Wet Bulb Dry Bulb Formula

The wet bulb temperature wbt is the temperature read by a thermometer covered in water soaked cloth wet bulb thermometer over which air is passed.

Wet bulb dry bulb formula.

By definition wet bulb temperature is the lowest temperature a portion of air can acquire by evaporative cooling only. Determine the wet bulb and dewpoint temperature the given temperature is 40 deg c relative humidity is 50 and then actual station pressure is 3 millibars. The dry bulb temperature is the ambient temperature. I can get hourly weather data that includes wet bulb temperature but i ll have to pay for it.

The conversion between wet bulb and dry bulb temperatures is surprisingly non trivial. When the psychrometer is swung around by its attached chain or handle the air causes the water on the wick to evaporate which. Given t 40 c rh 50 p sta 3 hpa. It includes a dry bulb thermometer a wet bulb thermometer and a psychrometric chart a graph that plots the relationships between the dry and wet bulb temperature relative humidity and dew point at constant pressure.

Relative humidity is measured using a device called a sling psychrometer this consists of 2 side by side conventional thermometers one of which the wet bulb thermometer has a wetted wick placed at the bottom the other the dry bulb thermometer has no wetted wick. It is therefore measured by wrapping a wet wick around the bulb of a thermometer and the measured temperature corresponds to the wet bulb temperature. At 100 relative humidity the wet bulb temperature is equal to the air temperature dry bulb temperature. The knowledge of only two of these values is enough to determine the state of the moist air including the content of water vapor and the sensible and latent energy enthalpy in the air.

If you re looking to calculate wet bulb temperature for many states basic excel is not going to be the best option. Wet bulb temperature is the lowest temperature to which air can be cooled by the evaporation of water into the air at a constant pressure. However dewpoint and wet bulb are not the same thing. At lower humidity the wet bulb temperature is lower than dry bulb temperature because of evaporative cooling.

For example at 70 degrees f dry bulb and 50 relative humidity the dewpoint is about 51 degrees f and the wet bulb is about 58 5 degrees f. You re really going to want an actual programming language for that. That is from a psychrometric chart for sea level. I assume you know the basic psychronetry.

My notation differs slightly from ashrae s to convert between the two you need. The dry bulb wet bulb and dew point temperatures are important to determine the state of humid air. 1 to find t d. Full details can be found in chapter 6 of the ashrae fundamentals handbook.

Dry bulb and wet bulb temperature. Notice that i stressed on double checking the results wit.