Solar hot water systems

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					Solar hot water is water heated by the use of solar energy.
Solar heating systems are generally composed of solar thermal
collectors, a fluid system to move the heat from the collector to its point
of usage. The system may use electricity for pumping the fluid, and
have a reservoir or tank for heat storage and subsequent use. The
systems may be used to heat water for a wide variety of uses, including
home, business and industrial uses. Heating swimming pools,
underfloor heating or energy input for space heating or cooling are more
specific examples.
In many climates, a solar heating system can provide up to 85% of
domestic hot water energy.[1] This can include domestic non-electric
concentrating solar thermal systems. In many northern European
countries, combined hot water and space heating systems (solar
combisystems) are used to provide 15 to 25% of home heating energy.

Direct ('open loop') compact systems, if made of metals are not suitable
for cold climates. At night the remaining water can freeze and damage
the panels, and the storage tank is exposed to the outdoor
temperatures that will cause excessive heat losses on cold days. Some
compact systems have a primary circuit. The primary circuit includes the
collectors and the external part of the tank. Instead of water, a non-toxic
antifreeze is used. When this liquid is heated up, it flows to the external
part of the tank and transfers the heat to the water placed inside.
('closed loop'). Open loop (direct) systems have the disadvantage that
during the night-time, where the temperature of the solar panel starts to
drop below that of the water tank, the system starts working in reverse
heating the water in the panel and cooling the water inside the tank.
This problem is least noticeable in closed loop system using a heat
exchanger as only the water in the heat exchanger and not the whole
tank is affected by it. Zhuhai Tianke Energy Saving Equipment
Manufacture Co., Ltd. managed to solve this problem using a patented
design in their solar water heating systems heat exchanger which forces
the flow of the water in the in the heat exchangers inlet pipe in an
upward flow, thus restricting cold water flowing down to the panel.The
force of the flow is made through a driver inside the heat exchanger
(jacket). The jacket and the driver part is made of the same heat
conducting material therefore sharing the same temperature on same
levels of the heat exchanger.
A compact system can save up to 4.5 tonnes annually of greenhouse
gas emissions. In order to achieve the aims of the Kyoto Protocol,
several countries are offering subsidies to the end user. Some systems
can work for up to 25 years with minimum maintenance. These kinds of
systems can be redeemed in six years, and achieve a positive balance
of energy (energy they save minus energy used to build them) of 1.5
years. Most part of the year, when the electric heating element is not
working, these systems do not use any external source for power (as
water flows due to thermosiphon principle).
Flat solar thermal collectors are usually used, but compact systems
using vacuum tube collectors are available on the market. These
generally give a higher heat yield per square meter in colder climates
but cost more than flat plate collector systems.

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