Buildings.Fluid.DXSystems.Heating.BaseClasses

Package with base classes for Buildings.Fluid.DXSystems.Heating

Information

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

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

Package Content

Name	Description
CoilDefrostTimeCalculations	Calculates defrost curve value at given temperature and mass flow rate
DefrostCapacity	Calculates defrost curve value at given temperature and mass flow rate
PartialDXHeatingCoil	Partial model for DX heating coil
Types	Package with base classes for DX heating coils

Buildings.Fluid.DXSystems.Heating.BaseClasses.CoilDefrostTimeCalculations

Calculates defrost curve value at given temperature and mass flow rate

Information

Block that calculates the defrost cycling time fraction tDefFra, the heating capacity multiplier heaCapMul and the input power multiplier inpPowMul.

The inputs are the measured temperature TOut and humidity ratio per kg total air XOut of the outdoor air. The calculation is based on Section 15.2.11.4 in the EnergyPlus 22.2 engineering reference document and is as decribed below.

Calculations

The model first estimates the outdoor coil temperature TCoiOut from the outdoor air drybulb temperature TOut using

TCoiOut = 0.82*TOut - 8.589.

The difference between the outdoor air humidity ratio XOutDryAir and the saturated air humidity ratio at outdoor coil temperature is used to determine frost formation on the outdoor coil as

delta_XCoilOut = max(1e-6, (XOutDryAir - XSatOutCoil)).

The block then calculates the time period fraction tDefFra for which the defrost operation is assumed to run, based on defrost calculation mode specified by the parameter defTri.
In the EnergyPlus model, tDefFra represents the fraction of the constant timestep in the simulation model for which the defrost operation is assumed to be active. This is calculated to be a higher value when the outdoor air temperature is lower and the relative humidity is higher. This results in a higher proportion of the consumed power going towards the defrost operation and lower heating of the condenser's air stream.

In this Modelica implementation of the model, while the timestep may not be constant and may vary based on the solver for the simulation, the same assumption is used for calculating the proportion of energy consumed for defrost mode operation. The coil does not actually enter defrost operation (with reverse flow of refrigerant) during this timestep fraction.

If defTri is set to timed, tDefFra is set to the user input parameter for defrost operation timestep fraction tDefRun. The heating capacity multiplier heaCapMul and input power multiplier inpPowMul are calculated as

tDefFra = tDefRun,
heaCapMul = 0.909 - 107.33*delta_XCoilOut,
inpPowMul = 0.9 - 36.45*delta_XCoilOut.

If defTri is set to onDemand, tDefFra, heaCapMul and inpPowMul are calculated as

tDefFra = 1/(1 + (0.01446/delta_XCoilOut)),
heaCapMul = 0.875*(1 - tDefFra),
inpPowMul = 0.954*(1 - tDefFra).

Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).

Parameters

Connectors

Modelica definition

Buildings.Fluid.DXSystems.Heating.BaseClasses.DefrostCapacity

Calculates defrost curve value at given temperature and mass flow rate

Information

Block that calculates the heat transfered to airloop QTotDef_flow, the total heating power consumption of the component PTot, the defrost input power consumption PDef and the crankcase heater input power consumption PCra.

The calculation are based on in Section 15.2.11.5 and 11.6 in the the EnergyPlus 22.2 engineering reference document, and are as

• the defrost cycle time fraction tDefFra, the heating capacity multiplier heaCapMul and the input power multiplier inpPowMul calculated by Buildings.Fluid.DXSystems.Heating.BaseClasses.CoilDefrostTimeCalculations.

• the total heat transfer QTot_flow and energy input ratio EIR calculated by Buildings.Fluid.DXSystems.BaseClasses.DryCoil.

• the measured temperature TConIn, humidity ratio per kg of total air XConIn and pressure pIn of the indoor coil inlet air temperature.

• the measured outdoor air temperature TOut.

Calculations

Based on the type of defrost method defOpe, different calculations are used:

• If defOpe = reverseCycle, the heat transfer rate from the airstream to the outdoor coil QDef_flow and the power consumption for defrost PDef are calculated as follows:

  QDef_flow = 0.01*tDefFra*(7.222 - TOut)*(QTot_flow/1.01667),
  PDef = defMod_T*(QTot_flow/1.01667)*tDefFra*RTF,

  where defMod_T is the defrost operation modifier calculated as

  defMod_T = defCur[1] + defCur[2]*TConInWetBul + defCur[3]*TConInWetBul² + defCur[4]*TOut + defCur[5]*TOut² + defCur[6]*TOut*TConInWetBul,

  and RTF is the runtime fraction of the heating coil, calculated from part load ratio PLR and part load fraction PLFra as

  RTF = PLR/PLFra.

  The part load ratio PLR is set to 1 since only a constant speed DX heating coil is implemented.

  The PLFra is calculated from the part load fraction curve defCur.PLFraFunPLR as

  PLFra = PLFraFunPLR[1] + PLFraFunPLR[2]*PLR + PLFraFunPLR[3]*PLR² + PLFraFunPLR[4]*PLR³.

• If defOpe = reverseCycle, the calculations are

  QDef_flow = 0,
  PDef = QDefResCap*tDefFra*RTF,

  where QDefResCap is the rated capacity of the resistive heating element on the outdoor coil.
  The remaining variable calculations for RTF, PLR and PLFra are the same as above.

The total power consumption PTot and total heat flowrate to the air stream QTotDef_flow (while accounting for defrost operation) is calculated as follows:

PTot = QTot_flow*EIR*PLR*inpPowMul/PLFra,
QTotDef_flow = QTot_flow*heaCapMul.

Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).

Parameters

Connectors

Modelica definition

Buildings.Fluid.DXSystems.Heating.BaseClasses.PartialDXHeatingCoil

Partial model for DX heating coil

Information

This partial model is the base class for Buildings.Fluid.DXSystems.Heating.AirSource.SingleSpeed.

Extends from Buildings.Fluid.Interfaces.TwoPortHeatMassExchanger (Partial model transporting one fluid stream with storing mass or energy).

Parameters

Connectors

Modelica definition