Sustainable Energy
2nd Edition
ISBN: 9781337551663
Author: DUNLAP, Richard A.
Publisher: Cengage,
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A typical exterior masonry wall of a house, as shown in the accompanying, consists of the items in the accompanying table. Assume an inside room temperature of 20º C and an outside air temperature of −12º C, with an exposed area of 15 m2 . Calculate the heat loss through the wall.
A 50-L electrical radiator containing heating oil is placed in a 50-m³ room. Both the room and the oil in the
radiator are initially at 5°C. The radiator with a rating of 3 kW is now turned on. At the same time, heat
is lost from the room at an average rate of 0.3 kJ/s. After some time, the average temperature is measured
to be 20°C for the air in the room, and 60°C for the oil in the radiator. Taking the density and the specific
heat of the oil to be 950kg/m³ and 2.2kJ/(kg °C), respectively, determine how long the heater is kept on.
Assume the room is well-sealed so that there are no air leaks.
Calculate the heat loss from a double-pane glass window consisting of two pieces of glass, each having a thickness of 10 mm with a thermal conductivity of k = 1.3 W/m.K . The two glass panes are separated by an air gap of 7 mm. Assume thermal conductivity of air to be k = 0.022 W/m.K .
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- A 100 W incandescent lamp (2725 lm) illuminates a 120 ft2 (11.15 m2 ) surface. Determine the average illuminance of the surface in foot candle and lux. (With explanation)arrow_forwardAssume an inside room temperature of 70°F and an attic air temperature of 15°F, with an exposed area of 885 ft2. Calculate the heat loss (in Btu/h) through the ceiling if the R-19 insulation batt is replaced by R-35 fiberglass insulation.arrow_forwardCalculate the amount of radiation emitted for a unit surface (1 m2) for the following situations: (a) a hot pavement in Arizona at 50 °C (122 °F) and 0.8, (b) a hood of a car at 40 °C (104 °F) and 0.9, and (c) a sunbather at 38 °C (100 °F) and 0.9. Express your answers in both SI and U.S. Customary units.arrow_forward
- A typical ceiling of a house consists of items shown in the accompanying table. Assume an inside room temperature of 70F and an attic air temperature of 15F, with an exposed area of 1000 ft2. Calculate the heat loss through the ceiling.arrow_forwardWhen the temperature was 3 deg. C, the distance from E to F was measured using a steel tape that has a standard length of 100m at 20 deg. C with a coefficient of thermal expansion of 0.0000116 / deg. C. If the correct distance from E to F is 836.5 m, what is the measured distance in meters?arrow_forwardProblem 8 Water enters the tubes of a cold plate at 65°C with an average velocity of 50 ft/min and leaves at 110°F. The diameter of the tubes is 0.2 in. Assuming 20 percent of the heat generated is dissipated from the components to the surroundings by convection and radiation, and the remaining 80 percent is removed by the cooling water, determine the amount of heat generated by the electronic devices mounted on the cold plate.arrow_forward
- A room 3.6m x 5m x 8m fully replaces inside air after 3 hours. If the temperature from the outside is 80 F and temperature inside is 60F. Determine the ventilation heat load in Watts. subject Engineering utilities 2arrow_forwardA double-pane glass window consists of two pieces of glass, each having athickness of 8 mm, with a thermal conductivity of k = 1.4 W⁄m ⋅ K . The twoglass panes are separated by an air gap of 10 mm, as shown in Figure 11.10 .Assuming the thermal conductivity of air to be k = 0.025 W⁄m ⋅ K , determinethe total R-value for this window. The total thermal resistance of the window is obtained by adding the resistance offered by each pane of glass and the air gap in the following manner:arrow_forward100°? air flows through a round aluminum tube of ID 60mm and OD 80mm at 4 ?? .The tube is covered in 5mm thick fiberglass insulation. The tube is surrounded by RT air flowing at 5?? over the outside of the insulation. What is the heat rate through the wall of the tube? Assume that the air temperature is constant throughout the tube. Note: RT is 25 celsiusarrow_forward
- Convert: Convert a (15.5 °C+ 17) temperature into °F temperature.arrow_forwardCalculate the decrease in heat loss in kilowatt-hours per day when a 1.2 m x 2.1 m uncoated single-pane window is replaced with a double-glazed window with a low-e coating and argon fill (a relatively common configuration for current win- dows). The inside temperature is a constant 20°C, and the outside temperature is a constant -5°C.arrow_forwardA 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 lightbulbs in the room, each1 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_forward
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