# 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

larry.brand@gastechnology.orgAHRI 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 addressedAHRI 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 costAHRI 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.AHRI 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 sensorAHRI CO Sensors for Appliances 6 

# Literature Survey 2003

Type Supplier Sensor Element Status

Catalytic Bead Nemoto Platinum/Alumina/Catalyst Available

MOS* Figaro SnO 2 /RuO 2 /Charcoal Available

MOS Figaro SnO 2 /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 SnO 2 /Pd doping Laboratory
MOS/Processing U. of Barcelona SnO 2 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/Na 2 CO 3 doping Laboratory



## Conclusion: MOS, electrochemical, and catalytic technologies widely available but

not suitable for gas appliance safety circuits.AHRI 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 condu ctivity 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 sampli ng.

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 ha ve 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.AHRI CO Sensors for Appliances 8 

# Literature 2006

– 2010

Source: Galatsis et al (2008)AHRI 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 sensorsAHRI 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.AHRI 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%AHRI 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 applianceAHRI 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 appliancesAHRI 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