Install Instructions

103
IM-PR 566442 1114 (Design Manual)
5.5 Selecting the percent glycol mixture
For typical freeze protection applications, Viega
recommends using 40% propylene glycol, though
a higher concentration may be required in your
area. Ethylene glycol is compatible with ViegaPEX
Barrier. Use Table 5-6 to determine the freezing
point of the water/glycol mixture based on percent
glycol by volume.
Glycol%
(by volume)
0% 10% 20% 30% 40% 50%
Ethylene 32 25 16 3 -12 -35
Propylene 32 26 18 8 -7 -28
Table 5-6 Freezing point of the water/glycol mixture
based on percent glycol by volume
NOTE:
Automotive antifreeze is not recommended; the
silicates in automotive antifreeze can coat and
foul heat transfer surfaces and plug the system,
reducing energy efficiency.
5.6 Sizing for flow rate, pressure drop and
expansion
Glycol solutions have higher densities than water
solutions, which means that to achieve equivalent
heat flow, 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.
5.6.1 Glycol flow rate
To estimate the flow rate required in the glycol
loop, you may use the following equation:
GPM =
(
Total Design Heat Load (Btu/hr)
∆T • 8.01 • C
p
• P
)
where
∆T is the system temperature drop from supply
to return.
c
p
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 5-7 for propylene glycol or Table 5-8 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/ft
3
). For
the density of glycol solutions, see Table 5-15 for
propylene glycol or Table 5-16 for ethylene glycol.