ESP-r Frequently Asked Questions


 

Several questions about ESP-r tend to be asked regularly. Here we gather these together by topic.

General
Compilation and installation
Interface
Databases
Surface and zone dimensions
Furniture and clutter
Entity names
Replicating and moving zones
Fictitious surfaces and zone subdivision
Model QA
Control (ideal and detailed)
Climate and site issues
Schedules (operations)
Windows and other transparent multilayer constructions
Optical properties
Daylighting assessments
Solar and shading
Air flow
View factors
Simulation
Results analysis

Odds & ends

 


General

Question:

What would a typical user of ESP-r be attempting? Also what professions are typical users?

Answer:

Architect/energy consultant/engineer/Einstein. ESP-r is used by all of these user types (with one obvious exception!). However, any user of ESP-r will need at least a basic understanding of energy flows within building and environmental control systems.

Currently, modelling of buildings is well supported by a graphically-based project manager, with numerous exemplars which can be browsed. Assuming the form and operation of the building is not complex, users should be able to learn to build and simulate a model in a few days.

When it comes to detailed representations of environmental systems the descriptive and analysis facilities are less mature. We find that such topics are best approached by those with knowledge of such systems.

Question:

ESP-r is different each release. Some of the new facilities appear to have some bugs. Why?

Answer:

ESP-r is a continuously evolving simulation environment, which is developing according to the interests of researchers and the needs of practitioners. Although we undertake testing before each release, using a number of benchmark models, inevitably there will occasionally be bugs introduced, particularly in areas of new functionality. The banner at the top of each application is there for a purpose - we welcome constructive criticism. We rely primarily on contributions and developments from the "ESP-r research community", including Ph.D students.

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Compilation and installation

Question:

ESP-r is rather painful to install and it looks like a Unix expert is required...

Answer:

ESP-r is a suite of applications running on Unix and which has traditionally been for research and leading-edge consultancies. It is serious software for demanding problems which demands a certain level of competence in its administrators and users. It is essential that the person installing the system is reasonably familiar with Unix. The install process has evolved over time. However, there is no way that we can provide fail safe instructions for installation, primarily because the environments on different machines vary and some knowledgeable intervention is occasionally required.

Currently ESP-r is acquired via ftp transfer. It should take only a short time to install, but this may depend on the machine environment and expertise of the installer.

Question:

How do I recompile one of the ESP-r modules which I want to test separately from the normal ESP-r executables?

Answer:

To rebuild one of the executables you use the Install script as follows:


./Install -d /home/username/esru module_name

where username is changed to match your folder name. The -d directive tells the compiler where to place the new executables as well as where to find some required files.

The module_name in this case might be bld. Using the Install script passes the names of the various libraries to the compiler - you can remove the extra library files that you added. The Makefile in esrubld should be identical to the file in the standard distribution.

The above assumes that you have in your top level user folder the following set of folders:


esru
esru/bin
esru/docs
esru/esp-r
esru/esp-r/bin
esru/esp-r/lib
esru/include
esru/tutorial

libxesru.a should be in folder esru/esp-r/lib, which is created by


./Install -d /home/username/esru esru

The recompiled module will be placed in esru/esp-r/bin. The folder esru/include should have all the same files as are in the source include folder. The module build makes use of code from several other folders such as esrucom. Make sure that these folders are available at the same level as your esrubld source folder. You will want to update your PATH environment variable to include the esru/esp-r/bin folder.

Question:

If I need more surfaces or zones than are provided for in the standard version of ESP-r, what do I do?

Answer:

The product model is represented as arrays whose sizes are based on parameters which are in the files in /usr/esru/include/*.h. After altering parameter(s) you must recompile the executables. Please email ESRU first, as some parameter changes will require that database sizes and I/O statements must be altered to match.

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Interface

Question:

I sometimes get trapped by a decision (by mistake or in confusion) and it would be useful to have a "CANCEL" option in the standard [OK ? default] dialogs.

Answer:

We have updated many of these choices to allow a user to cancel the action. However, not all user choices may have a cancel option. Please inform us of instances which have given problems.

Question:

What do you do when the feedback text becomes truncated?

Answer:

Either use the "environment" button to switch to a smaller font or use the window manager and mouse to resize the display.

Question:

Sometimes the project manager seems to be updating the problem as I progress, sometimes it asks me if this is ok.

Answer:

The choice between automatic updating facilities and asking for confirmation is difficult at times. Each upgrade reduces the chances of lost information. Certain combinations of user actions are rare enough that all the bugs have not been worked out - keep us informed of what you find and everyone benefits.

Question:

Sometimes a hidden line representation of a simulation problem would be useful - what facilities exist?

Answer:

The intrinsic wire frame viewing facilities do not provide hidden line views (although you could filter for only external surfaces). You can export to a 3rd party hidden line viewing package called [surprise] "viewer". If this is not in your distribution please contact ESRU. Another alternative is to export to the lighting and visualisation simulation suite "Radiance" for which there is a translator called "e2r" available.

Question:

The native graphing facilities in the results analysis module are fine as far as they go - how can I get higher quality output?

Answer:

Almost anything which can be graphed in the results analysis module can be exported as tabular information in a form which 3rd party graphing packages such as "grace" can accept. You can toggle the "output" selection in most of the command menus from "output >> screen" to "output >> file".

Question:

How do I get a hard-copy from ESP-r during a session?

Answer:

There is no in-built function for this. There are utilities which can capture all or part of a screen and place the information into a file in one of several formats. We have used the following:

Question:

How do I replay a series of images for a presentation?

Answer:

You can write a script which displays them in order (hint use the first character of the file name to set the order) with a "foreach" command sequence:

 foreach i (*.xwd);
 echo now showing $i;
 xwud -in $i;
      end;

which works for xwd format. We have had good luck with the utility "xv" which can take a number of command arguments as well as a range of image file formats.

Question:

In the wireframe images sometimes there are open circles or solid dots at some of the corners - what does this mean?

Answer:

The open circles signify that the vertex is only referenced once in the topology (ie. it has no other edges attached). All vertices must be associated with at least two surfaces. If there is a solid dot then the vertex is not associated with any surface. Note also that there is an item in the zone geometry menu which reports if the zone enclosure is properly bounded.

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Databases

Question:

I have a partition which is asymmetric, how do I represent such a thing?

Answer:

Asymmetric partitions (which look different depending on the side you are looking from) are typically set up by creating one construction in the multi-layer database then copying it and then using the "invert" command (remembering also to alter the name of the inverted item). When you then attribute the surfaces such an asymmetric partition is given the standard name on one side/zone and the inverted item's name on the other.

Question:

When running ESP-r, the application stops with messages like: 
    "cannot find /usr/esru/esp-r/databases/constr.db1"

Answer:

ESP-r expects a folder /usr/esru/esp-r/databases to exist on the machine (although this might be via a symbolic link). To see if this is the problem issue the command
    cd  /usr/esru/esp-r/databases

and then

     ls -l

and you should see something like
     lambda: esp-r/databases% ls -l

-rw-r--r--   1 esru        96160 Feb 25  1998 constr.db1
-rw-r--r--   1 esru        96160 Feb 25  1998 constr.db2
-rw-r--r--   1 esru        17994 Feb 25  1998 mould.db1
-rw-r--r--   1 esru         5183 Feb 25  1998 multicon.db1
-rw-r--r--   1 esru         5357 Feb 25  1998 multicon.db2
-rw-r--r--   1 esru         8157 Feb 25  1998 optics.db1
etc

If this is not the case then the databases need to be re-installed.
Linux binary files (e.g. constr.db1, constr.db2 and plantc.db1) are not identical to Sun or Silicon Graphics binaries. These databases are created from text versions included in the source distribution.  The `database maintenance' option in the opening menu of the Project Manager provides the necessary facilities.

Question:

I created an ESP-r model on Solaris Intel. It works fine. I then copied the files to another server which uses the previous version of ESP-r. The first problem was that the materials db in binary form was not recognized. I fixed this by exporting the db to ascii on my computer and importing that file on the remote server. Now I am getting an error with ISH:


Jan calculation commenced
Almost Complete
Surfaces don`t match: nsur<>nsurs
Geometry used in the SHADING/INSOLATION db
DOES NOT Correspond to the geometry file you
have specified. Try another database.
Warning: Error condition detected...
ceasing calculations.

Answer:

The shading databases are binary and therefore different on different machines. They need to be remade.

You should delete all the existing shading databases and remake them as usual. An easy way to update the shading files is to alter the site longitude by 0.1 degree in the project manager; this will force all the shading files to be removed and recalculated.

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Surface and zone dimensions

Question:

In defining the geometry of a zone do I use internal or external dimensions?

Answer:

One option is to relate dimensions to internal faces which preserves the bounded zone volume.

On the other hand, by using internal dimensions all transmission losses through edge effects are left out of consideration; ie:

            _____________________
                                 |
            ---------------------|___
                                 |   |
                                 |   |

and how about thermal exchanges on the outside ?

Using construction "heart-line" (centre) dimensions (you may draw the schematic yourself :-) seems like a better approach. The wall areas used for calculating transmission losses are then closer to reality, and there is only a relatively small error involved in evaluating ventilation rates (which are usually very error prone to begin with !).

A draw back is that for intra-zone longwave radiation exchange we would like to use the inside surface areas, although it is easy to see that in case of a cube it is in this context of no consequence whether you use construction inside or centre-line dimensions (or is it ?).


Question:

When defining zone dimensions and positions how do I treat the "real" thickness of partitions to adjacent zones?

Answer:

Internal dimensions of a room CAN be treated as independent of a room's physical location in space. In other words, a room 3.2m x 4.4m x 2.1m has the same volume and orientation whether its coordinates are represented exactly as positioned on the site, or for example, shifted 100mm to one side to coincide with an adjacent wall face. In either case ESP-r will take into account the thickness of all walls when it solves the heat flow. The `connections/topology` is used to link two surfaces thermally. The position of the two surfaces is allowed to be somewhat flexible.

Times when exact positions are useful is where solar shading is critical or where is some distance between a ceiling and the floor above. If ceiling to floor above is 1m then making a perfect match between the upper and lower zone will change the height for shading analysis. If this distance is 100mm then perhaps the difference will not matter.

If you are unsure about the model, I suggest you put the files (including the databases and climate data) on a disk and send them to us for comment. If you have email then this will be much better.


Question:

I am studying the simple, 3-zone exemplar. The partition between the office and roof space is defined twice, once for the office (ceiling) and once for the roof space (ceiling_rev). Does this not count the R-value twice, effectively doubling the insulation value of the partition between the two zones?

Answer:

ESP-r has a convention that each surface in a zone has an 'inside' face that takes its boundary conditions from the zone it is within and one defined boundary condition on its `other side` face. In the case of partitions, you specify a link to a particular surface in another zone. Checks are made that each of the surfaces is similar in area and composition and are complementary in orientation.

Following this convention, the two surfaces in the adjacent zones are cross-referenced. During the simulation, the state-variables within the finite volumes of the two surfaces are solved with reference to the boundary conditions at each of their faces. The apparent redundancy in the descriptive process is taken into account in the solution process.

It is also worth noting that the wall partitions in the exemplar are symmetrical and both surfaces make reference to the same construction. However, the ceiling composition is not symmetrical (the insulation layer is at the 'inside' face for the roof space and is at the 'other side' face from the point of view of the office) and the construction referenced in the roof space has an inverse ordering of layers to the construction referenced in the office

Question:

The geometric input for a solar obstruction contains the "zone bounds" min and max fields. What are the "zone bounds" and how does one typically define them?

Answer:

Zone bounds reported in the zone obstructions editing facility are derived from the current zone coordinates. You cannot edit/define them.

Such information is sometimes useful in creating obstruction blocks (the extents of the obstruction block is also reported) in case you need to check distances between the obstruction and the zone.

Question:

Azimuth orientation of surfaces: does this apply to the inside or outside surface, and is there a way of changing the orientation without rotating the actual zone, as mine do not seem to have lined up correctly. If my zone is bounded by glass on the north and south sides what azimuth should they each have to ensure they receive solar radiation?

Answer:

In ESP-r a north facing surface will have an azimuth or either 0deg or 360deg. One facing east is 90 deg and south is 180 degrees. The ordering of the vertices in the surface polygon tells ESP-r which side is the outside face.

The rule is: all surfaces should be defined anticlockwise looking from the outside. Therefore, if you can see the outside face in the wire-frame, then order the vertices anti-clockwise (preferably from the lower left hand corner). If what you see in the wire frame is the inside face of the surface then use a clockwise ordering.

If you omit some surfaces from the zone or have the vertex ordering incorrect then the menu will include the phrase "xx problem edges" where xx is the number of edges which it objects to. If you see this then you can use the "check vertices" option and it will highlight the edges.

If you know that a particular surface should be facing south and the wire frame view confirms this but the "surface details" reports zero azimuth then the vertex ordering is incorrect. You can correct this by selecting the "miscel transforms" option and then selecting "invert".

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Furniture and clutter

Question:

How is furniture taken into account in radiation exchanges and energy storage?

Answer:

Furniture is often modelled as two surfaces back-to-back inside the zone (not geometrically attached to other bounding surfaces). The combined surface area should match that of the actual furniture; composition is usually of a material half the actual thickness (to account for the mass); use an adiabatic connection between the surfaces. Often several items can be lumped together to reduce geometric complexity.

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Entity names

Question:

Names - of surfaces, zones, materials and the like - are these important?

Answer:

Names clarify the nature of a simulation problem and the reporting associated with it. ESP-r will provide a default string. However, surf-14 carries much less information than south_wall. IT REALLY IS WORTH NAMING ENTITIES in your problem. Look at the exemplar problems to see how naming conventions can be used.

Question:

Names - what rules apply to them.

Answer:

In almost all cases you can use any combination of numbers and characters (but no Unix wild card characters or white spaces). Each string has a maximum length (indicated by the width of the editing box). The editing facilities will take inappropriate characters "/*@!$~?<>{}[]%" and will usually substitute a '_'. Overly long names are truncated. There are a few places where such checks have yet to be put in place [so if you notice one let us know].

Question:

Why can't I name a multilayer construction named "Ext Wall 12"? Do capitals and lower case make any difference?

Answer:

ESP is expecting a single word and would stop after "Ext". Imagine if there was also an "Ext Wall 13" - so use something like Ext_Wall_12.

If you get warnings at the beginning of a simulation of "unmatched surfaces" then it might be due to spaces in such names (when everything else looks correct).

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Replicating and moving zones

Question:

Sometimes it would be useful to be able to "copy" a zone.

Answer:

It took 10 years to get a delete zone function... Currently we copy zones by using the operating system in conjunction with ESP-r as in the following steps:

After reading it in change the zone "name" and use the translation/rotation facility to move it. Remember to update the topology.

Question:

How do I move a zone without editing all the vertices - I have several identical offices and would like to copy and shift.

Answer:

There is a translate and rotate function in the zone geometry menu which will allow you to move a zone. Use the Unix command line to copy the zone and the read the copy in and then re-name and translate and/or rotate it.

Question:

I want to change the height of a zone without having to edit the "Z" values of half a dozen vertices.

Answer:

It is possible to select a surface and transform it (and all the vertices attached to it) along its normal axis. A positive distance moves it outwards, a negative distance will move it in.

Question:

After rotating a zone I have to pull out a calculator and muck around with trig functions to figure out where to move the obstruction blocks. Also when I try to edit the rotated zone it gets a bit painful - any tips?

Answer:

It is now possible to rotate obstruction blocks around a point just like thermal zones. To save the hassle of editing a rotated zone it is sometimes easier to unrotate the zone back to a cardinal direction and then edit it. When complete you can re-apply the rotation.

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Fictitious surfaces and zone subdivision

Question:

I want to subdivide a space with something which is fictitious. How do I do this?

Answer:

A thermal zone, as defined in ESP-r, assumes that the air in that zone is perfectly mixed. Occasionally it is necessary to divide a large space into several thermal zones. A typical example of this is an atrium or other high space with an air temperature gradient such that the perfectly mixed zone approach is not applicable.

It is relatively straightforward to create `imaginary' separation wall(s). Those who have a recent release of the program will find a matched set of material, multi-layer and optical properties for this in the constr.db2, multicon.db2 and optics.db2 databases.

Here is a multi-layer construction database entry:

# layers  description   optics

     1    fict          TRAN  SC_fictit

# db ref  thick   db name & air gap R

   245     0.005  fict

Here is a typical entry in the optics database:

SC_fictit     :Fictitious 99/99,      4mm, no blind

# def lyr, tmc lyr, vis trn, sol refl, sol absor, U val

 1,  1, 0.99,  0.01, 0.01, 9.0

 0.998, 0.987, 0.986, 0.985, 0.984, 0.98, 0.97, 0.96, 0.95, 0.94

 1.52, 0.001, 0.001, 0.001, 0.001, 0.001

And lastly, the materials database:

(conduc., density, specific heat, emiss, absorb, diffusion resistance)

 245   fict

      20.000,   10.000,   10.000,  0.830,  0.010,  19200.000

These database entries describe a material which is substantially transparent and which has a minor impact on thermal transmission.

The process is to first define the material and optical properties in the appropriate databases, and then link them via an entry in the multilayer construction database. The flow across the opening as represented by this fictitious construction can be described by either scheduled air flows or by setting up a network flow (often a door component is a good choice to allow bi-directional flow).

Setting convection coefficients to a small value for these surfaces in the convection coefficient files is also recommended.

As always, look closely at the results (in terms of temperatures and flux) to ensure the model is behaving as expected.

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Model QA

Question:

Could someone remind me how to update the connections file to match my geometry attribution

Answer:

In the project manager under "Problem Definition" -> "composition" -> "connections & anchors" is "topology tool (define/update/check)". It offers a number of facilities to scan through a model and establish which surfaces are adjacent to other surfaces. If it does not find a match it presents a list of other options (exterior, similar, ground, adiabatic etc.). It scans the whole model and, compared with surface-by-surface attribution of connections within the project manager, it requires much less time and it is comprehensive.

Experienced users make frequent use of the topology tool:

  1. to review their models (it highlights each surface in turn);

  2. re-confirm contiguity after multiple surface add/deletes;

  3. to finish linking in new zones to existing models or after zones have been replicated.

 

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Ideal and detailed control

Question:

'Control function' editing menu is not very clear. You cannot see the meaning of the miscellaneous data (parameters you input) without going through the input procedure again.

Answer:

Control has long been one of the more difficult portions of the interface - the facility is complex. A recent revision of the interface may help. However, because some controls use upwards of 15 parameters we have found it difficult to list all such parameters with sufficient documentation in the on-line help. Documentation is included the data model available in the manual section of the ESP-r distribution.

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Climate and site issues

Question:

The longitude of Kuwait city is 48 degrees. The time zone is +3 (i.e 45 deg). This means that the longitude difference is 3 deg (48-45). My problem is that I don't know if this should be +3 deg or -3 deg. In Joe's book, the longitude difference for countries to the east of the reference meridian is -ve. What is confusing is that if I enter -3 deg in 'clm' it is indicated as 3W (W for west I presume). Can you shed some light on this?

Answer:

The convention in ESP-r is: Longitude difference to the east of the reference meridian is +ve. Longitude difference to the west of the reference meridian is -ve.

However, it doesn't really matter what you put in the climate file, as this is not used directly in a simulation. The important one is the longitude difference that is set in the configuration file.

Question:

I want to run a simulation for the period Wed 9 Jan 1991 to Tue 15 Jan 1991. The simulator says that the first day of the simulation is a Monday. Am I missing something to define which days are weekdays? The file test1.ctl clearly indicates that the period is Tue 1 Jan 1991 to Tue 31 Dec 1991.

Answer:

The "problem" is not with the simulator. The year is defined in the climate file and presumably you have used 1967 (clm67 as supplied) for which the 9th January is a Monday. Either use another climate file or change the year in the one you are using.

Question:

I am converting ascii files to binary format using clm. If I change the delimiter to single space or tab, clm fails on the RH value.


Example of input file, tab delimited:
* day 1
0 -98 0 14 210 68.4983
0 -64 0 31 10 69.1675
0 -41 0 22 190 70.8395
0 -31 0 31 210 73.5296
0 -31 0 0 0 76.1165

Answer:

ESP-r climate data in its ascii format is held as an initial header followed by column data. The latter are in integer format, some of which are converted as they are read in. For instance the 2nd column (in the example below) is external dry bulb temperature in tenths degC so 49 is understood to be 4.9C.

However, column 1 and column 3 are W/m^2 of solar radiation and column 6 is RH(%) and the resolution is to the nearest Watt or %. In the example in the question, the final column had real numbers and the code expects an integer. The separator is assumed to be spaces.

Example climate file (this can be obtained by exporting a binary file to ascii in the clm module):


*CLIMATE
# ascii climate file from kew64 binary db,
# defined in: kew64.asc
# col 1: Diffuse solar on the horizontal (W/m**2)
# col 2: External dry bulb temperature (Tenths DEG.C)
# col 3: Direct normal solar intensity (W/m**2)
# col 4: Prevailing wind speed (Tenths m/s)
# col 5: Wind direction (clockwise deg from north)
# col 6: Relative humidity (Percent)
kew # site name
1964 51.50 0.30 0 # year, latitude, long diff, rad flag
1 365 # period (julian days)
* day 1 month 1
0 49 0 30 230 81
0 48 0 25 230 81
0 47 0 30 230 82
0 43 0 25 230 82
etc

Question:

How do I import an ascii text ESP-r climate file that someone sent me and make a binary ESP-r climate file?

Answer:
  1. Change to the folder where the ascii file is.

  2. Decide on what the name of the binary file you want to create. For this example, assume the file name is bolzano. Make sure that no file by that name already exists in the folder.

  3. Start the climate module with the following command:


    clm -file bolzano

  4. The editing box will show the name bolzano and you click ok. The text feedback will say opened new climate file.

  5. Select option "import data from ASCII file".

  6. The dialog will say "import data inclusive of 1 jan to 31 dec" and you click on 'yes'.

  7. The edit box now asks for the ascii climate file and you type in the name of your ascii file and then click on ok.

  8. The edit box will now say "update site info as well" and you click 'yes'.

  9. The edit box will ask if the file has day demarcation lines and you say 'yes'.

  10. The next thing you will see is the menu. To test the import of data, select graphical analysis and then select January. Then select db temperature and draw a graph to display the data.

  11. Exit from the clm module. You will now have a binary climate file which you can associate with your model.

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Schedules (operations)

Question:

I have some questions about the zone operation file which involve setting ranges in ventilation and infiltration and which isn't clear from the manual.

In this case upper and lower airflow and infiltration limits follow the upper and lower control values. (The control values can be temperature or windspeed depending on the control Index). Do these flow rates override the "default" rates specified later in the file?

According to the manual, when the temperature is between the upper and lower limits the airflow is considered "ON". Does this mean that it is determined by linear interpolation between the upper and lower limits?

The manual states that outside the upper and lower temperature limits "the appropriate substitute air flow information is assumed as supplied by the user." What is "appropriate?" Is this the default air flow defined later in the file?

Answer:

In the operation file, infiltration and ventilation controls are geared to the limited schemes that a user might be interested in early in the design/appraisal process.

In terms of air flow control the standard flow patterns apply unless you go above the upper set point or below the lower set point at which time the relevant (upper/lower) alternative set of flows will be used.

With windspeed or temperatures as an index the alternative rate is applied - there is no linear interpolation.

If you wish to have more complex flow regimes then the normal process is to specify a mass flow network and allow the system to derive the appropriate flows.

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Windows and other TMC's

Question:

I've defined double-glazed windows as Transparent Multilayer Constructions with blind control and shadings. How can I view the loads resulting from solar radiation on the zone balance results? The "air point solar" is always zero, since I have no "Windows" in the way ESP-r calls them.

Answer:

Modelling windows as Transparent Multilayer Constructions means that they are treated just as any other construction, except that solar radiation is absorbed at internal nodes within the construction. Thus there is no direct link between the solar radiation and the air-point - the link is through convection (and this will show up in the zone air-point energy balance).

If you look at a surface energy balance (use save option 4 when simulating) you will see the contribution of solar at any surface (in addition to conduction, longwave radiation etc).

If you want to get a separate breakdown of all the solar distribution, you will need to use the trace option when simulating. This will give a complete breakdown of all the solar radiation entering a zone - how much is absorbed at each surface, how much is transmitted to adjacent zones or lost to the outside and how much is absorbed within the glazing. Some of this information is now available through the results analysis module. (See also Solar and shading.)

Question:

Previous versions of ESP-r differentiated between default windows and transparent multilayer constructions. What was the difference?

Answer:

There were two ways of modelling windows in ESP-r. (The so-called 'default window' is not supported anymore.)


Which one you select will depend on the information available:

  1. Default windows - windows in this model are treated as a resistance element only. In this case, the user must define (in the optical database) the direct transmission and the total transmission. The total transmission is sometimes referred to as the solar heat gain - it is the direct transmission plus the heat absorbed in the window and subsequently transferred to the internal air by convection. These values must be input at 5 angles of incidence (0,40,55,70, and 80 degrees) - ESP-r interpolates for other angles; or

  2. at a higher level of resolution, as a transparent multilayer construction (TMC). In this case each layer of the glazing system is explicitly modelled, with conduction, convection and radiation occurring. For TMC's, the user must specify the direct transmission (as in (1) above) and the absorption in each layer of the glazing system, again for the 5 angles of incidence.

Question:

How do you model low-emissivity coatings or gas fills other than air?

Answer:

Advanced glazings can be modelled in two ways:

  1. Detailed treatment: model the air gap as a zone - then the radiative and convective exchanges can be explicitly modelled.

  2. Simplified treatment: in any air gap within a construction (transparent or opaque) ESP-r uses a fixed resistance (user-defined). For normal double glazing this is usually 0.17 m2K/W, but other values can be found (for example in a CEN standard) for different air gap widths, different gases and different low-emissivity coatings. Alternatively, the appropriate value can be calculated manually by taking the manufacturer's stated U-value at standard conditions and finding the resistance of the air/gas gap. ESP-r will then use this fixed value for the air/gas gap within the glazing/construction (but note it adjusts the external surface resistances as usual to cope with the non-standard conditions at each timestep, so it does not use a fixed U-value).

In tests with low-e glazing, approximately the same results were obtained with detailed and simplified approaches.

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Optical properties

Question:

Do the names of optical components in the optical db always have to start with a S or D?

Answer:

ESP-r interprets a beginning S as single glazing and a D for double/others (to limit the length of the list you choose from).

Question:

Are default windows properties found in any of the databases?

Answer:

The optical properties database holds data for transmission and heat gains associated with default windows, otherwise there are no databases which are associated. Note that solar heat gain properties in the optical database are now redundant as the default window option is no longer supported. See: Windows and other transparent multilayer constructions

Question:

How do I import optical data from LBL's program Window4?

Answer:

ESP-r can import data from the LBL dos program windows4.1 into the optical database. Here is a step by step guide:

  1. Start up W4.exe on your PC. Use the Function 5 key to enter the glazing system library.

  2. If you have existing glazing systems select one of them, and to ensure that angular properties have been calculated use the Function 9 key. If the angular properties have not been calculated press "A" to turn on angular calculations. This should fill up the table. Type "escape" to return to the main W4 window. For safety type "alt S" to save the current description. Then type "alt P" to print the data for the currently highlighted glazing system. You will be asked if it is Library or Detail, select Detail and then give it a file name (usually with a file name related to the name of the glazing system). It may take a few moments for it to complete the calculations before it finishes writing the file.

  3. If you want to create a new glazing system type "A" for Add and then either "N" for New or "C" for Copy. It is a good idea to have scanned the "Glass Lib" via Function key 3 prior to creating a new glazing system to confirm the code number of the glass that you want to use. Double check that the thickness of the layers is correct. In Window4.1 (as in ESP-r) layer 1 is at the outside face and subsequent layers are towards the room. Once the layers have been defined press the "space" key to force initial calculations. "Escape" back to the main menu, and the type Function 9 to calculate angular properties. Once this is done "escape" back to the main menu and use "alt S" to save and "alt P" to print (as described above).

  4. Use notepad (or any text editor) to edit the reports that you printed out. Window4.1 places a null character in the file before the word "Temperature Distribution", remove that character and save the file.

  5. The text reports you printed to file need to be transferred to the Unix/Linux environment where ESP-r is run. To be read properly on a Unix machine use dos2unix, example: dos2unix single3mm.txt single3mm.w41 where single3mm.w41 is the file which you will be importing within the project manager.

  6. Start the project manager and enter database management, select the optical database. Use the * import/add/delete/copy element selection and enter the name of the file you want to import. If the import works you should see a graphic of the optics and the word "Please edit the imported item providing an 'id' string and description". Change the 'id' string and decription, check that it has interpreted the number of layers correctly and that the data is correct.
    Note: the U-value and solar absoption fields are for documentation purposes and are not used by ESP-r. If the number of layers is incorrect or there are read errors it is likely that you forgot to convert the dos file format.

  7. If you have generated a series of *.w41 files you may continue to import files while within the optics database facility.

  8. You may wish to archive the *w41 files because they include useful information on the glazing systems which might be of interest (especially if you lose or corrupt the W4 database).

Question:

How do I represent an encapsulated blind (the blind is between the inner and outer glass)?

Answer:

You can represent the blind explicitly as a layer of metal (steel/aluminium with appropriate surface properties) in the air gap. Thus a three layer MLC (glass-air-glass) becomes (glass-air-metal-air-glass). You must match this to a set of optical properties.

Some tmc and optical sets are shown below as examples of blinds between glass which are open, closed and translucent:


DCF7671_6omb :Clear float 76/71, 6mm open mid blnd
# def lyr, tmc lyr, vis trn, sol refl, sol absor, U val
1, 5, 0.76, 0.11, 0.28, 2.8
# direct trn @ 5 angles, total heat gain @ 5 angles
0.611, 0.583, 0.534, 0.384, 0.170, 0.711, 0.690, 0.645, 0.487, 0.250
# refr index, absorption @ 5 angles for each tmc layer
1.52, 0.157, 0.172, 0.185, 0.201, 0.202
1.00, 0.001, 0.002, 0.003, 0.004, 0.005
1.00, 0.172, 0.181, 0.178, 0.151, 0.097
1.00, 0.001, 0.002, 0.003, 0.004, 0.005
1.52, 0.117, 0.124, 0.127, 0.112, 0.077

DCF7671_06mb :Clear float 76/71, 6mm, mid blnd
# def lyr, tmc lyr, vis trn, sol refl, sol absor, U val
1, 5, 0.09, 0.39, 0.38, 2.4
# direct trn @ 5 angles, total heat gain @ 5 angles
0.071, 0.070, 0.073, 0.070, 0.038, 0.233, 0.232, 0.232, 0.218, 0.147
# refr index, absorption @ 5 angles for each tmc layer
1.52, 0.216, 0.234, 0.242, 0.238, 0.209
1.00, 0.001, 0.002, 0.003, 0.004, 0.005
1.00, 0.316, 0.309, 0.395, 0.261, 0.181
1.00, 0.001, 0.002, 0.003, 0.004, 0.005
1.52, 0.014, 0.016, 0.018, 0.022, 0.019

DCF7671_06tb :Clear float 76/71, 6mm, trnsul blnd
# def lyr, tmc lyr, vis trn, sol refl, sol absor, U val
1, 5, 0.12, 0.39, 0.20, 2.4
# direct trn @ 5 angles, total heat gain @ 5 angles
0.128, 0.125, 0.125, 0.115, 0.062, 0.351, 0.346, 0.334, 0.277, 0.156
# refr index, absorption @ 5 angles for each tmc layer
1.52, 0.201, 0.216, 0.226, 0.232, 0.218
1.00, 0.001, 0.002, 0.003, 0.004, 0.005
1.52, 0.172, 0.181, 0.178, 0.151, 0.097
1.00, 0.001, 0.002, 0.003, 0.004, 0.005
1.00, 0.192, 0.183, 0.164, 0.116, 0.052

The optical properties tell the system where to distribute the incoming radiation. Note that a translucent blind has more transmission for the layer associated with the blind. Such optical properties come from Window4.1 or WIS and are imported or edited into the optical db.

The construction entries in the corresponding database would be similar to:


5 dg_45_std_b TRAN DCF7671_06mb
# db ref thick db name & air gap R
243 0.0060 4mm clear float
0 0.0080 air 0.240 0.240 0.240
44 0.0010 White_Steel
0 0.0080 air 0.240 0.240 0.240
243 0.0060 4mm clear float
# layers description optics
5 dg_45_daylt TRAN DCF7671_06mb
# db ref thick db name & air gap R
243 0.0060 4mm clear float
0 0.0080 air 0.240 0.240 0.240
47 0.0020 Alum_reflector
0 0.0080 air 0.240 0.240 0.240
243 0.0060 4mm clear float

The White_Steel and Alum_reflector are materials created in the materials database to represent the blind material.

Question:

How do I model electrochromic glazing?

Answer:

You can change the optical properties of glazing according to time, temperature, solar radiation level or lux level. You can have different control at different times of the day, but at the moment you can only change between 2 states at any particular time (it would not be difficult to extend the code to allow more than 2 states, or perhaps a proportional control between 2 different states, but this would require some additional coding).

To use it, you need to make at least 2 entries in the database: one of the standard optical properties, and one of the "replacement" properties. Make the model in the usual way with the standard optical properties. Then select constructions, choose "transparent layer properties" and answer the questions regarding the number of control periods, the type of control required etc. You will be asked to select which set of replacement properties from the optical database will be used if, for example, the specified lux level is exceeded. These replacement properties could be different from one control period to the next, if required.

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Daylighting assessments

Question:

I want to do a study of the contribution of natural lighting to energy savings - is this possible in ESP-r?

Answer:

Yes, such goals are possible and the facilities for it are described in the users manual under "casual gain control".

Question:

Please explain the definition of a DF (as used in ESP-r), allocated to a certain transparent component.

Answer:

The daylight factor (DF) is defined for the CIE overcast sky only and is as you say the ratio of internal illuminance to external illuminance.

In ESP-r the definition of the sensed illuminance (for historical reasons) requires that the daylight factor for each glazed surface treated in isolation be defined. However when this data is used in the simulation the total illuminance is calculated and used, hence as long as the daylight factors you give add up to the daylight factor at the sensor the file is OK. e.g. if the DF at the sensor is 3.5% and you have 3 glazed surfaces then 1, 1, 1.5 is a valid set of daylight factors and so is 3.5, 0, 0.

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Solar and shading

Question:

Insolation (solar radiation entering a zone) is treated in several ways as mentioned in default insolation scheme and there is also an "ish" module. In all cases is direct radiation distributed uniformly over the entire surface or distributed uniformly over the sunlit patch?

Answer:

The solar radiation that is absorbed by a surface is assumed to be spread evenly over that surface. Subdividing surfaces will allow a finer resolution. The default insolation scheme defaults to an assumption that insolation is distributed on an area/absorptivity weighting basis. You can specify a fixed distribution if you believe such to be appropriate. We recommend that you go beyond the default schemes and have ESP-r provide you with a temporal distribution of shading and insolation via the "ish" module. It takes only a few moments and can increase the accuracy of most simulations.

Question:

If ESP-r calculates accurately the point of injection of the solar beam impinging on internal surfaces, does it calculate the view factor or exchange factor between the sunlit patches and other room surfaces?

Answer:

With regard to short wave radiation, any solar reflected at an internal surface is treated diffusely and distributed on an area/ absorptivity basis (through an iterative solution) throughout the zone. A topic for future research is to improve the solar processor so that it deals with both specular and diffuse reflection.

Question:

I've defined a lot of obstructions for some windows. When making the "Shading & Insolation" analysis, I receive a message that some of them are being ignored. This message is repeated for several zones. Do you have any idea why this may be happening ?

Answer:

During a shading analysis you may get warnings that an obstruction block is "crossing the plane of a surface" and is being ignored. What is happening is that plane of the surface (if extended) passes through the named obstruction block. You need to subdivide the obstruction block to avoid this situation. It may also be that the obstructions are too close to the surface. Keep them at least 10mm away. These relationships are also shown graphically. The image shows the addition of obstructions to represent an overhang which conforms to the "not crossing the surface rule".  Of interest to those doing shading or daylighting analysis is a facility to automatically extrude window reveals.  For walls of greater than 100mm thickness, the reduction in solar insolation can be non-trivial and modelling the reveals may be necessary.

Question:

Is the shading of a thermal zone by another thermal zone automatically taken into account?

Answer:

ESP-r does not, currently, do mutual shading between zones unless you include further details within the model. If zone "X" is likely to shade zone "Y" then that part of zone "X" that will cause shading should be represented as an obstruction block associated with zone "Y".

Question:

I am modelling an atrium and I have created 4 stacked zones to represent stratification. Large delays in solar radiation appear for the base zone.

Answer:

Due to the way solar radiation is transferred from one thermal zone to another, you should define the top zone as zone 1, the zone beneath as zone 2, etc. Then no appreciable delay should be encountered. Alternatively, use shorter timesteps.

Question:

How do I get information about where the solar radiation goes in a room?

Answer:

If you run a simulation at save level 4 you can access the energy balance at each surface; one of the items is "solar absorbed", which is incident radiation multiplied by the surface solar absorptance in the case of opaque surfaces. The information can be obtained for any particular instant or integrated over time. Simply divide the solar absorbed by the surface absorptance to find out the incident solar radiation.

There is also a "solar processes" menu in the graphing facilities and in the timestep reports facilities. In this are solar entering from outside (i.e. what gets past the glazing), what enters from adjacent spaces (i.e. what gets past the partition glazing) and what is absorbed.

Lastly, turning on the trace option in the simulator and selecting the solar information gives a file containing details of the solar radiation distribution, including absorptances at each node in transparent multi-layer constructions.

Question:

Is it possible to model active solar collectors?

Answer:

The ESP-r system is designed to allow simultaneous detailed modelling of building and plant systems which may include fluid flow networks. It is therefore possible to model most solar air systems at various levels of detail. Because the performance of solar systems is sensitive to control and flow assumptions the user should be knowledgable about the systems being modelled.

All aspects of the building energy system are modelled simultaneously and dynamically. Each heat and mass transfer subsystem is modelled with its own state-of-the-art algorithm.

Most solar collectors are straightforward to model in ESP-r. They can be modelled either as one or more thermal zones or plant components. The simulation timestep can be adjusted between a fraction of a minute to an hour as required. For thermal zone, transient insolation patterns within the collector can be tracked.

Building mass is handled as a matter of course in all simulations. Rockbed, hypocausts and phase change materials can be modelled as plant components.

All temperatures (including intra-constructional temperatures) and heat fluxes, are provided in tabular (timestep by timestep or integrated) or graphical form.

If collectors are modelled as thermal zones, they would normally be represented by multiple zones, giving greater accuracy. Alternatively a single-node air heater plant component can be used.

System specifics:

Closed collector loop with open discharge loop. This system can easily be modelled without a plant network as both the solar-air collector and solid storage can be represented by a zone/air flow network.

Closed loop to heat exchanger.

A mass flow network coupled to a heat exchanger plant component with a zone model of the air heater will be needed to model this system. A plant/fluid flow network could model the coupled DHW system.

Double Envelope.

Again the best method of modelling this system would be with a building/mass flow model where the collector and envelope sections are explicitly represented as collections of zones. All flux and mass transfer paths are dynamically coupled and no specialised plant components are required. Both forced, non-forced and mixed circulation modes are possible.

Closed charging loop with radiant discharge.

This system can be modelled explicitly as in the above cases. In the case of phase change material (PCM), it may be possible to model this using current capabilities for modifying thermophysical properties according to the nodal temperatures. An alternative, more accurate, method would be to model the PCM as a plant component.

Open single loop.

This is the simplest model type and can be easily modelled by a zone/mass flow network model.

Closed loop charge, closed loop discharge.

With this model, again only a mass flow/zone model would be required. However, if the option of incorporating a heat exchanger for a DHW system is utilised then a plant network will be required with an air-water heat exchanger.

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Air flow

Question:

I am modelling a window cavity with 8 zones with air coming in at the bottom and leaving at the top at 8l/s. For some reason there is a huge time lag between solar radiation and temperature rises at the top of the cavity of the order of 6-8 hours where in fact the response should be in the order of minutes. This does not happen however when I use 1 zone for the cavity.

Answer:

Due to the way in which ESP-r processes the zones, make sure that your zone ordering places the first zone as the zone in which the air enters the cavity, the second zone as the adjacent zone and so on. Alternatively, shorter timesteps will reduce any delay.

Question:

Is a fan or an extractor (as part of the flow network) a component or a separate air node? If it is a component, can a component be defined without a connection with a second node?

Answer:

A fan is a component, and each component must be connected to two nodes. The following may help to clarify ESP-r's terminology and solution method.

A node represents a volume of air. For the purposes of defining a flow network the critical property of the air node is the pressure.

A component is any connecting device between any two volumes of air, or nodes.

When solving the network, the pressure difference between the nodes is calculated and the component's resistance to flow is used to calculate the mass flow between the two nodes.

The mass flow network must be fully defined i.e. if you have a fan connecting an external node with an internal node there must be another connection from the internal node to another node so as the mass can flow elsewhere, and so on throughout the network.

If ESP-r cannot solve the mass balance equations then you will be warned by the program. The most likely cause of the solution not converging is that the network is not properly defined.

It might be a good idea to experiment with the basic models in the exemplars with air flow networks. I suggest defining a fan and then changing one of the connections to use the fan instead of the current component. Then look at the results after running an integrated simulation. Are the results what you would have expected?

Question:

I have to refine my model of the mechanical ventilation. As the operation of ventilation changes between mechanical ventilation (with supply air and air extraction in different zones) and natural ventilation by opened windows (switched off mechanical ventilation), I assume I have to build a flow network model. During the training course I have once created a flow network, but only for natural ventilation. Thus please tell me, how to include a controlled mechanical ventilation into the air flow network (How to create an air supply node or an air extraction node? How to control the supply air temperature and/or the supply air volume rate ? How to swith on/off mechanical ventilation ?). Where can I find some helpful information?

Answer:

If the windows, openings etc are to be sized to allow a prescribed air change rate for the natural vent case then you can still use scheduled operations. However, if you want to know how the natural vent will perform then you will have to use a mass flow network. There are two basic exemplars which may be useful to look at. They are for the 3 zone model and both have a mass flow network. The difference is that one has control of the windows the other is uncontrolled.

The method you will need to use is to describe the mechanical vent and the natural vent in the mass flow network. The process in the latest version of ESP-r is semi-automatic: air nodes are assigned to thermal zones and a few other aspects of the mass flow model are derived from the thermal zones. You will need to describe the windows and doors and other components (eg fans).

To control the network, use the control of networks option from the main menu. Here you can control one or more connections or all connections using the same component.

Our preference for describing this type of system would be to describe half of the mass flow network first, say the mechanical system, and then describe the control of this system. I would then describe the rest of the system and the associated control.

At each stage I would run a simulation and check that the system is working as intended: define mechanical vent, run a test simulation, define control, run a test simulation... etc. The test simulation only needs to be for one day but allows easy checking of the model after each aspect has been defined.

There is more information in the web pages and in various ESRU publications.

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View factors

Question:

How are the surfaces numbered for the mrt sensor?

Answer:

The mean radiant temperature (mrt) mrt sensor has faces numbered the same way as a cuboid zone. So the first face faces south, 2=east, 3=north etc. If you rotate the sensor then the faces stay in the same relative position but obviously face a different direction.

The output fits into the following table (where x=a view factor):


Zone surface number
MRT sensor
face 1 2 3 4 5 6 ...
1 x x x x x x ...
2 x x x x x x ...
3 x x x x x x ...
4 x x x x x x ...
5 x x x x x x ...
6 x x x x x x ...

Make sure you toggle the sensor on before you start the calculation.

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Simulation

Question:

I would like to use a 'script' to automate a simulation task. Is there an example that would show what can be done?

Answer:

An example of using scripts to carry out a sequence of tasks can be found in the ESP-r distribution in the validation/QA/benchmark_model directory. The script TEST is a high level script which removes old results sets and then commission a sequence of simulations via the scripts SIMULATE.wc and SIMULATE.nc and then several data recovery tasks via the ANALYSE script.

Question:

While simulating a reference dwelling ESP-r gave the following announcement:

   MZELWE: a longwave flux of -530.6 Watts has been 
   calculated for external surface 1 of zone 9 
   at simulation increment 1188. This is considered to be 
   excessive and ESRUbps will use a correlation.
  sky = -336.9 buildings = -27.4 ground = -38.0

ESP-r gave this announcement several times, but each time with a different value for: the longwave flux, simulation increment and 
Are you familiar with this problem and is it possible to raise the maximum longwave flux value within the program?

Answer:

Messages like this occur at times in simulations and are the result of combinations of climatic conditions, orientation and thermophysical properties which lead to elevated levels of longwave radiant losses at external surfaces. Southern European climates and surfaces which face upwards have been associated with such warnings

The logic behind the method is that if longwave losses are greater than 450 W/m2 then the user should be warned and a lesser value substituted. Losses of this magnitude are primarily from the following causes:

We would not particularly wish to disable such warnings as they often give a clue as to a questionable model description. If over a multi-month simulation you get four or five such warnings it is not a cause for concern. If you get them hundreds of times then check your problem description or climate file. If it persists then perhaps consider passing the description on to ESRU for evaluation.

The sky temperature is calculated by the Berdahl and Martin algorithm (confirmed by the team at the University of Stuttgart as being most appropriate). If you turn on the trace facility when running the simulation, you can also display the sky temperature as calculated by a number of different algorithms.

At present, when the longwave flux is calculated to exceed 450W/m2, a warning is issued and a simple empirical correlation substituted for calculating the longwave flux to the surface (based on wind speed and the air-surface temperature difference). If you believe that the longwave flux can exceed this amount, then you can do a very simple edit of code and recompile the subroutine (routine MZELWE in subsys.F in esrubld). You should be able to trace the statement quite easily (search for 450).

Question:

I receive the following message when I run the simulator bps.


Zone save option : 2 (Moderate)
No. of warnings : 10

How can I find out what those warnings are?

Answer:

In the simulator opening menu there is a option "Warnings >> OFF/ON" If, after you read in a model, you change this toggle and the toggle "Reporting >> silent" to "Reporting >> detailed" and then re-read in the model you will get a report on the warnings.

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Results analysis

Question:

Is there a possibility to get the resultant temperature at certain locations within a zone ? What I require is the local operative temperature, defined as the average between the zone's dry bulb temperature and the LOCAL radiative temperature (measured by a sensor); thus I would like to get a local operative temperature, averaged of air temperature and MRT sensor's temperature. Does there exist a possibility to get such temperatures?

Answer:

ESP-r reports three zone temperatures:

  1. dry bulb temperature.

  2. MRT (mean radiant temperature) which is the area weighted average radiant temperature. If you have defined a mean radiant temperature sensor then you can report the MRT at the sensor's location (i.e. the view factors to the zone surfaces from the sensor are used).

  3. Resultant temperature. This is the average between the dry bulb temperature and the area weighted mean radiant temperature.

Question:

How do I export data from the results analysis module for use in an Excel spreadsheet?

Answer:

You can export data in the results analysis program. Look for command menus which include an entry in the form of:


feedback >> display

which toggles to


feedback >> file

If you select this entry you will be asked for a file name and then you select the data you want to export. There will also be a command menu toggle which changes the delimiter between the data items. For Excel you will probably want to use commas. In the case of timestep data you will also want to reset the format of the timestamp from hhmm to fraction of Julian day.

Lastly, choose !list and after the data is extracted you re-select the "feedback" toggle to close the export file. Before transferring the export file to a PC you should use the Unix command unix2dos (see the man page for more info on that).

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Odds and ends

Question:

I want to include a swimming pool in my model. How do I account for evaporative heat transfer and monitor the likelihood of condensation?

Answer:

For your initial assessment you can control the relative humidity in the swimming pool hall to the expected value. To do this use the ideal control law. In results analysis it is possible to look at the difference between dew point temperature and surface temperatures, or you can also list occurrences of surface condensation in the 'intra-fabric' section of graphical output.

To include evaporation in the model, you can select the special material option. Specify the internal surface of the construction (i.e. select the internal layer, and give the node number corresponding to the internal surface - number (2n+1) where n is the number of layers in the construction). Then select the evaporative surface option.

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