PROBLEM $2.(20$ POINTS$)$

An air conditioning system operating on the winter heating cycle, is required to maintain inside

conditions of $68F$ dry bulb, $48\mathrm{.}5F$ dew point, when the heating load is $250,000Bt\frac{u}{h}r($all

sensible$).$

The system airflow is $7250$ CFM $(f\frac{t^3}{m}in),$ of which $2400$ CFM is brought from outside for

ventilation. Outside conditions are $30F$ dry bulb, $60\%$ relative humidity. The heating and

humidification system consists of a preheater, a spray cabinet and a main heater. The main

heater is rated at $360,000Bt\frac{u}{h}r.$

a$.$ Make a diagram of the system; identify each characteristic point on the diagram, and

show for each significant point its dry bulb temperature and relative humidity.

b$.$ Draw the operating cycle on the psychrometric chart provided.

c$.$ Calculate the Btu$/$hr rating of the preheater.

d$.$ Calculate the adiabatic efficiency of the spray cabinet, and the quantity of make$-$up water

required in the operation of the spray cabinet.