7. Compressor selection
a) Selection criteria
When selecting compressors, or upgrading systems to larger capacity or to dual evaporators, the
compressor sizing (capacity) must match the system.
Compressor selection must be done using the following basic guidelines:
•
What is the operational speed of the compressor?
This varies dramatically in highway to city cycle.
•
What is the total net refrigerating capacity of the system? Evaporator rating.
•
What refrigerant is being used in the system?
Taking into consideration these three factors and if the evaporator capacity is adequate for the
application, the correct compressor can be selected.
Note:
Graphs will often incorporate three plots onto one grid – power
consumption, refrigerating capacity, and coefficient of performance. Coefficient
of performance relates to input
(power consumption)
versus output
(refrigerating
capacity).
If interpreting single plot graphs, ensure you have selected the
Refrigerating Capacity Graph. A complete range of graphs for each model is
available from Unicla upon request.
For single evaporator applications the compressor must cater for the net refrigerating capacity of
the evaporator at nominated operating speeds.
For dual evaporator units the compressor must cater for the net refrigerating capacity of all
evaporators.
8. Hose and pipe selection
a) Suction Line
Correct sizing of the suction line is critical to ensure adequate flow of refrigerant is maintained.
Too often the nominated capacity of the evaporator and the compressor are ideally matched, only
to be compromised by undersized piping in the suction line.
The following tables outline the required pipe or hose sizes for each Unicla compressor model
under common speed and capacity ratings.
The suction lines are sized to have pressure drop from friction no greater than the equivalent of
approximately 1 K change in saturation temperature. Selections are base on R134a saturation
temperature of 08C
(Referenced from ASHRAE Hand Book, Refrigeration Volume, 2006 Edition.)
6.
