In two solar heating systems, which system generally gives hotter water?

The system with pipes in a glass enclosure typically gives hotter water because the glass enclosure serves as a protective layer that traps heat through the greenhouse effect. When sunlight enters the enclosure, it warms the air and surfaces inside. This trapped heat raises the temperature of the water circulating in the pipes significantly more than in an open system, where water runs directly through pipes exposed to the sun.

In the open system exposed to the sun, while some heating occurs, there are greater losses due to convection and radiation, leading to a more moderate water temperature. The lack of insulation and a controlled environment means the water cannot reach the higher temperatures achievable in a sealed glass enclosure, where the trapped warm air can effectively transfer heat to the water pipes.

Therefore, the design of the system with pipes in a glass enclosure maximizes heat absorption and reduces heat loss, resulting in hotter water.