How to Calculate the VPD of Air?
To calculate the VPD of air, you need to know two things: the air temperature (°C or °F) and relative humidity (%). Then, you can use either the dew point calculation method or the wet bulb temperature calculation method.
For the dew point calculation method:
1. Calculate the dew point temperature (°C or °F) using a dew point calculator or formula.
2. Subtract the dew point temperature from the air temperature to find the VPD.
For the wet bulb temperature calculation method:
1. Measure the air temperature and relative humidity.
2. Use a psychrometric chart or calculator to find the corresponding wet bulb temperature.
3. Subtract the wet bulb temperature from the air temperature to find the VPD.
How to Calculate the VPD of Leaves?
To calculate the VPD of leaves, you need the following values:
1. Leaf temperature (Tleaf)
2. Air temperature (Tair)
3. Relative humidity (RH)
Once you have these values, you can use the following formula to calculate the VPD of leaves:
VPD = eair-eleaf
eair = saturation vapor pressure at air temperature (Tair)
eleaf = saturation vapor pressure at leaf temperature (Tleaf).
The saturation vapor pressure can be calculated using the Antoine equation.
If you find the calculations difficult, we have also provided links to the calculators. So if you need it, please click on it and try it out!
Utilization of VPD
VPD Detection Equipment
VPD detection equipment includes:
1. Hygrometers and thermometers to measure temperature and relative humidity.
2. Data loggers and sensors to continuously monitor and record VPD.
3. Portable VPD meters to measure VPD in the field.
4. Computer programs to calculate VPD using temperature, relative humidity, and pressure readings.
1. Decagon 5TM, EC5 Portable VPD Meter
2. DeltaT Devises VPD2 Evaporation and Transpiration Sensor
3. Rotronic HygroLog HLNT Data Logger with VPD Calculation
4. Extech RHT3 Hygro Thermometer with VPD Calculation.
How Growers Can Influence and Change VPD
Growers can influence and change VPD in several ways:
Way 1: Control the temperature
By controlling the temperature, growers can change the vapor pressure in the grow room. In addition, they can use HVAC equipment to keep the temperature within a desirable range.
Way 2: Control the humidity
By controlling the humidity, growers can change the vapor pressure in the grow room. They can use dehumidifiers to reduce humidity and humidifiers to increase humidity.
Way 3: Adjust the air flow
By adjusting the air flow, growers can help distribute moisture evenly throughout the grow room and prevent it from collecting on the leaves.
Way 4: Control the light
By controlling the amount and duration of light, growers can influence the transpiration rate of the plants, which affects VPD.
Relationship between VPD and HVAC
In addition to the four methods mentioned above, there is another method: the use of HVAC.
HVAC systems provide temperature and humidity control, which are key factors in determining VPD.
For example, HVAC systems can be used to maintain a temperature range that is suitable for plant growth and to regulate the humidity levels to prevent mold and other air quality problems. By controlling the air flow and air exchange, HVAC systems can also help to maintain a healthy indoor environment with an appropriate VPD.
How to Create the Best Growing Environment with VPD
To create the best growing environment with VPD, you need to consider the following steps:
Step 1: Measure the temperature and relative humidity of your grow room regularly.
Step 2: Use a VPD calculator to determine the VPD range for your plants based on their growth stage and the temperature and humidity readings.
Step 3: Use HVAC systems and dehumidifiers to control the temperature and relative humidity in your grow room, aiming to keep the VPD within the recommended range for your plants.
Step 4: Monitor your plants for signs of stress, such as discoloration or stunted growth, and adjust your HVAC and dehumidification systems accordingly.
Step 5: Regularly inspect your plants for signs of powdery mildew or mold, which can be a result of low VPD or high humidity.
By maintaining the right VPD for your plants, you can improve their growth, increase yields, and reduce the risk of disease and pest problems.
Q1. What is VPD in growing?
VPD is important for plant growth because it affects the ability of plants to transpire. Plants require a certain level of VPD for optimal transpiration and photosynthesis.
Q2. Is VPD more important than humidity?
While both VPD and humidity are important, VPD can be a more useful indicator of plant health and growth than humidity alone. This is because VPD takes into account both temperature and humidity, whereas humidity only measures the amount of moisture in the air.
Q3. How to lower VPD value?
To lower VPD values, you can increase the humidity in the growing area or reduce the temperature. Increasing humidity levels will decrease the VPD value by increasing the amount of moisture in the air. Lowering the temperature will decrease the VPD value by reducing the amount of moisture that the air can hold.