The Component Hybrid Cooling Tower
The Hybrid Cooling Tower component represents a general model for providing cooling by a cooling tower that works with the cooling media air and water and performs both convection and evaporation.
Component Template
The Component template Hybrid_Cooling_Tower.e-ctpl is located in the Component templates folder Cooling Supply.
Integration Into a Scheme
The following figure shows the Case 2 of the Tutorials 15 as an example of the integration of the component Hybrid Cooling Tower into a scheme.
How the Component Works
The Hybrid Cooling Tower component represents the removal of heat from another process by convection in the dry section of the cooling tower, evaporation of water in the wet section of the cooling tower, or a combination of both processes. The coolants are water and air.
The wet section forms an open recirculating cooling system in which most of the thermal energy is transferred to the air by evaporation of the water. Due to evaporation, water must be added regularly.
The same principles apply to the economic data as for the wet cooling tower.
Technical Input Data
The following Design parameters must be specified in the Technical input data (see following figure):
Select one of the two types of the Hybrid cooling tower:
- Parallel and forced air mass flow:
For the air induction in the wet and dry sections, there is one fan or a group of fans each (see following figure).
These must be parameterized independently of each other and can have different capacities and efficiencies.
Enter the Rated power of the fan for both parts separately:
\( P_{el\ fan\ dry\ nominal} \) for the dry part and
\( P_{el\ fan\ wet\ nominal} \) for the wet part.
- Parallel and induced air mass flow:
There is only one fan or a group of fans to draw air into both parts of the cooling tower (see figure below).
The various supply air flows are controlled by valves. The ratio between wet and dry cooling air is therefore not constant.
For water and air, the same information shall be provided as for the Wet Cooling Tower.
Part Load Behavior
The Part Load Behavior can be specified by the Constant efficiency in part-load (proportional electrical power consumption) or Characteristic curves (relative to nominal point) as with the Wet Cooling Tower. There is a difference between the two types of the Hybrid Cooling Tower.
Parallel and Induced Air Mass Flow
The following equations show the relationship between the flow rates and the electrical power consumption when selecting Constant efficiency in part-load (proportional electrical power consumption):
\( \begin{equation} \begin{aligned} \frac{ \dot{V}_{air\ dry}+\dot{V}_{air\ wet}} {\dot{V}_{air\ dry\ max}+\dot{V}_{air\ wet\ max}} = \frac{P_{el\ fan}} {P_{el\ fan\ nominal}} \end{aligned}\end{equation}\),
\( \begin{equation} \begin{aligned} \frac{ \dot{V}_{H_{2}O}} {\dot{V}_{H_{2}O\ nominal}} = \frac{P_{el\ pump}} {P_{el\ pump\ nominal}} \end{aligned}\end{equation}\).
When selecting Enter characteristic curve (relative to nominal point), two characteristic curves must be entered.
The first characteristic curve \( f_{el\ fan\ rel} \) establishes the relationship between the volume flow of air \( \dot{V}_{air} \) and the electrical power of the respective fan \( P_{el\ fan} \) (see following figure).
The second characteristic curve \( f_{el\ pump\ rel} \) shows the relationship between the volume flow of the cooling water \( \dot{V}_{H_{2}O} \) and the electrical power of the pump \( P_{el\ pump} \) (see following figure).
The same formulas as for the Wet Cooling Tower are used to calculate the part load behavior:
\( \begin{equation} \begin{aligned} f_{el\ fan\ rel} \left ( \frac{ \dot{V}_{air}} {\dot{V}_{air\ max}} \right) = \frac{P_{el\ fan}} {P_{el\ fan\ nominal}} \end{aligned}\end{equation} \),
\( \begin{equation} \begin{aligned} f_{el\ pump\ rel} \left ( \frac{ \dot{V}_{H_{2}O}} {\dot{V}_{H_{2}O\ nominal}} \right) = \frac{P_{el\ pump}} {P_{el\ pump\ nominal}} \end{aligned}\end{equation} \).
Parallel and Forced Air Mass Flow
For this type of cooling tower design, the Rated power of the fan shall be given for both the wet and dry sections of the cooling tower.
The following equations show the relationship between the mass flows and the electrical power consumption when selecting Constant efficiency in part-load (proportional electrical power consumption):
\( \begin{equation} \begin{aligned} \frac{ \dot{V}_{air\ dry}} {\dot{V}_{air\ dry\ max}} = \frac{P_{el\ fan\ dry}} {P_{el\ fan\ dry\ nominal}} \end{aligned}\end{equation}\),
\( \begin{equation} \begin{aligned} \frac{ \dot{V}_{air\ wet}} {\dot{V}_{air\ wet\ max}} = \frac{P_{el\ fan\ wet}} {P_{el\ fan\ wet\ nominal}} \end{aligned}\end{equation}\),
\( \begin{equation} \begin{aligned} \frac{ \dot{V}_{H_{2}O}} {\dot{V}_{H_{2}O\ nominal}} = \frac{P_{el\ pump}} {P_{el\ pump\ nominal}} \end{aligned}\end{equation}\).
When selecting Enter characteristic curve (relative to nominal point), three characteristic curves must be entered.
The first characteristic curve \( f_{el\ fan\ dry\ rel} \) establishes the relationship between the volume flow of air in the dry section \( \dot{V}_{air\ dry} \) and the electrical power of the fan in the dry section \( P_{el\ fan\ dry} \) (see following figure).
The second characteristic curve \( f_{el\ fan\ wet\ rel} \) shows the relationship between the volume flow of the air in the wet section \( \dot{V}_{air\ wet} \) and the electrical power of the fan in the wet section \( P_{el\ fan\ wet} \) (see following figure).
The third characteristic curve \( f_{el\ pump\ rel} \) shows the relationship between the volume flow of the cooling water \( \dot{V}_{H_{2}O} \) and the electrical power of the pump \( P_{el\ pump} \) (see previous figure).
The following formulas are used to calculate the part load behavior:
\( \begin{equation} \begin{aligned} f_{el\ fan\ dry\ rel} \left ( \frac{ \dot{V}_{air\ dry}} {\dot{V}_{air\ dry\ max}} \right) = \frac{P_{el\ fan\ dry}} {P_{el\ fan\ dry\ nominal}} \end{aligned}\end{equation} \),
\( \begin{equation} \begin{aligned} f_{el\ fan\ wet\ rel} \left ( \frac{ \dot{V}_{air\ wet}} {\dot{V}_{air\ wet\ max}} \right) = \frac{P_{el\ fan\ wet}} {P_{el\ fan\ wet\ nominal}} \end{aligned}\end{equation} \),
\( \begin{equation} \begin{aligned} f_{el\ pump\ rel} \left ( \frac{ \dot{V}_{H_{2}O}} {\dot{V}_{H_{2}O\ nominal}} \right) = \frac{P_{el\ pump}} {P_{el\ pump\ nominal}} \end{aligned}\end{equation} \).
Technical Output Data
In the Technical output data, the Cooling portion of the dry part of the total cooling and the Cooling efficiency are displayed. Cooling efficiency indicates the ratio of actually emitted heat to potentially maximum dissipated heat. It is calculated with the following formula:
\( \begin{equation} \begin{aligned} \eta = \frac{ T_{coolant\ in} – T_{coolant\ out}} {T_{coolant\ in} – T_{wet\ bulb}} \end{aligned}\end{equation}\).
Several output data are separated into dry and wet sections, such as Nominal cooling capacity, Nominal air mass flow rate (both depending on the selection of Input data, see above), Full load hours, and Operating hours (see following figure).
In the section Electric power consumption, the total calculated electrical power consumption and its shares of the fan (divided into Dry and Wet section in case of forced draught) and the Pump is output. For the heat Transfer medium (water), the Range (difference between Coolant inlet temperature and Outlet temperature), the actual Coolant inlet temperature, and the actual Water and Air volume flow rates are output (see following figure).
Finally, the volume flow of the Makeup water and its parts (Evaporation loss water, Drift loss water, and Blow down water) and the State of the inlet air including Wet bulb temperature are displayed (see following figure).
