Overview of Chapter 7 Continuing Chapter 7 Lecture #15 HNRS 228 Energy and the Environment Energy Conservation Space Heating Thermal Insulation Air Infiltration Lighting Appliances Some considerations of agriculture and industry 1 2 How many fewer power plants might be needed if every household changed to compact fluorescent lighting? A About one B More than one C More than 100 Which type of washing machine conserves the most energy and water? A Top loader B Front loader 3 4 Turning off your computer will harm it. A True B False Leaving your heat on is more efficient than turning it down because you need so much energy to heat the house back up. A True B False 5 6 1
Which unit is used to measure insulation of walls? A Q-value B R-value C S-value D T-value E U-value Which unit is used to measure insulation of windows? A Q-value B R-value C S-value D T-value E U-value 7 8 Which of the following will conserve more energy. A A wall with R-value 12 B A wall with R-value 14 C A wall with R-value 16 D A wall with R-value 18 E A wall with R-value 20 Which of the following will conserve more energy. A A window with U-value 0.12 B A window with U-value 0.14 C A window with U-value 0.16 D A window with U-value 0.18 E A window with U-value 0.20 9 10 National Average Home Energy Costs Why do we need Heating? 14% Heating and Cooling 44% Refrigrator 33% 9% Lighting, Cooking and other Appliances Water Heating 30 F 70 'F Furnace 11 12 2
Typical Heat losses- Conventional House Heat Transfer 5% through ceilings Conduction Convection Radiation 17% through frame walls 1% through basement floor 16% through windows 3% through door 38% through cracks 20% in walls, windows, through and doors basement walls 13 14 Conduction Convection Energy is conducted down the rod as the vibrations of one molecule are passed to the next, but there is no movement of bulk material Energy is carried by the bulk motion of the fluid 15 16 Radiation Energy is carried by electromagnetic waves. No medium is required Degree Days Index of fuel consumption indicating how many degrees the mean temperature fell below 65 degrees for the day Heating degree days (HDD) are used to estimate the amount of energy required for residential space heating during the cool season. Cooling degree days (CDD) are used to estimate the amount of air conditioning usage during the warm season 17 18 3
How do we calculate HDD? HDD = T base -T a if T a is less than T base HDD = 0 if T a is greater or equal to T base Where: T base = temperature base, usually 65 F Ta = average temperature, Ta = (T max + T min ) / 2 Heating Degree Days Calculate the number of degree days accumulated in one day in which the average outside temperature is 17ºF. Degree days = 1 day ( 65 T out ) = 1 (65-17) = 48 degree days 19 20 Heating Degree Days in a Heating Season Calculate the degree days accumulated during a 150-day heating season if the average outside temperature is 17ºF Solution: Heating Season Degree days = 150 days ( 65 T out ) = 150 (65-17) = 7,200 degree days Degree Days for the Heating Season PLACE DEGREE DAYS Birmingham, 2,780 ALABAMA Anchorage, 10,780 ALASKA Barrow, ALASKA 19,994 Tucson, ARIZONA 1,776 Miami, FLORIDA 173 State College??? 21 22 Significance of HDD Mrs. Young is moving from Anchorage, Alaska (HDD =10,780) to State college, PA (HDD = 6,000). Assuming the cost of energy per million Btu is the same at both places, by what percentage her heating costs will change? Solution HDD in Anchorage, Alaska = 10,780 HDD in State College PA = 6,000 Difference = 10,780-6,000 = 4,780 Saving in fuel costs are 4,780 100 44.3% 10,780 23 24 4
Home Energy Saver http://homeenergysaver.lbl.gov/ Home Heating Costs in State College, PA Average House $305 $232 $106 Heating Cooling $890 $227 $133 Total $1,891 $232 $52 Hot water Appliances Misc. Lighting Energy Effcient House Energy Efficient House $327 25 $205 $114 $89 26 Total $1,019 Home Heating Costs Related to amount of insulation, material that resists the flow of heat Insulation is rated in terms of thermal resistance, called R-value, which indicates the resistance to heat flow. The higher the R-value, the greater the insulating effectiveness. The R-value of thermal insulation depends on the type of material, its thickness, and density. R-30 better than R-11 Attic is usually the easiest ad most cost effective place to add insulation Floors above unheated basements should be insulated Heated basements should be insulated around the foundaton Places to Insulate 27 28 R-values for Building Materials Thickness of various materials for R-22 110" 18" 6" 7" Cellulose Fiber Fiberglass Pine wood Common brick 29 30 5
R-Value for a Composite Wall Home Heating Energy Heat loss depends on Surface Area (size) R-Value of material 1/2" Plasterboard 0.45 3 1/2" Fiberglass 10.90 3/4" Plywood 0.94 Temperature Difference Property of the wall ( R value) Inside 65 F Outside 30 F 1/2" Wood siding 0.81 R TOTAL = 13.10 ft 2 F hr BTU 31 Q (Btus) t (time, h) = 1 A (area) x Temperature Diff (T i T o ) R 32 Heat Loss Wall loss rate in BTUs per hour T hot T cold Q t Area x T T inside outside ( ThermalResistanceoftheWall, R) Area x T T inside outside Q ( ThermalResistanceoftheWall, R) Heat Loss = t Id Q/t is in Btu/h Area in ft 2 T in -T out in F Then the thermal resistance is R-value. The units of R-value are 2 o ft x F Btu/ hr For a 10 ft by 10 ft room with an 8 ft ceiling, with all surfaces insulated to R19 as recommended by the U.S. Department of Energy, with inside temperature 68 F and outside temperature 28 F: 2 0 320 ft x 68 F 28 F 674Btu hr Q Heatloss Rate / 2 0 t ft x F 19 BTU/ h 33 34 Calculation per Day Heat loss per day = (674 BTU/hr)(24 hr) = 16,168 BTU Note that this is just through the wall The loss through the floor and ceiling is a separate calculation, and usually involves different R-values Calculate loss per "degree day" This is the loss per day with a one degree difference between inside and outside temperature. 35 If the conditions of case II prevailed all day, you would require 40 degree-days of heating, and therefore require 40 degree-days x 404 BTU/degree day = 16168 BTU to keep the inside temperature constant. 36 6
Heat Loss for Entire Heating Season. Numerical Example The typical heating requirement for a Pittsburgh heating season, September to May, is 5960 degree-days (a long-term average). Heat loss = Q/t = 404 Btu/degree day x 5960 degree days = 2.4 MM Btus The typical number of degree-days of heating or cooling for a given geographical location can usually be obtained from the weather service. 37 38 Heat loss Calculation 1 Q total A / R Number of Annual deg ree days 24h day Problem A wall is made up of four elements, as follows ½ wood siding ½ plywood sheathing 3 ½ in of fibber glass ½ of sheet rock How many Btus per hour per sq.ft. will be lost through the wall when the outside temperature is 50F colder than inside? 39 40 Economics of Adding Insulation Years to Payback = C(i) x R(1) x R(2) x E ------------------------------------- C(e) x [R(2) - R(1)] x HDD x 24 C(i) = Cost of insulation in $/square feet C(e) = Cost of energy, expressed in $/Btu E = Efficiency of the heating system R(1) = Initial R-value of section R(2) = Final R-value of section R(2) - R(1) = R-value of additional insulation being considered HDD = Heating degree days/year 24 = Multiplier used to convert heating degree days to heating hours (24 hours/day). Pay Back Period Calculation Suppose that you want to know how many years it will take to recover the cost of installing additional insulation in your attic. You are planning to increase the level of insulation from R-19 (6 inch fiberglass batts with moisture barrier on the warm side) to R-30 by adding R-11 (3.5 inch unfaced fiberglass batts). You have a gas furnace with an AFUE of 0.88. You also pay $0.70/therm for natural gas. Given C(i) = $0.18/square foot; C(e) = ($0.70/therm)/(100,000 Btu/therm) = $0.000007/Btu; E = 0.88; R(1) = 19; R(2) = 30; R(2) - R(1) = 11; HDD = 7000 41 42 7
Household Heating Fuel Average Heating Value of Common Fuels 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 56% Natural Gas 26.00% 11.00% 10.00% Electricity Fuel Oil Other Heating Fuel Fuel Type No. of Btu/Unit (Kilocalories/Unit) Kerosene (No. 1 Fuel Oil) 135,000/gallon (8,988/liter) No. 2 Fuel Oil 140,000/gallon (9,320/liter) Electricity 3,412/kWh (859/kWh) Natural Gas 1,028,000/thousand cubic feet (7,336/cubic meter) Propane 91,333/gallon (6,081/liter) Bituminous Coal 23,000,000/ton (6,400,000/tonne) Anthracite Coal 24,800,000/ton (5,670,000/tonne) Hardwood (20% moisture)* 24,000,000/cord (1,687,500/cubic meter) Pine (20% moisture)* 18,000,000/cord (1,265,625/cubic meter) Pellets (for pellet stoves; premium) 16,500,000/ton (4,584,200/tonne) 43 44 Typical Heating Furnace Efficiencies Comparing the Fuel Costs Fuel Type - Heating Equipment Efficiency (%) Coal (bituminous) Central heating, hand-fired 45 Central heating, stoker-fired 60 Water heating, pot stove (50 gal.[227.3 liter]) 14.5 Oil High efficiency central heating 89 Typical central heating 78 Water heater (50 gal.[2227.3 liter]) 59.5 Gas High efficiency central heating 92 Typical central heating 82 Room heater, unvented 91 Room heater, vented 78 Water heater (50 gal.[227.3 liter]) 62 Electricity Central heating, resistance 97 Central heating, heat pump 200+ Ground source heat pump 300+ Water heaters (50 gal.[227.3 liter]) 97 Wood & Pellets Franklin stoves 30.0-40.0 Stoves with circulating fans 40.0-70.0 Catalytic stoves 65.0-75.0 Pellet stoves 85.0-95.0 45 Energy Cost Cost perunit offuel HeatingValue( MMBtu / unitoffuel) Efficiency 46 Fuel Costs Heating Systems Electric resistance heat cost = $0.082 (price per kwh) / [ 0.003413 x 0.97 (efficiency)] = $24.77 per million Btu. Natural gas (in central heating system) cost = $6.60 (per thousand cubic feet) / [ 1.0 x 0.80 (efficiency)] = $8.25 per million Btu. Oil (in central heating system) cost = $0.88 (price per gallon) / [ 0.14 x 0.80 (efficiency)] = $7.86 per million Btu. Propane (in central heating system) cost = $0.778 (price per gallon) / [ 0.0913 x 0.80 (efficiency)] = $10.65 per million Btu. 47 48 8
Some hot water systems circulate water through plastic tubing in the floor, called radiant floor heating. Heating Systems Electric Heating Systems 1. Resistance heating systems Converts electric current directly into heat 1. usually the most expensive 2. Inefficient way to heat a building 2. Heat pumps Use electricity to move heat rather than to generate it, they can deliver more energy to a home than they consume 1. Most heat pumps have a COP of 1.5 to 3.5. 2. All air-source heat pumps (those that exchange heat with outdoor air, as opposed to bodies of water or the ground) are rated with a "heating season performance factor" (HSPF) 49 50 Geothermal Heat Pumps They use the Earth as a heat sink in the summer and a heat source in the winter, and therefore rely on the relative warmth of the earth for their heating and cooling production. Benefits of a GHP System Low Energy Use Free or Reduced-Cost Hot Water Year-Round Comfort Low Environmental Impact Durability Reduced Vandalism Zone Heating and Cooling Low Maintenance Additional reading http://www.eren.doe.gov/erec/factsheets/geo_heatpumps.html#sidebar 51 52 Solar Heating and Cooling Most American houses receive enough solar energy on their roof to provide all their heating needs all year! Active Solar Passive Solar Passive Solar A passive solar system uses no external energy, its key element is good design: House faces south South facing side has maximum window area (double or triple glazed) Roof overhangs to reduce cooling costs Thermal mass inside the house (brick, stones or dark tile) 53 54 9
Passive Solar Deciduous trees on the south side to cool the house in summer, let light in in the winter. Insulating drapes (closed at night and in the summer) Greenhouse addition Indirect gain systems also such as large concrete walls to transfer heat inside Passive Solar Heating 55 56 Passive Heating Direct Gain Thermal Storage Wall Sunspace Passive Cooling Shading Ventilation Earth Contact Source: Global Science, Energy Resources Environment 57 58 Active Solar Heating Flat plate collectors are usually placed on the roof or ground in the sunlight. The sunny side has a glass or plastic cover. The inside space is a black absorbing material. Air or water is pumped (hence active) through the space to collect the heat. Fans or pumps deliver the heat to the house heat exchanger fan pump2 standby electric heater water tank solar water heater Active Solar Heating pump 1 59 60 10
Flat Plate Collector Solar Collectors heat fluid and the heated fluid heats the space either directly or indirectly Efficiency of Furnace The "combustion efficiency" gives you a snapshot in time of how efficient the heating system is while it is operating continuously The "annual fuel utilization efficiency" (AFUE) tells you how efficient the system is throughout the year, taking into account start-up, cooldown, and other operating losses that occur in real operating conditions. AFUE is a more accurate measure of efficiency and should be used if possible to compare heating systems. 61 62 Efficiencies of Home Heating Tips (Individual) to Save Energy and Environment Annual fuel input for space heat (106 Btu/1000 ft2) 110 100 90 80 70 60 50 40 30 20 U.S. stock 1975-1976 building practice (NAHB) LBL standard (medium infiltration) LBL standard (low infiltration) Brownell Saskatoon Mastin Ivanhoe Pasqua 10 Leger Phelps Balcomb 0 0 2000 4000 6000 8000 10,000 9 7 5 3 1 Saskatchewan house Btu/ft2 per degree day Set your thermostat as low as is comfortable in the winter and as high as is comfortable in the summer. Clean or replace filters on furnaces once a month or as needed. Clean warm-air registers, baseboard heaters, and radiators as needed; make sure they're not blocked by furniture, carpeting, or drapes. Bleed trapped air from hot-water radiators once or twice a season; if in doubt about how to perform this task, call a professional. Place heat-resistant radiator reflectors between exterior walls and the radiators. 1 Btu/ft 2 per degree day Degree days (base 65 F) 63 64 Tips (Individual) to Save Energy and Environment Tips (Individual) to Save Energy and Environment Use kitchen, bath, and other ventilating fans wisely; in just 1 hour, these fans can pull out a houseful of warmed or cooled air. Turn fans off as soon as they have done the job. During the heating season, keep the draperies and shades on your south-facing windows open during the day to allow sunlight to enter your home and closed at night to reduce the chill you may feel from cold windows. During the cooling season, keep the window coverings closed during the day to prevent solar gain. 65 Close an unoccupied room that is isolated from the rest of the house, such as in a corner, and turn down the thermostat or turn off the heating for that room or zone. However, do not turn the heating off if it adversely affects the rest of your system. For example, if you heat your house with a heat pump, do not close the vents closing the vents could harm the heat pump. Select energy-efficient equipment when you buy new heating and cooling equipment. Your contractor should be able to give you energy fact sheets for different types, models, and designs to help you compare energy usage. Look for high Annual Fuel Utilization Efficiency (AFUE) ratings and the Seasonal Energy Efficiency Ratio (SEER). The national minimums are 78% AFUE and 10 SEER. 66 11