Concept explainers
A typical household pays about $1200 a year on energy bills, and the U.S. Department of Energy estimates that 46 percent of this energy is used for heating and cooling, 15 percent for heating water, 15 percent for refrigerating and freezing, and the remaining 24 percent for lighting, cooking, and running other appliances. The heating and cooling costs of a poorly insulated house can be reduced by up to 30 percent by adding adequate insulation. If the cost of insulation is $200, determine how long it will take for the insulation to pay for itself from the energy it saves.
Want to see the full answer?
Check out a sample textbook solutionChapter 2 Solutions
Thermodynamics: An Engineering Approach
Additional Engineering Textbook Solutions
Heat and Mass Transfer: Fundamentals and Applications
Vector Mechanics for Engineers: Statics and Dynamics
Mechanics of Materials, 7th Edition
Fundamentals Of Thermodynamics
Thinking Like an Engineer: An Active Learning Approach (4th Edition)
Manufacturing Engineering & Technology
- You need an apartment for rent and as shown in the figure, you can see that the 3rd floors of each of the 2, 3 and 4 blocks of the buildings, whose front faces are adjacent, are for rent. You also learn that Block 2 is heated by a coal boiler operating at 75% efficiency, Block 3 is heated by a natural gas boiler operating at 92% efficiency and Block 4 is heated by a heat pump with a COP (coefficient Of Performance) of 4.5. We know that the heating process takes place uninterruptedly for 150 days, during these 150 days, the interior of the apartment remains constant at 22 °C. average outside temperature T∞ = 0 °C and average of wind speed u* = 5 m/s Find the total heating cost for all three blocks. The average heat transfer coefficient in apartment is h inside = 10 W/m2K thermal resistance of the wall Rwall = 1 m2K/W Assume that heat is lost only from the front and back of the blocks. In addition, the electricity unit price of 0.71 $/kWh, natural gas unit price of 0.14 $ / kWh, unit…arrow_forwardA used car salesman is trying to sell you a car by telling you that the cars engine, operating between 25 degrees Celsius and 125 degrees Celsius, has an efficiency of 82%. What is the efficiency of the car?arrow_forwardDescribe the heat and work are energy transfer mechanisms between a system and its surroundings, and there are many similarities between them?arrow_forward
- 1. Is a temperature difference necessary to operate a heat engine? State why or why not. 2. Definitions of efficiency vary depending on how energy is being converted. Compare the definitions of efficiency for the human body and heat engines. How does the definition of efficiency in each relate to the type of energy being converted into doing work? 3. Why-other than the fact that the second law of thermodynamics says reversible engines are the most efficient-should heat engines employing reversible processes be more efficient than those employing irreversible processes? Consider that dissipative mechanisms are one cause of irreversibility. 1. (a) What is the efficiency of a cyclical heat engine in which 75.0 kJ of heat transfer occurs to the environment for every 95.0 kJ of heat transfer into the engine? (b) How much work does it produce for 100 k) of heat transfer into the engine? 2. The engine of a large ship does 2.00×10°J of work with an efficiency of 5.00%. (a) How much heat…arrow_forwardIf a house needs a minimum heat transfer rate of 75 kJ/h (i.e., 75 kJ of heat needs to be transferred into the house during one hour) to maintain a pleasant indoor temperature. If one wants to use a heat pump with a COP of 5.55 to fulfill this heat transfer rate, what is the corresponding electricity (in kWh) consumption to run such a heat pump for one hour?arrow_forwardThe demand for electric power is usually much higher during the day than it is at night, and utility companies often sell power at night at much lower prices to encourage consumers to use the available power generation capacity and to avoid building new expensive power plants that will be used only a short time during peak periods. Utilities are also willing to purchase power produced during the day from private parties at a high price. Suppose a utility company is selling electric power for $0.06/kWh at night and is willing to pay $0.13/kWh for power produced during the day. To take advantage of this opportunity, an entrepreneur is considering building a large reservoir 50 m above the lake level, pumping water from the lake to the reservoir at night using cheap power, and letting the water flow from the reservoir back to the lake during the day, producing power as the pump-motor operates as a turbine-generator during reverse flow. Preliminary analysis shows that a water flow rate of 2…arrow_forward
- The demand for electric power is usually much higher during the day than it is at night, and utility companies often sell power at night at much lower prices to encourage consumers to use the available power generation capacity and to avoid building new expensive power plants that will be used only a short time during peak periods. Utilities are also willing to purchase power produced during the day from private parties at a high price. Suppose a utility company is selling electric power for $0.06/kWh at night and is willing to pay $0.13/kWh for power produced during the day. To take advantage of this opportunity, an entrepreneur is considering building a large reservoir 50 m above the lake level, pumping water from the lake to the reservoir at night using cheap power, and letting the water flow from the reservoir back to the lake during the day, producing power as the pump–motor operates as a turbine–generator during reverse flow. Preliminary analysis shows that a water flow rate of 2…arrow_forward14. A classroom that normally contains 40 people is to be air-conditioned with window air- conditioning units of 5- kW cooling capacity. A person at rest may be assumed to dissipate heat at a rate of about 360 kJ/h. There are 10 light bulbs in the room, each with a rating of 100 W. The rate of heat transfer to the classroom through the walls and the windows is estimated to be 15,000 kJ/h. If the room air is to be maintained at a constant temperature of 21°C, determine the number of window air-conditioning units required.arrow_forwardThe roofs of many homes in the United States are covered with photovoltaic (PV) solar cells that resemble roof tiles, generating electricity quietly from solar energy. An article stated that over its projected 30-year service life, a 4-kW roof PV system in California will reduce the production of CO2 that causes global warming by 433,000 lbm, sulfates that cause acid rain by 2900 lbm, and nitrates that cause smog by 1660 lbm. The article also claims that a PV roof will save 253,000 lbm of coal, 21,000 gallons of oil, and 27 million ft3 of natural gas. Making reasonable assumptions for incident solar radiation, efficiency, and emissions, evaluate these claims and make corrections if necessary.arrow_forward
- By supplying energy to a house at a rate of 25,000 kJ/hr, a heat pump maintains the temperature of the dwelling at 20 C when the outside air is at -10 C. If electricity costs 8 cents per kW-hr, determine the minimum theoretical operating cost to heat the house for 24 hours. $1.97 O $1.37 $1.75 O $1.51 O$1.64arrow_forwardAn electric resistance heater is used to provide space heating at an efficiency level of 100%. The electricity is sold at $0.13 per kWh. Question: How much money is needed if 1137.8 MBH is demanded? Hint: 1 MBH equals 1,000 btuharrow_forwardDuring a one year time period, how many gallons of water would the average household save by using an efficiency washer vs a regular washer? Is this one year savings more or less than the amount of water an average person drinks in a lifetime? Explain and show your assumptions, calculations, and conversions. Consider it to be essentially 2 separate problems: How much water is saved in a one year period when using an efficiency washer vs regular washer - answer based on your assumptions and calculations for full credit How much water does an average person drink in a lifetime – arrive at this answer based on your assumptions and calculations Compare the answers to those 2 questions to arrive at your conclusion Below are 2 pieces of information that you might find helpful there are 128 oz in a gallonthere are 365 days in a year and also 52 weeks in a yeararrow_forward
- Elements Of ElectromagneticsMechanical EngineeringISBN:9780190698614Author:Sadiku, Matthew N. O.Publisher:Oxford University PressMechanics of Materials (10th Edition)Mechanical EngineeringISBN:9780134319650Author:Russell C. HibbelerPublisher:PEARSONThermodynamics: An Engineering ApproachMechanical EngineeringISBN:9781259822674Author:Yunus A. Cengel Dr., Michael A. BolesPublisher:McGraw-Hill Education
- Control Systems EngineeringMechanical EngineeringISBN:9781118170519Author:Norman S. NisePublisher:WILEYMechanics of Materials (MindTap Course List)Mechanical EngineeringISBN:9781337093347Author:Barry J. Goodno, James M. GerePublisher:Cengage LearningEngineering Mechanics: StaticsMechanical EngineeringISBN:9781118807330Author:James L. Meriam, L. G. Kraige, J. N. BoltonPublisher:WILEY