复旦大学：《能源与环境 Energy and the Environment》教学课件_8_Energy and the environment VIII

Energy and the Environment CHEN HONG E-mail:chong@fudan.edu.cn Phone:021-65642526 复旦大学环境科学与工程系 Department of Environmental Science and Engineering, Fudan University

Energy and the Environment CHEN HONG E-mail: chong@fudan.edu.cn Phone: 021-65642526

Energy conservation a Penny Saved Is a penny earned The oil not taken from the earth One less barrel of oil is used to No emissions to foul the environment heat your home You save money in the bargain It is better to save a barrel of oil than to find a new one 复旦大学环境科学与工程系 Department of Environmental Science and Engineering, Fudan University

Energy Conservation A Penny Saved Is a Penny Earned One less barrel of oil is used to heat your home The oil not taken from the earth No emissions to foul the environment You save money in the bargain It is better to save a barrel of oil than to find a new one

Energy efficiency The addition of insulation to the outside walls of a house Use of fluorescent rather than incandescent Lower the thermostat setting Some temperature reduction can often be tolerated without undue discomfort, but carrying this approach too far may mean that saving energy carries with it a sacrifice of comfort on the part of the home occupants This element of sacrifice may appear in many situations Walk or ride a bicycle rather than driving a car Hanging the laundry out to dry rather than using a clothes dryer 复旦大学环境科学与工程系 Department of Environmental Science and Engineering, Fudan University

Energy efficiency The addition of insulation to the outside walls of a house Use of fluorescent rather than incandescent Lower the thermostat setting Some temperature reduction can often be tolerated without undue discomfort, but carrying this approach too far may mean that saving energy carries with it a sacrifice of comfort on the part of the home occupants. This element of sacrifice may appear in many situations. Walk or ride a bicycle rather than driving a car Hanging the laundry out to dry rather than using a clothes dryer

he Principle of Energy Conservation Energy conservation 1850-1975 energy consumption increased exponentially In 1970s, projection prediction 4.3%a year, 160Q Btu by 2000 1996,938QBtu/yr Oil embargo in 1973, the cost of energy rose very steep The increased fuel costs coupled with federally-sponsored energy conservation programs and help from public utilities and various community organizations have provided the incentives, education, and means for a significant drive toward a reduction in the use of energy The remarkable achievement In 1973 the ratio of energy consumption to gDP was 27X Btu/s 1990. decreased to 20X103 Btu/S 复旦大学环境科学与工程系 Department of Environmental Science and Engineering, Fudan University

Energy Conservation The Principle of Energy Conservation 1850-1975 energy consumption increased exponentially In 1970s, projection prediction 4.3% a year, 160QBtu by 2000 1996, 93.8 QBtu/yr. Oil embargo in 1973, the cost of energy rose very steeply. The increased fuel costs, coupled with federally-sponsored energy conservation programs and help from public utilities and various community organizations have provided the incentives, education, and means for a significant drive toward a reduction in the use of energy. The remarkable achievement: In 1973 the ratio of energy consumption to GDP was 27×103 Btu/$. 1990, decreased to 20×103 Btu/$ ≠

Main attention will be given to house hold use Buildings and appliances now use about 38% of the total energy consumed in Us, industry uses another 36%, and transportation 26% Se ource Use Natural Gas Electricity Fuel oil LPGa Space heating 3.32 0.39 0.58 0.28 Water heating 1.15 0.36 0.13 0.05 Appliances 0.37 1.67 0.05 Air-conditioning 0.62 Refrigerators Lighting al PGi stands for liquefied petroleum gas, most commonly propane, Source: Energy Information Administration, Washington, D.C. U.S. Department of Encrgy. 2004 复旦大学环境科学与工程系 Department of Environmental Science and Engineering, Fudan University

Main attention will be given to house hold use. Buildings and appliances now use about 38% of the total energy consumed in US, industry uses another 36%, and transportation 26%

The largest amount of house hold energy use in the Us is for space heating and natural gas is the predominant source of this energy. About 20% of the energy use in the us is for space heating. Prior to world war Ii in the 1940s, coal and wood were important sources of home heat Ideal house. perfect thermal insulation in the wall. windows roof and floors and no leakage of air into and out of the house and no radiation energy coming in or going out of the windows Any attempt to approach this ideal is limited in effectiveness by the cost and inconvenience of unreasonable amounts of insulation Nevertheless many well-designed houses have been built that require no separate heating system. They are heated adequately by existing internal sources of heat energy such as lights and cooking stoves 复旦大学环境科学与工程系 Department of Environmental Science and Engineering, Fudan University

The largest amount of house hold energy use in the US is for space heating, and natural gas is the predominant source of this energy. About 20% of the energy use in the US is for space heating. Prior to World War II in the 1940s, coal and wood were important sources of home heat. Ideal house, perfect thermal insulation in the wall, windows, roof, and floors and no leakage of air into and out of the house, and no radiation energy coming in or going out of the windows. …. Any attempt to approach this ideal is limited in effectiveness by the cost and inconvenience of unreasonable amounts of insulation. Nevertheless, many well-designed houses have been built that require no separate heating system. They are heated adequately by existing internal sources of heat energy such as lights and cooking stoves

5% through ceilings 16% 17% through frame walls 3% through door 20% through 38% through cracks basement in walls, windows 1% througi walls and doors basement floor Figure Heat loss from a typical conventionally insulated house. Solar energy entering through the windows can be a significant source of heat energy The amount of heat energy lost by air exchange through the cracks found in any typical home. As a general rule, 30-40% of the total heat loss is by this convective process 复旦大学环境科学与工程系 Department of Environmental Science and Engineering, Fudan University

Figure Heat loss from a typical conventionally insulated house. Solar energy entering through the windows can be a significant source of heat energy. The amount of heat energy lost by air exchange through the cracks found in any typical home. As a general rule, 30-40% of the total heat loss is by this convective process

Thermal Insulation The number of Btu/hr conducted outward through a surface such as a wall is given by Qt=kA(T1-T。)/l Where k is the thermal conductivity of the wall material in units of (Btu in.)/(hr ft*.F) a is the area of the wall surface in square feet, l is the thickness of the wall in inches, and (t - To)is the temperature difference in degrees Fahrenheit between the inside and outside Degree days For each day of the heating season, the number of degree days accumulated is given by the average temperature difference between inside and outside with the inside temperature taken to be a constant 65 F For an entire heating season, the total number of degree days is obtained by summing these degree days for the individual days of the heating season 复旦大学环境科学与工程系 Department of Environmental Science and Engineering, Fudan University

Thermal Insulation k l i o Q/t = A(T − T )/ (Btu in.)/(hr ft F) 2  ⋅ ⋅ ⋅ The number of Btu/hr conducted outward through a surface such as a wall is given by : Where k is the thermal conductivity of the wall material in units of : A is the area of the wall surface in square feet, l is the thickness of the wall in inches, and (Ti -To) is the temperature difference in degrees Fahrenheit between the inside and outside. Degree days For each day of the heating season, the number of degree days accumulated is given by the average temperature difference between inside and outside, with the inside temperature taken to be a constant 65 ̊F. For an entire heating season, the total number of degree days is obtained by summing these degree days for the individual days of the heating season

This number is taken as a measure of Location Degree Days the severity of the winter but it does not consider wind or sunshine or Barrow. Alaska 19,990 several other weather factors. It is only Fairbanks. Alaska 14160 a measure of the average outside air Park Rapids, Minnesota 9.50 temperature Portland Maine 7,680 Madison. Wisconsin 7,300 The right table lists the heating season Chicago, Illinois 6,310 degree days for a number of locations Reno, Nevada 6040 in the United States Denver, Colorado 5.670 eg: a) Calculate the number of New York. New York 050 degree days accumulated in one da Newark, New Jersey 4.810 in which the average outside Washington, D. c 430 San francisco, California 3.070 temperature is 17F.(48 degree days) Birmingham, Alabama 2,780 b) Calculate the number of degree Los Angeles, California 2,020 days accumulated during a 150-day Tucson. arizona 1,780 heating season in which the average Miami Florida 170 outside temperature is 17F (7200 degree days) 复旦大学环境科学与工程系 Department of Environmental Science and Engineering, Fudan University

This number is taken as a measure of the severity of the winter, but it does not consider wind or sunshine or several other weather factors. It is only a measure of the average outside air temperature. The right table lists the heating season degree days for a number of locations in the United States. eg: a). Calculate the number of degree days accumulated in one day in which the average outside temperature is 17 ̊F. (48 degree days) b) Calculate the number of degree days accumulated during a 150-day heating season in which the average outside temperature is 17 ̊F. (7200 degree days)

The thermal conductivity, k, is the property of a material without reference to its dimensions. In practice, one often knows the material and the dimensions of a wall. for instance In this case it is convenient to use the specification, R-value, which labeled on insulation and other building materials and it represents the en incorporates both the wall thickness and the material The r- value is ofte thermal resistance of a material For any slab of material it is given by r=l/, where l is the thickness of the slab and k is its thermal conductivity. This number can be obtained from standard reference books. The units of R are commonly hr. Fft2/Btu For a wall or any other surface built up of a layered series of material each having thickness 11, I2, I3..and conductivity ki, k2, k3..., the total R-values, Rr=R+R+R+ ++→+ k 复旦大学环境科学与工程系 Department of Environmental Science and Engineering, Fudan University

The thermal conductivity, k, is the property of a material without reference to its dimensions. In practice, one often knows the material and the dimensions of a wall, for instance. In this case it is convenient to use the specification, R-value, which incorporates both the wall thickness and the material. The R-value is often labeled on insulation and other building materials and it represents the thermal resistance of a material. For any slab of material it is given by R=l/k, where l is the thickness of the slab and k is its thermal conductivity. This number can be obtained from standard reference books. The units of R are commonly hr· ̊F·ft2/Btu For a wall or any other surface built up of a layered series of material each having thickness l1, l2 , l3 … and conductivity k1, k2 , k3 … , the total R-values, or RT = R1+R2+R3+… ... 3 3 2 2 1 1 = + + + k l k l k l