Indoor Pool and Aquatic Centre HVAC Duct Guide — Chloramine Control, Dehumidification, FINA, Olympic 2032

Why pool HVAC is the hardest envelope in commercial building services

An indoor pool is the only commercial space where four engineering disciplines collide simultaneously, each pulling the design in a different direction. The room must be warm enough that wet bathers do not feel cold as they leave the water, but not so warm that evaporation runs away and water heating cost balloons. The air must be dry enough to prevent condensation on every cold steel surface in the building envelope, but not so dry that pool surface evaporation accelerates further. The ventilation rate must be high enough to evacuate trichloramine respiratory irritants from the swimmer breathing zone, but the supply air velocity must be low enough that the spectator stand acoustic criterion holds at NC-40. And the ductwork itself must survive a corrosive chlorinated atmosphere at high humidity for a service life that local government clients increasingly specify at 30 years or more.

The cost of getting this wrong is measurable in the field. Australian aquatic centres built in the 1990s with galvanised G90 ductwork are now on their second or third duct replacement programme, often with the original steel structure also requiring partial replacement because chloride-laden condensation was allowed to migrate behind a discontinuous vapour barrier. The cost of a duct replacement on a live aquatic facility — closure of the pool hall, asbestos and lead disturbance assessments, rigging through ceiling voids built to be permanent — is routinely two to four times the original installed cost. The decisions made at the duct material specification stage of a new aquatic centre are 30-year decisions, and the engineering literature supporting them is dense and dispersed across half a dozen reference standards.

This guide consolidates the working references our engineers use when SBKJ supplies coil-fed duct fabrication machinery into Australian aquatic centre projects — from competitive 50 m FINA pool builds for the Olympic 2032 programme to Local Government redevelopments of regional Olympic-legacy pools across Queensland, New South Wales, Victoria, South Australia and Western Australia. The audience is the aquatic facility engineer, the mechanical consultant designing or auditing a natatorium HVAC system, and the Local Government recreation manager scoping a refurbishment. It is not a primer on basic HVAC. It assumes you know what a psychrometric chart is and that you can read a duct fabrication drawing.

Pool categories and their HVAC consequences

The single most expensive specification mistake on an aquatic project is treating all indoor water as the same load profile. The latent load on a competitive 50 m FINA pool with elite swimmers training at race pace is fundamentally different from the latent load on a wave pool with 200 children splashing at peak Saturday occupancy. The first design decision on any aquatic HVAC project is the use profile, not the geometry.

Competitive pools — FINA 50 m, training 25 m

A FINA-compliant competition pool is 50 m long, 25 m wide and a minimum 3.0 m deep, with two separate touch pads for finish-line redundancy and a moveable bulkhead optional for 25 m configuration. Water temperature is held tightly at 25 to 28 degrees C, with 26 to 27 degrees C the typical elite competition setpoint. Air temperature is held 1 to 2 degrees C above water — typically 28 to 30 degrees C dry bulb — and relative humidity targeted at 50 to 60 percent. Pool surface area for a 50 m by 25 m tank is 1,250 m squared. Activity factor under the Carrier evaporation equation runs 0.05 for unoccupied pool to 0.15 for a competitive training session — moderate by aquatic standards, but the surface area drives a moisture load of 125 to 225 kg per hour even at the lower activity factor.

Training pools at 25 m by 21 m or 25 m by 13 m share most specification requirements with the 50 m competition pool, scaled down. The activity factor on a training pool is typically higher than the competition pool because training pools host learn-to-swim, school squad, lane swimming and aquarobics simultaneously across the operating day. For a tier-1 aquatic facility programme of 50 m competition plus 25 m training, total moisture load typically lands in the 250 to 400 kg per hour band, demanding a dedicated pool dehumidifier with 350 to 500 kg per hour rated removal capacity at design conditions.

Recreation, leisure and wave pools

Recreation pools dominate the moisture load calculation in any modern aquatic centre. A wave pool, lazy river or kids splash zone runs an activity factor of 0.30 to 0.65 — three to ten times the activity factor of a competitive lane pool. A 600 m squared wave pool at activity factor 0.4 generates 240 kg per hour of evaporation by itself, equivalent to a 50 m competition pool at training conditions but in a fraction of the surface area. The supply air handling and dehumidification on a leisure pool must be sized for the peak weekend occupancy, not the average.

Leisure pool ductwork sizing also has to accommodate higher air change rates — 6 to 10 ACH versus 4 to 8 ACH for a natatorium — to evacuate the higher chloramine generation from concentrated child occupancy and the higher moisture load from active splashing. Source-capture exhaust at deck level is non-negotiable on a modern leisure pool because the dilution strategy cannot keep pace with the chloramine generation at the water surface. The Australian aquatic centres built since 2010 across south-east Queensland regional Local Government, Sydney metropolitan and Melbourne municipal council programmes are uniformly source-capture designs.

Therapy, hydrotherapy and rehabilitation pools

Hydrotherapy pools operate at 32 to 34 degrees C water temperature — five to six degrees warmer than a competition pool — driving a saturation pressure roughly 1.5 times higher and a corresponding 1.5 to 2 times increase in evaporation rate per unit surface area. Hospital and rehabilitation hydrotherapy pools are typically small — 6 m by 12 m to 10 m by 15 m — but the per-square-metre latent load is severe. Air temperature must still be held 1 to 2 degrees C above water, meaning the room is at 33 to 36 degrees C dry bulb. Relative humidity is held at 50 to 55 percent with a strict upper limit of 60 percent for both occupant comfort and infection control compliance.

Hospital hydrotherapy installations require dedicated air handling separate from the rest of the building HVAC, with HEPA filtration on the supply side for clinical infection control and dedicated exhaust to atmosphere. The duct material specification is identical to a competitive pool — 316L stainless throughout — but the redundancy specification is higher because the hydrotherapy pool typically supports clinical treatment programmes that cannot tolerate unplanned closure.

Spas, hot pools and steam rooms

Spas and hot pools run at 38 to 40 degrees C water temperature — in some commercial installations as high as 41 degrees C. The saturation pressure delta against any reasonable air condition is enormous, and the evaporation rate per square metre can exceed 0.6 kg per m squared per hour. A 4 m by 5 m commercial spa generates 12 kg per hour of moisture by itself — a small fraction of the total facility load by absolute number, but the per-square-metre intensity drives extremely tight requirements on local supply airflow and exhaust capture.

Spa zones are the highest-risk part of any aquatic facility for thermal stratification. Hot air rises, cool air sinks, and the natural convection plume above a 40 degrees C water surface can carry a chloramine and humidity column straight into the building structure and ceiling void unless the ductwork is positioned and sized to intercept it. SBKJ has supplied 316L stainless duct fabrication into multiple Australian commercial spa installations where the original galvanised duct failed within 4 years of commissioning — the most aggressive single environment in any commercial building.

Institutional and learn-to-swim pools

School and university learn-to-swim pools — typically 12 m by 25 m or 20 m by 25 m — sit in a different category again. Occupancy is high, activity factor is high, and the acoustic criterion is set by the swim instruction requirement rather than the spectator standard. NC-45 to NC-50 is typical, allowing slightly higher duct velocities than a competition pool, but the chloramine generation from sustained child occupancy is high and source-capture exhaust is mandatory.

Institutional aquatic facilities also have the highest demand variability — peak occupancy during school terms, near-zero occupancy during school holidays. Demand-controlled ventilation with CO2 sensing is increasingly specified to match outdoor air make-up to actual occupancy, with measurable energy savings on a 12-month operating cost basis.

Australia is an aquatic-first culture and the engineering follows

Australia operates more than 1,500 public aquatic facilities. Local Government swimming pool programmes are foundational community infrastructure across every state and territory, and the legacy of Sydney 2000 plus the build-up to Brisbane 2032 is driving the most concentrated aquatic facility investment cycle since the 1970s. Understanding the regulatory and operational context matters because it shapes the design briefs that mechanical consultants are working to.

The Olympic legacy thread

Sydney 2000 left behind the Aquatic Centre at Sydney Olympic Park — still operating as a major competition and training venue 25 years on, with HVAC system upgrades completed across multiple capital cycles. The Brisbane Aquatic Centre at the Sleeman Centre and the Olympic Park Aquatic Centre Cairns are products of the 1982 Commonwealth Games and the ongoing investment in Queensland regional aquatic infrastructure. The Adelaide Aquatic Centre upgrade and the Melbourne Sports and Aquatic Centre are anchored in the Victorian and South Australian state government recreation portfolios. Each generation of Olympic and Commonwealth Games activity in Australia has left a tier-1 aquatic facility legacy and a working specification base that newer projects benchmark against.

Brisbane 2032 is now driving the largest aquatic facility specification cycle in two decades. The Brisbane Aquatic Centre redevelopment, the South-East Queensland regional aquatic upgrades coordinated through state government and Local Government Authority programmes, and the federal Sport Australia funding round for community aquatic infrastructure are all referencing the same World Aquatics (formerly FINA) competition pool specification, ASHRAE Applications Chapter 6 HVAC reference and AS 1668.2 ventilation code. The mechanical specifications being written now are the operating standards that aquatic facilities will run on through the 2050s.

Local Government Authority programmes

More than 200 Queensland Local Government Authorities operate aquatic facilities — from major regional centres like Townsville, Cairns, Toowoomba and the Sunshine Coast to small council pools in the western and northern regions. New South Wales Sydney metropolitan councils — Inner West, Northern Beaches, Sutherland Shire, Liverpool, Penrith, Blacktown — collectively operate dozens of aquatic centres with active capital improvement programmes. Victorian municipal councils across metropolitan Melbourne and regional centres including Geelong, Ballarat, Bendigo and the Latrobe Valley operate similar portfolios. South Australia, Western Australia, Tasmania, the Northern Territory and the Australian Capital Territory all maintain LGA aquatic infrastructure investment programmes. The base specification standard across these programmes is increasingly aligned to ASHRAE Applications Chapter 6 with Australian-specific overlays for AS 1668.2 ventilation and the National Construction Code (NCC) Section J energy provisions.

Sport Australia and federal funding programmes

The federal Sport Australia funding programmes — Community Sport Infrastructure, Female-Friendly Sport Infrastructure, Better Ageing and others — have funded aquatic centre upgrades across regional Australia for the last decade. Federal grants typically require compliance with the World Aquatics facility rules for any pool that aspires to host competitive events, even at junior or regional level. This effectively pulls smaller LGA aquatic centre upgrades toward the same competition-grade specification base that the tier-1 city aquatic centres are working to. The economic consequence for HVAC design is that the engineering reference base is consolidating, not fragmenting — the same calculations and material specifications that apply to the Olympic 2032 projects also apply to a regional Queensland or Victorian municipal aquatic upgrade.

FINA, World Aquatics and the competition pool envelope

World Aquatics is the international governing body for elite competition swimming, diving, water polo, artistic swimming and open-water swimming — formerly known as FINA before the 2023 rebrand. The World Aquatics Facility Rules establish the geometric, water quality and environmental specifications for pools used in international competition. For HVAC design purposes, the relevant specifications are:

• Pool geometry. Olympic and World Championship competition: 50 m by 25 m, minimum 3 m depth. World Cup short course: 25 m by 25 m, minimum 2 m depth. Diving: 25 m by 25 m surface, 5 m minimum depth (10 m platform).
• Water temperature. 25 to 28 degrees C for swimming competition. 27 degrees C plus or minus 1 for synchronised swimming. 26 degrees C for water polo. 28 to 32 degrees C for diving.
• Air temperature. 1 to 2 degrees C above water, target 28 to 30 degrees C dry bulb for the swimming events.
• Relative humidity. 50 to 60 percent target.
• Air movement at the water surface. Less than 0.2 m per second, ideally less than 0.1 m per second for elite competition. Surface waves disrupt timing pad performance and competitive turnaround.
• Lighting. 1,500 to 2,500 lux at the water surface for broadcast competition. Heat gain from broadcast lighting is a significant secondary HVAC load — typically 8 to 15 W per m squared additional sensible heat.
• Acoustic. NC-40 to NC-45 typical for spectator areas. NC-30 to NC-35 sometimes specified for dedicated broadcast booths.

The 0.2 m per second water surface air velocity limit is the constraint that sizes most modern competition pool supply airflow design. A high-velocity supply jet at the wrong angle creates surface ripples that ruin the perceived integrity of timing pads — the camera evidence of close finishes — and elite competitive swimmers can detect cross-pool air movement that disrupts their stroke pattern. The combination of a low water-surface air velocity limit, a deck-level chloramine source-capture requirement and a high air change rate target produces a duct sizing problem that is dimensionally larger than equivalent commercial HVAC at the same conditioned floor area. Olympic competition pool supply ducts are typically 30 to 50 percent larger in cross-section than a commercial space at the same airflow because terminal velocity must drop into the low 1 to 2 m per second band before the air arrives at the pool deck.

ASHRAE Applications Chapter 6 — the dominant reference

The ASHRAE Handbook HVAC Applications Chapter 6 — Indoor Pool and Spa Facilities — is the dominant North American reference for natatorium HVAC and is referenced by Australian, European and Middle Eastern aquatic centre design teams as the working calculation base. The 2023 and 2027 editions consolidate calculations and field experience that were previously scattered across multiple ASHRAE Transactions papers and trade-press monographs. Every Australian mechanical consultant working on an aquatic project should have a current copy of ASHRAE Applications Chapter 6 on the desk.

The Carrier evaporation equation

The core calculation in Chapter 6 is the Carrier evaporation equation, which estimates pool water evaporation rate as a function of water temperature, air temperature, relative humidity, pool surface area and an empirical activity factor. In SI units the equation reads:

w_p = (A / Y) · (P_w − P_a) · F_a

Where w_p is the evaporation rate in kg per hour, A is pool surface area in m squared, Y is the latent heat of vaporisation in kJ per kg (approximately 2,430 at typical pool temperatures), P_w is the saturation vapour pressure at water temperature in kPa, P_a is the partial vapour pressure at room conditions in kPa, and F_a is the activity factor.

Activity factor values from ASHRAE Applications Chapter 6:

• Residential pool, unoccupied with cover: 0.05
• Residential pool, unoccupied without cover: 0.50
• Competitive lane swimming, occupied: 0.65
• Recreational/leisure pool, occupied: 0.65 to 1.0
• Wave pool, occupied: 1.5
• Therapy pool, occupied: 0.65
• Whirlpool/spa, occupied: 1.0

(Note that some practitioners use a normalised form of the activity factor that runs from 0.05 to 0.65 against a different equation coefficient — the underlying physics is identical, the literal values differ. Always check the equation form used in the reference document before substituting numbers.)

Worked example for a 50 m by 25 m FINA competition pool, occupied at competitive training intensity: water 27 degrees C (P_w = 3.567 kPa), air 28 degrees C and 55 percent RH (P_a = 0.55 · 3.778 = 2.078 kPa). Activity factor 0.65, surface area 1,250 m squared. Evaporation rate calculation per the ASHRAE-form equation produces a moisture removal load in the band of 180 to 220 kg per hour for the competitive condition, dropping to 35 to 50 kg per hour overnight when the pool is unoccupied and covered. This factor of four to six diurnal swing is exactly why pool dehumidification systems are sized with significant turn-down capability and modulating reheat — fixed-output dehumidifiers waste enormous quantities of energy on the off-peak operating cycle.

Latent and sensible load split

Pool hall HVAC has an unusual load split for a commercial space. Sensible load is dominated by lighting, solar gain through any clerestory glazing, and the 1 to 2 degrees C delta between supply air temperature and room setpoint. Latent load is dominated by pool surface evaporation and far exceeds sensible load on the design day — typical ratio is 3:1 latent to sensible, where commercial offices typically run 1:3 or 1:4 latent to sensible. The conventional cooling-only air handling unit selection process is meaningless for a pool hall — the unit is a dehumidifier first and a sensible cooler distant second, and the coil bypass factor and reheat capacity matter far more than the brochure cooling tonnage.

Outdoor air requirements

ASHRAE Standard 62.1 prescribes the outdoor air requirement at 0.48 cfm per square foot — approximately 87 L per second per m squared — of pool deck and water surface combined. This is a chloramine and respiratory irritant dilution requirement, not a CO2-driven IAQ requirement. For the worked-example FINA pool with 1,250 m squared water surface and approximately 1,250 m squared of deck, the total outdoor air rate becomes 2,500 m squared by 87 L per second, equal to 217,500 L per second — 783,000 m cubed per hour. Spread across a hall volume of approximately 25,000 m cubed (50 m by 25 m by 12 m typical), this represents 31 air changes per hour at the chloramine dilution rate, far in excess of the 4 to 8 ACH guideline for the natatorium.

The reconciliation between these two numbers is that the 87 L per second per m squared rate is an outdoor air supply rate, not a recirculation rate, and the 4 to 8 ACH guideline is a total supply rate including recirculation. Modern source-capture designs typically run total supply airflow at 6 to 8 ACH with outdoor air in the 25 to 50 percent of total supply band, depending on the heat recovery economics. The 87 L per second per m squared is the floor for outdoor air, not the total supply airflow.

Chloramine chemistry and the source-capture imperative

Chloramines — the reaction products of free chlorine with nitrogen-containing organics in pool water — are the single most important reason indoor pool HVAC design has diverged from generic commercial HVAC over the last two decades. Understanding chloramine chemistry is the foundation for understanding why source-capture exhaust at deck level is now best practice across competitive and recreational aquatic facilities.

The chloramine family

Free chlorine in pool water — typically dosed as sodium hypochlorite at 1 to 3 ppm — reacts with ammonia, urea, sweat amino acids, sunscreen residues and other nitrogen-containing organics introduced by bathers. The reaction sequence produces:

• Monochloramine (NH2Cl). First reaction product, mildly soluble in water, low volatility, low respiratory irritation profile.
• Dichloramine (NHCl2). Intermediate reaction product, higher volatility than monochloramine, contributes to characteristic indoor pool odour.
• Trichloramine (NCl3, also nitrogen trichloride). Highly volatile end-product, primary respiratory irritant, primary cause of swimmer asthma and lifeguard occupational health complaints, accumulates as a layer immediately above water surface and at deck level due to its higher density than air.

NCl3 trichloramine is the molecule that drives modern aquatic centre HVAC strategy. Its density is greater than air, it accumulates in a layer 200 to 600 mm above the water surface, and it migrates along the deck level from the pool tank toward any opening — change room doorways, stairwells to spectator galleries, building entry foyers. Lifeguards, learn-to-swim instructors and competitive coaches who spend their working day on the pool deck are exposed to chronic trichloramine inhalation at concentrations that can exceed occupational health thresholds even when the bulk pool hall air sample is well within compliance. The respiratory health literature now correlates competitive swimmer asthma incidence directly with cumulative pool deck NCl3 exposure during training.

Why dilution ventilation does not work

Conventional dilution ventilation supplies fresh air at high level — ceiling diffusers — and exhausts at high level. The supply air mixes through the entire hall volume before the exhaust path captures and removes any chloramine. By the time the air reaches the high-level exhaust, the trichloramine layer at the water surface has already had time to migrate laterally along the deck, accumulate in stairwells and door reveals, and reach swimmer breathing zones at concentrations that the bulk air sample never registers. Dilution ventilation reduces average pool hall NCl3 concentration but does very little to reduce peak exposure at the breathing zone where the swimmers and the deck staff actually inhale.

Source-capture as best practice

Source-capture ventilation extracts air at deck level — through linear slot diffusers, perforated trench grilles or low-level wall registers positioned 200 to 400 mm above the water surface — capturing the trichloramine layer at the source before it can migrate. Make-up air is supplied at high level along the perimeter walls in a configuration designed to wash gently down the wall surfaces and across the water toward the deck-level exhaust. The airflow pattern is engineered to maintain the cleanest air at the swimmer breathing zone — directly above the water — and concentrate the contaminated air in the exhaust path away from occupants.

The industrial design of source-capture exhaust ductwork is dominated by 316L stainless construction in trench format. A 200 mm wide stainless trench grille with internal baffles routes captured air to a 600 by 400 mm rectangular plenum running along the pool deck perimeter, which connects to the air handling unit return path. The deck-level supply air, where used, is delivered through a separate trench at the opposite side of the pool to wash air across the water surface in a controlled direction. This deck-level airflow design is exactly the application that drives the demand for high-quality 316L stainless rectangular duct fabrication — and it is the application that SBKJ stainless coil-fed auto duct lines are routinely supplied for on Australian and European aquatic centre projects.

Effectiveness in the field

Aquatic centres designed and commissioned with full source-capture exhaust report measurable improvements in lifeguard and instructor sick-leave rates, competitive swimmer training capacity and spectator complaint volume. The European aquatic centre design literature dating from the early 2010s — particularly the work in Belgium, Germany and the Netherlands following several high-profile competitive swimmer asthma studies — establishes source-capture as the standard of care. Australian aquatic centres built or refurbished since 2015 are uniformly source-capture designs, with the older stock progressively retrofitted at each major capital improvement cycle.

Dehumidification system options

The dehumidification system is the heart of any indoor pool HVAC plant. The selection between dedicated pool dehumidifier, refrigerant DX, desiccant wheel, heat pump and outdoor air economiser drives the energy operating cost, the heat recovery integration with pool water, and the ductwork plant interface design.

Dedicated pool dehumidifier with integrated heat recovery

The dedicated pool dehumidifier — branded by manufacturers including Dectron, Seresco, PoolPak, DesertAire and several European equivalents — is the dominant solution for tier-1 competitive aquatic facilities. The unit integrates a cooling coil for moisture removal, a heat recovery condenser for pool water heating, a secondary condenser for air reheat, and outdoor air mixing dampers in a single packaged plant. Heat removed from the pool hall air during the dehumidification cycle is rejected to pool water as the primary recovery path, with secondary heat rejection to outdoor air or to the building reheat circuit. The energy efficiency of an integrated pool dehumidifier substantially exceeds a generic split-DX-plus-electric-reheat configuration on the operating cost basis, and the payback against the higher capital cost is typically under 5 years in Australian commercial aquatic operating contexts.

Refrigerant DX dehumidification

Refrigerant DX dehumidification — using a conventional packaged or split air conditioning unit oversized for the latent load — is the legacy solution and is still installed on smaller school and community pool projects for capital cost reasons. The energy efficiency is poor because there is no heat recovery to pool water, and the dehumidified supply air must be reheated to room setpoint either electrically (high operating cost) or via a separate hydronic reheat coil (higher capital cost, better operating cost). Refrigerant DX is acceptable for therapy pools below 200 m squared surface area or for institutional pools with constrained capital budgets, but is not specified on competitive or major recreational aquatic facilities in Australia.

Desiccant wheel dehumidification

Desiccant wheel dehumidification uses a rotating wheel of solid desiccant — typically silica gel or molecular sieve — to adsorb moisture from the supply airstream, with regeneration in a separate hot air loop. The technology offers very low dew point capability and is well-suited to applications where outdoor air dew point falls below the natatorium dew point — northern European and northern American climates — providing free dehumidification of the outdoor air component. In Australian climates, the economic case is weaker because Brisbane, Sydney and northern Australian outdoor air conditions exceed natatorium conditions for much of the year, eliminating the free-dehumidification benefit. Desiccant systems are occasionally specified on tier-1 Australian aquatic projects in combination with refrigerant DX, but are not the dominant solution.

Heat pump dehumidifier

The heat pump dehumidifier is a variant of the dedicated pool dehumidifier that uses a single refrigerant circuit to extract moisture from the pool hall air and deliver the rejected heat directly to pool water. The technology has matured substantially over the last decade and is now competitive with the integrated pool dehumidifier on operating cost basis for medium-sized facilities. Capital cost can be lower than a packaged dehumidifier because the secondary air reheat condenser is omitted, with reheat instead provided by a separate hydronic loop fed from the same pool water heating system.

Outdoor air economiser

The outdoor air economiser provides free dehumidification when outdoor air dew point falls below natatorium dew point. Operating dew point in a natatorium at 28 degrees C and 55 percent RH is approximately 18.5 degrees C. Outdoor dew point falls below 18.5 degrees C in Melbourne, Adelaide, Hobart and Canberra for substantial portions of the winter and shoulder seasons, providing genuine free-dehumidification capacity. Brisbane, Sydney coastal and the northern Australian capitals rarely benefit from economiser operation. The economiser strategy is straightforward to integrate into the supply air handling — a modulating outdoor air damper and a return air damper coordinated by a control loop measuring outdoor and natatorium dew point — and the capital cost adder is modest. Inclusion of an economiser circuit is recommended for any aquatic project in southern Australia.

Air change rates and ventilation specification

The total supply airflow specification for a natatorium is determined by three independent constraints, the highest of which governs:

• Outdoor air rate. ASHRAE Standard 62.1 minimum 87 L per second per m squared of pool deck and water surface combined.
• Air change rate. 4 to 8 ACH for competitive natatorium hall, 6 to 10 ACH for high-activity wave or leisure pool, 6 to 8 ACH for therapy and learn-to-swim, 8 to 12 ACH for spa zones.
• Latent removal capacity. Total supply airflow times (room humidity ratio minus supply air humidity ratio) must equal or exceed the design moisture load.

For the worked-example FINA pool with 25,000 m cubed hall volume and 250 kg per hour latent load, the latent removal calculation typically gives 4 to 6 m cubed per second of supply airflow at a 5 g per kg humidity differential — 14,400 to 21,600 m cubed per hour, or approximately 0.6 to 0.9 ACH. The chloramine dilution requirement at 87 L per second per m squared on 2,500 m squared combined deck and water surface gives 217.5 L per second per m squared total — 217,500 L per second outdoor air, equivalent to 783,000 m cubed per hour and 31 ACH on outdoor air alone. The air change rate guideline at 6 ACH gives 150,000 m cubed per hour total supply airflow.

The reconciliation in practice is that the 87 L per second per m squared chloramine rate is far higher than required if the design adopts source-capture exhaust with effective deck-level capture velocity. Modern Australian aquatic centre designs frequently halve the bulk supply airflow against the 87 L per second per m squared dilution rate by designing for direct deck-level chloramine capture, with the verification metric being measured deck-level capture velocity (typically 2 to 5 m per second at the trench grille face) rather than bulk airflow. This is one of the active areas of ASHRAE Applications Chapter 6 evolution and the 2027 edition is expected to formalise the source-capture credit against the bulk dilution requirement.

Material specification — why galvanised fails and 316L wins

The duct material specification for an indoor pool is the single highest-leverage 30-year decision on the entire mechanical project. The chlorinated atmosphere of a natatorium is one of the most aggressive corrosion environments in commercial building services, and the wrong material choice writes a duct replacement programme into the operating budget at year 5, year 10 and year 15.

Galvanised G90 — why it fails

Galvanised G90 zinc-coated steel is the default ductwork material for commercial HVAC across Australia, the United States and most of the world. The G90 designation indicates 275 grams of zinc per square metre per side, providing approximately 25 to 50 years of service life in normal indoor commercial environments. In a natatorium, the zinc reacts with chlorine and chloramines in the atmosphere to form zinc chloride — a hygroscopic white powder that absorbs moisture from the air and continues to corrode the underlying steel even after the zinc layer is fully consumed. Field-documented galvanised duct failure timeline in Australian aquatic centres:

• Year 1 to 3. Surface zinc oxidation, white powder deposits at duct joints and hanger contact points, no functional impact.
• Year 3 to 5. Pinhole corrosion at high-stress points (joint flanges, hanger contact, condensate drip points). Joint sealant degradation. Insulation moisture infiltration begins.
• Year 5 to 8. Through-wall corrosion. Visible rust streaking on duct exteriors. Duct sag at hanger points due to corrosion-thinned wall section. First duct section replacements.
• Year 8 to 12. Wholesale duct replacement programme. Often coupled with structural steel inspection and partial replacement because chloride-laden condensation has migrated through compromised vapour barriers.

The 8 to 12 year duct replacement cost on a major aquatic facility — including pool hall closure, asbestos and lead disturbance assessments, ceiling void access, rigging and replumbing — routinely runs $2 to $5 million on a tier-1 facility. Spread across the design life, the lifecycle cost of a galvanised solution exceeds the initial capital cost of a 316L stainless solution by a factor of 2 to 4.

316L stainless — the established standard

316L stainless steel — the low-carbon (L) variant of the 316 alloy, with 10 to 14 percent nickel and 2 to 3 percent molybdenum — is the established standard for natatorium ductwork. The molybdenum content provides resistance to chloride pitting and stress corrosion cracking that the standard 304 stainless lacks, and the low-carbon variant resists sensitisation at welded joints. Field-documented service life in Australian aquatic centres is 25 to 40 years on the original installation, with maintenance limited to gasket replacement at joints and fixing torque inspection. SBKJ supplies 316L stainless coil-fed duct fabrication as a standard option on the SBAL-V auto duct line and the SBTF spiral tubeformer, with material thickness in the 0.8 to 1.5 mm band depending on duct cross-section and pressure class.

Aluminium-zinc coated steel (Galvalume)

Aluminium-zinc coated steel — branded Galvalume in Australia and Zincalume by BlueScope — substitutes 55 percent aluminium for the pure zinc coating, providing improved chloride resistance over galvanised G90. Galvalume is acceptable in pool dehumidifier outdoor sections and in plant rooms adjacent to but not directly connected to the pool hall atmosphere, but is not the specified material for the natatorium envelope itself on a tier-1 facility. Service life in pool atmosphere is typically 12 to 18 years versus 25 to 40 years for 316L stainless — better than galvanised but still demanding mid-life replacement.

FRP and PVDF-lined duct

Fibreglass-reinforced polyester (FRP) duct is specified for chemical store exhaust where direct chlorine vapour exposure is continuous — sodium hypochlorite storage, chlorine gas storage on older facilities, hydrochloric acid (pH adjustment) storage. PVDF-lined steel — polyvinylidene fluoride lining over a steel backbone — is used for the most aggressive chemical exhausts and for the immediate duct connection to the chlorination plant. Both materials have specialised fabrication requirements and are typically supplied by chemical-engineering ductwork specialists rather than HVAC duct fabricators.

EPDM gaskets and stainless fixings

The duct material specification extends to every component in contact with natatorium atmosphere. Gaskets must be EPDM (ethylene propylene diene monomer) elastomer for chlorine and chloramine resistance — silicone and standard rubber compounds degrade rapidly. Threaded rod, unistrut, hangers, fixings and structural support steel must all be 316L stainless or hot-dip galvanised after fabrication followed by epoxy paint topcoat. Carbon steel exposed to natatorium atmosphere fails within months. The cost adder for full 316L stainless support hardware is significant on a major project — frequently $200,000 to $500,000 — but it is the right specification for a 30-year service life.

Structural corrosion and the building envelope

The building envelope of an aquatic centre — wall panels, roof structure, ceiling void components, glazing frames and vapour barrier — is in continuous contact with the same chlorinated atmosphere as the ductwork. The structural design and material specification of the envelope is as important as the HVAC design itself, and the two disciplines must be coordinated through the entire project programme.

The vapour barrier discipline

Interstitial condensation — moisture condensing inside the wall or roof cavity rather than on the visible internal surface — is the single biggest cause of premature aquatic centre structural failure. The mechanism is straightforward: warm humid air from the natatorium migrates outward through any breach in the internal vapour barrier, hits the dewpoint at some point inside the insulation, condenses on the cold steel structure or backing material, and accumulates progressively over years until the structural steel is severely compromised by chloride-laden water exposure.

The defence is a continuous vapour barrier on the warm (natatorium-facing) side of the insulation, sealed at every penetration, every expansion joint, every corner and every fixing. The vapour barrier is detailed by the architect in coordination with the structural and mechanical engineers, with specific attention to:

• Duct penetrations through the vapour barrier — sealed with EPDM boot and stainless fixings, never with construction adhesive or generic silicone.
• Roof drainage outlets — sealed with prefabricated EPDM or TPO upstands, never field-detailed.
• Light fitting penetrations — flush LED fittings only, no recessed downlights with cavity exposure.
• Glazing frame interfaces — thermally broken aluminium frames with continuous EPDM gasket to the vapour barrier.
• Wall-to-roof junctions — continuous flashed transition with vapour barrier overlap.

Structural steel specification

Structural steel exposed to natatorium atmosphere must be 316L stainless or hot-dip galvanised after fabrication followed by an epoxy paint topcoat with a 25-year manufacturer warranty for chlorinated atmosphere exposure. Some Australian aquatic centres — particularly those near the coast where chloride loading is doubled by salt-laden coastal air — specify 6063-T6 aluminium structural members for roof and ceiling void components, providing inherent chloride resistance at lower mass than steel. Aluminium structural specifications must address galvanic isolation from any 316L stainless duct or fixing components — direct contact between aluminium and stainless in a chlorinated atmosphere produces galvanic corrosion of the aluminium.

Coordinating duct routing with structure

The duct routing strategy on a major aquatic project must coordinate with the structural design from concept stage. High-level supply ducts and exhaust returns share ceiling void space with structural steel, lighting, fire services, BMS cabling and the vapour barrier substrate. Duct hanger fixings transfer load into the structure and must use 316L stainless threaded rod, EPDM isolation washers and stainless backing plates — never carbon steel concrete anchors driven directly into the slab from the natatorium side. Pre-insulated duct sections with factory-applied vapour barrier reduce site detailing risk and accelerate the construction programme; this is a common requirement on tier-1 aquatic projects and it is one of the value-adds of off-site coil-fed duct fabrication.

Pool deck airflow design

The airflow pattern at the pool deck determines whether the source-capture exhaust strategy works in practice or fails. The supply air must be delivered in a controlled direction — gentle, low-velocity, washing across the water surface from one side toward the deck-level exhaust on the opposite side — without creating waves on the water surface that disrupt timing pad performance.

Supply diffuser positioning

Supply air is delivered from high-level perimeter diffusers along one long side of the pool, configured to wash air down the wall surface and across the deck toward the opposite long side. Linear slot diffusers with adjustable vanes are the standard, allowing the throw direction to be tuned during commissioning to achieve the design airflow pattern. Supply air must not impinge directly on the water surface — the resulting surface ripples disrupt swimmer stroke and timing pad operation. Terminal supply velocity at the water surface should be below 0.2 m per second for competitive use, below 0.3 m per second for recreational use.

Deck-level exhaust trench design

Deck-level exhaust is delivered through a continuous trench grille along the long side of the pool opposite the supply, positioned 200 to 400 mm above the water surface. The trench grille dimension is typically 100 to 200 mm wide by the full long-side length, with internal baffles channelling captured air to the air handling unit return path. Capture velocity at the grille face should be 2 to 5 m per second to ensure effective trichloramine capture — too low and the chloramine layer is not entrained, too high and turbulence at the water surface creates the same wave issue as direct supply impingement.

The deck-level exhaust trench is the application that drives demand for high-quality 316L stainless rectangular duct fabrication. The trench plenum running below the deck level — typically 600 by 400 mm or 800 by 500 mm cross-section — connects through the deck slab and routes around the pool perimeter to the air handling plant. SBKJ stainless coil-fed auto duct lines (SBAL-V variant) fabricate this duct work directly from 316L stainless coil at the same productivity as galvanised duct production, with the only programme adder being the longer lead time on 316L raw coil from the rolling mill.

Cross-section and velocity

Pool hall supply ducts run at lower terminal velocity than commercial HVAC ducts to satisfy the water surface air movement constraint and the spectator acoustic NC criterion. Main supply duct velocity is typically 5 to 7 m per second on the air handling unit discharge, dropping through expansion plenums to 3 to 4 m per second on branch ducts and below 2 m per second on the terminal diffuser approach. Cross-section sizing is correspondingly larger than equivalent commercial HVAC at the same airflow — 30 to 50 percent larger ducts for the same volume, with proportionally larger ceiling void allowances and structural support requirements.

Water heating integration with HVAC

Pool water heating and natatorium air dehumidification share the same physical heat — the latent heat of vaporisation of water removed from the air during dehumidification is identical to the heat that needs to be returned to the pool water to compensate for the surface evaporation losses. Integrating the two is the single highest-leverage energy efficiency move in any aquatic centre design.

Primary heat recovery to pool water

The dedicated pool dehumidifier — the dominant solution for tier-1 facilities — integrates a heat recovery condenser dedicated to pool water. The dehumidifier removes moisture from the pool hall air, and the rejected heat is delivered directly into a pool water heat exchanger via a refrigerant or hydronic loop. The pool water heater handles only the loads not covered by dehumidifier recovery — fresh make-up water heating, splash-out replacement and the residual delta after recovery. Operating cost for pool water heating in a properly integrated system can fall to 30 to 40 percent of an equivalent non-integrated configuration, with the largest savings in winter months when both dehumidification load and pool heating demand are high.

Secondary heat recovery to outdoor air make-up

Outdoor air make-up at the chloramine dilution rate represents a substantial fresh air heating load in winter and cooling load in summer. Heat recovery between exhaust air and outdoor air make-up via a plate heat exchanger, rotary thermal wheel or run-around glycol coil pair recovers 50 to 70 percent of the heating and cooling energy that would otherwise be required to condition the outdoor air to room conditions. The selection between plate, rotary and glycol depends on the project specifics:

• Plate heat exchanger. Cross-flow or counter-flow plate exchanger with 60 to 70 percent sensible recovery. No latent recovery. No cross-contamination risk between exhaust and make-up streams. Best suited where outdoor air is significantly drier than exhaust (winter operation in southern Australia).
• Rotary thermal wheel. 70 to 85 percent sensible recovery, 50 to 70 percent latent recovery (with enthalpy wheel desiccant coating). Some cross-contamination risk between streams (1 to 5 percent typical) — verify acceptable with project ventilation engineer. Wheel cassette material must be specified for chlorinated atmosphere — standard aluminium cassettes corrode within 3 to 5 years. Coated aluminium or 316L stainless cassettes are required.
• Glycol run-around coil. 40 to 55 percent sensible recovery. Zero cross-contamination. Highest capital cost. Most flexible plant room layout because the exhaust and make-up air handlers can be physically separated.

Pool cover use during off-hours

The single highest-impact operational measure on aquatic centre energy use is the pool cover during off-hours. A floating insulated cover reduces evaporation rate by 70 to 90 percent and reduces pool water heat loss by 50 to 70 percent overnight. The HVAC system can correspondingly drop into low-load mode during covered hours, reducing fan power, dehumidifier compressor runtime and outdoor air make-up to a small fraction of operating-hours load. Pool cover automation is straightforward to integrate with the BMS and is now standard specification on competitive aquatic facilities. The duct sizing and air handling plant capacity must still be sized for the open-pool design condition — covers reduce average load, not peak load.

Energy efficiency and demand-controlled ventilation

Beyond the major heat recovery and pool cover measures, there is a portfolio of incremental energy efficiency moves that compound across the operating life of the facility.

• Variable speed drives on supply and return fans. Modulate airflow to match instantaneous occupancy and latent load — significant savings against fixed-speed operation.
• CO2 sensors in the pool hall. Drive outdoor air make-up to actual occupancy rather than worst-case design occupancy. Suitable for institutional and learn-to-swim pools with high occupancy variability.
• Trichloramine sensors at deck level. Direct measurement of the chloramine layer informs source-capture exhaust modulation. Sensor technology is improving rapidly; expect this to be standard specification on tier-1 facilities by 2030.
• Building envelope thermal performance. NCC Section J compliance is the floor; tier-1 aquatic facilities increasingly target 30 to 50 percent better than NCC minimum to manage operating cost and reduce HVAC capacity.
• LED lighting throughout. Reduces broadcast lighting heat gain by 40 to 60 percent against legacy metal halide fittings. Reduces sensible cooling load and reduces glazing solar gain coupling.
• Solar PV on the roof structure. Where the roof structure permits, solar PV offsets a significant fraction of the annual electrical operating cost. Coordinate with roof penetration and vapour barrier discipline to avoid compromising the envelope integrity.

Major Australian aquatic centre projects

The Australian aquatic centre design and refurbishment programme is concentrated and active. Projects currently in delivery or in the immediate planning pipeline include:

• Aquatic Centre at Sydney Olympic Park — the original Sydney 2000 venue, ongoing capital improvement programmes across multiple capital cycles. Tier-1 reference for FINA/World Aquatics competition pool HVAC.
• Brisbane Aquatic Centre at the Sleeman Centre — Olympic 2032 redevelopment programme. Major HVAC capacity upgrade and source-capture exhaust retrofit anticipated.
• Adelaide Aquatic Centre — recent major upgrade programme delivered competitive 50 m, training, leisure and learn-to-swim pools with full source-capture HVAC. Reference for southern Australian aquatic centre best practice.
• Melbourne Sports and Aquatic Centre — long-running facility with progressive HVAC upgrade across multiple capital cycles. Reference for Victorian state government aquatic infrastructure.
• Olympic Park Aquatic Centre Cairns — northern Queensland tropical climate aquatic facility. Reference for high-humidity climate aquatic HVAC where outdoor air economiser delivers minimal benefit.
• Regional Queensland Local Government aquatic centres — concentrated upgrade programme across more than 200 LGAs, federally co-funded through Sport Australia community infrastructure rounds.
• Sydney metropolitan council aquatic centres — Inner West, Northern Beaches, Sutherland, Liverpool, Penrith, Blacktown and others operating active capital improvement programmes.
• Victorian municipal aquatic centres — metropolitan Melbourne and regional centres including Geelong, Ballarat, Bendigo and the Latrobe Valley.

The common specification thread across these projects is the consolidation around ASHRAE Applications Chapter 6 calculation methodology, source-capture exhaust strategy, 316L stainless ductwork material standard and integrated dehumidifier-pool water heat recovery. The design briefs being written today are the operating standards that aquatic facilities will run on through 2050 and beyond.

Hospital therapy pool HVAC

Hospital and rehabilitation hydrotherapy pools are a specialised subset of aquatic HVAC with stricter requirements than recreational or competitive pools. Key differences:

• Water temperature. 32 to 34 degrees C — significantly higher than competition pool, driving higher per-square-metre evaporation rate.
• Air temperature. 33 to 36 degrees C dry bulb to maintain the 1 to 2 degrees C delta above water — uncomfortable for staff but clinically required for patient thermoregulation.
• Relative humidity. 50 to 55 percent target with strict 60 percent upper limit for both clinical infection control and structural envelope protection.
• HEPA filtration. H13 or H14 HEPA on the supply side, dedicated exhaust to atmosphere with no recirculation. Pool hall pressurisation is typically negative relative to surrounding clinical spaces to prevent airborne pathogen migration.
• Redundancy. N+1 air handling unit configuration, dual dehumidifiers, automatic changeover. Hydrotherapy pool closure disrupts active clinical treatment programmes that the rest of the hospital cannot easily reschedule.
• Material specification. 316L stainless throughout. Hospital-grade EPDM gaskets with antimicrobial certification. Stainless fixings only.

Hospital hydrotherapy HVAC is typically delivered as a sub-package within the larger hospital HVAC contract and is procured to the same compliance standards as other clinical spaces. SBKJ stainless coil-fed duct fabrication is a common specification in this segment because the 316L material requirement dovetails directly with the broader clinical material specification.

Spa and hot pool HVAC

Spas, hot pools and steam rooms are the most aggressive single environment in any aquatic facility. Key engineering points:

• Water temperature 38 to 41 degrees C. Saturation pressure delta against any reasonable air condition is enormous. Per-square-metre evaporation rate can exceed 0.6 kg per m squared per hour.
• Thermal stratification. The buoyant plume above a hot water surface carries chloramines and humidity straight to the ceiling. Localised exhaust at the hot pool perimeter and at the ceiling above is mandatory.
• Compact volume. Spa zones are typically small — 30 to 80 m squared floor area — but the volumetric air change rate must be 8 to 12 ACH to manage the latent and chloramine load. Duct sizing and fan capacity are correspondingly sized to the spa zone independently of the bulk pool hall.
• Material specification. 316L stainless mandatory. Galvanised duct fails in spa zones within 24 to 48 months — the most aggressive failure mode in any commercial HVAC environment.
• Steam room integration. Where a steam room adjoins the spa zone, the steam room exhaust must be entirely separate with dedicated condensation drainage. Steam room atmosphere is pure water vapour at 100 percent RH and 45 to 50 degrees C — different problem set from the chlorinated pool atmosphere.

Construction phasing and programme

The construction programme on a major aquatic facility runs in a strict sequence dictated by the pool tank construction critical path. Mechanical works coordinate with this sequence as follows:

1. Site preparation and bulk excavation. Pool tank excavation, retaining wall construction, services pit excavation. No HVAC works at this stage beyond design coordination.
2. Pool tank shell-and-core. Reinforced concrete pool tank, deck slab, deck-level service trenches. Critical path for the entire mechanical programme — HVAC fitout cannot commence until shell-and-core is complete and weatherproof.
3. Building envelope close-up. Roof structure, wall panels, glazing, vapour barrier installation. Mechanical fitout commences in parallel once envelope is approximately 60 percent complete.
4. HVAC plant installation. Air handling units, dehumidifiers, fan coils, primary ductwork mains. Typically 10 to 18 weeks of mechanical fitout depending on facility scale.
5. HVAC distribution and terminal devices. Branch ductwork, deck-level supply and exhaust trenches, terminal diffusers, balancing dampers. 6 to 10 weeks.
6. Tile and grout. Pool tank and deck tiling. Coordinate carefully with mechanical services to ensure deck-level exhaust grilles are not fouled by grout overspray.
7. Pool fill, water treatment commissioning. Fresh water fill, chemical balance, filtration system commissioning. Pool hall HVAC commences trial operation at this stage.
8. HVAC commissioning and air balance. Test and balance to AIRAH DA-19 or equivalent, verify deck-level exhaust capture velocity, confirm RH and temperature setpoints, document commissioning report.
9. Defects Liability Period. 12 month observation period with monthly inspection of duct integrity, gasket condition and dehumidifier performance. Any field-observed corrosion or condensation issue is rectified at supplier risk.

The integration with off-site fabrication is the lever that compresses the HVAC fitout programme. Coil-fed auto duct line fabrication on 316L stainless can produce 2,000 to 3,500 m squared of finished duct per shift per line — the entire fabrication programme for a tier-1 aquatic facility can complete in 8 to 14 weeks of single-line operation, parallel to the building envelope close-up and shell-and-core completion. SBKJ has supplied SBAL-V stainless variant duct lines into multiple Australian aquatic centre projects where the off-site fabrication programme was the critical path enabler against tight Olympic or Commonwealth Games delivery deadlines.

SBKJ machinery for aquatic centre fabrication

SBKJ Group manufactures coil-fed HVAC duct fabrication machinery sized for the production volumes and material specifications of major aquatic centre projects. The relevant machine types for aquatic ductwork:

SBAL-V auto duct line (stainless variant)

The SBAL-V is the workhorse for rectangular pool deck supply, return and exhaust ductwork. The stainless variant is specified for 316L coil at 0.8 to 1.5 mm thickness, with all forming rollers, cutting tools and TDF flange formers selected for stainless steel processing. Single-shift output runs 1,200 to 1,800 m squared on 316L depending on duct size mix and operator experience. Output cross-sections range from 200 by 200 mm to 1,500 by 1,500 mm in single-piece construction, larger cross-sections by site-jointed sections. Joint format is TDF (Transverse Duct Flange) with EPDM gasket — the standard joint for SMACNA leakage class 3 and AS/NZS 4254 medium-pressure ducts.

SBTF spiral tubeformer (stainless variant)

The SBTF stainless variant produces round spiral-wound duct on 316L coil for branch and riser applications where round duct is preferred over rectangular for aerodynamic reasons. Diameter range 100 to 1,500 mm, wall thickness 0.6 to 1.2 mm. The lock-form spiral seam is leak-tight to SMACNA class 3 without additional sealing on most diameter ranges, and round duct provides 30 to 40 percent lower pressure drop per metre than equivalent-area rectangular duct — material savings on fan power compound across the operating life of the facility.

TDF flange former

The standalone TDF flange former produces transverse duct flanges for site-jointed duct sections — useful where on-site fabrication or modification is required to accommodate building services coordination late in the programme. The TDF flange standard provides leakage class 3 performance at lower joint cost than slip-and-drive or angle-iron flange systems.

Coil handling and material storage

316L stainless coil handling differs from galvanised in two respects: surface protection during handling (PE film overlay is standard, must be removed before forming) and slow-speed forming through the first pass to avoid surface galling. SBKJ stainless variant lines are configured with appropriate coil decoilers, surface-protected feed tables and lower-friction forming rollers as standard. The total programme adder for a stainless line over the equivalent galvanised line is typically 8 to 12 weeks of additional lead time on the rolling mill side, plus a 5 to 15 percent capital cost premium on the machine itself.

Lead time and project integration

For a tier-1 aquatic centre project — 50 m FINA pool, 25 m training pool, leisure pool and learn-to-swim — total duct quantity typically lands in the 15,000 to 30,000 m squared band depending on hall geometry and source-capture design. Single-shift fabrication on a properly sized SBAL-V stainless line completes the entire programme in 8 to 14 weeks, parallel to the building envelope close-up and shell-and-core completion. Plan 16 to 24 weeks from contract to first duct on site for a tier-1 aquatic project, including 6 to 10 weeks of 316L coil lead time from the rolling mill. For major Olympic or Commonwealth Games delivery deadlines, the duct fabrication programme is typically the critical path enabler — front-loading the 316L coil order is the single highest-leverage programme decision on the entire project.

Acoustic design

The acoustic environment of an aquatic centre is dominated by reverberant noise from water surfaces and tile finishes — the room is naturally a hard, echoing environment with reverberation times typically running 3 to 6 seconds untreated. The HVAC system noise contribution is layered on top of this reverberant background and must be controlled to maintain useful acoustic conditions for competition timing, public address intelligibility and occupant comfort.

NC criteria for natatorium spaces

• Olympic competition pool, spectator areas: NC-40 to NC-45.
• Olympic competition pool, broadcast booths and media positions: NC-30 to NC-35.
• Training and learn-to-swim halls: NC-45 to NC-50.
• Recreation and leisure pools: NC-45 to NC-50 acceptable; family environment can tolerate higher background.
• Therapy and hydrotherapy pools: NC-35 to NC-40 — clinical environment requires lower background for staff communication.
• Spa zones: NC-40 to NC-45.

Acoustic implications for duct sizing

Lower NC criterion drives lower duct velocity. NC-40 typically requires terminal supply velocity below 4 m per second, NC-30 below 2.5 m per second. Combined with the water surface air movement constraint and the relatively low pressure drop budget, this drives oversized duct cross-sections compared to commercial HVAC. Plan for ducts 30 to 50 percent larger in cross-section than a generic commercial space at the same airflow.

Attenuator and silencer specification

Inline silencers at the air handling unit discharge and at fan inlets are standard on tier-1 aquatic projects. Silencer media must be specified for chlorinated atmosphere — standard mineral wool silencer infill degrades within 5 to 10 years in pool atmosphere. Specify enclosed packs (mineral wool or fibreglass enclosed in perforated stainless or polyester film) for chlorine resistance. Silencer casings should be 316L stainless on the natatorium side and may transition to galvanised on the plant room side after a flexible isolator.

Breakout noise from ductwork

Rectangular sheet metal ductwork radiates breakout noise into the surrounding space at low frequencies — typically 63 to 250 Hz — and this is often the dominant noise source in the pool hall ceiling void. Mitigation strategies include external duct lagging (mass-loaded vinyl or similar), lateral cross-bracing on large rectangular ducts to suppress panel resonance, and conversion to round duct on long high-velocity runs where the geometry permits. Round duct breakout is 8 to 12 dB lower than equivalent rectangular at the same velocity and airflow.

Commissioning and air balancing

The commissioning and air balancing process on an aquatic facility is more rigorous than on a generic commercial HVAC project because the design intent is so closely tied to specific airflow patterns at the pool deck. Key commissioning verifications:

• Total supply airflow. Measured at the air handling unit discharge with a calibrated flow grid or pitot-tube traverse. Verify against design within plus/minus 10 percent.
• Outdoor air rate. Measured at the outdoor air intake duct with calibrated thermal anemometer or pitot. Verify against ASHRAE 62.1 minimum 87 L per second per m squared of pool deck and water surface combined.
• Deck-level exhaust capture velocity. Measured at the trench grille face with calibrated rotating-vane anemometer or hot-wire. Verify 2 to 5 m per second at the design point.
• Water surface air velocity. Measured at multiple points across the pool with hot-wire anemometer. Verify below 0.2 m per second for competitive use, below 0.3 m per second for recreational use.
• RH and temperature. Measured at multiple points across the hall and at the pool deck breathing zone. Verify within plus/minus 5 percent RH and plus/minus 1 degree C of design.
• Dehumidifier performance. Measured moisture removal rate at the design condition. Verify against unit nameplate and against calculated latent load.
• Pool water heat recovery rate. Measured heat delivery rate from dehumidifier to pool water. Verify against design and against sensible cooling rate at the dehumidifier coil.
• Chloramine concentration at deck level. Measured trichloramine concentration with portable photometric analyser at multiple points along the pool deck. Verify below the threshold concentration applicable in the project jurisdiction (typically 0.3 to 0.5 mg per m cubed for occupational exposure).
• Acoustic NC level. Measured A-weighted and octave-band sound pressure at spectator areas, breath positions and operator workstations. Verify against design NC criterion.

Commissioning is performed against a documented test procedure aligned with AIRAH DA-19 (Australia) or ASHRAE Guideline 1 (international). The commissioning report is the formal handover document that triggers the Defects Liability Period and is the reference for any subsequent retro-commissioning or capital improvement project. See our HVAC commissioning and air balancing guide for the broader commissioning methodology.

Maintenance regime through the operating life

Aquatic centre HVAC has the most aggressive operating environment in commercial building services. Maintenance must be proactive, not reactive, to deliver the design service life. Standard maintenance regime:

Monthly inspection

• Visual inspection of all visible duct surfaces for corrosion, condensation, gasket weeping or sealant failure.
• Dehumidifier coil inspection and condensate pan check.
• Filter change on supply air handling units (typically MERV 8 to MERV 13 for pool hall, HEPA for hydrotherapy).
• Pool cover automation function check.
• BMS trend log review for setpoint drift, runaway operation or sensor calibration drift.

Quarterly inspection

• Detailed inspection of source-capture exhaust trench grilles for blockage, grout fouling or accumulated debris.
• Air balance verification at random sample points — not full retest, but spot-check against commissioning baseline.
• Heat recovery exchanger inspection for dirt accumulation and corrosion.
• Dehumidifier performance trend review.

Annual inspection

• Full duct system internal inspection by camera or by removable duct section sampling.
• Gasket replacement at any duct joint showing degradation. Plan EPDM gasket replacement at 7 to 10 year intervals as a programmed activity.
• Vapour barrier continuity inspection at all duct penetrations and roof transitions. Repair any breaches before the next humid season.
• Structural fixing torque check on all 316L stainless threaded rod, unistrut and hangers.
• Dehumidifier coil chemical clean and refrigerant charge verification.
• Acoustic spot-check at spectator and breath positions to verify no drift from commissioning baseline.

5-year retro-commissioning

• Full air balance retest against original commissioning baseline.
• Chloramine concentration measurement at deck level and breathing zone.
• Energy consumption benchmarking against design intent and against industry peer facilities.
• BMS strategy review and tuning.
• Capital improvement scoping — identify any system elements approaching end-of-life within the next 5 to 10 years.

Cost benchmarks for aquatic HVAC ductwork

Indicative cost ranges for HVAC ductwork on a tier-1 Australian aquatic facility, supplied and installed, in 2026 currency:

• 316L stainless rectangular duct, supply and install: AUD 380 to 580 per m squared depending on cross-section mix, fitting density and access difficulty.
• 316L stainless spiral round duct, supply and install: AUD 320 to 480 per m squared.
• Galvanised G90 rectangular duct (acceptable in plant rooms only, not natatorium): AUD 180 to 280 per m squared.
• FRP duct for chemical store exhaust: AUD 600 to 900 per m squared.
• External duct insulation with vapour barrier, supply and install: AUD 80 to 140 per m squared.
• 316L stainless trench grille and supports for source-capture exhaust: AUD 1,200 to 2,200 per linear metre depending on width and depth.
• Pool dehumidifier with integrated heat recovery, packaged: AUD 250,000 to 1,200,000 depending on capacity (50 to 500 kg/h).

Total HVAC ductwork value on a tier-1 aquatic facility — 50 m competition pool plus 25 m training plus leisure plus learn-to-swim — typically lands in the AUD 4 to 9 million band, with the duct fabrication itself representing 35 to 45 percent of that total and installation, insulation, fixings and accessories making up the balance. Off-site fabrication on a coil-fed auto duct line typically delivers 15 to 25 percent cost reduction against fully site-fabricated duct, with the larger savings on tighter project programmes where site labour is the binding constraint.

FAQ

What duct material should be used in an indoor pool or aquatic centre?

316L stainless steel is the default for supply, return and exhaust ductwork inside the natatorium envelope. The chlorinated atmosphere — particularly the trichloramine layer at the water surface and the chloride salts deposited from evaporation — destroys galvanised G90 sheet and standard 304 stainless within 5 to 10 years. 316L with EPDM gaskets and stainless fixings is the only material combination with a documented 25-year service life in Australian aquatic centres. FRP and PVDF-lined steel are alternatives for chemical store exhausts where direct chlorine vapour exposure is continuous. See the galvanised vs stainless steel duct comparison guide for the broader material decision framework.

How is the dehumidification load calculated for an indoor pool?

The Carrier evaporation equation is the industry standard, reproduced in ASHRAE Handbook HVAC Applications Chapter 6. Evaporation rate equals an activity factor (0.05 to 1.5 depending on use) times pool surface area times the saturation pressure delta between water temperature and room conditions. For a 50 m by 25 m FINA pool at 27 degrees C water and 28 degrees C air at 55 percent RH, evaporation typically runs 125 to 225 kg per hour depending on activity — competitive training, recreational, or empty/covered overnight.

What is the difference between chloramine dilution and source-capture ventilation?

Dilution ventilation supplies and exhausts at high level, mixing chloramines through the entire pool hall volume before evacuation. Source-capture extracts at deck level — through linear slot diffusers or perforated trench grilles 200 to 400 mm above water — capturing chloramines at source before they reach the swimmer breathing zone. Source-capture is the modern best practice, specified on Australian and European tier-1 aquatic facilities since the mid-2010s.

What ventilation rate does ASHRAE require for a natatorium?

ASHRAE Standard 62.1 prescribes 87 L per second per m squared of pool deck and water surface combined for chloramine and respiratory irritant dilution. ASHRAE Applications Chapter 6 typically converts this to 4 to 8 ACH for a competitive natatorium hall, increasing to 6 to 10 ACH for high-activity wave or leisure pool. The 87 L/s/m squared is the floor for outdoor air, not the total supply airflow.

What relative humidity should be maintained in an indoor pool hall?

Target 50 to 60 percent RH at 28 to 30 degrees C dry bulb. Below 50 percent, evaporation accelerates and pool water heating cost rises. Above 60 percent, condensation risk on cold building surfaces becomes severe and interstitial condensation in wall cavities can cause structural failure within 15 years. Air temperature should be 1 to 2 degrees C above water temperature to suppress evaporation rate.

Why does galvanised duct fail in an indoor pool environment?

Galvanised G90 zinc reacts with chlorine and chloramines to form zinc chloride, which is hygroscopic and continues to corrode the underlying steel even after the zinc layer is consumed. Field experience documents galvanised duct failure within 5 to 8 years of commissioning. 316L stainless resists chloride pitting and stress corrosion cracking and is the established standard for the natatorium envelope. SBKJ supplies 316L stainless coil-fed duct fabrication as a standard option on the SBAL-V auto duct line and SBTF spiral tubeformer.

What are the FINA / World Aquatics requirements for an Olympic competition pool?

50 m length, 25 m width, minimum 3 m depth. Water temperature 25 to 28 degrees C with 26 to 27 degrees C the typical elite competition setpoint. Air temperature 1 to 2 degrees C above water (28 to 30 degrees C). RH 50 to 60 percent. Water surface air movement below 0.2 m per second for elite competition. Acoustic NC-40 to NC-45 for spectator areas. Lighting 1,500 to 2,500 lux at water surface for broadcast.

How long does it take to manufacture and deliver duct for a 50 m competition pool project?

For a tier-1 aquatic facility (50 m FINA + 25 m training + leisure + learn-to-swim), total duct quantity typically runs 15,000 to 30,000 m squared. Single-shift fabrication on a properly sized SBKJ SBAL-V stainless line completes in 8 to 14 weeks. Plan 16 to 24 weeks from contract to first duct on site, including 6 to 10 weeks of 316L coil lead time from the rolling mill. For Olympic or Commonwealth Games deadlines, front-loading the 316L coil order is the single highest-leverage programme decision.

How SBKJ supports aquatic centre projects

SBKJ Group manufactures coil-fed HVAC duct fabrication machinery sized for aquatic centre production volumes and 316L stainless material specifications. Where we add value to an aquatic project:

• Stainless variant SBAL-V auto duct line for rectangular pool deck supply, return and exhaust on 316L coil. Single-shift output 1,200 to 1,800 m squared. SBAL auto duct line catalogue.
• Stainless variant SBTF spiral tubeformer for round duct branches and risers on 316L coil, diameter 100 to 1,500 mm. SBTF tubeformer catalogue.
• TDF flange former for site-jointed sections and accommodation of late-programme building services coordination changes.
• Engineering pre-quotation review — SBKJ engineers review the project duct schedule and material specification before quotation to confirm correct machine sizing, coil specification and programme timing.
• Off-site fabrication co-ordination — for the largest tier-1 projects we have worked alongside the principal HVAC contractor to set up dedicated off-site fabrication facilities, accelerating the critical path against tight Olympic and Commonwealth Games deadlines.
• Australia office in Box Hill North VIC for English-speaking after-sales, parts continuity for at least 10 years on every machine model, and direct support for Australian aquatic facility owners and consultants.

Our work spans both Australian aquatic centre projects and exports into the Australian region and the Middle East, where the climate-driven dehumidification requirements share much of the same engineering reference base.

Talk to an SBKJ engineer about an aquatic centre HVAC duct fabrication brief →