.. _sec_H_surge_tower:

Surge tower
------------------------

.. _fig_heat_surge_tower:
.. figure:: ../media/heat/image1255.svg
   :width: 100in
   :align: center

   Schematic of a Heat Surge tower.



**Supplier type**

+-----------------+----------------------------------------------------------------------------------------------+--------+
| Type label      | Description                                                                                  | Active |
+=================+==============================================================================================+========+
| Heat Surgetower | Thermally isolated surge tower. Storage area is independent of liquid height (pressure head) | No     |
+-----------------+----------------------------------------------------------------------------------------------+--------+

.. _mathematical-model-60:

Mathematical model
^^^^^^^^^^^^^^^^^^

A surge tower or shaft or open tank (atmospheric pressure at fluid level) supplies fluid to the system according to the differential equation:

.. math::

  Q=-A_{tw} \frac{dH}{dt}

with:


============================= ====================================================================== =======================
Variable                      Description                                                            Units
============================= ====================================================================== =======================
:math:`Q`                     Discharge from the tower to the system                                 m\ :sup:`3`/s
:math:`A_w`                   Storage surface of the tower                                           m\ :sup:`2`
:math:`H`                     Fluid level in the tower                                               m
============================= ====================================================================== =======================

In steady-state the surge tower does not supply fluid:

.. math::

  Q=0

The temperature in the surge tower is modelled as instantaneously mixed. 
Therefore, the temperature at the connecting node (Temperature 1) can change instantaneously when the flow will reverse from direction. 
The bottom level needs to be defined to correctly calculate the tank temperature when fluid is supplied to the tank. 
The heat transfer between the fluid inside the tank and the air outside the taken is not taken into account (i.e., isolated tank).

Using an energy balance for the surge tower, the change of temperature can be expressed as:

.. math::
   :label: eq_energy_surge

    \begin{cases}
        \rho c_p T \frac{dV}{dt} = \dot{m} c_p T_{in}, & \text{if } \dot{m} < 0 \\
        \frac{dT}{dt} = 0, & \text{if } \dot{m} \geq 0  
    \end{cases}

.. _surge-tower-properties-1:

Surge tower properties
^^^^^^^^^^^^^^^^^^^^^^

.. _hydraulic-specifications-69:

Hydraulic specifications
""""""""""""""""""""""""

=================== ===== ============= =======
Description         Input SI-units      Remarks
=================== ===== ============= =======
Bottom level        real  m           
Tank area           real  m\ :sup:`2`
Temperature at t=0s real  °C          
=================== ===== ============= =======

.. _component-specific-output-63:

Component specific output
"""""""""""""""""""""""""

Fluid level [m]

Tank temperature [°C]

.. _component-messages-60:

Component messages
""""""""""""""""""

+-------------------------------------------------+---------+-------------------------------------------------------+
| Message                                         | Type    | Explanation                                           |
+=================================================+=========+=======================================================+
| Initial fluid level below bottom of surge tower | Warning | The fluid level is below the bottom level, initially. |
+-------------------------------------------------+---------+-------------------------------------------------------+
| Surge tower empty                               | Warning | The fluid level is below the bottom level,            |
+-------------------------------------------------+---------+-------------------------------------------------------+