Two important definitions for any HVAC technician to understand are the wet bulb temperature and the dry bulb temperature. These temperatures are measured differently, and knowing which temperature a person is referring to will help you understand how comfortable the temperature will feel, something that’s important in HVAC jobs.
Humidity and Temperature
Humidity is the amount of moisture (water vapor) present in the air. The level of humidity makes a big difference in how we perceive temperature. If you’ve done some traveling, you may have noticed that the “same” temperature can feel fairly pleasant in one place but unbearably exhausting in another.
Humid conditions mean there’s a lot of moisture in the air. That makes the air feel “thick” and makes the temperature feel higher than it is. One way our bodies cope with high temperatures is to sweat. When the sweat evaporates from our skin, it takes heat with it, helping us cool down. This is known as evaporative cooling. However, water can only evaporate if the air around it can absorb it. If there’s already a lot of moisture in the air, evaporative cooling is less effective. This is why high temperatures accompanied by high humidity feel more oppressively hot than “dry heat.”
What is the Dry Bulb Temperature (DBT)?
Dry bulb temperatures are measured using a standard thermometer. Most of the time, when people talk about the temperature in casual conversation, or you see a weather forecast that says what the predicted high temperature is, what’s being discussed is dry bulb temperature.
Dry bulb temperature is a measure of the temperature of the surrounding air, without taking into account any factors that might affect how that temperature feels. This is a useful measure, since it shows the true ambient temperature. However, one thing you’ll learn in HVAC training is that the ambient temperature alone doesn’t tell the whole story.
What is the Wet Bulb Temperature (WBT)?
Wet bulb temperature is a measure which accounts for humidity. The wet bulb temperature is measured using a psychrometer. This is a device which has two thermometers, with the bulb on one being wrapped in moistened cloth – hence the name “wet bulb.”
In dry, low-humidity conditions, the moisture on the cloth will evaporate quicker. In high humidity, the moisture on the cloth won’t evaporate as easily, making the temperature feel higher. If relative humidity is 100% (meaning that the air already contains all the moisture it possibly can under current conditions), then no evaporative cooling can take place, and wet bulb and dry bulb temperature would be identical.
This measurement is used to determine the lowest temperature achievable by evaporative cooling. Since wet bulb temperature takes humidity into account, it gives a better idea of the true level of impact the ambient temperature will have on humans.
Understanding weather trends, humidity, and the difference between wet and dry bulb temperatures is vital when planning HVAC installations.
Ambient Temperatures and HVAC Jobs
HVAC technicians are trained to consider both wet and dry bulb temperatures when assessing home comfort. The dry bulb temperature is useful for weather trends, while the wet bulb temperature will offer insight into how easily people can cope with that temperature. The HVAC training at ETI Campus covers different types of HVAC systems and other home comfort systems, helping would-be HVAC technicians better serve their clients.
Prepare for HVAC jobs with the in-depth HVAC training program we offer at ETI campus. We provide hands-on training to prepare you for work in the industry and offer practical advice to help graduates enter employment. Explore our HVAC/R program or contact us for more information.
Key Takeaways
What is the difference between dry bulb and wet bulb temperature?
Dry bulb temperature measures the actual air temperature, while wet bulb temperature accounts for humidity and shows how hot it really feels to the human body.
Why are wet and dry bulb temperatures important in HVAC?
HVAC technicians use both measurements to assess comfort levels and design systems that properly manage temperature and humidity in indoor environments.
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