Psychrometry: Understanding Air Properties and Processes

A: Miss this low and the coil looks undersized on paper, miss it high and you chase a phantom latent load that doesn't exist. At 30°C, saturation vapor pressure is about 4.2 kPa. Half of that gives roughly 2.1 kPa partial pressure. Using w ≈ 0.622·Pv/(P−Pv) with P near 101 kPa lands just over 0.013. That keeps mass balance and later condensate estimates from drifting.

A: Chasing sensors wastes days while mold keeps growing. High airflow shortens contact time and lifts coil surface temperature, so you get cold air without moisture removal. Low water temperature would help dehumidification, not block it. Bad sensors don't explain why the valve is already pegged.

A: Pick wrong and you'll be writing a corrosion NCR within a year. Chlorides plus condensation attack zinc and aluminum aggressively at seams. Field-applied coatings crack. Molybdenum-bearing stainless holds up when wet salt and oxygen are present.

A: Choose a sensible coil and the SAT looks fine while humidity sails past limits, killing the acceptance test. To hit both dry-bulb and RH without reheat, the air must cross the saturation curve and shed moisture. That means a coil with enough surface to reach a lower ADP.