Inputs
Example Data Table
| Scenario | Temp (°C) | RH (%) | Airflow (m/s) | Sun | Stage | Comfort Score (°C) | Comfort Band | RH Band |
|---|---|---|---|---|---|---|---|---|
| Morning beds, partial sun | 24 | 60 | 1.5 | Partial | Vegetative | ~25 | Comfortable | In Range |
| Greenhouse midday, heavy work | 32 | 75 | 0.5 | Full | Seedling | ~41 | Dangerous Heat | Humid |
| Cool evening pruning | 18 | 50 | 0.8 | Shade | Fruiting | ~18 | Comfortable | In Range |
Values are illustrative. Use real sensor readings for decisions.
Formula Used
- Dew Point (°C): Magnus approximation using temperature and relative humidity.
- Saturation Vapor Pressure (hPa): Tetens approximation at air temperature.
- Actual Vapor Pressure (hPa): saturation pressure × RH/100.
- VPD (kPa): (SVP − VP) converted from hPa to kPa.
- Humidex (°C): temperature plus a dew-point-based humidity term.
- Apparent Temperature (°C): T + 0.33×e − 0.70×wind − 4.00, where e is vapor pressure.
- Comfort Score (°C): apparent temperature adjusted for sun, setting, effort, clothing, and wetness.
Comfort scores are for guidance, not medical limits. For sensitive users, follow local heat advisories and workplace safety rules.
How to Use This Calculator
- Measure air temperature and humidity near the canopy.
- Estimate airflow: still air is near 0–0.5 m/s.
- Select sun exposure and whether you are enclosed.
- Choose plant stage to compare against typical targets.
- Pick your gardening effort and clothing level.
- Press Calculate and review the bands and tips.
- Use recommendations to adjust shading, venting, and watering timing.
Humidity, comfort, and task planning
Garden work feels harder when humidity slows sweat evaporation. This calculator converts temperature, relative humidity, airflow, and sun into an adjusted comfort score, so you can schedule pruning, potting, or digging at safer times. Record readings near canopy height, then compare morning, midday, and evening values before committing to long tasks.
Dew point as a stickiness indicator
Dew point summarizes moisture in the air. When dew point rises, surfaces dry slowly and workers feel clammy. The model uses a Magnus approximation to estimate dew point from temperature and relative humidity for quick comparisons between zones, such as shaded beds versus a closed tunnel. Dew point also helps predict condensation risk on glazing and cold irrigation lines.
VPD for plant transpiration control
Vapor pressure deficit (VPD) describes the drying power of air around leaves. Low VPD can encourage disease by keeping foliage damp, while high VPD can drive excessive transpiration and stress. The calculator reports VPD in kPa to support ventilation and misting decisions. Many growers aim for lower VPD during propagation, then gradually increase it as plants harden and root systems expand.
Interpreting comfort and humidity bands
Comfort bands use apparent temperature and practical adjustments for enclosure, clothing, effort, and wetness. Humidity bands compare your reading against common stage targets, helping you balance worker comfort with crop needs in beds, tunnels, or greenhouses. If comfort is warm but humidity is low, focus on shade and hydration. If humidity is high, prioritize airflow to reduce leaf wetness duration.
Operational actions that reduce risk
Use shade cloth, increase gentle airflow, and water earlier to moderate peaks. If humidity is high, avoid late overhead watering and improve air exchange to shorten leaf wetness periods. Track results over several days to confirm that changes move scores and VPD toward your goal with consistent weekly logging. For greenhouses, simple steps include opening leeward vents first, spacing plants to prevent stagnant pockets, and cleaning intake screens so fans deliver rated airflow.
FAQs
1) What humidity is comfortable for general gardening?
Many people feel comfortable around 40–60% RH with moderate airflow. Comfort still depends on temperature and sun exposure, so use the comfort score to compare times of day and choose safer work windows.
2) Why can high humidity feel hotter at the same temperature?
High humidity slows sweat evaporation, reducing the body’s cooling ability. Apparent temperature rises because moisture in the air limits heat loss, especially when airflow is low or you are working in full sun.
3) What does VPD tell me about plant stress?
VPD reflects how strongly air pulls moisture from leaves. Low VPD can keep foliage wet longer and raise disease risk. High VPD can accelerate transpiration and cause wilting if water uptake cannot keep up.
4) How accurate are dew point and humidex values?
They are calculated from widely used approximations that are reliable for day‑to‑day comparisons. For best accuracy, place sensors in shade near canopy level, avoid direct mist on probes, and allow sensors to stabilize.
5) My greenhouse feels worse than the readings suggest. Why?
Radiant heat, poor air mixing, and localized humidity pockets can increase discomfort. Try measuring in several spots, checking airflow at plant height, and opening vents or running fans to reduce stagnant zones.
6) How should I use the stage targets for humidity?
Use targets as a starting point, then adjust for your crop and disease pressure. Seedlings often tolerate higher RH, while flowering and fruiting usually benefit from lower RH and stronger airflow to limit mold.
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