Solar hot
water pump
Solar hot water heater pumps
A solar hot water pump is an essential component
of an active
solar water heater. Water pumps are the moving components
that circulate either the domestic water or the heat transfer fluid
throughout the solar powered water heating system.
Quality solar water pumps (also referred
to as water circulators) should effectively and efficiently
distribute fluid for several years without fail.
When choosing a pump for a solar hot water heater, there are three
major considerations to make; the materials used, the pump head and
fluid flow rate and the pumps' power source.
Components of a solar hot water pump
These hot water circulators are essentially made
up of three internal components; the motor, the impeller and the
impeller housing.
Pump
Motor
The water pump motor is either AC
powered or DC powered, and these pumps are activated by either a differential
thermostat control
or a PV
module.
Pump
Impeller
The solar pump impeller functions much like a
circulating fan. The pump motor, once activated, spins the impeller and
the impeller in return thrust the fluid in the loop forward and
through the pump housing unit.
Impeller
Housing
The solar water pumps' impeller housing
is
simply the area where the fluid enters before it's circulated
through the water heaters' pipes or solar loop.
Materials used
The material the solar hot water pump is made of
can
very well determine how long it will last. Many inexpensive solar hot
water pumps are made out of cast iron, and rust is the biggest
long term enemy of cast iron.
It's important to note that in open
loop or indirect
solar water heater designs, using a water pump with a cast
iron impeller housing unit is not advised. Oxygen breeds rust and in
open loop systems, oxygen is constantly introduced throughout the solar
loop.
Solar hot
water pumps with stainless steel, bronze and even plastic
impeller
housing units offer considerably more rust resistance than models with
cast iron.
Pump head and flow rate
In all active solar water heaters,
the panel or collector is mounted well above the storage
tank. Solar hot water pumps are required to overcome
this elevation difference . In order to overcome gravity, the water
pump
must generate enough pressure to circulate the fluid upward as well as
through
the system.
And it must do so efficiently and effectively
since the flow rate through the solar water panel and the flow rate
through the heat exchanger are both important to the water heaters'
overall
performance.
The pressure, vertical lift or vertical discharge
a
pump provides is referred to as pump head. The higher the head the more
powerful the solar hot water pump.
Feet
of Head
The pressure a pump provides is measured
in distance, or feet. Manufacturers often times classify they're hot
water circulators using terms such as high head, medium head
or low head. Such classifications serve as feet
of head ranges.
Cut
Off Head
The highest point, in terms of feet, at which a
solar hot water pump will provide vertical lift is commonly referred to
as the pumps cut off head.
GPM
at Head
GPM, or gallons per minute, at head is a
classification that determines the fluid volume or flow rate to expect
from a solar powered pump at a certain pump head or vertical lift.
High Head
Pumps
Medium Head Pumps
-
Ideal for
closed loop solar hot water heaters, especially those with moderately
sized pipe runs in the loop.
-
Can be used
in drainback designs with small sized pipe runs in the loop.
Low Head Pumps
More on pump head
It's important to
note, when determining how
powerful a pump a solar hot water heater will require, one must always
take into account the vertical length of the plumbing pipes within the
loop.
Solar hot water
heaters with large vertical pipe runs can be retro fitted with two or
more medium head pumps, but the solar water pumps must be
properly spaced out within the loop in order to achieve a suitable
fluid flow rate and overall head.
Warning
Drainback solar hot water heaters are designed not
to have fluid in the loop when the system is idle. So these systems
almost always require a high head solar hot water pump, because there
must be enough vertical lift to collect the fluid from the drainback
tank
before recirculating the fluid through the loop.
It's not advised to install two (or more) medium
or low head pumps in drainback systems, particularly if freezing is
even a
moderate concern. If one solar hot water pump were to fail, the
remaining
functioning pump will likely be unable to provide a suitable vertical
discharge and throughout the loop.
And in the cold season, the undrained fluid
remaining
in the loop can eventually freeze. This would seriously
compromise the entire function of the hot water heater, this could even
cause the pipes within the loop to eventually burst.
Power source
Another important consideration to make when
selecting a solar hot water pump is determining a suitable power
source. There are two options for powering your solar water
pump; AC and DC.
AC
Solar Water Pumps
AC pumps use the alternating current that's
provided by a home's or businesses existing electrical wiring. These
hot water pumps utilize just a small amount of this electricity to
circulate fluid. The
overwhelming majority of AC models use 120 volts. A differential
thermostat controller
will be required to operate the pump.
DC
Solar Water
Pumps
DC water pumps use direct current to
power the motor. PV
modules are used to harness solar electricity, and
this energy activates the hot water pumps' motor.
There are two types of DC solar water pumps; brush and brushless.
Brush models use carbon brushes to assist the
movement of the impeller. These brushes are prone to wear and tear,
potentially causing frequent replacement.
Brushless models rely only on the motor to spin
the impeller. Brushless DC solar hot water pumps generally last longer
and are known to activate quicker than DC pumps with brushes.
More on solar
hot water heaters
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