CO Sensing Safety Systems for Appliances

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

[email protected]

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


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

AHRI CO Sensors for Appliances 4

Manufacturer Survey

Nine surveys returned Sensor criteria based on survey responses

Type of Gas-Fired

Equipment Manufacturer

Number ofResponses

Boilers 4Furnaces 4

Water Heaters 2Infrared Heaters

1

Criteria RangeTemperature -40 to 500°F

Humidity Up to 100%Normal CO Sensor

Range0 to 400 ppm

Maximum CO Sensor Value*

3000 ppm

Lifespan 20 yearsAccuracy 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.


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


Literature Survey 2003Type Supplier Sensor Element Status

Catalytic Bead Nemoto Platinum/Alumina/Catalyst AvailableMOS* Figaro SnO2/RuO2/Charcoal AvailableMOS Figaro SnO2/Pd/Ir doping Available

IR Comag IR “SmartScan” Infrared AvailableElectrochemical Sixth Sense “SureCell” 3-electrode AvailableCatalytic 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 LaboratoryMOS/Processing U. of Barcelona SnO2 Array Laboratory

Mid-IR BRD Stanford U. Quantum Cascade Laser LaboratoryElectrochemical Loughborough U. Nafion/Pt/Au Laboratory

IR Stanford U. GaSb Diode Near IR Laser LaboratoryMOS Osaka Gas CuO/Na2CO3 doping Laboratory

Conclusion: MOS, electrochemical, and catalytic technologies widely available but not suitable for gas appliance safety circuits.


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.


Literature 2006 – 2010

Source: Galatsis et al (2008)


Sensors Available 2004

Manufacturer Sensor Type Products ApplicationsCity Technology LTD* EC Sensors Gas Sensors

Comag IR IRO Sensors/Alarms HVAC control, ventilationE2V** SMO, EC, IRO Sensors Gas SensorsFigaro SMO, EC Sensors Gas SensorsFiS Inc SMO Sensors Gas SensorsKidde EC Sensors/Alarms Nighthawk brand residential CO

alarmsKWJ Engineering Inc EC Sensors Gas Sensors

Monox*** NA Sensors Gas SensorsNemoto & Co., LTD EC Sensors Sensors for residential use and

boilersQuantum Group Inc IRO Sensors Sensors for Costar brand CO

Alarms

Note shift from semiconductor/oxide to electrochemical sensors


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.


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%


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

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


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

CO Sensing Safety Systems for Appliances

Government & Nonprofit

sensors available

ec sensors gas sensors

appliances ahri study

optical iro smo sensors

sensor technologies

sensor technology

sensor criteria

optical sensor