By Tom Burniston
Refrigerant leaks can be dangerous. There are a variety of reasons for employing refrigerant gas detectors to alert when a leak takes place. These include drivers such as reducing the amount refrigerant leaked in order to reduce costs; reducing emissions of greenhouse gases to protect the environment; optimising the performance and energy efficiency of a refrigeration system by maintaining the correct level of charge. One of the foremost reasons remains the safety of those working with or in proximity to refrigeration systems.
Depending on the gas used, the dangers presented by leaking refrigerant can include asphyxiation, oxygen depletion, flammability and toxicity. Measures to mitigate these risks are defined within refrigeration safety standards. In the United States, the standard to follow is ASHRAE 15, Safety Standard for Refrigeration Systems.
Within a commercial refrigeration environment, two of the areas of primary concern regarding safety and refrigerant leaks are refrigeration machinery rooms and walk-in cold rooms.
What does the standard say about refrigerant gas detection?
Section 188.8.131.52 of ASHRAE 15 states that –
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 therewith). 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 section shall be of the manual reset type with the reset located inside the refrigerating machinery room.
Machinery room locations are clearly called out by the standard text. With regard to occupied spaces, these are defined by Occupancy Classification in ASHRAE 15, Section 4. Cold rooms fall within the category of Industrial Occupancy. Section 4.1.6 is as follows:
Industrial occupancy is a premise or that portion of a premise that is not open to the public, where access by authorized persons is controlled, and that is used to manufacture, process, or store goods such as chemicals, food, ice, meat, or petroleum
Whereas refrigerant leak detection is called out for all machinery rooms, it is not required in an occupancy, such as a cold room, unless the refrigerant concentration limit can be surpassed, as detailed in ASHRASE 15 section 7.2:
The concentration of refrigerant in a complete discharge of each independent circuit of high-probability systems shall not exceed the amounts shown in Table 4-1 or 4-2 of ASHRAE Standard 34,1 except as provided in Sections 7.2.1 and 7.2.2 of this standard.
In the case that a refrigeration system has sufficient charge to fall under the limits imposed by section 7.2, one of the requirements needed in order to be able to use such a system is a refrigerant leak detection system. This is explicitly identified in section 7.2.2.d:
7.2.2 Industrial Occupancies and Refrigerated Rooms.
Section 7.2 does not apply in industrial occupancies and refrigerated rooms where the following seven conditions are met:
8. Refrigerant detectors are installed with the sensing location and alarm level as required in refrigerating machinery rooms in accordance with Section 184.108.40.206.
Based upon these definitions, we can summarise that, in addition to machinery rooms, cold rooms have a requirement for refrigerant leak detection where the amount of refrigerant that could leak into the space can rise to concentration within that space which is higher than the defined refrigerant concentration limit for the refrigerant in question. In the majority of commercial refrigeration applications using a centralised refrigeration system for all cooling needs, this will be the case and detection will be needed. The standard highlights that in this case the same refrigerant detection and alarm system requirements apply to a cold room as to a machinery room.
What we can determine from this is that audio-visual alarms are required inside and outside of a machinery room or cold room. These must be inside the monitored space and outside of each entrance, in order to warn against personnel entering a potentially dangerous space.
Tips for Selecting a Good System to Meet Compliance Requirements
There is a plethora of choice when it comes to selecting a refrigerant gas detection system. When regulatory compliance and safety is the main aim, the most common choice tends to be diffusion-based instruments monitoring a single point, which present an economically attractive option for achieving the desired result of safety standard compliance. However, not all solutions are equal and some thought should be given to what makes a good system for meeting these needs. Some keys areas of focus follow.
Audible and Visual Alarms
ASHRAE 15 clearly stipulates the need for audible and visual alarms inside both machinery rooms and cold rooms. Though this can be driven from a centralised controller, selecting a gas detector that has on-board audio-visual alarms is an attractive option. This complies with the standard, without necessitating the use additional hardware within the monitored space, which incurs cost both in terms of the hardware itself and its installation.
Outputs and Communications
The requirement for machinery rooms and cold rooms is to have additional audio-visual alarms outside of the monitored space. This means that it is important to consider what communication options and outputs are available from the refrigerant detector in the event of an alarm being triggered. Relays can be used to trigger additional horn/strobes directly, and in an ideal case these can be low powered devices powered directly from the gas detector, lowering the cost of electrical installation. Additional communication options are often desirable, such as Modbus for communicating with a refrigeration controller or a BMS. Some consideration should be given to the ease of wiring these communications. Multiple cable glands and wiring terminals can make it easy to daisy-chain both power and Modbus, as well as connecting relays for alarm and fault status. This can save significant time and money when installing the system.
It can be important for a refrigerant gas detector to be fully configurable. This can include the setting of different alarm thresholds to instigate different actions; configuring alarm behaviour for manual or automated reset; setting alarm delays to prevent false alarm situations due to transient cross-interference; configuring digital communication settings. Many legacy devices require the use of voltmeters, potentiometers and jumpers on circuit boards or programming via DIP switches. This can require a significant amount of training to perform correctly. In the increasingly digital world of communications technology, it now becoming more accessible to use intuitive mobile applications that link directly to devices for programming and configuration, simplifying the process. This also adds an additional layer security through password protection for access levels.
Detectors should have an appropriate maintenance period established should be installed to allow for checking, repair or replacement and be able to be functionally tested. The main maintenance requirement for a gas detector will usually be a periodic calibration, and in some cases a replacement of the sensor element (some have limited lifespan). Much like configuration processes, the calibration of gas detectors has often required interference with circuit boards to make manual adjustments. This can easily be done incorrectly. Selecting a system where the calibration gas data is entered (ideally by scanning the gas bottle to automatically populate the data) and then all adjustments are made electronically makes this process more user friendly and hard to do incorrectly. Using a mobile application can again make this very straightforward. Furthermore, manufacturers are in some cases now able to offer plug-and-play pre-calibrated sensor modules for simple field exchange, entirely removing the need for field calibration and saving significant time. A typical calibration can take circa 25 minutes per detector to perform; a sensor exchange can be done in fewer than 5 minutes. This also allows for a simple update of the detection system in an instance where the refrigerant is changed for a newer, lower GWP option.
It is important to comply with refrigeration safety standards. They are in place to protect persons working with and near to refrigeration systems. Ensuring the correct measures are in place to detect and alert in the event of potentially dangerous refrigerant leak is just one part of this equation. Many systems are available in the market place to use to meet these requirements. Consideration of the merits of each option with regards to its suitability for regulatory compliance, as well as its maintainability and configurability, can make this a straightforward solution. This allows focus to then be placed on the many other important aspects of refrigeration system safety, maintenance and operation.
By Tom Burniston, former Product Manager, Refrigerant Leak Detection at Bacharach. For further information on this topic, please contact Matt Eversole, Manager of Product Marketing at Bacharach.