Space at sea level, is to be maintained at 77 °F db and ϕ=50%. The total air supply to the space is 15,000 lbm/hr and the sensible heat factor SHF= 0.5. Return air is mixed with outdoor air, and the mixture dry bulb temperature is 85 °F. Before the mixing process, the outdoor air, at 115 °F and ϕ=10%, is passed through an Evaporative Cooling Device which reduce the outdoor air temperature to 105 °F, as shown in the figure. The mixture then cooled by a cooling coil and the air is provided to the space by using a fan. The electric power of the fan causes the temperature of the air to be raised by 2 °F, and the air is delivered to the space at 65 °F.
a. Plot the process on the psychrometric chart.
b. What is the mass of water added to the outdoor air in the Evaporative Cooling device?
c. What are the amounts of total heat, sensible heat, and latent heat that are removed by the cooling coil, and what is the coil b-pass factor?
d. What is the cooling coil SHF and what is the surface temperature of the cooling coil (ADP)?
e. Calculate the cost of running the fan of the system. Assume that:
i) The electrical power that is provided to the fan is converted to heat, which causes 2 °F increase of the air temperature through the fan.
ii) The air flow in the system is 15,000 lbm'hr.
iii) The system runs for 5000 hr/year and the cost of energy is $0.05/kw-hr.
f. What is the mass flow rate of outside air? Is it more energy efficient to eliminate the return air and use 100% fresh air? (Explain your answer with numbers and equations.)