Trane SYS-APM001-EN manual System Design Options, Consumption, Energy, System Load, 2.0 gpm/ton

System Design Options

and a more conservative zero condenser-water-pipe pressure drop, we can examine the effect of reducing flow rates.

Table 12. Reduced flow-rate effect

Condenser Water Pump	Base Case	Low Flow
Flow rate, gpm [L/s]	1350 [85.2]	900 [56.8]
System pressure drop, ft water [kPa]	0		0
Condenser bundle pressure drop, ft water [kPa]	19.9 [59.5]	9.6 [28.7]
Tower static lift, ft water [kPa]	19.1 [57.1]	12.6	[37.7]
Pump power output, hp [kW]	17.7 [13.2]	6.7	[5.0]
Pump fan electrical input, kW	14.2	5.4

Figure 24. System energy consumption (no pipes)

	350.0
	3.0 gpm/ton	2.0 gpm/ton
(kWh)	300.0
Consumption	250.0
	200.0
Energy	150.0
	100.0
System
	50.0
	0.0
	25%	50%	75%	100%

System Load

Energy consumption for the chiller, condenser-water pump, and cooling- tower fans is shown in Figure 24. Note that only at full load does the total power of the chilled-water plant increase. Recall that this is with absolutely no pressure drop through the condenser-water piping, valves, or fittings. It is interesting to note that the break-even point at full load is approximately

8 feet of head (water) [23.9 kPa]. Also note that at all part-load conditions, the total power of the low-flow system is less than that of the base system. It is easy to see that even for short piping runs, reducing flow rates can improve plant energy consumption.

40 Chiller System Design and Control SYS-APM001-EN