Chapter 5, Problem 5.3DP

1. A small metal building is to be constructed of corrugated steel sheet walls with a total wall surface area of about 300 m². The air conditioner consumes about 1 kW of electricity for every 4 kW of cooling supplied and two wall construction are to be compared on the basis of cooling costs. Assume that electricity costs S0.15/kWh. Determine the electrical energy savings per week of using 260 mm of fiberglass batt insulation to the steel sheet wall (U-0.17 W/m² "C) instead of 159 mm of fiberglass insulation (U-0.31 W/m² °C) assuming an overall temperature difference of 20 °C across the wall.

Calculate the amount of energy required to heat the air in a house 30 by 50 by 40 feet from 10 to 70°F. The density of air is about 0.080 lbs/ft3, and its specific heat at constant pressure is about 0.24 BTU/lb-°F. COMPLETE FBD SOLUTION AND REQUIREMENTS  PS. THIS IS A HEAT TRANSFER PROBLEM

Envision a solar water heater, a device which receives energy from the sun (solar radiation or thermal energy) and is used to heat water. The system is installed on the roof of a building where is receives energy from the sun at a rate of 500 Watts for every 1 m² of surface area. About 35% of the incoming thermal energy is lost to the surrounding environment. The remaining energy is absorbed by the liquid water and the temperature changes from 30 °C to 60 °C. Assuming the system is operating at steady state, find the amount of water (m) that this device can supply at 60 °C if the total surface area of the device is 3 m². Ignore any changes in kinetic energy, potential energy, or change in pressure that might occur in the system.