BOUNDARY
This tab lets you specify which lines of the frame are in contact with internal and external environments. Every boundary condition has three groups of parameters:
Flows: used in simulations whose purpose is the calculation of transmittances;
Mold: used in simulations whose purpose is the risk of mold formation, in which case you must use monthly average parameters for the external surfaces;
Dew: used in the simulations whose purpose is the risk of condensation, in which case you must use the annual average minimum temperatures and humidity to 95%.
By selecting one of the available boundary conditions you'll be able to set the following parameters:
Type:
Name: name of the boundary condition;
Air temperature type / Temperature type:
constant: constant in time;
by climatic zone: variable in time, depending on climatic zone;
houses internal: temperature specific to houses internal; see below for more details;
by month: temperature changes monthly;
proportional to internal/external: proportional to internal and external environments (specified by "main internal/external couple" parameter) temperature difference;
proportional to external: proportional to external environment temperature;
internal continental/tropical: see EN ISO 13788 Appendix A.
Air temperature / temperature: temperature of the environment's air; please note that you have to use default temperatures to perform a simulation respecting the standards;
T factor: proportionality factor used for temperature;
Resistance:
costant: constant in time;
internal ISO 6946: resistance depends on flow direction; see EN 10211 6.3 and ISO 6946.
Humidity type:
constant: constant in time;
by climatic zone: variable in time, depending on climatic zone;
by month: humidity changes monthly;
all the others: see EN ISO 13788 Appendix A.
φ sat. : saturation relative humidity;
Humidity: environment's humidity;
Color: boundary condition's color;
Group: group whose boundary is part of. See below for more information;
Analysis group: boundary conditions with the same value of this parameter will generate additional analysis that will appear in advanced results.
These are the commands:
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Assign selected boundary condition to a single line. |
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Assign selected boundary condition to every line having the same boundary condition of the line you're going to click. |
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Remove all the assigned boundary conditions from the project. |
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Select boundary condition by clicking on a line. |
U-factor surface
Each boundary condition has the ability to affect U-factors calculation (refer to U-factors documentation for more information). Leaving this setting to the default value ("use segment settings"), the U-factors calculation is not altered, but if you select a U-factor, all the segments to which is assigned the current boundary condition will be used for the calculation of that factor. By selecting "Create New", a new U-factor surface will be created with the same name of the current boundary condition.
The standard EN ISO 13788 prescribes to use different surface resistances for the computation of the linear thermal transmittance ψ of the thermal bridge and for the computation of the temperature distribution for the condensation test. For this reason, every boundary condition has two different surface resistances. The software will use the appropriate one depending on the case.
The surface and interstitial condensation test is done month by month using different values of temperature and humidity. For this reason it's necessary to specify those values monthly.
For the external environment, it's possible to specify manually the temperature and humidity, or to use the ones provided by the national standard.
As for the external conditions, the internal conditions can be specified monthly. In the case of houses, the internal temperature can be computed automatically by Mold Simulator (in which case it is necessary to specify the month the heating system is on) or specified month by month. The internal humidity, can be computed automatically according to the building's type, or can be specified monthly.
Boundary coupling
For the surface condensation test it's necessary to associate every internal boundary condition to an external condition. "Boundary coupling" interface allows to perform the association.
It's really important to specify a reference internal/external environment couple in case there is a boundary condition which temperature difference from internal environment is proportional to internal/external temperature difference.
Boundary grouping
Boundary conditions, together with their analysis, can be grouped by the following criteria:
none: every condition is considers as a separarate environment;
temperature: boundary conditions will be grouped by their temperature. In case "Connected boundaries only" option is on, only boundaries connected and with the same temperature will be grouped;
group: grouping will depend on "Group" parameter of each boundari condition. Also in this case "Connected boundaries only" option will be applied.
The parameter "group
analysis", in each type of simulation (flows, condensation and
mold) can be added for additional analysis of grouped contours, which
appear in the advanced results.
Here is a schematic example:
Assume
the following situations:
a) Grouping set to "none":
The five boundary conditions (A, B, C, D, E) will be treated as separate environments and there will be no grouping.
b)
Grouping set to "temperature", A, B and C have the same
temperature and D and E have the same temperature:
Will be identified two distinct environments: A-B-C and D-E.
c)
As b) but B and C have the parameter "group analysis" in
"mold" set to "Test Group 1":
Will
be identified two distinct environments (ABC and DE) and, in advanced
results of “mold” simulation, the table of group analysis
will contain a line labeled "Test Group 1".
d) A, B
and C have arbitrary temperatures and parameter "group" is
set to "group 1" and D and E have arbitrary temperatures
and parameter "group" is set to "Group 2":
Will be identified two distinct environments: A-B-C and D-E.
Multiple boundary conditions
Since windows and frames have a thermal inertia much lower than walls, the standard ISO 13788:2003 uses different external boundary conditions if the condensation analysis is performed on windows and frames or on walls.
Mold
Simulator allows to specify different boundary conditions depending
on the case considered.
An extremely useful feature of boundary
condition is "Temperature" parameter set to "Proportional
to internal/external". In this particular configuration,
temperature (T) will be choosen in order to satisfy the following
conditions:
Ti - T = (Ti - Te) * Ft
and also
(Ti - T) / (Ti - Te) = Ft
where:
Ti:
temperature of internal environment specified by internal/external
couple
Te: temperature of external environment specified by internal/external couple
Ft: factor that can be set by the field on the side of "Temperature" parameter
We suggest to read “Tutorial 3” for a real example of this feature.
In case of more than two environments it's not possible to identify a reference temperature difference and so to compute L2D in general. With three enviroments, thermal coupling coefficients, the values of most interest, will be computed anyway; ψ will also be computed with the following formula:
ψ = Lie – Σlie*Uie + (Lin – Σlin*Uin) * ((Ti – Tn) / (Ti – Te)) (when third environment is not heated)
ψ = Lie – Σlie*Uie + (Lin – Σlin*Uin) * ((Ti – Tn) / (Ti – Te)) + (Lne – Σlne*Une) * ((Tn – Te) / (Ti – Te)) (when third environment is heated)
With:
Lie: internal/external coupling coefficient;
lie: length of section element between internal and external enviroments;
Uie: transmittance of section element between internal and external enviroments;
Lin: internal/third enviroment coupling coefficient;
lin: length of section element between internal and third enviroments;
Uin: transmittance of section element between internal and third enviroments;
Lne: external/third enviroment coupling coefficient;
lne: length of section element between external and third enviroments;
Une: transmittance of section element between external and third enviroments;
Ti: internal environment's temperature;
Tn: third environment's temperature;
Te: external environment's temperature.
Please note that, in this particular case, linear thermal transmittance depends on environments' temperatures and can't be considered valid in general.
It is possible to identify three factors in the previous equation:
ψie = Lie – Σlie*Uie
ψin = (Lin – Σlin*Uin) * ((Ti – Tn) / (Ti – Te))
ψne = (Lne – Σlne*Une) * ((Tn – Te) / (Ti – Te))
In this way it is possible to separate the contributions to the thermal bridge.
As you can see, in this particular case, the linear thermal transmittance is dependent on the temperature of the environments and is therefore not considered a valid value in general; for this reason, the option described at the beginning of the paragraph is particularly useful.
Increased resistance algorithm
EN 10077-2 states that in some cases increased surface resistance has to be used on internal borders; by default this software identifies these lines automatically. You can disable this algorithm by unchecking "Active" box. "Tolerance" parameter allows you to control the algorithm's sensitivity: the higher the value, the more likely is increased resistances detection.
Additional climate data
It is possible to add climate data in Mold Simulator. Here's how:
inside installation folder (eg "c:\Program Files\FluidInteractive\MoldSimulator2") you will find a subfolder "Data";
open the folder "Data";
into the subfolder "Data" add a subfolder with the name of the zone (eg "Zone 1");
put the files "climaticCities.csv" and "climaticTowns.csv" in the folder you just created.
The
file "climaticCities.csv" will contain climate data for
cities and must have the following format:
Row 1: can be left
blank
Rows, columns 1 through 5:
city number, citiy initials,
climate zone index (0 - 4), city name, altitude (m)
Rows, columns
6 to 17:
temperatures in the 12 months (° C)
Rows, columns
18 to 29:
partial vapour pressure in the 12 months (Pa)
See the
file "climaticCities.csv" in the folder "Data\it_IT"
as an example.
The file "climaticTowns.csv" will
contain towns climate data and must have the following format:
Row
1: can be left blank
Following lines:
region, city initials,
town name, altitude, temperature, climate zone (0 - 4)
See the
file "climaticTowns.csv" in the folder "Data\it_IT"
as an example.