Indoor & Greenhouse formulas — 11 solvers

CO₂ to Enrich a Sealed Room

m = V \, (c_2 - c_1) \, \rho

Indoor & GreenhouseMass of carbon dioxide needed to raise a sealed growing space from ambient to a target concentration, from the room volume and the density of CO₂ at room conditions.

Daily Light Integral (DLI)

DLI = PPFD \times t

Indoor & GreenhouseCrop ProductionThe total photosynthetically active photons a crop banks in a day, from the light intensity at the canopy and the length of the photoperiod. The single number that best predicts how an indoor crop will grow.

Grow Space Air Exchange

Q = \frac{V}{t}

Indoor & GreenhouseExtraction airflow needed to replace the whole volume of a growing space in a given time — the basis on which a tent or room fan is sized.

Leaching Fraction

LF = 100 \, \frac{V_r}{V_a}

Indoor & GreenhouseCrop ProductionThe share of applied solution that drains away as runoff. Deliberate over-watering is how salts are flushed from a container before they accumulate to the point of damage.

Leaf Vapour Pressure Deficit

VPD_L = e_s(T_L) - e_s(T_a)\frac{RH}{100}

Indoor & GreenhouseThe deficit the plant actually experiences, measured between the saturated air inside the leaf and the room. Leaves under lights run cooler than the air by transpiration, and this is the form that accounts for it.

Light Intensity at a New Distance

E_2 = E_1 \left(\frac{d_1}{d_2}\right)^{2}

Indoor & GreenhouseHow photon flux density falls as a fixture is raised above the canopy: intensity drops with the square of distance, so doubling the height quarters the light.

Lighting Power Density

P_d = \frac{P}{A}

Indoor & GreenhouseElectrical lighting load per unit of growing area — the figure a grow space is planned and its cooling sized against.

Nutrient ppm from Fertiliser Weight

c = \frac{m \, f}{V}

Indoor & GreenhouseCrop ProductionThe concentration of a single nutrient element delivered to a reservoir, from the weight of fertiliser dissolved, the element's share of that fertiliser and the volume of water.

Stock Solution for an Injector

c_s = r \, c_t

Indoor & GreenhouseHow strong to mix the concentrate for a fertiliser injector: the dilution ratio times the concentration wanted at the emitter.

Vapour Pressure Deficit (Air)

VPD = e_s(T)\left(1 - \frac{RH}{100}\right)

Indoor & GreenhouseCrop ProductionHow much more water vapour the air could hold, from air temperature and relative humidity. The number that governs transpiration, and the one growers steer a room by instead of humidity alone.

Yield per Watt

Y = \frac{m}{P}

Indoor & GreenhouseDry yield divided by the lighting power that produced it, in grams per watt — the efficiency figure indoor growers compare rooms and fixtures by.