Hanbell RC2-AVI Series, Руководство пользователя

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6
V
P d
P d '
V
P d < P d '
P
P d , P d '
V
P d = P d '
P
P d > P d '
P d '
P d
P
2.8 Volume ratio (Vi)
The volume ratio (Vi) of the compressor can be defined as the ratio of suction volume to discharge volume in the
compressor. The smaller the concavity of slide valve in the discharge end, the larger the volume ratio. The volume ratio
directly affects the internal compression ratio (Pi). Low Vi corresponds to low Pi and high Vi corresponds to high Pi. In
the equation below, in order to prevent over or under compression, the system compression ratio (CR) should be equal
to compressor’s internal compression ratio (Pi). Please refer to P-V (pressure – volume) diagram below to figure out
this relation. Following the concept above, if the Vi varies with working condition, there will be less loss of work. High
efficiency can be achieved. In RC2-AVI series, Vi 1.6-2.0-2.4 or Vi 2.4-3.0-3.5 is provided to correspond to various
working condition.
CR = Pd/Ps
Pi = Vi
k
Vi = Vs/Vd
Where: CR: system compression ratio Pi: internal compression ratio
Vi: internal volume ratio Pd: system pressure (absolute pressure)
Pd’: discharge pressure (absolute pressure) Ps: suction pressure (absolute pressure)
Vs: suction volume Vd: discharge volume K: refrigerant specific heat ratio
In RC2-AVI, compression volume is adjustable through two solenoid valves. The mechanism improves the power
efficiency under different working conditions, especially when the compressor runs at part load. The control logic is
based on the equations belows
Vi = Vs/Vd; Vs: suction volume, Vd: discharge volume
(Vi)
k
= Pd/Ps; Ps: suction pressure (absolute pressure), Pd: system pressure (absolute pressure) k: coefficient
Figure 2:4: Mechanism of variable Vi
In water cooled and air cooled system, the volume ratio can be set at 1.6, 2.0, 2.4 and 2.4, 3.0, 3.5, respectively.
Following tables show the control logic of solenoid valve under different Vi:
Under compression (CR > Pi) Over compression (CR < Pi) CR = Pi
Loss of work
Loss of work
1 2
3
4
Ps
1 2
3
4
Ps
Ps
1
2
3
4
Figure 2.3: P-V Diagram