Quantech QWC3050T-200T, Installation Operation & Maintenance

Page: 45 / 186

SECTION 5 – TECHNICAL DATA
FORM QWC3-NM1
ISSUE DATE:11/20/2020
QUANTECH
45
5
ETHYLENE AND PROPOLYNE GLYCOL
CORRECTION FACTORS
Evaporator Pressure Drop
When using evaporator pressure drop to determine
flow, error may result due to actual pressure drops that
are below the published data. In all cases, the published
values are worst case values. Errors of 10 to 25% be-
low published values are not uncommon due to manu-
facturing differences. When attempting to operate with
flow near the high end of the pressure drop curve, al-
ways use a flowmeter to avoid excessive flow through
the evaporator, which will cause damage and prema-
ture failure.
Table 5 on page 45
lists glycol correction factors
that should be used in conjunction with pressure drops.
Pressure drop will increase at a given flow rate as the
glycol concentration is increased.
TABLE 5 - ETHYLENE AND PROPOLYNE GLYCOL
CORRECTION FACTORS
ETHYLENE GLYCOL
%
WEIGHT TONS
COMPR
KW
GPM PRESS
DROP
FREEZE
PT
10 0.993 1.002 1.029 1.095 26
20 0.980 1.004 1.040 1.191 18
30 0.964 1.007 1.055 1.302 7
40 0.945 1.009 1.071 1.435 -8
50 0.922 1.013 1.091 1.599 -29
PROPYLENE GLYCOL
%
WEIGHT TONS
COMPR
KW
GPM PRESS
DROP
FREEZE
PT
10 0.985 1.002 1.003 1.078 26
20 0.968 1.005 1.000 1.157 19
30 0.937 1.008 0.992 1.266 9
40 0.898 1.012 0.982 1.414 -6
50 0.862 1.019 0.985 1.605 -28
TABLE 6 - RECOMMENDED GLYCOL SOLUTION
STRENGTHS
ETHYLENE
GLYCOL
LCHLT °C
PROPYLENE
GLYCOL
CONCENTRATION
% W/W
CONCENTRATION
% W/W
6 5 5
4 12 13
2 18 20
0 23 25
-2 28 30
-4 32 34
-6 35 38
Pressure drop across the evaporator should only be
used as a guide for setting up flow. When very accu-
rate flows need to be measured, use a flowmeter. When
gauges are used to measure pressure drop and calculate
flow, always use a single gauge to measure the pressure
drop at both inlet and outlet of the evaporator to avoid
introducing more error into the measurement resulting
from the use of two gauges.
The cooler and condenser design allows
for an increase in pressure drop of up to
15% above the design value given. Debris
in the water may also cause additional
pressure drop.
When using glycol solutions, pressure
drops are higher than with water. Spe-
cial care must be taken not to exceed the
maximum allowed.
ETHYLENE GLYCOL
PROPYLENE GLYCOL
B
A
C
B
A
C
A = Correction Factor B = Temperature
C = Concentration % Through Cooler
LD06934
FIGURE 19 - GLYCOL SOLUTION STRENGTHS