22
C6.2.15/0815/E
operating outside the operating envelope published by Emerson Climate Technologies, whatever
the climatic conditions and the heating demand.
However, in some extreme cases
– for example loss of system charge, extreme heat transfer
restriction at the evaporator, any defect or blocked flow control component (expansion valve,
screens...)
– the evaporating conditions may be such that the compressor will tend to operate
outside the published operating envelope limits. All those conditions may starve the compressor
in refrigerant and oil, and may result in compressor failure.
Therefore, Emerson Climate Technologies strongly recommends the installation of a low
pressure limiter in the suction line that will shut down the compressor when it operates outside
the published envelope limits.
4.4 Discharge temperature protection
Internal discharge temperatures can reach unacceptable values under some extreme operating
conditions (such as operation outside the approved application limits, improper control operation
or loss of refrigerant injection charge). This could cause compressor damage.
Discharge gas temperature protection is required for any application with Copeland brand
compressors in order to guarantee positive compressor protection. This protection must not be
used as an operating envelope controller but as a safety device.
For some digital scroll compressors, an internal discharge temperature protector is included in
the compressor standard delivery. Otherwise an external discharge temperature protector must
be installed.
Models ZRD42K* to ZRD48K*, ZRD94K*, ZRD125K* and ZPD34K* to ZPD182K* do not have
internal temperature protection and therefore require an external thermostat or a discharge
temperature sensor (NTC thermistor) mounted as close as possible to the discharge fitting in
order for the Digital Scroll controller to operate properly. For best response the sensor should be
insulated. Emerson Climate Technologies provides the correct thermostat and the NTC
thermistor as accessories to fit the discharge line of these compressors.
Models ZRD61K* to ZRD81K* come with an internal discharge temperature sensor (NTC
thermistor) that is embedded in the top cap of the compressor. The output of the NTC thermistor
is used in the protection module of the Digital Scroll controller.
The resistance curve for the NTC thermistor is provided in
Table 5
below:
Temperature
(°C)
Resistance
(kOhm)
Temperature
(°C)
Resistance
(kOhm)
-40
2889.60
75
12.73
-35
2087.22
80
10.79
-30
1522.20
85
9.20
-25
1121.44
90
7.87
-20
834.72
95
6.77
-15
627.28
100
5.85
-10
475.74
105
5.09
-5
363.99
110
4.45
0
280.82
115
3.87
5
218.41
120
3.35
10
171.17
125
2.92
15
135.14
130
2.58
20
107.44
135
2.28
25
86.00
140
2.02
30
69.28
145
1.80
35
56.16
150
1.59
40
45.81
155
1.39
45
37.58
160
1.25
50
30.99
165
1.12
55
25.68
170
1.01
60
21.40
175
0.92
65
17.91
180
0.83
70
15.07
Table 5: Digital Scroll thermistor temperature / resistance values
