Psychrometric state and crop verdicts.

The strategy ladder

The hot-side ladder from this outdoor state. The first rung that reaches the envelope: semi-closed — holds 21.9 °C provisional; sensible 0.21 kW/m² and latent 0.12 kW/m² — total 0.33 kW/m².

• vent — Fully open vents deliver outdoor air itself — no outdoor fraction reaches the envelope; the tier above it: semi-closed.
  • CO₂ loss — cost, high. Enriched air leaves through the vents, so the dosing demand rises with the fraction of greenhouse air replaced.
  • Humidity exchange — import, high. The air the vents admit carries more water than the cooler part of the crop's own band can hold, so venting brings humidity in and spends condensation margin.
  • CO₂ demand — cost, high. A canopy warmer than its own band works faster, so the same enrichment setpoint is harder to hold.
• fog — reaches 32.9 °C provisional; water 3.48 g/kg — 0.68 kg/h·m² at 30 ACH; approach 3 K provisional. Does not reach the grading envelope — the tier above it: semi-closed. The approach to the outdoor wet bulb is an owner decision under engineering review; a different setting moves every fog figure on this page.
  • Water use — cost, moderate. Every kelvin of cooling is water evaporated into the greenhouse and lost through the vents, so in an arid siting the supply is a first-order constraint and often the binding one.
  • Condensation-margin spend — cost, moderate. Water put into the air raises its dew point toward the crop's coldest surfaces, so the cooling is bought with the margin that keeps water off the crop.
  • Water quality — cost, moderate. Evaporation concentrates whatever the water carries, so nozzles block and pads scale — and where the supply is desalinated or brackish that is a running cost rather than a footnote.
• pad-and-fan — pad end 32.7 °C, fan end 36.7 °C (mean 34.7 °C) provisional; end-to-end 4.0 K; water 3.59 g/kg. Does not reach the grading envelope — the tier above it: semi-closed.
  • Water use — cost, moderate. Every kelvin of cooling is water evaporated into the greenhouse and lost through the vents, so in an arid siting the supply is a first-order constraint and often the binding one.
  • Condensation-margin spend — cost, high. Water put into the air raises its dew point toward the crop's coldest surfaces, so the cooling is bought with the margin that keeps water off the crop.
  • Water quality — cost, moderate. Evaporation concentrates whatever the water carries, so nozzles block and pads scale — and where the supply is desalinated or brackish that is a running cost rather than a footnote.
  • Climate uniformity — cost, moderate. One crop stands in two climates: the air arrives cool at the pad and reaches the fans warmer, so the far end of the greenhouse is graded on a different state from the near end. That is the cost a ledger counting only water and energy cannot see.
• semi-closed — holds 21.9 °C provisional; sensible 0.21 kW/m² and latent 0.12 kW/m² — total 0.33 kW/m². Reaches the grading envelope.
  • Energy — cost, high. Holding a setpoint mechanically is a continuous demand for as long as the outdoor air sits away from it, and the water the greenhouse condenses out is charged to the same meter as the heat it removes.
  • CO₂ retention — benefit, high. A greenhouse that is not ventilating keeps enriched air where the crop is, so the period over which enrichment pays runs longer than it does in a greenhouse cooling itself through its vents.
• heat — lift 0.0 K provisional; load 0.00 kW/m². Does not reach the grading envelope — the tier above it: semi-closed.
  • Energy — cost, low. Lifting the greenhouse to the floor of the crop's band is a continuous heat demand for as long as the outdoor air stays below it.