User Manual

Use of the MVF661…N as a suction throttle valve
70177
+
–
MVF661...N
Bypass
Typical control range 50...100 %.
Minimum stroke limit control:
To ensure optimum cooling of the compressor,
either a capacity controller must be provided for
the compressor, or a minimum stroke must be set
via the valve electronics.
The minimum stroke can be limited to a maximum of 80 %. At zero load, the minimum
stroke must be sufficient to ensure that the minimum gas velocity in the suction line is >
0.7 m/s and that the compressor is adequately cooled.
As the control valve closes, the evaporating temperature rises and the air-cooling effect
decreases continuously. The electronic control system provides demand-based cooling
without unwanted dehumidification and costly retreatment of the air.
The pressure at the compressor inlet falls and the power consumption of the
compressor is reduced. The energy savings to be anticipated with low loads can be
determined from the compressor selection chart (power consumption at minimum
permissible suction pressure). Compressor energy savings of up to 40 % can be
achieved.
The recommended differential pressure ∆p
v100
across the fully open control valve is
between 0.15 <
∆p
v100
< 0.5 bar.
Application example
Refrigerant R134A; Q
0
= 9.5 kW; t
0
= 4 °C; t
c
= 40 °C;
Differential pressure across MVF661..N: ∆p
v100
= 0.25 bar
In this application example, t
0
, t
c
and ∆p
v100
are to be interpolated.
KS-R134a t
0
= 0 °C t
0
= 10 °C Interpolation at t
0
= 4 °C
0.15 / 20 2.2 2.7 2.2 + [(2.7 – 2.2) x (4 - 0) / (10 - 0)] 2,4
0.15 / 50 1.7 2.1 1.7 + [(2.1 – 1.7) x (4 - 0) / (10 - 0)] 1,9
0.45 / 20 3.6 4.5 3.6 + [(4.5 – 3.6) x (4 - 0) / (10 - 0)] 4,0
0.45 / 50 2.7 3.4 2.7 + [(3.4 – 2.7) x (4 - 0) / (10 - 0)] 3,0
t
0
= 4 °C t
c
= 20 °C t
c
= 50 °C
Interpolation at t
c
= 40 °C
∆p
v100
0.15
2.4 1.9 2.4 + [(1.9 – 2.4) x (40 - 20) / (50 - 20)] 2,1
∆p
v100
0.45
4.0 3.0 4.0 + [(3.0 – 4.0) x (40 - 20) / (50 - 20)] 3,3
t
c
= 40 °C
∆p
v100
0.15 ∆p
v100
0.45
Interpolation at
∆p
v100
0,25
2.1 3.3
2.1 + [(3.3 – 2.1) x (0.25 – 0.15) / (0.45 –
0.15)]
2,5
k
vs
theoretical = 9.5 kW / 2.5 = 3.8 m
3
/h
Valve MVF661.25-6.3N is suitable, since 3.8 m
3
/h / 6.3 m
3
/h x 100 % = 60 % (> 50 %)
It is recommended that the k
vs
value be set to 63 % = 4 m
3
/h
50941A
+
–
Typical control range 10...100 %.
The capacity controller ensures that the
compressor is adequately cooled, making it
unnecessary to set a minimum stroke in the
refrigerant valve.
MVF661...N
14/16
Building Technologies Refrigerant Valves PN 40 CE2N4716en
HVAC Products 08.06.2005