Sustainable Energy
2nd Edition
ISBN: 9781337551663
Author: DUNLAP, Richard A.
Publisher: Cengage,
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Chapter 8, Problem 6P
To determine
Find the heat loss in
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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.
A typical ceiling of a house consists of items shown in the accompanying table. Assume an inside room temperature of 21° C and an attic air temperature of −10° C, with an exposed area of 100 m2 . Calculate the heatloss through the ceiling.
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.
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- Consider a house that is approximated as a cube that is 8 m on a side and has no windows. The house loses heat from the four walls and the roof. For an inside temperature of 20°C and an outside temperature of –20°C, it is desired to keep the total heat loss less than 5 kW. What is the minimum RSj value that is required for the walls and roof?arrow_forwardA copper plate, with dimensions of 3 cm x 3 cm × 5 cm (length, width, and thickness, respectively), is exposed to a thermal energy source that puts out 150 J every second, as shown in the accompanying figure. The density of copper is 8900 kg/m³. Assuming no heat loss to the surrounding block, determine the temperature rise in the plate after 10 seconds. 150 J Copper Insulationarrow_forwardYour answer is partially correct. An insulated Thermos contains 110 cm3 of hot coffee at 83.0°C. You put in a 15.0 g ice cube at its melting point to cool the coffee. By how many degrees has your coffee cooled once the ice has melted and equilibrium is reached? Treat the coffee as though it were pure water and neglect energy exchanges with the environment. The specific heat of water is 4186 J/kg-K. The latent heat of fusion is 333 kJ/kg. The density of water is 1.00 g/cm³. Number i 20 Units C°arrow_forward
- Calculate the amount of energy required in BTU to heat the air in a 10°F house 30 by 50 by 40 ft and increase the temperature by 70F at constant pressure.arrow_forwardWe 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.arrow_forwardCalculate 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 .arrow_forward
- A 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_forward2.5 liters of water at initial temperature of 16?C absorbed 800 calories of heat. Calculate the final temperature.arrow_forwardHeat Transfer 1. If you have a piece of extruded polystyrene insulation that has an R-value of 5 hr ft?.°F/Btu per inch [or RSI = 0.8805 (m² · K)/W)]. How many inches of extruded polystyrene do you need in your wall if you want it to have an R-value of 20 hr ft2.°F/Btu [or RSI = 3.522 (m² · K)/W)]? L= 4" 2. What is the transfer of vibrational energy due to collisions between neighbouring atoms and molecules in a solid called? a. Conduction b. Convection c. Radiation d. Latent Heat Radiant Energy 3. Absorptance is a measure of the relative amount of radiant energy absorbed by a surface. Does a shiny and smooth polished aluminum surface have a high absorptance (closer to 1), or a low absortptance (closer to 0)? Absorptance is a ratio of the radiation absorbed to the radiation received, and thus is dimensionless. What about reflectance? Are absorptance and reflectance related? 4. Emissivity is a measure of the relative amount of radiant energy emitted by a surface. Does a shiny and smooth…arrow_forward
- 3. According to Newton's Law of cooling', the rate at which the heat is lost by a heated body is proportional to the difference in temperature between the body and the surrounding medium (when the temperatutre difference is very small). If a thermometer is taken outdoor, where the temperature is 6°C, from a room which temperature is 25C, and the reading drops 15°C in one minute, how long after its removal from the room will the reading be 8°C? after 45 secs what is the thermometer reading?arrow_forwardA glass windowpane in a home is 0.62 cm thick and has dimensions of 1.4 m x 1.9 m. On a certain day, the indoor temperatu 24°C and the outdoor temperature is 0°C. (a) What is the rate at which energy is transferred by heat through the glass? W (b) How much energy is lost through the window in one day, assuming the temperatures inside and outside remain constant?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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