COOLINGTOWER:TWOSPEED

This tower model is based on Merkel's theory, which is also the basis for the tower model in ASHRAE's HVAC1 Toolkit. The open wet cooling tower is modeled as a counter flow heat exchanger with a two-speed fan drawing air through the tower (induced-draft configuration). 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

Design Water Flow Rate

Type: real number
Leave field blank if Tower Performance Input Method is NominalCapacity
Unit: m3/s

High Fan Speed Air Flow Rate

Type: real number
Unit: m3/s

High Fan Speed Fan Power

Type: real number
This is the fan motor electric input power at high speed
Unit: W

High Fan Speed U-Factor Times Area Value

Type: real number
Leave field blank if Tower Performance Input Method is NominalCapacity
Unit: W/K
Maximum: 2100000.0

Low Fan Speed Air Flow Rate

Type: real number
Low speed air flow rate must be less than high speed air flow rate Low speed air flow rate must be greater than free convection air flow rate
Unit: m3/s

Low Fan Speed Air Flow Rate Sizing Factor

Type: real number
This field is only used if the previous field is set to autocalculate.
Default: 0.5

Low Fan Speed Fan Power

Type: real number
This is the fan motor electric input power at low speed
Unit: W

Low Fan Speed Fan Power Sizing Factor

Type: real number
This field is only used if the previous field is set to autocalculate.
Default: 0.16

Low Fan Speed U-Factor Times Area Value

Type: real number
Leave field blank if tower Performance Input Method is NominalCapacity Low speed tower UA must be less than high speed tower UA Low speed tower UA must be greater than free convection tower UA
Unit: W/K
Maximum: 300000.0

Low Fan Speed U-Factor Times Area Sizing Factor

Type: real number
This field is only used if the previous field is set to autocalculate and the Performance Input Method is UFactorTimesAreaAndDesignWaterFlowRate
Default: 0.6

Free Convection Regime Air Flow Rate

Type: real number
Unit: m3/s
Minimum: 0.0
Default: 0.0

Free Convection Regime Air Flow Rate Sizing Factor

Type: real number
This field is only used if the previous field is set to autocalculate.
Default: 0.1

Free Convection Regime U-Factor Times Area Value

Type: real number
Leave field blank if Tower Performance Input Method is NominalCapacity
Unit: W/K
Minimum: 0.0
Maximum: 300000.0
Default: 0.0

Free Convection U-Factor Times Area Value Sizing Factor

Type: real number
This field is only used if the previous field is set to autocalculate and the Performance Input Method is UFactorTimesAreaAndDesignWaterFlowRate
Default: 0.1

Performance Input Method

Type: choice (UFactorTimesAreaAndDesignWaterFlowRate or NominalCapacity)
User can define tower thermal performance by specifying the tower UA, the Design Air Flow Rate and the Design Water Flow Rate, or by specifying the tower nominal capacity
Default: UFactorTimesAreaAndDesignWaterFlowRate

Heat Rejection Capacity and Nominal Capacity Sizing Ratio

Type: real number
Default: 1.25

High Speed Nominal Capacity

Type: real number
Nominal tower capacity with entering water at 35C (95F), leaving water at 29.44C (85F), entering air at 25.56C (78F) wet-bulb temperature and 35C (95F) dry-bulb temperature, with the tower fan operating at high speed. Design water flow rate assumed to be 5.382E-8 m3/s per watt(3 gpm/ton). Nominal tower capacity times the Heat Rejection Capacity and Nominal Capacity Sizing Ratio (e.g. 1.25) gives the actual tower heat rejection at these operating conditions.
Unit: W

Low Speed Nominal Capacity

Type: real number
Nominal tower capacity with entering water at 35C (95F), leaving water at 29.44C (85F), entering air at 25.56C (78F) wet-bulb temperature and 35C (95F) dry-bulb temperature, with the tower fan operating at low speed. Design water flow rate assumed to be 5.382E-8 m3/s per watt of tower high-speed nominal capacity (3 gpm/ton). Nominal tower capacity times the Heat Rejection Capacity and Nominal Capacity Sizing Ratio (e.g. 1.25) gives the actual tower heat rejection at these operating conditions.
Unit: W

Low Speed Nominal Capacity Sizing Factor

Type: real number
This field is only used if the previous field is set to autocalculate
Default: 0.5

Free Convection Nominal Capacity

Type: real number
Tower capacity in free convection regime with entering water at 35C (95F), leaving water at 29.44C (85F), entering air at 25.56C (78F) wet-bulb temperature and 35C (95F) dry-bulb temperature. Design water flow rate assumed to be 5.382E-8 m3/s per watt of tower high-speed nominal capacity (3 gpm/ton). Tower free convection capacity times the Heat Rejection Capacity and Nominal Capacity Sizing Ratio (e.g. 1.25) gives the actual tower heat rejection at these operating conditions
Unit: W
Minimum: 0.0

Free Convection Nominal Capacity Sizing Factor

Type: real number
This field is only used if the previous field is set to autocalculate
Default: 0.1

Design Inlet Air Dry-Bulb Temperature

Type: real number
Enter the tower's design inlet air dry-bulb temperature
Unit: C
Minimum: 20.0
Default: 35.0

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. Autosized to 3.9 deltaC.
Unit: deltaC
Default: autosize

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. Autosized to 5.5 deltaC.
Unit: deltaC
Default: autosize

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 [%/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
Default: 0.008

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 some 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