Fundamentals of HVAC/R: Gas Fired Heating System Flashcards

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created 11 years ago by Cangetr1ght1980
updated 11 years ago by Cangetr1ght1980
unit 6 section 7, technology & engineering, construction, mechanical
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Discuss the origin of natural gas.

Natural gas comes from the sedimentation of trillions of tiny organisms at the bottom of the sea that are buried and initially chemically converted into dense organic material.


List the three broad categories of fuel gases.

natural, manufactured, and liquefied petroleum.


Complete this table of fuel gas characteristics.

gas heat capacity specific heat
methane 1000 0.6
ethane 1780 1.0
propane 2500 1.5
butane 3600 2.0


What are the products of complete combustion of a hydrocarbon gas?

fuel, oxygen, and heat


What are the products of incomplete combustion of a hydrocarbon gas?

excess oxygen is left which reduces combustion temperature and lowers combustion efficiency


Why are LP gases considered more hazardous than natural gas?

Because LP gases are heavier than air they collect in low areas. A leak in the gas line to an LP furnace in a crawl space or basement will create a
"puddle" of gas on the ground around the furnace. An unwary technician could be lying in this puddle of LP gas when it is ignited, surrounding the technician in flames.


Describe the two types of flames and their and their characteristics.

a yellow flame is produced when gas is burned by igniting the gas gushing from an open end of a gas pipe, such as is common for ornamental lighting. A blue flame is produced by a Bunsen burner such as those used in a laboratory, where 50% of the air requirements is mixed with the gas prior to ignition. Blue flames are characteristics of nonluminous combustion, a process that produces a little light, lots of heat, and no carbon monoxide.


Describe the gas combustion process as it applies to a gas furnace?

The by-products of combustion in furnaces are called flue gases and are vented to the outside. Insufficient combustion air can produce hazardous conditions. If too little oxygen is supplied, part of the by-products will be dangerous carbon monoxide gas rather than harmless carbon dioxide gas.


Explain the cause of flue gas condensation and how it can be stopped?

Low temperature corrosion can occur in exhaust systems components (heat exchangers, flues, vents, chimneys). In the high efficiency furnace where condensation is allowed to occur inside the furnace on a continuous basis, the flue passages must be constructed of corrosion resistant materials such as stainless steel and PVC.


Explain the cause of soot formation on the heat exchanger and how it can be stopped.

A properly burning gas appliance will never make soot. Proper burner adjustments can prevent the formation of soot. Soot can be caused by too much fuel, too little air, or improper mixing. To prevent soot formation,the technician should:

Make sure the burner orifices are the correct size.

Check the manifold gas pressure and adjust if necessary.

Check the combustion air opening in the appliance room.

Adjust the air shutters on the gas appliances to produce a blue flame.


Explain how carbon monoxide is formed?

Incomplete combustion produces carbon monoxide, an odorless, tasteless, and poisonous gas. As well as soot


Discuss furnace combustion air requirements.

Adequate combustion air is an essential element of the system's design, and central to indoor air quality. air quality can be greatly affected by the formation of nitrous oxides. Nitrogen represents about 80% of the earths atmosphere. Therefore, in conjunction with the excess air neccessary for complete combustion, it is clear that nitrogen consists the major portion of the exhaust gases


List agencies that establish standards for gas furnaces.

United States Department of Energy (DOE)
National Institute of Standards and Technology
National Science Foundation


List agencies that perform testing to verify equipment performance.

Underwriters Laboratories. (UL) is an independent, not-for-profit, product safety certification organization that has been testing products and writing standards as well as testing. There are many UL standards relating to gas heating equipment.


Explain AFUE.

The AFUE is determined for residential fan type furnaces by using the ANSI/ASHRAE Standard 103-1993 method of testing.


What is the minimum AFUE rating for a new furnace in the United States?

The federal law, effective January 1, 1992 requires that all new gas furnaces have a minimum AFUE efficiency of 78%.


What agencies set equipment standards and test equipment?

AHRI, CSA, AND UL, are involved in both setting standards and certifying equipment.


Which agencies are involved in setting equipment standards?

AHRI, CSA, AND UL, are involved in setting standards.


What can be done to minimize the pollutants produced by a gas furnace?

To prevent air pollution, air intakes, filters, ducts, and system components. And very importantly seal leaks.


What is the purpose of excess air in the furnace