Application Guide Gas detection in refrigeration systems GDIR.danfoss.
Application Guide | Gas detection in refrigeration systems Contents Page Commonly used abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Sensor technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Application Guide | Gas detection in refrigeration systems Introduction Gas detection and leak detection are two distinct activities that covers the same topic, but the methods are very different. Gas detection covers the analysis of air samples to determine whether they contain refrigerant gas. Leak detection is a systematic inspection of a refrigeration system to determine whether it is leaking. The terms gas detection and leak detection are not interchangeable, and must not be mixed.
Application Guide | Gas detection in refrigeration systems EC - Electrochemical sensor (continued) max. Sensitivity “Substantial” gas leak Tolerance range min. Important! Sensor must be calibrated or new sensor must be installed. 30% sensitivity If the sensitivity of the sensor falls below 30%; install new sensor Time Max. operating time before calibration Fig. 2: Large ammonia exposure shortens the lifetime of electrochemical sensors.
Application Guide | Gas detection in refrigeration systems P- Pellistor sensor Pellistors (sometimes called a bead or catalytic) are mainly used for combustible gases including ammonia, and are the most popular sensors for this application at high detection levels. The sensor functions by burning the gas at the surface of the bead and measuring the resultant resistance change in the bead (which is proportional to concentration).
Application Guide | Gas detection in refrigeration systems Sensor response time The response time is the elapsed time for a sensor to read a given percentage of the actual value for a step change in the target gas concentrations. As shown in the graphic, the sensor reaction above 90% becomes slower and takes longer to read the 100%. Response time for most sensors is given as t90, meaning the time that it takes the sensor to read 90% of the actual concentration. Fig.
Application Guide | Gas detection in refrigeration systems The need for gas detection There are several reasons why gas detection is required. Two obvious reasons are to protect people, production and equipment from the impact of potential gas leakages and to comply with regulations. Other good reasons include: • Reduced service cost (cost of replacement gas and the service call). • Reduced energy consumption cost due to lack of refrigerant. • Risk for damaging stock products due to a substantial leak.
Application Guide | Gas detection in refrigeration systems Requirements for gas detection according to EN 378:2016 and ISO 5149:2014 Start Charge limits for ventilated enclosure Y N Charge limits using alternative risk management Y Ammonia Y Charge > 100% practical limit Y Gas detector required N Charge > 50 kg Gas detector required N Using EN 378 and charge >m2 and A3 or B3 Y N Y N N Gas detector used to start fan or close valves Y Y Below ground in machinery room or open air N No req
Application Guide | Gas detection in refrigeration systems F-Gas legislation A periodical leakage check by certified personnel is required with the following frequency, depending on the quantity used: • 5 tCO2eq or more: At least once every 12 months – except for hermetically sealed systems containing less than 10 tCO2eq • 50 tCO2eq or more: At least once every 6 months (12 months with an appropriate leakage detection system) • 500 tCO2eq or more: At least once every 6 months.
Application Guide | Gas detection in refrigeration systems Installation guideline When it comes to installation of gas detection there are two approaches: • Perimeter detection • Point detection With perimeter detection, you place sensors all around the perimeter of the space in question, to make sure you monitor the whole space. With point detection, you locate a sensor at a particular position, where you are concerned about a leak (e.g. at the compressor).
Application Guide | Gas detection in refrigeration systems Location of gas detectors Gas detectors must be powered as specified in the installation guide and located within the specified cable length from the central control unit/monitor. In general: • Do not mount to a structure that is subject to vibration and shock, such as piping and piping supports. • Do not locate near excessive heat or in wet or damp locations. • Do not mount where it will be exposed to direct solar heating.
Application Guide | Gas detection in refrigeration systems Number of gas detectors in a facility The requirements for the number of gas detectors in a facility are not specifically stated in standards. As general guideline: • A gas detector can normally cover an area of about 50-100 m2 depending on the actual condition of the space to be covered. In spaces with several obstructions and lack of ventilation the coverage is approx.
Application Guide | Gas detection in refrigeration systems Calibration methods Two different methods are available for fulfilling the calibration requirements. • Replacing the sensor (sensor cartridge) with a new factory pre-calibrated sensor. • Performing a calibration to the sensor using calibration gas (gas mixture with known target gas concentration). In addition to these calibration methods, a “bump” test can be used, but only to test the responsiveness and operation of the sensor.
Application Guide | Gas detection in refrigeration systems Method II Calibration of gas detectors by means of calibration gas (Continued) Valve/Flow regulator + Generic calibration gas = GDU with display Gas detection unit tested and calibrated Calibration adapter Calibration equipment GDU without display Service tool Integrated digital calibration function Fig. 10 Bump test A bump test cannot supersede any tests involving calibration. It is only a function test (signal or no signal).
Application Guide | Gas detection in refrigeration systems Alarm / sensitivity range of gas detectors All commonly used gas detectors have a proportional output signal (4-20 mA, 0-10 V, or 0-5 V), and some pre-set alarm settings. Alarms can be chosen to warn against gas concentrations less than levels acceptable for personal safety on short term or long term. Alarm levels can also be chosen to specific levels due to flammability/explosion risk.
Application Guide | Gas detection in refrigeration systems [ppm] Machinery rooms Ammonia © Danfoss | DCS (MWA) | 2018.05 R717 Safety valves vent line DKRCI.PA.S00.A1.
Application Guide | Gas detection in refrigeration systems Actions triggered by gas detection Actions for Ammonia – R717 The actions to be triggered when leaked refrigerant is detected depends on the standard applied. National regulations, especially the “Occupational Exposure Limits”, varies from country to country. EN 378:2016 ISO 5149:2014 Up to 50 kg refrigerant At max.
Application Guide | Gas detection in refrigeration systems References © Danfoss | DCS (MWA) | 2018.05 • EN 378:2016 Refrigerating systems and heat pumps – Safety and environmental requirements • ASHRAE 15:2016 Safety Standard for Refrigeration Systems • ASHRAE 34:2016 Designation and Safety Classification of Refrigerants • ANSI/IIAR 2-2014 American National Standard for Safe Design of Closed-Circuit Ammonia Refrigeration Systems DKRCI.PA.S00.A1.
Application Guide | Gas detection in refrigeration systems Annex I Common refrigerant data Refrigerant type Refrigerant Name Formula Safety group Vapour density @ 25°C / 1 bar Relativ density ODP GWP100 Ozone Pepletion Global Warming Portential Potential (100 yr ITH/F gas regulation) [kg/m3] [–] [–] [–] – R717 Ammonia NH3 B2L 0.700 0.6 0 0 – R744 Carbon Dioxide CO2 A1 1.80 1.5 0 1 HCFC R22 Chlorodifluoromethane CHCIF2 A1 3.54 3.0 0.
Application Guide | Gas detection in refrigeration systems Annex III ASHRAE 15-2016 Refrigerant type Refrigerant Name RCL RCL RCL OEL/TWA (40 hours work week without effect) - R717 Ammonia B2L [g/m3] [lb/Mcf] [ppm] [ppm] 0.22 0.014 320 - R744 Carbon Dioxide 25 A1 54 3.
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