Sustainable Energy
2nd Edition
ISBN: 9781337551663
Author: DUNLAP, Richard A.
Publisher: Cengage,
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Chapter 1, Problem 18P
To determine
Find the annual heating cost of the second homeowner.
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Problem 10
A homeowner is trying to decide between a high-efficiency natural gas furnace with an efficiency of 95
percent and a ground-source heat pump with a COP of 3.3. The unit costs of electricity and natural gas are
$0.112/kWh and $1.44/therm (1 therm = 105, 500 kJ). Determine which system will have a lower energy
cost.
Replacing incandescent lights with energy-efficient fluorescent lights can reduce the lighting energy consumption to one-fourth of what it was before. The energy consumed by the lamps is eventually converted to heat, and thus switching to energy-efficient lighting also reduces the cooling load in summer but increases the heating load in winter. Consider a building that is heated by a natural gas furnace with an efficiency of 80 percent and cooled by an air conditioner with a COP of 3.5. If electricity costs $0.12/kWh and natural gas costs $1.40/therm (1 therm = 105,500 kJ), determine if efficient lighting will increase or decrease the total energy cost of the building (a) in summer and (b) in winter.
For a building located in London, England with annual heating degree-days (dd) of 5634, a heating load (heat loss) of 42,000 kj/h, and a design temperature difference of 35° C (20° C indoor), estimate the annual energy consumption. If the building is heated with a furnace with an efficiency of 98%, how much gas is burned to keep the home at 20° C? State yourassumptions.
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- An air-conditioning unit has a cooling capacity of two tons. If the unit has a rated energy efficiency ratio (EER) of 11, how much electrical energy is consumed by the unit in 1 h? If a power company charges 14 cents per kWh usage, how much would it cost to run the air-conditioning unit for a month (31 days), assuming the unit runs 8 h a day? What is the coefficient of performance (COP) for the given air-conditioning unit?arrow_forwardFor a building located in Madrid, Spain with annual heating degree-days (dd) of 4654, a heating load (heat loss) of 30,000 kj/h, and a design temperature difference of 30° C (20° C indoor), estimate the annual energy consumption. If the building is heated with a furnace with an efficiency of 92%, how muchgas is burned to keep the home at 20° C? State your assumptions.arrow_forwardWhen 1 cu ft of natural gas is burned, 1,050 Btu of heat are produced. In oneday, a building uses 761,250 Btu of heat. How many cubic feet of gas areburned?arrow_forward
- 1) Heating the water in a 55-gallon water heater requires about 2.0 x 103 kJ of energy. a) Assume the energy came from natural gas with 80% efficiency; how many grams of natural gas are required? b) Assume the energy came from electricity with 80% efficiency and that the electricity was produced from the combustion of coal with 30% efficiency; how many grams of coal are required? For problem above, calculate how much CO2 in grams is emitted to the atmosphere. For a: Use the balanced equation for the combustion of methane (CH4) to determine how many grams of CO2are produced from the amount of natural gas required. For b: Assume that coal produces 5.25 kJ of energy per gram of CO2 produced. Calculate how much CO2 in grams is produced.arrow_forwardA home is heated with propane with a 100,000 BTU furnace size and 95% efficiency. The monthly heating degree days is 5000. Using the energy estimation discussed in this chapter, estimate the monthly and annual gas consumption to heat the building if the home is to be kept 68°F.arrow_forwardThe Energy Efficiency Rating (EER) of an air-conditioning unit is defined asthe ratio of the heat removed in Btu/hr divided by the energy used in watts. Awindow air conditioner is rated at 5,170 Btu. It uses 470 watts of power. Whatis this unit’s EER?arrow_forward
- The Energy Efficiency Rating (EER) of an air-conditioning unit is defined asthe ratio of the heat removed in Btu/h divided by the energy used in watts.The EEI (Edison Electric Institute) names an air-conditioning unit as anEnergy Star unit if it has an EER of 13 or greater. A 21⁄2-ton air-conditioningunit uses 2.41 kilowatts (2,410 watts) of energy. One ton is equivalent to12,000 Btu/h. Can this unit be termed an Energy Star unit?arrow_forwardConsider a 400-MW, 32 percent efficient coal-fired power plant that uses cooling water withdrawn from a nearby river (with an upstream flow of 10-m3/s and temperature 20 °C) to take care of waste heat. The heat content of the coal is 8,000 Btu/lb, the carbon content is 60% by mass, and the sulfur content is 2% by mass. How much electricity (in kWh/yr) would the plant produce each year? How many pounds per hour of coal would need to be burned at the plant? Estimate the annual carbon emissions from the plant (in metric tons C/year). If the cooling water is only allowed to rise in temperature by 10 °C, what flow rate (in m3/s) from the stream would be required? What would be the river temperature if all the waste heat was transferred to the river water assuming no heat losses during transfer? Estimate the hourly SO2 emissions (in kg/h) from the plant assuming that all the sulfur is oxidized to SO2 during combustion.arrow_forwardWater falls from a height of 500 m and the mass of water is 50 kg. What is approximately the rise in temperature of water at the bottom if the whole energy is used to heat the water? Specific heat of water is 4.18 kJ/kg-deg C. O 5000 deg C O 1173 deg C O 500 deg C O 0.23 deg C O none of the abovearrow_forward
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