Sustainable Energy
2nd Edition
ISBN: 9781337551663
Author: DUNLAP, Richard A.
Publisher: Cengage,
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Chapter 8, Problem 17P
To determine
Calculate the outside temperature for which the heat loss through the wall is
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3.
6.0" wide wooden fence posts are embedded in a concrete driveway a distance 12.125" apart. There is
a 1/16" gap between the post and the concrete (see diagram). The posts are installed when the temperature is
12°C. Determine if the gap will close when the temperature increases to 32°C and if not how big the gap will
be at that temperature. The thermal expansion coefficients of wood and concrete are awood =32 x 105 °C and
aconcrete =13 x 106 °C. 1 inch3D2.54 cm.
6.0"
12.0"
0.0625"
Help your customer to calculate the heat losses through a composite wall that includes
an 8-mm-thick hardwood siding, 40-mm by 130-mm hardwood studs with glass fiber
insulation (paper faced, 28 kg/m3 ), and a 12-mm layer of gypsum (vermiculite) wall
board as shown. The wall is 2.5 m high by 6.5 m wide.
- 20 °C
Wood siding
Stud
130 mm
Insulation
Wall board
21 °C
40 mm
Figure 1: The top view of thecomposite wall.
Calculate the thickness of the masonry wall having thermalconductivity of 0.75 W/mK if the heat transfer is to be 80% of theheat transfer through a composite structural wall having athermal conductivity of 0.25 W/mK and a thickness of 100mm.Assume that both walls are subjected to same surfacetemperature.
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- A line measured with a 50-m long steel tape was determined to be 645.22 meter when the average temperature during taping was 15.750C. If the tape is of standard length at 200C and the coefficient of thermal expansion of steel is 0.0000116/10C, the correct length of the measured line isarrow_forwardDetermine the thermal conductivity of brickwork of cavity wall comprising 220mm brickwork, 12mm plaster, 80mm cavity, k values are plaster 0.6W/m°C, cavity resistance 0.18m"C/W, internal resistance 0.12m²"C/W, external resistance 0.06 m"C/W. U value of the wall is 1.78.arrow_forwardThe heat loss, in Btu/hr, for two different types of walls is given. Find in Btu/hrthe difference in the heat losses.arrow_forward
- Solar Slab Storage. A passive solar home has a concrete slab in its main living area, 22' x 28' x 5" thick. On a winter day, the average slab temperature is 64.2F in the morning, and 73.4F in the afternoon when the sun sets. How much heat was absorbed by the slab (in kBtu)?arrow_forwardQuestion 11 Which statement about thermal conductivity is FALSE? O a. The thermal conductivity of timber is greater in the longitudinal compared to the radial direction. O b. Lower density results in lower thermal conductivity. C. Thermal modification of wood reduces its thermal conductivity. Od. Thermal conductivity of air is higher compared to wood.arrow_forward80° -Sheathing 70° Gypsum wallboard 60° Fiberglass between studs Siding 50° Air inside room 40° at 72F Air outside at 0F 30° 20° 10° 0 1 2 3 4 5 6 7 Distance through wall (inches) The temperature changes in the wall - Insulation According to the figure materials is the best insulator? The poorest? Explain. which of the Temperature (°F)arrow_forward
- Question 5 Which statement about electrical conduction in wood is FALSE? O a. Electrical conduction increases very rapidly with increasing wood moisture content. O b. Electrical conduction is generally the same regardless of wood species. O C. Electrical conduction is greatest in the longitudinal direction of wood. Od. Electrical conduction increases with increased wood temperature.arrow_forwardA 5006 cm long by 4 m high wall is made of 25 cm concrete and 20 cm hollow clay tile with plaster of 1.5 cm thickness on its both sides surfaces. The temperature on inside surface is 19°C while the outside temperature is 45°C. What is the rate of heat transfer through the wall of the hall?arrow_forwardA well-mixed, insulated water storage tank is to be maintained at internal temperature 60°C. The environmental temperature around the tank varies from -25°C to 30°C. The tank's exterior surfaces (total = 125 m²) have four different levels of insulation as indicated in the table. Surface Component Area, Effective RSI, 2 m² 2 m². °C/W Surface A 60.0 Surface B 30.0 Surface C 30.0 Surface D 5.0 Say that just one surface can be selected to have its insulation upgraded such that its effective RSI would be doubled. Which should be selected to achieve the greatest reduction in heat loss? 10.0 15.0 4.0 0.5arrow_forward
- Calculate 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_forwardExplane of Heat Treatment.arrow_forwardDo a quick calculation of the thermal conductance (U value) across a cavity wall consisting of:1. Outer skin 220mm brickwork (North facing, exposed aspect) 2. 20mmcavity 3. Inner skin of 10mm plasterboard Compare this with the worked example of an insulated brick veneer wall in the worked example. Show your working.arrow_forward
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