Quantech QCC3, Manual

Page: 13 / 60

FORM QCC3-EG1 (517)
QUANTECH 13
Selection Data
The ratings shown on pages 18 through 24 are based on unit operation in a well designed
and properly piped system.
SELECTION RULES
1. Capabilities are based on Refrigerant R-410A.
2. Ratings may interpolated, but must not be extrapolated.
3. Ratings shown are at saturated suction temperatures corresponding to pressures
at the compressor. In actual practice, suction line pressure drop has the effect of
reducing compressor capacity, forcing the compressor to operate at a lower suction
pressure to maintain the desired evaporator temperature.
For normal air conditioning applications, size the suction line for a pressure drop of 3 PSI,
corresponding to 2°F, for R-410A refrigerant. Thus, the evaporator temperature will be ap-
proximately 2°F higher than the compressor suction temperature. Line loss must be taken
into consideration when selecting the evaporator.
SELECTION PROCEDURE
The air-cooled condensing unit may be selected from the Ratings on pages 12 through
17, if the ambient air temperature at the condenser and the saturated suction temperature
at the compressor are known. The ambient air temperature is a known design parameter,
but the suction temperature at the compressor, in many cases, is known only within cer-
tain allowable limits. The actual compressor operating suction temperature and the overall
performance of the system will depend directly upon the choice of the evaporator. Starting
with a preliminary evaporator selection at a nominal evaporator temperature and using
data supplied by the evaporator manufacturer, enter the ratings tables and select a unit to
meet the required cooling load at a suction temperature at least 2°F below the evaporator
temperature. The 2°F allows for normal suction line loss.
If more accurate selection is required, the evaporator capacity should be plotted against
the condensing unit capacity to determine the balanced system performance. Again, it is
necessary to factor in the suction line loss.
After the system balance point has been determined, the compressor KW input may be
interpolated from the ratings tables.