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measuring dry-bulb temperature in a ventilated weather shield
We often get asked what the difference is between the wet-bulb temperature and the dry-bulb temperature. And which temperature sensor does the frost alarm of a WolkyTolky work on?
What is the dry-bulb temperature?
The dry-bulb temperature is the normal air temperature. To make a clear distinction, though, this temperature is often called the dry-bulb temperature when it is used alongside a wet-bulb temperature.
At WolkyTolky we measure this temperature in a ventilated weather shield. That shields your sensor from direct sunlight. Because fresh air can flow through the shield, you measure the actual air temperature (the dry-bulb temperature).
What is the wet-bulb temperature?
The wet-bulb temperature is the lowest possible temperature the air can have if you let water evaporate into it until the air is saturated (100% relative humidity).
If the air is dry, more water can evaporate and the wet-bulb temperature will be lower. The bigger the difference between the dry-bulb temperature (or the ordinary temperature) and the wet-bulb temperature, the drier the air and the more water can evaporate.
How do we measure the wet-bulb temperature?
We measure the wet-bulb temperature with a thermometer that has a wet sock around the sensor. Heat is needed to evaporate the water from the sock. This heat is drawn from the sensor, which cools it down. The thermometer with the wet bulb then shows a lower temperature than the thermometer with the dry bulb.
measuring wet-bulb temperature
Why does the wet-bulb temperature matter in fruit growing?
A similar process takes place in the crop. Heat is drawn out of the crop, which means it can start to freeze before the air temperature (dry-bulb temperature) drops below zero.
In situations with high humidity, you can compare the wet-bulb temperature with the temperature of the flower bud, where evaporation also takes place. In humid air, air temperature, wet-bulb temperature and crop temperature are close together.
However, when the humidity is low, heat loss to the dry air is large, so the crop temperature can end up even lower than the (already lower) wet-bulb temperature.
That is why we always put the frost alarm on a wet-bulb temperature sensor, so a grower can be warned as early as possible. Of course, a grower can set at which wet-bulb temperature they want to get an alarm. Up to 5 phone numbers can then be called so action can be taken quickly.
Are you also interested in a frost alarm based on wet-bulb temperature? Then take a look at our products and request a no-obligation quote.
