Buildings.Fluid.HeatExchangers.BaseClasses

Package with base classes for Buildings.Fluid.HeatExchangers

Information

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

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

Package Content

Name	Description
CoilHeader	Header for a heat exchanger register
CoilRegister	Register for a heat exchanger
DuctManifoldFixedResistance	Manifold for a heat exchanger air duct connection
DuctManifoldNoResistance	Duct manifold without resistance
HACoilInside	Calculates the hA value for water inside a coil
HADryCoil	Sensible convective heat transfer model for air to water coil
HANaturalCylinder	Calculates an hA value for natural convection around a cylinder
HexElementLatent	Element of a heat exchanger
HexElementSensible	Element of a heat exchanger with humidity condensation of fluid 2
MassExchange	Block to compute the latent heat transfer based on the Lewis number
PartialDuctManifold	Partial manifold for heat exchanger duct connection
PartialDuctPipeManifold	Partial heat exchanger duct and pipe manifold
PartialEffectiveness	Partial model to implement heat exchangers based on effectiveness model
PartialHexElement	Element of a heat exchanger 2
PartialPipeManifold	Partial pipe manifold for a heat exchanger
PipeManifoldFixedResistance	Pipe manifold for a heat exchanger connection
PipeManifoldNoResistance	Manifold for heat exchanger register
RayleighNumber	Calculates the Rayleigh number for a given fluid and characteristic length
appartusDewPoint	Computes the apparatus dewpoint temperature
dynamicViscosityWater	Returns the dynamic viscosity for water
epsilon_C	Computes heat exchanger effectiveness for given capacity flow rates and heat exchanger flow regime
epsilon_ntuZ	Computes heat exchanger effectiveness for given number of transfer units and heat exchanger flow regime
isobaricExpansionCoefficientWater	Returns the isobaric expansion coefficient for water
lmtd	Log-mean temperature difference
ntu_epsilonZ	Computes number of transfer units for given heat exchanger effectiveness and heat exchanger flow regime
prandtlNumberWater	Returns the Prandtl number for water
Examples	Collection of models that illustrate model use and test models
Internal	Solve f(x, data) for x with given f

Buildings.Fluid.HeatExchangers.BaseClasses.CoilHeader

Header for a heat exchanger register

Information

Header for a heat exchanger coil.

This model connects the flow between its ports without modeling flow friction. Currently, the ports are connected without redistributing the flow. In latter versions, the model may be changed to define different flow reroutings in the coil header.

Extends from Buildings.BaseClasses.BaseIcon (Base icon).

Parameters

Connectors

Modelica definition

Buildings.Fluid.HeatExchangers.BaseClasses.CoilRegister

Register for a heat exchanger

Information

Register of a heat exchanger with dynamics on the fluids and the solid. The register represents one array of pipes that are perpendicular to the air stream. The hA value for both fluids is an input. The driving force for the heat transfer is the temperature difference between the fluid volumes and the solid in each heat exchanger element.

Extends from Buildings.Fluid.Interfaces.FourPortFlowResistanceParameters (Parameters for flow resistance for models with four ports).

Parameters

Connectors

Modelica definition

Buildings.Fluid.HeatExchangers.BaseClasses.DuctManifoldFixedResistance

Manifold for a heat exchanger air duct connection

Information

Duct manifold with a fixed flow resistance.

This model causes the flow to be distributed equally into each flow path by using a fixed flow resistance for each flow path.

Extends from PartialDuctManifold (Partial manifold for heat exchanger duct connection).

Parameters

Connectors

Modelica definition

Buildings.Fluid.HeatExchangers.BaseClasses.DuctManifoldNoResistance

Duct manifold without resistance

Information

Duct manifold without flow resistance.

This model connects the flows between the ports without modeling flow friction. The model is used in conjunction with a manifold which contains pressure drop elements and that is added to the other side of the heat exchanger registers.

Extends from PartialDuctManifold (Partial manifold for heat exchanger duct connection).

Parameters

Connectors

Modelica definition

Buildings.Fluid.HeatExchangers.BaseClasses.HACoilInside

Calculates the hA value for water inside a coil

Information

Model for convective heat transfer coefficients inside a coil. Optionally, the convective heat transfer coefficient can be computed as a function of temperature and mass flow rate.

Extends from Buildings.BaseClasses.BaseIcon (Base icon).

Parameters

Connectors

Modelica definition

Buildings.Fluid.HeatExchangers.BaseClasses.HADryCoil

Sensible convective heat transfer model for air to water coil

Information

Model for sensible convective heat transfer coefficients for an air to water coil.

This model computes the convective heat transfer coefficient for an air to water coil. The parameters allow a user to enable or disable, individually for each medium, the mass flow and/or the temperature dependence of the convective heat transfer coefficients. For a detailed explanation of the equation, see the references below.

References

• Wetter Michael, Simulation model finned water-air-coil without condensation, LBNL-42355, Lawrence Berkeley National Laboratory, Berkeley, CA, 1999.
• Wetter Michael, Simulation model air-to-air plate heat exchanger, LBNL-42354, Lawrence Berkeley National Laboratory, Berkeley, CA, 1999.

Extends from Buildings.BaseClasses.BaseIcon (Base icon).

Parameters

Connectors

Modelica definition

Buildings.Fluid.HeatExchangers.BaseClasses.HANaturalCylinder

Calculates an hA value for natural convection around a cylinder

Information

This model calculates the convection coefficient h for natural convection from a cylinder submerged in fluid. h is calcualted using Eq 9.34 from Incropera and DeWitt (1996). Output of the block is the hA value.

The Nusselt number is computed as

Nu_D = (0.6 + (0.387 Ra_D^(1/6))/(1+(0.559 Pr) ^(9/16))^(8/27))²);

where Nu_D is the Nusselt number, Ra_D is the Rayleigh number and Pr is the Prandtl number.
This correclation is accurate for Ra_D less than 10¹².

h is then calculated from the Nusselt number. The equation is

h = Nu_D k/D

where k is the thermal conductivity of the fluid and D is the diameter of the submerged cylinder.

References

Fundamentals of Heat and Mass Transfer (Fourth Edition), Frank Incropera and David DeWitt, John Wiley and Sons, 1996

Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).

Parameters

Connectors

Modelica definition

Buildings.Fluid.HeatExchangers.BaseClasses.HexElementLatent

Element of a heat exchanger

Information

Element of a heat exchanger with humidity condensation of fluid 2 and with dynamics of the fluids and the solid.

See Buildings.Fluid.HeatExchangers.BaseClasses.PartialHexElement for a description of the physics.

Extends from Buildings.Fluid.HeatExchangers.BaseClasses.PartialHexElement (Element of a heat exchanger 2).

Parameters

Connectors

Modelica definition

Buildings.Fluid.HeatExchangers.BaseClasses.HexElementSensible

Element of a heat exchanger with humidity condensation of fluid 2

Information

Element of a heat exchanger with humidity condensation and with dynamics of the fluids and the solid.

See Buildings.Fluid.HeatExchangers.BaseClasses.PartialHexElement for a description of the physics.

Extends from Buildings.Fluid.HeatExchangers.BaseClasses.PartialHexElement (Element of a heat exchanger 2).

Parameters

Connectors

Modelica definition

Buildings.Fluid.HeatExchangers.BaseClasses.MassExchange

Block to compute the latent heat transfer based on the Lewis number

Information

This model computes the mass transfer based on similarity laws between the convective sensible heat transfer coefficient and the mass transfer coefficient.

Using the Lewis number which is defined as the ratio between the heat and mass diffusion coefficients, one can obtain the ratio between convection heat transfer coefficient h in (W/(m^2*K)) and mass transfer coefficient h_m in (m/s) as follows:

h ⁄ h_m = ρ c_p Le^(1-n) ⁄ h_m

where ρ is the mass density, c_p is the specific heat capacity of the bulk medium and n is a coefficient from the boundary layer analysis, which is typically n=1/3. From this equation, we can compute the water vapor mass flow rate n_A in (kg/s) as

n_A = G_c ⁄ (c_p Le^(1-n)) (X_s - X_∞),

where G_c is the sensible heat conductivity in (W/K) and X_s and X_∞ are the water vapor mass per unit volume in the boundary layer and in the bulk of the medium. In this model, X_s is the saturation water vapor pressure corresponding to the temperature T_sur which is an input.

Extends from Buildings.BaseClasses.BaseIcon (Base icon).

Parameters

Connectors

Modelica definition

Buildings.Fluid.HeatExchangers.BaseClasses.PartialDuctManifold

Partial manifold for heat exchanger duct connection

Information

Partial duct manifold for a heat exchanger.

This model defines the duct connection to a heat exchanger. It is extended by other models that model the flow connection between the ports with and without flow friction.

Extends from PartialDuctPipeManifold (Partial heat exchanger duct and pipe manifold).

Parameters

Connectors

Modelica definition

Buildings.Fluid.HeatExchangers.BaseClasses.PartialDuctPipeManifold

Partial heat exchanger duct and pipe manifold

Information

Partial heat exchanger manifold. This partial model defines ports and parameters that are used for air-side and water-side heat exchanger manifolds.

Extends from Buildings.BaseClasses.BaseIcon (Base icon).

Parameters

Connectors

Modelica definition

Buildings.Fluid.HeatExchangers.BaseClasses.PartialEffectiveness

Partial model to implement heat exchangers based on effectiveness model

Information

Partial model to implement heat exchanger models.

Classes that extend this model need to implement heat and mass balance equations in a form like

  // transfered heat
  Q1_flow = eps * QMax_flow;
  // no heat loss to ambient
  0 = Q1_flow + Q2_flow;
  // no mass exchange
  mXi1_flow = zeros(Medium1.nXi);
  mXi2_flow = zeros(Medium2.nXi);

Thus, if medium 1 is heated in this device, then Q1_flow > 0 and QMax_flow > 0.

Extends from Fluid.Interfaces.StaticFourPortHeatMassExchanger (Partial model transporting two fluid streams between four ports without storing mass or energy).

Parameters

Connectors

Modelica definition

Buildings.Fluid.HeatExchangers.BaseClasses.PartialHexElement

Element of a heat exchanger 2

Information

Element of a heat exchanger with dynamics of the fluids and the solid. The hA value for both fluids is an input. The driving force for the heat transfer is the temperature difference between the fluid volumes and the solid.

The heat capacity C of the metal is assigned as follows. Suppose the metal temperature is governed by

C dT ⁄ dt = (hA)₁ (T₁ - T) + (hA)₂ (T₂ - T)

where hA are the convective heat transfer coefficients times heat transfer area that also take into account heat conduction in the heat exchanger fins and T₁ and T₂ are the medium temperatures. Assuming (hA)₁=(hA)₂, this equation can be rewritten as

C dT ⁄ dt = 2 (UA)₀ ( (T₁ - T) + (T₂ - T) )

where (UA)₀ is the UA value at nominal conditions. Hence we set the heat capacity of the metal to

C = 2 (UA)₀ τ_m

where τ_m is the time constant that the metal of the heat exchanger has if the metal is approximated by a lumped thermal mass.

Note: This model is introduced to allow the instances Buildings.Fluid.HeatExchangers.BaseClasses.HexElementLatent and Buildings.Fluid.HeatExchangers.BaseClasses.HexElementSensible to redeclare the volume as final, thereby avoiding that a GUI displays the volume as a replaceable component.

Extends from Buildings.Fluid.Interfaces.FourPortHeatMassExchanger (Model transporting two fluid streams between four ports with storing mass or energy).

Parameters

Connectors

Modelica definition

Buildings.Fluid.HeatExchangers.BaseClasses.PartialPipeManifold

Partial pipe manifold for a heat exchanger

Information

Partial pipe manifold for a heat exchanger.

This model defines the pipe connection to a heat exchanger. It is extended by other models that model the flow connection between the ports with and without flow friction.

Extends from PartialDuctPipeManifold (Partial heat exchanger duct and pipe manifold).

Parameters

Connectors

Modelica definition

Buildings.Fluid.HeatExchangers.BaseClasses.PipeManifoldFixedResistance

Pipe manifold for a heat exchanger connection

Information

Pipe manifold with a fixed flow resistance.

This model causes the flow to be distributed equally into each flow path by using a fixed flow resistance for each flow path.

Extends from PartialPipeManifold (Partial pipe manifold for a heat exchanger).

Parameters

Connectors

Modelica definition

Buildings.Fluid.HeatExchangers.BaseClasses.PipeManifoldNoResistance

Manifold for heat exchanger register

Information

Pipe manifold without flow resistance.

This model connects the flows between the ports without modeling flow friction. The model is used in conjunction with a manifold which contains pressure drop elements and that is added to the other side of the heat exchanger registers.

Extends from PartialPipeManifold (Partial pipe manifold for a heat exchanger).

Parameters

Connectors

Modelica definition

Buildings.Fluid.HeatExchangers.BaseClasses.RayleighNumber

Calculates the Rayleigh number for a given fluid and characteristic length

Information

This model calculates the rayleigh number for a given fluid and characteristic length. It is calculated using Eq 9.25 in Incropera and DeWitt (1996). The equation is:

Ra_L = Gr_L Pr (g B (T_S - T_F) L³) /(ν*α)

where:
Ra_L is the Rayleigh number, Gr_L is the Grashof number, Pr is the Prandtl number, g is gravity, B is the isobaric expansion coefficient, T_S is the temperature of the surface, T_F is the temperature of the fluid, L is the characteristic length, ν is the kinematic viscosity and α is the thermal diffusivity.

This model is currently only used in natural convection calculations for water. As a result, the calculations reference functions to identify properties of water instead of a medium model.

References

Fundamentals of Heat and Mass Transfer (Fourth Edition), Frank Incropera and David DeWitt, John Wiley and Sons, 1996

Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).

Parameters

Connectors

Modelica definition

Buildings.Fluid.HeatExchangers.BaseClasses.appartusDewPoint

Computes the apparatus dewpoint temperature

Information

This function computes iteratively the apparatus dew point temperature for a cooling coil. The apparatus dew point temperature is defined as in the HVAC2 Toolkit (Brandemuehl et al. 1993), namely as the intersection of the line between coil air inlet state (T,X) and outlet state, and the saturation line.

This function does its own iterations to find a solution because a solution may not exist or not be unique because the saturation line is convex. Therefore, this function searches for the solution starting at the air inlet temperature and progressively reduces the guess value for the apparatus dew point temperature. When a temperature below the apparatus dew point temperature has been found, it is rejected, and the search continues with a smaller step until the step size is smaller than a prescribed value. This ensures that the solution corresponding to the higher temperature is found. If no solution can be found, the function stops the simulation.

References

Brandemuehl, Michael, Shauna Gabel and Inger Andresen. HVAC2 Toolkit, A toolkit for secondary HVAC system energy calculations. ASHRAE, Atlanta. 1993.

Inputs

Outputs

Modelica definition

Buildings.Fluid.HeatExchangers.BaseClasses.dynamicViscosityWater

Returns the dynamic viscosity for water

Information

This function is used to identify the dynamic viscosity of water at a given temperature. The function used is a fourth order polynomial fit to data from Incropera and Dewitt (1996).

References

Fundamentals of Heat and Mass Transfer (Fourth Edition), Frank Incropera and David P. Dewitt, John Wiley & Sons, 1996

Inputs

Outputs

Modelica definition

Buildings.Fluid.HeatExchangers.BaseClasses.epsilon_C

Computes heat exchanger effectiveness for given capacity flow rates and heat exchanger flow regime

Information

This function computes the heat exchanger effectiveness, the Number of Transfer Units, and the capacity flow ratio for given capacity flow rates.

The implementation allows for zero flow rate. As CMin_flow crosses delta*CMin_flow_nominal from above, the Number of Transfer Units and the heat exchanger effectiveness go to zero.

Inputs

Outputs

Modelica definition

Buildings.Fluid.HeatExchangers.BaseClasses.epsilon_ntuZ

Computes heat exchanger effectiveness for given number of transfer units and heat exchanger flow regime

Information

Inputs

Outputs

Modelica definition

Buildings.Fluid.HeatExchangers.BaseClasses.isobaricExpansionCoefficientWater

Returns the isobaric expansion coefficient for water

Information

This function is used to identify the isobaric expansion coefficient of water at a given temperature. The function used is a fourth order polynomial fit to data from Incropera and Dewitt (1996).

References

Fundamentals of Heat and Mass Transfer (Fourth Edition), Frank Incropera and David P. Dewitt, John Wiley & Sons, 1996

Inputs

Outputs

Modelica definition

Buildings.Fluid.HeatExchangers.BaseClasses.lmtd

Log-mean temperature difference

Information

This function computes the log mean temperature difference of a heat exchanger.

Note that the implementation requires the temperature differences to be non-zero.

Inputs

Outputs

Modelica definition

Buildings.Fluid.HeatExchangers.BaseClasses.ntu_epsilonZ

Computes number of transfer units for given heat exchanger effectiveness and heat exchanger flow regime

Information

This function computes the number of transfer units for a given heat exchanger effectiveness, capacity flow ratio and heat exchanger flow regime.

Note that for the flow regime CrossFlowUnmixed, computing the function requires the numerical solution of an equation in one variable. This is handled internally and not exposed to the global solver.

Inputs

Outputs

Modelica definition

Buildings.Fluid.HeatExchangers.BaseClasses.prandtlNumberWater

Returns the Prandtl number for water

Information

This function is used to identify the Prandtl number of water at a given temperature. The function used is a fourth order polynomial fit to data from Incropera and Dewitt (1996).

References

Fundamentals of Heat and Mass Transfer (Fourth Edition), Frank Incropera and David P. Dewitt, John Wiley & Sons, 1996

Inputs

Outputs

Modelica definition