1 hvacr115 – mechanical for gas properties of gas general characteristics properties of gas...
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HVACR115 – Mechanical for Gas
HVACR115 – Mechanical for Gas
Properties of Gas
General Characteristics
Properties of Gas
General Characteristics
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Chemical Composition of GasChemical Composition of Gas
• All gasses used to supply heat are called “Fuel Gas”
• The major part of fuel gas is “Hydrocarbons”.– Hydrocarbons are compounds of hydrogen and carbon.
• All gasses used to supply heat are called “Fuel Gas”
• The major part of fuel gas is “Hydrocarbons”.– Hydrocarbons are compounds of hydrogen and carbon.
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Chemical Composition of GasChemical Composition of Gas
• Different numbers of hydrogen and carbon atoms make up different types of gasses.
• Different numbers of hydrogen and carbon atoms make up different types of gasses.
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MethaneMethane
• Makes up the largest portion of natural gas.• One carbon atom linked with four hydrogen
atoms.• CH4 is its chemical name.
• Makes up the largest portion of natural gas.• One carbon atom linked with four hydrogen
atoms.• CH4 is its chemical name.
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MethaneMethane
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EthaneEthane
• Has two carbon atoms linked with six hydrogen atoms
• C2H6 is the chemical name
• Has two carbon atoms linked with six hydrogen atoms
• C2H6 is the chemical name
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EthaneEthane
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PropanePropane
• Has three carbon atoms and eight hydrogen atoms
• C3H8 is the chemical name
• Has three carbon atoms and eight hydrogen atoms
• C3H8 is the chemical name
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PropanePropane
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ButaneButane
• Has four carbon atoms and 10 hydrogen atoms.• C4H10 is the chemical name
• Has four carbon atoms and 10 hydrogen atoms.• C4H10 is the chemical name
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ButaneButane
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Carbon and HydrogenCarbon and Hydrogen
• The number of carbon and hydrogen atoms in these fuel gasses affect the nature of the gas.
• More atoms in the compound make it heavier than air.
• Larger numbers of hydrogen and carbon atoms in the fuel, the more heat is released.
• The number of carbon and hydrogen atoms in these fuel gasses affect the nature of the gas.
• More atoms in the compound make it heavier than air.
• Larger numbers of hydrogen and carbon atoms in the fuel, the more heat is released.
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Carbon and Hydrogen Carbon and Hydrogen
• Some additional characteristics of the fuel gas, such as how easy it is to control the flame depend on the number of carbon and hydrogen atoms.
• Some additional characteristics of the fuel gas, such as how easy it is to control the flame depend on the number of carbon and hydrogen atoms.
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Common Fuel GassesCommon Fuel Gasses
• The common fuel gasses are not simply one kind of hydrocarbon, but are mixtures of many gasses.
• The fuel gasses seen in the HVAC industry may also contain other gasses such as carbon dioxide, nitrogen, and free hydrogen. They are not pure.
• The common fuel gasses are not simply one kind of hydrocarbon, but are mixtures of many gasses.
• The fuel gasses seen in the HVAC industry may also contain other gasses such as carbon dioxide, nitrogen, and free hydrogen. They are not pure.
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Natural GasNatural Gas
• Organic in nature from dead and dying plants long ago.
• Usually found in areas where oil is present as well.
• Some natural gas from garbage and cow manure is now being used.
• Organic in nature from dead and dying plants long ago.
• Usually found in areas where oil is present as well.
• Some natural gas from garbage and cow manure is now being used.
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Liquefied Petroleum GasLiquefied Petroleum Gas• LPG or LP gas• Can be propane or butane or a mix of the two.• LP gasses are transported and stored in tanks.• LP gasses are usually used in areas where gas
pipelines are not available.
• LPG or LP gas• Can be propane or butane or a mix of the two.• LP gasses are transported and stored in tanks.• LP gasses are usually used in areas where gas
pipelines are not available.
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LPGLPG
• LPG is stored under pressure, much of the gas is in a liquid form in the tanks.
• As the fuel is drawn from the tank it turns to gas and is burned in the same way as the other gasses.
• LPG is stored under pressure, much of the gas is in a liquid form in the tanks.
• As the fuel is drawn from the tank it turns to gas and is burned in the same way as the other gasses.
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Odorants added to gassesOdorants added to gasses
• Natural gas has little or no odor and has no color.• Odorants are added to the gas prior to distribution
to aid in leak detection and for safety.• Most odorants used contain sulfur which is what
people identify as a “gassy” smell.
• Natural gas has little or no odor and has no color.• Odorants are added to the gas prior to distribution
to aid in leak detection and for safety.• Most odorants used contain sulfur which is what
people identify as a “gassy” smell.
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Specific GravitySpecific Gravity
• Specific gravity is the weight of a substance compared with the same volume of another substance.
• Fresh water is used as the reference substance for liquids and solids.– If the specific gravity of a liquid is 2.0 it is twice the
weight of the same amount of water.
• Specific gravity is the weight of a substance compared with the same volume of another substance.
• Fresh water is used as the reference substance for liquids and solids.– If the specific gravity of a liquid is 2.0 it is twice the
weight of the same amount of water.
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Specific GravitySpecific Gravity
• For gasses, air is used as the reference substance.
• Specific Gravity of a gas is calculated by weighing 1 cubic foot of the gas and comparing it to 1 cubic foot of air.
• Both the air and the gas must be at the same temperature and pressure when the comparison is made.
• For gasses, air is used as the reference substance.
• Specific Gravity of a gas is calculated by weighing 1 cubic foot of the gas and comparing it to 1 cubic foot of air.
• Both the air and the gas must be at the same temperature and pressure when the comparison is made.
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Specific GravitySpecific Gravity
• The amount of gas in a given volume will change or vary with pressure.
• The pressure will vary with temperature as gasses expand and contract with temperature change.
• The amount of gas in a given volume will change or vary with pressure.
• The pressure will vary with temperature as gasses expand and contract with temperature change.
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Specific GravitySpecific Gravity
• The specific gravity of air is 1.0 as it is used for the reference material.
• This is measured with a standard temperature of 69.8 degrees F. and a pressure of 29.92 inches of mercury.
• The specific gravity of air is 1.0 as it is used for the reference material.
• This is measured with a standard temperature of 69.8 degrees F. and a pressure of 29.92 inches of mercury.
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Specific Gravity of Nat. GasSpecific Gravity of Nat. Gas
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SG of Natural GasSG of Natural Gas
• Natural Gas has a specific gravity ranging from .4 to .8
• This means that Natural Gas is lighter than air.
• Natural Gas has a specific gravity ranging from .4 to .8
• This means that Natural Gas is lighter than air.
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Specific Gravity of PropaneSpecific Gravity of Propane
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SG of PropaneSG of Propane
• Propane has a specific gravity of 1.5• Butane has a specific gravity of 2.0
• If these gasses are released into the air they will fall instead of rising.
• They will not mix readily with air.
• Propane has a specific gravity of 1.5• Butane has a specific gravity of 2.0
• If these gasses are released into the air they will fall instead of rising.
• They will not mix readily with air.
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SG of PropaneSG of Propane
• Propane and Butane will drift into low spots and “pool” creating explosion hazards if open flames are present.
• Propane and Butane will drift into low spots and “pool” creating explosion hazards if open flames are present.
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Why know about specific gravity?Why know about specific gravity?
• It has an important effect on the flow of gas through orifices, and effects the ratings of burners.
• A gas “orifice” is a small hole in a fitting (spud) and is used to limit the gas flow to the burners.
• It has an important effect on the flow of gas through orifices, and effects the ratings of burners.
• A gas “orifice” is a small hole in a fitting (spud) and is used to limit the gas flow to the burners.
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Why know about specific gravity?Why know about specific gravity?
• The gas flow rate through an orifice depends on the orifice size and the pressure upstream of the orifice.
• The specific gravity also effects the gas flow as more of the lighter gas will flow through than a heavier gas at the same pressure.
• The gas flow rate through an orifice depends on the orifice size and the pressure upstream of the orifice.
• The specific gravity also effects the gas flow as more of the lighter gas will flow through than a heavier gas at the same pressure.
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Heating Value of GasHeating Value of Gas
• Heat energy produced when burning a fuel is commonly expressed in British Thermal Units, or BTU’s.
• One BTU will raise the temperature of one pound of fresh water one degree Fahrenheit.
• Burning an ordinary wooden kitchen match produces about 1 BTU of heat.
• Heat energy produced when burning a fuel is commonly expressed in British Thermal Units, or BTU’s.
• One BTU will raise the temperature of one pound of fresh water one degree Fahrenheit.
• Burning an ordinary wooden kitchen match produces about 1 BTU of heat.
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Heating Value of GasHeating Value of Gas
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Heating Value of GasHeating Value of Gas
• Example:– Need to heat 10 pounds of water 100 degrees requires
1000 btu’s of heat.
• The heating value of gas is the amount of heat released when one cubic foot of gas is completely burned.
• Example:– Need to heat 10 pounds of water 100 degrees requires
1000 btu’s of heat.
• The heating value of gas is the amount of heat released when one cubic foot of gas is completely burned.
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Heating Value of GasHeating Value of Gas
• Natural Gas, primarily methane, has a heating value of about 950 to 1150 btu’s per cubic foot of gas. (use 1000).
• Propane has a heating value of about 2500 btu’s per cubic foot.
• Butane has a heating value of about 3000 btu’s per cubic foot.
• Natural Gas, primarily methane, has a heating value of about 950 to 1150 btu’s per cubic foot of gas. (use 1000).
• Propane has a heating value of about 2500 btu’s per cubic foot.
• Butane has a heating value of about 3000 btu’s per cubic foot.
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The ThermThe Therm
• Another unit of heat energy used by the fuel industry is the “Therm”.
• A THERM is 100,000 BTU’s of heat energy.• A therm of natural gas is 100 cubic feet of gas.
– 100,000 / 1000 = 100
• Another unit of heat energy used by the fuel industry is the “Therm”.
• A THERM is 100,000 BTU’s of heat energy.• A therm of natural gas is 100 cubic feet of gas.
– 100,000 / 1000 = 100
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The ThermThe Therm
• Forty Cubic Feet of Propane contain a therm of heat energy.– 100,000 / 2500 btu = 40
• Forty Cubic Feet of Propane contain a therm of heat energy.– 100,000 / 2500 btu = 40
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Hourly Use of GasHourly Use of Gas
• Input rates are the measurement of the hourly use of gas in an appliance.
• Input rates will be in Cubic Feet per hour.• Input rates can be converted to and from BTU’s
per hour.
• Input rates are the measurement of the hourly use of gas in an appliance.
• Input rates will be in Cubic Feet per hour.• Input rates can be converted to and from BTU’s
per hour.
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Input RatesInput Rates
• Input Rate (BTU/hr) = (heating value of gas per cubic foot) X (Gas flow rate in cubic feet per hour)
• Gas Flow Rate in Cubic Feet per hour = (input rate (BTU/Hr) / (Heating Value of the gas in BTU/Ft3)
• Input Rate (BTU/hr) = (heating value of gas per cubic foot) X (Gas flow rate in cubic feet per hour)
• Gas Flow Rate in Cubic Feet per hour = (input rate (BTU/Hr) / (Heating Value of the gas in BTU/Ft3)
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Input RatesInput Rates
• A natural gas water heater needs 35,000 btu/hr. find the required gas flow.– CFH = 35,000 / 1,000– CFH = 35
• A natural gas water heater needs 35,000 btu/hr. find the required gas flow.– CFH = 35,000 / 1,000– CFH = 35
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Input RatesInput Rates
• Input rates are important for the gas pipe sizing for appliance and furnaces.
• Bottom line, the appliance must have enough gas to run efficiently.
• Input rates are important for the gas pipe sizing for appliance and furnaces.
• Bottom line, the appliance must have enough gas to run efficiently.
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