The main goal of the IDEAS Buildings library is to set up models that allow simulating building envelope models. These models may be coupled to models from the Fluid or Electric packages. In this user guide we outline the main principles of the library.
The main physical principles that are modelled in IDEAS are
Furthermore models for specifying additional boundary conditions are
A qualitative description of these models can be found below. If you need to know the implementation then look at the Modelica equation sections.
Interior convection
Interior convection is modelled between surfaces
and the zone air volume. Correlations are
used to compute the heat flow rate from the temperature difference.
By default these correlations are non-linear but they may be linearised as well.
Air cavities within walls are simulated using a correlation
that takes into account both radiative and convective heat transfer.
It is assumed that the cavity is not ventilated.
Exterior convection
Exterior convection is modelled using a wind speed dependent correlation.
Interior longwave radiation
Interior longwave radiation between surfaces may be modelled using two appraoches;
either using an
equivalent radiative star point
or using
view factors
.
Longwave radiation equations are linearised by default to avoid
large non-linear algebraic loops.
Computations using a fourth order equation may be enabled by setting
linIntRad=false in the zone model.
Surface emissivities are taken into account in these computations.
The view factor implementation assumes the zone to have a rectangular geometry.
Exterior longwave radiation
Exterior longwave radiation is simulated by computing heat exchange with a weighted temperature of
the outside air and the sky temperature.
The weighting factor depends on the surface orientation.
These equations are linear by default, but may be computed using a fourth order
equation using linExtRad=false.
Interior shortwave radiation
Interior shortwave radiation occurs
whenever sun light enters the zone through a window.
When passing through the window, part of the sun light
is absorbed.
In
IDEAS.Buildings.Components.BaseClasses.RadiativeHeatTransfer.ZoneLwGainDistribution
we assume that the light always hits the floor.
A fraction of the light, equal to the emissivity of the material,
will be absorbed. The remaining fraction is reflected within the
zone and is absorbed by the remaining surfaces.
Exterior shortwave radiation
Exterior shortwave radiation injects heat on
the outer surface of surfaces.
The magnitude of this heat injection depends on the surface emissivity and orientation and
the weather conditions (direct and diffuse solar radiation).
Surface shading by objects is currently not supported.
Thermal conduction
Thermal conduction through solids is modelled using
a series discretisation of the wall.
Window shading
A few models allow to compute the shading of windows.
These models limit the amount of direct or diffuse
solar irradation hitting the window.
Long wave radiation computations are not affected.
Air infiltration
Air infiltration is computed for each zone
independently, assuming a user provided constant n50 value.
Air exchange between zones is not modelled by default,
but may be added manually.
The main models in the Buildings package are:
We refer to the examples for some demonstrations of how to use the Building models.
Note that you must make sure that each model contains an instance of
IDEAS.BoundaryConditions.SimInfoManager
since this defines the boundary conditions of the model.
This instance must have the keyword inner.
The SimInfoManager may be used to define
some general model properties (see the parameters list),
as well as the location of the modelled building,
which affects the solar calculations.
The user should make sure that the propsBus ports
of each surface are connected to one zone model.
The IDEAS Templates may be used to provide some structure to your model but they need not be used.
IDEAS.Buildings.Examples contains examples that demonstrate several functionalities of the library. IDEAS.Buildings.Components.Examples contains examples that focus more on the component level and that are primarily used for unit test purposes. IDEAS.Buildings.Validation.Tests contains examples that verify the implementation of some models. These models often contain a 'Command' that runs the model and shows some results.
IDEAS is validated using BESTEST. The validation models may be found in package IDEAS.Buildings.Validation.
In addition to this conservation of energy may be checked. An example of how to do this may be found in IDEAS.Buildings.Validation.Tests.EnergyConservationValidation.
Many of the example models are unit tested. Developers use this to check model consistency when model equations are changed.