Relative humidity and dew point are two different ways to measure moisture in the air, and understanding the difference between relative humidity and dew point are necessary for managing an environment. Relative humidity is a percentage that describe how much water vapor is currently in the air compared to the maximum amount of water vapor that the air can hold at a specific temperature. Because the capacity of air to hold water vapor change when the temperature changes, relative humidity will change even if the actual amount of water vapor stays the same.
For example, if you increase the temperature in a room, the relative humidity will decrease because the warmer air can hold more water vapor. Therefore, relative humidity is a relative measurement than an absolute measurement of moisture. The dew point is the actual temperature at which the air become fully saturated, and the dew point is the temperature at which water vapor must condense into liquid water.
What Are Relative Humidity and Dew Point
While relative humidity fluctuate as the temperature changes throughout the day, the dew point remains a more consistent indicator of the actual amount of moisture in the air. If the temperature of a surface drop below the dew point, water vapor will condense into liquid droplets on that surface. Many people focuses on relative humidity, but the dew point is a more accurate way to determine how much moisture are available for mold, mildew, or condensation to form.
Managing moisture levels is important because different living thing have different requirements for moisture. For many people in a home, low moisture levels can cause dry skin and irritated sinuses, but high moisture levels can cause mold to grow. Livestock managers must also monitor the relationship between temperature and humidity because animals cannot cool themselves through evaporation when the humidity is too high.
When humidity is high, animals cannot effectively use evaporation to regulate their body temperature, and this can lead to heat stress in animals. Plants also require specific moisture levels to grow, and high humidity can cause problem for plant health. Fungal pathogen, such as powdery mildew or botrytis, grow when the humidity is high and the leaves of the plants remain wet.
If the humidity spikes during the night, the moisture can settle on the plants, and this moisture provides the conditions that fungal pathogens need to grow. Thus, maintaining a stable environment is necessary to prevent fungal pathogens from damaging a crop. You can control the moisture in an environment by managing air movement and temperature.
In a greenhouse, you can open vent in the morning to prevent humidity from building up, and you can also manage the temperature of surfaces to prevent condensation. If water is dripping from metal pipe, it is because the metal pipes have cooled below the dew point, and you may need to insulate the metal pipes or raise the temperature of the air to prevent the water from condensing. Additionally, you should consider how you provide water to plants because the method of watering affect the humidity in the air.
Overhead sprinkler add liquid water directly to the leaves, and adding liquid water to the leaves increases the local humidity and the risk of disease. Drip irrigation is an alternative because drip irrigation deliver water to the roots and keeps the air around the leaves drier. Finally, you should monitor the air using tools like a digital hygrometer or a data logger.
A digital hygrometer allow you to track relative humidity, and a data logger allow you to track changes in moisture over time. The goal of monitoring is to find a balance where the air is breathable and the plants is growing without excess moisture settling on the leaves. By monitoring the relationship between temperature and moisture, you can prevent problems before those problem occur.