Is it true that evacuated tubes are less prone to freezing than flat plates?

Freezing Point of Water Inside Evacuated Tubes

The freezing point of water inside evacuated tubes is significantly lower than that of flat plates. This is because the vacuum insulation reduces convective heat transfer, allowing the water to maintain a higher temperature. As a result, the water inside the tubes may not freeze even at temperatures as low as -20°C (-4°F). This is because the heat loss from the water is reduced, allowing the water to maintain a higher temperature.

Design Considerations for Evacuated Tubes in Cold Climates

When designing a solar hot water system using evacuated tubes in cold climates, it’s essential to consider the temperature and the freeze protection measures. Evacuated tubes are often used in combination with a freeze protection system, such as a glycol or antifreeze solution, to prevent damage to the tubes. The system should be designed to allow for some degree of temperature drop, typically no more than 10-15°C (18-27°F), without causing damage to the tubes.

Comparison with Flat Plates

In comparison, flat plates have a higher risk of freezing due to the convective heat transfer from the water to the plate. This can cause the water inside the plate to freeze, leading to damage to the plate and the system. In contrast, evacuated tubes have a lower risk of freezing, making them a more reliable option for cold climates. However, it’s essential to note that evacuated tubes still require some form of freeze protection to prevent damage.