Buildings.Fluid.Actuators.BaseClasses

Package with base classes for Buildings.Fluid.Actuators

Information

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

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

Package Content

Name	Description
ActuatorSignal	Partial model that implements the filtered opening for valves and dampers
PartialDamperExponential	Partial model for air dampers with exponential opening characteristics
PartialThreeWayValve	Partial three way valve
PartialTwoWayValve	Partial model for a two way valve
PartialTwoWayValveKv	Partial model for a two way valve using a Kv characteristic
ValveParameters	Model with parameters for valves
der_equalPercentage	Derivative of valve opening characteristics for equal percentage valve
equalPercentage	Valve opening characteristics for equal percentage valve
exponentialDamper	Damper opening characteristics for an exponential damper
Examples	Collection of models that illustrate model use and test models

Buildings.Fluid.Actuators.BaseClasses.ActuatorSignal

Partial model that implements the filtered opening for valves and dampers

Information

This model implements the filter that is used to approximate the travel time of the actuator. Models that extend this model use the signal y_actual to obtain the current position of the actuator.

The filter order can be changed to modify the transient response of the actuator.

See Buildings.Fluid.Actuators.UsersGuide for a description of the filter.

Parameters

Connectors

Modelica definition

Buildings.Fluid.Actuators.BaseClasses.PartialDamperExponential

Partial model for air dampers with exponential opening characteristics

Information

Partial model for air dampers with exponential opening characteristics. This is the base model for air dampers. The model implements the functions that relate the opening signal and the flow coefficient. The model also defines parameters that are used by different air damper models.

The model is as in ASHRAE 825-RP except that a control signal of y=0 means the damper is closed, and y=1 means the damper is open. This is opposite of the implementation of ASHRAE 825-RP, but used here for consistency within this library.

For yL < y < yU, the damper characteristics is:

k_d(y) = exp(a+b (1-y))

where kd is the loss coefficient (total pressure drop divided by dynamic pressure) and y is the fractional opening.

Outside this range, the damper characteristics is defined by a quadratic polynomial that matches the damper resistance at y=0 and y=yL or y=yU and y=1, respectively. In addition, the polynomials are such that k_d(y) is differentiable in y and the derivative is continuous.

The damper characteristics is then used to compute the flow coefficient k(y) as:

k(y) = (2 ρ ⁄ k_d(y))^1/2 A

where A is the face area, which is computed using the nominal mass flow rate m_flow_nominal, the nominal velocity v_nominal and the density of the medium.

ASHRAE 825-RP lists the following parameter values as typical (note that the default values in the model correspond to opposed blades).

(The loss coefficient in fully closed position k0 is computed based on the leakage coefficient and the coefficient in fully open position.)

References

P. Haves, L. K. Norford, M. DeSimone and L. Mei, A Standard Simulation Testbed for the Evaluation of Control Algorithms & Strategies, ASHRAE Final Report 825-RP, Atlanta, GA.

Extends from Buildings.Fluid.BaseClasses.PartialResistance (Partial model for a hydraulic resistance), Buildings.Fluid.Actuators.BaseClasses.ActuatorSignal (Partial model that implements the filtered opening for valves and dampers).

Parameters

Connectors

Modelica definition

Buildings.Fluid.Actuators.BaseClasses.PartialThreeWayValve

Partial three way valve

Information

Partial model of a three way valve. This is the base model for valves with different opening characteristics, such as linear, equal percentage or quick opening. The three way valve model consists of a mixer where valves are placed in two of the flow legs. The third flow leg has no friction. The flow coefficient Kv for flow from port_1 → port_2 is a parameter. The flow coefficient for the bypass flow from port_3 → port_2 is computed as

         Kv(port_3 → port_2)
  fraK = ----------------------
         Kv(port_1 → port_2)

where 0 < fraK ≤ 1 is a parameter with a default value of fraK=0.7.

Since this model uses two way valves to construct a three way valve, see Buildings.Fluid.Actuators.BaseClasses.PartialTwoWayValve for details regarding the valve implementation.

Extends from Buildings.Fluid.BaseClasses.PartialThreeWayResistance (Flow splitter with partial resistance model at each port), Buildings.Fluid.Actuators.BaseClasses.ActuatorSignal (Partial model that implements the filtered opening for valves and dampers), Buildings.Fluid.Actuators.BaseClasses.ValveParameters (Model with parameters for valves).

Parameters

Connectors

Modelica definition

Buildings.Fluid.Actuators.BaseClasses.PartialTwoWayValve

Partial model for a two way valve

Information

Partial model for a two way valve. This is the base model for valves with different opening characteristics, such as linear, equal percentage, quick opening or pressure-independent.

To prevent the derivative d/dP (m_flow) to be infinite near the origin, this model linearizes the pressure drop versus flow relation ship. The region in which it is linearized is parameterized by

  m_turbulent_flow = deltaM * m_flow_nominal

Because the parameterization contains Kv_SI, the values for deltaM and dp_nominal need not be changed if the valve size changes.

In contrast to the model in Modelica.Fluid, this model uses the parameter Kv_SI, which is the flow coefficient in SI units, i.e., it is the ratio between mass flow rate in kg/s and square root of pressure drop in Pa.

Options

This model allows different parameterization of the flow resistance. The different parameterizations are described in Buildings.Fluid.Actuators.BaseClasses.ValveParameters.

Implementation

The two way valve models are implemented using this partial model, as opposed to using different functions for the valve opening characteristics, because each valve opening characteristics has different parameters.

Extends from Buildings.Fluid.BaseClasses.PartialResistance (Partial model for a hydraulic resistance), Buildings.Fluid.Actuators.BaseClasses.ValveParameters (Model with parameters for valves), Buildings.Fluid.Actuators.BaseClasses.ActuatorSignal (Partial model that implements the filtered opening for valves and dampers).

Parameters

Connectors

Modelica definition

Buildings.Fluid.Actuators.BaseClasses.PartialTwoWayValveKv

Partial model for a two way valve using a Kv characteristic

Information

Partial model for valves with different opening characteristics, such as linear, equal percentage or quick opening. This partial extends from Buildings.Fluid.Actuators.BaseClasses.PartialTwoWayValve and also contains the governing equations for these three two way valve models.

Implementation

Models that extend this model need to provide a binding equation for the flow function phi. An example of such a code can be found in Buildings.Fluid.Actuators.Valves.TwoWayLinear.

Extends from Buildings.Fluid.Actuators.BaseClasses.PartialTwoWayValve (Partial model for a two way valve).

Parameters

Connectors

Modelica definition

Buildings.Fluid.Actuators.BaseClasses.ValveParameters

Model with parameters for valves

Information

Model that computes the flow coefficients of valves. This base class allows the following modeling options, which have been adapted from the valve implementation in Modelica.Fluid to specify the valve flow coefficient in fully open conditions:

• CvData = Buildings.Fluid.Types.CvTypes.Av: the flow coefficient is given by the metric Av coefficient (m^2).
• CvData = Buildings.Fluid.Types.CvTypes.Kv: the flow coefficient is given by the metric Kv coefficient (m^3/h).
• CvData = Buildings.Fluid.Types.CvTypes.Cv: the flow coefficient is given by the US Cv coefficient (USG/min).
• CvData = Buildings.Fluid.Types.CvTypes.OpPoint: the flow is computed from the nominal operating point specified by dp_nominal and m_flow_nominal.

The treatment of parameters Kv and Cv is explained in detail in the Users Guide.

In contrast to the model in Modelica.Fluid, this model uses the protected parameter Kv_SI, which is the flow coefficient in SI units, i.e., it is the ratio between mass flow rate in kg/s and square root of pressure drop in Pa. The value of Kv_SI is computed based on the parameters Av, Kv, Cv, or, if CvData = Buildings.Fluid.Types.CvTypes.OpPoint, based on m_flow_nominal and dpValve_nominal. Conversely, if CvData <> Buildings.Fluid.Types.CvTypes.OpPoint, then dpValve_nominal is computed based on Av, Kv, or Cv, and the nominal mass flow rate m_flow_nominal. Therefore, if CvData <> Buildings.Fluid.Types.CvTypes.OpPoint, then specifying a value for dpValve_nominal is a syntax error.

Parameters

Modelica definition

Buildings.Fluid.Actuators.BaseClasses.der_equalPercentage

Derivative of valve opening characteristics for equal percentage valve

Information

This function computes the derivative of the opening characteristics of an equal percentage valve.

The function is the derivative of Buildings.Fluid.Actuators.BaseClasses.equalPercentage.

Extends from Modelica.Icons.Function (Icon for functions).

Inputs

Outputs

Modelica definition

Buildings.Fluid.Actuators.BaseClasses.equalPercentage

Valve opening characteristics for equal percentage valve

Information

This function computes the opening characteristics of an equal percentage valve.

The function is used by the model Buildings.Fluid.Actuators.Valves.TwoWayEqualPercentage.

For y < delta/2, the valve characteristics is linear. For y > 3*delta/2 the valve characteristics is equal percentage. In between, a cubic spline is used to ensure that the valve characteristics is once continuously differentiable with respect to y.

Extends from Modelica.Icons.Function (Icon for functions).

Inputs

Outputs

Modelica definition

Buildings.Fluid.Actuators.BaseClasses.exponentialDamper

Damper opening characteristics for an exponential damper

Information

This function computes the opening characteristics of an exponential damper.

The function is used by the model Buildings.Fluid.Actuators.Dampers.Exponential.

For yL < y < yU, the damper characteristics is

k_d(y) = exp(a+b (1-y)).

Outside this range, the damper characteristic is defined by a quadratic polynomial.

Note that this implementation returns sqrt(k_d(y)) instead of k_d(y). This is done for numerical reason since otherwise k_d(y) may be an iteration variable, which may cause a lot of warnings and slower convergence if the solver attempts k_d(y) < 0 during the iterative solution procedure.

Extends from Modelica.Icons.Function (Icon for functions).

Inputs

Outputs

Modelica definition