Appendix B: The Chilled Water System Optimizer Commissioning view of the Properties page
Chilled Water System Optimizer v2
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Installation and Start-up Guide
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Condenser Water Temperature Optimizer Reset
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Control Program
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Condenser Water Temperature Optimizer Reset
Overall operation
Like the Chilled Water Temperature Optimizer Reset section, the condenser water reset searches for the condenser water
supply temperature that best lowers the kW/ton on the condenser water side. The reset lowers condenser water supply
temperature for the approach temperature that balances energy savings at the chiller with energy increases at the tower
fans and condenser water pumps.
Approach temperature
The approach temperature is the difference between condenser water supply temperature and current wet bulb temperature
(cws temp – oa wb). The rated approach temperature equates to the lowest condenser water temperature that the tower is
likely to produce. A 7°F approach rating is common for most cooling towers, although more efficient towers can go down to a
5°F degree approach, or less, in a few cases.
Condenser water reset function
After the program is enabled, the algorithm begins its optimizing routine with
Section 2 - Manual Overrides of Condenser
Water Reset - and other Settings
(page 83) >
First Reset
. Each response period, the program determines the next reset
signal that best lowers energy demand. The 0-10 (deg) output is converted to a condenser water supply approach to wet-
bulb temperature, which is a setpoint between the maximum and minimum approach. Since the wet bulb temperature varies
during the day, the actual condenser water supply setpoint also varies within the approach window (maximum approach –
minimum approach). See example setpoint chart below (assuming a very efficient tower with a minimum 5 degree approach.
No Reset of 0
= 12 degree (max approach, adj.)
Warmer Condenser Supply Temp
Full Reset of 10
= 5 degree (min approach, adj.)
Cooler Condenser Supply Temp
EXAMPLE
The current outside air wet-bulb temperature is 70°F.
The program calculates an optimal approach setpoint of 6°F.
The condenser water setpoint will be 70°+ 6°=76°F (based on current wet bulb)
If the tower is rated at a 7°F approach, then this is a cooler approach temperature with tower fans likely running at or near 100%. But the chiller would
experience lower lift and possibly greater energy savings at such a low approach temperature.
The program attempts to find the balance of energy saved at the chiller and energy expended at the fans through a
calculated approach temperature. So the approach temperature setpoint would likely change throughout the day in a
constant search for the optimal temperature.
