P/N 558756_C
U.S. & Canada 1-800-922-1919 • Mexico 01-800-890-2900 • www.hussmann.com
22
If a mechanical EPR is used, sizing to the
new load must be considered.
If an electronic EPR is used, the existing
valve will need to be checked for full function
at the new load.
B. Each line-up of cases has a liquid and suction
line from a loop served by the rack, or a run
from the rack to the line-up.
The liquid line does not normally need to be
changed.
The suction line in every line up needs to be
checked and changed as required.
The suction riser is the most important line that
must be evaluated. If the new load requires a
different line size, it must be changed to ensure
proper lubricant volume returns back to the
compressors.
REFRIGERATION SYSTEM (DX SYSTEM)
A. The DX system itself has many components
that must be evaluated. They include:
Compressors: After determining the new BTU/
hr load, determine if the existing
compressor selection will allow steps from
8% to 20%. If not, a compressor or more
compressors may need to be removed or
replaced.
When the existing design uses evenly sized com-
pressors (where all compressor models are the
same), a compressor change should be consid-
ered if the load was reduced by more than one
compressor capacity. Adjusting the compressor
output by means of un-loaders, variable fre-
quency drives, or digital technology, may be
acceptable alternate solutions.
NOTE: Pay particular attention to affected
circuits that are fed by a satellite compressor or
conventional unit. That compressor may now
be grossly oversized.
Gas Defrost: If the rack is equipped with gas
defrost, the main liquid line solenoid and the
discharge differential valves should be
evaluated. If the existing valve is oversized, a
new valve should be considered.
Heat Reclaim - If the rack is equipped with
heat reclaim, the new value for available heat
should be recalculated. It is possible that the
heat reclaim coil will now be oversized. This is
especially true if compressor changes have been
made. Typically, whole rack BTU/hr reduc-
tions of 35 percent and greater would need to
be seen.
Discharge Riser: Depending on the drop of
BTU/hr to the entire rack, the discharge riser
(the piping that goes from the rack to the
condenser), may need to be resized. Under
most applications this will just need to be
checked. If the drop in the total BTU/hr is
greater than 35%, a resize is more than likely
necessary. If this line is not resized when it is
necessary to do so, lubricant return back to the
compressors may be an issue.
