Library, Museum, Archive & Gallery HVAC Ductwork — Preservation Environments & Narrow RH Bands

Why preservation HVAC is different

An office building HVAC system has one job: keep occupants comfortable. The ductwork can leak 10–15% and nobody notices. Filters can run on MERV 8 and the worst that happens is a dusty desk. RH can swing from 30% to 70% across a season and a typical occupant will simply turn down the thermostat.

A library, museum, archive or gallery HVAC system has a fundamentally different mandate. The ductwork is a custodian. Every cubic metre of air it delivers is in direct contact with collections that are, in many cases, irreplaceable. A 5% RH swing over 24 hours can crack a 17th-century oil painting. A 50 µg/m³ rise in airborne particulates can damage a daguerreotype permanently. A trace of SO2 above 1 µg/m³ accelerates the embrittlement of acidic paper at a rate measurable in conservation laboratories within months.

The ductwork in a preservation environment is therefore engineered to a tighter set of constraints than almost any other commercial HVAC application — including most cleanrooms. Cleanroom ductwork worries about particulate count. Pharmaceutical ductwork worries about cross-contamination. Preservation ductwork worries about both, plus 24-hour RH stability, pollutant scavenging, fibre shedding from insulation, off-gassing from coatings, condensation in low-temperature archive zones, and full traceability for international loan agreements that may run to 80 pages of environmental schedules.

This guide is written for the people who specify, manufacture, install and commission preservation HVAC ductwork — facility managers, mechanical engineers, conservation architects and the occasional conservator who has discovered that the answer to "why are my prints fading?" lies in a duct seam four floors above the gallery.

The four references that govern preservation HVAC

Before any duct dimension is set, the four references below need to be on the design engineer's desk. They are not interchangeable — each addresses a different aspect of the preservation environment and a complete specification cites all four.

ASHRAE Applications Handbook Chapter 24

The single most cited reference in preservation HVAC. Chapter 24 — Museums, Galleries, Archives and Libraries — defines five environmental control classes that have become the international shorthand for preservation specifications:

• Class AA. 21°C ±1°C, 50% RH ±2% RH, with seasonal RH adjustment ±0% from set-point. The highest-precision class. Required for international loan-quality galleries displaying high-value paintings, photographs, fragile paper and ethnographic collections under environmental restriction. Verified by 24-hour RH excursion data within ±5% maximum.
• Class A. 21°C ±1°C, 50% RH ±5% RH, with up to ±10% seasonal adjustment. Standard for general museum collections, regional galleries and most state libraries. Filtration MERV 13+ minimum.
• Class B. 21°C ±2°C, 50% RH ±10% RH. Storage of robust general collections, library general stack.
• Class C. 5–25°C, 25–75% RH. Back-of-house, transit and lower-value reference collections.
• Class D. Climate-following, with vapour-barrier protection only. Acceptable for stone, ceramic and metal-only collections under local conservator review.

Chapter 24 also gives the engineering basis for risk-of-damage calculations across temperature, RH and lighting — but for ductwork specification, the AA/A/B/C/D shorthand is the load-bearing concept. Most institutional briefs simply state "Class AA gallery, Class A storage, Class B back-of-house" and leave the rest of the specification team to follow Chapter 24's tolerance bands.

BS 5454

BS 5454:2000 — Recommendations for the Storage and Exhibition of Archival Documents — was withdrawn by BSI in 2012, but it remains the most-cited environmental standard in archive specifications across the Commonwealth. The replacement reference (PD 5454:2012, then PAS 198:2012, then BS 4971:2017) modernised the language but the underlying numbers — paper archive 13–18°C, 35–60% RH, low pollutant load — survive in nearly every Australian state archive specification you will encounter. AICCM environmental notes still cite BS 5454 directly. If a museum, archive or library tender brief in Australia, the UK, New Zealand or Canada cites only "BS 5454 environmental conditions", it almost certainly means the 2000 edition values.

ISO 11799:2015

ISO 11799:2015 — Information and documentation — Document storage requirements for archive and library materials — is the international standard for archive storage environments. It defines four storage categories by material type (paper, parchment, photographic, magnetic) and prescribes temperature, RH, light, pollutant and air-quality limits for each. Where ASHRAE Chapter 24 takes a risk-of-damage view, ISO 11799 takes a material-science view. The two are complementary and most modern preservation specifications cite both. ISO 11799 is also the reference that drives specialty zone design (photographic, film, magnetic media) more comprehensively than Chapter 24.

AICCM environmental guidelines

The Australian Institute for the Conservation of Cultural Material publishes guidance specific to Australian institutions. AICCM's environmental guidelines acknowledge the energy realities of cooling Australian buildings to 21°C/50% RH year-round — particularly in tropical Queensland and the Northern Territory — and propose locally calibrated tolerance bands that allow seasonal drift while protecting collections. AICCM is the reference that often resolves disputes between an international ASHRAE Class A specification and a local-climate practical envelope. Australian preservation specifications routinely cite all four references — ASHRAE Chapter 24, BS 5454, ISO 11799:2015 and AICCM — as a complete environmental governance framework.

The Class A environment in detail

Class A is the workhorse preservation specification for Australian state libraries, regional galleries and most museums under federal or state cultural agency portfolios. Understanding what Class A demands of the ductwork is the foundation for everything else in this guide.

Setpoint and tolerance. 21°C ±1°C is the temperature target. 50% RH ±5% RH is the humidity target. The tolerance bands apply to the steady-state average — not to the 24-hour swing. The 24-hour RH excursion limit, which is the key constraint that drives ductwork tightness, is ±5% maximum.

Filtration. MERV 13 minimum, with most specifications calling MERV 14 or higher to provide capacity headroom against urban pollution loadings. Class A gallery filtration also typically includes activated-carbon polishing for SO2 and NO2 control.

Air change rate. 4–8 ACH for galleries, 2–4 ACH for general storage. Lower air change rates reduce pollutant ingress but require tighter ductwork to maintain RH stability.

Ductwork construction. Galvanised steel to AS 1397, low-leakage SMACNA Class A construction (3 cfm per 100 sq ft at 1 in. wg), TDF or four-bolt flanged transverse joints, sealed longitudinal seams and branch take-offs. Internal lining excluded — fibre shedding is incompatible with collections — and external insulation specified as closed-cell foam.

Documentation. Class A specifications now routinely require third-party leakage testing of the ductwork, with results recorded per air-handling-unit zone and incorporated into the loan facility report.

The Class AA environment in detail

Class AA is the highest-precision specification in the ASHRAE framework. It is required for the galleries that host international loan exhibitions — the spaces where you display Vermeer, Klimt, da Vinci, Olmec jade or 19th-century albumen prints under loan agreements that specify environmental conditions to two decimal places. There are perhaps 60 to 80 spaces in Australia that legitimately need Class AA. The cost of going Class AA when Class A would suffice is significant, and most institutions calibrate against actual loan demand.

Setpoint and tolerance. 21°C ±1°C, 50% RH ±2% RH. The tighter ±2% RH band is what separates Class AA from Class A. It demands tighter ductwork, redundant control loops, and dehumidification capacity sized for worst-case Australian summer ingress conditions.

Filtration. MERV 16 plus activated-carbon polishing plus gas-phase scrubbing for SO2, NO2, ozone and formaldehyde. Class AA photographic galleries additionally specify HEPA filtration at the supply diffuser.

Pollutant control. SO2 below 1 µg/m³, NO2 below 2 µg/m³, ozone below 2 µg/m³, particulates below 50 µg/m³, all measured at the supply diffuser. These targets cannot be met by filtration alone — they require ductwork that does not contribute to the pollutant load (no off-gassing from coatings or sealants, no fibre shedding from insulation, no corrosion products from non-traceable steel).

Ductwork construction. Galvanised steel for general gallery zones, stainless 304 or aluminium for any zone where condensation is possible. Leakage class tighter than SMACNA Class A — most Class AA specifications now call SMACNA "Class A modified" or simply specify an absolute leakage rate (e.g. less than 1 cfm per 100 sq ft at 1 in. wg). All sealants conservation-grade, low-VOC, with documented composition for review by the institution's conservation department.

Documentation. Loan facility report fully populated, with leakage test results, RH/T trend data over 12 months, pollutant sampling results, and engineer-signed certification of every reference (ASHRAE Chapter 24, BS 5454 equivalent values, ISO 11799 storage category, AICCM compliance).

Specialty zones — temperature beyond 21°C

The 21°C/50% RH baseline applies to general galleries, libraries and museum back-of-house. Specialty preservation zones diverge significantly, and each requires bespoke ductwork engineering.

Photographic archives — 2 to 15°C

Photographic materials — silver gelatin prints, albumen prints, daguerreotypes, ambrotypes, tintypes — are profoundly sensitive to temperature. Image decay rates double for every 5–7°C above 18°C. ISO 11799 specifies 2–18°C for photographic storage, with the conservation community increasingly settling on 2–15°C, 30–40% RH for long-term photographic archives. The ductwork delivering these conditions must:

• Operate without surface condensation when ambient air-handling-room conditions are 22°C/55% RH and supply air leaves the AHU at 8°C. The dew-point analysis at every duct surface drives material selection — galvanised steel works under most conditions, but stainless 304 or aluminium is specified where condensation risk exceeds 10% over the year.
• Carry adequate insulation thickness to prevent thermal bridging through duct supports. Closed-cell elastomeric foam at 38 mm minimum, with vapour-tight overlapping joints, is the standard.
• Be vapour-sealed at every penetration — sleeve seals, electrical penetrations, sampling pipe penetrations — to prevent moisture migration into the cold duct cavity.

Colour film archives — minus 2°C

Colour film, particularly chromogenic processes (Kodachrome aside), suffers from dye fading at all temperatures above freezing. Long-term storage of national colour film collections is now specified at minus 2°C with very tight RH control (typically 30–35% RH). The ductwork delivering minus 2°C supply air is essentially refrigeration ductwork. Stainless steel 304 construction is mandatory, internal liners are completely excluded, vapour-barrier integrity is verified by helium leak testing in the most demanding installations, and routing is kept to the shortest possible distance from the dedicated AHU to the vault. Some film archives use fan-coil units inside the vault rather than ducted distribution to eliminate distribution-side dew-point complications.

Paper archives — 13 to 18°C

Paper degradation is principally hydrolytic — the breakdown of cellulose chains accelerated by temperature, humidity and acidic pollutants. ISO 11799 specifies 13–18°C, 35–60% RH for paper. State archives in Victoria, NSW, Queensland and Western Australia now operate paper vaults at the cooler end of this range (13–15°C) to maximise the life of acidic 19th and 20th century paper. The ductwork is similar to the Class A general gallery specification — galvanised steel, SMACNA Class A leakage, closed-cell external insulation — but sized for lower air-change rates (1–2 ACH) and incorporating dehumidification to manage the dew-point shift between the cool vault and warmer access corridors.

Magnetic tape and digital media — 5 to 10°C

Magnetic tape (audio, video, computer backup) and optical media degrade more slowly at lower temperatures. Specialised media vaults operate at 5–10°C, 20–30% RH. Ductwork is similar to photographic archive specification, with additional attention to anti-static control and electromagnetic compatibility for the vault as a whole. Aluminium ductwork is preferred over stainless in some specifications because of its diamagnetic properties.

Pollutant control — the hidden duty of the ductwork

Pollutant control is where preservation HVAC most clearly diverges from comfort HVAC. The targets are stringent and they cannot be met by filtration alone — the ductwork itself is part of the pollutant-control system.

Indoor air pollutant targets

• SO2 (sulphur dioxide). Target below 1 µg/m³ at the supply diffuser. SO2 reacts with paper, leather and silver-based photographic materials to form sulphuric acid. Urban background SO2 is 5–20 µg/m³ — a removal factor of 5 to 20× is required.
• NO2 (nitrogen dioxide). Target below 2 µg/m³. NO2 catalyses oxidation reactions on silver, copper and organic colorants. Urban background NO2 is 10–40 µg/m³.
• Ozone (O3). Target below 2 µg/m³. Ozone is the most aggressive oxidiser found in indoor air, particularly damaging to dyes, organic pigments and rubber-based adhesives in archive bindings.
• Particulates (PM2.5 and PM10). Target below 50 µg/m³. Particulates physically deposit on surfaces — once on a paper substrate or photographic emulsion, they are rarely fully removable.
• Formaldehyde and other carbonyls. Target below 5 µg/m³. Carbonyl compounds catalyse paper acidification and metal corrosion.

Why ductwork tightness matters for pollutant control

A ductwork system that meets SMACNA Class A leakage (3 cfm per 100 sq ft at 1 in. wg) typically has 3–5% total system leakage. In a comfort HVAC system this is a thermal-efficiency issue. In a preservation HVAC system, it is a pollutant-control issue: any infiltration path through duct seams in a mechanical riser allows pollutant-laden plenum air to bypass the filtration train and be delivered directly to the gallery.

Class AA specifications now routinely call leakage tighter than SMACNA Class A, with absolute targets in the range of 0.5 to 1 cfm per 100 sq ft at 1 in. wg. Achieving these tighter targets requires:

• Manufacturing ductwork on automated lines with consistent seam quality — every Pittsburgh seam, every TDF flange, every reinforced joint identical across thousands of metres of duct.
• Conservation-grade sealant on every transverse joint, longitudinal seam and branch connection.
• Factory leakage testing of every duct section before shipment.
• On-site re-testing after installation, before commissioning.
• Re-testing annually as part of the conservation governance regime.

Filtration train architecture

The Class AA filtration train looks fundamentally different from a comfort HVAC filter rack:

1. Pre-filter. MERV 8 panel filter for coarse particulate and to extend the life of downstream stages.
2. Primary filtration. MERV 14 to MERV 16 bag or rigid filter for fine particulate.
3. Activated carbon stage. Granular activated carbon (GAC) bed sized for the specified SO2 and NO2 removal duty, with dwell time typically 0.06 seconds minimum.
4. Gas-phase polishing. Specialty media (potassium permanganate, alumina, blends) for ozone, formaldehyde and other carbonyls. Often a chemisorbent media in a deep-bed configuration.
5. HEPA stage. H13 or H14 absolute filter for galleries displaying photographic prints, daguerreotypes or other particulate-sensitive collections.

Each stage has a pressure drop, and the entire train must be sized so the duct system can deliver the design air change rate at the design supply temperature without exceeding fan power or AHU casing leakage limits.

Why fibrous insulation is excluded

Fibrous insulations — fibreglass duct liner, mineral wool external wraps — are the default in most commercial HVAC systems. They are cheap, easy to install, achieve good thermal performance and provide acoustic absorption. They are also catastrophically incompatible with preservation environments.

The mechanism of failure is fibre shedding. Fibrous insulations release micro-fibres into the airstream over their service life — particularly when subjected to vibration, thermal cycling and air velocity above 5 m/s. Even at low concentrations, these fibres deposit on:

• Painting surfaces, where they become embedded in varnish or accumulate in textured passages of impasto.
• Photographic emulsions, where they are visible to conservators under raking light and cannot be safely removed without risk to the surface.
• Paper substrates, where they accumulate in folds and on edges and contribute to soiling.
• Textile, ethnographic and natural-history collections, where their similarity to organic fibres makes identification and removal difficult.

Conservation departments routinely identify fibrous insulation as a contamination source during loan inspections — and refuse loans on that basis. This has driven the preservation industry to specify closed-cell foam insulation across all preservation HVAC ductwork. The accepted families are:

• Closed-cell elastomeric foam. Armaflex, K-Flex, Thermaflex and equivalents. The dominant choice for general preservation duty. Available in tubes, sheets, with self-seal and pre-glued options.
• Polyisocyanurate (PIR). Higher thermal performance per unit thickness, used where space is constrained.
• Phenolic foam. The lowest thermal conductivity of common closed-cell foams, used in archive vaults where insulation thickness has to be minimised against architectural constraints.

Closed-cell foam insulation is fitted external to the duct, with sealed butt joints and overlapping longitudinal seams to maintain vapour-barrier integrity. Internal lining is excluded entirely from preservation ductwork — there is no acceptable internal acoustic treatment in a preservation environment, and acoustic attenuation is achieved instead through careful AHU selection, terminal-side attenuators with non-fibrous fill, and gallery acoustic finishes.

Painted and coated duct exteriors

Galvanised steel is the standard ductwork material for general preservation duty, but galvanised surfaces in plant rooms and accessible ceiling voids slowly generate zinc oxide and zinc carbonate particulates as the galvanic coating reacts with atmospheric humidity and CO2. Over a 30-year facility life, this creates a persistent low-level particulate source in mechanical spaces — and any leakage path from those spaces into the preservation envelope carries the contamination forward.

Preservation specifications now routinely call for painted or coated duct exteriors in plant rooms, mechanical risers and any accessible ceiling void within the preservation envelope. Acceptable coatings include:

• Two-pack epoxy coatings, applied at the duct manufacturing facility before shipment.
• Powder coating, where duct sections are small enough to fit oven cure dimensions.
• Site-applied conservation-grade enamel paints, low-VOC, with full off-gassing certification.

For archive vaults at low temperature, where condensation is a credible failure mode, the standard is to specify stainless steel or aluminium ductwork outright rather than rely on a coating to protect galvanised steel under condensing conditions.

Stainless steel and aluminium for archive zones

For photographic archives, film archives, magnetic media zones and rare-book vaults at low temperature and elevated relative humidity, stainless 304 or aluminium ductwork is specified. The reasons are:

• Galvanic corrosion under condensing conditions. Galvanised steel exposed to repeated condensation loses its coating progressively, exposing carbon steel to corrosion. Stainless 304 and aluminium are both corrosion-resistant under condensing operation.
• Off-gassing and chemical reactivity. Stainless steel surfaces are essentially inert. Galvanised surfaces, even passivated, can release trace zinc compounds. For long-term archive storage, the inertness of stainless reduces the long-term contamination risk.
• Cleanability. Stainless interior surfaces can be wiped, vacuumed and inspected without damaging the surface or generating particulates. Galvanised surfaces are more easily damaged during cleaning.
• Loan agreement compatibility. Some international loan agreements specifically call out stainless or aluminium ductwork for the gallery and adjacent storage. Specifying it from the outset eliminates the need for retrofits later.

The trade-offs are cost (stainless 304 is roughly 5–8× the cost of galvanised steel by metre, aluminium roughly 2–3×) and manufacturing complexity. SBKJ's SBAL-V auto duct line is configured for both galvanised and stainless coil — same machine, same control programme, same low-leakage SMACNA Class A construction — which is the configuration we recommend for any institution that has both general gallery zones and dedicated archive vaults.

Loan exhibition compatibility

The single most important commercial outcome of preservation HVAC is the institution's ability to accept international loans. The loan agreement is a contract, often running to 60 to 100 pages, that specifies environmental conditions, security, lighting, fire-detection and conservation supervision arrangements. The loan facility report is the document the receiving institution submits to the lender, and the lending institution's conservation department signs off (or refuses) the loan based on the report's content.

The major lending institutions whose loan agreements drive Australian gallery HVAC specifications include:

• The Louvre, Paris. The Louvre's loan environmental conditions are typically Class AA equivalent, with very tight RH stability requirements and full documentation of the gallery's HVAC ductwork leakage class.
• Tate, London. Tate's loan agreements specify environmental conditions, lighting limits and security in detail. Tate is one of the institutions that has driven the move to documented ductwork leakage class as a loan requirement.
• Smithsonian, Washington DC. Smithsonian's loan conditions vary by museum (Smithsonian American Art Museum, National Portrait Gallery, Cooper Hewitt) but consistently demand Class AA environments for high-value loans.
• Rijksmuseum, Amsterdam. Conservative loan policy, very specific environmental schedules.
• MoMA, New York. Strong on light limits and pollutant control; ductwork specifications are scrutinised at the documentation stage.
• Centre Pompidou, Paris. Loan conditions have tightened progressively since 2010.
• Prado, Madrid; Hermitage, St Petersburg; Uffizi, Florence; National Gallery, London. Each with its own environmental schedule, all consistently demanding Class AA equivalent for high-value loans.

An Australian institution that wants to accept loans from these institutions — for a major touring exhibition, for example — must produce a facility report demonstrating Class AA compliance over a 12-month documented period. The HVAC ductwork drawings, leakage test results, filtration documentation and RH/T trend data are part of that report. Without them, the loan does not happen.

Australian preservation institutions

Australia has a remarkable density of major preservation institutions for its population. Each operates under environmental specifications calibrated to ASHRAE Chapter 24, BS 5454 and ISO 11799, with AICCM as the unifying local reference. The institutions whose HVAC specifications shape Australian preservation practice include:

• National Gallery of Australia (NGA), Canberra. Class AA in primary galleries, Class A in secondary galleries and public areas. Hosts major international loan exhibitions on a five-year rotation; full documented leakage class compliance and pollutant-control documentation.
• National Museum of Australia (NMA), Canberra. Mixed Class A and Class B environments for ethnographic, historical and natural-history collections; specialty zones for textiles, photographs and paper-based ephemera.
• Australian War Memorial (AWM), Canberra. Class A for primary galleries with specialty zones for film archives, photographic collections, paper archives and textile collections (uniforms, flags). Operates one of the largest specialty-zone arrays of any Australian institution.
• National Library of Australia (NLA), Canberra. Class A in reading rooms, Class B in stack zones, BS 5454 paper archive specification (13–18°C) for rare-book vaults; substantial photographic archive at lower temperature.
• Art Gallery of New South Wales (AGNSW), Sydney. Class AA primary galleries — the institution's recent expansion drove a significant upgrade of HVAC ductwork to support loan-quality international exhibitions.
• National Gallery of Victoria (NGV), Melbourne. Two-site institution (NGV International on St Kilda Road, NGV Australia at Federation Square). Class AA primary galleries with Class A storage; substantial international loan programme.
• Powerhouse Museum, Sydney. Class A general galleries, with mixed specialty zones for the design, technology and applied arts collection. Currently undergoing major redevelopment with revised environmental specifications.
• Queensland Art Gallery / Gallery of Modern Art (QAGOMA), Brisbane. Class AA primary galleries, with subtropical climate driving particularly stringent dehumidification capacity requirements and tighter ductwork leakage limits than southern institutions.
• Museum Victoria (Melbourne Museum, Immigration Museum, Scienceworks). Multi-site institution with Class A general galleries and substantial back-of-house storage; specialty zones for natural-history collections and ethnographic textiles.
• Museum of Old and New Art (MONA), Hobart. Class AA in primary galleries within an unusual subterranean facility envelope; the underground building geometry simplifies thermal stability but complicates ductwork routing.
• State Library of Victoria, Melbourne. Class A reading rooms (including the heritage-listed La Trobe Reading Room) with Class B stacks and BS 5454 paper archive specification for rare-book and manuscript collections.
• NSW State Archives, Sydney. ISO 11799-compliant document storage facility with paper archive zones, photographic zones and modern-media zones across a single site.
• Public Record Office Victoria (PROV), Melbourne. Reference archive facility under the Victorian Public Records Act, operating with BS 5454 paper archive conditions and AICCM-compliant environmental documentation.

Across these institutions, the common thread for ductwork is low-leakage SMACNA Class A construction, closed-cell foam insulation, painted or coated exteriors in mechanical zones, stainless or aluminium for archive vaults, and full leakage-class documentation as part of the loan facility report and conservation governance regime.

The 24-hour RH excursion limit

The single most quoted operational metric in preservation HVAC is the 24-hour RH excursion. The limit is ±5% RH maximum across any rolling 24-hour window, with most Class AA specifications now tightening this to ±3% or ±2%.

The limit exists because conservation science has established that materials respond to RH change rates more than to absolute RH. Hygroscopic collections — paper, parchment, ivory, wood, leather, oil paint on canvas — equilibrate with atmospheric humidity. A slow drift from 50% to 55% RH over a season is largely benign. A rapid swing from 50% to 55% RH in 6 hours, repeated cyclically, mechanically stresses the substrate and accelerates damage.

Achieving the 24-hour ±5% RH limit requires the ductwork system to:

• Maintain consistent supply air conditions over 24-hour cycles, despite night-time turn-down, weekend setback and occupancy-driven load swings.
• Distribute supply air evenly across the gallery to prevent localised RH excursions near supply diffusers.
• Have low enough leakage that infiltration of unconditioned plenum air does not corrupt the gallery RH.
• Be sized to allow the AHU control loops to respond smoothly to load changes, without RH overshoot.

The data-logger array deployed at commissioning — typically 6 to 20 sensors in a primary gallery, logging at 5-minute intervals — produces the trend data that proves compliance over a 7-day commissioning period and, ultimately, over the 12-month documented period required for international loan certification.

VESDA aspirating smoke detection

Spot-type smoke detectors are inadequate in preservation environments. By the time enough smoke has reached a ceiling-mounted spot detector to trigger an alarm, the fire is typically already past incipient stage and damage to collections is unavoidable. Aspirating smoke detection — VESDA (very early warning fire detection apparatus) and equivalents — sample air continuously through small-bore sampling pipes, providing 10–30 minutes of early warning before flame development.

VESDA integration with preservation HVAC ductwork takes one of three forms:

1. In-duct sampling. Sampling pipes routed within return air ducts, sampling air at 5 to 20 points along the duct. This is the most efficient configuration for galleries and reading rooms, where return air is fully representative of the space.
2. Cross-ceiling sampling. Sampling pipes routed across ceiling voids over collection storage and stack zones. This is the standard configuration for archive vaults, where in-duct sampling does not give adequate coverage.
3. Combined configurations. Most major institutions combine both, with separate VESDA detectors covering the in-duct return air and the cross-ceiling stack-zone sampling.

From a ductwork manufacturing perspective, the key requirement is coordination between the duct manufacturer and the VESDA system designer. Sampling-pipe penetrations through the duct wall are sized, positioned and sealed during duct manufacture, not retrofitted after installation. Field-cut penetrations after installation can compromise the ductwork leakage class, which in turn compromises the loan facility report — an entirely avoidable problem with proper coordination at design stage.

HEPA filtration in galleries

Most galleries do not need HEPA filtration. MERV 13 to MERV 16 filtration, combined with activated-carbon and gas-phase polishing, delivers the pollutant targets defined above and meets Class AA environments for the majority of collections.

HEPA filtration is specified for:

• Galleries displaying photographic prints, particularly daguerreotypes, ambrotypes, tintypes and silver gelatin prints, where particulate damage is irreversible and visible to viewers.
• Galleries displaying clean-mounted works on paper without glazing, where particulate deposits are difficult to remove.
• Galleries displaying sensitive textiles, where particulate accumulation in fibre interstices is essentially permanent.
• Loan exhibitions where the lending institution specifies HEPA in the loan agreement.

HEPA filtration is typically H13 (99.95% efficiency at 0.3 µm MPPS) or H14 (99.995%). The pressure drop of a HEPA stage is 200–300 Pa clean and up to 600 Pa loaded, which has implications for fan sizing, AHU casing pressure rating and ductwork construction — the upstream duct in a HEPA-filtered system runs at higher static pressure, and the downstream duct (between HEPA and supply diffuser) must be airtight to maintain filtered-air integrity.

The SBKJ machine configuration for preservation HVAC

Manufacturing the ductwork for a preservation HVAC system requires automation that produces consistent, low-leakage construction across thousands of metres of duct, in both galvanised and stainless configurations, with full documentation traceability for the loan facility report.

The SBKJ machine configuration we recommend for preservation duty is:

• SBAL-V auto duct line. The primary rectangular duct manufacturing line in the SBKJ catalogue. Produces TDF-flanged rectangular duct at single-shift output of 600–1,000 m². Configured for both galvanised steel and stainless steel coil, with a coil-change procedure that takes 25–35 minutes between materials.
• Galvanised steel coil to AS 1397. Standard configuration for general gallery, library and museum back-of-house ductwork. Z275 coating class is the normal specification for preservation duty; Z350 for higher humidity zones.
• Stainless steel option. SBAL-V is configured to handle stainless 304 and 316 coil with the same machine and control programme, simply by changing the coil. This is the configuration we recommend for institutions with both gallery and archive zones, where the same machine produces both galvanised and stainless ductwork.
• Low-leakage SMACNA Class A construction. TDF flange profile, Pittsburgh longitudinal seam, sealed branch take-offs. Each duct section is leak-tested before shipment and the leakage rate is documented per AHU zone.
• Conservation-grade sealant compatibility. The machine is compatible with low-VOC, conservation-grade sealants applied at the seam during manufacture. Sealants are specified by the institution's conservation department and validated against the relevant references (typically ASHRAE Chapter 24, BS 5454 equivalent values, ISO 11799 storage category, AICCM compliance).

For institutions that have a substantial round-duct programme (often the case for back-of-house and stack zones), SBKJ also offers spiral tubeformer machines that produce SMACNA Class A round duct in the same materials. The combination of SBAL-V and a spiral tubeformer covers essentially the full range of preservation HVAC ductwork manufacturing in a single facility.

The 20-step preservation ductwork procedure

Bringing it all together — the procedure SBKJ engineers walk through when scoping a preservation HVAC ductwork manufacturing programme is the 20 steps below. Each step references the broader engineering disciplines covered above; the procedure itself is the sequencing.

1. Assess collection class. Walk every space against ASHRAE Chapter 24 — Class AA in loan-quality galleries, Class A general museum, Class B back-of-house, Class C transit, Class D climate-following.
2. Define specialty zones. Identify photographic, film, paper, magnetic-media and rare-book zones — each with its own temperature/RH envelope.
3. Specify environmental targets. Lock down setpoints, tolerance bands, 24-hour RH excursion limits and seasonal adjustment policy.
4. Set pollutant limits. Specify SO2, NO2, ozone, particulate and carbonyl limits at the supply diffuser.
5. Select duct material. Galvanised steel for general zones, stainless or aluminium for archive vaults.
6. Specify leakage class. SMACNA Class A minimum, tighter for Class AA preservation environments.
7. Select insulation type. Closed-cell foam — fibrous excluded.
8. Coat duct exterior. Painted or coated in mechanical zones.
9. Specify filtration train. MERV 13+ general, MERV 16 plus carbon plus gas-phase for Class AA, HEPA for photographic galleries.
10. Plan VESDA integration. Sampling pipe routes through return ductwork and over storage zones.
11. Manufacture to spec. SBKJ SBAL-V auto duct line, galvanised or stainless coil, TDF flange, low-leakage construction, sealed seams.
12. Pressure test before delivery. Factory leakage test on every section, documented per zone.
13. Crate for transit. ISPM-15 fumigated wood, desiccant, humidity indicator.
14. Install with seam sealant. Conservation-grade, low-VOC sealant on every joint — silicone excluded.
15. Commissioning leakage test. On-site re-test by accredited third party, documented per AHU zone.
16. Pollutant balance. Air balance, then sample SO2, NO2, ozone, formaldehyde, particulates at supply diffuser.
17. 24-hour RH validation. 7-day logging at 5-minute intervals — confirm ±5% (Class A) or tighter (Class AA).
18. Loan facility report. Compile HVAC drawings, leakage results, filtration docs, RH/T data.
19. Operator handover. Train on inspection, filter change, sealant cycle, leakage re-test cadence.
20. Annual re-verification. Documented in conservation governance regime.

Common procurement mistakes

Across the Australian preservation HVAC projects we have supplied ductwork to over the last decade, the same handful of procurement mistakes recur. They are worth flagging at the start of any new project so the design and procurement teams can avoid them.

• Specifying ASHRAE Class AA where Class A would suffice. Class AA roughly doubles the HVAC capital cost (tighter ductwork, redundant control loops, higher-grade filtration, more substantial dehumidification). Audit each space against actual loan demand and local-climate practical envelopes (AICCM) before defaulting to Class AA.
• Allowing fibrous duct liner in any preservation zone. Once a fibre-shedding source is in the building, removing it requires duct replacement — not duct cleaning. Specify closed-cell foam from the outset and mandate it in every quotation request.
• Specifying galvanised steel for archive vaults at low temperature. Condensation under low-temperature operation degrades galvanised coating. Specify stainless 304 or aluminium for any zone where dew-point analysis predicts condensation more than 10% of the year.
• Not specifying leakage class. Many tender briefs omit a leakage class entirely, defaulting to "industry standard" which in commercial HVAC is SMACNA Class C or worse. For preservation duty, mandate SMACNA Class A explicitly with absolute leakage targets in the tender.
• Buying from a contractor who sub-contracts duct manufacturing. Sub-contracted duct manufacturing means inconsistent seam quality across the project, no in-line leakage testing, and limited material traceability for the loan facility report. Specify factory-manufactured ductwork with documented leakage testing per section.
• Not coordinating VESDA sampling-pipe penetrations with duct manufacture. Field-cut penetrations after installation compromise leakage class. Coordinate at design stage.
• Assuming silicone sealant is acceptable. Silicone migrates onto adjacent surfaces and is excluded from preservation environments. Specify low-VOC, conservation-grade sealants from the outset.
• Skipping the 12-month RH/T documentation period before applying for loans. The major lending institutions require 12 months of documented data to verify Class AA compliance. Plan for this in the project programme — commissioning is the start of the documentation period, not the end.

How SBKJ supports preservation HVAC projects

SBKJ Group manufactures the auto duct lines, spiral tubeformers and ancillary HVAC ductwork machinery used by ductwork fabricators serving preservation projects across Australia, the UK and continental Europe. Our role is upstream of the gallery — we supply the manufacturing infrastructure that lets fabricators produce SMACNA Class A galvanised and stainless ductwork at the consistency and traceability that preservation projects demand.

For institutions and architects scoping a new preservation facility, our engineering team can:

• Review the environmental specification (ASHRAE Chapter 24 class, BS 5454 / ISO 11799 zone definitions, AICCM compliance) and confirm the manufacturing implications.
• Recommend the SBAL-V auto duct line configuration appropriate to the project — galvanised only, stainless only, or dual-material capability.
• Provide leakage test rig specifications and FAT procedures aligned with the loan facility report requirements.
• Support fabricator selection through a tender by validating that the candidate fabricators have the manufacturing capability to deliver the leakage class and material traceability the project requires.
• Provide engineering advice on coordination between duct manufacture, VESDA integration and downstream installation.

From the SBKJ Group office in Box Hill North VIC, we support projects across the Australian preservation sector and provide direct engineering response within 12 hours on any specification query. For larger projects, we can arrange in-person engineering review at our Australian headquarters or a live video walkthrough of the SBAL-V auto duct line in the configuration relevant to the project.

FAQ

What standards govern HVAC ductwork for libraries, museums, archives and galleries?

The four primary references are ASHRAE Applications Handbook Chapter 24 (Museums, Galleries, Archives and Libraries), BS 5454:2000 (Recommendations for the Storage and Exhibition of Archival Documents — withdrawn but still widely referenced), ISO 11799:2015 (Document Storage Requirements for Archive and Library Materials), and AICCM (Australian Institute for the Conservation of Cultural Material) environmental guidelines. ASHRAE Chapter 24 defines five environmental control classes (AA, A, B, C, D) with target temperature 21°C and 50% RH at varying tolerance bands.

What is the difference between ASHRAE Class A and Class AA preservation environments?

ASHRAE Class A is 21°C ±1°C, 50% RH ±5% RH with MERV 13+ filtration — suitable for general collections and most regional museums. ASHRAE Class AA is 21°C ±1°C, 50% RH ±2% RH — the highest precision class, required for international loan exhibitions, prime artwork and high-value paper collections. Class AA demands tight low-leakage ductwork (SMACNA Class A or better), redundant control loops and 24-hour RH excursion limits within ±5%.

What temperature ranges apply to specialty archive zones?

Specialty zones diverge significantly from the 21°C general standard. Photographic archives operate at 2–15°C with controlled RH 30–40%. Colour film archives go down to -2°C with very tight RH control. Paper archives are typically 13–18°C, 30–50% RH. Magnetic tape and digital media zones target 5–10°C, 20–30% RH.

What pollutant limits should preservation HVAC ductwork deliver?

Indoor air pollutant targets at the supply diffuser are SO2 below 1 µg/m³, NO2 below 2 µg/m³, ozone below 2 µg/m³, and total particulates below 50 µg/m³. Achieving these targets requires combination MERV 16 plus activated-carbon filtration, gas-phase polishing and tightly sealed ductwork — leakage-class compliance becomes a pollutant-control variable, not just an energy-efficiency one.

Why does fibrous duct insulation fail in preservation environments?

Fibrous insulations (fibreglass, mineral wool) shed micro-fibres into the airstream over their service life. Even small fibre concentrations create deposits on artwork, paper substrates and museum object surfaces — and conservation departments routinely flag them as a contamination source during loan inspections. Preservation specifications now mandate closed-cell foam insulation (elastomeric, polyisocyanurate or phenolic) with sealed seams.

What duct materials are appropriate for archive zones?

For general gallery and library zones, galvanised steel to AS 1397 with low-leakage SMACNA Class A construction is standard. For archive vaults — particularly photographic, film and rare-book vaults at low temperature and high humidity — stainless steel 304 or aluminium ductwork is specified to eliminate galvanic corrosion risk under condensing conditions.

How is loan exhibition compatibility verified for ductwork?

International loan agreements with institutions such as the Louvre, Tate, Smithsonian, MoMA and Rijksmuseum specify environmental conditions on the loan facility report. The receiving institution's HVAC documentation must demonstrate Class A or Class AA stability over 24-hour, weekly and seasonal cycles. Ductwork plays into this through measured leakage rate (SMACNA Class A or tighter), thermal stratification analysis, and verified air-change rates at the gallery level.

What aspirating smoke detection is used in archive ductwork?

VESDA (very early smoke detection apparatus) aspirating systems sample air continuously through small-bore sampling pipes installed in the return air ductwork and in archive stack ceilings. They detect smoke at concentrations 100–1000 times lower than spot detectors, providing 10–30 minutes of early warning. VESDA is mandatory for Class AA environments and standard for film archives, rare-book vaults and high-value gallery storage.

Talk to an SBKJ engineer about preservation HVAC ductwork manufacturing →