Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses

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Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses

Package with base classes for DX cooling coil model

Information

This package contains base classes that are used to construct the models in Buildings.Fluid.HeatExchangers.DXCoils.

Extends from Modelica.Icons.BasesPackage (Icon for packages containing base classes).

Package Content

Name Description

ApparatusDewPoint Calculates air properties at apparatus dew point

ApparatusDryPoint Calculates air properties at dry coil surface

Condensation Calculates rate of condensation

CoolingCapacity Calculates cooling capacity at given temperature and flow fraction

DryCoil Calculates dry coil condition

DryWetSelector Selects results from dry or wet coil

DXCooling DX cooling coil operation

EssentialParameters A partial block for essential parameters

Evaporation Model that computes evaporation of water that accumulated on the coil surface

InputPower Electrical power consumed by the unit

NominalCondition Calculates inlet and outlet fluid parameters at nominal condition

PartialCoilCondition Partial block for dry and wet coil conditions

PartialCoilInterface Partial block for DX coil

PartialDXCoil Partial model for DX coil

PartialSurfaceCondition Partial block for apparatus dew and dry point calculation

SensibleHeatRatio Calculates the sensible heat ratio

SpeedSelect Selects the lower specified speed ratio for multispeed model

SpeedShift Interpolates values between speeds

UACp Calculates UA/Cp of the coil

WetCoil Calculates wet coil condition

Functions Package with functions

Examples Package with examples of base class components for DX cooling coil model

Name	Description
ApparatusDewPoint	Calculates air properties at apparatus dew point
ApparatusDryPoint	Calculates air properties at dry coil surface
Condensation	Calculates rate of condensation
CoolingCapacity	Calculates cooling capacity at given temperature and flow fraction
DryCoil	Calculates dry coil condition
DryWetSelector	Selects results from dry or wet coil
DXCooling	DX cooling coil operation
EssentialParameters	A partial block for essential parameters
Evaporation	Model that computes evaporation of water that accumulated on the coil surface
InputPower	Electrical power consumed by the unit
NominalCondition	Calculates inlet and outlet fluid parameters at nominal condition
PartialCoilCondition	Partial block for dry and wet coil conditions
PartialCoilInterface	Partial block for DX coil
PartialDXCoil	Partial model for DX coil
PartialSurfaceCondition	Partial block for apparatus dew and dry point calculation
SensibleHeatRatio	Calculates the sensible heat ratio
SpeedSelect	Selects the lower specified speed ratio for multispeed model
SpeedShift	Interpolates values between speeds
UACp	Calculates UA/Cp of the coil
WetCoil	Calculates wet coil condition
Functions	Package with functions
Examples	Package with examples of base class components for DX cooling coil model

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.ApparatusDewPoint

Calculates air properties at apparatus dew point

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.ApparatusDewPoint

Information

This blocks outputs the state of the moist air at the dew point of the coil. The bypass factor of the coil and the resulting enthalpy difference is computed by its base class Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.PartialSurfaceCondition.

Extends from Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.PartialSurfaceCondition (Partial block for apparatus dew and dry point calculation).

Parameters

Type Name Default Description

DXCoil datCoi Performance data

replaceable package Medium PartialCondensingGases Medium model

Boolean variableSpeedCoil Flag, set to true to interpolate data

Initialization

Real bypass.start 0.25 Bypass factor

Type	Name	Default	Description
DXCoil	datCoi		Performance data
replaceable package Medium	PartialCondensingGases	Medium model
Boolean	variableSpeedCoil		Flag, set to true to interpolate data
Initialization
Real	bypass.start	0.25	Bypass factor

Connectors

Type Name Description

input RealInput speRat Speed index

input RealInput Q_flow Cooling capacity of the coil [W]

input RealInput m_flow Evaporator air mass flow rate [kg/s]

input RealInput p Evaporator air static pressure [Pa]

input RealInput XEvaIn Evaporator inlet air mass fraction

input RealInput hEvaIn Evaporator air inlet specific enthalpy [J/kg]

input IntegerInput stage Stage of coil, or 0/1 for variable-speed coil

output RealOutput hADP Specific enthalpy of air at apparatus dew point [J/kg]

output RealOutput XADP Humidity mass fraction of air at apparatus dew point

output RealOutput TADP Dry bulb temperature of air at apparatus dew point [K]

Type	Name	Description
input RealInput	speRat	Speed index
input RealInput	Q_flow	Cooling capacity of the coil [W]
input RealInput	m_flow	Evaporator air mass flow rate [kg/s]
input RealInput	p	Evaporator air static pressure [Pa]
input RealInput	XEvaIn	Evaporator inlet air mass fraction
input RealInput	hEvaIn	Evaporator air inlet specific enthalpy [J/kg]
input IntegerInput	stage	Stage of coil, or 0/1 for variable-speed coil
output RealOutput	hADP	Specific enthalpy of air at apparatus dew point [J/kg]
output RealOutput	XADP	Humidity mass fraction of air at apparatus dew point
output RealOutput	TADP	Dry bulb temperature of air at apparatus dew point [K]

Modelica definition

block ApparatusDewPoint 
  "Calculates air properties at apparatus dew point"
  extends Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.PartialSurfaceCondition;
  Modelica.Blocks.Interfaces.RealOutput hADP(
    nominal=40000,
    quantity="SpecificEnergy",
    unit="J/kg") "Specific enthalpy of air at apparatus dew point";
  Modelica.Blocks.Interfaces.RealOutput XADP(
    min=0,
    max=1.0) "Humidity mass fraction of air at  apparatus dew point";
  Modelica.Blocks.Interfaces.RealOutput TADP(
    quantity="Temperature",
    unit="K",
    displayUnit="degC",
    min=233.15,
    max=373.15) "Dry bulb temperature of air at apparatus dew point";
protected 
  parameter Modelica.SIunits.Temperature TSatMin = 273.15+3 
    "Minimum apparatus saturation temperature";
  parameter Modelica.SIunits.MassFraction XSatMin = 0.004667 
    "Mass fraction at saturation of coil inlet conditions";
  parameter Modelica.SIunits.SpecificEnthalpy hMin(fixed=false) 
    "Minimum enthalpy of apparatus dew point";

initial equation 
/*  XSatMin = Medium.Xsaturation(
        Medium.setState_pTX(p=p,
                            T=273.15+3,
                            X=cat(1,{XSatMin},{1-sum({XSatMin})})));
*/
  hMin = Medium.h_pTX(
           p=   Medium.p_default,
           T=   TSatMin,
           X=   cat(1,{XSatMin},{1-sum({XSatMin})}));
equation 
  hADP = Buildings.Utilities.Math.Functions.smoothMin(
    x1=  Buildings.Utilities.Math.Functions.smoothMax(
      x1=hEvaIn - delta_h,
      x2=hMin,
      deltaX=10),
    x2=  hEvaIn+100,
    deltaX=10);
  XADP = Buildings.Utilities.Psychrometrics.Functions.X_pW(p_w=Medium.saturationPressure(TADP), p=p);
  TADP= Medium.temperature(Medium.setState_phX(p=p, h=hADP, X=cat(1,{XADP},{1-sum({XADP})})));
end ApparatusDewPoint;

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.ApparatusDryPoint

Calculates air properties at dry coil surface

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.ApparatusDryPoint

Information

This blocks outputs the state of the moist air at of the coil, assuming no condensation occurs. The bypass factor of the coil and the resulting enthalpy difference is computed by its base class Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.PartialSurfaceCondition.

Extends from Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.PartialSurfaceCondition (Partial block for apparatus dew and dry point calculation).

Parameters

Type	Name	Default	Description
DXCoil	datCoi		Performance data
replaceable package Medium	PartialCondensingGases	Medium model
Boolean	variableSpeedCoil		Flag, set to true to interpolate data
Initialization
Real	bypass.start	0.25	Bypass factor

Connectors

Type Name Description

input RealInput speRat Speed index

input RealInput Q_flow Cooling capacity of the coil [W]

input RealInput m_flow Evaporator air mass flow rate [kg/s]

input RealInput p Evaporator air static pressure [Pa]

input RealInput XEvaIn Evaporator inlet air mass fraction

input RealInput hEvaIn Evaporator air inlet specific enthalpy [J/kg]

input IntegerInput stage Stage of coil, or 0/1 for variable-speed coil

output RealOutput TDry Dry bulb temperature of air at dry coil condition [K]

Type	Name	Description
input RealInput	speRat	Speed index
input RealInput	Q_flow	Cooling capacity of the coil [W]
input RealInput	m_flow	Evaporator air mass flow rate [kg/s]
input RealInput	p	Evaporator air static pressure [Pa]
input RealInput	XEvaIn	Evaporator inlet air mass fraction
input RealInput	hEvaIn	Evaporator air inlet specific enthalpy [J/kg]
input IntegerInput	stage	Stage of coil, or 0/1 for variable-speed coil
output RealOutput	TDry	Dry bulb temperature of air at dry coil condition [K]

Modelica definition

block ApparatusDryPoint 
  "Calculates air properties at dry coil surface"
  extends Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.PartialSurfaceCondition;
  Modelica.Blocks.Interfaces.RealOutput TDry(
    quantity="Temperature",
    unit="K",
    displayUnit="degC",
    min=253.15,
    max=373.15) "Dry bulb temperature of air at dry coil condition";
  output Modelica.SIunits.SpecificEnthalpy hDry 
    "Enthalpy of air at coil surface";
protected 
  Modelica.SIunits.MassFraction XEvaInVec[Medium.nX] 
    "Mass fraction of air inlet condition";
  Modelica.SIunits.Temperature TADP(start=283.15) 
    "Apparatus dew point temperature";
  Modelica.SIunits.SpecificEnthalpy hMin 
    "Minimum enthalpy of apparatus dew point";
equation 
  XEvaInVec =cat(1,{XEvaIn},{1-sum({XEvaIn})});

  XEvaIn = Buildings.Utilities.Psychrometrics.Functions.X_pW(
     p_w=Medium.saturationPressureLiquid(TADP), p=p);

  hMin = Medium.specificEnthalpy(Medium.setState_pTX(p=p, T=TADP, X=XEvaInVec));

  hDry = Buildings.Utilities.Math.Functions.smoothMin(
    x1=  Buildings.Utilities.Math.Functions.smoothMax(
      x1=hEvaIn - delta_h,
      x2=hMin,
      deltaX=10),
    x2=  hEvaIn+100,
    deltaX=10);

  TDry= Medium.temperature(Medium.setState_phX(p=p, h=hDry, X=XEvaInVec)) 
    "XEvaIn=XDry assumption for dry coil";

end ApparatusDryPoint;

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.Condensation

Calculates rate of condensation

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.Condensation

Information

This block computes the water mass flow rate that condenses.

Extends from Modelica.Blocks.Interfaces.BlockIcon (Basic graphical layout of input/output block).

Parameters

Type Name Default Description

replaceable package Medium Modelica.Media.Interfaces.Pa... Medium model

Type	Name	Default	Description
replaceable package Medium	Modelica.Media.Interfaces.Pa...	Medium model

Connectors

Type Name Description

replaceable package Medium Medium model

input RealInput TDewPoi Dew point temperature [K]

input RealInput Q_flow Heat flow [W]

input RealInput SHR Sensible heat ratio

output RealOutput mWat_flow Mass flow rate of water condensed at cooling coil [kg/s]

Type	Name	Description
replaceable package Medium	Medium model
input RealInput	TDewPoi	Dew point temperature [K]
input RealInput	Q_flow	Heat flow [W]
input RealInput	SHR	Sensible heat ratio
output RealOutput	mWat_flow	Mass flow rate of water condensed at cooling coil [kg/s]

Modelica definition

block Condensation "Calculates rate of condensation"
  extends Modelica.Blocks.Interfaces.BlockIcon;
  replaceable package Medium =
    Modelica.Media.Interfaces.PartialCondensingGases "Medium model";
  Modelica.Blocks.Interfaces.RealInput TDewPoi(
    start=278.15,
    unit="K",
    displayUnit="degC") "Dew point temperature";
  Modelica.Blocks.Interfaces.RealInput Q_flow(
    max=0,
    unit="W") "Heat flow";
  Modelica.Blocks.Interfaces.RealInput SHR(
    min=0,
    max=1) "Sensible heat ratio";
  Modelica.Blocks.Interfaces.RealOutput mWat_flow(
    quantity="MassFlowRate",
    unit="kg/s") "Mass flow rate of water condensed at cooling coil";
algorithm 
  mWat_flow := (1-SHR)*Q_flow/Medium.enthalpyOfVaporization(T=TDewPoi);
end Condensation;

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.CoolingCapacity

Calculates cooling capacity at given temperature and flow fraction

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.CoolingCapacity

Information

Cooling capacity modifiers

There are two cooling capacity modifier functions: The function cap_θ accounts for a performance change due to different air temperatures and the function cap_FF accounts for a performance change due to different air flow rates, relative to the nominal condition. These cooling capacity modifiers are multiplied with nominal cooling capacity to obtain the cooling capacity of the coil at given inlet temperatures and mass flow rate as

Q̇(θ_e,in, θ_c,in, ff) = cap_θ(θ_e,in, θ_c,in) cap_FF(ff) Q̇_nom,

where θ_e,in is the evaporator inlet temperature and θ_c,in is the condenser inlet temperature in degrees Celsius. θ_e,in is the dry-bulb temperature if the coil is dry, or the wet-bulb temperature if the coil is wet.

The temperature dependent cooling capacity modifier function is

cap_θ(θ_e,in, θ_c,in) = a₁ + a₂ θ_e,in + a₃ θ_e,in ² + a₄ θ_c,in + a₅ θ_c,in ² + a₆ θ_e,in θ_c,in,

where the six coefficients are obtained from the coil performance data record.

The flow fraction dependent cooling capacity modifier function is a polynomial with the normalized mass flow rate ff (flow fraction) as the time dependent variable. The normalized mass flow rate is defined as

ff = ṁ ⁄ ṁ_nom,

where ṁ is the mass flow rate and ṁ_nom is the nominal mass flow rate. If the coil has multiple stages, then the nominal mass flow rate of the respective stage is used. Hence,

cap_FF(ff) = b₁ + b₂ ff + b₃ ff² + b₄ff³ + ...

The coefficients of the equation are obtained from the coil performance data record.

It is important to specify limits of the flow fraction to ensure validity of the cap_FF(⋅) function in performance record. A non-zero value of cap_FF(0) will lead to an infinite large change in fluid temperatures because Q̇ ≠ 0 but ṁ = 0. Hence, when ṁ ≠ 0 is below the valid range of the flow modifier function, the coil capacity will be reduced and set to zero near ṁ = 0.

Energy Input Ratio (EIR) modifiers

The Energy Input Ratio (EIR) is the inverse of the Coefficient of Performance (COP). Similar to the cooling rate, the EIR of the coil is the product of a function that takes into account changes in condenser and evaporator inlet temperatures, and changes in mass flow rate. The EIR is computed as

EIR(θ_e,in, θ_c,in, ff) = EIR_θ(θ_e,in, θ_c,in) EIR_FF(ff) ⁄ COP_nominal

As for the cooling rate, EIR_θ(⋅, ⋅) is

EIR_θ(θ_e,in, θ_c,in) = c₁ + c₂ θ_e,in + c₃ θ_e,in ² + c₄ θ_c,in + c₅ θ_c,in ² + c₆ θ_e,in θ_c,in.

where the six coefficients are obtained from the coil performance data record, and θ_e,in is the dry-bulb temperature if the coil is dry, or the wet-bulb temperature otherwise.

Similar to the cooling ratio, the change in EIR due to a change in air mass flow rate is

EIR_FF(ff) = d₁ + d₂ ff + d₃ ff² + d₄ff³ + ...

Obtaining the polynomial coefficients

The package Buildings.Fluid.HeatExchangers.DXCoils.Data.PerformanceCurves contains performance curves. Alternatively, users can enter their own performance curves by making an instance of a curve in Buildings.Fluid.HeatExchangers.DXCoils.Data.PerformanceCurves and specifying custom coefficients for the above polynomials. The polynomial coefficients can be obtained by doing a curve fit that fits the polynomials to a set of data. The site http://www.scipy.org/Cookbook/FittingData shows examples for how to fit data. If a coil has multiple stages, then the fit need to be done for each stage. For variable frequency coils, multiple fits need to be done for user selected compressor speeds. For intermediate speeds, the performance data will be interpolated by the model Buildings.Fluid.HeatExchangers.DXCoils.VariableSpeed.

The table below shows the polynomials explained above, the name of the polynomial coefficients in Buildings.Fluid.HeatExchangers.DXCoils.Data.PerformanceCurves and the independent parameters against which the data need to be fitted.

Modelica name of coefficient in data record Polynomial of the above info section Parameters for curve fit

capFunT cap_θ(θ_e,in, θ_c,in) = a₁ + a₂ θ_e,in + a₃ θ_e,in ² + a₄ θ_c,in + a₅ θ_c,in ² + a₆ θ_e,in θ_c,in cap_θ, θ_e,in, θ_c,in

capFunFF cap_FF(ff) = b₁ + b₂ ff + b₃ ff² + b₄ff³ + ... cap_FF, ff

EIRFunT EIR_θ(θ_e,in, θ_c,in) = a₁ + a₂ θ_e,in + a₃ θ_e,in ² + a₄ θ_c,in + a₅ θ_c,in ² + a₆ θ_e,in θ_c,in EIR_θ, θ_e,in, θ_c,in

EIRFunFF EIR_FF(ff) = b₁ + b₂ ff + b₃ ff² + b₄ff³ + ... EIR_FF, ff

Modelica name of coefficient in data record	Polynomial of the above info section	Parameters for curve fit
`capFunT`	cap_θ(θ_e,in, θ_c,in) = a₁ + a₂ θ_e,in + a₃ θ_e,in ² + a₄ θ_c,in + a₅ θ_c,in ² + a₆ θ_e,in θ_c,in	cap_θ, θ_e,in, θ_c,in
`capFunFF`	cap_FF(ff) = b₁ + b₂ ff + b₃ ff² + b₄ff³ + ...	cap_FF, ff
`EIRFunT`	EIR_θ(θ_e,in, θ_c,in) = a₁ + a₂ θ_e,in + a₃ θ_e,in ² + a₄ θ_c,in + a₅ θ_c,in ² + a₆ θ_e,in θ_c,in	EIR_θ, θ_e,in, θ_c,in
`EIRFunFF`	EIR_FF(ff) = b₁ + b₂ ff + b₃ ff² + b₄ff³ + ...	EIR_FF, ff

Note that for the above polynomials, the units for temperature is degree Celsius and not Kelvins.

Implementation

A parameter of the performance curve is the range of mass flow fraction ff for which the data are valid. Below this range, this model reduces the cooling capacity and the energy input ratio so that both are zero if ff < ff_min/4, where ff_min is the minimum flow fraction for which the performance curves are valid.

Extends from Modelica.Blocks.Interfaces.BlockIcon (Basic graphical layout of input/output block).

Parameters

Type Name Default Description

Integer nSta Number of coil stages (not counting the off stage)

MassFlowRate m_flow_small Small mass flow rate for regularization [kg/s]

Stage sta[nSta] Performance data for this stage

Type	Name	Description
Integer	nSta	Number of coil stages (not counting the off stage)
MassFlowRate	m_flow_small	Small mass flow rate for regularization [kg/s]
Stage	sta[nSta]	Performance data for this stage

Connectors

Type Name Description

input IntegerInput stage Stage of coil, or 0/1 for variable-speed coil

input RealInput TConIn Temperature of air entering the condenser coil [K]

input RealInput m_flow Air mass flow rate at the evaporator [kg/s]

input RealInput TEvaIn Temperature of air entering the evaporator (wet bulb for wet coil and dry bulb for dry coil) [K]

output RealOutput Q_flow[nSta] Total cooling capacity [W]

output RealOutput EIR[nSta] Energy Input Ratio

Type	Name	Description
input IntegerInput	stage	Stage of coil, or 0/1 for variable-speed coil
input RealInput	TConIn	Temperature of air entering the condenser coil [K]
input RealInput	m_flow	Air mass flow rate at the evaporator [kg/s]
input RealInput	TEvaIn	Temperature of air entering the evaporator (wet bulb for wet coil and dry bulb for dry coil) [K]
output RealOutput	Q_flow[nSta]	Total cooling capacity [W]
output RealOutput	EIR[nSta]	Energy Input Ratio

Modelica definition

block CoolingCapacity 
  "Calculates cooling capacity at given temperature and flow fraction"
  extends Modelica.Blocks.Interfaces.BlockIcon;

  Modelica.Blocks.Interfaces.IntegerInput stage(final min=0) 
    "Stage of coil, or 0/1 for variable-speed coil";
  Modelica.Blocks.Interfaces.RealInput TConIn(
    quantity="Temperature",
    unit="K",
    displayUnit="degC") "Temperature of air entering the condenser coil ";
  Modelica.Blocks.Interfaces.RealInput m_flow(
    quantity="MassFlowRate",
    unit="kg/s") "Air mass flow rate at the evaporator";
  Modelica.Blocks.Interfaces.RealInput TEvaIn(
    quantity="Temperature",
    unit="K",
    displayUnit="degC") 
    "Temperature of air entering the evaporator (wet bulb for wet coil and dry bulb for dry coil)";
    
  parameter Integer nSta(min=1) 
    "Number of coil stages (not counting the off stage)";
  parameter Modelica.SIunits.MassFlowRate m_flow_small 
    "Small mass flow rate for regularization";
  parameter Buildings.Fluid.HeatExchangers.DXCoils.Data.Generic.BaseClasses.Stage
                                                                          sta[nSta] 
    "Performance data for this stage";
  output Real[nSta] ff(each min=0) 
    "Air flow fraction: ratio of actual air flow rate by rated mass flwo rate";
  Modelica.Blocks.Interfaces.RealOutput Q_flow[nSta](
    each max=0,
    each unit="W") "Total cooling capacity";
  Modelica.Blocks.Interfaces.RealOutput EIR[nSta](each min=0) 
    "Energy Input Ratio";
//------------------------------Cooling capacity---------------------------------//
  output Real cap_T[nSta](each min=0, each nominal=1, each start=1) 
    "Cooling capacity modification factor as a function of temperature";
  output Real cap_FF[nSta](each min=0, each nominal=1, each start=1) 
    "Cooling capacity modification factor as a function of flow fraction";
//----------------------------Energy Input Ratio---------------------------------//
  output Real EIR_T[nSta](each min=0, each nominal=1, each start=1) 
    "EIR modification factor as a function of temperature";
  output Real EIR_FF[nSta](each min=0, each nominal=1, each start=1) 
    "EIR modification factor as a function of flow fraction";
  output Real corFac[nSta](each min=0, each max=1, each nominal=1, each start=1) 
    "Correction factor that is one inside the valid flow fraction, and attains zero below the valid flow fraction";
protected 
  output Boolean checkBoundsTEva[nSta] 
    "Flag, used to check for out of bounds data";
  output Boolean checkBoundsTCon[nSta] 
    "Flag, used to check for out of bounds data";

initial algorithm 
  // Verify correctness of performance curves, and write warning if error is bigger than 10%
   for iSta in 1:nSta loop
     Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.Functions.warnIfPerformanceOutOfBounds(
       Buildings.Utilities.Math.Functions.biquadratic(
         a=sta[iSta].perCur.capFunT,
         x1=Modelica.SIunits.Conversions.to_degC(sta[iSta].nomVal.TEvaIn_nominal),
         x2=Modelica.SIunits.Conversions.to_degC(sta[iSta].nomVal.TConIn_nominal)),
         msg="Capacity as a function of temperature ",
         curveName="sta[" + String(iSta) + "].perCur.capFunT");

     Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.Functions.warnIfPerformanceOutOfBounds(
       Buildings.Fluid.Utilities.extendedPolynomial(
         x=1,
         c=sta[iSta].perCur.capFunFF,
         xMin=sta[iSta].perCur.ffMin,
         xMax=sta[iSta].perCur.ffMin),
         msg="Capacity as a function of normalized mass flow rate ",
         curveName="sta[" + String(iSta) + "].perCur.capFunFF");

     Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.Functions.warnIfPerformanceOutOfBounds(
       Buildings.Utilities.Math.Functions.biquadratic(
         a=sta[iSta].perCur.EIRFunT,
         x1=Modelica.SIunits.Conversions.to_degC(sta[iSta].nomVal.TEvaIn_nominal),
         x2=Modelica.SIunits.Conversions.to_degC(sta[iSta].nomVal.TConIn_nominal)),
         msg="EIR as a function of temperature ",
         curveName="sta[" + String(iSta) + "].perCur.EIRFunT");

     Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.Functions.warnIfPerformanceOutOfBounds(
       Buildings.Fluid.Utilities.extendedPolynomial(
         x=1,
         c=sta[iSta].perCur.EIRFunFF,
         xMin=sta[iSta].perCur.ffMin,
         xMax=sta[iSta].perCur.ffMin),
         msg="EIR as a function of normalized mass flow rate ",
         curveName="sta[" + String(iSta) + "].perCur.EIRFunFF");
   end for;
   for iSta in 1:nSta loop
     checkBoundsTEva[iSta] :=true;
     checkBoundsTCon[iSta] :=true;
   end for;

equation 
    // Modelica requires to evaluate the when() block for each element in iSta=1...nSta.
    // But we only want to check the stage that is currently running.
    // Hence, the test starts with stage == iSta.
    for iSta in 1:nSta loop
   // Check whether data are outside of bounds
      when ( stage == iSta and pre(checkBoundsTEva[stage])) then
        assert( not (TEvaIn > sta[stage].perCur.TEvaInMax or TEvaIn < sta[stage].perCur.TEvaInMin),
        "*** Warning: Evaporator temperature TEvaIn is out of bounds in DX coil model at time = " + String(time) + ".
        stage     = " + String(iSta) + "
        TEvaInMin = " + String(sta[iSta].perCur.TEvaInMin) + " Kelvin (" +
                        String(Modelica.SIunits.Conversions.to_degC(sta[iSta].perCur.TEvaInMin)) + " degC)
        TEvaIn    = " + String(TEvaIn) + " Kelvin (" + String(Modelica.SIunits.Conversions.to_degC(TEvaIn)) + " degC)
        TEvaInMax = " + String(sta[iSta].perCur.TEvaInMax) + " Kelvin (" +
                        String(Modelica.SIunits.Conversions.to_degC(sta[iSta].perCur.TEvaInMax)) + " degC)
        Extrapolation can introduce large errors.
        This warning will only be reported once for each stage.",
        level=  AssertionLevel.warning);
        checkBoundsTEva[iSta] = false;
      end when;
      when ( stage == iSta and pre(checkBoundsTCon[stage])) then
        assert( not ( TConIn > sta[stage].perCur.TConInMax or TConIn < sta[stage].perCur.TConInMin),
        "*** Warning: Condenser temperature TConIn is out of bounds in DX coil model at time = " + String(time) + ".
        stage     = " + String(iSta) + "
        TConInMin = " + String(sta[iSta].perCur.TConInMin) + " Kelvin (" +
                        String(Modelica.SIunits.Conversions.to_degC(sta[iSta].perCur.TConInMin)) + " degC)
        TConIn    = " + String(TConIn) + " Kelvin (" + String(Modelica.SIunits.Conversions.to_degC(TConIn)) + " degC)
        TConInMax = " + String(sta[iSta].perCur.TConInMax) + " Kelvin (" +
                        String(Modelica.SIunits.Conversions.to_degC(sta[iSta].perCur.TConInMax)) + " degC)
        Extrapolation can introduce large errors.
        This warning will only be reported once for each stage.",
        level=  AssertionLevel.warning);
        checkBoundsTCon[iSta] = false;
      end when;
    end for;

if stage > 0 then
    for iSta in 1:nSta loop

    // Compute performance
    ff[iSta]=Buildings.Utilities.Math.Functions.smoothMax(
      x1=m_flow,
      x2=m_flow_small,
      deltaX=m_flow_small/10)/sta[iSta].nomVal.m_flow_nominal;
  //-------------------------Cooling capacity modifiers----------------------------//
    // Compute the DX coil capacity fractions, using a biquadratic curve.
    // Since the regression for capacity can have negative values
    // (for unreasonable temperatures), we constrain its return value to be
    // non-negative.
    cap_T[iSta] =Buildings.Utilities.Math.Functions.smoothMax(
      x1=Buildings.Utilities.Math.Functions.biquadratic(
        a=sta[iSta].perCur.capFunT,
        x1=Modelica.SIunits.Conversions.to_degC(TEvaIn),
        x2=Modelica.SIunits.Conversions.to_degC(TConIn)),
      x2=0.001,
      deltaX=0.0001) 
        "Cooling capacity modification factor as function of temperature";
    cap_FF[iSta] = Buildings.Fluid.Utilities.extendedPolynomial(
      x=ff[iSta],
      c=sta[iSta].perCur.capFunFF,
      xMin=sta[iSta].perCur.ffMin,
      xMax=sta[iSta].perCur.ffMin);
    //-----------------------Energy Input Ratio modifiers--------------------------//
    EIR_T[iSta] =Buildings.Utilities.Math.Functions.smoothMax(
      x1=Buildings.Utilities.Math.Functions.biquadratic(
        a=sta[iSta].perCur.EIRFunT,
        x1=Modelica.SIunits.Conversions.to_degC(TEvaIn),
        x2=Modelica.SIunits.Conversions.to_degC(TConIn)),
      x2=0.001,
      deltaX=0.0001);
    EIR_FF[iSta] = Buildings.Fluid.Utilities.extendedPolynomial(
       x=ff[iSta],
       c=sta[iSta].perCur.EIRFunFF,
       xMin=sta[iSta].perCur.ffMin,
       xMax=sta[iSta].perCur.ffMin) 
        "Cooling capacity modification factor as function of flow fraction";
    //------------ Correction factor for flow rate outside of validity of data ---//
    corFac[iSta] =Buildings.Utilities.Math.Functions.smoothHeaviside(
       x=ff[iSta] - sta[iSta].perCur.ffMin/4,
       delta=sta[iSta].perCur.ffMin/4);

    Q_flow[iSta] = corFac[iSta]*cap_T[iSta]*cap_FF[iSta]*sta[iSta].nomVal.Q_flow_nominal;
    EIR[iSta]    = corFac[iSta]*EIR_T[iSta]*EIR_FF[iSta]/sta[iSta].nomVal.COP_nominal;
    end for;
  else //cooling coil off
   ff     = fill(0, nSta);
   cap_T  = fill(0, nSta);
   cap_FF = fill(0, nSta);
   EIR_T  = fill(0, nSta);
   EIR_FF = fill(0, nSta);
   corFac = fill(0, nSta);
   Q_flow = fill(0, nSta);
   EIR    = fill(0, nSta);
  end if;
end CoolingCapacity;

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.DryCoil

Calculates dry coil condition

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.DryCoil

Information

This block calculates the rate of cooling and the coil surface condition under the assumption that the coil is dry.

The wet coil conditions are computed in Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.WetCoil. See Buildings.Fluid.HeatExchangers.DXCoils.UsersGuide for an explanation of the model.

Extends from Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.PartialCoilCondition (Partial block for dry and wet coil conditions).

Parameters

Type Name Default Description

DXCoil datCoi Performance data

Boolean variableSpeedCoil Flag, set to true for coil with variable speed

replaceable package Medium Modelica.Media.Interfaces.Pa... Medium model

Type	Name	Default	Description
DXCoil	datCoi		Performance data
Boolean	variableSpeedCoil		Flag, set to true for coil with variable speed
replaceable package Medium	Modelica.Media.Interfaces.Pa...	Medium model

Connectors

Type Name Description

input IntegerInput stage Stage of coil, or 0/1 for variable-speed coil

input RealInput speRat Speed ratio

input RealInput m_flow Air mass flow rate

input RealInput TEvaIn Temperature of air entering the cooling coil

input RealInput XEvaIn Inlet air mass fraction

input RealInput p Pressure at inlet of coil

input RealInput hEvaIn Specific enthalpy of air entering the coil

input RealInput TConIn Outside air dry bulb temperature for an air cooled condenser or wetbulb temperature for an evaporative cooled condenser [K]

output RealOutput EIR Energy Input Ratio

output RealOutput Q_flow Total cooling capacity [W]

replaceable package Medium Medium model

output RealOutput TDry Dry bulb temperature of air at ADP [K]

Type	Name	Description
input IntegerInput	stage	Stage of coil, or 0/1 for variable-speed coil
input RealInput	speRat	Speed ratio
input RealInput	m_flow	Air mass flow rate
input RealInput	TEvaIn	Temperature of air entering the cooling coil
input RealInput	XEvaIn	Inlet air mass fraction
input RealInput	p	Pressure at inlet of coil
input RealInput	hEvaIn	Specific enthalpy of air entering the coil
input RealInput	TConIn	Outside air dry bulb temperature for an air cooled condenser or wetbulb temperature for an evaporative cooled condenser [K]
output RealOutput	EIR	Energy Input Ratio
output RealOutput	Q_flow	Total cooling capacity [W]
replaceable package Medium	Medium model
output RealOutput	TDry	Dry bulb temperature of air at ADP [K]

Modelica definition

model DryCoil "Calculates dry coil condition"
 extends Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.PartialCoilCondition;
  replaceable package Medium =
      Modelica.Media.Interfaces.PartialCondensingGases "Medium model";
  Modelica.Blocks.Interfaces.RealOutput TDry(
    quantity="Temperature",
    unit="K",
    min=233.15,
    max=373.15) "Dry bulb temperature of air at ADP";
  Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.ApparatusDryPoint appDryPt(
    redeclare package Medium = Medium,
    final datCoi=datCoi,
    final variableSpeedCoil=variableSpeedCoil) 
    "Calculates air properties at dry coil condition";
equation 
  connect(appDryPt.TDry, TDry);
  connect(hEvaIn, appDryPt.hEvaIn);
  connect(XEvaIn, appDryPt.XEvaIn);
  connect(p, appDryPt.p);
  connect(m_flow, appDryPt.m_flow);
  connect(speRat, appDryPt.speRat);

  connect(speShiQ_flow.y, appDryPt.Q_flow);
  connect(TEvaIn, cooCap.TEvaIn);
  connect(appDryPt.stage, stage);
end DryCoil;

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.DryWetSelector

Selects results from dry or wet coil

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.DryWetSelector

Information

This block smoothly transitions the results from the dry coil and the wet coil computation. The independent variable for the transition is the difference between the water mass fractions at the apparatus dew point, as computed by the wet coil model, and the coil inlet mass fraction.

Connectors

Type Name Description

input RealInput XEvaIn Inlet air mass fraction

input RealInput XADP Mass fraction at ADP

input RealInput EIRWet Energy Input Ratio

input RealInput QWet_flow Total cooling capacity [W]

input RealInput SHRWet Sensible Heat Ratio: Ratio of sensible heat load to total heat load

input RealInput TADPWet Dry bulb temperature of air at ADP [K]

input RealInput mWetWat_flow Mass flow rate of water condensed at cooling coil [kg/s]

input RealInput EIRDry Energy Input Ratio

input RealInput QDry_flow Total cooling capacity [W]

input RealInput TADPDry Dry bulb temperature of air at ADP [K]

output RealOutput EIR Energy Input Ratio

output RealOutput Q_flow Total cooling capacity [W]

output RealOutput SHR Sensible Heat Ratio: Ratio of sensible heat load to total heat load

output RealOutput TADP Dry bulb temperature of air at ADP [K]

output RealOutput mWat_flow Mass flow rate of water condensed at cooling coil [kg/s]

Type	Name	Description
input RealInput	XEvaIn	Inlet air mass fraction
input RealInput	XADP	Mass fraction at ADP
input RealInput	EIRWet	Energy Input Ratio
input RealInput	QWet_flow	Total cooling capacity [W]
input RealInput	SHRWet	Sensible Heat Ratio: Ratio of sensible heat load to total heat load
input RealInput	TADPWet	Dry bulb temperature of air at ADP [K]
input RealInput	mWetWat_flow	Mass flow rate of water condensed at cooling coil [kg/s]
input RealInput	EIRDry	Energy Input Ratio
input RealInput	QDry_flow	Total cooling capacity [W]
input RealInput	TADPDry	Dry bulb temperature of air at ADP [K]
output RealOutput	EIR	Energy Input Ratio
output RealOutput	Q_flow	Total cooling capacity [W]
output RealOutput	SHR	Sensible Heat Ratio: Ratio of sensible heat load to total heat load
output RealOutput	TADP	Dry bulb temperature of air at ADP [K]
output RealOutput	mWat_flow	Mass flow rate of water condensed at cooling coil [kg/s]

Modelica definition

block DryWetSelector "Selects results from dry or wet coil"

 constant Modelica.SIunits.MassFraction deltaX=0.0001 
    "Range of x where transition between dry and wet coil occurs";
  Modelica.Blocks.Interfaces.RealInput XEvaIn "Inlet air mass fraction";
  Modelica.Blocks.Interfaces.RealInput XADP "Mass fraction at ADP";

  Modelica.Blocks.Interfaces.RealInput EIRWet "Energy Input Ratio";
  Modelica.Blocks.Interfaces.RealInput QWet_flow(
    max=0,
    unit="W") "Total cooling capacity";
  Modelica.Blocks.Interfaces.RealInput SHRWet(
    min=0,
    max=1.0) 
    "Sensible Heat Ratio: Ratio of sensible heat load to total heat load";
  Modelica.Blocks.Interfaces.RealInput TADPWet(
    quantity="Temperature",
    unit="K",
    min=273.15,
    max=373.15) "Dry bulb temperature of air at ADP";
  Modelica.Blocks.Interfaces.RealInput mWetWat_flow(
    quantity="MassFlowRate",
    unit="kg/s") "Mass flow rate of water condensed at cooling coil";
  Modelica.Blocks.Interfaces.RealInput EIRDry "Energy Input Ratio";
  Modelica.Blocks.Interfaces.RealInput QDry_flow(max=0, unit="W") 
    "Total cooling capacity";
  Modelica.Blocks.Interfaces.RealInput TADPDry(
    quantity="Temperature",
    unit="K",
    min=273.15,
    max=373.15) "Dry bulb temperature of air at ADP";

  Modelica.Blocks.Interfaces.RealOutput EIR "Energy Input Ratio";
  Modelica.Blocks.Interfaces.RealOutput Q_flow(
    max=0,
    unit="W") "Total cooling capacity";
  Modelica.Blocks.Interfaces.RealOutput SHR(
    min=0,
    max=1.0) 
    "Sensible Heat Ratio: Ratio of sensible heat load to total heat load";
  Modelica.Blocks.Interfaces.RealOutput TADP(
    quantity="Temperature",
    unit="K",
    min=273.15,
    max=373.15) "Dry bulb temperature of air at ADP";
  Modelica.Blocks.Interfaces.RealOutput mWat_flow(
    quantity="MassFlowRate",
    unit="kg/s") "Mass flow rate of water condensed at cooling coil";

 output Real fraDry(min=0, max=1) 
    "Fraction of results that are taken from the dry coil model";
 output Real fraWet(min=0, max=1) 
    "Fraction of results that are taken from the wet coil model";
protected 
  output Modelica.SIunits.MassFraction dX 
    "Difference between apparatus dew point mass fraction of wet coil and inlet air mass fraction";
equation 
  dX = XADP-XEvaIn;
  fraDry=Buildings.Utilities.Math.Functions.spliceFunction(
    pos=+1,
    neg=0,
    x= dX+deltaX,
    deltax= deltaX);
  fraWet=1-fraDry;
  EIR       = fraDry * EIRDry    + fraWet * EIRWet;
  Q_flow    = fraDry * QDry_flow + fraWet * QWet_flow;
  SHR       = fraDry             + fraWet * SHRWet;
  TADP      = fraDry * TADPDry   + fraWet * TADPWet;
  mWat_flow =                      fraWet * mWetWat_flow;

end DryWetSelector;

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.DXCooling

DX cooling coil operation

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.DXCooling

Information

This block combines the models for the dry coil and the wet coil. Output of the block is the coil performance which, depending on the mass fraction at the apparatus dew point temperature and the mass fraction of the coil inlet air, may be from the dry coil, the wet coil, or a weighted average of the two.

Extends from Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.PartialCoilInterface (Partial block for DX coil).

Parameters

Type Name Default Description

DXCoil datCoi Performance data

replaceable package Medium Modelica.Media.Interfaces.Pa... Medium model

Boolean variableSpeedCoil Flag, set to true for coil with variable speed

Type	Name	Default	Description
DXCoil	datCoi		Performance data
replaceable package Medium	Modelica.Media.Interfaces.Pa...	Medium model
Boolean	variableSpeedCoil		Flag, set to true for coil with variable speed

Connectors

Type	Name	Description
input IntegerInput	stage	Stage of coil, or 0/1 for variable-speed coil
input RealInput	speRat	Speed ratio
input RealInput	m_flow	Air mass flow rate
input RealInput	TEvaIn	Temperature of air entering the cooling coil
input RealInput	XEvaIn	Inlet air mass fraction
input RealInput	p	Pressure at inlet of coil
input RealInput	hEvaIn	Specific enthalpy of air entering the coil
input RealInput	TConIn	Outside air dry bulb temperature for an air cooled condenser or wetbulb temperature for an evaporative cooled condenser [K]
output RealOutput	EIR	Energy Input Ratio
output RealOutput	Q_flow	Total cooling capacity [W]
replaceable package Medium	Medium model
output RealOutput	TCoiSur	Coil surface temperature [K]
output RealOutput	mWat_flow	Mass flow rate of water condensed at cooling coil [kg/s]
output RealOutput	SHR	Sensible Heat Ratio: Ratio of sensible heat load to total heat load

Modelica definition

model DXCooling "DX cooling coil operation "
  extends Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.PartialCoilInterface;
  replaceable package Medium =
      Modelica.Media.Interfaces.PartialCondensingGases "Medium model";

  constant Boolean variableSpeedCoil 
    "Flag, set to true for coil with variable speed";

  Modelica.Blocks.Interfaces.RealOutput TCoiSur(
    quantity="Temperature",
    unit="K",
    min=240,
    max=400) "Coil surface temperature";
  WetCoil wetCoi(
    redeclare final package Medium = Medium,
    final variableSpeedCoil = variableSpeedCoil,
    final datCoi=datCoi) "Wet coil condition";
  DryCoil dryCoi(
    redeclare final package Medium = Medium,
    final variableSpeedCoil = variableSpeedCoil,
    final datCoi=datCoi) "Dry coil condition";
  Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.DryWetSelector dryWet 
    "Actual coil condition";
  Modelica.Blocks.Interfaces.RealOutput mWat_flow(
    quantity="MassFlowRate",
    unit="kg/s") "Mass flow rate of water condensed at cooling coil";
  Modelica.Blocks.Interfaces.RealOutput SHR(
    min=0,
    max=1.0) 
    "Sensible Heat Ratio: Ratio of sensible heat load to total heat load";
equation 

  connect(TConIn, wetCoi.TConIn);
  connect(TConIn, dryCoi.TConIn);
  connect(m_flow, wetCoi.m_flow);
  connect(m_flow, dryCoi.m_flow);
  connect(TEvaIn, wetCoi.TEvaIn);
  connect(TEvaIn, dryCoi.TEvaIn);
  connect(p, wetCoi.p);
  connect(XEvaIn, wetCoi.XEvaIn);
  connect(hEvaIn, wetCoi.hEvaIn);
  connect(hEvaIn, dryCoi.hEvaIn);
  connect(p, dryCoi.p);
  connect(XEvaIn, dryCoi.XEvaIn);
  connect(speRat, wetCoi.speRat);
  connect(speRat, dryCoi.speRat);

  connect(XEvaIn, dryWet.XEvaIn);
  connect(stage, dryCoi.stage);
  connect(stage, wetCoi.stage);
  connect(dryWet.EIRWet, wetCoi.EIR);
  connect(wetCoi.Q_flow, dryWet.QWet_flow);
  connect(wetCoi.SHR, dryWet.SHRWet);
  connect(wetCoi.mWat_flow, dryWet.mWetWat_flow);
  connect(dryCoi.EIR, dryWet.EIRDry);
  connect(dryCoi.Q_flow, dryWet.QDry_flow);
  connect(dryCoi.TDry, dryWet.TADPDry);
  connect(wetCoi.TADP, dryWet.TADPWet);
  connect(dryWet.EIR, EIR);
  connect(dryWet.Q_flow, Q_flow);
  connect(dryWet.SHR, SHR);
  connect(dryWet.TADP, TCoiSur);
  connect(dryWet.mWat_flow, mWat_flow);
  connect(wetCoi.XADP, dryWet.XADP);
end DXCooling;

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.EssentialParameters

A partial block for essential parameters

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.EssentialParameters

Information

This partial block declares parameters that are required by most classes in the package Buildings.Fluid.HeatExchangers.DXCoils.

Parameters

Type Name Default Description

DXCoil datCoi Performance data

Type	Name	Default	Description
DXCoil	datCoi		Performance data

Modelica definition

partial block EssentialParameters 
  "A partial block for essential parameters"

  parameter Buildings.Fluid.HeatExchangers.DXCoils.Data.Generic.DXCoil
                                                                 datCoi 
    "Performance data";
protected 
  parameter Integer nSta=datCoi.nSta "Number of stages";
end EssentialParameters;

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.Evaporation

Model that computes evaporation of water that accumulated on the coil surface

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.Evaporation

Information

This model computes the water accumulation on the surface of a cooling coil. When the cooling coil operates, water is accumulated on the coil surface up to a maximum amount of water before water starts to drain away from the coil. When the coil is off, the accumulated water evaporates into the air stream.

Physical description

The calculations are based on Shirey et al. (2006).

Parameters

The maximum amount of water that can be accumulated is computed based on the following model, where we used the convention that latent heat removed from the air is negative: The parameter t_wet defines how long it takes for condensate to drip of the coil, assuming the coil starts completely dry and operates at the nominal operating point. Henderson et al. (2003) measured values for t_wet from 16.5 minutes (990 seconds) to 29 minutes (1740 seconds). Thus, we use a default value of t_wet=1400 seconds. The maximum amount of water that can accumulate on the coil is

m_max = -Q̇_L,nom t_wet ⁄ h_fg

where Q̇_L,nom<0 is the latent capacity at the nominal conditions and h_fg is the latent heat of evaporation.

When the coil is off, the water that has been accumulated on the coil evaporates into the air. The rate of water vapor evaporation at nominal operating conditions is defined by the parameter γ_nom. The definition of γ_nom is

γ_nom = Q̇_e,nom ⁄ Q̇_L,nom,

where Q̇_e,nom<0 is the rate of evaporation from the coil surface into the air stream right after the coil is switched off. The default value is γ_nom = 1.5.

Time dependent calculations

First, we discuss the accumulation of water on the coil. The rate of water accumulation is computed as

dm(t)⁄dt = -ṁ_wat(t)

where ṁ_wat(t) ≤ 0 is the water vapor mass flow rate that is extracted from the air at the current operating conditions. The actual water vapor mass flow rate that is removed from the air stream is as computed by the steady-state cooling coil performance model because for the coil outlet conditions, it does not matter whether the water accumulates on the coil or drips away from the coil. The initial value for the water accumulation is zero at the start of the simulation, and set to whatever water remains after the coil has been switched off and the water partially or completely evaporated into the air stream.

Now, we discuss the evaporation of the water on the coil surface into the air when the coil is off. The model in Shirey et al. (2006) is based on the assumption that the wet coil acts as an evaporative cooler. The change of water on the coil is

dm(t)⁄dt = -ṁ_max(t) η(t),

where ṁ_max(t) > 0 is the maximum water mass flow rate from the coil to the air and η(t) ∈ [0, 1] is the mass transfer effectiveness. For an evaporative cooler,

η(t) = 1-exp(-NTU(t)),

where NTU(t)=(hA)_m/Ċ_a are the number of mass transfer units and Ċ_a is the air capacity flow rate. The mass transfer coefficient (hA)_m is assumed to be proportional to the wet coil area, which is assumed to be equal to the ratio m(t) ⁄ m_max(t). Hence,

(hA)_m(t) ∝ m(t) ⁄ m_max(t).

Furthermore, the mass transfer coefficient depends on the velocity, and hence mass flow rate, as

(hA)_m(t) ∝ ṁ_a(t)^0.8,

where ṁ_a(t) is the current air mass flow rate, from which follows that

NTU(t) ∝ ṁ_a(t)^-0.2.

Therefore, the water mass flow rate from the coil into the air stream is

ṁ_wat(t) = ṁ_max(t) (1-exp(-K (m(t) ⁄ m_tot) (ṁ_a(t) ⁄ ṁ_a,nom)^-0.2 )),

where K > 0 is a constant to be determined below and the rate of change of water on the coil surface is as before

dm(t)⁄dt = -ṁ_wat(t).

The maximum mass transfer is

ṁ_max = ṁ_a (x_wb(t) - x(t)),

where x_wb(t) is the moisture content of air at the wet bulb state and x(t) is the actual moisture content of the air.

The constant K is determined from the nominal conditions as follows: At the nominal condition, we have m(t) ⁄ m_tot=1 and ṁ_a(t) ⁄ ṁ_a,nom=1, and, hence,

ṁ_nom = ṁ_max,nom (1-e^-K).

Because

ṁ_nom = - γ Q̇_L,nom ⁄ h_fg,

it follows that

K = -ln( 1 + γ_nom Q̇_L,nom ⁄ ṁ_a,nom ⁄ h_fg ⁄ (x_wb,nom-x_nom) ),

where x_nom is the humidity ratio at the coil at nominal condition and x_wb,nom is the humidity ratio at the wet bulb condition. Note that the ln(·) in the above equation requires that the argument is positive. See the implementation section below for how this is implemented.

Implementation

Potential for moisture transfer

For the potential that causes the moisture transfer, the difference in mass fraction between the current coil air and the coil air at the wet bulb conditions is used, provided that the air mass flow rate is within 1⁄3 of the nominal mass flow rate. For smaller air mass flow rates, the outlet conditions are used to ensure that the outlet conditions are not supersaturated air. The transition between these two driving potential is continuously differentiable in the mass flow rate.

Computation of mass transfer effectiveness

To evaluate

K = -ln( 1 + γ_nom Q̇_L,nom ⁄ ṁ_a,nom ⁄ h_fg ⁄ (x_wb,nom-x_nom) ),

the argument of the ln(·) function must be positive. However, often the parameter γ_nom is not known, and the default value of γ_nom = 1.5 may yield negative arguments for the function ln(·). We therefore set a lower bound on γ_nom as follows: Note that γ_nom must be such that 0 < ṁ_wat,nom < ṁ_max,nom. This condition is equivalent to

0 < γ_nom < ṁ_a,nom (x_wb,nom-x_nom) h_fg ⁄ (-Q̇_L,nom)

If γ_nom were equal to the right hand side, then the mass transfer effectiveness would be one. Hence, we set the maximum value of γ_nom,max to

γ_nom,max = 0.8 ṁ_a,nom (x_wb,nom-x_nom) h_fg ⁄ Q̇_L,nom,

which corresponds to a mass transfer effectiveness of 0.8. If γ_nom > γ_nom,max, the model sets γ_nom=γ_nom,max and writes a warning message.

Regularization near zero air mass flow rate

To regularize the equations near zero air mass flow rate and zero humidity on the coil, the following conditions have been imposed in such a way that the model is once continuously differentiable with bounded derivatives on compact sets:

We impose that ṁ_wat(t) → 0 as m → 0 to ensure that there is no evaporation if no water remains on the coil.
We impose that ṁ_wat(t) ⁄ ṁ_a(t) → 0 as ṁ_a(t) → 0 to ensure that the evaporation mass flow rate remains bounded at zero air flow rate and that it is symmetric near zero without having to trigger an event.

This is implemented by replacing for |ṁ_a(t)| < δ the equation for the evaporation mass flow rate by

ṁ_wat(t) = C m ṁ_a²(t) (x_wb,nom-x_nom),

where C=K δ^-0.2 which approximates continuity at |ṁ_a|=δ. Note that differentiability is ensured because the two equations are combined using the function Buildings.Utilities.Math.Functions.spliceFunction. Also note that based on physics, we would not have to square ṁ_a, but this was done to avoid an event that would be triggered if |ṁ_a| would have been used. Since the equation is active only at very small air flow rates when the fan is off, the error is negligible for typical applications.

References

Hugh I. Henderson, Jr., Don B. Shirey III and Richard A. Raustad. Understanding the Dehumidification Performance of Air-Conditioning Equipment at Part-Load Conditions. CIBSE/ASHRAE Conference, Edinburgh, Scotland, September 2003.

Don B. Shirey III, Hugh I. Henderson, Jr. and Richard A. Raustad. Understanding the Dehumidification Performance of Air-Conditioning Equipment at Part-Load Conditions. Florida Solar Energy Center, Technical Report FSEC-CR-1537-05, January 2006.

Extends from Modelica.Blocks.Interfaces.BlockIcon (Basic graphical layout of input/output block).

Parameters

Type Name Default Description

replaceable package Medium Modelica.Media.Interfaces.Pa... Medium model

NominalValues nomVal Nominal values

Boolean computeReevaporation true Set to true to compute reevaporation of water that accumulated on coil

Advanced

MassFlowRate mAir_flow_small 0.1*abs(nomVal.m_flow_nominal) Small mass flow rate for regularization of zero flow [kg/s]

Type	Name	Default	Description
replaceable package Medium	Modelica.Media.Interfaces.Pa...	Medium model
NominalValues	nomVal		Nominal values
Boolean	computeReevaporation	true	Set to true to compute reevaporation of water that accumulated on coil
Advanced
MassFlowRate	mAir_flow_small	0.1*abs(nomVal.m_flow_nominal)	Small mass flow rate for regularization of zero flow [kg/s]

Connectors

Type Name Description

replaceable package Medium Medium model

input BooleanInput on Control signal, true if compressor is on

input RealInput mWat_flow Water flow rate added into the medium [kg/s]

input RealInput TWat Temperature of liquid that is drained from or injected into volume [K]

input RealInput mAir_flow Air mass flow rate [kg/s]

input RealInput XEvaOut Water mass fraction [1]

input RealInput TEvaOut Air temperature [K]

output RealOutput mTotWat_flow Total moisture mass flow rate into the air stream [kg/s]

Type	Name	Description
replaceable package Medium	Medium model
input BooleanInput	on	Control signal, true if compressor is on
input RealInput	mWat_flow	Water flow rate added into the medium [kg/s]
input RealInput	TWat	Temperature of liquid that is drained from or injected into volume [K]
input RealInput	mAir_flow	Air mass flow rate [kg/s]
input RealInput	XEvaOut	Water mass fraction [1]
input RealInput	TEvaOut	Air temperature [K]
output RealOutput	mTotWat_flow	Total moisture mass flow rate into the air stream [kg/s]

Modelica definition

model Evaporation 
  "Model that computes evaporation of water that accumulated on the coil surface"
  extends Modelica.Blocks.Interfaces.BlockIcon;
  replaceable package Medium =
    Modelica.Media.Interfaces.PartialCondensingGases "Medium model";

  parameter Buildings.Fluid.HeatExchangers.DXCoils.Data.Generic.BaseClasses.NominalValues
     nomVal "Nominal values";

    parameter Modelica.SIunits.MassFlowRate mAir_flow_small(min=0)=
      0.1*abs(nomVal.m_flow_nominal) 
    "Small mass flow rate for regularization of zero flow";

  final parameter Modelica.SIunits.Mass mMax(min=0, fixed=false) 
    "Maximum mass of water that can accumulate on the coil";

  parameter Boolean computeReevaporation=true 
    "Set to true to compute reevaporation of water that accumulated on coil";

  ////////////////////////////////////////////////////////////////////////////////
  // Input and output signals
  Modelica.Blocks.Interfaces.BooleanInput on 
    "Control signal, true if compressor is on";

  Modelica.Blocks.Interfaces.RealInput mWat_flow(final quantity="MassFlowRate",
                                                 final unit = "kg/s") 
    "Water flow rate added into the medium";

  Modelica.Blocks.Interfaces.RealInput TWat(final quantity="Temperature",
                                            final unit = "K",
                                            displayUnit = "degC") 
    "Temperature of liquid that is drained from or injected into volume";

  Modelica.Blocks.Interfaces.RealInput mAir_flow(final quantity="MassFlowRate",
                                                 final unit = "kg/s") 
    "Air mass flow rate";

  Modelica.Blocks.Interfaces.RealInput XEvaOut(min=0, max=1, unit="1") 
    "Water mass fraction";

  Modelica.Blocks.Interfaces.RealInput TEvaOut(
    final quantity="Temperature",
    final unit="K",
    displayUnit="degC") "Air temperature";

  Modelica.Blocks.Interfaces.RealOutput mTotWat_flow(final quantity="MassFlowRate",
                                                     final unit = "kg/s") 
    "Total moisture mass flow rate into the air stream";

  Modelica.SIunits.Mass m(start=0, nominal=-5000*1400/2257E3) 
    "Mass of water that accumulated on the coil";

  Modelica.SIunits.MassFlowRate mEva_flow(max=0) 
    "Moisture mass flow rate that evaporates into air stream";
  ////////////////////////////////////////////////////////////////////////////////
  // Protected parameters and variables
protected 
  final parameter Modelica.SIunits.HeatFlowRate QSen_flow_nominal(max=0, fixed=false) 
    "Nominal sensible heat flow rate (negative number)";
  final parameter Modelica.SIunits.HeatFlowRate QLat_flow_nominal(max=0, fixed=false) 
    "Nominal latent heat flow rate (negative number)";
  final parameter Modelica.SIunits.MassFraction XEvaIn_nominal(fixed=false) 
    "Mass fraction at nominal inlet conditions";
  final parameter Modelica.SIunits.MassFraction XEvaOut_nominal(fixed=false) 
    "Mass fraction at nominal outlet conditions";
  final parameter Modelica.SIunits.Temperature TEvaOut_nominal(fixed=false) 
    "Dry bulb temperature at nominal outlet conditions";
  final parameter Modelica.SIunits.Temperature TEvaWetBulOut_nominal(fixed=false) 
    "Wet bulb temperature at nominal outlet conditions";
  final parameter Modelica.SIunits.MassFraction XEvaWetBulOut_nominal(fixed=false) 
    "Water vapor mass fraction at nominal outlet wet bulb condition";
  final parameter Modelica.SIunits.MassFraction dX_nominal(max=0, fixed=false) 
    "Driving potential for mass transfer";

  final parameter Modelica.SIunits.SpecificEnthalpy h_fg(fixed=false) 
    "Latent heat of vaporization";
  final parameter Real gammaMax(min=0, fixed=false) "Maximum value for gamma";
  final parameter Real logArg(min=0, fixed=false) 
    "Argument for the log function";
  final parameter Real K(min=0, fixed=false) 
    "Coefficient used for convective mass transfer";
  final parameter Real K2(min=0, fixed=false) 
    "Coefficient used for convective mass transfer";

  Modelica.SIunits.MassFraction XEvaWetBulOut 
    "Water vapor mass fraction at wet bulb conditions at air inlet";

   // off = not on is required because Dymola 2013 fails during model
   // check if on, which is an input connector, is used in the edge() function
  Boolean off=not on "Signal, true when component is off";

  Modelica.SIunits.Temperature TEvaWetBulOut "Wet bulb temperature at coil";
  Modelica.SIunits.MassFraction dX 
    "Difference in water vapor concentration that drives mass transfer";

  constant Modelica.SIunits.SpecificHeatCapacity cpAir_nominal=
     Buildings.Media.PerfectGases.Common.SingleGasData.Air.cp 
    "Specific heat capacity of air";
  constant Modelica.SIunits.SpecificHeatCapacity cpSte_nominal=
     Buildings.Media.PerfectGases.Common.SingleGasData.H2O.cp 
    "Specific heat capacity of water vapor";
initial equation 
  QSen_flow_nominal=nomVal.SHR_nominal * nomVal.Q_flow_nominal;
  QLat_flow_nominal=nomVal.Q_flow_nominal-QSen_flow_nominal;
  h_fg = Medium.enthalpyOfVaporization(nomVal.TEvaIn_nominal);

  mMax = -QLat_flow_nominal * nomVal.tWet/h_fg;

  XEvaIn_nominal=Buildings.Utilities.Psychrometrics.Functions.X_pSatpphi(
     pSat=Medium.saturationPressure(nomVal.TEvaIn_nominal),
     p=nomVal.p_nominal,
     phi=nomVal.phiIn_nominal);
  XEvaOut_nominal = XEvaIn_nominal + QLat_flow_nominal/nomVal.m_flow_nominal/h_fg;

  // Compute outlet air temperature
  TEvaOut_nominal =
  (nomVal.TEvaIn_nominal*Medium.specificHeatCapacityCp(
      Medium.setState_pTX(p=nomVal.p_nominal,
                          T=nomVal.TEvaIn_nominal,
                          X=cat(1, {XEvaIn_nominal, 1-XEvaIn_nominal})))
     + QSen_flow_nominal/nomVal.m_flow_nominal)
     / Medium.specificHeatCapacityCp(
      Medium.setState_pTX(p=nomVal.p_nominal,
                          T=nomVal.TEvaIn_nominal,
                          X=cat(1, {XEvaOut_nominal, 1-XEvaOut_nominal})));
  // Compute wet bulb temperature.
  // The computation of the wet bulb temperature requires an iterative
  // solution. It therefore cannot be done in a function.
  // The block Buildings.Utilities.Psychrometrics.WetBul_pTX
  // implements the equation below, but it cannot
  // be used here because blocks cannot be used to assign parameter
  // values.
  XEvaWetBulOut_nominal   = Buildings.Utilities.Psychrometrics.Functions.X_pSatpphi(
      pSat=  Medium.saturationPressureLiquid(Tsat=TEvaWetBulOut_nominal),
      p=     nomVal.p_nominal,
      phi=   1);
  TEvaWetBulOut_nominal = (TEvaOut_nominal
       * ((1-XEvaOut_nominal) * cpAir_nominal + XEvaOut_nominal * cpSte_nominal)
       + (XEvaOut_nominal-XEvaWetBulOut_nominal) * h_fg)/
            ( (1-XEvaWetBulOut_nominal)*cpAir_nominal + XEvaWetBulOut_nominal * cpSte_nominal);

  // Potential difference in moisture concentration that drives mass transfer at nominal condition
  dX_nominal = XEvaOut_nominal-XEvaWetBulOut_nominal;
  if (dX_nominal > 1E-10) then
     Modelica.Utilities.Streams.print("Warning: In DX coil model, dX_nominal = " + String(dX_nominal) + "
       This means that the coil is not dehumidifying air at the nominal conditions.
       Check nominal parameters.
         " + Buildings.Fluid.HeatExchangers.DXCoils.Data.Generic.BaseClasses.nominalValuesToString(
                                                                                           nomVal));
  end if;

  gammaMax = 0.8 * nomVal.m_flow_nominal * dX_nominal * h_fg / QLat_flow_nominal;

  // If gamma is bigger than a maximum value, write a warning and then
  // use the smaller value.
  if (nomVal.gamma > gammaMax) then
     Modelica.Utilities.Streams.print("Warning: In DX coil model, gamma is too large for these coil conditions.
  Instead of gamma = " + String(nomVal.gamma) + ", a value of " + String(gammaMax) + ", which 
  corresponds to a mass transfer effectiveness of 0.8, will be used.
  Coil nominal performance data are:
   nomVal.m_flow_nominal = " + String(nomVal.m_flow_nominal) + "
   dX_nominal = XEvaOut_nominal-XEvaWetBulOut_nominal = " + String(XEvaOut_nominal) + " - " +
      String(XEvaWetBulOut_nominal) + " = " + String(dX_nominal) + "
   QLat_flow_nominal  = " + String(QLat_flow_nominal) + "\n");
  end if;

  logArg = 1-min(nomVal.gamma, gammaMax)*QLat_flow_nominal/nomVal.m_flow_nominal/h_fg/dX_nominal;

  K = -Modelica.Math.log(logArg);
  K2 = K/mMax*nomVal.m_flow_nominal^(-0.2);

  assert(QLat_flow_nominal < 0, "QLat_nominal must be a negative number. Check parameters.");

  assert(K > 0, "Require K>0 but received " + String(K) + "
    The parameter are:
    QSen_flow_nominal     = " + String(QSen_flow_nominal) + "
    QLat_flow_nominal     = " + String(QLat_flow_nominal) + "
    XEvaOut_nominal        = " + String(XEvaOut_nominal) + "
   " + Buildings.Fluid.HeatExchangers.DXCoils.Data.Generic.BaseClasses.nominalValuesToString(
                                                                                     nomVal) + "
  Check parameters. Maybe the sensible heat ratio is too big, or the mass flow rate too small.");

equation 
  // When the coil switches off, set accumulated water to
  // lower value of actual accumulated water or maximum water content
  if computeReevaporation then
    when edge(off) then
      reinit(m, min(m, mMax));
    end when;

    if on then
      dX = 0;
      mEva_flow = 0;
      mTotWat_flow = mWat_flow;
      der(m) = -mWat_flow;
      TEvaWetBulOut = 293.15;
      XEvaWetBulOut = 0;
    else
      // Compute wet bulb temperature.
      // The computation of the wet bulb temperature requires an iterative
      // solution. It therefore cannot be done in a function.
      // The block Buildings.Utilities.Psychrometrics.WetBul_pTX
      // implements the equation below, but it is not used here
      // because otherwise, in each branch of the if-then construct,
      // an iteration would be done. This would be inefficient because
      // the wet bulb conditions are only needed in this branch.
      XEvaWetBulOut = Buildings.Utilities.Psychrometrics.Functions.X_pSatpphi(
        pSat=  Medium.saturationPressureLiquid(Tsat=TEvaWetBulOut),
        p=     nomVal.p_nominal,
        phi=   1);
      TEvaWetBulOut = (TEvaOut * ((1-XEvaOut) * cpAir_nominal + XEvaOut * cpSte_nominal)
         + (XEvaOut-XEvaWetBulOut) * h_fg)/
              ( (1-XEvaWetBulOut)*cpAir_nominal + XEvaWetBulOut * cpSte_nominal);

      dX = smooth(1, noEvent(
         Buildings.Utilities.Math.Functions.spliceFunction(
         pos=XEvaOut,
         neg=XEvaWetBulOut,
         x=abs(mAir_flow)-nomVal.m_flow_nominal/2,
         deltax=nomVal.m_flow_nominal/3)))
        - XEvaWetBulOut;
      mEva_flow = -smooth(1, noEvent(dX *
        Buildings.Utilities.Math.Functions.spliceFunction(
         pos=if abs(mAir_flow) > mAir_flow_small/3 then 
            abs(mAir_flow) * (1-Modelica.Math.exp(-K2*m*abs(mAir_flow)^(-0.2))) else 0,
         neg=K2*mAir_flow_small^(-0.2)*m*mAir_flow^2,
         x=abs(mAir_flow)- 2*mAir_flow_small/3,
         deltax=2*mAir_flow_small/6)));
      der(m) = -mEva_flow;
      mTotWat_flow = mWat_flow + mEva_flow;
    end if;

  else // The model is configured to not compute reevaporation
    dX = 0;
    mEva_flow = 0;
    mTotWat_flow = mWat_flow;
    m = 0;
    TEvaWetBulOut = 293.15;
    XEvaWetBulOut = 0;
  end if;

end Evaporation;

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.InputPower

Electrical power consumed by the unit

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.InputPower

Information

This block calculates total electrical energy consumed by the unit using the rate of cooling and the energy input ratio EIR.

The electrical energy consumed by the unit is

P = -Q_cool EIR

Extends from Modelica.Blocks.Interfaces.BlockIcon (Basic graphical layout of input/output block).

Connectors

Type Name Description

input RealInput Q_flow Cooling capacity of the coil [W]

input RealInput EIR Energy input ratio

input RealInput SHR Sensible heat ratio

output RealOutput P Electrical power consumed by the unit [W]

output RealOutput QSen_flow Sensible heat flow rate [W]

output RealOutput QLat_flow Latent heat flow rate [W]

Type	Name	Description
input RealInput	Q_flow	Cooling capacity of the coil [W]
input RealInput	EIR	Energy input ratio
input RealInput	SHR	Sensible heat ratio
output RealOutput	P	Electrical power consumed by the unit [W]
output RealOutput	QSen_flow	Sensible heat flow rate [W]
output RealOutput	QLat_flow	Latent heat flow rate [W]

Modelica definition

block InputPower "Electrical power consumed by the unit"
  extends Modelica.Blocks.Interfaces.BlockIcon;
   Modelica.Blocks.Interfaces.RealInput Q_flow(
    quantity="Power",
    unit="W") "Cooling capacity of the coil";
  Modelica.Blocks.Interfaces.RealInput EIR "Energy input ratio";
  Modelica.Blocks.Interfaces.RealInput SHR(min=0, max=1) "Sensible heat ratio";

  Modelica.Blocks.Interfaces.RealOutput P(
    quantity="Power",
    unit="W") "Electrical power consumed by the unit";
  Modelica.Blocks.Interfaces.RealOutput QSen_flow(quantity="Power", unit="W") 
    "Sensible heat flow rate";
  Modelica.Blocks.Interfaces.RealOutput QLat_flow(quantity="Power", unit="W") 
    "Latent heat flow rate";
equation 
  P = -EIR*Q_flow;
  QSen_flow = Q_flow * SHR;
  QLat_flow = Q_flow - QSen_flow;
end InputPower;

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.NominalCondition

Calculates inlet and outlet fluid parameters at nominal condition

Information

This block calculates inlet and outlet fluid parameters at the nominal condition. These parameters are required to determine the apparatus dew point at the nominal condition.

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

Parameters

Type Name Default Description

replaceable package Medium Modelica.Media.Interfaces.Pa... Medium model

NominalValues per Performance data

Type	Name	Default	Description
replaceable package Medium	Modelica.Media.Interfaces.Pa...	Medium model
NominalValues	per		Performance data

Modelica definition

record NominalCondition 
  "Calculates inlet and outlet fluid parameters at nominal condition"
  extends Modelica.Icons.Record;
  replaceable package Medium =
      Modelica.Media.Interfaces.PartialCondensingGases "Medium model";
  parameter Buildings.Fluid.HeatExchangers.DXCoils.Data.Generic.BaseClasses.NominalValues
                                                                          per 
    "Performance data";
  final parameter Modelica.SIunits.MassFraction XEvaIn_nominal=
     Buildings.Utilities.Psychrometrics.Functions.X_pSatpphi(
        pSat=Medium.saturationPressure(per.TEvaIn_nominal),
        p=per.p_nominal,
        phi=per.phiIn_nominal) 
    "Rated/Nominal mass fraction of air entering coil";
  final parameter Modelica.SIunits.SpecificEnthalpy hEvaIn_nominal=
   Medium.h_pTX(
     p=per.p_nominal,
     T=per.TEvaIn_nominal,
     X=cat(1,{XEvaIn_nominal}, {1-sum({XEvaIn_nominal})})) 
    "Rated enthalpy of air entering cooling coil";
  final parameter Modelica.SIunits.SpecificEnthalpy hOut_nominal=
    hEvaIn_nominal + per.Q_flow_nominal / per.m_flow_nominal 
    "Rated enthalpy of air exiting cooling coil";
  final parameter Modelica.SIunits.Temperature TOut_nominal=
    per.TEvaIn_nominal + (per.SHR_nominal * per.Q_flow_nominal)/(per.m_flow_nominal * Cp_nominal) 
    "Dry-bulb temperature of the air leaving the cooling coil at nominal condition";
  final parameter Modelica.SIunits.MassFraction XEvaOut_nominal(start=0.005, min=0, max=1.0)=
     XEvaIn_nominal + (hOut_nominal- hEvaIn_nominal)*(1-per.SHR_nominal)/
     Medium.enthalpyOfCondensingGas(T=per.TEvaIn_nominal) 
    "Rated/Nominal mass fraction of air leaving the coil";
protected 
  parameter Modelica.SIunits.SpecificHeatCapacity Cp_nominal=
    Medium.specificHeatCapacityCp(Medium.setState_pTX(
          p=per.p_nominal, T=per.TEvaIn_nominal, X=cat(1,{XEvaIn_nominal}, {1-sum({XEvaIn_nominal})}))) 
    "Specific heat of air at specified nominal condition";
end NominalCondition;

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.PartialCoilCondition

Partial block for dry and wet coil conditions

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.PartialCoilCondition

Information

This partial block is the base class for Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.DryCoil and Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.WetCoil.

Extends from Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.PartialCoilInterface (Partial block for DX coil).

Parameters

Type Name Default Description

DXCoil datCoi Performance data

Boolean variableSpeedCoil Flag, set to true for coil with variable speed

Type	Name	Default	Description
DXCoil	datCoi		Performance data
Boolean	variableSpeedCoil		Flag, set to true for coil with variable speed

Connectors

Type	Name	Description
input IntegerInput	stage	Stage of coil, or 0/1 for variable-speed coil
input RealInput	speRat	Speed ratio
input RealInput	m_flow	Air mass flow rate
input RealInput	TEvaIn	Temperature of air entering the cooling coil
input RealInput	XEvaIn	Inlet air mass fraction
input RealInput	p	Pressure at inlet of coil
input RealInput	hEvaIn	Specific enthalpy of air entering the coil
input RealInput	TConIn	Outside air dry bulb temperature for an air cooled condenser or wetbulb temperature for an evaporative cooled condenser [K]
output RealOutput	EIR	Energy Input Ratio
output RealOutput	Q_flow	Total cooling capacity [W]

Modelica definition

partial block PartialCoilCondition 
  "Partial block for dry and wet coil conditions"
  import Buildings;
  extends Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.PartialCoilInterface;

  constant Boolean variableSpeedCoil 
    "Flag, set to true for coil with variable speed";

  Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.CoolingCapacity cooCap(
    final sta=datCoi.sta,
    final nSta=datCoi.nSta,
    final m_flow_small=datCoi.m_flow_small) "Performance data";

protected 
  SpeedShift speShiEIR(
    final variableSpeedCoil=variableSpeedCoil,
    final nSta=nSta,
    final speSet=datCoi.sta.spe) "Interpolates EIR";
  SpeedShift speShiQ_flow(
    final variableSpeedCoil=variableSpeedCoil,
    final nSta=nSta,
    final speSet=datCoi.sta.spe) "Interpolates Q_flow";
equation 

  connect(cooCap.EIR, speShiEIR.u);
  connect(cooCap.Q_flow, speShiQ_flow.u);
  connect(speShiEIR.y, EIR);
  connect(speRat, speShiEIR.speRat);
  connect(speRat, speShiQ_flow.speRat);
  connect(speShiQ_flow.y, Q_flow);
  connect(stage, speShiQ_flow.stage);
  connect(speShiEIR.stage, stage);
  connect(cooCap.m_flow, m_flow);
  connect(cooCap.TConIn, TConIn);
  connect(cooCap.stage, stage);
end PartialCoilCondition;

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.PartialCoilInterface

Partial block for DX coil

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.PartialCoilInterface

Information

This partial block declares the inputs and outputs that are common for Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.CoilCondition and Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.DXCooling.

Extends from Modelica.Blocks.Interfaces.BlockIcon (Basic graphical layout of input/output block), Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.EssentialParameters (A partial block for essential parameters).

Parameters

Type Name Default Description

DXCoil datCoi Performance data

Type	Name	Default	Description
DXCoil	datCoi		Performance data

Connectors

Type	Name	Description
input IntegerInput	stage	Stage of coil, or 0/1 for variable-speed coil
input RealInput	speRat	Speed ratio
input RealInput	m_flow	Air mass flow rate
input RealInput	TEvaIn	Temperature of air entering the cooling coil
input RealInput	XEvaIn	Inlet air mass fraction
input RealInput	p	Pressure at inlet of coil
input RealInput	hEvaIn	Specific enthalpy of air entering the coil
input RealInput	TConIn	Outside air dry bulb temperature for an air cooled condenser or wetbulb temperature for an evaporative cooled condenser [K]
output RealOutput	EIR	Energy Input Ratio
output RealOutput	Q_flow	Total cooling capacity [W]

Modelica definition

partial block PartialCoilInterface "Partial block for DX coil"
  extends Modelica.Blocks.Interfaces.BlockIcon;
  extends Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.EssentialParameters;
  Modelica.Blocks.Interfaces.IntegerInput stage 
    "Stage of coil, or 0/1 for variable-speed coil";
  Modelica.Blocks.Interfaces.RealInput speRat "Speed ratio";
  Modelica.Blocks.Interfaces.RealInput m_flow "Air mass flow rate";
  Modelica.Blocks.Interfaces.RealInput TEvaIn 
    "Temperature of air entering the cooling coil";
  Modelica.Blocks.Interfaces.RealInput XEvaIn "Inlet air mass fraction";
  Modelica.Blocks.Interfaces.RealInput p "Pressure at inlet of coil";
  Modelica.Blocks.Interfaces.RealInput hEvaIn 
    "Specific enthalpy of air entering the coil";
  Modelica.Blocks.Interfaces.RealInput TConIn(
    unit="K",
    displayUnit="degC") 
    "Outside air dry bulb temperature for an air cooled condenser or wetbulb temperature for an evaporative cooled condenser";
  Modelica.Blocks.Interfaces.RealOutput EIR "Energy Input Ratio";
  Modelica.Blocks.Interfaces.RealOutput Q_flow(
    max=0,
    unit="W") "Total cooling capacity";

end PartialCoilInterface;

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.PartialDXCoil

Partial model for DX coil

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.PartialDXCoil

Information

This partial model is the base class for Buildings.Fluid.HeatExchangers.DXCoils.SingleSpeed Buildings.Fluid.HeatExchangers.DXCoils.MultiStage and Buildings.Fluid.HeatExchangers.DXCoils.VariableSpeed.

See Buildings.Fluid.HeatExchangers.DXCoils.UsersGuide for an explanation of the model.

Extends from Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.EssentialParameters (A partial block for essential parameters), Buildings.Fluid.BaseClasses.IndexWater (Computes the index of the water substance), Buildings.Fluid.Interfaces.TwoPortHeatMassExchanger (Partial model transporting one fluid stream with storing mass or energy).

Parameters

Type Name Default Description

DXCoil datCoi Performance data

replaceable package Medium PartialCondensingGases Medium model

Nominal condition

MassFlowRate m_flow_nominal datCoi.sta[nSta].nomVal.m_fl... Nominal mass flow rate [kg/s]

Pressure dp_nominal Pressure [Pa]

Initialization

MassFlowRate m_flow.start 0 Mass flow rate from port_a to port_b (m_flow > 0 is design flow direction) [kg/s]

Pressure dp.start 0 Pressure difference between port_a and port_b [Pa]

Assumptions

Boolean allowFlowReversal system.allowFlowReversal = true to allow flow reversal, false restricts to design direction (port_a -> port_b)

Advanced

MassFlowRate m_flow_small 1E-4*abs(m_flow_nominal) Small mass flow rate for regularization of zero flow [kg/s]

Boolean homotopyInitialization true = true, use homotopy method

Diagnostics

Boolean show_V_flow false = true, if volume flow rate at inflowing port is computed

Boolean show_T false = true, if actual temperature at port is computed (may lead to events)

Flow resistance

Boolean from_dp false = true, use m_flow = f(dp) else dp = f(m_flow)

Boolean linearizeFlowResistance false = true, use linear relation between m_flow and dp for any flow rate

Real deltaM 0.1 Fraction of nominal flow rate where flow transitions to laminar

Dynamics

Nominal condition

Time tau 30 Time constant at nominal flow (if energyDynamics <> SteadyState) [s]

Equations

Dynamics energyDynamics Modelica.Fluid.Types.Dynamic... Formulation of energy balance

Dynamics massDynamics energyDynamics Formulation of mass balance

Moisture balance

Boolean computeReevaporation true Set to true to compute reevaporation of water that accumulated on coil

Initialization

AbsolutePressure p_start Medium.p_default Start value of pressure [Pa]

Temperature T_start Medium.T_default Start value of temperature [K]

MassFraction X_start[Medium.nX] Medium.X_default Start value of mass fractions m_i/m [kg/kg]

ExtraProperty C_start[Medium.nC] fill(0, Medium.nC) Start value of trace substances

Type	Name	Default	Description
DXCoil	datCoi		Performance data
replaceable package Medium	PartialCondensingGases	Medium model
Nominal condition
MassFlowRate	m_flow_nominal	datCoi.sta[nSta].nomVal.m_fl...	Nominal mass flow rate [kg/s]
Pressure	dp_nominal		Pressure [Pa]
Initialization
MassFlowRate	m_flow.start	0	Mass flow rate from port_a to port_b (m_flow > 0 is design flow direction) [kg/s]
Pressure	dp.start	0	Pressure difference between port_a and port_b [Pa]
Assumptions
Boolean	allowFlowReversal	system.allowFlowReversal	= true to allow flow reversal, false restricts to design direction (port_a -> port_b)
Advanced
MassFlowRate	m_flow_small	1E-4*abs(m_flow_nominal)	Small mass flow rate for regularization of zero flow [kg/s]
Boolean	homotopyInitialization	true	= true, use homotopy method
Diagnostics
Boolean	show_V_flow	false	= true, if volume flow rate at inflowing port is computed
Boolean	show_T	false	= true, if actual temperature at port is computed (may lead to events)
Flow resistance
Boolean	from_dp	false	= true, use m_flow = f(dp) else dp = f(m_flow)
Boolean	linearizeFlowResistance	false	= true, use linear relation between m_flow and dp for any flow rate
Real	deltaM	0.1	Fraction of nominal flow rate where flow transitions to laminar
Dynamics
Nominal condition
Time	tau	30	Time constant at nominal flow (if energyDynamics <> SteadyState) [s]
Equations
Dynamics	energyDynamics	Modelica.Fluid.Types.Dynamic...	Formulation of energy balance
Dynamics	massDynamics	energyDynamics	Formulation of mass balance
Moisture balance
Boolean	computeReevaporation	true	Set to true to compute reevaporation of water that accumulated on coil
Initialization
AbsolutePressure	p_start	Medium.p_default	Start value of pressure [Pa]
Temperature	T_start	Medium.T_default	Start value of temperature [K]
MassFraction	X_start[Medium.nX]	Medium.X_default	Start value of mass fractions m_i/m [kg/kg]
ExtraProperty	C_start[Medium.nC]	fill(0, Medium.nC)	Start value of trace substances

Connectors

Type Name Description

replaceable package Medium Medium in the component

FluidPort_a port_a Fluid connector a (positive design flow direction is from port_a to port_b)

FluidPort_b port_b Fluid connector b (positive design flow direction is from port_a to port_b)

input RealInput TConIn Outside air dry bulb temperature for an air cooled condenser or wetbulb temperature for an evaporative cooled condenser [K]

output RealOutput P Electrical power consumed by the unit [W]

output RealOutput QSen_flow Sensible heat flow rate [W]

output RealOutput QLat_flow Latent heat flow rate [W]

Type	Name	Description
replaceable package Medium	Medium in the component
FluidPort_a	port_a	Fluid connector a (positive design flow direction is from port_a to port_b)
FluidPort_b	port_b	Fluid connector b (positive design flow direction is from port_a to port_b)
input RealInput	TConIn	Outside air dry bulb temperature for an air cooled condenser or wetbulb temperature for an evaporative cooled condenser [K]
output RealOutput	P	Electrical power consumed by the unit [W]
output RealOutput	QSen_flow	Sensible heat flow rate [W]
output RealOutput	QLat_flow	Latent heat flow rate [W]

Modelica definition

partial model PartialDXCoil "Partial model for DX coil"
  extends Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.EssentialParameters;
  extends Buildings.Fluid.BaseClasses.IndexWater;
  extends Buildings.Fluid.Interfaces.TwoPortHeatMassExchanger(
    redeclare package Medium = Medium,
    redeclare final Buildings.Fluid.MixingVolumes.MixingVolumeMoistAir vol,
    final m_flow_nominal = datCoi.sta[nSta].nomVal.m_flow_nominal);

  Modelica.Blocks.Interfaces.RealInput TConIn(
    unit="K",
    displayUnit="degC") 
    "Outside air dry bulb temperature for an air cooled condenser or wetbulb temperature for an evaporative cooled condenser";
  Modelica.Blocks.Interfaces.RealOutput P(
    quantity="Power",
    unit="W") "Electrical power consumed by the unit";
  Modelica.Blocks.Interfaces.RealOutput QSen_flow(quantity="Power", unit="W") 
    "Sensible heat flow rate";
  Modelica.Blocks.Interfaces.RealOutput QLat_flow(quantity="Power", unit="W") 
    "Latent heat flow rate";

  Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.DXCooling dxCoo(
    redeclare final package Medium = Medium,
    final datCoi=datCoi) "DX cooling coil operation";

  Evaporation eva(redeclare final package Medium = Medium,
                  final nomVal=datCoi.sta[nSta].nomVal,
                  final computeReevaporation = computeReevaporation) 
    "Model that computes evaporation of water that accumulated on the coil surface";
  parameter Boolean computeReevaporation=true 
    "Set to true to compute reevaporation of water that accumulated on coil";

  // Flow reversal is not needed. Also, if ff < ffMin/4, then
  // Q_flow and EIR are set the zero. Hence, it is safe to assume
  // forward flow, which will avoid an event
protected 
  Modelica.SIunits.SpecificEnthalpy hEvaIn=
    inStream(port_a.h_outflow) "Enthalpy of air entering the cooling coil";
  Modelica.SIunits.Temperature TEvaIn = Medium.T_phX(p=port_a.p, h=hEvaIn, X=XEvaIn) 
    "Dry bulb temperature of air entering the cooling coil";
  Modelica.SIunits.MassFraction XEvaIn[Medium.nXi] = inStream(port_a.Xi_outflow) 
    "Mass fraction/absolute humidity of air entering the cooling coil";

  Modelica.Blocks.Sources.RealExpression p(final y=port_a.p) 
    "Inlet air pressure";
  Modelica.Blocks.Sources.RealExpression X(final y=XEvaIn[i_w]) 
    "Inlet air mass fraction";
  Modelica.Blocks.Sources.RealExpression T(final y=TEvaIn) 
    "Inlet air temperature";
  Modelica.Blocks.Sources.RealExpression m(final y=port_a.m_flow) 
    "Inlet air mass flow rate";
  Modelica.Blocks.Sources.RealExpression h(final y=hEvaIn) 
    "Inlet air specific enthalpy";
  Buildings.HeatTransfer.Sources.PrescribedHeatFlow q "Heat extracted by coil";
  BaseClasses.InputPower pwr "Electrical power consumed by the unit";

  Modelica.Thermal.HeatTransfer.Sensors.TemperatureSensor TVol 
    "Temperature of the control volume";
initial algorithm 
  // Make sure that |Q_flow_nominal[nSta]| >= |Q_flow_nominal[i]| for all stages because the data
  // of nSta are used in the evaporation model
  for i in 1:(nSta-1) loop
    assert(datCoi.sta[i].nomVal.Q_flow_nominal >= datCoi.sta[nSta].nomVal.Q_flow_nominal,
    "Error in DX coil performance data: Q_flow_nominal of the highest stage must have
    the biggest value in magnitude. Obtained " + Modelica.Math.Vectors.toString(
    {datCoi.sta[i].nomVal.Q_flow_nominal for i in 1:nSta}, "Q_flow_nominal"));
   end for;


equation 
  connect(TConIn, dxCoo.TConIn);
  connect(m.y, dxCoo.m_flow);
  connect(T.y, dxCoo.TEvaIn);
  connect(p.y, dxCoo.p);
  connect(X.y, dxCoo.XEvaIn);
  connect(h.y, dxCoo.hEvaIn);
  connect(dxCoo.EIR, pwr.EIR);
  connect(dxCoo.Q_flow, pwr.Q_flow);
  connect(dxCoo.SHR, pwr.SHR);
  connect(q.port, vol.heatPort);

  connect(pwr.P, P);
  connect(dxCoo.Q_flow, q.Q_flow);
  connect(eva.mWat_flow, dxCoo.mWat_flow);
  connect(dxCoo.TCoiSur, vol.TWat);
  connect(dxCoo.TCoiSur, eva.TWat);
  connect(m.y, eva.mAir_flow);
  connect(TVol.port, q.port);
  connect(pwr.QSen_flow, QSen_flow);
  connect(pwr.QLat_flow, QLat_flow);

  connect(eva.mTotWat_flow, vol.mWat_flow);
  connect(TVol.T, eva.TEvaOut);
  connect(vol.X_w, eva.XEvaOut);
end PartialDXCoil;

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.PartialSurfaceCondition

Partial block for apparatus dew and dry point calculation

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.PartialSurfaceCondition

Information

This partial block is the base class for Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.ApparatusDewPoint and Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.ApparatusDryPoint.

This block calculates the UA/c_p value, the bypass factor and the enthalpy difference across the coil. It uses the function Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.Functions.speedShift for intermediate compressor speeds.

Implementation

For coils that only have discrete compressor speeds, this block does not do an interpolation for intermediate speeds. For coils with variable speed compressors, the computations are also done if the coil is off, as this ensures that the derivatives are continuous near the off conditions.

Parameters

Type Name Default Description

DXCoil datCoi Performance data

replaceable package Medium Modelica.Media.Interfaces.Pa... Medium model

Boolean variableSpeedCoil Flag, set to true to interpolate data

Type	Name	Default	Description
DXCoil	datCoi		Performance data
replaceable package Medium	Modelica.Media.Interfaces.Pa...	Medium model
Boolean	variableSpeedCoil		Flag, set to true to interpolate data

Connectors

Type Name Description

replaceable package Medium Medium model

input RealInput speRat Speed index

input RealInput Q_flow Cooling capacity of the coil [W]

input RealInput m_flow Evaporator air mass flow rate [kg/s]

input RealInput p Evaporator air static pressure [Pa]

input RealInput XEvaIn Evaporator inlet air mass fraction

input RealInput hEvaIn Evaporator air inlet specific enthalpy [J/kg]

input IntegerInput stage Stage of coil, or 0/1 for variable-speed coil

Type	Name	Description
replaceable package Medium	Medium model
input RealInput	speRat	Speed index
input RealInput	Q_flow	Cooling capacity of the coil [W]
input RealInput	m_flow	Evaporator air mass flow rate [kg/s]
input RealInput	p	Evaporator air static pressure [Pa]
input RealInput	XEvaIn	Evaporator inlet air mass fraction
input RealInput	hEvaIn	Evaporator air inlet specific enthalpy [J/kg]
input IntegerInput	stage	Stage of coil, or 0/1 for variable-speed coil

Modelica definition

partial block PartialSurfaceCondition 
  "Partial block for apparatus dew and dry point calculation"
  extends Modelica.Blocks.Interfaces.BlockIcon;
  extends Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.EssentialParameters;
  replaceable package Medium =
      Modelica.Media.Interfaces.PartialCondensingGases "Medium model";

  constant Boolean variableSpeedCoil "Flag, set to true to interpolate data";

  final parameter Modelica.SIunits.MassFlowRate m_flow_small = datCoi.m_flow_small 
    "Small mass flow rate for the evaporator, used for regularization";
  final parameter Modelica.SIunits.AngularVelocity maxSpe(displayUnit="1/min")= datCoi.sta[nSta].spe 
    "Maximum rotational speed";
  Modelica.Blocks.Interfaces.RealInput speRat "Speed index";
  Modelica.Blocks.Interfaces.RealInput Q_flow(
    quantity="Power",
    unit="W") "Cooling capacity of the coil";
  Modelica.Blocks.Interfaces.RealInput m_flow(
    quantity="MassFlowRate",
    unit="kg/s") "Evaporator air mass flow rate";
  Modelica.Blocks.Interfaces.RealInput p(
    quantity="Pressure",
    unit="Pa") "Evaporator air static pressure";
  Modelica.Blocks.Interfaces.RealInput XEvaIn 
    "Evaporator inlet air mass fraction"; //(start=0.005, min=0, max=1.0)
  Modelica.Blocks.Interfaces.RealInput hEvaIn(
    quantity="SpecificEnergy",
    unit="J/kg") "Evaporator air inlet specific enthalpy";
  output Real bypass(
    start=0.25,
    min=0,
    max=1.0) "Bypass factor";
 output Modelica.SIunits.AngularVelocity spe(displayUnit="1/min") 
    "Rotational speed";

  final parameter Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.UACp uacp[nSta](
      final per=datCoi.sta.nomVal,
      redeclare final package Medium = Medium) "Calculates UA/Cp of the coil";

protected 
  output Modelica.SIunits.MassFlowRate m_flow_nonzero 
    "Evaporator air mass flow rate, bounded away from zero";
  output Modelica.SIunits.SpecificEnthalpy delta_h(
    start=40000,
    min=0.0) 
    "Enthalpy required to be removed from the inlet air to attain apparatus dry point condition";
  output Real UAcp(
    min=0,
    fixed=false) "UA/Cp of coil";

public 
  Modelica.Blocks.Interfaces.IntegerInput stage 
    "Stage of coil, or 0/1 for variable-speed coil";
algorithm 
  if not variableSpeedCoil and stage == 0 then
    m_flow_nonzero := 0;
    UAcp           := 0;
    bypass         := 0;
    delta_h        := 0;
  else
    // Small mass flow rate to avoid division by zero
    m_flow_nonzero := Buildings.Utilities.Math.Functions.smoothMax(
      x1=m_flow,
      x2=m_flow_small,
      deltaX=0.1*m_flow_small);
    spe:=speRat*maxSpe;

    if variableSpeedCoil then
      UAcp := Buildings.Utilities.Math.Functions.smoothMax(
         x1=Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.Functions.speedShift(
           spe=spe,
           speSet={datCoi.sta[iSpe].spe for iSpe in 1:nSta},
           u={uacp[iSpe].UAcp for iSpe in 1:nSta}),
         x2=uacp[nSta].UAcp/1E3,
         deltaX=uacp[nSta].UAcp/1E4);
     else
      UAcp := uacp[stage].UAcp;
     end if;

    bypass := Buildings.Utilities.Math.Functions.smoothLimit(
      x=  Modelica.Math.exp(-UAcp / m_flow_nonzero),
      l=  0.01,
      u=  0.99,
      deltaX=  0.001);
   delta_h:=Buildings.Utilities.Math.Functions.smoothMin(
      x1=-Q_flow/m_flow_nonzero/(1 - bypass),
      x2=0.999*hEvaIn,
      deltaX=0.0001);
    end if;
end PartialSurfaceCondition;

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.SensibleHeatRatio

Calculates the sensible heat ratio

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.SensibleHeatRatio

Information

This block computes the sensible heat ratio.

Extends from Modelica.Blocks.Interfaces.BlockIcon (Basic graphical layout of input/output block).

Parameters

Type Name Default Description

replaceable package Medium Modelica.Media.Interfaces.Pa... Medium model

Type	Name	Default	Description
replaceable package Medium	Modelica.Media.Interfaces.Pa...	Medium model

Connectors

Type Name Description

replaceable package Medium Medium model

input BooleanInput on Set to true to enable compressor, or false to disable compressor

input RealInput p Pressure at inlet of coil

input RealInput TEvaIn Temperature of air entering the cooling coil

input RealInput XADP Humidity mass fraction of air at ADP

input RealInput hADP Specific enthalpy of air at ADP [J/kg]

input RealInput hEvaIn Specific enthalpy of air entering the coil

output RealOutput SHR Sensible Heat Ratio: Ratio of sensible heat load to total heat load

Type	Name	Description
replaceable package Medium	Medium model
input BooleanInput	on	Set to true to enable compressor, or false to disable compressor
input RealInput	p	Pressure at inlet of coil
input RealInput	TEvaIn	Temperature of air entering the cooling coil
input RealInput	XADP	Humidity mass fraction of air at ADP
input RealInput	hADP	Specific enthalpy of air at ADP [J/kg]
input RealInput	hEvaIn	Specific enthalpy of air entering the coil
output RealOutput	SHR	Sensible Heat Ratio: Ratio of sensible heat load to total heat load

Modelica definition

block SensibleHeatRatio "Calculates the sensible heat ratio"
  extends Modelica.Blocks.Interfaces.BlockIcon;
  replaceable package Medium =
      Modelica.Media.Interfaces.PartialCondensingGases "Medium model";
  Modelica.Blocks.Interfaces.BooleanInput on 
    "Set to true to enable compressor, or false to disable compressor";
  Modelica.Blocks.Interfaces.RealInput p "Pressure at inlet of coil";
  Modelica.Blocks.Interfaces.RealInput TEvaIn 
    "Temperature of air entering the cooling coil";
  Modelica.Blocks.Interfaces.RealInput XADP(
    min=0,
    max=1.0) "Humidity mass fraction of air at ADP";
  Modelica.Blocks.Interfaces.RealInput hADP(
    nominal=40000,
    quantity="SpecificEnergy",
    unit="J/kg") "Specific enthalpy of air at ADP";
  Modelica.Blocks.Interfaces.RealInput hEvaIn 
    "Specific enthalpy of air entering the coil";
  Modelica.Blocks.Interfaces.RealOutput SHR(
    min=0,
    max=1.0) 
    "Sensible Heat Ratio: Ratio of sensible heat load to total heat load";

protected 
  Modelica.SIunits.SpecificEnthalpy h_TEvaIn_XADP 
    "Enthalpy at inlet air temperature and humidity mass fraction at ADP";
  Real entRat "Enthalpy ratio";
  parameter Modelica.SIunits.SpecificEnthalpy epsH = 100 
    "Small value for enthalpy to avoid division by zero";
algorithm 
//===================================Sensible heat ratio calculation===========================================//
  //Coil on-off condition
  if on then
   //Calculate enthalpy at inlet air temperature and absolute humidity at ADP i.e. h_TEvaIn_wADP
    h_TEvaIn_XADP := Medium.h_pTX(
      p=p,
      T=TEvaIn,
      X=cat(1, {XADP}, {1-XADP}));
    //Calculate Sensible Heat Ratio
    entRat := (h_TEvaIn_XADP - hADP)/
      Buildings.Utilities.Math.Functions.smoothMax(
        x1=      epsH,
        x2=      hEvaIn - hADP,
        deltaX=  0.1*epsH);
    SHR := Buildings.Utilities.Math.Functions.smoothMin(
      x1=entRat,
      x2=0.999,
      deltaX=0.0001) 
      "To restrict the value of SHR in case of zero mass flow rate or dry coil condition";
  else  //Coil off
    h_TEvaIn_XADP := 0;
    entRat     := 1;
    SHR        := 0;
  end if;

end SensibleHeatRatio;

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.SpeedSelect

Selects the lower specified speed ratio for multispeed model

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.SpeedSelect

Information

This blocks outputs the normalized speed of the compressor, whereas the highest stage is assigned a normalized speed of one, and all other stages are proportional to their actual speed.

Extends from Modelica.Blocks.Interfaces.BlockIcon (Basic graphical layout of input/output block).

Parameters

Type Name Default Description

Integer nSta Number of standard compressor speeds

Real speSet[nSta] Array of standard compressor speeds

Type	Name	Default	Description
Integer	nSta		Number of standard compressor speeds
Real	speSet[nSta]		Array of standard compressor speeds

Connectors

Type Name Description

input IntegerInput stage Stage of cooling coil (0: off, 1: first stage, 2: second stage...)

output RealOutput speRat Standard speed ratio

Type	Name	Description
input IntegerInput	stage	Stage of cooling coil (0: off, 1: first stage, 2: second stage...)
output RealOutput	speRat	Standard speed ratio

Modelica definition

block SpeedSelect 
  "Selects the lower specified speed ratio for multispeed model"
  extends Modelica.Blocks.Interfaces.BlockIcon;

  parameter Integer nSta(min=1) "Number of standard compressor speeds";
  parameter Real speSet[nSta] "Array of standard compressor speeds";
  Modelica.Blocks.Interfaces.IntegerInput stage 
    "Stage of cooling coil (0: off, 1: first stage, 2: second stage...)";
  Modelica.Blocks.Interfaces.RealOutput speRat "Standard speed ratio";
protected 
  final parameter Real speRatNor[nSta](each min=0, max=1)=
    {speSet[i]/speSet[nSta] for i in 1:nSta} 
    "Array of normalized speed ratios for the compressor";

algorithm 
 assert(stage >= 0 and stage <= nSta, "Compressor speed is out of range.
  Model has " + String(nSta) + " speeds, but received control signal " +
  String(stage));
 speRat :=if stage == 0 then 0 else speRatNor[stage];
end SpeedSelect;

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.SpeedShift

Interpolates values between speeds

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.SpeedShift

Information

This block uses the Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.Functions.speedShift function to interpolate the input array. Depending on input speed ratio and speed set array the input array u is interpolated.

Parameters

Type Name Default Description

Integer nSta Number of standard compressor speeds

AngularVelocity speSet[nSta] Compressor speeds [rad/s]

Boolean variableSpeedCoil Flag, set to true to interpolate data

Type	Name	Description
Integer	nSta	Number of standard compressor speeds
AngularVelocity	speSet[nSta]	Compressor speeds [rad/s]
Boolean	variableSpeedCoil	Flag, set to true to interpolate data

Connectors

Type Name Description

input RealInput speRat Speed ratio

input RealInput u[nSta] Array to be interpolated

output RealOutput y Interpolated value

input IntegerInput stage Stage of coil, or 0/1 for variable-speed coil

Type	Name	Description
input RealInput	speRat	Speed ratio
input RealInput	u[nSta]	Array to be interpolated
output RealOutput	y	Interpolated value
input IntegerInput	stage	Stage of coil, or 0/1 for variable-speed coil

Modelica definition

block SpeedShift "Interpolates values between speeds"
  parameter Integer nSta "Number of standard compressor speeds";
  parameter Modelica.SIunits.AngularVelocity speSet[nSta](each displayUnit="1/min") 
    "Compressor speeds";
  constant Boolean variableSpeedCoil "Flag, set to true to interpolate data";

  Modelica.Blocks.Interfaces.RealInput speRat "Speed ratio";
  Modelica.Blocks.Interfaces.RealInput u[nSta] "Array to be interpolated";
  Modelica.Blocks.Interfaces.RealOutput y "Interpolated value";
  Modelica.Blocks.Interfaces.IntegerInput stage 
    "Stage of coil, or 0/1 for variable-speed coil";
equation 
  if variableSpeedCoil then
    y=Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.Functions.speedShift(
      spe=speRat*speSet[nSta],
      speSet=speSet,
      u=u);
  else
    y = if stage == 0 then 0  else u[stage];
  end if;
end SpeedShift;

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.UACp

Calculates UA/Cp of the coil

Information

This model calculates the UA/c_p value and the bypass factor of the coil from the nominal inlet and outlet air properties. The nominal conditions are calculated using Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.NominalCondition.

For a heat exchanger where one medium changes phase, the NTU-ε relation is

ε = 1 - exp(-NTU) = 1-exp(-UA ⁄ c_p ⁄ ṁ)

Since the bypass factor b is defined as b=1-ε, one can write

b = exp(-UA ⁄ c_p ⁄ ṁ)

and, hence,

UA ⁄ c_p = - ṁ log(b)

Extends from Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.NominalCondition (Calculates inlet and outlet fluid parameters at nominal condition), Modelica.Blocks.Interfaces.BlockIcon (Basic graphical layout of input/output block).

Parameters

Type Name Default Description

replaceable package Medium PartialCondensingGases Medium model

NominalValues per Performance data

Advanced

Boolean homotopyInitialization true = true, use homotopy method

Type	Name	Default	Description
replaceable package Medium	PartialCondensingGases	Medium model
NominalValues	per		Performance data
Advanced
Boolean	homotopyInitialization	true	= true, use homotopy method

Modelica definition

model UACp "Calculates UA/Cp of the coil"
  extends Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.NominalCondition;
  extends Modelica.Blocks.Interfaces.BlockIcon;
  final parameter Modelica.SIunits.MassFraction XADP_nominal(
    start=0.008,
    min=0,
    max=1.0,
    fixed=false) 
    "Rated/Nominal mass fraction of air at coil apparatus dew point";
  final parameter Modelica.SIunits.Temperature TADP_nominal(
    start=273.15+10,
    fixed=false) "Coil apparatus dew point temperature";
  final parameter Modelica.SIunits.SpecificEnthalpy hADP_nominal(
    fixed=false) 
    "Enthalpy of air at coil apparatus dew point (at rated condition)";
  final parameter Real bypass_nominal(
    start=0.25,
    min=0,
    max=1.0,
    fixed=false) "Bypass factor for nominal condition";
  final parameter Real UAcp(
    min=0,
    unit="kg/s",
    fixed=false) "UA/Cp of coil";
  parameter Boolean homotopyInitialization = true "= true, use homotopy method";
protected 
  constant Real phiADP_nominal = 1.0 "Realtive humidity at ADP";
  final parameter Modelica.SIunits.AbsolutePressure psat_ADP_nominal(
    start=1250,
    fixed=false) "Saturation pressure";
initial equation 
//------------------------Apparatus Dew Point (ADP) calculations---------------------//
  //Solve Eq. 1 , 2 and 3 for air properties (XADP_nominal and TADP_nominal)
  //of saturated air at coil apparatus dew point
//---------------------------------------Eq.1---------------------------------------//
  (XEvaIn_nominal - XEvaOut_nominal)*(per.TEvaIn_nominal - TADP_nominal)
     =(XEvaIn_nominal  - XADP_nominal)*(per.TEvaIn_nominal - TOut_nominal);
//---------------------------------------Eq.2---------------------------------------//
  if homotopyInitialization then
    psat_ADP_nominal=homotopy(
      actual=Medium.saturationPressureLiquid(Tsat=TADP_nominal),
      simplified=1252.393+83.933*(TADP_nominal-283.15));
  else // do not use homotopy
    psat_ADP_nominal=Medium.saturationPressureLiquid(TADP_nominal);
  end if;
  //  Taylor series
  //  psat_ADP_nominal=1252.393+83.933*(TADP_nominal-283.15);
  //  Non-linear equation
  //  psat_ADP_nominal =  Medium.saturationPressureLiquid(TADP_nominal);
//---------------------------------------Eq.3---------------------------------------//
  if homotopyInitialization then
    XADP_nominal=homotopy(
      actual=Buildings.Utilities.Psychrometrics.Functions.X_pSatpphi(
        pSat=psat_ADP_nominal,
        p=per.p_nominal,
        phi=phiADP_nominal),
      simplified=0.007572544+6.19495*(10^(-6))*(psat_ADP_nominal-1228));

  else // do not use homotopy
    XADP_nominal=Buildings.Utilities.Psychrometrics.Functions.X_pSatpphi(
        pSat=psat_ADP_nominal,
        p=per.p_nominal,
        phi=phiADP_nominal);
  end if;
//-----------------------------------uACp calculations-----------------------------//
  hADP_nominal = Medium.h_pTX(
              p=per.p_nominal,
              T=TADP_nominal,
              X=cat(1,{XADP_nominal}, {1-sum({XADP_nominal})}));
  bypass_nominal=Buildings.Utilities.Math.Functions.smoothLimit(
              x=(hOut_nominal-hADP_nominal)/(hEvaIn_nominal-hADP_nominal),
              l=1e-3,
              u=0.999,
              deltaX=1e-4);
  UAcp = -per.m_flow_nominal * Modelica.Math.log(bypass_nominal);

end UACp;

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.WetCoil

Calculates wet coil condition

Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.WetCoil

Information

This block calculates the rate of cooling and the coil surface condition under the assumption that the coil is wet.

The dry coil conditions are computed in Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.DryCoil. See Buildings.Fluid.HeatExchangers.DXCoils.UsersGuide for an explanation of the model.

Extends from Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.PartialCoilCondition (Partial block for dry and wet coil conditions).

Parameters

Type	Name	Default	Description
DXCoil	datCoi		Performance data
Boolean	variableSpeedCoil		Flag, set to true for coil with variable speed
replaceable package Medium	Modelica.Media.Interfaces.Pa...	Medium model

Connectors

Type	Name	Description
input IntegerInput	stage	Stage of coil, or 0/1 for variable-speed coil
input RealInput	speRat	Speed ratio
input RealInput	m_flow	Air mass flow rate
input RealInput	TEvaIn	Temperature of air entering the cooling coil
input RealInput	XEvaIn	Inlet air mass fraction
input RealInput	p	Pressure at inlet of coil
input RealInput	hEvaIn	Specific enthalpy of air entering the coil
input RealInput	TConIn	Outside air dry bulb temperature for an air cooled condenser or wetbulb temperature for an evaporative cooled condenser [K]
output RealOutput	EIR	Energy Input Ratio
output RealOutput	Q_flow	Total cooling capacity [W]
replaceable package Medium	Medium model
output RealOutput	TADP	Dry bulb temperature of air at ADP [K]
output RealOutput	SHR	Sensible Heat Ratio: Ratio of sensible heat load to total heat load
output RealOutput	mWat_flow	Mass flow rate of water condensed at cooling coil [kg/s]
output RealOutput	XADP	Humidity mass fraction of air at apparatus dew point

Modelica definition

model WetCoil "Calculates wet coil condition "
  extends Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.PartialCoilCondition;
  replaceable package Medium =
      Modelica.Media.Interfaces.PartialCondensingGases "Medium model";
  Modelica.Blocks.Interfaces.RealOutput TADP(
    quantity="Temperature",
    unit="K",
    min=273.15,
    max=373.15) "Dry bulb temperature of air at ADP";
  Modelica.Blocks.Interfaces.RealOutput SHR(
    min=0,
    max=1.0) 
    "Sensible Heat Ratio: Ratio of sensible heat load to total heat load";
  Modelica.Blocks.Interfaces.RealOutput mWat_flow(
    quantity="MassFlowRate",
    unit="kg/s") "Mass flow rate of water condensed at cooling coil";

  Buildings.Utilities.Psychrometrics.TWetBul_TDryBulXi wetBul(
    redeclare package Medium = Medium) "Calculates wet-bulb temperature";
  Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.ApparatusDewPoint appDewPt(
    redeclare package Medium = Medium,
    final datCoi=datCoi,
    final variableSpeedCoil=variableSpeedCoil) 
    "Calculates air properties at apparatus dew point (ADP) at existing air-flow conditions";
  Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.SensibleHeatRatio shr(
    redeclare package Medium = Medium) "Calculates sensible heat ratio";
  Buildings.Fluid.HeatExchangers.DXCoils.BaseClasses.Condensation conRat(
      redeclare package Medium = Medium) "Calculates rate of condensation";
protected 
  Modelica.Blocks.Math.IntegerToBoolean onSwi(final threshold=1) 
    "On/off switch";
public 
  Modelica.Blocks.Interfaces.RealOutput XADP 
    "Humidity mass fraction of air at  apparatus dew point";
equation 

  connect(appDewPt.TADP, TADP);
  connect(XEvaIn, appDewPt.XEvaIn);
  connect(p, appDewPt.p);

  connect(m_flow, appDewPt.m_flow);
  connect(p, wetBul.p);
  connect(XEvaIn, wetBul.Xi[1]);
  connect(speRat, appDewPt.speRat);
  connect(appDewPt.XADP, shr.XADP);
  connect(appDewPt.hADP, shr.hADP);
  connect(shr.SHR, SHR);
  connect(p, shr.p);
  connect(TEvaIn, wetBul.TDryBul);
  connect(TEvaIn, shr.TEvaIn);
  connect(hEvaIn, shr.hEvaIn);
  connect(hEvaIn, appDewPt.hEvaIn);
  connect(appDewPt.TADP, conRat.TDewPoi);
  connect(conRat.mWat_flow, mWat_flow);
  connect(shr.SHR, conRat.SHR);
  connect(speShiQ_flow.y, conRat.Q_flow);
  connect(speShiQ_flow.y, appDewPt.Q_flow);
  connect(onSwi.y, shr.on);
  connect(onSwi.u, stage);
  connect(wetBul.TWetBul, cooCap.TEvaIn);
  connect(appDewPt.XADP, XADP);
  connect(appDewPt.stage, stage);
end WetCoil;

Automatically generated Wed May 15 11:55:59 2013.