issue: November 2006 APPLIANCE Magazine
Fueling System Efficiency
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Electronic fuel injection technology (efi) is not just for automobiles anymore. It is now used in gas appliances such as furnaces, boilers and water heaters to increase system efficiency.
Opti Control is designed to provide a systematic solution to the HVAC industry by optimizing the efficiency of gas appliances. It’s said to solve issues related to geographic location, air quality, heating value of gas, and safety.
With factors such
as geographic altitude, air quality, temperature, and heating value due
to gas blending affecting the combustion efficiency of gas appliances,
engineers are looking for new ways to keep their systems running
efficiently. That’s why Dexen Industries decided to explore the use of
efi technology in gas appliance applications.
The company believes that combustion efficiency can be controlled by
monitoring carbon dioxide (CO2)—not oxygen—in the flue gas and
modulating gas flow. The higher the CO2 concentration, the lower the
pressure needed to generate less gas flow to the combustion chamber.
Applying that knowledge, the South El Monte, California, U.S.-based
supplier developed Opti Control™. The device samples and measures flue
gases and signals the gas control to modulate the gas flow and air
intake. This is said to create a closed loop of the system after
feedback with adjusted concentration level to the sensor.
Here’s how it works: Gas pressure of the control is adjusted by an
electronically modulating regulator. A 5-V CO2 sensor monitors CO2
concentration in the exhaust coming out of the appliance’s combustion
chamber. A 5-V controller then takes the data from the sensor and
activates the modulation of gas control and the speed of the fan for
induced air. Increased gas flow to the combustion chamber mixes with a
proportional amount of air and generates a higher concentration of CO2.
This higher concentration triggers the system to lower gas pressure and
gas flow, resulting in a lower concentration of CO2.
For example, if a system reaches a CO2 concentration level of 9
percent, the controller takes data from the sensor and activates the
gas control to lower the gas pressure. The benchmark combustion
efficiency is 7.5 to 8.0 percent CO2. For added safety, the controller
shuts off gas flow when CO2 reaches above 11 percent. When CO2 drops
below 7 percent, the sensor shuts down, and gas control returns to the
high-pressure setting and fan speed.
According to Dexen, the device simplifies gas control and gas appliance
designs. Fewer parts means fewer points of failure and increased
reliability, the company says, resulting in a gas appliance that is
easier to manufacture, operate and maintain with greatly enhanced
functionality. The company does warn, however, that the control’s
performance is tied to the burner for which it is designed, so it is
critical to properly maintain burners.
Possible applications for the control include gas ranges, washers and
dryers, although the technology is currently being used in furnaces,
burners and water heaters.