Sustainable Energy
2nd Edition
ISBN: 9781337551663
Author: DUNLAP, Richard A.
Publisher: Cengage,
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Chapter 8, Problem 11P
To determine
Find the heating degree days per year and check the result with Table 8.4
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A 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.
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.
Discuss the systems and equipment available for cooling systems in large buildings.
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- Complete the following sentences (showing your calculation): The R- value for a 50 mm wood fiber insulation board (k= 0.044 W/m.K)= ……….................................................................................................... The U- value for a 120 mm clay roofing tile (k= 0.75 W/m.K)= .................. The light solar gain ratio for a window with the following characteristics (U= 1.11 W/m2.K, SHGC = 86%, VT= 90%)…………………………………………………………. In a room (8*6*3.5) if the total heat losses is 1000 Watt and the percentage of ceiling losses from total was 20% , if we treat just the ceiling such that we reduce her losses by the half what will be the new total losses for the room …………………………………………………….........................................................…..arrow_forwardWhat is passive cooling of buildings? explain various passive cooling technologies with the help diagrams. Which technologies are suitable for UAE climate? Hint: UAE climate is very hot sometimes 45 degrees and 30% humidity.arrow_forwardEstimate the vapor pressure, air pressure, relative humidity, and air density at a height of 1500 m into the atmosphere. The total pressure is 100 kPa, air temperature is 28°C and the dew point temperature is 16°C near the ground, the lapse rate 6°C/km, which is constant for both air temperature and dew point temperature. The gas constant R is 287 J/kg-K and constant with respect to altitude. Relative Humidity at 1500m, in % Round to one (1) decimal placearrow_forward
- 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.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_forwardDuring the midday 2pm, the temperature of the water that is left out on a table is 18° If the temperature of the surrounding is 34°C and the water’s temperature heated up to 26°C at 2:25pm. After how many minutes will the water’s temperature be 32°C?arrow_forward
- 1)When designing forced hot water heating system for a residential building, which of the following mass flow rate values is acceptable for stainless steel pipe's diameter of 40 mm. (Given that water density= 983 kg/m3) Select one: a. 3 kg/s b. 1 kg/s c. 2 kg/s 2)When designing forced hydronic heating system, which of the following pressure drop values is recommended for equivalent length of 60 m : Select one: a. 50 kPa b. 30 kPa c. 20 kPaarrow_forwardResidential annual energy use. For a house with: Air exchange rate of 0.5 h−1 Cp = 1000 J/kg.K Density of air = 1.2 kg/m3 Roof area = 144 m2; opaque wall area = 96 m2; window area = 24 m2; volume = 360 m3 Conductivity of Uwall = 0.60 W/(m2-K); Uwin = 3.0 W/(m2-K); Uroof = 0.40 W/(m2-K) Heating system efficiency of 0.85 Heating degree days (HDD) of 3500 K-days Calculate the Ktot for this house. Calculate the annual energy used to heat this house (in GJ).arrow_forwardIn order to compute the airport reference temperature and the standard temperature with respect to elevation, the monthly mean of average daily temperature and the monthly mean of the maximum daily temperature of the hottest month of the year is found to be 31° C and 42.5° C respectively. The airport reference temperature is:arrow_forward
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