Buildings.Fluid.Movers.UsersGuide

This package contains models that can be used for fans and pumps.

Model description

This package contains models for fans and pumps. The same models are used for both devices. The models are parameterized by performance curves that compute pressure rise, electrical power draw or efficiency as a function of the flow rate. These performance curves are described in Buildings.Fluid.Movers.BaseClasses.Characteristics.

The models Buildings.Fluid.Movers.FlowMachine_y and Buildings.Fluid.Movers.FlowMachine_Nrpm take as an input a control signal, and then compute the pressure difference for the current flow rate. The models Buildings.Fluid.Movers.FlowMachine_dp and Buildings.Fluid.Movers.FlowMachine_m_flow take as an input signal the pressure difference or the mass flow rate. This pressure difference or mass flow rate will be provided by the fan or pump. These two models do not have a performance curve for the flow characteristics. The reason is that at zero pressure difference, solving for the flow rate and the revolution leads to a singularity.

All models can be configured to have a fluid volume at the low-pressure side. Adding such a volume sometimes helps the solver to find a solution during initialization and time integration of large models.

All models compute the motor power draw PEle, the hydraulic power input WHyd, the flow work WFlo and the heat dissipated into the medium Q_flow. From the first law and the definition of efficiency, we have

  WFlo = | V_flow * dp |
  WHyd = WFlo + Q_flow
  eta = WFlo / PEle = etaHyd * etaMot
  etaHyd = WFlo/WHyd
  etaMot = WHyd/PEle

All models take as a parameter an efficiency curve for the motor. This function has the form

  etaMot = f(V_flow/V_flow_max)

where V_flow_max is the maximum flow rate. The models Buildings.Fluid.Movers.FlowMachine_y and Buildings.Fluid.Movers.FlowMachine_Nrpm set

  V_flow_max = flowCharacteristics(dp=0, r_N=1);

where r_N is the ratio of actual to nominal speed. Since Buildings.Fluid.Movers.FlowMachine_dp and Buildings.Fluid.Movers.FlowMachine_m_flow do not have a flowCharacteristics, the parameter V_flow_max must be set by the user for these models.

For a detailed description of the models with names FlowMachine_*, see their base class Buildings.Fluid.Movers.BaseClasses.PartialFlowMachine.

The model Buildings.Fluid.Movers.FlowMachinePolynomial is in this package for compatibility with older versions of this library. It is recommended to use the other models as they optionally allow use of a medium volume that provides state variables which are needed in some models when the flow rate is zero.

Differences to models in Modelica.Fluid.Machines

The models with names FlowMachine_* have similar parameters than the models in the package Modelica.Fluid.Machines. However, the models in this package differ primarily in the following points:

• They use a different base class, which allows to have zero mass flow rate. The models in Modelica.Fluid restrict the number of revolutions, and hence the flow rate, to be non-zero.
• For the model with prescribed pressure, the input signal is the pressure difference between the two ports, and not the absolute pressure at port_b.
• The pressure calculations are based on total pressure in Pascals instead of the pump head in meters. This change was done to avoid ambiguities in the parameterization if the models are used as a fan with air as the medium. The original formulation in Modelica.Fluid.Machines converts head to pressure using the density medium.d. Therefore, for fans, head would be converted to pressure using the density of air. However, for fans, manufacturers typically publish the head in millimeters water (mmH20). Therefore, to avoid confusion when using these models with media other than water, we changed the models to use total pressure in Pascals instead of head in meters.
• Additional performance curves have been added to the package Buildings.Fluid.Movers.BaseClasses.Characteristics.