DEPARTMENT OF PLANNING AND NATURAL RESOURCES
VIRGIN ISLANDS ENERGY OFFICE
45 ESTATE MARS HILL
FREDERIKSTED, VIRGIN ISLANDS 00840
TELEPHONE 340 773-1082 STX FAX 340 772-0063
340 774-3320 STT FAX 340 714-9531
SOLAR HOT WATER
AND SPACE HEATING & COOLING
Solar hot water heaters use the sun to heat either water or a heat-transfer
fluid in collectors. There are passive systems and active systems. A
typical system will reduce the need for conventional water heating by
about two-thirds. High-temperature solar water heaters can provide
energy-efficient hot water and hot water heat for large commercial and
SOLAR HOT WATER SYSTEMS
This system uses a pump to circulate potable water from the water
storage tank through one or more collectors and back into the tank. An
electronic controller, an appliance timer, or a photovoltaic panel
regulates the pump.
Integral Collector Storage (ICS) System is
-. passive and direct, the collector and tank are
combined. Pumps and controls are not
required. Water is heated and stored in a
combined heat storage and collection unit.
Acwte, Closed-Loop Solar Water Heater
In this system, a heat exchanger
heats a fluid that circulates in tubes
through the water storage tank,
transferring the heat from the fluid
to the potable water. Active, indirect
systems are often used in freezing
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A thermosiphon solar water
heating system has a tank
mounted above the collector. As
the collector heats the water, it
rises to the storage tank, while
heavier cold water sinks down to
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Thermosiphon systems are an economical
and reliable choice, especially in new
Drain down Systems
In cold climates, this system prevents water from freezing in the
collector by using electric valves that automatically drain the water from
the collector when the temperature drops to freezing. "Drain back
systems," a variation of this approach, automatically drain the collector
whenever the circulating pump stops.
Swimming Pool Systems
In solar heated swimming pools, the pool's
Unglued Solar Calle~dar
..Twk Coo filter pump pumps water through a solar
collector, and the pool itself stores the hot
sf piL .r Unglazed solar collectors are typically used for
pip--Aeor swimming pool heating.
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SOLAR ENERGY COLLECTORS
Flat Plate Collectors
-lab l -l o0 Flat-plate collectors are used for
residential water-heating and space-
The most common collector for solar hot water is the flat plate collector.
It is a rectangular box with a transparent cover, installed on a building's
roof. Small tubes run through the
box and carry fluid-either water
or other fluid, such as an
antifreeze solution. The tubes
attach to a black absorber plate.
As heat builds up in the
collector, it heats the fluid
passing through the tubes. The
hot water or liquid goes to a
storage tank. If the fluid is not
hot water, water is heated by
passing it through a tube inside the storage tank full of hot fluid.
Evacuated Tube Collectors
These collectors consist of rows of parallel transparent glass tubes, each
containing an absorber and covered with a selective coating. Sunlight
enters the tube, strikes the absorber,
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and heats the liquid flowing through "- .
the absorber. These collectors are ''
manufactured with a vacuum
between the tubes, which helps them
achieve extremely high temperatures,,
(170-350 degrees F); so they are
appropriate for commercial and industrial uses.
Parabolic trough-shaped reflectors concentrate sunlight onto an absorber
or receiver to provide hot water and steam, usually for industrial and
commercial applications. Paraboi- Tourb Collect
Transpired Solar Collectors "'""""
A transpired collector is a south '
facing outside wall covered by "
a dark sheet metal collector.
The collector heats outside air, -,4-l ,.or,.....
which is then sucked into the
building's ventilation system
through perforations in the
collector. They have been used
for pre-heating ventilation air and crop drying. They are inexpensive to
make, and commercially, have achieved efficiencies of more than 70
Batch or Breadbox Heaters
This system is also referred to as a 'k solasroleor
batch heater and a breadbox. It
consists of an approximately 40- '' .
gallon insulated tank, lined with '
glass on the inside and painted
black on the outside. It is mounted
on the roof, or on the ground in
the sun. Plumbing from the house A1 '
supplies the box with cold water
through an inlet that extends down
to the bottom of the tank. The box ,,, i........,
itself acts like a collector,
absorbing and trapping the sun's
heat and heating the water. An
outlet supplies the house with Batch solar collectors can be a reliable and
heated water from the top of the economical choice for heating domestic
tank. water in mild-freeze climates.
Solar Process Heat
These systems consists of several thousand square feet of ground-
mounted collectors, pumps, heat exchangers, controls, and one or more
large storage tanks. Typically, they provide hot water and hot water
space heating for large institutions such as schools, office buildings,
prisons, and military bases.
Active Solar Cooling
As water evaporates, it cools the air. Evaporative cooling systems,
usually appropriate for hot dry climates, can be powered with solar
technology. In humid climates, desiccant evaporative cooling systems
use the same evaporative concept to cool air, but they also include a
desiccant wheel to dry incoming air. Waste heat from the building,
natural gas, or solar technologies can be used to regenerate the desiccant
wheel. Evaporative cooling is a CFC-free and energy-efficient way to
cool commercial buildings. In absorption solar cooling, an absorption
device uses a heat source, such as natural gas or a large solar collector,
to evaporate refrigerant.
Certification of Solar Water Heaters
Solar research facilities have developed testing and certification
requirements for solar collectors and design and installation criteria for
solar systems. Thermal performance ratings, derived from testing and
certification programs, are a useful tool in comparing the efficiency and
economics of various flat-plate solar collectors.
Builders, utilities, and the Department of Energy have joined together on
several occasions to offer tax credits and utility rebates to encourage the
use of solar hot water for residential and commercial projects.