Danfoss ADAP-KOOL AK-HP 780 Design Manual page 85

a) Variable capacity bigger than following compressor steps:
When the variable part of the speed controlled compressor is
bigger than the following compressors there will be no "holes" in
the capacity curve.
Example:
1 speed controlled compressor with a nominal capacity at 50Hz of
10kw - Variable speed range 30 – 90Hz
2 one step compressors of 10 kW
Fixed capacity = 30 HZ / 50 HZ x 10 kW = 6 kW
Variable capacity = 60 HZ / 50Hz x 10 kW = 12 kW
The capacity curve will look like this:
As the variable part of the speed controlled compressor is bigger
than the following compressor steps, the capacity curve will be
without holes.
1) The speed controlled compressor will be cutin when the
requested capacity has reached the start speed capacity.
2) The speed controlled compressor will increase speed until it
reaches max speed at a capacity of 18 kw.
3) The one step compressor C2 of 10 kW is cut in and the speed on
C1 is reduced too so that it corresponds to 8kW (40Hz)
4) The speed controlled compressor will increase speed until the
total capacity reaches 28 kw at max speed
5) The one step compressor C3 of 10kW is cut in and the speed on
C1 is reduced too so that it corresponds to 8kW (40Hz)
6) The speed controlled compressor will increase speed until the
total capacity reaches 38 kw at max speed
7) When reducing capacity the one step compressors will be cut
out when the speed on C1 is at minimum
AK-HP 780 Heat pump controller RS8GF202 © Danfoss 2015-08
b) Variable part smaller than following compressor steps:
If the variable part of the speed controlled compressor is smaller
than the following compressors there will be "holes" in the
capacity curve.
Example:
1 speed controlled compressor with a nominal capacity at 50Hz of
20kw - Variable speed range 25 – 50Hz
2 one step compressors of 20 kW
Fixed capacity = 25 HZ / 50 HZ x 20 kW = 10 kW
Variable capacity = 25 HZ / 50Hz x 20 kW = 10 kW
The capacity curve will look like this:
As the variable part of the speed controlled compressor is smaller
than the following compressor steps the capacity curve will have
some holes that can not be filled out by the variable capacity.
1) The speed controlled compressor will be cutin when the
requested capacity has reached the start speed capacity.
2) The speed controlled compressor will increase speed until it
reaches max speed at a capacity of 20 kw.
3) The speed controlled compressor will stay at max speed until
the requested capacity has increased to 30 kW.
4) The one step compressor C2 of 20 kW is cut in and the speed
on C1 is reduced to min. so that it corresponds to 10kW (25Hz).
Total capacity = 30 kW.
5) The speed controlled compressor will increase speed until the
total capacity reaches 40 kW at max speed
6) The speed controlled compressor will stay at max speed until
the requested capacity has increased to 50 kW.
7) The one step compressor C3 of 20kW is cut in and the speed
on C1 is reduced to min. so that it corresponds to 10kW (25Hz).
Total capacity = 50 kW
8) The speed controlled compressor will increase speed until the
total capacity reaches 60 kw at max speed
9) When reducing capacity the one step compressors will be cut
out when the speed on C1 is at minimum speed.
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