Refrigerant Charge Limit; Reversible Heat Pump Systems; Minimum Sump Superheat; Preventing Liquid Ood Back - Danfoss VRJ Application Manuallines

Application Guidelines

Refrigerant charge limit

Reversible heat pump
systems

Minimum sump superheat

Preventing liquid ood back

16
AB141686422149en-US0401
System design recommendations
Scroll compressors can tolerate liquid refrigerant
up to a certain extend without major problems.
However, excessive liquid refrigerant in the
compressor is always unfavourable for service
life. Besides, the installation cooling capacity may
be reduced because of the evaporation taking
place in the compressor and/or the suction line
Transients are likely to occur in reversible heat
pump systems, i.e. a changeover cycle from
cooling to heating, defrost or low-load short
cycles. These transient modes of operation may
lead to liquid refrigerant carryover (or ood
back) or excessively wet refrigerant return
conditions. As such, reversible cycle applications
The minimum sump temperature is in the range
from 10°F to 30°F above saturated suction
40
35
30
25
20
15
10
5
0
-10 0
Danfoss recommends the use of an electronic
expansion valve for all air conditioning and heat
pump applications with VRJ compressors. An
EXV has two key bene ts: it provides modulating
control of the system under varying load
conditions, and it protects the compressors from
ood back during adverse running conditions.
instead of the evaporator. System design must be
such that the amount of liquid refrigerant in the
compressor is limited. In this respect, follow the
guidelines given in the section: "Essential piping
design recommendations" in priority.
require speci c precautions for ensuring a long
compressor life and satisfactory operating
characteristics. Speci c tests for repetitive ood
back are required to con rm whether or not
special system design considerations should be
considered.
temperature. Refer to the ood back test criteria.
Floodback requirement
Acceptable
10 20
Saturated suction temp. °F
Exceptions to the use of EXV's with Danfoss
VRJ must be approved by Danfoss application
engineering.
Unacceptable
30 40 50 55