Additional tunnel components
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Additional Tunnel components
Rail tunnel branch
The mathematical model for the air flow in the branching component is valid for a wye consisting of a straight uniform section with a connected branch, with a possibly different cross section area. For a thorough description of the equations see section 2.1.8 of the Theoretical Reference.
The input parameter φ is the angle between branch, location 3, and location 1 of the straight section. The empirical model is derived for angles in the interval [45˚, 135˚].
The parameter r/D is the ratio of the radius of the rounding of the edge where the branch meets the main section, and the main diameter.
Figure 1. A branch form
Damper
Figure 2. A damper form
At fully open position, flow through the damper is governed by a loss coefficient (kLoss) and at closed by an Equivalent Leakage Area (ela). The parameter tArea is the tunnel area and has to be equal to the tunnel area of the neighbouring components (area changes not allowed at connection points between components). See also Section for a discussion of pressure losses.
tau is the time constant for opening/closing the damper.
The parameter hFloor has to be given if neighbouring components have no specification of floor level. However, if e.g. tunnel sections are neighbours of the damper their floor level towards the damper has to be the same and hFloor isn’t needed.
The opening and closing of the damper can be bound to a separate source, such as an input file, a given graphically defined time series (a table), or to the output of a control component.
By default, the damper is symmetric when fully open. If you wish to make the fully open damper asymmetric, first set the symmetric Boolean parameter to false in the parameters list. Then, set the loss coefficient for the reverse direction (kLossR2L, in the parameters list).
By default, IDA Tunnel estimates the loss coefficient for partially open dampers using interpolation between the loss coefficient of fully open and the equivalent loss coefficient of a fully closed damper (set by leakage area). Alternatively, if laboratory test data is available, users can set the loss coefficients for partially open dampers. If the Boolean parameter 'PartiallyOpenDamperData' is set to 'True',
, users can input these data for the loss coefficients (editable by the user) 
at three different partial opening percentages (also editable by the user) 
.
Additionally, if laboratory pressure test data for a closed damper are available based on the AMCA**,
users can set these test data in the parameters. If the Boolean parameter 'LeackageDamperClosed' is set to 'true',
the aforementioned parameters will be used to calculate the loss coefficient of the fully closed damper, instead of relying on the default leakage area concept.
For a thorough description of the equations see section 2.1.13 of the Theoretical Reference.
Passage (Rail tunnel)
Figure 3. A passage form
The passage model is used to describe air flow through parallel and/or serial automatic sliding doors. Both stochastic and intermittent passenger flows are handled. We assume that a door section consists of a user defined number of doors, nl and nr, and in the case of two serial door sections that these are far enough apart so that in the statistical treatment they can be considered as independent. (The first door closes before the second opens for the same passenger.)
The parameter tArea is the cross section area and has to be equal to the tunnel area of the neighbouring components. (Area changes are not allowed at connection points between components).
The parameter passMax is the capacity in terms of passengers per hour when all individual doors are open and nGate gives the number of door sections (gates), one for a single door section and two for serial door sections.
When a door section is fully open, flow through the section is governed by a loss coefficient (kLoss) and when closed by an Equivalent Leakage Area (ela). Air resistance constituted by passengers themselves is neglected. See also Section for a discussion of pressure losses.
The parameters passStoch specify stochastic passenger flows (passengers/hour), respectively, from left and right through the passage at rush hour.
The parameters passPulse specify intermittent passenger flows (passengers/hour), respectively, from left and right through the passage at rush hour.
The parameter hFloor (displayed in the Outline tab) has to be given if neighbouring components have no specification of floor level. However if e.g. tunnel sections are neighbours of the passage their floor level towards the passage has to be the same and hFloor isn’t needed.
Parameters tau are the time intervals a door is open for a single passenger passage in left and right door section, respectively.
The time variation of passenger flow is given as a fraction of the rush hour passenger flows (variable passFract_var in interface passFract) and can be bound to a separate source, such as an input file, a given graphically defined time series (a table) or a schedule.
Below, the behaviour of the model is illustrated in three cases. The passage has one door in each section, capacity (passMax) 10000 passengers/hour and door opening time (tau) 4 sec for a passenger. The figure shows the normalized airflow as a function of passenger flow.
- One door section with stochastic passenger flow.
- Two similar serial door sections with stochastic passenger flow.
- Two similar serial door sections with intermittent passenger flow.
Figure 4. Normalized airflows as functions of passenger flow.
When passengers come intermittently (in groups), case c, the doors don’t need to be opened for each individual passenger and the total opening time reduces considerably. This is obvious when comparing the resulting airflow with case b, where the passengers pass the two door sections randomly. In case c the airflow becomes proportional to the passenger flow while in case b, with stochastic passenger flow, we have approximately exponential dependence. One also notes that serial door sections reduce the airflow (compare cases a and b).
For a thorough description of the mathematical model see section 2.1.14 of the Theoretical Reference.
Axial fan
Figure 5. An axial fan form
Axial fans are used to create physically realistic ventilation systems. The downside is that a realistic fan curve has to be specified. Alternative components for moving air, in early stages of a project, are the Given flow and Simplified air injection or extraction components. For the Axial fan, the fan curve, pressure difference as a function of volume air flow, is given as a spline. Note that the end points on the curve should be given outside the interval of operation to avoid numerically problematic boundary effects. (heat loss to tunnel air??)
The fan efficiency is similarly given as a spline.
The parameter tArea is the tunnel area and has to be equal to the tunnel area of the neighbouring components (area changes not allowed at connection points between components).
The parameter hFloor has to be given if neighbouring components have no specification of floor level. However if e.g. tunnel sections are neighbours of the axial fan their floor level towards the axial fan have to be the same and hFloor isn’t needed.
The inertia (start up time) of the fan is governed by a time constant tau.
The action of the fan, speedRel (quotient fan speed to nominal fan speed) can be bound to a separate source, such as the output of a control component, varying between –1 and 1, where negative values indicate reverse action.
For a thorough description of the equations see section 2.1.15 of the Theoretical Reference.
Given flow
Figure 6. A given flow component form
In order to get a certain flow through a tunnel without having to select a suitable fan curve, the given flow component may be used. It will deliver a constant flow under all conditions, irrespective of pressure, until it is less than the MAXPressRise, and will behave as a fan with feedback flow control (that would have a limited pressure head). Use this model with caution, as it may easily lead to unphysical situations particularly if the MAXPressRise parameter is set to a very high value. One can for example does not connect two Given flow components in series.
The wanted air volume flow is given as the product of parameter VFNom and control signal cntr, which can be bound to a separate source. The fan efficiency is specified with parameter effic.
The parameter tArea is the tunnel area and has to be equal to the tunnel area of the neighbouring components (area changes not allowed at connection points between components).
The parameter hFloor has to be given if neighbouring components have no specification of floor level. However if e.g. tunnel sections are neighbours of the given flow component their floor level towards the given flow component have to be the same and hFloor isn’t needed.
The parameter MAXPressRise serves as a threshold at which the fan operates with a constant pressure rise once this threshold is reached.
For a thorough description of the equations see section 2.1.11 of the Theoretical Reference.
Filter (Rail tunnel)
Figure 7. A filter component form
The filter component is used to remove particles from the incoming air. The particle content of the incoming airflow is reduced by the factor filterEff (Filter efficiency).
The wanted air volume flow is given as variable VFFilter, which can be bound to a separate source. The filter component will deliver a constant flow under all conditions, irrespective of pressure and will thus not behave as containing a physically realistic fan. One can not connect two filter components in series.
The parameter tArea is the tunnel area and has to be equal to the tunnel area of the neighbouring components (area changes not allowed at connection points between components).
The parameter hFloor has to be given if neighbouring components have no specification of floor level. However if e.g. tunnel sections are neighbours of the given flow component their floor level towards the given flow component have to be the same and hFloor isn’t needed.
For a thorough description of the equations see sections 2.1.12 and 2.3.5 of the Theoretical Reference.
Saccardo nozzle
Figure 8. A Saccardo nozzle form
Saccardo nozzles may be used to drive a large flow through a tunnel by injection of a small amount of air at high speed. The equations are not valid for a case where the air reverses direction, and exits out of the nozzle branch.
The input parameter Fi is the angle between the nozzle, location 3, and location 1 of the tunnel section.
Kmx is the momentum exchange coefficient. This governs how much of the jet momentum that is useful for driving tunnel air.
For a thorough description of the equations see section 2.1.16 of the Theoretical Reference.
Simplified air injection or extraction point
Figure 9. An air supply/exhaust form
The model consists of a fan with an optional damper mounted in an undivided branch of ductwork. The fan-damper-duct assembly connects ambient air with the tunnel via an integrated branch component. The action of the fan, supply or exhaust, is defined by the parameter Fandir.
The parameter Damper (open or closed) determines the state of the damper when the fan is off (fanCntr = 0).
The pressure-flow behaviour for the fan-damper-duct part is defined in the following way. At no external pressure difference and fanCntr = 1, the given flow VFNom is obtained. When fanCntr = 0 and Damper = Open, air will flow according to external pressure difference (including stack effect) with a system characteristic through the point pHead and VFNom. When fanCntr = 0 and Damper = Closed, there is no air flow.
The input parameter Fi is the angle between branch, location 3, and location 1 of the straight section. The mathematical model is derived for angles in the interval [45˚, 135˚]. The parameter r is the ratio of the radius of the rounding of the edge where branch meets main section and the main diameter. (See Branch component for a figure of Fi and r.)
For a thorough description of the equations see section 2.1.9 of the Theoretical Reference.
Heater (Rail tunnel)
Figure 10. A heater form
The heater tries to increase temperature of air flowing in specified direction (Heatdir = forward or reverse) to desired TSet with available power QMax·cntr, where cntr is an input control signal.
The parameter tArea is the tunnel area and has to be equal to the tunnel area of the neighbouring components (area changes not allowed at connection points between components).
The parameter hFloor has to be given if neighbouring components have no specification of floor level. However if e.g. tunnel sections are neighbours of the heater their floor level towards the heater have to be the same and hFloor isn’t needed.
For a thorough description of the equations see section 2.2.5 of the Theoretical Reference.
Doors and leaks
Figure 11. A door/leak form
The door/leak component should be connected to a hall/platform component. It is characterized by the parameters hLeak (height above platform/hall floor), ar (full opening area) and by the control variable partOpen, which may be bound to e.g. a time schedule (table). Wind pressure may, as in the entry/exit component be given explicitly or calculated from global parameters WindDir (wind direction) and WindVel (wind speed) together with phiPort (orientation of leak).
You can connect multiple doors/leaks to a hall/platform. The color rule does not apply, allowing you to connect the yellow link of a door/leak to the cyan link of the hall/platform.
The leak model is described in section 2.1.10 of the Theoretical Reference.
Heating coil
Figure 12. A heating coil form
The heating coil component contains a simplified air-to-liquid heating coil with liquid mass flow control.
The heating coil has two important parameters, etaAir, the air side temperature efficiency and dtLiq, the desired waterside temperature reduction. Capacity control is achieved by adapting the actual efficiency up to the given maximum efficiency level. The necessary water flow is calculated and the water temperature is reduced, if possible, by the desired number of degrees. There is no bypass on the liquid side; control is achieved by simply restricting the water flow.
The maximum capacity for the boiler’s heat production QMax can be given here. When the limit is reached, the boiler will no longer be able to maintain the setpoint ToutReq for the hot water supply temperature.
The boiler produces hot water with efficiency etaPrimary in relation to the supplied, so-called, primary energy.
The air flow in the heating coil is uni-directional, i.e. when using a heating coil one has to make certain that the air flows in the right direction and use connection components from the Other library. A Bi2UniDir component 
is inserted before the heating coil and a Uni2BiDir component 
after.
Cooling coil
Figure 13. A cooling coil form
The cooling coil component contains a simplified air-to-liquid cooling coil with liquid mass flow control.
The cooling coil works in the same way as the heating coil but is mathematically more complicated because air dehumidification is calculated. The given efficiency etaAir is defined as (1 - "bypass factor") according to ASHRAE’s nomenclature. Physically, this means that the state of the cooled air in the psychometric chart is on a straight line between the state for the incoming air and the apparatus dew point temperature on the saturation curve.
Qmax isThe maximum capacity for the chiller’s production QMax can be given he. When the limit is reached the chiller will no longer be able to maintain the setpoint ToutReq[1] for the coolant temperatures.
COP is the efficiency at which the chiller produces cooling power in relation to the supplied electrical power. This is kept constant independent of temperatures and any part loads.
The air flow in the cooling coil is also uni-directional, i.e. when using a cooling coil one has to make certain that the air flows in the right direction and use connection components from the Other library. A Bi2UniDir component is inserted before the cooling coil and a Uni2BiDir component after.
Air Washer
Figure 14. An air washer form
The air washer component incorporates a simplified adiabatic evaporative cooler with On/Off control. It is characterized by three important parameters: etaAir, representing the air side saturation efficiency; PressDrop, indicating the air pressure drop through the air washer; and TSet, defining the leaving air set point temperature.
The cooler is characterized by the saturation efficiency (etaAir). In the psychrometric chart, the leaving air state is located along a straight line between the entering air state and a point on the saturation curve. This point, defined as the inlet air wet-bulb temperature (Tmin), is determined based on the saturation efficiency.
A temperature setpoint signal determines the leaving air dry bulb temperature within a control band defined by the entering air temperature TAirIn and TAirIn - etaAir. (TAirIn - Twetbulb). The pressure drop through the air washer is determined by the PressDrop parameter. Additionally, the necessary makeup water mass flow rate, required for evaporative cooling inside the air washer, is calculated.
Variables such as outlet air temperature, the inlet air wet-bulb temperature, sensible cooling power of air washer, outlet air specific humidity and the necessary makeup water mass flow rate are shown in the form.
The air flow in the air washer is uni-directional, i.e. when using a air washer one has to make certain that the air flows in the right direction and use connection components from the Other library. A Bi2UniDir component is inserted before the cooling coil and a Uni2BiDir component after.
Road tunnel branch
Figure 15 A branch form
The mathematical model for the air flow in the branching component is valid for a wye consisting of a straight uniform section with a connected branch, with a possibly different cross section area. For a thorough description of the equations see section 2.1.8 of the Theoretical Reference.
The input parameter φ is the angle between branch, location 3, and location 1 of the straight section. The empirical model is derived for angles in the interval [45˚, 135˚].
The parameter r/D is the ratio of the radius of the rounding of the edge where the branch meets the main section, and the main diameter.
Any traffic flow cases occurring in a branch depend on the traffic directions (left to right, right to left, bidirectional or no traffic) allowed in the surrounding sections.
The situation when the traffic flow is split is described in terms of a main stream, not necessarily along the straight section of the branch, and an exit fraction (for each vehicle type and possibly time dependent) of exiting traffic. The exiting traffic stream is modelled with a queue model in the same way as at the tunnel entry. Possible queues of exiting traffic do not affect the main stream.
The situation when two traffic streams are joined into one stream is modelled such that the smallest of the incoming traffic flows reduces the capacity of the outgoing stream. This is a symmetric model as opposed to the splitting model.
The traffic models are described in Section .
Recirculation (Road tunnel)
Figure 16. An air recirculation form
This model takes care of the situation where two tunnel entries are so close that air flowing out of one tunnel can recirculate into the other. The model has two parameters (part1_2 and part2_1) specifying the maximum percentage flowing from each entry to the other.
For a thorough description of the equations see section 2.1.7 of the Theoretical Reference.
Plenum with portals (Road tunnel)
Figure 17. A plenum form
Air in a plenum is assumed to be well mixed, so conditions are mainly described by scalar variables, e.g. air temperature, pressure, wall temperature and air fractions. The plenum component does not allow traffic through it and is predominantly used as a pressure chamber for parallel fans.
Note that the z-coordinate (height) at the neighbouring end of the tunnel sections/ventilation shafts sections has to fall between floor level (hFloor) and floor level plus height of plenum.
The surrounding wall is specified in the same way as in the section model. See Section .
In sections 2.1.4 and 2.2.3 of the Theoretical Reference the mathematical models for mass and heat balance are presented.
The connection of the plenum to tunnel sections should be done via portal components (by default sharp-edged). This is already prepared in the Side bar component library. To copy a plenum with two portals from the Side bar place the cursor e.g. above and left of the left portal, click, hold and drag the cursor diagonally down to the right and below the right portal and release the left button when the dashed frame encloses the set of components. Then drag the components into the system form. (Pre-connected groups of components may always be dragged between open systems without severing internal connections.)
When more than two tunnel sections are connected to a plenum extra portals are needed. When connecting the extra portal between the plenum and the tunnel section the Connect dialog Figure 5 .24 is shown.
Figure 18. The connect dialog
To confirm that the opening interface of the portal is to be connected to tunnel interface 3 of the plenum press the OK button.
Figure 19. A portal form
Loss coefficients determine the viscous losses of entering or exiting air. The given default values are valid for a sharp-edged portal
In section 2.1.4 of the Theoretical Reference the mathematical model for air flow is presented.