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Types of Solar Hot Water
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ACTIVE SYSTEMS (Pump)
 Direct
Open Loop (or Direct Domestic Hot Water Open Loop)
- Typical method used in what is called an active
open-loop Solar Domestic Hot Water (SDHW)* system; water
is heated by flowing directly through solar hot water “collectors”.
- Cold water taken from the bottom of the solar storage
tank, circulated through the solar collectors, and returned
to
the middle of the tank with a low energy circulator.
- When
a faucet is turned on, the solar heated water in the
solar storage tank feeds the water heater. If it is a sunny
day, the water heater will not turn on and the solar
heated
water will pass through it to the faucets.
Closed-Loop Glycol
- Glycol, a food-grade antifreeze, is circulated
through the hot water collectors in a closed loop system.
- The
glycol transfers its heat to the water through a heat exchanger(s);
multiple heating loops are possible
- Glycol is held under
low pressure throughout the system; lower-power pumping
is required (as the collectors are always full
of glycol).
- As with any “active” SDHW system, when the
collector temperature is 8 degrees higher than the tank
temperature;
pumping is activated. When the solar storage tank has reached
its set temperature, usually around 180 degrees, pumping
is stopped.
- Utilizes less expensive cast iron pump w/ no
pump corrosion problems.
- Two pumps, one on either
side of the heat exchanger, are needed for this application.
Drain-Back (or Closed Loop Water)
- A closed-loop active system that lifts water,
with use of a pump, from an unpressurized solar storage
tank through the collectors.
- Water drains back into the
solar storage tank when not pumping leaving the collectors
on the roof empty to prevent
freezing.
- A temperature differential set point is established
between the collector temperature and the storage tank
temperature;
water pumping is activated when the set point is reached.
PASSIVE SYSTEMS (NO PUMP)
Thermal Siphon
- Tank is placed above collectors, typically on the roof,
to allow the solar heat to rise into the tank without the
use of a pump.
- The tank adds significant weight to the roof
and may require structural upgrades.
Batch Heaters
- The storage tank is the collector.
- Least efficient, lowest
maintenance of all solar thermal systems.
- Heat is gained
during the day, but lost at night.
- The collector/tank
adds significant weight to the roof and may require structural
upgrades.
POOL SYSTEMS
Drain-Back Pool
- Pool water is circulated
directly through the collectors.
- Water drains back into
the pool when not pumping in order to prevent freezing.
- This
system uses the existing pool pump along with a controller
that is programmed to activate a 3-way valve that diverts
pool water to the collectors when solar heat is available.
- When
the desired pool temperature is reached, the solar collectors
are drained.
Closed-Loop Pool
- Glycol, a food-grade antifreeze, is circulated
through the collectors and the solar heat is transferred
to the pool
water through a heat exchanger.
- The solar pump is turned
on when there is solar heat available.
- When the desired
pool temperature is reached, the solar pump is turned
off.
To learn more about the features and benefits
of Solar Thermal, please go to: Solar
Hot Water Benefits
Please phone a Sun Light & Power representative at
(510) 845-2997
for more information or to schedule a
consultation.
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