Carpark & HVAC

Carpark gas detection is unusual in that it earns its keep twice. It protects people from carbon monoxide, and it saves the building money by running the fans only when they are needed. Most systems are justified on the second point and specified against the first.

Most of what follows comes from work our Technical Consultants have done on Australian buildings and plant rooms.

What The Detection Is Actually Controlling

In an enclosed carpark, vehicles produce carbon monoxide when they start and idle, and it has nowhere to go. Detection exists to manage that, but the control logic runs both ways. Where no vehicle exhaust pollution is present, ventilation rates can be reduced, which is where the energy saving comes from.

The design limit is specific. AS 1668.2 sets a primary carbon monoxide exposure limit for enclosed carparks of 60 parts per million averaged over one hour, with further limits over shorter periods. Detectors are typically ranged to 200 ppm so the instrument has headroom above the alarm points rather than sitting at the top of its scale.

A practical arrangement puts multiple fixed transmitters around the carpark reporting to a multi-channel controller installed near the fan controller, or connected to the building management system. Alarm levels are set to the standard and automatically control the fan system, whether single speed, dual speed or variable speed. Fan activation and deactivation time delays are built in to prevent premature fan activity, which matters because a fan starting and stopping each time a car passes is both irritating and hard on the plant.

Detector placement decides whether any of this works. The polluted air has to be in physical contact with the sensor, so distance from the likely source is the design variable rather than an afterthought. A detector in the wrong position produces a system that either runs constantly or never runs at all.

Two environmental requirements follow. Instruments should be IP65 or better to survive water, fumes and dust. And dust and fumes build up an agglomerate that can obstruct a sensor filter over time, so the maintenance interval needs setting against the actual environment rather than a catalogue figure. Vandalism is the other consideration, which is why carpark detectors are specified as vandal resistant and finished to blend into the wall rather than advertise themselves.

The Gastech C-Guard was designed for this application, and the GTA-VSD20i provides the variable speed fan control alongside it.

AS 1668.2 Changed In 2024, And Carparks Changed With It

Worth knowing if your last carpark project was designed before mid 2024.

AS 1668.2:2024 was published in June 2024 and replaces the 2012 edition, which had been the working document for over a decade. It is referenced by the National Construction Code for deemed-to-satisfy compliance, so it applies to buildings requiring mechanical ventilation rather than being optional guidance.

Two changes matter here.

Carpark ventilation rates were revised. Contaminant generation rates have been updated to reflect low emission fuels and modern engine technology, which allows reduced ventilation rates. In practice that can mean smaller fans and smaller ducts on a new project, and lower running costs.

And non-quantified performance requirements were replaced with precise prescriptive values. The 2012 edition left some requirements open to individual engineering interpretation. The 2024 edition puts numbers against them.

The practical question for anyone with existing drawings is which edition they were designed to. Equipment sized against the 2012 edition was sized to higher ventilation rates, and older NCC editions still cite the 2012 standard, so both are in circulation. Worth asking your mechanical engineer directly rather than assuming.

Refrigerant Gas Detection Is Not Leak Detection

These two get used interchangeably and they are different activities with different equipment. Getting them confused leads to buying the wrong thing.

Gas detection analyses air samples to determine whether they contain refrigerant gas. It is a fixed installation, with sensors positioned where refrigerant would accumulate in the event of a plant leak. Where those positions are depends on the machinery room layout, the adjacent spaces, the plant configuration and the particular refrigerant involved, since different refrigerants behave differently.

Leak detection is a systematic inspection of the refrigeration system itself to find out whether it is leaking. It is handheld equipment carried by a technician, ranging from soapy water at one end to sophisticated electronic instruments at the other.

One tells you the room has a problem. The other tells you which joint caused it. A plant room needs both, and neither substitutes for the other.

Before specifying fixed detection, a set of questions has to be answered rather than assumed. Which gases have to be measured and in what quantities. Which sensor principle suits them. How many sensors are needed. Where and how they should be positioned and calibrated. Which alarm limits are appropriate, and how many. And how the alarm information gets processed once it is generated.

The AirScan IRF9 covers refrigerant detection across thirteen refrigerants plus ammonia and carbon dioxide, and the Ax60+ covers carbon dioxide and oxygen monitoring in plant rooms and cool rooms.

Ice Rinks And Resurfacing Machines

An application most people would not think of until it appears in the news, and it has in Australia.

Ice rinks use resurfacing machines to maintain the ice surface. Where those machines run internal combustion engines on propane or petrol, they emit carbon monoxide as a product of incomplete combustion, inside an enclosed building with spectators and children in it. Suspected carbon monoxide poisoning at an Australian ice arena has been reported, and similar incidents have occurred overseas at hockey tournaments.

Detection is both fixed in the rink space and portable on the operator, with ranges to 1,000 ppm rather than the 200 ppm typical of a carpark, because a resurfacing machine working in a confined volume produces considerably more than idling cars.

The environmental challenge is temperature. Instruments have to work reliably at freezing and below, and service and calibration intervals need setting for that rather than for a temperate plant room.

Indoor Air Quality And Air Change Rate

Ventilation performance in occupied buildings has moved from generic tables toward measurement.

Air change rates were historically set by venue type from a table. Practice has shifted toward using carbon dioxide concentration in parts per million as the measure, because it is the most reliable available indicator of how well air is genuinely being replaced. The required rate depends on the target carbon dioxide level, the outdoor level, the volume of the space, how many people are in it and what they are doing.

A four step check confirms a system is performing: measure the incoming air flow, measure the outgoing air flow, check the overpressure inside the space, and check the carbon dioxide level. If carbon dioxide is climbing while the fan is running, the fan is not achieving what the design assumed.

Who Regulates It

Building ventilation and indoor air quality sit across two frameworks.

Construction and design compliance runs through the National Construction Code, which references AS 1668.2 for deemed-to-satisfy mechanical ventilation, and is enforced through state building authorities and certifiers rather than through work health and safety regulators.

Worker exposure to carbon monoxide and refrigerants is work health and safety, so the regulator is WorkSafe WA, SafeWork NSW or Workplace Health and Safety Queensland depending on location. Safe Work Australia publishes the exposure standards that the carbon monoxide limits derive from.

Other relevant standards include AS/NZS 5149 for refrigerating systems, including detection and ventilation requirements for machinery rooms, AS 1668.4 for natural ventilation, and AS/NZS 60079.29.2 for gas detector selection, installation, use and maintenance.

What Gastech Supplies

Fixed gas detection for carparks, plant rooms, machinery rooms, cool rooms and enclosed vehicle areas, including purpose built carpark detectors rated for washdown and vandalism.

Controllers providing variable speed fan control to AS 1668.2, with the relay and analogue capacity to drive fans, dampers and building management systems.

Leak detectors for refrigeration technicians finding the source once a fixed system has reported a problem.

Portable single gas and multi-gas instruments for maintenance, plant room entry and commissioning checks.

Behind them sit project engineering, NATA calibration and service, field service, fleet management and hire, from WA, NSW and QLD.

If you are designing a carpark ventilation system, or working out whether an existing one still meets the current standard, talk to our Technical Consultants.