4-Select the evaporative
water cooler
Closed circuit cooling towers operate in a
manner similar to open cooling towers, except
that the heat load to be rejected is transferred
from the process fluid (the fluid being cooled)
to the ambient air through a heat exchange coil.
The coil serves to isolate the process fluid
from the outside air, keeping it clean and contaminate
free in a closed loop. This creates two separate
fluid circuits: (1) an external circuit, in
which spray water circulates over the coil and
mixes with the outside air, and (2) an internal
circuit, in which the process fluid circulates
inside the coil. During operation, heat is transferred
from the internal circuit, through the coil
to the spray water, and then to the atmosphere
as a portion of the water evaporates.
Summarize the total rated cooling capacity
of all terminal units in kcal/h or kW.
Select evaporative cooler from
manufacturer’s data which indicate
performance in terms of total capacity vs. summer
design wet bulb temperature.
Apply diversity, if other than 80%, to permit
selection of proper size cooler. Note that the
flow rate remains con stant for a given total
connected capacity and wet bulb condition at
any diversity.
Never select cooler for 100% diversity (100%
of the units running 100% of the time) or cooler
selection will be oversized to no benefit. A
few
large units will require a larger diversity
factor than a sys tem composed of small increments.
Probable diversity
factors based on total system flow rate are:
85% for up to 100 total system gpm (6.31 total
system L/s) ,(22,7 m3/h)
80% for 100 to 150 total system gpm (6.31 to
9.46 total system L/s) (22,7 to 24m3/h)
75% for over 150 total system gpm (9.46 total
system L/s) (24m3/h)
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