Chapter 3, Problem 3.42P

Consider a space heating system designed as shown in Fig. 3-21. The total space heating load is 500,000 Btufhr (145 kW), and the space design conditions are 70 F (21 C) and 30 percent relative humidity (RH). Outdoor air enters the preheat coil at 6 F $\text{(-14 C)}$ and essentially 0 percent RH where it is heated to 60 F (16 C) and mixed with return air. The mixture is first heated and then humidified in a separate process to 105 F (40 C) and 30 percent (RH) for supply to the space. Saturated vapor at 2.0 psig is used for humidification. Twenty-five percent of the supply air is outdoor air by mass. Sketch the psychrometric processes, and compute the supply air volume flow rate, the heat transfer rates in both coils, and the steam flow rate in (a) English units and (b) SI units.I