Discharge Temperature Protection; High And Low Pressure Protection - Danfoss SH090 Application Manuallines

Application Guidelines
Discharge temperature
protection
High and low pressure
protection
High pressure
Operating conditions
The discharge gas temperature must not exceed
135°C.
SH485 includes a PTC sensor located in the
fixed scroll and wired in series with the motor
PTC thermistor chain. Excessive discharge
temperature will result in electronic module
output relay to trip.
For SH090 to 380, 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, which illustrate
where DGT protection is required (Ex.1) and
where it is not (Ex.2).
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.
Example 1 (R410A, SH = 11 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 applica-
tion envelope.
DGT protection required.
Example 2 (R410A, SH = 11 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.
A high-pressure (HP) safety switch is required to
shut down the compressor should the discharge
pressure exceed the values shown in the table
section "System pressure test". The high-pressure
switch can be set to lower values depending on
the application and ambient conditions. The HP
Discharge line
The discharge gas thermostat accessory kit (code
7750009) includes all components required for
installation as shown above. The thermostat must
be attached to the discharge line within 150 mm
from the compressor discharge port and must be
thermally insulated and tightly fixed on the pipe.
The DGT should be set to open at a discharge gas
temperature of 135°C.
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!
70
65
60
55
50
45
40
35
LP1 LP2
30
25
20
15
10
-30 -25 -20 -15
-10
Evap. temp. (°C)
switch must either be placed in a lockout circuit
or consist of a manual reset device to prevent
cycling around the high-pressure limit. If a
discharge valve is used, the HP switch must be
connected to the service valve gauge port, which
must not be isolated.
Thermostat
Insulation
Bracket
HP1
Example 1
HP2
Example 2
R410A
-5 0 5 10 15
AB243586442172en-001301
20
25