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ABS-PRC001-EN
Selection
Procedure
Selection Procedure
Absorption refrigeration machines are
usually selected to provide the required
refrigeration capacity with the smallest
practical machine of sufficient size.
Machine size is based on chilled-water
flow rates and temperatures specified for
the air side of the system.
Total air-conditioning system first cost
can be minimized by a careful analysis of
system operating parameters. The effect
of flow rates and temperatures, on both
the building air side and the refrigeration
machine selections, should be
investigated to determine which system
represents the best investment for the
owner.
The information on the following pages
provides performance data, at ARI
standard conditions, for capacity in tons,
efficiency, flow rates and water pressure
drops. All capacities are in accordance
with the expected ARI 560 Standard
revision, and are based on fouling
factors of .0001 for the evaporator
waterside tubing and .00025 for the
absorber and condenser tubing.
Standard Fouling
Unit performance at non-standard
fouling factors may vary from standard
performance. Fouling factors estimate
the heat transfer penalty that coincides
with the effect of typical fouling in
evaporator and absorber/condenser
(cooling) water circuits. All selections
should use the standard fouling factor to
more accurately estimate the chiller
performance in an equipment room and
to comply with ARI 560.
ARI Standard Fouling Factors
Evaporator Condenser/Absorber
English Units – hr-ft
2
-F/Btu
0.0001 0.00025
SI Units – m
2
-K/kW
0.018 0.044
Final Selection
A final selection must be done by the
local Trane sales engineer using the
Trane Horizon
®
Single-Stage Absorption
Selection Program. For applications
higher than 1600 feet [500 meters] above
sea level, final selection requires review
by Absorption Product Marketing. Prior
to accessing the computer selection
program, the following data inputs
should be tabulated:
• Temperature or pressure of the hot
water or steam
• Two of the following three values must
be provided
1
:
– Evaporator Delta-T
– Evaporator Flow
– Cooling Capacity
• Leaving-Evaporator Water Temperature
• Entering-Absorber Water Temperature
• Cooling Water Flow
• Chilled water and tower water fouling
factors
Other options that may also be selected
are:
• Type and thickness of tube material
• Type of solution flowing through the
evaporator and tower loop
2
.
1
Any limitations or restrictions should
also be given (i.e., pressure drop, gpm
etc.).
2
Absorption chillers can be selected with
a wide variety of media other than
water (evaporator and absorber/
condenser, or both). For media other
than water, contact the local Trane sales
office for chiller selections and
information.
Additional Fouling
Any selection that uses a fouling factor
greater than 0.0001 for the evaporator
tubes, and 0.00025 for the condenser/
absorber tubes, is a more conservative
estimate that should only be used if
there is an abnormal amount of fouling
contaminants in the water systems. The
ARI 560 Standard defines “additional
fouling” as “Conditions such as water
hardness, organic material, suspended
solids and/or water velocity may
necessitate the use of a greater field
fouling allowance than that provided in
the Standard Rating of equipment.” The
Trane single-stage Horizon Selection
program should be used to determine
the effect of nonstandard fouling factors.
The following guidelines can be used for
estimation prior to the selection:
ARI Standard Fouling Factors For
Additional Fouling
Evaporator Condenser/Absorber
English Units – hr-ft
2
-F/Btu
0.0002 0.00026 – 0.00075
SI Units – m
2
-K/kW
0.035 0.046
Part Load Performance
The Horizon
®
single-stage absorption
chiller exhibits excellent part-load
performance characteristics. Air
conditioning system loads are usually
significantly less than full-load design
conditions. Therefore, the absorption
chiller operates at full load a small
percentage of the time. Part-load
absorption chiller operation is normally
associated with reduced tower-water
temperatures. At part-load operation, the
heat rejected to the cooling tower is less
than at full-load operation. Also, part-
load operation is typically associated
with reduced outside wet-bulb
temperatures, resulting in improved
cooling tower performance. The net
result of less heat rejection and lower
wet-bulb temperature is cooler tower
water entering the chiller and improved
unit performance.