TRG-TRC010-EN 25
period three
Compressor Capacity Control
notes
Consider a given-diameter compressor impeller that rotates at a constant
speed. As the load on the chiller decreases, the inlet vanes partially close and
the flow rate of refrigerant through the compressor drops. Radial velocity (Vr),
which is proportional to refrigerant flow, decreases as well.
Even though the speed of rotation and diameter of the impeller are constant,
the tangential velocity (Vt) (which is proportional to the product of impeller
rotational speed and impeller diameter) drops because of the pre-swirling of
the refrigerant caused by the inlet vanes.
The result is a shorter resultant velocity vector (R), which means that less static
pressure is generated.
Compressor Unloading
V
Vr
r
R
R
V
Vt
t
V
Vr
r
V
Vt
t

full load part load

R
R
Figure36
trgtrc010_book.book Page 25 Wednesday, September 1, 1999 10:39 AM