Download Applications Engineering Manual - Chilled

Primary System Components
temperature and a 10°F (5.5°C) fluid temperature rise ('T). To provide the
required 525 MBh (154 kW) of cooling capacity, the coil requires 105 gpm (6.6
L/s) of water.
The right-hand column shows the performance of same coil, but in this case
it is selected with 40°F (4.4°C) entering fluid and a 15.5°F (8.7°C) 'T. To
provide the equivalent capacity, the coil requires only 67.5 gpm (4.3 L/s) of
water.
Table 11. Impact of entering fluid temperature and flow rate on cooling coil
Coil face area, ft2 (m2)
Face velocity, fpm (m/s)
Coil rows
Fin spacing, fins/ft (fins/m)
Total cooling capacity, MBh (kW)
“Conventional”
system design
“Low-flow”
system design
29.90 (2.78)
29.90 (2.78)
435 (2.2)
435 (2.2)
6 rows
6 rows
83 (272)
83 (272)
525 (154)
525 (154)
Entering fluid temperature, °F (°C)
44 (6.7)
40 (4.4)
Leaving fluid temperature, °F (°C)
54 (12.2)
55.5 (13.1)
Fluid 'T, °F (°C)
Fluid flow rate, gpm (L/s)
Fluid pressure drop, ft H2O (kPa)
10 (5.5)
15.5 (8.7)
105 (6.6)
67.5 (4.3)
13.6 (40.6)
6.2 (18.4)
By lowering the entering fluid temperature, this coil can deliver the same
cooling capacity with 36 percent less flow, at less than half of the fluid
pressure drop, with no impact on the airside system.
For water-cooled systems, this “low-flow” strategy can also be used for the
condenser-water distribution system.
The benefits of applying this coil in a “low-flow” chilled-water system include
reduced installed cost (lower flow rates can allow the pipes, fittings, pumps,
valves, and cooling tower to be smaller) and/or reduced pumping energy
(since the system has to pump less water). And, although the chiller will
consume more energy to make the colder water, in most applications, the
total system (chillers, pumps, and cooling tower for water-cooled systems)
energy consumption will be reduced (Figure 73).
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Chilled-Water VAV Systems
SYS-APM008-EN