Buildings.Fluid.DataCenters.Racks.Air

Package with models for air-cooled IT racks

Information

This package contains models for air-cooled IT racks. For air-cooled IT racks with rear door heat exchangers, see the package Buildings.Fluid.DataCenters.Racks.Hybrid.

Extends from Modelica.Icons.VariantsPackage (Icon for package containing variants).

Package Content

Name	Description
Rack_P	Model of an air-cooled rack, and utilization is input
Data	Package with data records for racks
Examples	Collection of models that illustrate model use and test models

Buildings.Fluid.DataCenters.Racks.Air.Rack_P

Model of an air-cooled rack, and utilization is input

Information

Model of an air-cooled IT rack.

Electrical and fluid characterization

The model takes as a parameter the thermal design power (TDB) P_nominal and as an input the utilization u. The heat added to the coolant fluid is then calculated as

Q_flow = u P_nominal.

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.

Because the pressure drop of the rack is typically no a known design quantity, the model computes it internally based on the fan power consumption and the fan efficiency.

Fan

The model has a built-in fan which uses a constant total efficiency, specified through the parameter dat.eta_nominal. The fan has a PI controller that maintains a temperature difference across the rack equal to the parameter dTSet.

Implementation

The implementation uses a fan model with prescribed speed, and, as explained above, it computes a flow resistance which is then used in the simulations. This implementation is used to allow use of this model with active rear door heat exchangers. As active rear-door heat exchangers also have a fan, in such a configuration there will be two fans in series. Prescribing the mass flow rate instead of the fan may give in this situation an overspecified system of equations. Thefore, rack model and rear-door heat exchangers use the fan model Buildings.Fluid.DataCenters.Racks.BaseClasses.ControlledFan.

Extends from Buildings.Fluid.DataCenters.Racks.BaseClasses.PartialRack (Partial model of an IT rack, with utilization as input).

Parameters

Connectors

Modelica definition