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© SOLARHOT 2006-2009
If you are nstallng a glycol system, or a dranback/open loop system wth a relatvely hgh lmt on the
storage tank (170
0
F+), you wll need to use rubberzed nsulaton for nsulatng the ppes. The more
common polyethylene nsulaton can’t handle the hgh heat and wll melt. If you use a lower hgh lmt
on your tank you can use the less expensive insulation. If you use a 150
0
F hgh lmt on your open
loop or drainback system you can save money by using Pex piping and polyethylene insulation. When
the insulation is exposed to the sunlight, you need to provide jacketing for the insulation. Visit your
local HVAC supply house and ask what sze and styles of jacketng they have for ther nsulaton. If the
exterior insulation is not protected from U.V. it will disintegrate over time.
It is also a good idea to make sure that you have extra insulation on the storage tank(s) as well. You
can purchase a water heater blanket from the hardware store for $30. I would also recommend that you
insulate about 4 feet of the cold line coming in to the storage tank. By taking these extra precautions,
you wll nsure that you keep as much of the solar energy as possble.
Chapter 7: Temperature Sensors and Control Wires
All solar hot water systems should have a dfferental control to turn the pumps on and off. A dfferental
control uses a temperature sensor mounted on the collector as well as a temperature sensor mounted
on the bottom of the tank. The control detects when the collectors are hotter than the storage tank and
turns the pumps on to circulate the heat transfer fluid through the collectors to harness the heat that has
been ganed. When the storage tank temperature matches or s greater than the collector temperature,
the pumps are turned off. The dfferental control s the brans of the solar hot water system.
In order for a differential control to work, it has two sensors wired to the control. The first sensor (the
collector sensor) should be attached to the ppe leadng out of the top of the collector array. Use a strap
clamp to secure the sensor to the ppe. Be sure to provde adequate nsulaton around the sensor and
ppe to allow an accurate readng of the temperature n the collectors. The second sensor should be
stuffed under the nsulaton at the base of the tank. If you are usng a standard 80 gallon, two element
electrc water heater as your storage tank/back-up heater, then the tank bottom sensor can be mounted
under the nsulaton under the lower element tucked between the nsulaton and the tank wall.
You should use 18/2-shelded wre wth a hgh temperature jacket for runnng the sensor wre to the
dfferental controller. Never run control wre wthn 12” and parallel, or n the same wre way as power
wres. If you have to pass power wres, run the control wre perpendcular to the power wre as you cross
ther paths. By followng ths rule, you should avod ntermttent problems wth the control temperatures
sensed.
Chapter 8: Pumps
Pumps circulate the heat transfer fluid through the collectors and the heat exchanger. Depending on
whether you nstall a sngle pump or dual pump system you wll requre a small amount of knowledge
about pumps to make an appropriate selection. If your pump is exposed to a supply of air, you should
use bronze pumps rather than cast ron. (Note: f your pump s on the storage tank sde of the loop t
will be regularly exposed to air entrained in the water coming from the city or your well. If your pump is
on the collector side of a freeze protected system you can use a cast iron pump and flanges). Bronze
pumps are not necessary if the pump is not regularly exposed to air although you may desire one for
overall pump body longevty. The pump that you requre s also based on the head requrements of
your system.
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