Download IDA Early Stage Building Optimization (ESBO)

IDA Early Stage Building Optimization (ESBO)
User guide
Version 1.09, Oct 2013
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Contents
What is IDA ESBO? .................................................................................................................................... 4
How do I use IDA ESBO? ........................................................................................................................... 4
IDA ESBO user interface ............................................................................................................................ 7
Rooms tab ............................................................................................................................................. 7
Building tab ......................................................................................................................................... 32
Start simulation tab............................................................................................................................. 65
Technical description of the default generated systems ........................................................................ 68
Purpose and ambition of the default generated systems .................................................................. 68
The default tank models ..................................................................................................................... 68
An example of a generated system .................................................................................................... 69
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What is IDA ESBO?
IDA ESBO is a simulation program for building design optimization. It allows you to experiment with
variations in a building design and to predict the consequences on energy consumption and comfort.
IDA ESBO comes in two variants: Template and General. The free Template version allows you to
experiment with everything except the building geometry. A number of template geometries are
available to choose from. In the General version, you can adapt the model to suit the geometry of a
particular project.
The ESBO application does not include the effect of heat transmission or air flow between rooms. For
projects where these effects are essential to the overall performance of the building, the full IDA ICE
application should be used instead.
In the next section, a general overview of usage is given. After this, help texts on key input screens are
presented roughly in the order they are used.
How do I use IDA ESBO?
If you are using the Template version, typical rooms and geometry have already been selected, but read
this anyway to get an overview of how the application works.
The first thing to do is to describe the typical rooms of a building. This is done on the Rooms tab. Typical
rooms are rooms that can be expected to have different indoor climate or service systems, e.g. if you
have a building with 100 similar south facing offices, you only need to model a single one of these
rooms. If you are only modeling a small building, you can describe all individual rooms of the building.
However, for a large project, it is always better to model only a selection of rooms such as, for example,
South facing single office room, North facing single office room, Open plan office, Conference room,
Corridor space etc.
Once the typical rooms have been described in terms of geometry on the Rooms tab, you enter the total
floor area of each room type in the table at the bottom of the Rooms tab until the whole building floor
space has been accounted for. Other significant total areas of the building are then automatically
computed. By adapting the typical rooms slightly, e.g. by changing window areas or adding external wall
area, you arrive at a model that matches the actual building in the key figures: total window area, total
external wall, roof and ground area. These key areas should fall within a few percent of your actual
building.
After this, the Template and General versions are identical.
Once the typical rooms of the building have been defined, you describe internal heat gains for each
typical room by selecting (and then possibly editing) usage patterns from a palette of common patterns.
Similarly, the indoor climate standard for each typical room is selected.
At this stage, you switch to the Building tab.
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In the Building tab, the first thing to do is to select the building location from the drop down list. Next,
you open the Defaults form, where typical constructions and window glazing are specified. Note that the
default settings will be used for any part of the building where nothing else has been selected in the
actual room. For the template buildings no other particular constructions or glazing have been selected,
so the default selections will apply.
Now, double click on the Ventilation system of the building. By default here, an air handling unit with a
return air heat exchanger, a heating and a cooling coil has been defined. If you are happy with this
setup, just select the heat exchanger efficiency, the pressure rise of the supply and return fans (or SFP),
and the supply air temperature setpoint. If you want a different type of system, drag it in from the
palette. Note that air flows in the rooms have already been selected in the Rooms tab. The default
central system will be able to supply any amount of tempered air. If you have selected exhaust only
ventilation in the typical rooms (or unbalanced supply and return), the makeup air will come from
increased infiltration.
Also in the Building tab, specify the domestic hot water consumption and the infiltration rate and then
we are ready for a first simulation.
The rooms of the building are initially equipped with idealized room units for heating and cooling, called
“Generic” units. These will heat and cool the rooms to maintain temperatures within requirements, but
are not connected to the water based central system that is described on the Building tab. The Generic
units provide heating and cooling to the rooms by directly converting some energy source (such as
electricity, fuel or district heating). The systems that are described on the Building tab will always supply
any hot or cold water needed by the air handling unit (AHU). When you start, a fixed efficiency boiler
and similar chiller are present in the Building tab for this purpose.
If you don’t want mechanical cooling, remove the cooling systems from your typical rooms as well as the
default chiller (that supplies the AHU cooling coil) from the Building tab. The cold storage tank is
mandatory and will not be used unless any water based cooling equipment is present in any room or in
the air handling unit. To remove the cooling coil from the air handling unit, just set its effectiveness to
zero. It is nearly always best to make rough calculations with idealized systems first to compute needed
sizes of other types of equipment.
To make a first set of simulations, switch to the Simulation tab. The first thing to do here is to simulate a
severe winter day (Heating design). This will compute a heating need in all rooms that will later on be
useful to select non-idealized room units and central systems.
Similarly, if you want to size a cooling system or check for summer overheating, run a summer day
simulation (Cooling design).
If you are in a truly early stage of the project and have not yet started to think about what particular
supply systems to use for the building, go ahead with a whole-year energy simulation. This will enable
you to optimize the building envelope first and then turn to a more sophisticated system description.
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Once you are ready to start experimenting with different real system components, first go back to the
Building tab. Here you specify the design temperatures of the hot and, optionally, cold water
distribution systems. The next stop is the Rooms tab, where you replace the ideal room units with other
options from the palette, such as radiators, fan coils or floor heating. In order to select a radiator or
similar device, you must both have access to the heating demand of the room and of the system design
temperatures. Note that the design power of most components, such as for example the radiator, are
given with respect to a “rating condition”. If the actual temperature conditions differ from these, the
emitted maximum power will not match the number that is given. Usually, the default rated conditions
are standardized and will match those found in commercial technical data sheets. If you want the
maximum power to match the given number, you can manually set the rated conditions to match the
water and air temperatures of your simulation.
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IDA ESBO user interface
Rooms tab
Figure 1
The rooms tab is active when a case is opened. Here the typical rooms of the building are specified.
Rooms can be either shoebox shaped, prismatic or have a locked arbitrary geometry that has been
imported. In the Template version all rooms have locked prismatic-shaped geometry.
Objects in the palette to the left on the screen can be used to replace the default objects in a room.
Some objects, such as windows and doors, are inserted directly into the 3D view by dragging them.
HVAC system objects and settings are dragged directly into the corresponding place in the form. Most of
the default objects can either be removed, e.g. remove the default generic cooler to study a room
without cooling, or replaced with other objects with different properties. The generic objects that are
described in this help text are always available. In addition to these, there may be objects that represent
products of given manufacturers. There may also be combination objects that fulfill more than a single
function, for example a four pipe fan coil that can both heat and cool the room.
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Rooms table
New room Add a new shoebox shaped room 4 x 2.5 x 2.6 m with default internal wall construction on all
surfaces. The geometry of the room is shown in the 3D view and the properties of the room are shown
in the fields above. In the Template version this button is unavailable.
Rename Change the name of the selected room.
Duplicate Add a copy of the selected room. In the Template version this button is unavailable.
Remove Remove the selected room. In the Template version this button is unavailable.
Rooms summary table All rooms of the building are shown in the table and key figures of the rooms are
displayed. The floor area and the room multiplier can be edited. When either one of these are changed,
the other figures of the room are updated. The building totals are shown at the bottom of the table. A
target row is displayed at the bottom of the table where the actual building key totals can be entered for
easy reference. When a room is selected in the table, its geometry and other properties of the room are
displayed.
Expand table The Rooms summary table is opened in a separate resizable window for easy viewing of a
larger number of typical rooms.
3D view
Help for 3D view Displays the following text as a tooltip when the mouse is pointed at the button, and in
a dialog when the button is clicked:
“Left mouse button: Click Select object. Selected object is shown in red.
Left mouse button: Press down and move mouse Rotate the model.
Middle mouse button (or both the left and the right mouse buttons on a two button mouse):
Press down and move the mouse Pan the model.
Right mouse button: Press down and move the mouse Zoom in/zoom out. Move the mouse
upwards to zoom in and downwards to zoom out.
The x+, x-, y+, y-, z+, z- buttons create a section through the room. When section is activated,
press Ctrl-key, click within the red frame and move the mouse pointer, to move the section.
A window, door or surface part can be dragged to a new position. When the window, door or
surface part object is selected, press Ctrl-key, click on the object and move the mouse pointer,
to move the object. ”
Restore default view Zoom and pan the model so that the entire model is visible and undo any cut of
the model.
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x+ Cut the 3D model along the x-axis removing all geometry on the positive side of the cut plane.
x- Cut the 3D model along the x-axis removing all geometry on the negative side of the cut plane.
y+ Cut the 3D model along the y-axis removing all geometry on the positive side of the cut plane.
y- Cut the 3D model along the y-axis removing all geometry on the negative side of the cut plane.
z+ Cut the 3D model along the z-axis removing all geometry on the positive side of the cut plane.
z- Cut the 3D model along the z-axis removing all geometry on the negative side of the cut plane.
Mouse operations
Left mouse button: Click Select object. Selected object is shown in red.
Left mouse button: Hold down and move mouse Rotate the model. The model is always oriented so
that the positive z-axis is up.
Left mouse button: At cut, press Ctrl-key, click within red frame, hold down and move mouse Move
the cut plane.
Left mouse button: Press Ctrl-key, click within selected window or surface part and move mouse Move
window/surface part.
Middle mouse button (or both the left and the right mouse buttons on a two button mouse): Hold down
and move the mouse Move the model up, down, right or left.
Right mouse button: Click Open right mouse button menu.
Right mouse button: Hold down and move the mouse Zoom in/zoom out. Move the mouse upwards to
zoom in and downwards to zoom out.
Right mouse button menu: Set focus Set the point around which the model is rotated and towards
which it is zoomed.
Right mouse button menu: Zoom extents Zoom and pan the model so that the entire model is visible.
Geometry
Length Length of room, inside measurement [m]. Editable for shoebox shaped rooms.
Width Width of room, inside measurement [m]. Editable for shoebox shaped rooms.
Height Height of room, inside measurement [m]. Editable for shoebox shaped and prismatic rooms.
Edit Open 2D editor to edit shape of prismatic room. Unavailable for of rooms with locked geometry.
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Import Import arbitrary polygon based geometry. The imported geometry will be locked and uneditable.
In the Template version this button is unavailable.
Orientation Orientation of room with respect to north [°]. In the Template version this field is
unavailable. All rooms can be collectively rotated from the Building tab.
Orientation widget Set room orientation by selecting corresponding radio button. In the Template
version this control is unavailable.
Room systems and settings
Internal gains Drag an internal gains object from the palette to the rooms tab. Double click to open the
internal gains object, Figure 5.
Indoor Climate Standard Drag an indoor climate standard object from the palette to the rooms tab.
Double click to open the indoor climate standard object, Figure 6.
Heating Drag a heating object from the palette to the rooms tab. Double click to open the heating
object, Figure 8. Click the wastebasket to remove the object.
Ventilation Drag a ventilation object from the palette to the rooms tab. Double click to open the
ventilation object, Figure 14. Click the wastebasket to remove the object.
Cooling Drag a cooling object from the palette to the rooms tab. Double click to open the cooling object.
Click the wastebasket to remove the object. Removing this object will avoid local room unit cooling, but
the room may still be supplied with mechanically cooled air. To remove all cooling, remove also the
Cooling object from the Building tab (but not the Cold storage).
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Figure 2
Window Drag a window from the palette to a surface of the room in the 3D view, Figure 2. Double click
to open the window object, Figure 24 and Figure 25. Right click and choose Delete to remove the
window. Right click and choose Duplicate to insert a copy of the window, slightly shifted from the
original position. When a window is added to a surface with internal construction, the surface is
assigned the default external construction. A selected window can be moved by holding down the ctrlkey and dragging the window to a new position, which can be on another wall.
Door Drag a door from the palette to a surface of the room in the 3D view. Double click to open the
door object, Figure 26. Right click and choose Delete to remove the door. Right click and choose
Duplicate to insert a copy of the door, slightly shifted from the original position. When a door is added
to a surface with internal construction, the surface is assigned the default external construction. A
selected door can be moved by holding down the ctrl-key and dragging the door to a new position,
which can be on another wall.
Surface part: part of a surface with different construction and/or boundary conditions.
Drag a surface part from the palette to a surface of the room in the 3D view, Figure 3. Double click to
open the surface part object, Figure 27. Right click and choose Delete to remove the surface part. Right
click and choose Duplicate to insert a copy of the surface part, slightly shifted from the original position.
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A selected surface part can be moved by holding down the ctrl-key and dragging the surface part to a
new position, which can be on another wall. These operations are not available in the Template version.
Figure 3
Wall construction Drag a wall construction from the palette to a surface of the room in the 3D view.
Double click on the surface in the 3D view to open the wall construction dialog. Right click and choose
Delete to remove the construction assignment. When a wall construction is removed, the surface is
assigned the default internal construction, unless there is a window or door on the surface, in which
case it is assigned the default external construction. To specify a surface as default external, internal or
ground construction, drag the default external, internal or ground construction object on to it from the
palette.
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Editing room
Figure 4
Dialog for editing the rectangular shape of a room into an arbitrary polygon. The dialog is opened by
clicking the Edit button on the rooms tab.
The perimeter of the room is shown as a polyline. A polyline consists of line segments and break points,
the latter marked by small rectangles. The polyline can be edited as follows:
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Its breakpoints can be dragged to the desired positions for the room’s corners.
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Its line segments can be dragged to the desired positions for the room’s walls.
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A new breakpoint can be introduced by clicking on or close to the line.
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An existing breakpoint can be deleted by clicking on it.
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Breakpoints for non right-angled corners can be introduced by holding down the ctrl-key and
simultaneously clicking on a line segment.
Internal gains
Figure 5
Dialog defining the internal gains in the room.
Equipment Dry convective heating power from appliances in the room [W/m2]. Click hyperlink to open
dialog for setting other equipment details.
Schedule Schedule determining when equipment is on [selection from available resources]. Click
hyperlink to open schedule dialog.
Occupants Number of occupants that load the room (dry and wet) [number/m2]. Click hyperlink to open
dialog for setting other occupant details.
Schedule Schedule determining when occupants are present [selection from available resources]. Click
hyperlink to open schedule dialog.
Lights Rated input power when lights are on [W/m2]. Click hyperlink to open dialog for setting other light
details.
Schedule Schedule determining when lights are on [selection from available resources]. Click hyperlink
to open schedule dialog.
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Basic indoor climate settings
Figure 6
Dialog defining a variant of the indoor climate standard in the room.
Heating setpoint The air temperature that heating units attempt to maintain [°C].
Cooling setpoint The air temperature that cooling units attempt to maintain [°C].
Method Type of air quality measure [CO2 limit].
CO2 limit - maintain CO2 below the limit.
Limit The air quality setpoint.
Generic heater
Figure 7
The generic heater has by default unlimited capacity. It heats the room directly, using the given energy
source, i.e. it does not rely on any central systems that have been defined on the Building tab. The
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generic heater is normally used in the initial stages, to find required system capacity. By default, 40% of
the heat is emitted as long wave radiation. This ratio can be changed in the Building defaults form.
Water based radiator or convector
Figure 8
Device type Type of radiator or convector [selection from available resources]. Click hyperlink to access
radiator parameters that are stored in the database.
Size Size radiator/convector based on [power, front area].
power Emitted power at rating conditions. [W/m2].
Copy Copy data from previous room unit heating calculation. Design power is shown in the (grey) input
field. Corresponding area is shown in the (grey) front area field.
front area Front area of radiator/convector [m2].
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Radiator rating conditions
Figure 9
Room and water temperatures at which the given power radiator power will be emitted. Note that
actual radiator capacity is strongly dependent on these.
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Air to air, non-ducted, heat pump
Figure 10
Model for an air-to-air direct expansion on-off controlled unit for heating of room air. At the given rating
condition (press button to see), the model will yield given total power and COP, if it is physically
possible. If a physically unrealistic COP is given, the model may yield the required performance at the
actual rated point, but may render completely erroneous results at other operating points and may also
become numerically unstable.
It is generally not recommended for most users to change any other parameter than the total heating
power.
Away from the rated point, the performance will be determined by the additionally specified
parameters. With the exception of compressor parameters, the input data are measurable quantities
but may not always be made available by equipment manufacturers. If parameters have been identified
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with respect to measured data from a real device, the model will predict the performance over the
whole operating range within the accuracy of a few percent, typically around one.
Floor heating
Figure 11
The floor heating circuit is assumed to cover the whole floor of a room. Net design mass flow into the
circuit from the hot tank is given in terms of a design power and temperature difference. Note that all of
this power may not be accessible to the room, if for example the pipes have been located in the middle
of an insulation layer.
If the water temperature from the hot tank (that is specified in the Building tab, Heat Distribution
system) is unsuitably high for direct injection into a floor coil circuit, the constant coil mass flow option
should be chosen (default).
The coil location in the slab may be critical to the resulting heat emission. Overall heat transfer from the
pipes to the surrounding material is governed by the H-water-pipe-fin parameter. Some approximate
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values are given in the form. For more accurate simulations, measurement data or computational
results from a more detailed simulation model should be used.
Heated beam
Figure 12
Given power is extracted from the water when temperatures are according to the rating conditions and
air flow is at the given design air flow. Some power must also be emitted at zero air flow, otherwise the
model may become unstable. If the design air flow is lower than the total supply air flow to the room,
the surplus air is injected into the room without passing the beam.
Figure 13
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Generic ventilation
Figure 14
Dialog defining a variant of the ventilation in the room.
Type Type of ventilation system [Constant Air Volume, Variable Air Volume].
supply Mechanical supply airflow for CAV systems [l/s m2].
return Mechanical return airflow for CAV systems [l/s m2].
min Minimum airflow at VAV [l/s m2].
max Maximum airflow at VAV [l/s m2].
control Control of VAV system [ CO2, Temperature, Temperature + CO2].
Generic cooler
Figure 15
The generic cooler has by default unlimited capacity. It cools the room by convection, using the given
energy source, i.e. it does not rely on any central systems that have been defined. The generic cooler is
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normally used in the initial stages, to find required system capacity. By default, the cooling coil is
assumed to hold 15⁰C and may remove moisture from the air. This temperature can be changed in the
Building defaults form.
Water based cooling device
Figure 16
Device type Type of cooling device [selection from available resources]. Click hyperlink to edit basic
device parameters.
Size Size cooling device based on [power, front area].
power Emitted power [W/m2].
Copy Copy data from previous room unit cooling calculation. Design power is shown in the (grey) input
field. Corresponding area is shown in the (grey) front area field.
front area Front area of cooling device [m2].
Rating conditions
Figure 17
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Temperature conditions at which the device will remove the specified amount of heat.
Air to air, non-ducted, air conditioner
Figure 18
Model for an air-to-air direct expansion on-off controlled unit for cooling and dehumidifying room air. At
the given rating condition (press button to see), the model will yield given total power and EER (cooling
COP), if it is physically possible. If a physically unrealistic COP is given, the model may yield the required
performance at the actual rated point, but may render completely erroneous results at other operating
points.
It is generally not recommended for most users to change any other parameter than the total cooling
power.
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Away from the rated point, the performance will be determined by the additionally specified
parameters. With the exception of compressor parameters, the input data are measurable quantities
but may not always be made available by equipment manufacturers. If parameters have been identified
with respect to measured data from a real device, the model will predict the performance over the
whole operating range within the accuracy of a few percent, typically around one.
Figure 19
Rating conditions, by default according to EN 14511.
Floor cooling
Figure 20
See help text on p. 19 for floor heating.
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Chilled beam
Figure 21
Given power is absorbed by the water in the beam when temperatures are according to the rating
conditions and air flow is at the given design air flow. Some power must also be absorbed at zero air
flow, otherwise the model may become unstable. If the design air flow is lower than the total supply air
flow to the room, the surplus air is injected into the room without passing the beam.
Figure 22
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Heating/cooling floor
Figure 23
Object for combined heating and cooling by the same floor coil. See help text on p. 19 for floor heating.
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Window
Figure 24
Form for defining a window on a surface.
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Frame fraction The unglazed area of the window divided by the whole window area, defined by the
outer frame measures [%].
Glazing Choice of glass configuration, includes g, T, Tviz and U-value for the glass [selection from
available resources]. Click hyperlink to open glazing dialog.
Integrated shading Choice of curtains or blinds [selection from available resources]. Click hyperlink to
open integrated shading dialog .
External shading Include external window shading. When checked the image of the window, Figure 24,
changes to show an awning, Figure 25.
Opening control Selection of control strategy for window opening. [Schedule, PI temperature control +
schedule]
Schedule - The opening is controlled by time schedule (or not controlled at all)
PI temperature control + schedule - The opening is controlled by air temperatures (both internal
and external) in the range from 0 (fully closed) to the value given by the schedule
Opening schedule Schedule for degree of window opening. 0 = fully closed, 1 = fully open.
X Position in x-direction [m].
Y Position in y-direction [m].
Width The window’s extension along the x-direction (frame outside measurement) [m].
Height The window’s extension along the y-direction (frame outside measurement) [m].
Recess depth The distance between the window outer pane and the façade surface [m].
Awning width The total width of the awning [m], see Figure 25.
Awning height The total height of the awning projected on the façade [m], see Figure 25.
Awning extension The largest distance the sunblind is from the façade surface [m], see Figure 25.
Awning, mounting distance above window Distance between the awning bracket and the window
recess [m], see Figure 25.
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Figure 25
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Door
Figure 26
Dialog defining a door on a surface.
Construction Construction of door [selection from available resources]. Click hyperlink to open
construction dialog.
X Position in x-direction [m].
Y Position in y-direction [m].
Width The door’s extension along the x-direction [m].
Height The door’s extension along the y-direction [m].
Surface part
Figure 27
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Dialog defining a surface part on a surface.
Construction Construction of surface part [selection from available resources]. Click hyperlink to open
construction dialog.
X Position in x-direction [m].
Y Position in y-direction [m].
Width The surface part’s extension along the x-direction [m].
Height The surface part’s extension along the y-direction [m].
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Building tab
Figure 28
The building tab is used to specify both general information about the simulation and the HVAC systems
that serve the building. Similarly to the room tab p. 7, the default objects for HVAC systems and settings
may be replaced by those available on the left hand side bar palette. Most combinations of HVAC
system components will automatically be connected into meaningful systems. See p. 68 for a more
technical description of the systems that are generated.
Project data
Project data Click to open project the data object, an object for documentation of the simulation case
and the current choice of parameters. Project data is written on reports etc.
Global data
Location Location of the building [selection from available resources]. The object contains a reference to
a location and a climate file. Click hyperlink to open location dialog.
Wind profile Choice of wind profile object [selection from available resources]. Click hyperlink to open
wind profile dialog.
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Rotate building Angle to rotate building incrementally [°].
Clockwise Click to rotate the building clockwise by the specified angle around the center of the building.
Counter-clockwise Click to rotate the building counter-clockwise by the specified angle around the
center of the building.
Defaults Click to open defaults form, which contains defaults for all rooms, Figure 29.
Thermal bridges Click to open thermal bridges object, which contains coefficients for calculation of loss
factors for thermal bridges in rooms, Figure 30.
Ground properties Click to open ground properties object, which contains model and parameters for
temperature conditions below the building, Figure 31.
Infiltration Click to open infiltration object, which contains method and parameters for building air
leakage, Figure 32.
Extra energy and losses Click to open extra energy and losses object, which contains information about
extra energy consumers of the building that do not take part in the building heat balance, such as
external lighting, Figure 33.
Building 3D and shading Click to open building 3D and shading window, Figure 41, Figure 42 and Figure
43.
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Defaults
Figure 29
Input given here will be used unless other data has been given in the room or subsystem.
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External walls Construction for external walls lacking descriptions in the room.
Internal walls Construction for internal walls lacking descriptions in the room.
Internal floors Construction for internal floors lacking descriptions in the room.
Roof Construction for roofs lacking descriptions in the room.
External floor Construction for floor slabs lacking descriptions in the room. A ground insulation layer is
normally described as part of the ground structure.
Glazing Glazing for windows lacking descriptions in the window.
Door construction The default construction for doors. The default setting for this parameter is "[use wall
construction]" which means that there will be no special treatment of wall material.
Integrated window shadings The default shading device for the window.
Default heating Default type of heating for plant components and ideal room units.
Heating COP Default heating efficiency.
Default cooling Default type of cooling for plant components and ideal room units.
Cooling COP (EER) Default cooling efficiency.
Ideal cooler coil temperature [°C]
Ideal heater radiative fraction
Ideal heater emission efficiency
Ideal cooler emission efficiency
IDA resources Open form containing the IDA-resources currently or previously used in this project.
Database Open the IDA database.
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Thermal bridges
Figure 30
These coefficients are used to calculate the loss factors in thermal bridges in rooms. The total loss factor
for a room is calculated as the sum of loss factors in bridges created by different construction elements.
The coefficients are given per unit of element size (in most cases per meter). The sizes of elements are
calculated from room geometry.
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Ground properties
Figure 31
Ground layers under basement slab Ground layers under slab down to constant temperature.
Ground layer outside basement walls Ground layers outside wall to ambient temperature.
The ground layer under the basement floor is connected to a constant temperature, which is computed
as the mean air temperature of the selected climate file. The layers around the basement walls are
coupled to a facade object for crawl space, which is kept at ground surface temperature. Note that no
2D or 3D effects are modelled for either of these couplings.
Infiltration
Figure 32
Data in the infiltration form is used to specify unintentional air flows over the building envelope without
having to visit each room. Constant envelope air flows to and from each room are introduced.
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Extra energy and losses
Figure 33
In this form, losses from HVAC distribution systems and additional energy use items (external lighting
etc.) are specified.
Distribution System Losses are specified to account for leakage from pipes and ducts that pass through
the building without having to describe their exact path and insulation properties. For water circuits, the
sign is positive when heating the room for DHW and heat, and positive when cooling for cold water
circuits. The loss from air ducts is defined as positive when the duct is cooler than the room.
Duct losses include both thermal conduction and air leakage losses, although the actual loss of mass
through the duct wall is not modeled. Duct losses take account of actual temperature difference
between the duct system and rooms, while water circuit losses are independent of actual temperatures.
Units for heat and cold distribution may be changed for convenience.
Rough estimates of possible loss levels are provided for convenience via sliders, but these levels vary
greatly between countries.
A given percentage of the heat (or cold) from each distribution system is deposited to the room heat
balance. Remaining heat is simply lost to ambient.
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Any number of Additional Energy Use items may be specified (right click to rename them). This is energy
which should be accounted for in total supplied energy, but does not enter the building heat balance.
Ice melting equipment or external lights are examples.
For each item, both an absolute and a per-floor-area contribution may be given. The total of both is
displayed for convenience. Each item must also refer to a schema and an energy meter.
Distribution systems
Air Drag an air distribution system object from a palette to the building tab. Double click to open air
distribution system object, Figure 34.
Figure 34
The air distribution object contain general settings for the mechanical ventilation system. When
applicable, these parameters will be referenced by the selected air handling unit. They may also be used
elsewhere.
Heat Drag a heat distribution system object from a palette to the building tab. Double click to open heat
distribution system object, Figure 35.
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Figure 35
The hot water distribution object contains general settings for the water based heating system. These
parameters will be used for the generation of a plant model. Three points may be given on the curve for
supply temperature as function of ambient temperature. All water based heating units in the rooms will
be fed with the same water temperature. A separate setpoint is available for hot water to the air
handling system.
Cold Drag a cold distribution system object from a palette to the building tab. Double click to open cold
distribution system object, Figure 36.
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Figure 36
The cold water distribution object contains general settings for the water based cooling system These
parameters will be used for the generation of a plant model. Three points may be given on the curve for
supply temperature as function of ambient temperature. All water based heating units in the rooms will
be fed with the same water temperature. A separate setpoint is available for hot water to the air
handling system.
Domestic hot water
Drag a domestic hot water object from a palette to the building tab. Double click to open domestic hot
water object, Figure 37.
Figure 37
Domestic Hot Water Use may be specified here using different units. Note that when a unit that
includes the number of building occupants is used, the relevant number of occupants should be set here
as well. The Number of occupants field is by default bound to the sum of all defined occupant thermal
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gains. However, in many situations, this number is quite different from a relevant "water consuming
occupant", for example a conference room will hold a lot of occupant loads that have their normal
"base" in some other room.
Energy
Electricity rate Drag an electricity rate object from a palette to the building tab. Double click to open
electricity rate object, Figure 38.
Fuel rate Drag a fuel rate object from a palette to the building tab. Double click to open fuel rate object,
Figure 38. Note that the pricing is given with respect to fuel heating value, not consumed mass or
volume.
District heating rate Drag a district heating rate object from a palette to the building tab. Double click to
open district heating rate object, Figure 38.
District cooling rate Drag a district cooling rate object from a palette to the building tab. Double click to
open district cooling rate object, Figure 38.
Figure 38
CO2 emission factors Drag a CO2 emission factors object from a palette to the building tab. Double click
to open CO2 emission factors object, Figure 39.
Figure 39
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The CO2 emission factors are used to determine the amount of CO2 that will be released into the
atmosphere as the energy source is used. For Fuel the reference energy is counted in terms of fuel
heating value.
Primary energy factors Drag a primary energy factors object from a palette to the building tab. Double
click to open primary energy factors object, Figure 40.
Figure 40
The primary energy factors are used to determine the amount of so called primary energy that will be
used for delivery of each unit of each category of energy. Many countries have politically determined
primary energy factors that are used to compare the relative environmental impact of different systems.
Central systems
Solar thermal Drag a solar thermal object from a palette to the building tab. Double click to open solar
thermal object. Click the wastebasket to remove the object.
Photovoltaics Drag a photovoltaics object from a palette to the building tab. Double click to open
photovoltaics object. Click the wastebasket to remove the object.
Ventilation Drag a ventilation object from a palette to the building tab. Double click to open ventilation
object. Click the wastebasket to remove the object.
Hot storage Drag a hot storage object from a palette to the building tab. Double click to open hot
storage object. Click the wastebasket to remove the object.
Cold storage Drag a cold storage object from a palette to the building tab. Double click to open cold
storage object. Click the wastebasket to remove the object.
Topup heating Drag a topup heating object from a palette to the building tab. Double click to open
topup heating object. Click the wastebasket to remove the object.
Base heating Drag a base heating object from a palette to the building tab. Double click to open base
heating object. Click the wastebasket to remove the object.
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Cooling Drag a cooling object from a palette to the building tab. Double click to open cooling object.
Click the wastebasket to remove the object.
Ambient heat exchange Drag an ambient heat exchange object from a palette to the building tab.
Double click to open ambient heat exchange object. Click the wastebasket to remove the object.
Ground heat exchange Drag a ground heat exchange object from a palette to the building tab. Double
click to open ground heat exchange object. Click the wastebasket to remove the object.
All ambient or ground heat exchangers are connected to a brine loop. The brine loop will always be
connected to heat exchangers in the hot and cold tanks. This way, a ground heat exchanger can directly
cool the building without the assistance of a chiller. However, should a Brine to water chiller be dragged
in, its condenser will also be cooled by the brine loop (and the resulting hot brine may even be warm
enough to be utilized directly in the hot tank).
When two or more central system boxes are graphically connected the added system covers the
function of both boxes.
Select Plant details under Requested output in the Simulation tab in order to see the time-evolution of
key Central system variables.
Building 3D and shading
The building 3D and shading window is opened by clicking Building 3D and shading on the building tab.
Rooms
In the building 3D and shading window, rooms can be given a position in 3D space to form a sensible
building. Drag rooms from the table in the Rooms tab to the building 3D and shading window, Figure 41.
In the 3D view, the room will move in the x-y plane. Hold down the shift-key to move the room in the zdirection. To reposition a room: select it, hold down the ctrl-key and drag it. By default all rooms of the
building are placed at the origin.
The rooms do not shade windows or solar panels.
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Figure 41
Shading objects
In the building 3D and shading window, shading objects can be added to produce additional shading of
windows and solar panels. Drag shading objects from the palette to the building 3D and shading tab,
Figure 42. Right click and choose Delete to remove the shading object. Right click and choose Duplicate
to insert a copy of the shading object, slightly shifted from the original position. A selected shading
object can be moved by holding down the ctrl-key and dragging the shading object to a new position.
The shading-object will move in the x-y plane. Hold down the shift-key to move the shading object in the
z-direction. Right click and choose Edit to edit the shape of the shading object, Figure 43.
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Figure 42
46
Figure 43
When in edit mode, Figure 43, the shading object can be modified as follows:
-
To edit the shape and location of the shading object, place the cursor over a handle, click the
left mouse button, and drag the handle.
-
To move the entire shading object, place the cursor over the shading object, in-between two
handles, click the left mouse button, and drag the shading object. The shading object follows the
cursor while remaining fixed in the z-axis.
-
To move the shading object along the z-axis, hold down the shift-key while moving the mouse.
-
To rotate the shading object around the z-axis, place the cursor above the shading object, hold
down the shift-key and the middle mouse button, and move the mouse.
-
To scale the shading object (bring the handles closer/further apart), place the cursor above the
shading object, hold down the shift-key and the right mouse button, and move the mouse.
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-
To insert a new handle, hold down the ctrl-key, and click the left mouse button.
-
To remove a handle, place the cursor above the handle, hold down the ctrl-key, and click the
right mouse button.
Exit the edit mode by clicking the right mouse button and choosing Done or Cancel from the right mouse
button menu.
Solar panel
If solar thermal or photovoltaics systems have been added to the building, these will be visible in the
building 3D and shading window as solar panels, Figure 44. The solar panels can be given a sensible
position in 3D space by holding down the ctrl-key and dragging the panel to a new position. The panel
will move in the x-y plane. Hold down the shift-key to move the panel in the z-direction.
Solar panels are shaded by other shading objects. Solar panels themselves shade other solar panels and
windows if they have been moved to a sensible position, i.e. if they are left at the origin they will not
shade.
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Figure 44
Help for 3D view Displays the following text as a tooltip when the mouse is pointed at the button, and in
a dialog when the button is clicked:
“Left mouse button: Click Select object. Selected object is shown in red.
Left mouse button: Press down and move mouse Rotate the model.
Middle mouse button (or both the left and the right mouse buttons on a two button mouse):
Press down and move the mouse Pan the model.
Right mouse button: Press down and move the mouse Zoom in/zoom out. Move the mouse
upwards to zoom in and downwards to zoom out.
The x+, x-, y+, y-, z+, z- buttons create a section through the building. When section is activated,
press Ctrl-key, click within the red frame and move the mouse pointer, to move the section.
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A room, shading object or solar panel can be dragged to a new position. When the room,
shading or solar panel object is selected, press Ctrl-key, click on the object and move the mouse
pointer, to move the object. The object will move in the x-y plane. Hold down the Shift-key to
move the object in the z-direction.
When in edit mode, a shading object can be modified as follows:
To edit the shape and location, place cursor over a handle, click left mouse button, drag handle.
To move the entire object, place cursor in-between two handles, click left mouse button, drag
object. The object will move in the x-y plane. Hold down the Shift-key to move the object in the
z-direction.
To rotate the object in the x-y plane, place cursor over object, hold down Shift-key and middle
mouse button, move the mouse.
To scale the object (bring the handles closer/further apart), place cursor over object, hold down
Shift-key and right mouse button, move the mouse.
To insert a new handle, hold down Ctrl-key, click left mouse button.
To remove a handle, place cursor over the handle, hold down Ctrl-key, click right mouse
button.”
Restore default view Zoom and pan the model so that the entire model is visible and undo any cut of
the model.
x+ Cut the 3D model along the x-axis removing all geometry on the positive side of the cut plane.
x- Cut the 3D model along the x-axis removing all geometry on the negative side of the cut plane.
y+ Cut the 3D model along the y-axis removing all geometry on the positive side of the cut plane.
y- Cut the 3D model along the y-axis removing all geometry on the negative side of the cut plane.
z+ Cut the 3D model along the z-axis removing all geometry on the positive side of the cut plane.
z- Cut the 3D model along the z-axis removing all geometry on the negative side of the cut plane.
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Generic solar thermal
Figure 45
Select a solar collector model from the drop down list. Either total area or number of units of the
selected type can be specified.
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Generic photovoltaics
Figure 46
PV can be specified in terms of area and overall efficiency. All generated electricity shows up as a
negative contribution in the delivered energy report.
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Standard air handling unit
Figure 47
The standard air handling system consists of the following components Figure 47: supply air
temperature setpoint controller (1), exhaust fan (2), heat exchanger (3), heating coil (4), cooling coil (5),
supply fan (6), schedule (7) for operation of both fans and a schedule for the operation of the heat
exchanger (8). The unit provides temperature-controlled air at a given pressure. Some key parameters of
individual components are presented in the form; open them to edit. The supply air temperature
setpoint is set in the Air distribution system dialog opened by double-clicking on the Air distribution
control box (1).
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Return air only AHU
Figure 48
See section on Standard air handling unit.
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AHU with electrical heating coil
Figure 49
See section on Standard air handling unit.
Generic topup heater
Figure 50
The top-up heater is employed when temperature in the hot tank drops more than 2⁰C below the
highest requested temperature. Energy source as well as a constant production efficiency (or COP) can
be selected. The total capacity can optionally be limited.
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Ambient air to water heat pump
Figure 51
Figure 52
Model for an air-to-water, on-off controlled, unit for water heating. At the given rating condition (press
button to see dialog below), the model will yield given total power and COP.
It is generally not recommended for most users to change any other parameter than the total heating
capacity.
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Away from the rated point, the performance will be determined by the additionally specified
parameters. These are measurable quantities but may not always be made available by equipment
manufacturers. If parameters have been identified with respect to measured data from a real device,
the model will predict the performance over the whole operating range within the accuracy of a few
percent, typically around one.
Figure 53
Brine to water heat pump
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Figure 54
Model for a brine to water on-off controlled unit for hot water heating. At the given rating condition
(press button to see), the model will yield given total power and COP.
It is generally not recommended for most users to change any other parameter than the total heating
capacity.
Away from the rated point, the performance will be determined by the additionally specified
parameters. Most of these are measurable quantities but may not always be made available by
equipment manufacturers. If parameters have been identified with respect to measured data from a
real device, the model will predict the performance over the whole operating range within the accuracy
of a few percent, typically around one.
The cold (evaporator) side of the Brine to water heat pump, will automatically be connected to the brine
circuit. In most situations, some ambient or ground heat exchanger must also be added by the user to
the brine loop in order to collect heat for the heat pump. This is done by simply dragging such a
component into the form. The cold side of the heat pump will always be connected to a heat exchanger
in the cold tank and thus provide “free” cooling to the building whenever this is possible.
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Figure 55
Generic hot water tank
Figure 56
Some hot water storage facility is required in an Esbo simulation. See further discussion about the tanks
and Esbo plant models on p. 68. If you do not want to consider a real water tank, select the volume to
be small with respect to the size of the modeled system. The tank will then represent general mass of
the piping system and connected devices. If the tank size is too small, the model is likely to have
numerical difficulties.
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Generic cold water tank
Figure 57
Some cold water storage facility is required in an Esbo simulation. See further discussion about the tanks
and Esbo plant models on p. 68. If you do not want to consider a real water tank, select the volume to
be small with respect to the size of the modeled system. The tank will then represent general mass of
the piping system and connected devices. If the tank size is too small, the model is likely to have
numerical difficulties.
Generic chiller
Figure 58
Energy source as well as a constant production efficiency (or cooling COP) can be selected. The total
capacity can optionally be limited.
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Brine to water chiller
Figure 59
Model for a brine to water on-off controlled unit for water cooling. At the given rating condition (press
button to see), the model will yield given total power and EER (cooling COP).
It is generally not recommended for most users to change any other parameter than the total cooling
capacity.
Away from the rated point, the performance will be determined by the additionally specified
parameters. These are measurable quantities but may not always be made available by equipment
manufacturers. If parameters have been identified with respect to measured data from a real device,
the model will predict the performance over the whole operating range within the accuracy of a few
percent, typically around one.
The hot (condenser) side of the Brine to water chiller, will automatically be connected to the brine
circuit. In most situations, some ambient or ground heat exchanger will must also be connected to the
brine loop in order to dispose of the waste heat. This is done by simply dragging such a component into
the form. The hot side of the chiller will always be connected to a heat exchanger in the hot tank and
thus provide “free” heating to the building when possible.
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Figure 60
62
Heat exchange with given temperature source
Figure 61
The model is used to specify the option of heat exchange with a temperature source with a practically
infinite capacity, such as sea water or in some approximations the ground. In place of the default
constant temperature, a schedule that prescribes the temperature variation as a function of time can be
given.
The given power, temperature difference and pressure loss are used to determine sizes of the heat
exchanger and associated pumps and pipes. Pumps are regarded to be capacity controllable down to
zero flow with given constant efficiency.
Dry or wet air to brine heat exchanger
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Figure 62
Model for a fan assisted ambient heat exchanger. In heat production mode, condensation may occur
and therefore a wet coil rating point is required. The efficiency is defined with respect to an apparatus
dew point which is the average of entering and leaving brine temperature. Wet coil leaving air
conditions will lie on a straight line between entering conditions in the psychometric chart and the
apparatus dew point. The dimensionless distance along this line is defined as the efficiency.
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Start simulation tab
Figure 63
Results
Requested output Select Open dialog to specify what diagrams and reports that will be created during
the simulation. Note in particular the Plant details option, that will provide the time-evolution of key
Central system variables.
Simulation
Heating design Setup Open dialog to define key parameters to be applied in the calculation.
Heating design Run Run heating design simulation.
Cooling design Setup Open dialog to define key parameters to be applied in the calculation.
Cooling design Run Run cooling design simulation.
Energy Setup Open dialog to define key parameters to be applied in the calculation.
Energy Run Run energy simulation.
Standard level
Available only if the full IDA ICE application is accessible.
Build model Click to build and open an IDA ICE model of the system.
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Results tab
Figure 64
The Results tab is shown automatically, after a completed simulation.
Results summary table All rooms of the building are shown in the table and key results of the rooms are
displayed. Use Summary, Heating design and Cooling design radio buttons to switch between results.
Report The results summary table is exported to Excel.
Expand table The results summary table is opened in a separate resizable window of easy viewing of
more rooms and columns than can fit in the results tab table.
Detailed results A list of all result objects requested before the simulation.
Modified The time when the model was last changed. Only shown if the model was changed after the
latest simulation.
Saved The time when the case was last saved on disk.
Simulated The time when the latest simulation was run.
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Make report When pressed, the input data and results are combined into a single Word document.
Implemented only for Word 2000 or later.
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Technical description of the default generated systems
In the Building tab, many different system configurations can be described by dragging in various
components. Based on these, systems are automatically generated in the standard level of IDA ICE. For
users who have access to the IDA ICE application, these systems can be inspected in detail, and if an
Expert edition license is available, the systems can also be reconnected and configured.
In this section, we describe the principles for the construction and control of the default systems. Note
that combination components, for example a solar collector and tank combination from a particular
manufacturer, may lead to other system configurations that may or may not be compatible with the
available generic set of components. For example, if a solar-collector and tank combination only allows
built-in electrical top-up heating, both the hot tank, the solar thermal, the base heating and the top-up
heating slots will be occupied by the combination system and no other systems will be allowed to feed
into the hot water tank.
Here, the narrative will rely on system schematic diagrams as displayed in the Standard level. For a user
with access to the full IDA ICE application, these can be reached by the Build model button on the “Start
Simulation” tab. Open the Plant model from the “General” tab in the full application.
Purpose and ambition of the default generated systems
In economically feasible real systems many compromises must be made. The total number of valves,
pumps and connections must be reasonable and control logic must not be overly complex. In contrast,
the purpose of the Esbo default systems is to exploit all significant energy flows based on a minimum of
input data from the user even if the physical components needed are not justifiable in a real system. The
generated systems are technically realistic but might, at least for smaller installations, contain too many
parts to be economically attractive for realization in real life.
Furthermore, the control systems employed are extraordinarily “decentralized.” In order to avoid the
combinatorial explosion of having to define a central control system for each possible system
configuration, each subsystem is maximally self sufficient. A flow controller for, e.g., a ground source
circuit will simply check when it is possible to deliver heat (or cold) and does this until it is not energywise economical to continue (when pumping costs will exceed the benefits). Long-term control
strategies, for example to try to seasonally balance a large thermal store, is out of scope of the
automatically generated default systems. Whenever the short-term benefit of a certain flow is in place,
the flow will be activated.
The default tank models
All default generated systems are centered around two stratified water tanks, one for hot and one for
cold water. These two tanks are mandatory for most system combinations, also for situations where a
real system would not include a tank. Furthermore, the tanks are by default equipped with valves that
will allow each entering and exiting flow to be made at the optimal height in the tank. This way, minimal
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buoyant mixing will occur. Real tanks exist that behave in a similar fashion, using for example heat lance
technology.
For situations where a storage tank is not part of the concept to be investigated, the volume of the
mandatory tanks can be set fairly small with respect to surrounding systems, but not to zero. The tanks
can then be thought of as “temperature switchboards” that minimize the amount of temperature mixing
in the system. Tank volume would then represent the thermal mass of the actual HVAC system.
The default height to diameter ratio (shape factor) of the tanks is set to 5, representing a fairly tall tank
with, correspondingly, only a small amount of conduction between the (default) ten water layers. In
order to create a less ideal tank and ultimately approaching a completely mixed tank, the shape factor
can be set smaller, so that conduction will even out temperature differences between layers.
When working at the Advanced level, it is possible to turn off the ideal heat lance feature of the tanks
and select fixed vertical positions for tank ports. The model will then automatically compute buoyant
mixing
An example of a generated system
Figure 65 shows an example of how the building tab may be populated with models. Some model has
been chosen for each of the possible functions. Brine to water vapor compression machines have been
defined for base heating as well as for cooling. Both ground heat exchange and ambient heat exchange
have been defined.
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Figure 65
Figure 66 shows the generated system at the Advanced level of IDA ICE. We will go through and explain
each major subsystem below.
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Figure 66
Organized around the two water tanks, the top one for heat and bottom one for cold storage, are the
various circuits that draw or feed tempered water from and to the tanks. Let us start with the client
circuits to the right, starting from the top right corner with the DHW circuit.
Domestic hot water is drawn from the hot tank, by the leftmost PMT-object, which has a mass flow
signal into it that gives the required DHW mass flow. The make-up water from the water mains is
furnished by the rightmost PMT-object and a given temperature (which is computed to be the yearly
average temperature of the current climate file). Each client circuit, including this one, feeds a
temperature setpoint into the tank. In this case this is the temperature setpoint for the DHW (55⁰C).
As a simplification, no separate “tank-in-tank” has been defined for the DHW in the default
configuration. The heat exchange between DHW and surrounding water is regarded to be infinite and
immediate.
The meter objects to the top right are used to record results about DHW production.
Next below is the AHU hot water circuit, which is connected via a pump to the air handling unit,
providing it with heated water at given pressure and temperature. Similarly as for the DHW, a
temperature setpoint (60⁰C in the example) informs the tank about the temperature that is required by
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this client. Also in the AHU box is an on-off controller for turning off the hot water circulation to both
AHU and zones when the ambient temperature is higher than, here, 18 degrees. Actually a 3⁰C
deadband is applied to this switch (only visible if the component is opened) to avoid frequent switching
events.
The Zone hot water circuit is similar, but has a more elaborate arrangement for the calculation of the
temperature setpoint, allowing it to be a function of ambient temperature as well as a of a night set
back schedule.
The AHU cold water and Zone cold water circuits connected to the cold tank are found in the lower
right corner. They have in this example simple fixed setpoints, 5⁰C and 14⁰C, respectively, throughout
the year.
On the production side, in the leftmost upper corner we have the PV (photovoltaics) production circuit.
It is, by default, not connected to any other model, but simply receives appropriately shaded sunlight
from the components feeding into it and converts it to electricity, the amount of which is recorded by
the connected meter.
To the right of the PV circult, the Solar thermal collector model is located, with a circulation pump and a
separate expansion vessel. This separate brine circuit feeds into a heat exchanger that is located at the
bottom of the hot tank. In-tank heat exchangers are also served by idealized heat lance technology. In
the default situation, the solar collector will never prioritize the production of hot water, but a fixed (in
the example 5⁰C) temperature difference is upheld in the circuit by a PI controller connected to the
pump. When there is no sun, the pump will not operate because the temperature difference over the
collector will be negative or below 5⁰C even at the minimal circuit flow which is always maintained.
Next to the right is the Top heating circuit, which is the backup for keeping the top of the tank at the
maximal required client temperature. It feeds directly into the tank water, and since expansion vessels
are included in the tanks, only a pump is required in this circuit. The control circuit measures the top
level water temperature and asks the top up heater to heat if the Base heating is already fully engaged.
Below is the Base heating circuit, where the condenser of the brine to water heat pump feeds into the
tank directly. The heat pump and the condenser circuit pump are controlled by a PI controller which
attempts to keep the fill ratio of the tank at a constant level (by default 0.2 if a free heating system is
present, otherwise at 0.8). The fill ratio is defined as the degree at which the tank is filled with water at
the highest required setpoint, i.e. if all water is heated to the highest setpoint, the fill ratio is 1, while if
the whole tank holds the ambient temperature (20⁰C), the fill ratio is zero.
Base heating heat pumps will have a speed limitation of the condenser pump circuit that will be active
when the heat pump should prioritize hot water production, i.e. the top heating circuit is engaged only
when the base heating is already running at full capacity.
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On the evaporator side, the brine to water heat pump is connected to the Brine circuit. The brine circuit
is a more unconventional design and we will explain how it works here. The basic idea is that all free
heat and cold sources are connected in parallel to a single brine circuit. The circuit will alternate to feed
units that require heat (such as the present heat pump) and cold, i.e. if free sources are available at the
same time for both heating and cooling and both a heating and a cooling need exists, a choice has to be
made as to which one of these will be satisfied. The idea behind the design is that this is a comparatively
rare situation.
To illustrate the function of the brine circuit, let us look at what happens with the present base heating
evaporator brine flow. Once the base heating heat pump starts to operate, the temperature of the
return side brine will drop after the condenser. First the brine passes through a “PMT tap” component,
which also receives a signal to open the circuit through the evaporator as the heat pump starts. Should it
be beneficial to run the cooled water through a heat exchanger at the top of the cool tank, this is done.
After returning back through the PMT tap, the brine is returned to the return brine manifold in the Brine
box.
In the event that no free supply circuits exist or are able to operate, and the evaporator was able to
discharge to the cold tank, the flow in the brine circuit will be upheld by the pump in the brine box,
which monitors both PMT tap components for possible beneficial flows. More commonly, one or several
of the free supply circuits will instead pick up the heating need of the heat pump evaporator. Let us look
at one of these, the ambient heat exchanger.
The current Ambient HX circuit, found immediately to the left of the brine box, is in the example a fan
assisted ambient heat exchanger, that is able to both cool and heat the brine when needed. All of the
free supply circuits rely on a pump/controller object “FreeSupCtr” that monitors the temperature
difference between the supply and return brine manifolds. When the temperature of the return
manifold drops, it is a signal that heating is required, and if the free source circuit is able to meet such a
need, it will start its flow (and in the example, the fan of the ambient hx). The circuit will, in heating
mode, be operated at a degree which keeps the contributed flow above (by default 5⁰C) the brine
return. The operation will be continued until it is no longer beneficial, for example because the fan
power is getting close to the useful delivered power.
All Free supply circuits operate independently of each other in trying to satisfy the current predominant
need. Any circuit which can help rise the supply side brine temperature will be operated in a heating
situation.
The free supply circuits can also be operated without any condenser or evaporator in the loop. Suppose
for example that the bottom of the hot tank has a temperature which is well below outside air
temperature. In this situation, the PMT tap component will open its circuit and the ambient heat
exchange circuit will start charging the tank directly. This type of situation is of course much more
common when it comes to cooling; the free sources will often be able to directly feed into the cold tank.
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In the example, the Cooling brine to water chiller operates in a similar way. Any useful heat after the
condenser is directly tapped into the hot tank, a free supply circuit will pick up the cooling need and
start to operate.
There is nothing that formally prevents both the heat pump and the liquid chiller in the example to
operate in parallel, both cooling and heating the brine circuit simultaneously. In this situation, the brine
pump will initially keep the flow in the circuit going but after some time one of the two compression
cycles will “win” and create a net cooling (or heating) need, which then is likely to be fulfilled by a free
supply circuit.
The present example, with two brine connected vapor compression machines and multiple free supply
circuits represent the most complex type of system that can be described. In all other situations, some
of these components or connections are missing, creating a simpler system schemata with a lower
number of operation modes.
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