P.20
SUNSIPHON
missioning the system to ensure that there are no
leaks in the glycol loop piping and that the HTF has
maintained the proper level. The normal operating
pressure of the collector and heat exchanger loop is
approximately 0 to 10 psig.
Your SunSiphon solar water heating system must be
charged and the fluid quality maintained by an expe-
rienced contractor. If the system is drained during
the winter, or you notice a significant drop in collec-
tor loop pressure, contact your installation contrac-
tor immediately for service. The propylene glycol
HTF provides the freeze protection for your system
and must be properly maintained. An experienced
contractor should periodically check the HTF fluid
quality.
4.8 Heat Transfer Fluid (HTF)
The specified HTF is Dowfrost HD, or approved
equal. To ensure maximum effectiveness for cor-
rosion protection, the glycol inhibitor package is
designed for a minimum 25-30 percent concentration
of glycol in water. Table 5 shows the concentrations
of Dowfrost HD required to provide freeze and burst
protection at various temperatures. Use the mixture
most appropriate for your climate. Do not use a
higher glycol to water concentration than necessary,
as this will adversely impact the relative heat transfer
efficiency of the solution.
Generally, for an extended margin of protection, you
should select a temperature that is at least 5°F lower
than the expected lowest ambient temperature. These
figures are examples only and should not be regarded
as specifications. As use conditions are not within our
control, neither SunEarth nor Dow Chemical guaran-
tees that freeze damage may not occur at temperatures
other than shown.
Water used to dilute the HTF must meet certain mini-
mum standards for purity. Impurities in the dilution
water can increase metal corrosion, reduce the effec-
tiveness of corrosion inhibitors, increase inhibitor
depletion rate, and cause the formation of scale and
other deposits on the heat exchanger’s internal heat
transfer surfaces.
Distilled or deionized water shall be used.
Propylene glycol can degrade over time. The process
of degradation is accelerated in presence of oxygen
and/or heat. We strongly encourage you to establish a
preventative maintenance schedule with your installa-
tion contractor. The HTF pH level must be maintained
between 8 and 10 in order to prevent glycol oxidation
and corrosion of the collector piping. SunEarth’s col-
lector warranty specifically excludes freeze damage
for any reason and absorber plate damage resulting
from the oxidation of the propylene glycol HTF.
4.9 Pipe Insulation Requirements
The cold water manifold running between the solar
storage tank and the bottom of the collector array
should not be insulated.
The hot water manifold piping between the solar col-
lectors and the solar storage tank must be insulated
with a high quality flexible closed cell insulation to
minimize heat loss.
All exterior and attic piping between the SunSiphon
and the rest of the home’s plumbing system also must
be properly insulated. The insulation shall have a
maximum operating temperature of 220oF or higher.
The wall thickness of all required pipe insulation
should not be less than 3/4”. A 1” wall thickness is
required in all areas prone to annual hard freeze con-
ditions. When it comes to pipe insulation the rule is
simple: thicker is better.
To the extent possible, slide the insulation material
over the pipe without cutting or taping. All butt joints
must be sealed with contact adhesive. The use of rigid
polyethylene pipe insulation is prohibited. The tem-
peratures generated by your collector in the summer
months or under stagnation conditions can melt this
type of material.
Any above ground exterior pipe insulation is subject
to UV degradation and must be wrapped with foil tape
or painted with two coats of high quality water-based
acrylic resin coating as supplied by the insulation
manufacturer.
In two tank systems the 3/4” cold water supply line
to the back-up water heater must be insulated with
minimum 7/8” X 1/2” pipe insulation to a minimum
distance of 5’ behind the storage tank, or to the wall
if closer than 5’.
4.10 Supplemental Water Heater Insulation
Conventional back-up electric water heaters have
insulation values between R-12 and R-20. The R
value expresses the thermal resistance of the tank
insulation. The higher the “R-value” value the more
effective the insulation material is at preventing heat
loss.
