10 AGL_HP_VS_YHV2P_E_Rev0
2.4.4 Discharge line temperature control mode
In the lower part of the envelope (Control Suction Superheat) shown below the suction gas at the
compressor inlet has to be superheated without liquid droplets. For superheat requirements please
also refer to chapter 2.4.3 "Application limits & operating envelopes".
Figure 9: Schematics of expansion valve control mode
In the upper part of the envelope (DLT Control) with operation at low evaporating and high
condensing with superheat control mode, the discharge temperature will exceed the limit of 125 °C
inside the application envelope – also see chapter 3.3 "Suction line accumulators". In this area, the
expansion valve of the evaporator is to be controlled not by superheat but by the discharge line
temperature so that some liquid droplets return to the compressor to cool it down. The discharge line
temperature DLT must be controlled to stay between minimum 115 °C and maximum 125 °C.
The move from superheat control to DLT control is demand-driven by the discharge line temperature.
In the transition phase DLT control and superheat control have to be balanced by the system
controller. The superheat at compressor inlet should be reduced gradually to 0 K. As the demand to
move to DLT control depends, eg, on system design such as compressor insulation and ambient
temperature, there is no specified line at which this will happen.
2.4.5 Design features
The variable speed scroll YHV*2P has a number of design features that improve efficiency and
reliability.
All the YVH* models are equipped with a positive displacement oil pump to ensure an adequate
supply of oil to the bearing system throughout the operating speed range.
The motor in the variable speed scroll is a three-phase, brushless permanent magnet (BPM) design
coupled with a rotor embedded with high energy magnets. The input voltage is a series of +DC pulses,
spaced in time to create an alternating current frequency.
2.4.6 Oil recovery
For oil return the exact parameters for an oil recovery cycle need to be evaluated for each system by
oil return tests, as they may differ depending on system application. Please contact
and review with
Application Engineering at Emerson for any
desired changes to this oil recovery cycle requirements.
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