CO Sensing Safety Systems for Appliances


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Discussion of available CO/combustion sensing technologies and gas appliance industry views on sensor technology


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CO Sensing Safety Systems for Appliances

  1. 1. Technical Feasibility Study, CO Sensing Safety Systems for Appliances AHRI Study - September 8, 2010 Presented: June 3, 2014 to CPSC Forum Larry Brand, Gas Technology Institute
  2. 2. AHRI CO Sensors for Appliances 2AHRI CO Sensors for Appliances 2 Summary > AHRI study conducted in 2009 - 2010 by GTI > Objective: ─ Understand the types of CO sensor technologies available ─ Establish a technical baseline for integrating CO sensors into appliances ─ Identify critical areas needing further investigation > Approach: ─ Literature survey and manufacturer survey with analysis > Results: ─ No sensor technology was fully adequate for this application ─ Temperature and humidity limits, sensor poisoning, lifespan, and cost are factors that need to be addressed
  3. 3. AHRI CO Sensors for Appliances 3AHRI CO Sensors for Appliances 3 Objective > Provide a technical baseline for evaluating the feasibility of applying CO sensor safety systems to gas appliances ─ Establish the technical requirements for the application > Identify critical areas needing further development or research Temperature limits Contaminant resistance Accuracy Reliability Calibration needs Durability Service life Initial cost Operating cost
  4. 4. AHRI CO Sensors for Appliances 4 Manufacturer Survey Nine surveys returned Sensor criteria based on survey responses Type of Gas- Fired Equipment Manufacturer Number of Responses Boilers 4 Furnaces 4 Water Heaters 2 Infrared Heaters 1 Criteria Range Temperature -40 to 500°F Humidity Up to 100% Normal CO Sensor Range 0 to 400 ppm Maximum CO Sensor Value* 3000 ppm Lifespan 20 years Accuracy 5% Electrical Voltage 24 VAC Several respondents noted that the CO sensors would need to be impervious to different contaminants that could be caused by condensate in the flue or household cleaning products: chlorides, phosphates, out-gassing of binders, manufacturing oils, hydrochloric, carbonic, hydrofluoric, nitric, and sulfuric acids.
  5. 5. AHRI CO Sensors for Appliances 5AHRI CO Sensors for Appliances 5 Literature Survey – 1996 and 2003 > 1996 – GRI report concludes that no commercially available CO sensor met all the technical requirements > 2003 – GTI literature survey on available technologies ─ Solid state ceramic ─ Copper oxide with alkaline metal ─ Tin oxide in a sensor array ─ Tin oxide with platinum or palladium doping ─ Catalytic bead sensor ─ Gallium lead diode laser absorption sensor ─ Zirconia sensor
  6. 6. AHRI CO Sensors for Appliances 6AHRI CO Sensors for Appliances 6 Literature Survey 2003 Type Supplier Sensor Element Status Catalytic Bead Nemoto Platinum/Alumina/Catalyst Available MOS* Figaro SnO2/RuO2/Charcoal Available MOS Figaro SnO2/Pd/Ir doping Available IR Comag IR “SmartScan” Infrared Available Electrochemical Sixth Sense “SureCell” 3-electrode Available Catalytic Bead Tokyo Gas Platinum/Alumina/Catalyst Field Trials MOS Los Alamos National Laboratory Ceramic/Noble Metal Patent Applied For MOS Sigma Delta Processing U. of Pavia Multi-Sensor Laboratory MOS Micro-fabrication EVE Group SnO2/Pd doping Laboratory MOS/Processing U. of Barcelona SnO2 Array Laboratory Mid-IR BRD Stanford U. Quantum Cascade Laser Laboratory Electrochemical Loughborough U. Nafion/Pt/Au Laboratory IR Stanford U. GaSb Diode Near IR Laser Laboratory MOS Osaka Gas CuO/Na2CO3 doping Laboratory Conclusion: MOS, electrochemical, and catalytic technologies widely available but not suitable for gas appliance safety circuits.
  7. 7. AHRI CO Sensors for Appliances 7AHRI CO Sensors for Appliances 7 Literature survey 2006-2010 >Galatsis (2008) identifies 3 types of CO sensors as predominant: metal oxide or semiconductors (SMO), electrochemical (EC) and infrared or optical (IRO) SMO sensors have a small heated element that cause oxidizing gases such as CO to react with a metal oxide film. The film’s conductivity is measured and is proportional to the gas concentration. SMO sensors tend to be small, reliable, durable and inexpensive, but have poor gas selectivity and can be influenced by temperature and humidity, which could be an issue for flue gas sampling. EC sensors have an electrode in contact with a liquid electrolyte. Sample gas is diffused into the electrolyte which changes the electrical potential of the electrode proportionally to the gas concentration. EC sensors tend to be small, but can have poisoning and temperature issues. IRO sensors have an optical sensor that changes in light transmission properties based on the concentration of sample gas present. IRO sensors tend to be small, low power consumption, good selectivity and have longer life spans compared to other sensors. However, IRO sensors are not as common as the other types, generally cost more and have slower response times.
  8. 8. AHRI CO Sensors for Appliances 8AHRI CO Sensors for Appliances 8 Literature 2006 – 2010 Source: Galatsis et al (2008)
  9. 9. AHRI CO Sensors for Appliances 9AHRI CO Sensors for Appliances 9 Sensors Available 2004 Manufacturer Sensor Type Products Applications City Technology LTD* EC Sensors Gas Sensors Comag IR IRO Sensors/Alarms HVAC control, ventilation E2V** SMO, EC, IRO Sensors Gas Sensors Figaro SMO, EC Sensors Gas Sensors FiS Inc SMO Sensors Gas Sensors Kidde EC Sensors/Alarms Nighthawk brand residential CO alarms KWJ Engineering Inc EC Sensors Gas Sensors Monox*** NA Sensors Gas Sensors Nemoto & Co., LTD EC Sensors Sensors for residential use and boilers Quantum Group Inc IRO Sensors Sensors for Costar brand CO Alarms Note shift from semiconductor/oxide to electrochemical sensors
  10. 10. AHRI CO Sensors for Appliances 10AHRI CO Sensors for Appliances 10 Sensors Available in 2010 >Market moved toward SMO and EC sensors with new materials or chemicals on small surfaces ─ Micro machined, micro platforms, nanoparticles or nanowire sensors ─ Smaller surfaces to reduce heating and cooling times and reduce power >All in early development stage in 2010 – need 5 more years of development. Suitable sensor life key missing requirement.
  11. 11. AHRI CO Sensors for Appliances 11AHRI CO Sensors for Appliances 11 2010 Sensor Shortfalls >Figaro (SMO) and City Technology (EC) sensors evaluated. ─ Figaro limited to applications without high heat or humidity due to lower sensor life ─ City Technology sensor life impacted by high humidity. Limited to temperatures below 105°F and RH between 15 to 90%
  12. 12. AHRI CO Sensors for Appliances 12AHRI CO Sensors for Appliances 12 Limits on Appliance Application >None of the sensors listed had a suitable life in an environment greater than 300°F >The sensors would have to be placed downstream of the heat exchanger(s) in the appliance
  13. 13. AHRI CO Sensors for Appliances 13 Summary Requirements > Temperature Range: -40 to 500° F > Humidity Range: 0% to 100% RH > Normal CO Sensor Range: 0 to 400 ppm > Maximum CO Sensor Value: 3000 ppm > Lifespan: 20 years > Accuracy: ±5% > Electrical Voltage: 24 VAC Findings > Sensor range, maximum sensor value, accuracy and voltage are not limitations > Temperature and humidity levels in the appliances are barriers > Sensor poisoning due to flue gas contaminants is a barrier > Current life span of sensors is 6 years; well short of the 20 year life expectancy of some gas appliances
  14. 14. AHRI CO Sensors for Appliances 14AHRI CO Sensors for Appliances 14 Summary SMO: Semiconductor /Metal Oxide EC: Electrochemical IRO: Infrared /Optical Size No Issues No Issues No Issues Reliability No Issues No Issues No Issues Durability No Issues No Issues No Issues Cost Potential Issues Potential Issues Issues Temperature/Humidity Influenced Potential Issues Potential Issues Insufficient Data Selectivity Issues No Issues No Issues Poisoning Issues Potential Issues Insufficient Data Life Issues Issues Potential Issues Response Time No Issues No Issues Potential Issues Power Usage No Issues No Issues No Issues *Matrix based on usage in CO sensing on gas fired appliances and in comparison with each other type