ALTERNATIVE REFRIGERANTS Locating CO2 detection. ) is R


egulations, market drivers and trends refl ect that carbon dioxide (CO2


increasingly being used as a refrigerant in a variety of applications. CO2


is less environmentally harmful than many of the gases previously used in these refrigeration applications, having a signifi cantly lower global warming potential (GWP) than HFC and HCFC refrigerants. Some of these gases, such as R404A, are beginning to be phased out of use due to environmental impact and regulations. These factors contribute towards CO2


becoming


an increasingly attractive option for use when balanced against the requirements of regulations such as F-Gas and the US EPA Clean Air Act Section 608.


Furthermore, the manufacturers of refrigeration systems continue to develop a growing range


of ever more effi cient and cost-eff ective CO2 refrigeration system options, enabling their wider adoption into commercial applications. While benefi cial in environmental impact, CO2


contribute to a signifi cantly higher risk of leaks. Due to design requirements, CO2


refrigeration


leak, the gas can escape into a space at very high leak rates.


Taking an example of a walk-in cold room / freezer with a room volume of 1,000ft3


/28.3m3


and a typical rate of one air exchange per hour, the following can be determined: ■ A leak of CO2


hour, will create an atmosphere containing 5,240 ppm of CO2


in fi ve minutes. This


surpasses the OEL and reaches a level to which workers should not be exposed.


■ A leak of CO2 at a higher rate of 1lb/minute,


or 454g/minute, will create an atmosphere containing 41,920 ppm of CO2


in just fi ve is


a potentially harmful gas to humans if suffi ciently high concentrations are present. Typical fi gures stipulated for CO2


exposure by OSHA are:


■ 5,000 ppm – Occupational Exposure Limit (OEL)


■ 40,000 ppm – Immediately Dangerous to Life or Health (IDLH).


Refrigerant safety standards, including EN 378-1:2016 and ASHRAE 34-2013, include these exposure levels to determine the safety of a refrigerant system and the cases in which refrigerant leak detection is mandated. These use-cases will typically include refrigerant detection in machinery rooms and other refrigerated spaces including cold rooms and walk-in freezers. Where larger refrigerant charge sizes are used, the potential for mandated refrigerant leak detection in larger spaces, such as storage freezers, is increased.


As with all refrigeration systems, over time there is the potential for leaks to occur. Causes can include improper maintenance, mechanical wear, inadvertent damage or improper installation. With pressurized systems, these factors can


44 December 2017


minutes. This surpasses the IDLH level, and would be highly and immediately dangerous to personnel entering the space.


These theoretical examples show that CO2 leaks


in refrigerated spaces have the potential to become dangerous very quickly. Eff ective CO2


leak


detection can be an essential tool in maintaining a safe environment.


Selecting an effective CO2 CO2


leak detector


is monitored in a wide variety of applications, including indoor air quality (IAQ), occupational workplaces and refrigeration applications.


However, it should be noted that not all CO2 monitoring devices are suitable for leak detection in refrigeration applications.


Two key factors that should be considered when looking for a suitable CO2


leak detector relative to


the applicable application are response time and operating temperature. The rate at which CO2


can leak and create a


dangerous environment makes response time a critical factor in delivering eff ective CO2


leak


detection. Instruments suited for monitoring of gradual changes in the atmospheric CO2


level, such as used in IAQ applications, may not be suitable


systems typically operate at high pressures; subcritical or transcritical system pressure ratings often operate in excess of 2,000 PSI. These high pressure ranges mean that in the event of a major CO2


leaks


Tom Burniston, product manager of fi xed instrumentation at Bacharach examines the benefi ts and pitfalls of CO2


leak


sensor. Operating temperature is also a key factor in selecting an appropriate CO2


leak


detector for a refrigeration application. There are comparatively few CO2


sensors available on the at a rate of 7.5lb/hour, or 3.4kg/


market that are specifi ed for use at temperatures lower than 0°C/32°F with response times required for eff ective use in the refrigerant gas detection applications.


As the use of CO2 in refrigeration continues


to grow, it becomes imperative to ensure that sensors appropriate for use in low temperature environments are used by instrument manufacturers whose products are intended for leak detection in refrigerated spaces. Fundamentally, it can’t be determined what behavior a sensor would exhibit if run outside of its specifi ed operating range without test data, as each sensor may behave diff erently. What can be stated is that any reading could be invalid and the device behaviour could be undefi ned. At best, the sensor may be inoperable and a fault detected. At worst, an invalid or inaccurate reading may be provided.


refrigeration systems are increasingly used in commercial applications, a trend which is expected to continue. In turn, this creates an increasing need for eff ective CO2


It could be argued that a sensor operating outside of its designed specifi cations is less useful than none at all, as it may provide false confi dence that the gas level is being accurately monitored and its benefi t of installation and use is nullifi ed, creating risk of exposure. CO2


for leak detection purposes where a fast response is needed to ensure that a dangerous working environment is not created or entered. It should be advocated to review both the stated response time of the sensor being used in a leak detector, and most importantly the response time of the instrument. Diff erent instrument designs can aff ect how quickly gas can diff use into a CO2


leak detection


can be a dangerous gas in suffi cient volumes, so care should be taken in selecting an eff ective solution with an appropriate response time and operating temperature.


systems to be employed, helping to enhance the safety of those working in refrigerated spaces. CO2


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