Question

facilities services use a “cooling with dehumidification” system campus-wide. The system is designed to have two stages where in the first stage, the moist air is cooled down while the condensate is exctracted to dehumidify the mixture. Then, in the second stage, the saturated moist air is heated up using heating coils that utilize steam. Assume that the operating pressure is uniform at 1 atm. On a typical hot and humid summer day, air enters the air-conditioning system at 30◦ C with 90% relative humidity and is supplied to the air-conditioned spaces at 18◦ C and 60% relative humidity:

(a) Clearly mark the inlet and exit states of this air-conditioning process on a standard psychrometric chart (use Figure A-31 from your textbook). Also, show on this chart the complete air-conditioning process in between the inlet and exit states.

(b) Calculate the amount of condensed water that will be extracted from the moist air per unit mass of the dry air (in kg H2O/kg of dry air) inside the dehumidifier?

(c) Assume that moist air enters this system at a volumetric flow rate of 100 m3/min. Determine the mass flow rate of dry air (in kg/s) throughout the system.

(d) Determine the rate of heat removed from moist air in the cooling/dehumidifier section (in kJ/s or kW)

(e) Determine the rate of heat added to moist air in the heating section (in kJ/s or kW)

(f) Assume the steam system that is used for heating the moist air stops working due to a malfunction. Determine the temperature of the saturated moist air that will be supplied to conditioned spaces (in ◦ C)

(g) Technicians work on restoring the steam power for the heating section but the system is at 50% operational conditions. Determine the temperature (in ◦ C) and the relative humidity of the moist air that will be supplied to the conditioned spaces.

Answer 1