Renewable Energy

1. UNIT 2 Solar Energy
SOLAR AIR HEATERS
BY MR.K.STALIN
AP/MECH/AMET UNIVERSITY

2. Introduction:
In order to produce process heat for drying of agricultural, textile, marine products, heating
of buildings and re-generating dehumidify agent, solar energy is one of the promising heat
sources for meeting energy demand without putting adverse impact of environment.
Solar air heating is a solar thermal technology in which the energy from the sun, insolation,
is captured by an absorbing medium and used to heat air.
Solar air heating is a renewable energy heating technology used to heat or condition air for
buildings or process heat applications.

3. Classification of Solar air Collectors:
Solar air collectors can be divided into two categories:
•Unglazed Air Collectors:The "unglazed air collector" refers to a solar air heating system
that consists of an absorber without any glass or glazing over top.
•Glazed Solar Collectors: The "glazed air collector" refers to a solar air heating system
that consists of an absorber with glass or glazing over top.

4. Solar air Heater collectors:

5. Solar Air Heater Advantages
• The need to transfer heat from working fluids to another fluid is eliminated as air is being used directly
as the working substance. The system is compact and less complicated.
• Corrosion is a great problem in solar water heater. And this problem is not experienced in solar air
heaters.
• Leakage of air from the duct does not create any problem.
• Freezing of working fluid virtually does not exist.
• The pressure inside the collector does not become very high.
• Thus air heater can be designed using cheaper as well as lesser amount of material and it is simpler to
use than the solar water heaters.

6. Solar Air Heater Disadvantages
• The first and foremost is the poor heat transfer properties of air. Special care is required to improve
the heat transfer.
• Another disadvantage is the need for handling large volume of air due to its low density.
• Air cannot be used as a storage fluid because of its low thermal capacity.
• In the absence of proper design the cost of solar air heaters can be very high.

7. Solar air heat applications
• Space heating applications : Space heating for residential and commercial applications.
• Process heat applications : Drying laundry, crops (i.e. tea, corn, coffee).
• Night cooling applications
• Ventilation applications

8. Concentrating Collectors
A concentrating collector comprises a receiver, where the radiation is absorbed and
converted to some other energy form, and a concentrator, which is the optical system
that directs beam radiation onto the receiver.
In concentrating collectors, solar energy is optically concentrated before being
transferred into heat.
Concentration can be obtained by reflection or refraction of solar radiation by the use
of mirrors or lens.

9. Classification of concentrating collectors
Parabolic trough collector (PTC);
Linear fresnel reflector (LFR); and
Parabolic dish reflector (PDR).

10. The working fluid can achieve higher
temperatures in a concentrator
system when compared to a flat-
plate system
Some form of tracking system is
required so as to enable the
collector to follow the Sun.
No Pollution and Global Warning
Effects:
Solar reflecting surfaces may lose
their reflectance with time and may
require periodic cleaning and
refurbishing.
The thermal efficiency is greater
because of the small heat-loss area
relative to the receiver area.
Concentrators can focus only direct
solar radiation, this performance is
poor on cloudy days.
Advantages Disadvantages