The core idea
Every cooling job splits into two kinds of heat. Sensible heat changes a substance's temperature — you can feel it on a thermometer: Q = m · cp · ΔT, with m the mass, cp the specific heat (≈ 1.0 kJ/kg·K for air, 4.19 for water), ΔT the temperature change. Latent heat hides inside a phase change: energy absorbed while evaporating or released while condensing, with no temperature change at all. For water near room temperature, h_fg ≈ 2 450 kJ/kg — evaporating one kilogram of water absorbs roughly as much heat as it would take to warm that kilogram of liquid from freezing to boiling.
Air is rarely dry, so "cooling a room" is really two jobs: drop the dry-bulb temperature (sensible) and wring out water vapour (latent). When a cooling coil runs below the room's dew point, moisture condenses on it — the water dripping out of the drain is the latent bill being paid. The split between the two is the sensible heat ratio (SHR): SHR 0.75 means three quarters of the capacity goes to temperature, one quarter to dehumidification.
Real-world example
Phoenix and Houston can both sit at 32 °C dry-bulb, but the wet-bulb — the temperature a wet wick settles at as water evaporates off it — tells them apart: roughly 16 °C in the desert, 26 °C on the Gulf coast. Evaporative ("swamp") coolers exploit the huge h_fg directly: they evaporate water into the airstream and drive its temperature down toward the wet-bulb, using a fraction of a compressor's power — brilliant in Phoenix, nearly useless in Houston, because air near saturation cannot accept more vapour. Meanwhile Houston's air conditioner devotes a large share of its capacity to condensing moisture. That is why "32 °C and humid" feels heavier than "32 °C and dry", and why two homes with identical thermostat settings can draw very different power. Cooling towers at power plants and data centres play the same trick in reverse at industrial scale: evaporating a few kilograms of water per second rejects many megawatts.
Common pitfall
Judging or sizing an air conditioner by temperature drop alone. A unit pulling air down 11 K in humid weather may be spending half its capacity on latent heat — its sensible delivery is modest — while the same ΔT in dry air is nearly all sensible. Matching a unit to a building on total capacity without checking its SHR leaves humid-climate rooms cold but clammy. The related trap is oversizing: a unit that cools too fast short-cycles and shuts off before it has dehumidified, leaving a room cold and damp at once.