Active solar energy for space & water heating

Solar heating is one of the oldest uses of the sun’s energy, and with energy costs rising again its benefits are attracting renewed interest. The two types of solar heating are passive and active, both similar but different in one important way. Passive solar heaters rely on the thermosyphon effect to move fluid around their system, while active solar heaters use a pump. The use of a pump allows active systems to operate without the height difference required by the thermosyphon effect. The main uses for active solar heating are air heating, space heating, heat storage, and pool heating.

The thermosyphon effect occurs when a temperature difference is present in a column of fluid that is not horizontal. The warmer fluid has a lower density than the colder fluid surrounding it, and gravity forces the heavier colder fluid to fall below it. The warm fluid cools as it moves away from the heat source and falls back down. This cycle of rising and falling continues for as long as there is a temperature difference in the fluid.

Cold air can be heated by passing it through solar collectors mounted on roofs and walls, with ducts used to move the air between the house and the collectors. Metal ducts that have been painted black to increase solar absorption are used as collectors, and often have glazing on the front to allow sunlight to heat their interior. Passive heaters are limited to walls to create their thermosyphon effect but active heaters can also be mounted on roofs, increasing the amount of heat available. Using a fan increases the volume of air moved through active heaters, and allows their collectors to be further away from the vents. While fan noise is a disadvantage of active solar heating, it is a minor problem common to most air conditioning systems.

Space heating involves pumping a fluid through a solar collector to absorb heat, and then pumping it through piping in floors and walls to release the heat. Water is often used as the fluid but colder climates require a glycol solution to prevent freezing which can break the pipes. The collectors are usually made of long lengths of black plastic pipe which has a small diameter to maximize the fluid contact area and the heat transferred. The collectors are installed on roofs facing the sun, but also work on walls and ground racks.

Heating pool water is perhaps the most common use for active solar heating. The collectors are similar to those used for space heating, and are connected directly to the pool’s filtration system. Sensors measure the water temperature in the collector and pool, and a control unit uses this to decides if the pump should be activated. An average pool heater can increase the pool water temperature by up to fifteen degrees, allowing the pool to be used for several months more than it normally would. In milder climates, the pool can be kept warm all year round.

Active solar heating has many advantages, including its low cost and minimal maintenance. Most systems are easy to install and last more than twenty years, but installing pipes in floors and walls can be difficult if it’s not done when the home is built. The collectors can be mounted on roofs without breaking through them, reducing the potential damage from leaking. The pumps and fans are typically small and quiet, and can even be powered by solar panels. The disadvantages include the risk of leaking, unattractive appearance, and the risk of damage from freezing. Overall, the advantages of active solar heating are far greater than the minor disadvantages, and the energy savings it creates over many years are enormous.

One Response to “Active solar energy for space & water heating”

  1. Doris Tang Says:

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