKJ Engineering

SBKJ Group's engineering team supports EPC mechanical leads, balance-of-plant designers and project HVAC subcontractors from initial bid through to commissioning. The engagement covers bid-stage bill-of-quantities review and machine configuration recommendation, detailed design review of project HVAC drawings for fabrication compatibility, machinery supply with commissioning and operator training, remote technical support for the life of the equipment, and a 10-year spare parts continuity guarantee with stocked items shipped within 14 days to Australian destinations.

For project teams preparing AEMO connection submissions, SBKJ can provide a ductwork scope and quality control narrative suitable for the commissioning evidence pack — covering material selection, sealing class, leakage testing, balancing, acoustic verification and as-built documentation. Talk to the engineering team via the SBKJ Group contact page, or browse the product range and the insights library.