Evaporative Cooler
Saturation Efficiency Index
Audit ambient dry-bulb values against localized wet-bulb depressions to calculate entering matrix moisture drops.
Psychrometric Evaporative Physics, Wet-Bulb Depression, & Saturation Efficiency Laws Overview
Direct evaporative cooling systems (frequently classified as swamp coolers) reject structural heat energy using adiabatic fluid transformations rather than mechanical compressor vapor-compression cycles. When raw, low-humidity outdoor air is forced across a continuously wetted porous pad matrix, the air’s sensible heat energy drives water molecules to shift states from liquid to gaseous vapor. Because this phase change requires absorbing latent energy, the air stream converts its own sensible temperature into latent absolute humidity, forcing the dry-bulb temperature downward along a constant enthalpy line. The maximum theoretical cooling threshold is governed by the wet-bulb temperature, and the total operational boundary is defined as the wet-bulb depression ($T_{\text{dry-bulb}} – T_{\text{wet-bulb}}$). Real-world pad configurations can never hit 100% molecular transformation. Sizing equations rely on pad saturation efficiency metrics, where media density and air stream face velocity dictate the final temperature drop profile.
Frequently Asked Questions
A: Direct evaporative cooling is physically dependent on the air’s ability to absorb extra water vapor. In high-humidity environments, the air is already saturated with moisture, leaving a tight wet-bulb depression gap. Because the air cannot accept substantial water evaporation masses, the sensible cooling temperature drop remains negligible while raising indoor relative humidity to uncomfortable, sticky levels.
A: A direct system evaporates water straight into the primary supply air stream, cooling the air while increasing its moisture content. An indirect system passes outdoor air through secondary wetted channels to chill a metal heat exchanger surface. The primary indoor air is then routed across the dry side of that plate, absorbing sensible cooling benefits via conduction without introducing extra absolute humidity into the building envelope.