Brick-Walled Evaporative Cooler for Fruits and Vegetables
8.69 - Brick-Walled Evaporative Cooler for Fruits and Vegetables
Charlotte Pilapil, University of Guelph, Canada
Suggested citation for this chapter.
Pilapil, C. (2026) Brick-Walled Evaporative Cooler for Fruits and Vegetables. In Farmpedia, The Encyclopedia for Small Scale Farmers. Editor, M.N. Raizada, University of Guelph, Canada. farmpedia.org
Background
In rural areas of developing countries, methods to keep crops at a lower temperature have been developed using an evaporative cooling chamber for use during harvest and post-harvest periods (Kitinoja et al., 2002). These technologies are required due to the lack of refrigeration and electricity, which results in a loss of high value fruits and vegetables that would otherwise bring nutrition and income (Practical Action, n.d). While refrigeration and electricity preserve the crops in one of the best ways, it is expensive to buy and operate. Alternatively, the low-cost evaporative cooling chamber is simple to build, cheap and does not require any external power supply (Practical Action, n.d).
Figure 1. Diagram of brick-walled evaporative cooling chamber (Practical Action, n.d)
Description of a Cooling Chamber
Smallholder farmers construct the brick-walled evaporative cooling chamber (also known as Zero-Energy Cooling Chamber) from bricks, sand, and water as shown in Figure 1 (Practical Action, n.d). A single layer of bricks is made, then a cavity wall is built that is filled with sand that is kept moist; once the food is stored inside the chamber it is then covered with a thatched shed (bamboo or straw) (Mehmood et al., 2022). The basic principle of the method relies on cooling by evaporation, but the efficiency of the chamber heavily relies on the humidity of the surrounding air. The evaporation draws energy from its surroundings, which then produces the cooling effect. When the air is very dry, it absorbs more moisture, thus creating a greater amount of cooling. While air that is too saturated with water, little to no evaporation can take place (Practical Action, n.d). It is reported to maintain an inside chamber temperature between 15 and 18°C, with ~95% humidity (Kitinoja et al., 2002).
What the Chamber Does and How it Helps Crops and Farmers
The evaporative cooling chamber helps preserve fruits and vegetables by lowering the temperature inside the storage chamber, compared to the surrounding atmospheric conditions. Zero Energy Cooling Chambers have been shown to have relatively higher humidity levels inside the chamber compared to the outside (Mehmood, 2022). Since the atmosphere has a limited capacity to hold water vapour and cannot absorb unlimited moisture, its ability to take in additional water vapor decreases as relative humidity increases, approaching saturation (Gwinner et al., 1996). These chambers generally maintain more stable conditions than an open-air chamber outside, despite environmental factors such as rainfall that can affect the humidity levels (Mehmood, 2022).
Studies conducted with tomatoes demonstrate the effectiveness of a ZECC. The higher relative humidity of ZECC's were shown to help tomatoes last longer after harvest (Mehmood, 2022). Tomatoes in particular are sensitive to temperature and humidity changes, but the evaporation cooling chamber slowed down respiration rates and reduced moisture loss (helps extend storage life for perishable foods) by maintaining high humidity (Kabir & Ali, 2020). Tomatoes do not tolerate low temperatures below 10°C, as high temperatures accelerate their respiration rate and lead to rapid deterioration (Kabir & Ali, 2020). Humidity plays a crucial role in maintaining tomato quality. If the humidity levels are below 85-95%, they can shrivel, whereas at saturated atmospheres with 100% humidity, tomatoes can grow fungal molds (Kabir & Ali, 2020). Ultimately, a ZECC in Pakistan was shown to increase the shelf life of tomatoes by maintaining ~8-10°C lower temperatures and 60-70% higher relative humidity compared to the atmospheric temperature. This resulted in longer storage life and higher quality produce than tomatoes that were held at atmospheric conditions (Mehmood, 2022).
Timing is crucial: immediately after harvest, controlling the humidity and temperature is essential to maintaining a good quality and shelf life for tomatoes and similar crops (Kader, n.d). Research has shown that delays in cooling horticultural products can result in direct losses (water loss) or indirect losses (decrease in nutritional value) by maintaining cooler and more humid storage conditions, resulting in improved shelf life (Kabir & Ali, 2020).
Brick-walled evaporative cooling chambers are beneficial for smallholder farmers, especially women farmers who often rely on high value crops for income. Studies indicate women farmers make on average $4,484 USD per year, and in some cases as little as $0.51 USD per hour (Dail, 2017). Since farming requires year-round efforts, technologies that are low-cost and also reduce crop losses can improve their economic opportunities by allowing them to store crops long enough to sell in markets.
How to Construct a Cooling Chamber
Step 1: Farmers first choose a small piece of land on a slope, so that groundwater can drain away (see Figure 2. Khurdiya et al., 1982).
Figure 2. Final cooling chamber constructed on a small parcel of land (Energypedia, n.d)
Step 2: Sand is then spread on the ground where the chamber is to be built, and a layer of bricks is placed on top (see Figure 3. Khurdiya et al., 1982). Bricks are laid out parallel to each other (with no mortar needed to bind); normally a 1.22 x 0.92 meter rectangular brick structure is built to a height of around 1.22 meters (Practical Action, n.d). A double walled chamber is created, with a gap between the cavity about 125 mm.
Figure 3. Floor of chamber being built (Energypedia, n.d)
Step 3: The cavity is filled with clean sand (soil free) (see Figure 4. Khurdiya et al., 1982).
Figure 4. Cavity being filled with sand (Energypedia, n.d)
Step 4: Wet the walls of the chamber by hand or attached water system (see Figure 5. Khurdiya et al., 1982). A hose is used at the end to spread the water released from a tank through the sand.
Figure 5. Chamber being kept wet (Energypedia, n.d)
Step 5: A thatched roof made from bamboo or straw is placed on top of the chamber, to help prevent rain from leaking in and sun exposure (see Figure 6. Khurdiya et al., 1982) (Practical Action, n.d). If the chamber is not built in shade, it is advised to build an extra roof covering the chamber (Access Agriculture, n.d).
Figure 6. Top cover made from bamboo or straw to protect the food in the chamber (Energypedia, n.d)
Critical Analysis
Although brick-walled evaporative cooling chambers are a low-cost alternative for storing fruits and vegetables, several practical factors affect their adoption by smallholder farmers. One of the main advantages of this system is that they require materials farmers might already have. If not, the chamber requires approximately 400-1500 bricks, 400-500 kg of sand, a 6-meter polythene hose, a 100 L capacity water bucket, and 2 bundles of bamboo/straw (Practical Action, n.d). Since most of these materials are commonly available in many rural areas, the cost of building the chamber is much lower than installing a refrigerator (which would require electricity), which is good for small-scale farmers who have limited financial and logistical resources.
An important factor to consider is the labor required to build and maintain the chamber. The construction of the chamber is relatively simple and does not require any machinery or technical skills, but farmers must invest time into building it. Furthermore, ongoing maintenance is necessary to keep the chamber well-functioned (Practical Action, n.d). Sand between the double walls also must be watered to maintain the evaporative cooling effect. This requires farmers to have a regularly accessible water source; however, the water does not need to be clean since the food is not in direct contact with it. The flow of the water must be regulated through the hose, to avoid excessive watering or uneven watering (Practical Action, n.d). The loss of water is often associated with loss of quality for produce (Kader, 2002). The entire system is located outside and thus is potentially exposed to wildlife that could eat the contents; therefore, the chamber cover (e.g. weight on the cover) is very important.
Evaporative cooling chambers ultimately cannot replace conventional refrigeration, and if electricity is available, mechanical refrigeration systems provide the most reliable and consistent source of cold to preserve crops (Kader, 2002). However, a variety of methods are available if electricity is unavailable or too expensive, including night air ventilation, shade from trees, and evaporative cooling (Kader, 2002).
Conclusion
In conclusion, brick-walled evaporative cooling chambers offer smallholder farmers a less expensive alternative to a refrigerator. The chamber is low labor and effectively keeps produce cooled if properly built and maintained, which is suitable for farmers in rural or developing countries. Produce that requires specific storage conditions have thrived in the chamber due to the humidity levels inside compared to the atmospheric conditions (Mehmood, 2002). Tomatoes are a produce that require those conditions and evidence has shown that in a study conducted over 15 days, the tomatoes were evaluated at intervals and showed relatively low weight loss of 1.41%, 1.86%, and 1.69% under controlled storage, proving temperature and humidity management slows post-harvest spoilage (Kabir & Rasool, 2020). However, this chamber cannot fully replace the refrigerator due to the ability to control the temperature.
Helpful links to get started
References
Energypedia. (n.d.) Evaporative cooling chamber. Energypedia.
Gwinner, Joost. (1996). The Fundamentals of Storage. Food and Agriculture Organization of the United Nations, Rome. Link
Kabir, Md. S. N., Ali, M., Lee, W.-H., Cho, S.-I., & Chung, S.-O. (2020). Physicochemical Quality Changes in Tomatoes during Delayed Cooling and Storage in a Controlled Chamber. Agriculture (Basel), 10(6), 196. Link
Kader, L. (n.d.). Small-Scale postharvest handling practices. Food and Agricultural Organization of the United Nations, Rome. Link
Mehmood, Z. (2022). Agricultural post-harvest sustainability through the development of low-cost zero energy cooling chambers (ZECC) - a case study of tomatoes. Journal of Global Innovations in Agricultural Sciences, 10(3), 159-164. Link
Practical Action. (n.d.). Evaporative cooling. Food and Agricultural Organization of the United Nations, Rome. Link
Shaha Nur Kabir, M., Rasool, K., Lee, W.-H., Cho, S.-I., & Chung, S.-O. (2020). Influence of delayed cooling on the quality of tomatoes (Solanum lycopersicum L.) stored in a controlled chamber. AIMS Agriculture and Food, 5(2), 272–285. Link