COOLINGTOWER:VARIABLESPEED

This open wet tower model is based on purely empirical algorithms derived from manufacturer's performance data or field measurements. The user can select from two existing algorithms (CoolTools or YorkCalc), or they can enter their own correlation for approach temperature by using a variable speed tower model coefficient object. For a multi-cell tower, the capacity and air/water flow rate inputs are for the entire tower.

Name

Type: alphanumeric
Tower Name

Water Inlet Node Name

Type: node
Name of tower water inlet node

Water Outlet Node Name

Type: node
Name of tower water outlet node

Model Type

Type: choice (CoolToolsCrossFlow, CoolToolsUserDefined, YorkCalc or YorkCalcUserDefined)
Determines the coefficients and form of the equation for calculating approach temperature
Default: YorkCalc

Model Coefficient Name

Type: list of objects (COOLINGTOWERPERFORMANCE:YORKCALC or COOLINGTOWERPERFORMANCE:COOLTOOLS)
Name of the tower model coefficient object. Used only when tower Model Type is either CoolToolsUserDefined or YorkCalcUserDefined.

Design Inlet Air Wet-Bulb Temperature

Type: real number
Enter the tower's design inlet air wet-bulb temperature
Unit: C
Minimum: 20.0
Default: 25.6

Design Approach Temperature

Type: real number
Enter the approach temperature corresponding to the design inlet air wet-bulb temperature and design range temperature. Design approach temp = outlet water temperature minus inlet air wet-bulb temperature at design conditions.
Unit: deltaC
Default: 3.9

Design Range Temperature

Type: real number
Enter the range temperature corresponding to the design inlet air wet-bulb temperature and design approach temperature. Design range = inlet water temperature minus outlet water temperature at design conditions.
Unit: deltaC
Default: 5.6

Design Water Flow Rate

Type: real number
Water flow rate through the tower at design conditions
Unit: m3/s

Design Air Flow Rate

Type: real number
Design (maximum) air flow rate through the tower
Unit: m3/s

Design Fan Power

Type: real number
Enter the fan motor electric input power at design (max) air flow through the tower Standard conversion for horsepower is 1 HP = 745.7 W
Unit: W

Fan Power Ratio Function of Air Flow Rate Ratio Curve Name

Type: list of objects (CURVE:QUARTIC, CURVE:EXPONENTIALDECAY, CURVE:DOUBLEEXPONENTIALDECAY, CURVE:FUNCTIONAL:PRESSUREDROP, CURVE:SIGMOID, CURVE:RECTANGULARHYPERBOLA1, CURVE:CUBIC, CURVE:QUADRATIC, CURVE:EXPONENTIALSKEWNORMAL, CURVE:LINEAR, TABLE:LOOKUP, CURVE:RECTANGULARHYPERBOLA2 or CURVE:EXPONENT)
FPR = a + b*AFR + c*AFR**2 + d*AFR**3 FPR = fraction of the design fan power AFR = fraction of the design air flow rate If left blank, then fan power is assumed to be proportional to (air flow rate ratio)^3

Minimum Air Flow Rate Ratio

Type: real number
Enter the minimum air flow rate ratio. This is typically determined by the variable speed drive that controls the fan motor speed. Valid entries are from 0.2 to 0.5.
Minimum: 0.2
Maximum: 0.5
Default: 0.2

Fraction of Tower Capacity in Free Convection Regime

Type: real number
Enter the fraction of tower capacity in the free convection regime. This is the fraction of the tower capacity, at the current inlet air wet-bulb temperature, that is available when the tower fan is off. Manufacturers typically estimate the free convection capacity at approximately 10-15%. Values are entered as a fraction and can range from 0 to 0.2.
Minimum: 0.0
Maximum: 0.2
Default: 0.125

Basin Heater Capacity

Type: real number
This heater maintains the basin water temperature at the basin heater setpoint temperature when the outdoor air temperature falls below the setpoint temperature. The basin heater only operates when water is not flowing through the tower.
Unit: W/K
Minimum: 0.0
Default: 0.0

Basin Heater Setpoint Temperature

Type: real number
Enter the outdoor dry-bulb temperature when the basin heater turns on
Unit: C
Minimum: 2.0
Default: 2.0

Basin Heater Operating Schedule Name

Type: list of objects (SCHEDULE:FILE, EXTERNALINTERFACE:SCHEDULE, SCHEDULE:YEAR, EXTERNALINTERFACE:FUNCTIONALMOCKUPUNITIMPORT:TO:SCHEDULE, SCHEDULE:CONSTANT or SCHEDULE:COMPACT)
Schedule values greater than 0 allow the basin heater to operate whenever the outdoor air dry-bulb temperature is below the basin heater setpoint temperature. If a schedule name is not entered, the basin heater is allowed to operate throughout the entire simulation.

Evaporation Loss Mode

Type: choice (LossFactor or SaturatedExit)

Evaporation Loss Factor

Type: real number
Rate of water evaporated from the cooling tower and lost to the outdoor air [%/K] Evaporation loss is calculated as percentage of the circulating condenser water rate Value entered here is percent-per-degree K of temperature drop in the condenser water Typical values are from 0.15 to 0.27 [percent/K].
Unit: percent/K
Default: 0.2

Drift Loss Percent

Type: real number
Rate of drift loss as a percentage of circulating condenser water flow rate Typical values are between 0.002 and 0.2% The default value is 0.008%
Unit: percent

Blowdown Calculation Mode

Type: choice (ConcentrationRatio or ScheduledRate)

Blowdown Concentration Ratio

Type: real number
Characterizes the rate of blowdown in the cooling tower. Blowdown is water intentionally drained from the tower in order to offset the build up of solids in the water that would otherwise occur because of evaporation. Ratio of solids in the blowdown water to solids in the make up water. Typical values for tower operation are 3 to 5. The default value is 3.
Minimum: 2.0
Default: 3.0

Blowdown Makeup Water Usage Schedule Name

Type: list of objects (SCHEDULE:FILE, EXTERNALINTERFACE:SCHEDULE, SCHEDULE:YEAR, EXTERNALINTERFACE:FUNCTIONALMOCKUPUNITIMPORT:TO:SCHEDULE, SCHEDULE:CONSTANT or SCHEDULE:COMPACT)
Makeup water usage due to blowdown results from occasionally draining a small amount of water in the tower basin to purge scale or other contaminants to reduce their concentration in order to maintain an acceptable level of water quality. Schedule values should reflect water usage in m3/s.

Supply Water Storage Tank Name

Type: list of objects ( or WATERUSE:STORAGE)

Outdoor Air Inlet Node Name

Type: node
Enter the name of an outdoor air node

Number of Cells

Type: integer
Minimum: 1
Default: 1

Cell Control

Type: choice (MinimalCell or MaximalCell)
Default: MinimalCell

Cell Minimum Water Flow Rate Fraction

Type: real number
The allowable minimal fraction of the nominal flow rate per cell
Maximum: 1.0
Default: 0.33

Cell Maximum Water Flow Rate Fraction

Type: real number
The allowable maximal fraction of the nominal flow rate per cell
Minimum: 1
Default: 2.5

Sizing Factor

Type: real number
Multiplies the autosized capacity and flow rates
Default: 1.0

End-Use Subcategory

Type: alphanumeric
Any text may be used here to categorize the end-uses in the ABUPS End Uses by Subcategory table.
Default: General