Environmental Control Systems
🌡️ Environmental Control Systems
Plants are biological machines with specific operating conditions. Get the temperature, humidity, airflow, and CO₂ right, and they'll reward you with explosive growth. Get them wrong, and you'll wonder why your lettuce is bolting or your tomatoes won't fruit. In a sealed shipping container, you control every variable — which is both the superpower and the challenge.
The Four Pillars of Climate Control
1. Temperature: The Metabolic Thermostat
Plants are cold-blooded. Their metabolism — photosynthesis rate, nutrient uptake, transpiration — is directly governed by temperature. Most vegetables thrive in a 65–80°F (18–27°C) range during lights-on, with a 5–10°F drop during lights-off to simulate natural day/night cycles.
| Crop Type | Day Temp | Night Temp | Notes |
|---|---|---|---|
| Lettuce / leafy greens | 65–70°F | 55–60°F | Above 75°F = bolting risk |
| Tomatoes | 70–80°F | 60–65°F | Below 55°F = blossom drop |
| Peppers | 70–80°F | 60–65°F | Hot peppers tolerate higher |
| Basil / herbs | 70–80°F | 60–65°F | Cold-sensitive, wilts below 50°F |
| Cucumbers | 75–82°F | 65–70°F | Warmth-loving, fast growers |
2. Humidity: The VPD Connection
Humidity isn't just about comfort — it drives transpiration, the engine that pulls water and nutrients up from roots to leaves. The metric that matters is Vapor Pressure Deficit (VPD): the difference between how much moisture the air could hold and how much it actually holds.
| Growth Stage | Target VPD (kPa) | RH at 75°F |
|---|---|---|
| Propagation / seedlings | 0.4–0.8 | 70–80% |
| Vegetative growth | 0.8–1.2 | 55–70% |
| Flowering / fruiting | 1.0–1.5 | 40–55% |
Too high VPD (dry air): plants close stomata to conserve water → photosynthesis slows. Too low VPD (humid air): plants can't transpire enough → nutrient deficiencies, fungal disease risk.
3. Airflow: Don't Let Stale Air Kill Your Crop
In a sealed container, air stratifies. Hot air rises, cold air sinks, and pockets of stagnant air develop. You need continuous, gentle circulation across every leaf surface. Why?
- Leaves need fresh CO₂ — the boundary layer of still air around each leaf depletes quickly
- Transpiration carries heat away — moving air prevents leaf surface overheating
- Prevents microclimates where mold, mildew, and pests thrive
Use oscillating wall fans (4–6 per container) positioned to create a circular flow pattern. Target 0.3–1.0 m/s air speed at leaf level — enough to make leaves tremble gently.
4. CO₂: The Hidden Growth Booster
Ambient CO₂ is ~415 ppm. Plants can use up to 1,200–1,500 ppm for significantly faster growth (20–40% yield increase). In a sealed container with dense planting, CO₂ can drop below 200 ppm within hours of lights-on as plants consume it — that's growth-stalling territory.
Lighting: The Indoor Sun
| Type | Efficacy | Lifespan | Cost | Best Use |
|---|---|---|---|---|
| LED (full spectrum) | 2.5–3.5 µmol/J | 50,000 hrs | $$ | All-purpose; most efficient |
| LED (red/blue "blurple") | 2.0–3.0 µmol/J | 50,000 hrs | $ | Vegetative growth (less ideal for fruiting) |
| CMH (Ceramic Metal Halide) | 1.5–1.8 µmol/J | 20,000 hrs | $ | Full spectrum, good UV output |
| HPS (High Pressure Sodium) | 1.3–1.7 µmol/J | 24,000 hrs | $ | Flowering/fruiting (but hot!) |
| T5 Fluorescent | 1.0–1.3 µmol/J | 20,000 hrs | $ | Seedlings, microgreens only |
For LED lighting per tier in NFT: aim for PPFD of 200–400 µmol/m²/s for leafy greens and 500–800 µmol/m²/s for fruiting crops. Modern LED bars (Samsung LM301H diodes are the industry standard) running at 40–60W per 4-foot bar, spaced 6–8 inches apart, hit these targets efficiently.
🧠 Quick Check
Q1: What happens to CO₂ levels in a sealed grow container during the lights-on period?
Q2: What's VPD and why does it matter?