Wet-Bulb Temperature
Wet-bulb temperature is the lowest temperature air can reach through the cooling effect of evaporating water. It combines heat and humidity into one reading, measured with a thermometer whose bulb is wrapped in a wet cloth while air moves across it. In dry desert air like Southern Nevada's, moisture evaporates quickly, so the wet-bulb reading sits well below the actual (dry-bulb) air temperature. In humid air the two readings move closer together, because the air cannot hold much more moisture.
💡 Key Takeaways
- ✓Wet-bulb temperature is the lowest temperature air can reach through the cooling effect of evaporating water. It combines heat and humidity into one reading, measured with a thermometer whose bulb is wrapped in a wet cloth while air moves across it. In dry desert air like Southern Nevada's, moisture evaporates quickly, so the wet-bulb reading sits well below the actual (dry-bulb) air temperature. In humid air the two readings move closer together, because the air cannot hold much more moisture.
- ✓Wet-bulb temperature is always equal to or lower than the regular (dry-bulb) air temperature.
- ✓The drier the air, the bigger the gap between the wet-bulb and dry-bulb readings.
- ✓HVAC pros use wet-bulb data to calculate your home's true cooling load and size equipment correctly.
Wet-Bulb Temperature
/wɛt bʌlb ˈtɛm.pər.ə.tʃər/
Definition
Wet-bulb temperature is the lowest temperature air can reach through the cooling effect of evaporating water. It combines heat and humidity into one reading, measured with a thermometer whose bulb is wrapped in a wet cloth while air moves across it. In dry desert air like Southern Nevada's, moisture evaporates quickly, so the wet-bulb reading sits well below the actual (dry-bulb) air temperature. In humid air the two readings move closer together, because the air cannot hold much more moisture.
What is wet-bulb temperature?
Wet-bulb temperature is the lowest temperature air can reach by evaporating water into it, combining heat and humidity in one reading. It is measured with a wet-wrapped thermometer, and in dry desert air it runs well below the actual air temperature.
Source: The Cooling Company
Quick Facts
Real-World Application
In a Las Vegas home, wet-bulb temperature explains why an evaporative (swamp) cooler can chill the air on a dry day: low humidity means a low wet-bulb reading and strong evaporative cooling. It also feeds the load calculation a pro uses to size your central air conditioner correctly for our climate.
Pro Tip
Before leaning on a swamp cooler during a muggy monsoon afternoon, check the humidity. When the wet-bulb temperature climbs, evaporative cooling loses its punch and your central AC has to carry the real load.
“Before leaning on a swamp cooler during a muggy monsoon afternoon, check the humidity. When the wet-bulb temperature climbs, evaporative cooling loses its punch and your central AC has to carry the real load.”
Important Things to Keep in Mind
- Wet-bulb temperature is always equal to or lower than the regular (dry-bulb) air temperature.
- The drier the air, the bigger the gap between the wet-bulb and dry-bulb readings.
- HVAC pros use wet-bulb data to calculate your home's true cooling load and size equipment correctly.
Did You Know?
In Southern Nevada's dry summer air, the wet-bulb temperature can sit 30 or more degrees below the actual air temperature, which is exactly why evaporative coolers thrive in the desert.
FAQ
What is the difference between wet-bulb and dry-bulb temperature?
Dry-bulb is the plain air temperature a normal thermometer reads. Wet-bulb factors in humidity by measuring how much cooling evaporation adds. In dry air, the wet-bulb reading is much lower than the dry-bulb.
Why does wet-bulb temperature matter for evaporative coolers?
Evaporative (swamp) coolers cool by evaporating water, and their practical limit is the wet-bulb temperature. Las Vegas's low humidity keeps wet-bulb low, so swamp coolers cool effectively on typical dry days.
Does wet-bulb temperature affect my air conditioner?
Yes. Contractors use wet-bulb readings in load calculations to size your AC and gauge how hard it must work. Higher humidity raises the wet-bulb value and the latent load your system has to remove.
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