Plant Care
- • Climate Control & VPD16
- • Disease & Pest Management14
- • Nutrient Solutions & EC34
- • Plant Health Monitoring7
Inputs
10 parameters · live recalculation on every change
M³
10m³
100m³ default
1000m³
°C
15°C
25°C default
35°C
%
30%
60% default
90%
°C
20°C
28°C default
40°C
°C
10°C
20°C default
30°C
Pro Settings — Lab Controls
%/H
0%/h
10%/h default
60%/h
%
80%
90% default
98%
Advanced Settings — Deterministic Corrections
ACH
0ACH
0.5ACH default
5ACH
PPM
400ppm
1200ppm default
2000ppm
Deterministic model
10 inputs · 10 outputs
Runs 100% in your browser
This is a deterministic model: the same inputs always produce the same outputs, calculated entirely in your browser with nothing sent to any server. It is a planning aid — not a quote, not a dosing instruction, and not a yield forecast. Treat every line as a working estimate and validate it against your own prices and measurements.
It models one system: The climate blueprint for the sealed grow room. Room volume, target temperature and humidity, and the lights-on/off swing feed the VPD, dehumidifier, HVAC and CO2 arms. VPD runs the archived Tetens saturation curve with the leaf pegged −2 °C under LED; the dehumidifier arm sizes transpiration at 0.5 L per plant per day into pints; the HVAC arm prices sensible cooling at a 23.5 W/m³ design factor by envelope (poor 1.5 → excellent 0.5) and air change, converted to BTU at 3.412; the CO2 arm fills to your target ppm at 1.8e-6 kg per m³ per ppm with the leak added to the sustained daily dose. Outputs: HVAC sizing in BTU/h, dehumidifier pints, CO2 kg/day, leaf VPD, CFM exchange, cooling and heating watts, the $/day run cost, and the green—yellow—red safety read.
What the Climate Controller & HVAC Sizer — VPD, Dehumidifier & CO2 Blueprint returns
The engine computes 10 outputs from your 10 inputs. The headline number is HVAC Sizing (BTU/h), alongside Dehumidifier, CO2 Feed, Leaf VPD. Every output updates live as you change a parameter.
What it does not do
Outputs depend on the inputs and assumptions shown here. Confirm relevant measurements and local conditions before acting.
STEP 01
Measure the room in cubic metres and enter canopy target temperature and humidity.
STEP 02
Set the day swing — lights-on and lights-off temperatures — the ΔT the HVAC arm must smooth.
STEP 03
Pick the envelope (insulation k-factor) and air change rate; sealed rooms run near 0 ACH.
STEP 04
Read the four sized arms: HVAC BTU/h, dehumidifier pints/day, CO2 kg/day, CFM exchange.
STEP 05
Check the leaf VPD safety band — green 0.8–1.2 kPa keeps stomata open and transpiration moving.
STEP 06
Cost check: cooling kWh × $0.15 plus CO2 kg × $2.00, then raise efficiency (SEER × derates) to cut the bill.
VPD = e_{sat} \left(1 - \frac{RH}{100}\right), \qquad e_{sat} = 0.61078 \cdot \exp\left(\frac{17.27 \, T_{leaf}}{T_{leaf} + 237.3}\right), \qquad T_{leaf} = T - 2\,°\text{C}
Leaf VPD — Tetens saturation curve
P_{pints} = N_{plants} \cdot 0.5 \, \frac{\text{L}}{\text{plant} \cdot \text{day}} \cdot 2.113 \, \frac{\text{pints}}{\text{L}}, \qquad N_{plants} = \frac{V}{5.3 \, \text{m}^3}
Dehumidifier sizing — transpiration load
\Phi_{BTU} = V \cdot 23.5 \, \frac{\text{W}}{\text{m}^3} \cdot k_{ins} \cdot (1 + ACH) \cdot 3.412, \qquad k_{ins}: \text{poor } 1.5 \to \text{excellent } 0.5
HVAC BTU — sensible cooling load
m_{CO_2} = V \cdot (T_{ppm} - 400) \cdot \frac{1.8}{10^6} \cdot \left(1 + \frac{L}{100}\right)
CO2 dosing — fill + leak makeup
Q_{CFM} = \frac{V \cdot 35.31 \cdot ACH}{60}
Air exchange — ventilation makeup
W_{cool} = \frac{\Phi_{BTU}}{3.412}
Cooling load in watts
W_{heat} = W_{cool} \cdot 0.8
Heating load — inverse arm
\text{GREEN}: 0.8 \le VPD \le 1.2 \quad \mid \quad \text{YELLOW}: 0.4 \le VPD < 0.8 \ \text{or} \ 1.2 < VPD \le 1.6 \quad \mid \quad \text{RED}: VPD < 0.4 \ \text{or} \ VPD > 1.6
VPD safety bands
VPD sweet spot: leaf VPD 0.8–1.2 kPa is green. At 25 °C / 60% RH with the leaf −2 °C under LED the engine lands near 0.9 kPa — the classic veg centre.
Transpiration at 0.5 L/plant/day: a 100 m³ room (~19 plants) pushes roughly 20 pints of moisture per day the dehumidifier must pull.
Envelope k-factor multiplication: poor 1.5, average 1.0, good 0.7, excellent 0.5 — sealing the shell can nearly halve the HVAC arm.
Air change adds linearly: CFM = V·35.31·ACH/60. A vented 100 m³ room at 1 ACH needs ~59 CFM of fresh-air conditioning on top of the load.
CO2 isolation: the one-time fill is V·Δ·1.8e-6 kg; at a 10%/h leak the sustained daily dose runs ~10% above the static fill. Price contrast $2.00/kg tank vs $0.50/kg burner.
Safety: below 0.4 or above 1.6 kPa forces stomata; keep the sealed-room CO2 inside the 8-h exposure guidance and vent before any occupant enters.
- VPD — Tetens: e_sat = 0.61078 × exp(17.27T / (T + 237.3)) kPa and VPD = e_sat × (1 − RH/100); the True Leaf VPD pegs the leaf at −2 °C under LED, landing the default 25 °C / 60% at ~0.9 kPa (archived VPD calculator).
- Dehumidifier: plant count ≈ volume ÷ 5.3 m³ per plant, transpiration 0.5 L/plant/day, 2.113 pints per litre — a 100 m³ room ≈ 19 plants ≈ 20 pints/day of moisture to pull.
- HVAC BTU: sensible cooling at a 23.5 W/m³ design factor × envelope k (poor 1.5, average 1.0, good 0.7, excellent 0.5) × (1 + ACH), converted × 3.412 to BTU/h; the archived 4×4×6.5 ft shell with a 480W LED at 85% heat ≈ 408 W ≈ 1,390 BTU/hr of lift.
- CO2: kg = V × (CO2 target − 400 ppm) × 1.8e-6 kg/m³·ppm × (1 + leak/100) — 100 m³ from 400 to 1200 ppm is a 0.14 kg fill, ~0.16 kg/day sustained at 10%/h leak; priced $2.00/kg tank or $0.50/kg burner (archived CO2 calculators).
- Air exchange: CFM = V × 35.31 × ACH ÷ 60 — 0.5 ACH on a 100 m³ room ≈ 29 CFM of fresh-air makeup the HVAC arm must also condition.
- Safety: leaf VPD band 0.8–1.2 kPa green, 0.4–0.8 and 1.2–1.6 yellow, below 0.4 or above 1.6 red — humidity stall below, stomata stress above.
This model combines the earlier Climate-controller, Dehumidifier-sizing, Hvac-calculator, Co2-controller models.
Q1: How to size a dehumidifier for a grow room? ▾
Size it to transpiration, not room volume. The engine estimates one transpiring plant per 5.3 m³ and pulls 0.5 L per plant per day, then converts at 2.113 pints per litre. A 100 m³ room therefore works out to about 19 plants and roughly 20 pints of moisture per day. Look for a unit with at least that clearance headroom, and treat lights-on peaks as the sizing event.
Q2: What is the HVAC BTU calculator for grow tents and grow rooms? ▾
This calculator prices the sensible cooling load a tent or room must reject. It starts at a 23.5 W/m³ design factor, multiplies by an envelope k-factor (poor 1.5, average 1.0, good 0.7, excellent 0.5) and by (1 + ACH), then converts to BTU/h at 3.412. A sealed 100 m³ room at average insulation works out to about 12,000 BTU/h — a useful first sizing before matching a mini-split.
Q3: What is VPD climate control and what VPD should a grow room target? ▾
Vapor pressure deficit is the gap between the water vapor the leaf holds and the vapor pressure of the surrounding air. It is computed from the Tetens saturation curve — e_sat = 0.61078 × exp(17.27T/(T+237.3)) — times (1 − RH/100), with the leaf pegged at −2 °C under LED. Target 0.8–1.2 kPa leaf VPD (green): below 0.4 kPa transpiration stalls, above 1.6 kPa the stomata clamp shut.
Q4: How much CO2 does a CO2 controller ppm need to add to reach 1200 ppm? ▾
The fill is V × (target − 400 ppm) × 1.8e-6 kg per m³ per ppm. A 100 m³ room moving from 400 to 1200 ppm needs a 0.14 kg fill. At a 10%/h leak, the sustained dose rises about 10% — call it 0.16 kg/day with the controller on the photoperiod. Surpass 1500 ppm and enrichment stops paying; above 2000 ppm the sealed room is not occupiable.
Q5: How many CFM does a grow room need for 0.5 air changes per hour? ▾
CFM = V × 35.31 × ACH ÷ 60. A 100 m³ room at the 0.5 ACH default wants about 29 CFM of fresh-air makeup; a vented room at 1 ACH wants roughly 59 CFM. Exhaust that pulls filtered air into — not out of — the tent keeps the envelope at its k-factor so the HVAC arm stays honest.
Q6: How much does climate control cost to run per day? ▾
Run cost combines the HVAC draw and the CO2 dose: cooling watts at your efficiency derate, run 24 h, charged at about $0.15/kWh, plus CO2 kg sustained at $2.00/kg tank gas. A 100 m³ sealed room at 90% efficiency works out near $14–15/day before burner-swap savings (CO2 at $0.50/kg) shave the gas line to a fraction.