# Passive solar and natural cooling: Techniques

From windcatchers and ice houses to sky-cooling paint

Source page: https://www.materialinsights.org/energy/e_passive/techniques/

What this tab covers The methods used to capture this energy: how each works, and how they compare on efficiency, cost, life-cycle emissions, maturity and scale.

Passive methods range from ancient windcatchers and ice houses to new materials that radiate heat to the sky. They are cheap when designed in but depend on climate.

#### Comparison

| Method | Efficiency | Cost | Life-cycle emissions | Maturity | Scale |
|---|---|---|---|---|---|
| **Sun-facing glazing, Trombe walls, sunrooms and daylighting**^[1](https://www.crses.sun.ac.za/files/services/events/workshops/4_Solar Collectors.pdf)^[6](https://www.nrel.gov/docs/fy04osti/36277.pdf) | Trombe wall 13% of incident sunlight, 20% of the building's heating (Zion) | No figure in the sources used | Avoids heating and lighting energy | mature | No global figure |
| **Natural ventilation and windcatchers**^[8](https://doi.org/10.1016/j.rser.2023.114048) | Effective in favourable weather; energy performance little studied | Very few economic studies | Near zero in operation | mature | No global figure; uptake limited by low awareness, cost and regulation |
| **Earth tubes and earth-sheltered buildings**^[7](https://www.mdpi.com/1996-1073/6/8/3734) | Supply air warmed by 6-15 C in cold-climate studies | No figure in the sources used | Fan energy only | mature (niche) | No global figure |
| **Evaporative and radiative cooling**^[3](https://basc.pnnl.gov/resource-guides/evaporative-cooling-systems)^[4](https://doi.org/10.1038/nature13883) | Evaporative effectiveness 70-95%; radiative 40.1 W/m2 under full sun, 4.9 C below air (laboratory) | Evaporative: under half the cost of air conditioning to install and run | Fan and pump electricity only | mature (evaporative); early commercial (radiative) | No global figure |
| **Traditional cooling: ice houses, stored snow and thermal mass**^[2](https://energy-transitions.org/wp-content/uploads/2025/01/ETC_Buildings-Decarbonisation-Report_Summary_Cooling.pdf) | No figure in the sources used | No figure | Near zero | mature (thermal mass); largely historical (ice houses) | No global figure |
| **Seawater air conditioning**^[5](https://blogs.worldbank.org/en/latinamerica/sustainable-cooling--a-deep-dive-into-seawater-air-conditioning-) | 83-94.5% less electricity (estimates) | USD 16.5-70 million per Caribbean proposal (854-7,100 tons of cooling) | Avoids up to 63,000 barrels of fuel a year per project (estimates) | early commercial | Operating systems include Tahiti's largest hospital complex |

Passive measures are usually the cheapest comfort, because the energy is free and the cost lies in design choices made anyway. Their weakness is reliability: evaporative coolers fail in humid weather, ventilation on still hot nights, and unshaded glass overheats. Seawater cooling saves most electricity but needs deep water near shore and costly pipework.

#### How each method works
**Sun-facing glazing, Trombe walls, sunrooms and daylighting**

Sun-facing windows warm floors and walls, with overhangs for summer shade. A Trombe wall is dark masonry behind glass that releases the day's heat indoors 8-10 hours later.^[1](https://www.crses.sun.ac.za/files/services/events/workshops/4_Solar Collectors.pdf)^[6](https://www.nrel.gov/docs/fy04osti/36277.pdf)
**Natural ventilation and windcatchers**

Cross-ventilation and the stack effect move air through buildings; windcatchers, towers used for centuries in Iran and the Gulf, channel rooftop breezes into rooms.^[8](https://doi.org/10.1016/j.rser.2023.114048)
**Earth tubes and earth-sheltered buildings**

Air drawn through buried pipes is tempered by soil that stays near the yearly average temperature.^[7](https://www.mdpi.com/1996-1073/6/8/3734)
**Evaporative and radiative cooling**

A fan pulls dry air through wet pads, cooling it by 15-40 F (8-22 C, calculated). Radiative surfaces reflect sunlight while emitting infrared to space, staying below air temperature.^[3](https://basc.pnnl.gov/resource-guides/evaporative-cooling-systems)^[4](https://doi.org/10.1038/nature13883)
**Traditional cooling: ice houses, stored snow and thermal mass**

Winter ice or snow was stored in insulated buildings through summer; thick walls absorb daytime heat and release it at night.^[2](https://energy-transitions.org/wp-content/uploads/2025/01/ETC_Buildings-Decarbonisation-Report_Summary_Cooling.pdf)
**Seawater air conditioning**

A pipe draws cold water from about 900 m deep; heat exchangers chill a fresh-water loop for buildings, replacing most chiller work.^[5](https://blogs.worldbank.org/en/latinamerica/sustainable-cooling--a-deep-dive-into-seawater-air-conditioning-)

#### Sources

1. [Solar Collectors (workshop lecture, W. Weiss, AEE INTEC)](https://www.crses.sun.ac.za/files/services/events/workshops/4_Solar Collectors.pdf) Centre for Renewable and Sustainable Energy Studies, Stellenbosch University, 2013
2. [Buildings Decarbonisation Report: Summary, Cooling](https://energy-transitions.org/wp-content/uploads/2025/01/ETC_Buildings-Decarbonisation-Report_Summary_Cooling.pdf) Energy Transitions Commission, 2025
3. [Evaporative Cooling Systems (Building America Solution Center)](https://basc.pnnl.gov/resource-guides/evaporative-cooling-systems) Pacific Northwest National Laboratory / US Department of Energy, 2024
4. [Passive radiative cooling below ambient air temperature under direct sunlight (Raman, Anoma, Zhu, Rephaeli and Fan, Nature 515, 540-544)](https://doi.org/10.1038/nature13883) Nature, 2014
5. [Sustainable cooling: a deep dive into seawater air-conditioning solutions for the Caribbean](https://blogs.worldbank.org/en/latinamerica/sustainable-cooling--a-deep-dive-into-seawater-air-conditioning-) World Bank Blogs, 2024
6. [Trombe Walls in Low-Energy Buildings: Practical Experiences (Torcellini and Pless, NREL/CP-550-36277)](https://www.nrel.gov/docs/fy04osti/36277.pdf) National Renewable Energy Laboratory, 2004
7. [A Literature Review on Heating of Ventilation Air with Large Diameter Earth Tubes in Cold Climates (Tan and Love, Energies 6(8), 3734-3743)](https://www.mdpi.com/1996-1073/6/8/3734) MDPI, 2013
8. [A critical review of windcatcher ventilation: Micro-environment, techno-economics, and commercialisation (Liu et al., Renewable and Sustainable Energy Reviews 191, 114048)](https://doi.org/10.1016/j.rser.2023.114048) Elsevier, 2024

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_passive/index.md)
- [Overview](https://www.materialinsights.org/energy/e_passive/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_passive/correlation/index.md)
- [Efficiency](https://www.materialinsights.org/energy/e_passive/efficiency/index.md)
- [Resources and labour](https://www.materialinsights.org/energy/e_passive/resources/index.md)
- [Impact on the biosphere](https://www.materialinsights.org/energy/e_passive/biosphere/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_passive/links/index.md)