The SimInfoManager manages all simulation information. It loads TMY3 weather data files and applies transformations for computing the solar irradiance on the zone surfaces.
filNam and filDir can be used to set the path to the TMY3 weather file.
This file should include the latitude, longitude and time zone corresponding to the weather file.
See the included weather files for the correct format.
incAndAziInBus.
incAndAziInBus determines for which inclination and azimuth the solar radiation is pre-computed.
computeConservationOfEnergy=true.
Conservation of energy is checked by computing the internal energy for
all components that are within "the system" and by adding to this the
integral of all heat flows entering/leaving the system.
There are two options for choosing the extent of the system based
on parameter openSystemConservationOfEnergy.
Either conservation of energy for a closed system is computed,
or it is computed for an open system. Buildings package.
I.e. all heat flows at embedded ports port_emb of walls,
fluid ports of the zones, zone.gainCon and zone.gainRad are
considered to be a heat gain to the system and every other component
is considered to be outside of the system for which conservation of energy is checked. openSystemConservationOfEnergy=true
these heat flow rates are not taken into account because they are assumed
to flow between components that are both within the bounds of the system.
The user then needs to choose how large the system is and he should make sure that
all heat flow rates entering the system are added to sim.Qgai.Q_flow and
that all internal energy of the system is added to sim.E.E.
IDEAS supports several levels of detail for simulating interzonal airflow and air infiltration,
which can be selected by setting the value of the parameter interzonalAirFlowType.
By default, interzonalAirFlowType=None and a fixed n50 value is assumed for each zone.
The n50 value represents the airtightness of a building or building zone.
It is equal to the number of air changes per hour (due to air leakage) at a pressure difference of 50 Pa,
and is expressed in h-1.
The corresponding fixed mass flow rate is divided by a fixed factor n50toAch and is pushed
into (with ambient properties) and extracted from each zone model.
In practice, however, air infiltration depends on the wind pressure and temperature differences,
and occurs only in zones that have an exterior/outer wall or windows.
The other interzonalAirFlowType options model this effect in more detail.
When setting unify_n50=true while interzonalAirFlowType=None,
the n50 values are automatically redistributed across the zones as described below
and a corrected fixed infiltration flow rate is assumed.
While this implementation is more detailed and comes at no added computational cost,
it is disabled by default for backward compatibility reasons.
When interzonalAirFlowType=OnePort or interzonalAirFlowType=TwoPort,
by default, the OuterWall and Window leakage coefficients
are computed using the building's n50 value set in the SimInfoManager.
The zone volumes are added together to compute the total nominal air infiltration
at a 50 Pa pressure difference based on the building's n50 value set by the user.
Then, the total exterior building area,
which is the sum of the area of all OuterWall and Window components,
is used to compute an average q50 value.
The q50 value represents the airtightness of a surface.
It is equal to the average air leakage flow per hour at a pressure difference of 50 Pa per surface area,
and is expressed in m3/h/m2.
Each airflow path is represented by an IDEAS.Airflow.Multizone.Point_m_flow class
which will compute the real air flow rates at lower pressure differences.
When a custom q50 value for a wall or window is known, it can be
assigned by the user using the parameters use_custom_q50 and custom_q50.
The algorithm considers these q50 values as known and recomputes all remaining q50 values
such that the imposed n50 value at the building level is reached.
In a similar way, the total n50 value for one zone can be forced by using
the zone parameters use_custom_n50 and n50.
In this case, the q50 parameter values of the outer surfaces
connected to that zone will correspond to the custom n50 parameter value of the zone.
Subsequently, all other zones and surfaces will be adjusted such that
the building's total air leakage still corresponds to the building's n50 value.
In case interzonalAirFlowType=OnePort, then one flow path is
used to model the air exchange through each surface
and through cavities in internal walls (open doors).
No buoyancy driven airflow (stack-effect) is modelled in this case.
This implementation is recommended when naturally driven airflows
are expected to be negligble (e.g. limited building height, good airtightness)
or when the HVAC system pressure differences and
corresponding air flow rates are of higher orders of magnitude.
More information regarding the one-port implementation can be found in [DeJonge2021].
When interzonalAirFlowType=TwoPorts, then two flow paths are
used for each external surface and
buoyancy/temperature driven airflow (stack-effect) is added by consistent implementation
of the IDEAS.Airflow.Multizone.MediumColumnReversible class.
This increases the level of detail at the cost of having to solve a more complex flow network,
thereby allowing the more detailed modelling of multi-zone air flow.
In this implementation, larger openings (e.g. open doors in internal walls or open windows)
are represented by the IDEAS.Airflow.Multizone.DoorDiscretizedOperable class.
It is important to set the parameters hFloor and hZone correctly at zone level.
The wind pressure depends on the wind speed, but this one is typically measured at a meteorological station. The wind speed at the building is different from this measured one due to the local terrain and elevation effects. This is taken into account by the wind speed modifier coefficient Cs, which is calculated as [CONTAM2020]:
Cs = A02 · (H/Href)2a
where H is the building height, Href is the height at which the wind speed is measured, A0 is the local terrain constant, and a is the velocity profile exponent.
The AHRAE Fundamentals handbook of 1993 provided values for A0 and a for different terrain types (e.g. urban and suburban). Since the 2005 version of the ASHRAE Fundamentals handbook [ASHRAE2005], the wind boundary layer thickness δ is reported instead of the coefficient A0. However, the latter can be calculated from the former as [CONTAM2020]:
A0 = (δref/Href)aref · (Href/δ)aref
where δref, Href, and aref are the wind boundary layer thickness, wind measurement height, and velocity profile exponent at the meteorological station, respectively.
The model allows to set the terrain type parameter locTer to
Urban, Suburban, Unshielded, or Custom.
For the former three, coefficients a and δ are taken from [ASHRAE2005]
and A0 is calculated using the equation above, assuming
a meteorological station in an unshielded area.
The height at which the wind is measured (Href) is set by the parameter Hwind.
If Custom is selected, the user needs to provide values for a and A0.
| Terrain type | a | δ [m] | A0 |
|---|---|---|---|
| Urban (large city center) | 0.33 | 460 | (270/Href)0.14 · (Href/460)0.33 |
| Suburban | 0.22 | 370 | (270/Href)0.14 · (Href/370)0.22 |
| Unshielded (default) | 0.14 | 270 | (270/Href)0.14 · (Href/270)0.14 |
| Custom | acustom | / | A0,custom |
[ASHRAE2005]
American Society of Heating Refrigerating and Air-Conditioning Engineers.
2005 ASHRAE handbook: Fundamentals, SI Edition.
Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, 2005.
[CONTAM2020]
W. Stuart Dols and Brian J. Polidoro.
Washington, DC: US Department of Commerce, National Institute of Standards and Technology, 2015.
doi:10.6028/NIST.TN.1887r1.
[DeJonge2021]
Klaas De Jonge, Filip Jorissen, Lieve Helsen and Jelle Laverge.
Wind-Driven Air Flow Modelling in Modelica: Verification and Implementation in the IDEAS Library.
Proceedings of Building Simulation 2021: 17th Conference Of IBPSA. Bruges, Belgium, September, 2021.
doi:10.26868/25222708.2021.30165.