Catalogue

CG-PRC017H-EN 7
Application Considerations
Water Flow Limits
The minimum water flow rates are given in the General Data section of this catalog. Evaporator
flow rates below the tabulated values will result in laminar flow causing freeze-up problems,
scaling, stratification and poor control.The maximum evaporator water flow rate is also given.
Flow rates exceeding those listed may result in very high pressure drop across the evaporator.
Flow Rates Out of Range
Many process cooling jobs require flow rates that cannot be met with the minimum and maximum
published values within the CGAM evaporator. A simple piping change can alleviate this problem.
For example: a plastic injection molding process requires 80 gpm (5.0 l/s) of 50°F (10°C) water and
returns that water at 60°F (15.6°C).The selected chiller can operate at these temperatures, but has
a minimum flow rate of 106 gpm (6.6 l/s).The system layout in Figure 1 can satisfy the process.
Flow Proving
Trane provides a factory-installed water flow switch monitored by CH530 which protects the chiller
from operating in loss of flow conditions.
Variable Flow in the Evaporator
An attractive chilled water system option may be a Variable Primary Flow (VPF) system. VPF
systems present building owners with several cost-saving benefits when compared with Primary/
Secondary chilled water systems.The most obvious cost savings results from eliminating the
constant volume chiller pump(s), which in turn eliminates the related expenses of the associated
piping connections (material, labor), and electrical service and switch gear. In addition to the
installed cost advantage building owners often cite pump related energy savings as the reasons
that prompted them to select a VPF system.
The CGAM has the capability to handle variable evaporator flow without losing leaving water
temperature control.The microprocessor and capacity control algorithms are designed to take a
10 percent change in water flow rate per minute while maintaining a ±2°F (1.1°C) leaving water
temperature control accuracy.The chiller tolerates up to 30 percent per minute water flow variation
as long as the flow is equal or above the minimum flow rate requirement.
With the help of a software analysis tool such as System Analyzer™, DOE-2 orTRACE™, you can
determine whether the anticipated energy savings justify the use of variable primary flow in a
particular application. Existing constant flow chilled water systems may be relatively easily
converted to VPF and benefit greatly from the inherent efficiency advantages.
Figure 1. Flow rate out of range systems solution
50°F (10°C)
112 gpm (7 l/s)
50°F (10°C)
80 gpm (5 l/s)
60°F (15.6°C)
80 gpm (5 l/s)
50°F (10°C)
32 gpm (2 l/s)
57°F (14°C)
112 gpm (7 l/s)