On a hot summer day, the flat roof of a tall building reaches 50° C in temperature. The area of the roof is 400m2. Estimate the heat radiated from this roof to the sky in the evening when the temperature of the surrounding air or sky is at 20° C. The temperature of the roof decreases as it cools down. Estimate the rate of energy radiated from the roof, assuming roof temperatures of 50, 40, 30, and 25° C. Assume ε = 0 9 . for the roof.

On a hot summer day, the flat roof of a tall building reaches 50° C in temperature. The area of the roof is 400m2. Estimate the heat radiated from this roof to the sky in the evening when the temperature of the surrounding air or sky is at 20° C. The temperature of the roof decreases as it cools down. Estimate the rate of energy radiated from the roof, assuming roof temperatures of 50, 40, 30, and 25° C. Assume ε = 0 9 . for the roof.

Sustainable Energy

2nd Edition

ISBN:9781337551663

Author:DUNLAP, Richard A.

Publisher:DUNLAP, Richard A.

Chapter8: Direct Use Of Solar Energy

Section: Chapter Questions

Problem 9P

See similar textbooks

Similar questions

A wooden shelter has walls constructed of wooden planks 1.00 cm thick. If the exterior temperature is -20.0°C and the interior is 5.00°C, find the rate of energy loss through a wall that has dimensions 1.95 m by 2.30 m.
A heat pump supplies heat energy to a house at the rate of 140,000 kJ/h when the house is maintained at 25°C. Over a period of one month, the heat pump operates for 100 hours to transfer energy from a heat source outside the house to inside the house. Consider a heat pump receiving heat from two different outside energy sources. In one application the heat pump receives heat from the outside air at 0°C. In a second application the heat pump receives heat from a lake having a water temperature of 10°C. If electricity costs $0.105/kWh, determine the maximum money saved by using the lake water rather than the outside air as the outside energy source.
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 .
A 75 gal. electric hot water heater provides 9000 Watts of power to heat water. If the heater is filled with water at an initial temperature of 50ºF, how long will it take for the water to reach 140ºF? Assume that there are no heat losses.
Solve the heat equation ut=cuxx on the domaion 0≤x≤2, t>0 subject to u(x,0)=x(x−2), u(0,t)=0,u(2,t)=0
The heat exchanger radiates thermal energy at the rate of 2500 kJ/h for each square meter of its surface area. Determine how many joules (J) are radiated within a 5-hour period.
at 38 degrees celsius and 218 kpa gage, the specific weight of a certain gas was 15.0 n/m^3. determine the gas constant of this gas in j/(kg-kelvin).
Suppose the pump of Fig. is situated between two water tanks with their free surfaces open to the atmosphere. Which free surface is at a higher elevation—the one corresponding to the tank supplying water to the pump inlet, or the one corresponding to the tank connected to the pump outlet? Justify your answer through use of the energy equation between the two free surfaces.
The air inside a hot-air balloon is heated to 72.00 °C (Tinitial) and then cools to 52.00 °C (Tfinal). By what percentage does the volume of the balloon change?
A steel bridge span is normally 300m long. What is the difference in length, in cm between January (-35 degree C) and August (40 degree C)? Assume coefficient of thermal expansion for steel as 11.7* 10^-6/degree.
For 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.
We have exposed 1 kg of water, 1 kg of brick, and 1 kg of concrete each to a heat source that puts out 100 J every second. Assuming that all of the supplied energy goes to each material and they were all initially at the same temperature, which one of these materials will have a greater temperature rise after 10 s? We can answer this question using Equation as shown . We will first look up the values of the specific heat for water, brick, and concrete, which are cwater = 4180 J⁄kg K, cbrick = 960 J⁄kg K and cconcrete = 880 J⁄kg K . Now applying as shown , Ethermal = mc(Tfinal Tinitial) to each situation, it should be clear that although each material has the same amount of mass and is exposed to the same amount of thermal energy, the concrete will experience a higher temperature rise because it has the lowest heat capacity value among the three given materials.