period three
System Variations
notes
Greater Focus on System Efficiency
Figure 69
Realize, however, that the chiller is only one component of the chilled-water system. Although chiller efficiency is important, overall system efficiency is more important because the building owner pays to operate the entire system, not just the chiller. Said another way, “The meter is on the building!”
With this in mind, many system design engineers are looking for ways to optimize the efficiency of the entire system, not just the chiller.
Trend Toward Lower Flow Rates
electric-driven chiller | yesterday | today |
| | |
evaporator | 2.4 gpm/ton | 1.5 gpm/ton |
flow rate | [0.043 L/s/kW] | [0.027 L/s/kW] |
| | |
leaving | 44°F | 41°F |
chilled-water | [6.7°C] | [5°C] |
temperature | | |
| | |
condenser | 3.0 gpm/ton | 2.0 gpm/ton |
flow rate | [0.054 L/s/kW] | [0.036 L/s/kW] |
| | |
entering | 85°F | 85°F |
condenser-water | [29.4°C] | [29.4°C] |
temperature | | |
Figure 70
One approach to increase overall system efficiency has been to reduce pump and cooling-tower energy by reducing the amount of water being pumped through the system. In the past, the conditions shown in the center column of the table in Figure 70 were often used when designing a water-cooled, chilled- water system. These flow rates result in a 10°F [5.6°C] temperature difference (∆T) through both the evaporator and the condenser. In fact, they are the standard conditions at which electric, vapor-compression chillers are rated by
