Buildings.Fluid.HeatExchangers.CoolingTowers.Data

Cooling tower performance data

Information

Package with performance data for cooling towers.

Extends from Modelica.Icons.MaterialPropertiesPackage (Icon for package containing property classes).

Package Content

Name	Description
UAMerkel	UA correction factors for Merkel cooling towers

Buildings.Fluid.HeatExchangers.CoolingTowers.Data.UAMerkel

UA correction factors for Merkel cooling towers

Information

This data record contains the cooling tower performance data for Buildings.Fluid.HeatExchangers.CoolingTowers.Merkel. Similar to the CoolingTower:VariableSpeed:Merkel model in EnergyPlus, Merkel's theory is modified to include Scheier's adjustment factors that adjust UA values at off-design conditions. The three factors are:

cDifWB- Corrected UA based on the difference between the current wetbulb temperature and the design wetbulb temperature.
cAirFra- Corrected UA based on the ratio of the current air flow rate and the design air flow rate.
cWatFra- Corrected UA based on the ratio of the current water flow rate and the design water flow rate.

The user can update the values in this record based on the performance characteristics of their cooling tower.

These three adjustment factors are used to calculate the UA value as

UA_e = UA₀ · f_UA,wetbulb · f_UA,airflow · f_UA,waterflow,

where UA_e and UA₀ are the equivalent and design overall heat transfer coefficent-area products, respectively.

The factors f_UA,wetbulb, f_UA,airflow, and f_UA,waterflow adjust the current UA value for the current wetbulb temperature, air flow rate, and water flow rate, respectively. These adjustment factors are third-order polynomial functions defined as

f_UA,x = c_x,0 + c_x,1 x + c_x,2 x² + c_x,3 x³,

where x = {(T_0,wetbulb - T_wetbulb), ṁ_air ⁄ ṁ_0,air, ṁ_wat ⁄ ṁ_0,wat} for the respective adjustment factor, and the coefficients c_x,0, c_x,1, c_x,2, and c_x,3 are the user-defined values for the respective adjustment factor functions obtained from Buildings.Fluid.HeatExchangers.CoolingTowers.Data.UAMerkel.

Extends from Modelica.Icons.Record (Icon for records).

Parameters

Type	Name	Default	Description
Performance curves
Real	cDifWB[3]	{1,0.0081,0}	Polynomial coefficients for correction of design wet bulb minus actual wet bulb temperature
Real	cAirFra[3]	{0,1.3,-0.3}	Polynomial coefficients for correction for fractional air flow rate
Real	cWatFra[3]	{0.1082,1.667,-0.7713}	Polynomial coefficients for correction for fractional water flow rate
Real	FRAirMin	0.2	Minimum value for air flow fraction
Real	FRAirMax	1.0	Maximum value for air flow fraction
Real	FRWatMin	0.3	Minimum value for water flow fraction
Real	FRWatMax	1.0	Maximum value for water flow fraction
TemperatureDifference	TDiffWBMin	-10	Minimum value for leaving evaporator temperature difference [K]
TemperatureDifference	TDiffWBMax	25	Maximum value for leaving evaporator temperature difference [K]

Modelica definition

record UAMerkel "UA correction factors for Merkel cooling towers" extends Modelica.Icons.Record; parameter Real cDifWB[3]={1,0.0081,0} "Polynomial coefficients for correction of design wet bulb minus actual wet bulb temperature"; parameter Real cAirFra[3]={0,1.3,-0.3} "Polynomial coefficients for correction for fractional air flow rate"; parameter Real cWatFra[3]={0.1082,1.667,-0.7713} "Polynomial coefficients for correction for fractional water flow rate"; parameter Real FRAirMin(min=0) = 0.2 "Minimum value for air flow fraction"; parameter Real FRAirMax(min=0)= 1.0 "Maximum value for air flow fraction"; parameter Real FRWatMin(min=0) = 0.3 "Minimum value for water flow fraction"; parameter Real FRWatMax(min=0) = 1.0 "Maximum value for water flow fraction"; // Range for the curves parameter Modelica.SIunits.TemperatureDifference TDiffWBMin( max=0, displayUnit="K")= -10 "Minimum value for leaving evaporator temperature difference"; parameter Modelica.SIunits.TemperatureDifference TDiffWBMax( min=0, displayUnit="K")= 25 "Maximum value for leaving evaporator temperature difference"; end UAMerkel;