Install Instructions

IM-PR 566442 1114 (Design Manual)
46
Glycol
(% by volume)
0% 10% 20% 30% 40% 50%
Ethylene 32 25 16 3 -12 -35
Propylene 32 26 18 8 -7 -28
Table 1-14 Freezing point (°F) of glycol solutions,
based on type and percent by volume.
NOTE:
Automotive antifreeze is not recommended, as
the silicates in automotive antifreeze can coat and
foul heat transfer surfaces, reducing performance;
further, automotive antifreeze may not be compatible
with PEX products. Please contact Viega Technical
Support for approved antifreeze solutions.
GPM =
(
Total Design Heat Load (Btu/hr)
∆T • 8.01 • C
p
• P
)
where
∆T is the system temperature drop from supply
to return.
Cp is the specific heat of the fluid, taken at the
average of the supply and return temperature
(Btu/lb/°F). For the specific heat of glycol solutions,
see Table 1-15 for propylene glycol or Table 1-17
for ethylene glycol.
8.01 is a constant to convert between units
P is the density of the fluid, taken at the average
of the supply and return temperature (lbs/ft³). For
the density of glycol solutions, see Table 1-16 for
propylene glycol or Table 1-18 for ethylene glycol.
1.11 Freeze protection – glycol mixtures
If freeze protection is required for your system (e.g.,
snow melting, turf conditioning, seasonal use, some
agricultural and commercial applications, etc.), then
use this section to determine the percent of glycol
to specify as well as the effects of the glycol on
system specifications.
1.11.1 Selecting the percent glycol mixture
Use Table 1-14 to determine the percent glycol
solution necessary based on the freezing point
of the solution as a function of the percent glycol
by volume.
1.11.2 Glycol system effects
Although glycol solutions have higher densities than
water solutions, they have a lower specific heat,
which means that to achieve equivalent Btu output,
these systems must operate at a higher flow rate
and pressure drop than would a system with the
same piping layout that uses 100% water as the
working fluid. The higher flow rate and pressure
drop must be taken into account when sizing the
glycol system’s circulator pumps and piping.
1.11.2.1 Glycol flow rate
To estimate the flow rate required in the glycol
loop, you may use the following equation: