Unit Piping
24 CG-SVX038A-EN
Low Suction Temperature and Pressure Cutouts/
Percent Glycol Recommendations
Tab le 9 shows the low suction temperature and pressure
cutouts for different glycol levels.
Additional glycol beyond the recommendations will
adversely affect unit performance. The unit efficiency will
be reduced and the saturated evaporator temperature will
be reduced.
For some operating conditions this effect can be
significant.
If additional glycol is used, then use the actual percent
glycol to establish the Low and Unsafe refrigerant suction
pressure cutout set points.
Table 9. Minimum recommended setpoints
Ethylene Glycol/Water Propylene Glycol/Water
Glycol
%
(By
Mass)
Solution
Freeze
Point
(°F)
LOW
SUCTION
(a)
(psig)
UNSAFE
SUCT
(b)
(psig)
FREEZE
(c)(d)
(°F)
CORE FREEZE
(e)
(°F)
Glycol
%
(By
Mass)
Solution
Freeze
Point
(°F)
LOW
SUCTION
(a)
(psig)
UNSAFE
SUCT
(b)
(psig)
FREEZE
(c)(d)
(°F)
CORE FREEZE
(e)
(°F)
0
2
4
32.0
30.9
29.9
101.12
98.87
96.86
71.58
69.79
68.18
38.0
36.9
35.9
0
2
4
32.0
30.9
29.7
101.12
98.87
96.46
71.58
69.79
67.86
38.0
36.9
35.7
5
6
8
29.4
28.8
27.5
95.86
94.67
92.13
67.39
66.44
64.42
35.4
34.8
33.5
5
6
8
29.1
28.5
27.3
95.26
94.08
91.75
66.91
65.97
64.12
35.1
34.5
33.3
10
12
14
26.2
24.6
23.0
89.64
86.63
83.69
62.44
60.06
57.73
32.2
30.6
29.0
10
12
14
26.1
24.8
23.6
89.45
87.00
84.78
62.29
60.35
58.60
32.1
30.8
29.6
15
16
18
22.2
21.3
19.6
82.24
80.63
77.65
56.59
55.32
52.98
28.2
27.3
25.6
15
16
18
22.9
22.1
20.7
83.51
82.0
6
79.57
57.59
56.45
54.49
28.9
28.1
26.7
20
22
24
17.9
15.9
13.7
74.75
71.42
67.86
50.69
48.08
45.30
23.9
21.9
19.7
20
22
24
19.2
17.5
15.6
76.96
74.07
70.92
52.43
50.16
47.69
25.2
23.5
21.6
25
26
28
12.7
11.4
9.2
66.28
64.27
60.95
44.07
42.50
39.91
18.7
17.4
15.2
25
26
28
14.6
13.7
11.5
69.30
67.86
64.42
46.42
45.30
42.62
20.6
19.7
17.5
30
32
34
6.7
4.2
1.4
60.65
60.65
60.65
39.68
39.68
39.68
15.0
15.0
15.0
30
32
34
9.2
6.6
3.9
60.95
60.65
60.65
39.91
39.68
39.68
15.2
15.0
15.0
35
36
38
-0.2
-1.5
-4.6
60.65
60.65
60.65
39.68
39.68
39.68
15.0
15.0
15.0
35
36
38
2.5
0.8
-2.5
60.6
5
60.65
60.65
39.68
39.68
39.68
15.0
15.0
15.0
40
42
44
-8.1
-11.7
-15.5
60.65
60.65
60.65
39.68
39.68
39.68
15.0
15.0
15.0
40
42
44
-6.0
-9.8
-14.0
60.65
60.65
60.65
39.68
39.68
39.68
15.0
15.0
15.0
45
46
48
-17.6
-19.7
-24.0
60.65
60.65
60.65
39.68
39.68
39.68
15.0
15.0
15.0
45
46
48
-16.1
-18.3
-23.1
60.65
60.65
60.65
39.68
39.68
39.68
15.0
15.0
15.0
50 -28.9 60.65 39.68 15.0 50 -28.3 60.65 39.68 15.0
(a) “LOW SUCTION” refers to the low suction pressure cutout.
(b)“UNSAFE SUCT” refers to the unsafe suction pressure cutout.
(c) “FREEZE” refers to the low leaving fluid temperature cutout.
(d)The minimum leaving fluid temperature set point, “CW OUT TRGT,” should not be less than 5°F above the low fluid temperature cutout, “FREEZE,” and
the core fluid temperature cutout, “CORE FREEZE.”
(e) “CORE FREEZE” refers to the evaporator core fluid temperature cutout.
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