![]() Flat plate collectors on the other hand, are less efficient and therefore release more heat, melting snow quicker than evacuated tube systems. The high insolation of these systems prevents excess heat from melting snow or frost on the collector. Though low heat loss in evacuated tubes is usually seen as an advantage, it can actually harm the water heater's performance in snow. These systems need racking systems to optimize their tilt angle. In contrast, flat plat collectors are more sensitive to the direction of incoming radiation. ![]() So evacuated tubes collectors work more efficiently in cloudy or rainy days. Throughout the day the incoming light passes through the collector fairly continuously at different angles. To prevent overheating in an evacuated solar water heater, you need to purchase a heat dump.Ĭylindrical evacuated tubes can absorb sunlight efficiently from a wide range of directions due to their shape. However, overheating is a serious issue because you can't drainback the evacuated tubes the way you do with a flat plate collector. Even if the device uses water, the system's design makes freezing impossible. In an evacuated solar water heater, there is no risk of freezing. The flat plat collector, though it is less efficient per absorbing unit, may perform just as well as its competitor due to a larger absorber area. Therefore two collectors with the same gross size may have very different overall efficiencies depending on whether they are flat plate or evacuated tube. The ratio for flat plate collectors is generally above 90% while the ratio for evacuated tube collectors usually stays between 60%-80%. This is defined as the absorber size divided by the gross size. You should look at the absorber area ratio. However, a more important factor is the size of the absorber in which the liquid is actually heated, which is the active absorbing area. When describing a collector, gross size is often used, like 4 x 7 sq ft. Although evacuated tube collectors have a higher efficiency, especially in winter, flat plate collectors can match their efficiency during summer when there is a small difference between the temperature of the heated water and that of the ambient environment. Absorber area ratio and collector's gross size will determine the active area together. Pay close attention to the term "efficiency" here, which means heating efficiency per active absorber unit, not the total device efficiency or output. Evacuated tube collectors usually cost 20%-40% more than flat plate collectors.Īs there is no heat loss through convection and conduction in evacuated tube collectors, these systems heat water more efficiently than flat plate absorbers. The advantage goes clearly to flat plate collectors. In the rest of this learning article, we compare based on various criteria these two major solar thermal collectors for solar water heating.Ĭost is obviously one of the most important factors when choosing a solar water heater. The air in the space between the two tubes is removed to create a vacuum, which prevents convective or conductive heat loss. Solar evacuated-tube collectors, on the other hand, contain rows of tubes which are constructed by encasing metal absorber tubes inside transparent glass tubes. In these devices a glazed flat-plate collector is mounted on insulated, weatherproofed boxes fitted with a dark absorber plate under one or more plastic or glass covers (known as glazing). Solar flat plate collectors are more commonly used. ![]() There are two main kinds of collectors, solar flat plate collectors and solar evacuated tube collectors. It is one of the key devices in a solar water heating system. A solar thermal collector, also just called a solar collector, is a device that collects heat by absorbing sunlight. Solar Thermal Water Heaters: Highly Cost-Effective Renewable EnergyĮnergy from the sun comes to Earth in the form of electromagnetic radiation as infrared, visible and ultraviolet light. In this learning article, we compare and contrast the two main kinds of solar thermal collectors : flat plate heaters and evacuated tube heaters. These solar energy products are important as resellers often classify solar water heaters based on collectors. In this article, we discuss another key component of any solar water heating system: solar thermal collectors. In our Guide to Choosing a Solar Water Heater, we talked about different types of solar water heaters such as active, passive, thermosyphon, and drainback systems.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |