Psychrometric state and crop verdicts.

The queried state

Dry-bulb 43 °C at 12 % relative humidity.

The air state

Dry-bulb temperature	43.0 °C
Relative humidity	12.0 %
Humidity ratio	0.0064 kg/kg
Vapour pressure	1038 Pa
Dew point	7.5 °C
Wet bulb	20.9 °C
Specific enthalpy	59871 J/kg
Air vapour-pressure deficit	7611 Pa
Density	1.112 kg/m³
Pressure	101325 Pa

The psychrometric chart

The crop recipe — TOM-TOV

Day climate

Temperature	20.5 °C (range 19–23)
Relative humidity	85 % (range 82–88)
Vapour-pressure deficit	0.36 kPa (range 0.28–0.45)
Daily light integral	28 mol/m²/d (range 18–35)
Photoperiod	16 h (range 16–18)
CO₂	600–800 ppm
Root-zone temperature	17–20 °C

Night climate

Temperature	18.5 °C (range 17–20)
Relative humidity	88 % (range 85–90)
Vapour-pressure deficit	0.26 kPa (range 0.2–0.34)
Daily light integral	No published value. The crop record states none. (mol/m²/d)
Photoperiod	No published value. The crop record states none. (h)
CO₂	420–500 ppm
Root-zone temperature	17–20 °C

Stress limits

Hard low temperature	Held for engineering review — not published. (°C)
Hard high temperature	Held for engineering review — not published. (°C)
VPD alert	Held for engineering review — not published. (kPa)
Disease humidity alert	Held for engineering review — not published. (%)
Dew-point margin	Held for engineering review — not published. (°C)
High-DLI alert	Held for engineering review — not published. (mol/m²/d)

Irrigation

Irrigation pH	5–6.2 pH
Irrigation EC	3.5–4.5 mS/cm
Drain fraction	20–30 %
Dosing capacity	2 L/m²/h
Daily water use	1–5 L/m²/d

Transpiration

Mature leaf-area index	Held for engineering review — not published. (m²/m²)
Light extinction coefficient	Held for engineering review — not published. (-)
Minimum stomatal resistance	Held for engineering review — not published. (s/m)
Daily transpiration	Held for engineering review — not published. (kg/m²/d)
Peak transpiration	Held for engineering review — not published. (kg/m²/h)

Verdicts

Day — graded at full light, 200 W/m², the engine's own day threshold provisional

Temperature — risk (damage_risk). Air temperature lies beyond the tolerance limit the crop record states by more than the stress margin. Tissue damage and loss of the crop follow while the state holds. Fog cools by evaporating water into the air the crop stands in, so the temperature falls and the humidity rises together, down to the margin that keeps water off the crop.

Vapour-pressure deficit — tolerance (outside_dry). Leaf-level vapour-pressure deficit runs above the recipe envelope. The crop transpires faster than its recipe intends; stomata close to protect the plant and assimilation carries a penalty while the state holds. Fog cools by evaporating water into the air the crop stands in, so the temperature falls and the humidity rises together, down to the margin that keeps water off the crop.

Condensation margin — comfort (comfortable). The coldest plant surface stays clear of the dew point of its air. Water stays off the crop at this state.

Night — graded with no sun

Temperature — risk (damage_risk). Air temperature lies beyond the tolerance limit the crop record states by more than the stress margin. Tissue damage and loss of the crop follow while the state holds. A semi-closed greenhouse holds a setpoint mechanically rather than evaporatively, and dries the air by controlled condensation to the margin the crop record states, keeping enriched air where the crop is.

Vapour-pressure deficit — tolerance (outside_dry). Leaf-level vapour-pressure deficit runs above the recipe envelope. The crop transpires faster than its recipe intends; stomata close to protect the plant and assimilation carries a penalty while the state holds. A semi-closed greenhouse holds a setpoint mechanically rather than evaporatively, and dries the air by controlled condensation to the margin the crop record states, keeping enriched air where the crop is.

Condensation margin — comfort (comfortable). The coldest plant surface stays clear of the dew point of its air. Water stays off the crop at this state.

The strategy ladder

The hot-side ladder from this outdoor state. The first rung that reaches the envelope: fog — reaches 23.9 °C provisional; water 7.89 g/kg — 1.57 kg/h·m² at 30 ACH; approach 3 K provisional.

• vent — Fully open vents deliver outdoor air itself — no outdoor fraction reaches the envelope; the tier above it: fog.
  • CO₂ loss — cost, high. Enriched air leaves through the vents, so the dosing demand rises with the fraction of greenhouse air replaced.
  • Humidity exchange — export, moderate. The air the vents admit is drier than the crop's own band can hold, so venting carries humidity out of the house.
  • CO₂ demand — cost, high. A canopy warmer than its own band works faster, so the same enrichment setpoint is harder to hold.
• fog — reaches 23.9 °C provisional; water 7.89 g/kg — 1.57 kg/h·m² at 30 ACH; approach 3 K provisional. Reaches the grading envelope. Limits: approach. 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, high. 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, high. 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 25.4 °C, fan end 29.4 °C (mean 27.4 °C) provisional; end-to-end 4.0 K; water 7.30 g/kg. Does not reach the grading envelope — the tier above it: semi-closed.
  • Water use — cost, high. 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, high. 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 21.0 °C provisional; sensible 0.23 kW/m² and latent 0.06 kW/m² — total 0.29 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 — Heating has no headroom here — the closed greenhouse already sits above the band floor.
  • 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.

Worked examples

Riyadh — July

Outdoor: 43 °C at 12 % by day, 31 °C at 22 % by night; day length 13.6 h.

Tiers	Day °C	Night °C	24 h mean °C	Grade	Class	Next rung	Link
vent, fog	23.9	19.8	22.16	inside	comfort	none	open
Air temperature sits outside the recipe band and within the grading envelope. The envelope is about as wide as the leaf model resolves, so the state reads as comfort rather than as a departure from target.
vent	43.0	31.0	37.80	above	risk	fog	open
Air temperature lies beyond the tolerance limit the crop record states by more than the stress margin. Tissue damage and loss of the crop follow while the state holds. Fog cools by evaporating water into the air the crop stands in, so the temperature falls and the humidity rises together, down to the margin that keeps water off the crop.
baseline	76.7	31.0	56.91	above	risk	fog	open
Air temperature lies beyond the tolerance limit the crop record states by more than the stress margin. Tissue damage and loss of the crop follow while the state holds. Fog cools by evaporating water into the air the crop stands in, so the temperature falls and the humidity rises together, down to the margin that keeps water off the crop.

Dubai — August

Outdoor: 41 °C at 45 % by day, 33 °C at 70 % by night; day length 13.4 h.

Tiers	Day °C	Night °C	24 h mean °C	Grade	Class	Next rung	Link
vent, fog	32.9	31.2	32.17	above	stress	semi_closed	open
Air temperature has passed the tolerance limit the crop record states and stays within the stress margin beyond it. The crop survives; yield and quality carry a direct penalty for as long as the state holds. A semi-closed greenhouse holds a setpoint mechanically rather than evaporatively, and dries the air by controlled condensation to the margin the crop record states, keeping enriched air where the crop is.
semi_closed	21.0	18.5	19.90	inside	comfort	none	open
Air temperature sits inside the blended recipe band for this radiation level. The crop holds its target temperature.
baseline	72.8	33.0	55.20	above	risk	semi_closed	open
Air temperature lies beyond the tolerance limit the crop record states by more than the stress margin. Tissue damage and loss of the crop follow while the state holds. A semi-closed greenhouse holds a setpoint mechanically rather than evaporatively, and dries the air by controlled condensation to the margin the crop record states, keeping enriched air where the crop is.

Beja — July

Outdoor: 36 °C at 25 % by day, 18 °C at 60 % by night; day length 14.6 h.

Tiers	Day °C	Night °C	24 h mean °C	Grade	Class	Next rung	Link
vent, fog	23.9	16.4	20.97	inside	comfort	none	open
Air temperature sits inside the blended recipe band for this radiation level. The crop holds its target temperature.
baseline	67.8	18.0	48.27	above	risk	fog	open
Air temperature lies beyond the tolerance limit the crop record states by more than the stress margin. Tissue damage and loss of the crop follow while the state holds. Fog cools by evaporating water into the air the crop stands in, so the temperature falls and the humidity rises together, down to the margin that keeps water off the crop.

Naaldwijk — July

Outdoor: 22 °C at 70 % by day, 15 °C at 85 % by night; day length 16.3 h.

Tiers	Day °C	Night °C	24 h mean °C	Grade	Class	Next rung	Link
vent	25.0	15.0	21.79	inside	comfort	none	open
Air temperature sits inside the blended recipe band for this radiation level. The crop holds its target temperature.
baseline	42.9	15.0	33.96	above	stress	vent	open
Air temperature has passed the tolerance limit the crop record states and stays within the stress margin beyond it. The crop survives; yield and quality carry a direct penalty for as long as the state holds. Ventilation moves the greenhouse toward the outdoor air, which is as far as opening the vents can take it.

Provenance

Computed by the DGH Climate Engine, version 0.2.0.

Two layers, stated separately: the psychrometric-core layer is validated; the greenhouse-model layer is design-stage.

Licence: Apache-2.0, covering software-implementation.

Attribution: DutchGreenhouses® — DGH Climate Engine

Citation: DutchGreenhouses B.V. (2026). DGH Climate Engine v0.2.0. Apache-2.0.

Sources: plant_empowerment, bakker_1995, ashrae_2017, dgh_crop_model_db.

Methodology · Canonical link for this view

Indicative, design-stage. Engineering confirms.