Buildings.Fluid.DataCenters.Racks.BaseClasses

Package with base classes for racks

Information

This package contains base classes that are used to construct the classes in Buildings.Fluid.DataCenters.Racks.

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

Package Content

Name	Description
Fan	Preconfigured server fan
PartialRack	Partial model of an IT rack, with utilization as input
Data	Package with data records for racks
Validation	Validation models for BaseClasses

Buildings.Fluid.DataCenters.Racks.BaseClasses.Fan

Preconfigured server fan

Buildings.Fluid.DataCenters.Racks.BaseClasses.Fan

Information

Preconfigured fan model.

The fan is modelled using Buildings.Fluid.Movers.SpeedControlled_y. The fan pressure rise at the nominal volumetric flow rate is

dp₀ = P_fan,0 η₀ ⁄ V̇₀.

The fan uses a constant total efficiency, which is set by the parameters eta_nominal.

Extends from Buildings.Fluid.Movers.SpeedControlled_y (Fan or pump with ideally controlled normalized speed y as input signal).

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Medium in the component
Boolean	addPowerToMedium	true	Set to false to avoid any power (=heat and flow work) being added to medium (may give simpler equations)
Control
InputType	inputType	Buildings.Fluid.Types.InputT...	Control input type
Fan
Real	eta_nominal	0.7	Fan and motor combined efficiency at nominal conditions [1]
MassFlowRate	m_flow_nominal		Design air mass flow rate [kg/s]
Power	PFan_nominal		Fan electricity consumption at design flow rate [W]
Dynamics
Conservation equations
Dynamics	energyDynamics	Modelica.Fluid.Types.Dynamic...	Type of energy balance: dynamic (3 initialization options) or steady state
Time	tau	1	Time constant of fluid volume for nominal flow, used if energy or mass balance is dynamic [s]
Motor speed
Boolean	use_riseTime	true	Set to true to continuously change motor speed
Time	riseTime	2	Time needed to change motor speed between zero and full speed [s]
Init	init	Modelica.Blocks.Types.Init.I...	Type of initialization (no init/steady state/initial state/initial output)
Real	y_start	0	Initial value of speed [1]
Advanced
MassFlowRate	m_flow_small	1E-4*abs(_m_flow_nominal)	Small mass flow rate for regularization of zero flow [kg/s]
Diagnostics
Boolean	show_T	false	= true, if actual temperature at port is computed
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
ExtraProperty	C_nominal[Medium.nC]	fill(1E-2, Medium.nC)	Nominal value of trace substances. (Set to typical order of magnitude.)
Assumptions
Boolean	allowFlowReversal	true	= false to simplify equations, assuming, but not enforcing, no flow reversal

Connectors

Type	Name	Description
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 IntegerInput	stage	Stage input signal for the pressure head
output RealOutput	y_actual	Actual normalised fan or pump speed that is used for computations [1]
output RealOutput	P	Electrical power consumed [W]
HeatPort_a	heatPort	Heat dissipation to environment
input RealInput	y	Constant normalized rotational speed [1]

Modelica definition

model Fan "Preconfigured server fan" extends Buildings.Fluid.Movers.SpeedControlled_y( energyDynamics=Modelica.Fluid.Types.Dynamics.SteadyState, use_riseTime=true, riseTime=2, tau=1, per( pressure( V_flow={ 0, 2*V_flow_nominal}, dp={ 2*dp_nominal, 0}), etaHydMet=Buildings.Fluid.Movers.BaseClasses.Types.HydraulicEfficiencyMethod.EulerNumber, etaMotMet=Buildings.Fluid.Movers.BaseClasses.Types.MotorEfficiencyMethod.Efficiency_VolumeFlowRate, motorEfficiency(V_flow={0}, eta={sqrt(eta_nominal)}), etaMot_max=sqrt(eta_nominal), powerOrEfficiencyIsHydraulic=false)); parameter Real eta_nominal( final unit="1", final min=Modelica.Constants.small) = 0.7 "Fan and motor combined efficiency at nominal conditions"; parameter Modelica.Units.SI.MassFlowRate m_flow_nominal(min=0) "Design air mass flow rate"; parameter Modelica.Units.SI.Power PFan_nominal(min=0) "Fan electricity consumption at design flow rate"; protected parameter Modelica.Units.SI.VolumeFlowRate V_flow_nominal = m_flow_nominal / rho_default "Nominal volumetric flow rate"; parameter Modelica.Units.SI.PressureDifference dp_nominal(displayUnit="Pa") = PFan_nominal * eta_nominal / V_flow_nominal "Fan pressure rise at nominal conditions"; end Fan;

Buildings.Fluid.DataCenters.Racks.BaseClasses.PartialRack

Partial model of an IT rack, with utilization as input

Buildings.Fluid.DataCenters.Racks.BaseClasses.PartialRack

Information

Partial model of an IT rack.

Electrical and fluid characterization

The model takes as an input the electrical power consumption, and assumes all is converted to the heat that needs to be rejected through the fluid ports, e.g.,

Q_flow = P.

The fluid outlet temperature is computed using a first order delay to mimic the transient effect. This first order delay is characterized by the user-configurable time constant tau, set by default to tau=2 seconds. For exact transient response, this value should be identified based on measurements.

To compute the pressure drop, the model uses Buildings.Fluid.FixedResistances.PressureDrop. Therefore, the mass flow rate and pressure drop are related as

m_flow ⁄ m_flow_nominal = (dp ⁄ dp_nominal)^m,

where m_flow_nominal is a parameter for the design flow rate, dp is the pressure difference between inlet and outlet, dp_nominal is a parameter for the design pressure difference, and m is a parameter for the flow exponent.

Extends from Buildings.Fluid.Interfaces.PartialTwoPort (Partial component with two ports).

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Medium in the component
Generic	dat	redeclare parameter Building...	Performance data
Assumptions
Boolean	allowFlowReversal	true	= false to simplify equations, assuming, but not enforcing, no flow reversal
Dynamics
Conservation equations
Dynamics	energyDynamics	Modelica.Fluid.Types.Dynamic...	Type of energy balance: dynamic (3 initialization options) or steady state
Time	tau	2	Time constant of fluid outlet temperature at nominal flow [s]
Initialization
Temperature	T_start	Medium.T_default	Start value of temperature [K]

Connectors

Type	Name	Description
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)
replaceable package Medium		Medium in the component
input RealInput	P	Electrical power consumption [W]

Modelica definition

partial model PartialRack "Partial model of an IT rack, with utilization as input" extends Buildings.Fluid.Interfaces.PartialTwoPort; replaceable package Medium = Modelica.Media.Interfaces.PartialMedium "Medium in the component"; replaceable parameter Buildings.Fluid.DataCenters.Racks.BaseClasses.Data.Generic dat "Performance data"; parameter Modelica.Fluid.Types.Dynamics energyDynamics=Modelica.Fluid.Types.Dynamics.DynamicFreeInitial "Type of energy balance: dynamic (3 initialization options) or steady state"; parameter Modelica.Units.SI.Time tau=2 "Time constant of fluid outlet temperature at nominal flow"; // Initialization parameter Medium.Temperature T_start = Medium.T_default "Start value of temperature"; Modelica.Blocks.Interfaces.RealInput P(final unit="W", min=0) "Electrical power consumption"; output Real utiIT( final unit="1", final min=0) = P / dat.PIT_nominal "IT utilization"; Fluid.Delays.DelayFirstOrder vol( redeclare final package Medium = Medium, final energyDynamics=energyDynamics, final T_start=T_start, final m_flow_nominal=dat.m_flow_nominal, final allowFlowReversal=allowFlowReversal, final tau=tau, final prescribedHeatFlowRate=true) "Fluid control volume"; Modelica.Units.SI.MassFlowRate m_flow = port_a.m_flow "Mass flow rate from port_a to port_b"; protected Buildings.HeatTransfer.Sources.PrescribedHeatFlow preHea "Prescribed heat flow rate"; equation connect(preHea.port,vol. heatPort); end PartialRack;