Question

Space air at 20°C DBT and 50% RH is mixed with outdoor air at 45 °C DBT and 28 °C WBT in the ratio of 4:1. The mixture is passed through a cooling coil whose temperature is maintained at 8 °C and whose bypass factor is 0.25. Find the following: (a) Condition of air entering the coil.

Answer 1

The condition of air entering the coil is approximately 28.4°C dry-bulb temperature and 16.8°C wet-bulb temperature.

The condition of the air entering the cooling coil is determined by calculating the weighted average of the two air streams based on the given mixing ratio. The space air, with a dry-bulb temperature of 20°C and a relative humidity of 50%, is mixed with outdoor air having a dry-bulb temperature of 45°C and a wet-bulb temperature of 28°C in a 4:1 ratio.

To find the weighted average conditions, the contributions of each air stream are multiplied by their respective mixing ratios and then summed. This calculation yields an entering condition for the air entering the cooling coil. In this case, the calculated dry-bulb temperature is approximately 28.4°C, and the wet-bulb temperature is approximately 16.8°C. This represents the composite condition of the air mixture entering the cooling coil for further processing.