Solar energy is available abundantly, is cheap and environmentally friendly. This energy can be used either to heat houses or water, or even to generate electricity. For heating applications, a heat transfer fluid is pumped trough a solar collector, where the fluid is warmed up. The heat transfer fluid is then pumped either to areas where it gives off its heat again to warm up rooms, or it is sent through a water storage tank where it warms up the water needed for bath or shower.
Typical dosage rates are
35-40 %
Zitrec LC.
Every day, the sun sends out an enormous amount of energy which is used to
evaporate water, is absorbed by plants, land and oceans, or is reflected
back into space. Solar energy is a clean and abundant energy source that
can be used to supplement many of our energy needs. It can be utilized as a
form of heat, such as solar water heating, or as electricity, such as solar
photovoltaics.
The challenge confronting solar heating is heat storage. Solar heating
systems must have some way to store the heat that is collected on sunny days
to keep people warm at night or on cloudy days. This heat may be stored
either in a large tank as a hot liquid, or in rock bins beneath a house to
store hot air.
Solar collectors
A solar collector is the most known way to collect heat from the sun. It exists of dark-colored metal plates inside a box that absorb the sunlight and change it into heat. A closed car on a sunny day is like a solar collector. As sunlight passes through the car's glass windows, it is absorbed by the seat covers, walls, and floor of the car. The light that is absorbed changes into heat. The car's glass windows let light in, but don't let all the heat out.
So, a solar collector does three things:
it allows sunlight inside the glass (or plastic);
it absorbs the sunlight and changes it into heat;
it traps most of the heat inside.
One or more collectors are placed on a southerly-facing slope, often on high roofs where they can collect the most sunlight. A heat transfer fluid, such as Zitrec L, is pumped through the collector. As the fluid passes through the collector, it is heated by the sun. The heated fluid is then circulated to a heat exchanger, which transfers the energy into e.g. a water tank.
Various
types of solar panels result in different fluid temperatures. Some types
result in temperatures around or even above 200°C. In those cases we
recommend to contact our technical department to consult on the suitability
for the particular application. Solar heating systems should be designed as
closed systems and we prefer by far hard solder connections above soft
solder
Heat transfer fluids
Heat transfer fluids carry
heat from solar heat collectors to the heat storage tanks in solar heating
(and cooling) systems. The fluids most commonly used are based on water,
propylene glycol and ethylene glycol.
When selecting a transfer fluid, you should consider the following criteria:
the coefficient of expansion, viscosity, thermal capacity, freezing point,
boiling point, and flash point. For example, in a cold climate, solar
systems require fluids with low freezing points. Fluids exposed to high
temperatures, as in a desert climate, should have a high boiling point.
Viscosity and thermal capacity determine the amount of pumping energy
required. A fluid with low viscosity and high specific heat is easier to
pump, because it is less resistant to flow and transfers more heat. Other
properties that help determine the effectiveness of a fluid, are its
corrosiveness and stability. The following compares the most commonly
used heat transfer fluids and their properties.
Water is non-toxic, inexpensive, has a high specific heat, and a very low viscosity, but it also has a relatively low boiling point, a high freezing point, and can also be quite corrosive if the pH is not maintained at a neutral level. This makes it unfit for use.
Glycol/water
mixtures have a 50/50 or 60/40 glycol-to-water ratio. Ethylene glycol has
the disadvantage of being harmful when swallowed, and should therefore only
be used in a double-walled, closed-loop system. Monopropylene glycol is a
non-toxic alternative, and propylene glycol/water mixtures are often used in
a single-walled heat exchanger. For a long-life corrosion protection, it
is important that the tap water used for making the mixture with the heat
transfer fluid should contain maximum 100 mg/kg chloride. The information
on your tap water quality can be obtained from your regional water supply
company. Glycols
can deteriorate at very high temperatures. You must check the pH value,
freezing point, and concentration of inhibitors annually to determine
whether the mixture needs any adjustments or replacements to maintain its
stability and effectiveness.
Applications
Solar energy can be utilized as a form of heat, such as solar water heating, or as electricity, such as solar photovoltaics. The latter will not be discussed.
Solar space
heating : By means of mechanical equipment, such as pumps and blowers, houses are
warmed up by means of solar energy. Usually an outside source of energy is
also available to help heat the house when solar energy is not enough. The
heat transfer fluid flows through the collectors and is warmed up.
The heated liquid is then distributed to the rest of the house just
as it would be with an ordinary furnace system.
Solar water
heating : Water heating is an important home energy expense. Using solar energy to provide hot water for showers,
dishwashers and clothes washers will significantly reduce this expense.
In a solar water heater system, a solar
collector is mounted on the roof, or in an area of direct sunlight, and
collects sunlight and converts it to heat. A pump then circulates a heat transfer
fluid through the collector for heating. The heated fluid then goes to the
water storage tank where it heats water. In order to minimize heat loss,
the distance from the collector to the water tank should be as short as
possible. Once there, the solar heat is transmitted from the heat transfer
fluid to the water through a heat exchanger. Separate circuits are used to
assure the heat-transfer fluid and the domestic water do not mix. The heated
water can then flow to the hot-water faucets or showerhead.
Solar energy and the environment
In the 1970s, the push for
renewable energy sources was driven by oil shortages and price increases.
Today, the push for renewable energy sources is driven by a renewed concern
for the environment. Solar energy is the prototype of an environmentally
friendly energy source. It consumes none of our precious energy resources,
makes no contribution to air, water, or noise pollution, does not pose a
health hazard, and contributes no harmful waste products to the
environment. And solar energy cannot be embargoed or controlled by any one
nation. Nor will it run out until the sun goes out.
We would also like to draw your attention to an existing regulation DIN 4757 part 1 (www.din.de) on the design, construction and safe installation of solar heating systems as well as on the required frost protection level.
APPLICATIONS -> SOLAR HEATING SYSTEMS
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