In recent years, the adoption of electric fans in urban households across China has reached an impressive 200%, while air conditioner ownership remains below 10%. This significant gap is largely driven by cost and energy consumption. Electric fans are much more affordable compared to single-cooling window air conditioners, with a price difference ranging from 300 to 2000 yuan. Moreover, there's a lack of a mid-range cooling solution that bridges this gap. Over the past decade (from April 1985 to December 1995), China's patent system saw over 200 related applications aimed at filling this market void, focusing on non-mainstream cooling technologies.
From the perspective of cooling sources, water evaporation-based systems have dominated, accounting for about one-third of all applications. Other methods include underground cooling, semiconductor refrigeration, refrigerator-based cooling, low-power air conditioning, solar cooling, gas refrigeration, and heat pipe cooling. Among these, water evaporation is the most popular due to its low cost and high vaporization efficiency. Water has a latent heat of vaporization of 2451 J/g at 30°C, meaning that 1 gram of water can absorb 2451 J of heat. If this process occurs within one second, it equates to a cooling power of 245 watts—comparable to a KC24 single-cooling window air conditioner. This makes it a highly attractive option.
However, the effectiveness of such systems depends heavily on ambient humidity and airflow velocity. As a result, they perform well in dry and hot regions but struggle in humid southern areas where high humidity limits evaporation. To address this, Fuzhou has proposed innovative solutions like separating dry and wet air using cold plates and exchanging heat between them. Another approach involves dehumidifying air with calcium chloride or lithium chloride before re-humidifying it to achieve cooling.
Underground cooling systems can be divided into three categories: groundwater, tap water, and underground wind. These require significant water usage, making them unsuitable for urban households. Similarly, underground wind systems are limited to specific locations and often suffer from poor air quality.
Semiconductor cooling fans, based on the Peltier effect, offer advantages such as quiet operation, compact size, and adjustable cooling. However, their low energy efficiency and need for DC power limit their use to specialized environments like vehicles.
Refrigerator-based cooling systems either integrate fans into existing units or use cooled cores or ice blocks to provide localized cooling. While effective, they have limited capacity and are best suited for small spaces.
Low-power air conditioners, such as those designed for beds or small rooms, consume around 200 watts but suffer from poor energy efficiency and limited air circulation.
Solar refrigeration systems, though promising, face challenges due to high costs and low COP values. For example, achieving 2000 watts of cooling requires 10 square meters of solar collectors, which is impractical for most households.
Other experimental systems, such as heat pipe or gas-fired refrigeration, remain in early stages and require further development. Overall, while many innovative cooling solutions exist, practical implementation still faces technical and economic hurdles.
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