REFRIGERANTS


Advances in leak detection


Tom Burniston, product manager, refrigerant leak detection, for Bacharach explores the development of refrigerant detection.


T


here are many reasons for facilities to install refrigerant detectors to monitor for leaks in their refrigeration systems. These can vary significantly depending on the application in question. For example, the requirements and drivers for refrigerant leak detection of a supermarket with a 3,500lb refrigeration system for cooling an entire store will be very different to those of a hotel room or apartment building, which will in turn be different from industrial refrigeration for food processing and cold storage. All users of HFO refrigerants over certain system sizes are required to have monitoring for safety standards and building code compliance in order to detect leaks that could lead to asphyxiation, and heavy users of commercial refrigeration will benefit in multiple ways from detecting low level leaks. Refrigerant costs, particularly of those with a high global warming potential (GWP), are increasing. Therefore, the cost of topping-up a refrigeration system as a result of lost charge due to leaks is no longer economically viable. In the case of multi-site enterprises, such as a regional or national supermarket chains, the cost of frequent refrigerant top-ups can run into the millions of dollars per year.


Refrigeration accounts for 60–70% of the energy consumed in the typical supermarket. Depending on the system, a loss of only 15% of the refrigerant charge can decrease the systems energy efficiency by as much as 50%. This additional energy consumption can significantly affect the profits of an individual location and can have dramatically more impact across a large enterprise.


Unchecked, refrigerant leaks can result in sub- optimal operation or system failure. Such a loss of cooling can be critical for food safety and result in the spoiling and disposal of refrigerated produce, increasing waste and costing money. Most commonly used refrigerants will have an environmental impact if released to the


40 August 2018


atmosphere, with GWPs hundreds or thousands of times that of carbon dioxide. For instance, R410A has a GWP of 2,088 tCO2


e. Regulations, such the


Environmental Protection Agency’s Clean Air Act Section 608 regulate the unmitigated emissions of these refrigerants and may impose fines if refrigerant leaks are beyond thresholds. Although most refrigerants are not acutely toxic, at high concentrations they will displace oxygen and create a risk of asphyxiation. Globally, a number of standards are in place to ensure the safe use of refrigeration systems, including EN 378 in the European Union and ASHRAE 15 in the United States. While these regulations cover the whole refrigeration system installation, they contain specific clauses that reference the appropriate use of refrigerant leak detectors aligned with alarm requirements at concentrations that do not exceed dangerous levels.


There is a paradigm shift in the way users interface with instruments designed to assist with compliance concerning refrigerant safety standards as new products develop. As technology continues to advance, it is being implemented into new product design.


Refrigerant safety standards apply across all refrigeration applications. In addition to supermarkets and hotels, chiller rooms, data centres, transport refrigeration and industrial cold storage facilities are also regulated by these safety standards.


The primary standard relating to refrigerant use in the USA is ASHRAE 15-2013. The stated scope of the standard is to establish safeguards for life, limb, health and property and prescribe safety requirements. Typically, it must be referenced in conjunction with ASHRAE 34-2013, which establishes safety classifications for refrigerants and determines Refrigerant Concentration Limits (RCL) or the threshold at which the gas concentration presents an immediate danger to health.


Refrigeration system specifiers should consider the maximum system charge calculations derived from Section 7 of ASHRAE 15-2013. Taking an example of a system using the refrigerant R134a, which as stipulated in ASHRAE 34-2013 has an eight-hour Occupational Exposure Limit (OEL) of 1,000 parts per million (ppm), which is the maximum level for human exposure over the designated period. ASHRAE 34 stipulates a RCL of 50,000 ppm. The RCL for R134a equates to a limit of 13lb of refrigerant per 1,000 ft3 of occupied space, as detailed with the standards. When applying the following equation, which is derived from Section 7 of ASHRAE 15-2013, a refrigeration system specifier may find that the refrigerant’s RCL is exceeded in applications such as chiller rooms, or enclosed spaces such as walk-in coolers and freezers.


Maximum total system refrigerant charge (lbs)= RCL (lbs⁄(1,000ft3


) × Occupied space volume(ft3 1,000


The volume of the occupied space should be calculated in line with the guidance in ASHRAE 15-2013, Section 7.3.


The provisions outlined by ASHRAE 15 designate safety requirements for personnel who may be in the machinery room where a refrigerant could leak and where the total system charge of refrigerant may exceed the RCL. Clause 8.11.2.1 states: “Each refrigerating machinery room shall contain a detector, located in an area where refrigerant from a leak will concentrate, that actuates an alarm and mechanical ventilation in accordance with Section 8.11.4 at a value not greater than the corresponding TLV-TWA (or toxicity measure consistent there with). The alarm shall annunciate visual and audible alarms inside the refrigerating machinery room and outside each entrance to the refrigerating machinery room. The alarms required in this


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