Unit 50 Review Questions Flashcards
What is the origin of natural gas?
Natural gas is a fossil fuel formed from the decomposition of organic matter over millions of years. It primarily consists of methane and is extracted from underground reservoirs.
What are the three broad categories of fuel gases?
- Natural gas (methane-based)
- Liquefied petroleum (LP) gas (propane and butane)
- Manufactured gas (synthetic or mixed gases)
What are the characteristics of methane?
Methane: 950-1,150 Btu/ft³, Specific Gravity ~0.4-0.8
What are the characteristics of ethane?
Ethane: ~1,750 Btu/ft³, Specific Gravity ~1.04
What are the characteristics of propane?
Propane: 2,500 Btu/ft³, Specific Gravity ~1.5
What are the characteristics of butane?
Butane: 3,200 Btu/ft³, Specific Gravity ~2.
What are the products of complete combustion of a hydrocarbon gas?
Carbon dioxide and water vapor
What are the products of incomplete combustion of a hydrocarbon gas?
Carbon monoxide (CO), soot (carbon), aldehydes, and other unburned hydrocarbons.
Why are LP gases considered more hazardous than natural gas?
LP gases (propane and butane) are heavier than air, so they can accumulate in low-lying areas, creating an increased risk of explosion and suffocation.
What are the characteristics of a primary (blue) flame?
Indicates complete combustion, efficient burning, and proper air-fuel mixture.
What are the characteristics of a secondary (yellow) flame?
Indicates incomplete combustion, excessive soot, and potential carbon monoxide formation.
What is the gas combustion process in a gas furnace?
The process includes gas flow to the burner, mixing with air, ignition, heat transfer to the heat exchanger, and venting of combustion gases.
What causes flue gas condensation and how can it be stopped?
Flue gas condensation occurs when combustion gases cool below their dew point, leading to water accumulation and corrosion. It can be prevented by proper venting, maintaining correct combustion temperatures, and using high-efficiency heat exchangers.
What causes soot formation on the heat exchanger and how can it be stopped?
Soot forms due to incomplete combustion, which can result from dirty burners, restricted airflow, or improper air-fuel mixtures. It can be stopped by regular maintenance and ensuring proper combustion air supply.
How is carbon monoxide formed?
Carbon monoxide is formed when there is incomplete combustion of fuel due to insufficient oxygen supply.
What are the furnace combustion air requirements?
Adequate combustion air is necessary for complete fuel combustion. This includes primary air (mixed with fuel before combustion) and secondary air (supplied during combustion). Ventilation must be adequate to prevent dangerous byproducts.
Which agencies establish standards for furnace performance?
DOE, National Institute of Standards and Technology (NIST)
Which agencies perform testing to verify equipment performance?
Underwriters Laboratories (UL), CSA International (CSA), American National Standards Institute (ANSI)
What does AFUE stand for?
AFUE (Annual Fuel Utilization Efficiency) measures furnace efficiency, representing the percentage of fuel converted into usable heat over a heating season.
What is the minimum AFUE rating for a new furnace in the United States?
78% for non-condensing furnaces
90%+ for high-efficiency condensing furnaces for North (as per DOE regulations)
80%+ for high-efficiency condensing furnaces for South (as per DOE regulations)
Which agencies set equipment standards and test equipment?
AHRI, CSA, and UL
Which government agencies are involved in setting equipment standards?
National Science Foundation (NSF), U.S. Department of Energy (DOE), National Institute of Standards and Technology (NIST)
What can be done to minimize the pollutants produced by a gas furnace?
Regular maintenance, ensuring proper combustion air supply, using high-efficiency furnaces, and installing filters and venting systems to reduce emissions.
What is the purpose of excess air in furnace combustion?
Excess air ensures complete combustion, preventing carbon monoxide formation and reducing soot buildup.
