Discharge Gas Thermostat - Danfoss VZH028 Application Manuallines

Application Guidelines

Discharge gas thermostat

26
FRCC.PC.034.A2.02
Operating conditions
Discharge gas temperature (DGT) protection
is required if the high and low pressure switch
settings do not protect the compressor against
operations beyond its specific application
envelope. Please refer to the examples below,
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
-40 -35 -30
Example 1 (R410A, SH = 6 K)
LP switch setting:
LP1 = 3.3 bar (g) (-15.5°C)
HP switch setting:
HP1 = 38 bar (g) (62°C)
Risk of operation beyond the application envelope.
DGT protection required.
The discharge gas temperature must not exceed
135°C.
A discharge gas temperature protection device
must be installed on all heat pumps. In reversible
air-to-air and air-to-water heat pumps, the
discharge temperature must be monitored
during development test by the equipment
manufacturer.
The compressor must not be allowed to cycle
on the discharge gas thermostat. Continuous
operations beyond the compressor's operating
range will cause serious damage to the
compressor.
VZH028-044 can install a discharge sensor/ dome
sensor at the top of shell through a bracket and
the sensor has to been connected and controlled
by OEM controller. By installing it at the top of
shell, the discharge sensor can monitor discharge
temperature and work with OEM controller to
limit discharge temperature within 135°C, also
could observe extreme high temperature caused
which illustrate where DGT protection is required
(Ex. 1) and where it is not (Ex. 2). Please notice the
envelope boundaries change based on different
speed limits.
Example 1
Example 2
LP1 LP2
-25 -20 -15 -10 -5 0
Evaporating temperature (°C)
Example 2 (R410A, SH = 6 K)
LP switch setting:
LP2 = 4.6 bar (g) (-10.5°C)
HP switch setting:
HP2 = 31 bar (g) (52°C)
No risk of operation beyond the application envelope.
No DGT protection required.
by reverse rotation or loss of charge. A customer
might select NTC thermistor, 10KOhm@25°C type
from "TOD Company" and this type of sensor
could be fit into VZH top shell directly. However,
if OEM would like to use their own thermostat,
the thermostat is recommended to install on
top of the shell for monitoring high discharge
temperature and reverse rotation as well as
loss of charge. The thermostat could also be
attached to the discharge line within 150 mm
from the compressor discharge port and must
be thermally insulated and tightly fixed to the
pipe. Then another sensor should be installed at
top of shell to monitor loss of charge and reverse
rotation.
Bracket at the shell top
Single compressors
HP1
HP2
R410A
5 10 15 20 25
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