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Heating and Cooling of Buildings Principles and Practice of Energy Efficient Design

214 SOLVED PROBLEMS

Question: 24.2

Use of the Solar Load Ratio Method Find the auxiliary heating energy for the building of Figure 24.7 in Denver, Colorado, in January. Given: Ti = 68°F (20°C) Qgain = 4200 Btu/h (1231 W) Sunspace design type D1 (12 in. [0.3 m] masonry wall between sunspace and conditioned space) Sunspace being ...

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The projected area is A_{proj} = 550  ft^{2...
Question: 17.2

Rotational Speed for Centrifugal Chillers What is the diameter of a centrifugal compressor rotor needed to isentropically compress R-22 from a saturated suction temperature of 5°C (41°F) to a condensing temperature of 50°C (122°F) and a pressure of 1.94 MPa (145 psia)? The compressor rotates at ...

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Equation 17.8 is used to find the tangential veloc...
Question: 17.1

Vapor Compressor Analysis A compressor using R-22 operates between an inlet condition of 90.8 psia (626 kPa) and a discharge pressure of 290 psia (2000 kPa). Refrigerant enters the compressor as saturated vapor. The polytropic exponent for the actual process is 1.2. Find the isentropic compressor ...

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The actual work input is found from Equation 17.1:...
Question: 13.14

Cooling of Moist Air Outdoor air at sea level enters an air conditioner’s cooling coil at 2000 ft³/min (944 L/s). The inlet dry-bulb condition is 100°F (38°C) and the wetbulb condition is 75°F (24°C). The air is cooled to a dry-bulb temperature of 55°F (13°C) and 90% RH. Assume that the liquid ...

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(a) First, we will find the mass flow rate: [latex...
Question: 13.13

Latent and Sensible Cooling Process on Psychrometric Chart Consider an ideal process where moist air is cooled from 40°C (104°F) and 30% RH to 15°C (50°F). Does moisture condense? What are the values of the RH and the humidity ratio at the process endpoint? Given: Tdb1 = 40°C, ϕ1 = 0.30, and Tdb2 = ...

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The inlet conditions are identical to those in Exa...
Question: 13.11

Adiabatic Saturation Process on Psychrometric Chart If an adiabatic saturator (an idealization of an evaporative cooler) operates at 1 atm with an inlet dry-bulb temperature of 82°F (28°C) and an exit dry-bulb temperature of 65°F (18.5°C), what are the entering humidity ratio and RH? Given: Tdb1 ...

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As indicated in Figure 13.12, this process is a co...
Question: 12.10

Natural Convective Flow Inside an Air Space Consider double-glazed window plates with spacing of 12.7 mm and height of 0.6 m kept at temperatures of 17°C and 0°C. Calculate the natural convective heat transfer coefcient. Given: Spacing L = 0.0127 m, height H = 0.60 m Find: hcon using Equation ...

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First, the Rayleigh number is determined from Equa...
Question: 12.9

Forced Airflow on Roof of Building† Consider a 10 m × 6 m at roof of a building at sea level over which wind blows at 10 m/s. The air temperature is 20°C while the temperature of the roof is 67°C. Calculate the convective heat transfer coefficient when the wind blows along the 10 m long side. ...

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First, the Reynolds number is determined from Equa...
Question: 14.3

Lithium Bromide Absorption Cycle A lithium bromide chiller operates between a condensing temperature of 104°F (40°C) and an evaporator temperature of 50°F (10°C). Heat is added to the generator at 212°F (100°C) and removed from the absorber at 86°F (30°C). If the pump flow rate is 4800 lbm/h (0.605 ...

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The solution consists of, first, finding thermodyn...
Question: 12.7

First Law of Thermodynamics: Closed System A closed tank of refrigerant R22 has a volume of 700 ft³ and is filled with 2800 lbm of a wet mixture of R22 at an initial pressure of 136.19 psia. The tank is moved outdoors and absorbs sufficient solar heat to cause saturated vapor alone to exist within ...

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The initial (and final) specic volume is v ...
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