Buildings.Experimental.DHC.Loads.BaseClasses

Package with base classes

Information

This package contains base classes that are used to construct the classes in Buildings.Experimental.DHC.Loads.

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

Package Content

Name	Description
ConstraintViolation	Block that outputs the fraction of time when a constraint is violated
PartialBuilding	Partial class for building model
PartialBuildingWithPartialETS	Partial model of a building with an energy transfer station
PartialTerminalUnit	Partial model for HVAC terminal unit
getPeakLoad	Function that reads the peak load from the load profile
Validation	Collection of validation models

Buildings.Experimental.DHC.Loads.BaseClasses.ConstraintViolation

Block that outputs the fraction of time when a constraint is violated

Information

Block that outputs the running fractional time during which any element u_i of the input signal is not within u_min ≤ u_i ≤ u_max.

Parameters

Connectors

Modelica definition

Buildings.Experimental.DHC.Loads.BaseClasses.PartialBuilding

Partial class for building model

Information

Partial model to be used for modeling the thermal loads on an energy transfer station or a dedicated plant. Models extending this class are typically used in conjunction with Buildings.Experimental.DHC.Loads.FlowDistribution and models extending Buildings.Experimental.DHC.Loads.BaseClasses.PartialTerminalUnit as described in the schematics here under. The fluid ports represent the connection between the production system and the building distribution system.

Scaling

Scaling is implemented by means of a multiplier factor facMul. Each extensive quantity (mass and heat flow rate, electric power) flowing out through fluid ports, or connected to an output connector is multiplied by facMul. Each extensive quantity (mass and heat flow rate, electric power) flowing in through fluid ports, or connected to an input connector is multiplied by 1/facMul. This allows modeling, with a single instance, multiple identical buildings served by the same energy transfer station.

Examples

See various use cases in Buildings.Experimental.DHC.Loads.Examples.

Parameters

Connectors

Modelica definition

Buildings.Experimental.DHC.Loads.BaseClasses.PartialBuildingWithPartialETS

Partial model of a building with an energy transfer station

Information

Partial model to be used for modeling

• an energy transfer station and the optional in-building primary systems, based on a model extending Buildings.Experimental.DHC.EnergyTransferStations.BaseClasses.PartialETS, and
• the served building, based on a model extending Buildings.Experimental.DHC.Loads.BaseClasses.PartialBuilding.

See the schematics below for a description of the physical boundaries of the composing systems.

The parameters defining the set of outside connectors of this class are propagated up from the ETS and building components. The connect clauses between the ETS and the building connectors are automatically generated based on the previous parameters and the additional parameters nPorts_heaWat and nPorts_chiWat that need to be specified. In case of a heating service line, the model allows for using two different media at the inlet port_aSerHea and at the oulet port_bSerHea to represent a steam supply and condensate return.

Scaling

Scaling is implemented by means of a multiplier factor facMul. Each extensive quantity (mass and heat flow rate, electric power) flowing out through fluid ports, or connected to an output connector is multiplied by facMul. Each extensive quantity (mass and heat flow rate, electric power) flowing in through fluid ports, or connected to an input connector is multiplied by 1/facMul. This allows modeling, with a single instance, multiple identical buildings with identical energy transfer stations, served by the same service line.

Parameters

Connectors

Modelica definition

Buildings.Experimental.DHC.Loads.BaseClasses.PartialTerminalUnit

Partial model for HVAC terminal unit

Information

Partial model to be used for modeling an HVAC terminal unit.

The models inheriting from this class are typically used in conjunction with Buildings.Experimental.DHC.Loads.FlowDistribution. They must compute a so-called required mass flow rate defined as the heating or chilled water mass flow rate needed to meet the load. It can be approximated using a control loop to avoid inverting a heat exchanger model as illustrated in Buildings.Experimental.DHC.Loads.Examples.

The model connectivity can be modified to address various use cases:

• On the source side (typically connected to Buildings.Experimental.DHC.Loads.FlowDistribution):
  • Fluid ports for chilled water and heating water can be conditionally instantiated by respectively setting have_chiWat and have_heaWat to true.
• On the load side (typically connected to a room model):
  • Fluid ports can be conditionally instantiated by setting have_fluPor to true.
  • Alternatively heat ports (for convective and radiative heat transfer) can be conditionally instantiated by setting have_heaPor to true.
  • Real input connectors can be conditionally instantiated by setting have_QReq_flow to true. Those connectors can be used to provide heating and cooling loads as time series, see Buildings.Experimental.DHC.Loads.Examples.CouplingTimeSeries for an illustration of that use case. The impact on the room air temperature of an unmet load can be assessed with Buildings.Experimental.DHC.Loads.SimpleRoomODE.

The heating or cooling nominal capacity is provided for the water based heat exchangers only. Electric heating or cooling systems are supposed to have an infinite capacity.

Connection with the flow distribution model

When connecting the model to Buildings.Experimental.DHC.Loads.FlowDistribution:

• The nominal pressure drop on the source side (heating or chilled water) is irrelevant as the computation of the pump head relies on a specific algorithm described in Buildings.Experimental.DHC.Loads.FlowDistribution.
• The parameter allowFlowReversal must be set to false (default) in consistency with Buildings.Experimental.DHC.Loads.FlowDistribution. This requirement only applies to the source side. On the load side one is free to use whatever option suitable for the modeling needs. Note that typically for an air flow network connected to the outdoor (either at the room level for modeling infiltration or at the system level for the fresh air source), the unidirectional air flow condition cannot be guaranted. The reason is the varying pressure of the outdoor air that can lead to a negative pressure difference at the terminal unit boundaries when the fan is off.

Scaling

Scaling is implemented by means of two multiplier factors.

• The parameter facMul serves as a terminal unit multiplier. Each extensive quantity (mass and heat flow rate, electric power) flowing out through fluid or heat ports, or connected to an output connector is multiplied by facMul. Each extensive quantity (mass and heat flow rate, electric power) flowing in through fluid or heat ports, or connected to an input connector is multiplied by 1/facMul. This parameter allows modeling, with a single instance, multiple identical units served by the same distribution system, and serving an aggregated load (e.g., a thermal zone representing several rooms).
• The parameter facMulZon serves as a thermal zone multiplier. Except for the variables connected to the load side, which are not affected by facMulZon, the logic is otherwise identical to the one described for facMul. This parameter allows modeling, with a single instance (of both the terminal unit model and the load model), multiple identical units served by the same distribution system, and serving multiple identical loads (e.g., a thermal zone representing a single room).

Both multiplier factors are of type real (as opposed to integer) to allow for instance modeling a set of terminal units based on manufacturer data, while still being able to size the full set based on a peak load. See Buildings.Experimental.DHC.Loads.Validation.TerminalUnitScaling for an illustration of the use case when heating and cooling loads are provided as time series.

Change-over mode

When modeling a change-over system:

• The parameters have_chiWat and have_chaOve must both be set to true and have_heaWat must be set to false.
• The heat exchanger is sized by providing the nominal parameters for the cooling configuration (suffix ChiWat). The nominal mass flow rate on the source and the load side must also be provided for the heating configuration (suffix HeaWat) as it can differ from the cooling configuration.
• The computed heat flow rate must be split into its positive part that gets connected to QActHea_flow and its negative part that gets connected to QActCoo_flow.
• The computed required mass flow rate must be connected to mReqChiWat_flow.

Base class parameters

All the parameters of this base class that pertain to the nominal conditions shall not be exposed in the derived class, as this would lead to an overdetermined model. For instance, the nominal mass flow rate may not be exposed but rather computed from the nominal heat flow rate, entering and leaving fluid temperature. However, those parameters are included in the base class because other components are likely to reference them. For instance the distribution system model may use the nominal mass flow rate of each terminal unit to compute the nominal mass flow rate of the circulation pump.

Parameters

Connectors

Modelica definition

Buildings.Experimental.DHC.Loads.BaseClasses.getPeakLoad

Function that reads the peak load from the load profile

Information

Function that reads a double value from a text file.

This function scans a file that has a format such as

#1
#Some other text
#Peak space cooling load = -383165.6989 Watts
#Peak space heating load = 893931.4335 Watts
double tab1(8760,4)
0,0,5972.314925,16
3600,0,4925.839944,1750.915684
...

The parameter string is a string that the function searches for, starting at the first line. If it finds the string, it expects an equality sign, and returns the double value after this equality sign. If the function encounters the end of the file, it terminates the simulation with an assertion.

See Buildings.Experimental.DHC.Loads.BaseClasses.Validation.GetPeakLoad for how to invoke this function.

Inputs

Outputs

Modelica definition