24
IMM AGS-2
Note:
The procedure below does not specify the type of glycol. Use the derate factors
found in Table 14 for corrections when using propylene glycol and those in Table 15 for
ethylene glycol.
1.
Capacity
- Cooling capacity is reduced from that with plain water. To find the
reduced value, multiply the chiller’s water system tonnage by the capacity correction
factor to find the chiller’s capacity when using glycol.
2.
Flow
- To determine flow (or Delta-T) knowing Delta-T (or flow) and capacity:
( ) (
) (
)
T
Delta
factor
flow
tons
GPM
−
=
24
3.
Pressure drop
- To determine pressure drop through the evaporator when using
glycol, enter the water pressure drop curve at the water flow rate. Multiply the water
pressure drop found there by the "PD" factor to obtain corrected glycol pressure drop.
4.
Power
- To determine glycol system kW, multiply the water system kW by the factor
designated "Power".
Test coolant with a clean, accurate glycol solution hydrometer (similar to that found in
service stations) to determine the freezing point. Obtain percent glycol from the freezing
point table below. On glycol applications, the supplier normally recommends that a
minimum of 25% solution by weight be used for protection against corrosion or that
additional inhibitors should be employed.
NOTE
: Do not use automotive grade antifreeze. Industrial grade glycols must be used.
Automotive antifreeze contains inhibitors that will cause plating on the copper tubes within
the chiller evaporator. The type and handling of glycol used must be consistent with local
codes.
Water Flow and Pressure Drop
Adjust the chilled water flow through the evaporator to meet specified conditions. The
flow rates must fall between the minimum and maximum values shown in the table on the
following page. Flow rates below the minimum values shown will result in laminar flow
that will reduce efficiency, cause erratic operation of the electronic expansion valve and
could cause low temperature cutouts. On the other hand, flow rates exceeding the
maximum values shown can cause erosion on the evaporator water connections and tubes.
Measure the chilled water pressure drop through the evaporator at field-installed pressure
taps. It is important not to include valve or strainer pressure drops in these readings.
Table 14, Ethylene Glycol Factors
Freeze
Point
%
E.G.
o
F
o
C
Capacity Power
Flow
PD
10
26
-3.3
0.996
0.998
1.036 1.097
20
18
-7.8
0.988
0.994
1.061 1.219
30
7
-13.9
0.979
0.991
1.092 1.352
40
-7 -21.7
0.969
0.986
1.132 1.532
50
-28 -33.3
0.958
0.981
1.182 1.748
Table 15, Propylene Glycol Factors
Freeze
Point
% P.G.
o
F
o
C
Capacity Power
Flow
PD
10
26 -3.3
0.991
0.996
1.016 1.092
20
19 -7.2
0.981
0.991
1.032 1.195
30
9 -12.8
0.966
0.985
1.056 1.345
40
-5 -20.6
0.947
0.977
1.092 1.544
50
-27 -32.8
0.932
0.969
1.140 1.906
