Cooling Tower
System
Cooling Tower Type
Specify the Cooling Tower Type, offering a choice between Constant Speed Fan or Variable Speed Fan.
Design Wet bulb Temp.
Specify the Design Wet bulb Temp., setting the inlet air wet-bulb temperature (˚C) at design conditions.
Design Approach Temp.
Specify the Design Approach Temp., setting the tower approach temperature (˚C) at design conditions. The approach temperature is calculated as the outlet water temperature minus the inlet air wet-bulb temperature.
Design Range Temp
Specify the Design Range Temp, defining the range temperature (˚C) at design conditions. The range temperature is calculated as the inlet water temperature minus the outlet water temperature.
Design Cycles of Concentration
Specify the Design Cycles of Concentration, a field used to dynamically adjust the blowdown rate in the cooling tower based on the rate of evaporation. This value, dimensionless, represents the ratio of solids in the blowdown water to solids in the make-up water.
Drift Loss
Specify Drift Loss, setting the percentage (%) of design water flow rate lost to the atmosphere at the design air flow rate due to drift. Drift consists of water droplets entrained in the airstream as it passes through the tower and is additional to water lost due to evaporation and/or blowdown.
Evaporation Loss Mode
Specify the Evaporation Loss Mode, choosing between LossFactor or SaturatedExit. The default is SaturatedExit. If LossFactor is selected, the user-defined Evaporation Loss Factor is entered in the following field.
Evaporation Loss Factor
Specify the Evaporation Loss Factor, applicable when Evaporation Calculation Mode is set to Loss Factor. This field specifies the rate of water evaporated from the cooling tower and lost to the outside air in [percent/K]. The evaporation loss is calculated as a fraction of the circulating condenser water flow and varies with the temperature change in the condenser water. Typical values range from 0.15 to 0.27 [percent/K], with the default set at 0.2.
Fraction Tower Capacity In Free Convection Regime
Specify the Fraction Tower Capacity In Free Convection Regime, a numeric field denoting the fraction of tower capacity available during free convection (when the tower fan is off). The fan remains inactive when free convection capacity meets or exceeds the exiting water set point temperature. The air flow rate through the tower in free convection is assumed to be the specified fraction of the tower design air flow rate. Ensure the fraction is between 0 and 0.2, with a default value of 0.125 if left blank.
Sizing
Min. Air Flow Rate Ratio
Specify the Min. Air Flow Rate Ratio, a numeric field indicating the minimum air flow rate ratio. The tower fan is allowed to operate between the defined ratio and a maximum air flow rate ratio of 1.0 (corresponding to the design [maximum] tower air flow rate). Below this value, the tower operates in the "free convection" regime with the fan off or cycles on/off to maintain the exiting water set point temperature. Ensure the minimum air flow rate ratio is between 0.2 and 0.5, with a default value of 0.2 if left blank.
Sizing Factor
This optional numeric field enables users to specify a sizing factor for this component. When the component design inputs are auto-sized, the calculations are performed as usual, and the results are multiplied by the sizing factor. This allows sizing the component to meet part of the design load while still benefiting from autosizing. The inputs affected by the sizing factor for this component include:
Design Water Flow Rate;
Design Air Flow Rate;
Design Fan Power.
Sizing Method
Choose between Autosize or Manual for the Sizing Method. If Manual is selected, ensure all numerical fields are completed with valid entries.
Design Water Flow Rate
Specify the Design Water Flow Rate, a numeric field representing the design water flow rate through the tower in m3/s. The entered value should be within ±25% of the tower's rated water mass flow rate as specified by the manufacturer.
This value corresponds to the flow rate of the condenser loop water being cooled by the tower. It must be greater than zero or can be autosized. If autosized, a Plant Sizing object must be defined to derive the design water flow rate from the design load and design loop delta T. Ensure the design water flow rate aligns with the specified design values for the inlet air wet-bulb temperature, approach temperature, range temperature, and air flow rate. If not autosized, the condenser loop flow rate specified in other objects should be within ±25% of the tower's rated water flow rate.
Design Air Flow Rate
Specify the Design Air Flow Rate, a numeric field representing the design (maximum) air flow rate through the tower in m3/s.
Design Fan Power
Specify the Design Fan Power, a numeric field containing the fan power in watts at the design (maximum) air flow rate through the tower.
Number of Cells
Specify the Number of Cells, an integer field indicating the number of cells in the multi-cell cooling tower. If not entered, the program will assume it is a single-cell cooling tower.
Cell Control
Specify the Cell Control method by choosing between MinimalCel and MaximalCel. If left blank, the default value is MaximalCel. In the MinimalCel mode, the program uses the minimum number of cells needed, shutting down others to conserve energy while meeting the load. The flow per cell is controlled not to exceed the maximum defined value. Conversely, MaximalCel activates as many cells as possible, ensuring the load is met without allowing the flow per cell to drop below the specified minimum. This setting provides flexibility in controlling the number of cells based on specific system requirements, balancing energy efficiency and cooling demand.
Cell Min. Water Flow Rate Fraction
Specify the Cell Min. Water Flow Rate Fraction is a numeric field specifying the allowable smallest fraction of the design water flow rate. If left blank, the default value is 0.33.
Cell Max. Water Flow Rate Fraction
Specify the Cell Max. Water Flow Rate Fraction is a numeric field specifying the allowable largest fraction of the design water flow rate. If left blank, the default value is 2.5.
Staging
Specify the Staging configuration to control the activity of the Cooling Tower during various duty ranges. Add Stages to manage the component's operation based on the total condenser water loop cooling demand within specific ranges. This allows for fine-tuned control over the Cooling Tower's activity to optimize performance across different operational scenarios.
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