An open office room holds 50 employees, each dissipating 430 kJ of energy as heat per hour. In addition, twenty 80 W light bulbs are all left on at all times. Calculate how many 6 kW air-conditioning units are required to keep the office room at a constant temperature of 22°C, if:
a. The walls and windows are adiabatic;
b. The rate of energy transfer as heat into the office room through the walls and windows is 18 000 kJ/hr.