Greenhouse climate

A potato in a cold greenhouse grows more slowly, without CO₂ hardly at all. Before you control anything, you need to know what the plant wants and what the chip can measure of it.

What plants need#

The game data (plantliferequirements.xml) describes a comfort range for every plant. For most crops:

There are exceptions: cocoa likes it warmer with a centre at 35 °C, switchgrass sits at 30 °C. Mushrooms work the other way round, breathing in oxygen and out CO₂, and need no light. The exact limits also depend on the genes of the individual plant. The Stationpedia shows them on the plant's page.

Plants breathe the room air. So a gas sensor in the greenhouse measures what matters. Then there is the water in the tray: its temperature has to be in the growth range as well.

CO₂: when is it enough?#

In the game code a plant breathes in nothing below 0.1 % CO₂ and fully from 1 %, in between it rises evenly. A greenhouse with plain breathing air therefore slows the plants down. A digital valve on a CO₂ line keeps the share up:

slt tmp co2 CO2_CLOSE      # below 4 %: stay open
and valve valve tmp
slt tmp co2 CO2_OPEN     # below 2 %: open
or valve valve tmp
sbn VALVE HASH("CO2") On valve

Light#

A grow light (StructureGrowLight) needs 70 W and lights the trays near it, sun through windows counts as well. How long the light should be on comes next week.

Target range and limit#

Tell two kinds of limits apart:

• Target range: this is where the value should be. The control works with hysteresis inside this range, for example heater on below 20 °C and off above 24 °C.
• Limit: beyond it things get dangerous. Below 15 °C or above 35 °C there is an alarm, whatever the control is doing.

slt alarm temp T_MIN     # too cold
sgt tmp temp T_MAX       # too warm
or alarm alarm tmp