"I have 20 m² — I'll buy some shelves, some fixtures, and get started." But between "I have floor space" and "the system runs efficiently" lies a series of decisions most people skip before buying: how much of those 20 m² is actually usable growing area, what lighting will cover it without dark zones, whether ventilation and cooling can handle that many fixtures, and which bottleneck will limit output first. Buying equipment is easy. Buying the right equipment in the right quantity requires calculation.
Quick Glossary
- Usable area — the area of trays or shelves actually occupied by crops; differs from total room area due to walkways, equipment, and dead zones
- Bottleneck — the component that first limits output or quality growth: it may be lighting, ventilation, cooling, labour hours, or the sales channel
- Utilisation — the ratio of actually used growing area to the maximum possible; production only becomes economically viable when utilisation exceeds the break-even point
Why "Area × Shelves" Doesn't Give the Right Answer
A shelf in a room takes up more than just its footprint — it requires access space, working space, and room for equipment. In a typical grow room, usable area is 50–65% of total floor area:
Walkways — minimum 60–70 cm between shelves for normal operation. With shelves on both sides, an aisle wide enough for two people to work simultaneously requires 90–120 cm.
Equipment space — reservoirs, pumps, controllers, chiller, sowing table. All of this occupies real square metres that "weren't in the plan."
Vertical clearance for lighting — there must be at least 30–50 cm between the fixture and plant canopy for LED (depending on power). With 2 m shelves and 30 cm plants, clearance exists — but with 60 cm plants, precise calculation is required.
Practical first step: draw the room to scale, including walkways and equipment positions — only then calculate actual usable area.
How to Calculate Lighting Needs from Area
Lighting is the most common point of error when scaling up. Two parameters determine the choice:
PPFD (µmol/m²/s) — photon flux density at canopy level. For microgreens: 150–250 µmol/m²/s. For leafy greens: 200–400 µmol/m²/s. For fruiting crops: 400–800+ µmol/m²/s.
DLI (mol/m²/day) = PPFD × hours of light × 0.0036. At PPFD 250 and 16 hr/day: DLI = 250 × 16 × 0.0036 = 14.4 mol/m²/day — adequate for most greens and microgreens.
Calculation sequence: define the target PPFD for the crop → measure or obtain from the fixture datasheet the PPFD at working height → calculate how many fixtures are needed for even coverage → verify they fit the layout.
A principle often ignored: one powerful fixture in the centre of a shelf creates uneven PPFD — two lower-power fixtures with overlapping zones is better. Uniformity is more critical than peak PPFD.
Ventilation and Thermal Load: What to Calculate
Every fixture is a heat source. A 600 W LED fixture dissipates 600 W of heat (all consumed power becomes heat — part as light, the rest as direct thermal output). With 10 fixtures at 600 W — 6 kW of heat load.
Ventilation — minimum air change rate for a grow room: 20–30 room volumes per hour during active lighting. For a 20 m³ room — 400–600 m³/hr. This is a real fan requirement — not "I'll buy any exhaust fan."
Cooling (AC or chiller) — with 6 kW of heat from fixtures plus heat from pumps and people, the cooling demand to hold 22–24°C in warm seasons is significant. Rule of thumb: 1 kW of cooling capacity for every 1 kW of heat load — this is the minimum estimate.
Where the Bottleneck Is and How to Find It Before Launch
The bottleneck is whatever first limits output growth. Typical candidates:
Lighting — if PPFD is insufficient or uneven, yield per area will be below potential regardless of how many trays are in use.
Refrigeration — in microgreen or greens production: fridge capacity and post-harvest cooling speed determine maximum weekly output. If the fridge holds 30 kg but production is 60 kg — the problem appears on harvest day.
Labour hours — sowing 100 trays per week takes a defined number of hours. If one person is sowing, watering, harvesting, and packing, the real limit is person-hours, not floor area.
Sales channel — if real weekly sales are 20 kg but production capacity is 60 kg, extra shelves and fixtures won't increase revenue, only costs. The bottleneck here is not in production.
Three Mistakes That Cost the Most
Buying equipment "at maximum capacity" before validating sales. Shelves, fixtures, and pumps for 60 trays/week with actual sales of 15 trays/week — frozen capital and an empty system. Start with the minimum setup that reaches break-even and expand from real demand.
Not calculating electricity in the planning stage. 10 fixtures × 600 W = 6 kW × 16 hr/day × 30 days = 2,880 kWh/month. At UAH 4–6/kWh — that's UAH 11,500–17,000/month in lighting alone. For microgreens selling 20 kg/week at UAH 300/kg — that is the entire week's revenue. Calculate before buying.
Ignoring internal logistics. "I'll carry trays back and forth" — at 50 trays/week this is exhausting and slow. Organising flow from sowing through growing to harvest in a single direction without cross-traffic saves 20–30% of working time.
How to Know the Planning Is Correct
- Room layout drawn to scale with actual walkways and equipment positions
- Usable area calculated from total area
- Lighting requirements calculated from target PPFD
- Heat load and ventilation requirements calculated
- Monthly electricity costs calculated
- Bottleneck identified before launch — not after the first month of operation