Lowtech Graph lists low-tech options for every need of a home. Here you can compare them, find tutorials to build them, and link them together into a circular system. Why low-tech?
Night-sky radiative cooling
Needs the grid
One of 6 ways to meet this need. Cost, carbon, footprint and rankings are relative to other solutions for the same need, not absolute.
What your site needs
A roof or ground area with an unobstructed view of the sky, and a climate with clear nights in the season you want cooling. Under the cloudy summer nights of an oceanic climate this gives back much less than it does in a dry one.
A surface facing the open sky loses heat by radiating it upward, and on a clear night it can fall below the air temperature around it. Circulating water or air past such a panel after dark carries that cooling into the house. It needs a clear sky to work: cloud reflects the radiation back.
Levels are relative to the other options for this need, not absolute. Fewer dots is lighter.
Night-sky radiative cooling (This page) Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: Medium · Skill to build: Intermediate · Upkeep: Light · Change to daily life: None · Works without the grid: No Choose it if your summer nights are usually clear and you want to cool with the night sky.
Night-flush cooling Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: Low · Skill to build: Basic · Upkeep: Light · Change to daily life: Daily · Works without the grid: Yes Choose it if your nights are cool and you want to cool the house for free.
Evaporative cooling Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: Low · Skill to build: Basic · Upkeep: Light · Change to daily life: Occasional · Works without the grid: Yes Choose it if your summers are dry and you want cheap cooling.
Heat pump (air- or ground-source), reversible mode Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: High · Skill to build: Specialist · Upkeep: Heavy · Change to daily life: None · Works without the grid: No Choose it if you already need a heat pump for winter and want the same machine to cool.
Ceiling fan Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: Low · Skill to build: Basic · Upkeep: Light · Change to daily life: None · Works without the grid: No Choose it if you want to feel cooler where you sit, for a fraction of a cooling machine’s power.
Whole-house fan Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: Medium · Skill to build: Intermediate · Upkeep: Light · Change to daily life: Occasional · Works without the grid: No Choose it if you want night cooling that works even on still nights.
We don’t list sizing or quantities, as the yield of each technique depends on the quality of its build. The catalogue compares options but doesn’t dimension them. Regulatory notes are indicative, with a French example, and need to be confirmed locally.