# Te **chnical Feasibility**

**Study , CO Sensing Safety**  **Systems for Appliances** 

AHRI Study - September 8, 2010 Presented: June 3, 2014 to CPSC Forum Larry Brand, Gas Te chnology 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

─ Te mperature 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 Te mperature limits Contaminant resistance Accuracy Re liability 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 **Ty pe of Gas**  **** **Fired Equipment**  **Manufacturer Number of** 

**Responses** Boilers 4 Furnaces 4 Wa ter Heaters 2 Infrared Heaters 1 **Criteria Range**  Te mperature -40 to 500 ° F Humidity Up to 100% Normal CO Sensor Range 0 to 400 ppm Maximum CO Sensor V

alue* 3000 ppm Lifespan 20 years Accuracy 5% Electrical V

oltage 24 V

AC Several respondents not ed that the CO sensors would need to be impervious to different contaminants that could be caused by condensat e in the flue or household cleaning products: chlorides, phosphat es, out - ga ssing of binders, manufacturing oils, h yd ro chloric, carbonic, hyd ro fluoric, 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

─ Ti n oxide in a sensor array

─ Ti n 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

**Ty pe**  **Supplier Sensor**  **Element Status**  Catalytic Bead Nemoto Platinum/ Alumina/Catalyst Available MOS* Fig aro SnO 2/RuO 2/Charcoal Available MOS Fig aro SnO 2/P d/Ir doping Available IR Comag IR “SmartScan” Infrared Available Electrochemical Sixth Sense “SureCell” 3 - electrode Available Catalytic Bead To kyo 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/P d 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 t echnologies widely available but not suit able for g as 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 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 electrol yte. 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 ty pes, 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 **Av ailable 2004** 

**Manufacturer Sensor T**  **yp e**  **Products Ap**  **plications** City T echnology L

TD* EC Sensors Gas Sensors Comag IR IRO Sensors/Alarms HV AC 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., L

TD EC Sensors Sensors for residential use and boilers Quantum Group Inc IRO Sensors Sensors for Costar brand CO Alarms Not e shift from semiconductor/ox ide to electrochemical sensorsAHRI CO Sensors for Appliances 10 

# Sensors **Av ailable 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 Te chnology (EC) sensors evaluated.

─ Figaro limited to applications without high heat or humidity due to lower sensor life

─ City Te chnology 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 > Te mperature Range: -40 to 500 ° F > Humidity Range: 0% to 100% RH > Normal CO Sensor Range: 0 to 400 ppm > Maximum CO Sensor Va lue: 3000 ppm > Lifespan: 20 years > Accuracy: ± 5% > Electrical V

oltage: 24 VAC 

# Findings > Sensor range, maximum sensor value, accuracy and voltage are not limitations > Te mperature 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; we ll short of the 20 year life expectancy of some gas appliancesAHRI CO Sensors for Appliances 14 

# Summary

**SMO: Semiconductor**  **/Metal Oxide EC**  **:**

**Electrochemical IRO:**  **Infr ared**  **/Optical** Siz e No Issues No Issues No Issues Reliability No Issues No Issues No Issues Durability No Issues No Issues No Issues Cost Po tential Issues Po tential Issues Issues Te mperature/Humidity Influenced Po tential Issues Po tential Issues Insufficient Data Selectivity Issues No Issues No Issues Po isoning Issues Po tential Issues Insufficient Data Life Issues Issues Po tential Issues Response Time No Issues No Issues Po tential Issues Po wer Usage No Issues No Issues No Issues 

### *Ma **trix based on usag e in CO sensing on g** **as fir ed appliances and in**  **comparison with each other type**