# Cooling Tower (TL-MA)

**Libraries:**

Simscape /
Fluids /
Heat Exchangers /
Thermal Liquid - Moist Air

## Description

The Cooling Tower (TL-MA) block models a cooling tower between moist air and a thermal liquid network. The block models sensible and latent heat transfer from the thermal liquid side to the moist air side based on an analogous effectiveness-NTU method for heat and water vapor mass transfer. The thermal liquid side represents the water in the tower while the moist air side represents the environmental air. The block is performance based rather than geometry based, which means that the block sizes the cooling tower to match the nominal operating conditions that you specify.

### Cooling Tower Geometry

Large HVAC systems use cooling towers to reject heat from water to the environment in applications where the amount of heat is too large for regular water-air heat exchangers to be practical. In a cooling tower, the hot water and air are in direct contact, which allows some of the water to evaporate into the air and cools the rest of the water by the evaporative cooling effect.

A cooling tower works by spreading and spraying hot water from the top of the tower over a large area to encourage it to evaporate into the air. Typically, there is a fill material underneath the spray nozzles with a large surface area that allows the water to form a thin film and spread out. The fill material increases the contact area between the water and the air for more evaporation. Because there is no heat source, the latent heat needed to turn liquid water into water vapor comes from the water itself. As a result, the water that did not evaporate cools. The cold water collects at the bottom of the cooling tower in a basin, and can be returned to the HVAC system.

You can use the **Flow arrangement** parameter to specify if the
cooling tower uses a cross flow or counter flow. This block only models direct-flow
cooling towers, which means the water is in direct contact with the air. The block
also only models mechanical-draft cooling towers, where a fan moves the air through
the cooling tower.

This figure shows a diagram of a counter-flow, direct-contact, induced mechanical-draft cooling tower.

This figure shows a diagram of a direct-contact, induced mechanical-draft cooling tower with two air entries.

### Heat Transfer and Evaporation Rate

The combined heat and water vapor mass transfer is

$${Q}_{combined}=\u03f5{Q}_{combined,max}=\u03f5{C}_{min}\left({\overline{h}}_{{s}_{T{L}_{in}}}-{\overline{h}}_{M{A}_{in}}\right),$$

where:

*Q*is the theoretically maximum combined heat and water vapor mass transfer, $${Q}_{combined,max}={C}_{min}\left({\overline{h}}_{{s}_{T{L}_{in}}}-{\overline{h}}_{M{A}_{in}}\right).$$_{combined,max}$$\overline{h}$$

is the enthalpy of the saturated moist air evaluated at the temperature of the inlet at the thermal liquid side._{sTLin}$$\overline{h}$$

is the mixture enthalpy of the moist air at the inlet._{MAin}*C*is the smaller capacity ratio between the moist air and thermal liquid._{min}

When **Flow arrangement** is ```
Counter
flow
```

, the effectiveness factor, *ε*, is

$$\u03f5=\frac{1-\text{exp}[-(1-CR)NTU]}{1-CR\text{exp}[-(1-CR)NTU]},$$

where *CR* is the capacity ratio and
*NTU* is the number of transfer units.

When **Flow arrangement** is ```
Cross
flow
```

, the block assumes that one fluid is mixed and the other is
unmixed. If the fluid with the lower value for *C* is
unmixed,

$$\u03f5=\frac{1-\text{exp}\left(-CR[1-\text{exp}(-NTU)]\right)}{CR}.$$

Typically, the moist air will have the lower value for *C*. If
the fluid with the lower value for *C* is mixed,

$$\u03f5=1-\mathrm{exp}\left[-\frac{1-\text{exp}(-CR\ast NTU)}{CR}\right].$$

The capacity ratio is

$$CR=\frac{{C}_{min}}{{C}_{max}}=\frac{\mathrm{min}\left\{{C}_{TL},{C}_{MA}\right\}}{\mathrm{max}\left\{{C}_{TL},{C}_{MA}\right\}}.$$

*C _{MA}* and

*C*are the capacity rates for the moist air and thermal liquid, respectively,

_{TL}$$\begin{array}{l}{\text{C}}_{TL}=\frac{{\dot{m}}_{TL}{c}_{{p}_{TL}}}{{\overline{c}}_{{s}_{TL}}}\\ {C}_{MA}={\dot{m}}_{a{g}_{MA}}\end{array}$$

where:

*ṁ*is the thermal liquid mass flow rate._{TL}*c*is the thermal liquid specific heat at constant pressure._{pTL}*ṁ*is the mass flow rate of the dry air and trace gas._{agMA}

The number of transfer units, *NTU*, is

$$\text{NTU=}\frac{{U}_{MA}A}{{C}_{min}{\overline{c}}_{{p}_{MA}}},$$

where:

*A*is the heat transfer surface area.*U*is the heat transfer conductance on the moist air side._{MA}$$\overline{c}$$

is the moist air specific heat at constant pressure._{pMA}

The combined heat and water vapor mass transfer,
*Q _{combined}*, accounts for the
sensible heat transfer, latent heat, and energy debit due to lost liquid,

$${\text{Q}}_{combined}=\text{Q+}\Delta {h}_{f{g}_{eff}}{\dot{m}}_{e}+{h}_{{l}_{eff}}{\dot{m}}_{e},$$

where:

*Q*is the sensible heat transfer between thermal liquid and moist air in the cooling tower. The block calculates this value with $${\text{Q=Q}}_{combined}-{h}_{{w}_{eff}}{\dot{m}}_{e}$$. This term represents the portion of the cooling due to the temperature difference between the thermal liquid and moist air.*Δh*is the water vapor specific enthalpy of vaporization. When multiplied by_{fgeff}*ṁ*, this term gives the latent heat transfer between the thermal liquid and moist air in the cooling tower. This term represents the portion of the cooling due to the energy extracted from the liquid water when converted into water vapor._{e}*h*is the liquid water specific enthalpy. When multiplied by_{leff}*ṁ*, this term gives the energy debited from the energy balance of the thermal liquid flow due to the removal of a portion of the liquid._{e}

The evaporation rate in the cooling tower is

$${\dot{m}}_{e}={C}_{min}\left({W}_{{s}_{eff}}-{W}_{M{A}_{in}}\right)\left[1-\mathrm{exp}\left(-NTU\right)\right],$$

where:

*W*is the effective saturated humidity ratio._{seff}*W*is the humidity ratio at the moist air inlet._{MAin}

The effective saturated humidity ratio is

$${W}_{{s}_{eff}}=\frac{{R}_{a}+G\left({R}_{g}-{R}_{a}\right)}{{R}_{w}\left(\frac{p}{{\phi}_{ws}{p}_{ws}\left({T}_{eff}\right)}-1\right)},$$

where:

*R*is the specific gas constant of dry air._{a}*G*is the trace gas ratio.*R*is the specific gas constant of the trace gas._{g}*R*is the specific gas constant of the water vapor._{W}*p*is the pressure.*φ*is the value of the_{ws}**Relative humidity at saturation**parameter.*p*is the water vapor saturation pressure evaluated at the effective liquid film surface temperature._{ws}(T_{eff})

The effective liquid film surface temperature is

$${T}_{eff}={T}_{T{L}_{in}}-\frac{{\overline{h}}_{{s}_{T{L}_{in}}}-{\overline{h}}_{{s}_{eff}}}{{\overline{c}}_{{s}_{TL}}},$$

where:

*T*is the temperature of the thermal liquid at the inlet._{TLin}$$\overline{c}$$

is the specific heat of the saturated moist air along the saturation curve when evaluated at the temperature of the thermal liquid._{sTL}$$\overline{h}$$

is the saturated mixture enthalpy along the liquid film surface_{seff}$${\overline{h}}_{{s}_{eff}}={\overline{h}}_{M{A}_{in}}+\frac{\u03f5\left({\overline{h}}_{{s}_{T{L}_{in}}}-{\overline{h}}_{M{A}_{in}}\right)}{1-\mathrm{exp}\left(-NTU\right)}.$$

The heat transfer conductance at the moist air side,
*U _{MA}A*, is

$${U}_{MA}A=\mathrm{max}\left\{{\left(\frac{{\dot{m}}_{MA}}{{\mu}_{MA}}\right)}^{b}{\mathrm{Pr}}_{MA}^{c}k{\left(\frac{{D}_{ref}}{{S}_{ref}}\right)}^{b}a,N{u}_{lam}{k}_{MA}\right\}{G}_{fill},$$

where:

*U*is the heat transfer coefficient._{MA}*ṁ*is the moist air mass flow rate._{MA}*μ*is the moist air dynamic viscosity._{MA}*a*is the coefficient for the proportionality in the Nusselt number correlation.*b*is the coefficient for the Reynolds number exponent in the Nusselt number correlation.*c*is the coefficient for the Prandtl number exponent in the Nusselt number correlation.*Pr*is the moist air Prandtl number._{MA}*k*is the thermal conductivity of the moist air._{MA}*D*is an arbitrary diameter. The block uses this value with_{ref}*S*to nondimensionalize with respect to length._{ref}*S*is the flow area corresponding to_{ref}*D*._{ref}*Nu*is 3.66, which is the theoretical Nusselt number for a laminar flow through a circular pipe._{lam}*G*is the geometry scale factor for the cooling tower fill material. The block calculates this value at nominal operating conditions._{fill}

### Cooling Tower Sizing

The block sizes the cooling tower to match the nominal performance at nominal
operating conditions. On the thermal liquid side, the **Nominal capacity
specification** parameter specifies how the block determines the
nominal data:

`Water mass flow rate`

or`Water volumetric flow rate`

— The block infers the nominal capacity from the nominal flow rate and the nominal inlet and outlet temperatures.`Rate of cooling in cooling tower`

or`Rate of cooling in evaporator`

— The block infers the nominal flow rate from the nominal capacity.

On the moist air side, the nominal data depends on the **Specify full
moist air nominal conditions** parameter.

If you clear the **Specify full moist air nominal conditions**
check box, the only nominal condition you specify is the value of the
**Nominal inlet wet-bulb temperature** parameter. Use this
option if your manufacturer datasheet provides only the nominal wet-bulb
temperature. The block calculates the other nominal conditions:

The block calculates the nominal inlet temperature based on the value of the

**Nominal inlet wet-bulb temperature**parameter so that the relative humidity is 50%.The block calculates the nominal flow rate from the nominal water flow rate so that the capacity ratio at nominal operating condition is

`1`

.

The block assumes that the nominal inlet pressure is atmospheric and that there is no nominal trace gas..

If you select **Specify full moist air nominal conditions**, you
must specify the nominal inlet pressure, nominal inlet temperature, nominal inlet
humidity level, and nominal inlet trace gas level.

The block uses nominal operating conditions to solve for the geometry scale factor
for the cooling tower fill material,
*G _{fill}*. This value describes the size of
the cooling tower. The block inverts the expression for the heat transfer
conductance of the moist air side,

*U*, and calculates

_{MA}A*G*from the heat transfer conductance at nominal operating conditions. The block then uses

_{fill}*G*to calculate the heat transfer conductance on the moist air side at actual operating conditions during simulation. The block does not model convective heat transfer in the thermal liquid film.

_{fill}*G _{fill}* at nominal operating conditions is

$${G}_{fill}=\frac{{\left({U}_{MA}A\right)}_{nom}}{{\left(\frac{{\dot{m}}_{M{A}_{nom}}}{{\mu}_{M{A}_{nom}}}\right)}^{b}{\mathrm{Pr}}_{M{A}_{nom}}^{c}{k}_{M{A}_{nom}}{\left(\frac{{D}_{ref}}{{S}_{ref}}\right)}^{b}a},$$

where the subscript *nom* denotes the variable
value at the specified nominal operating condition.

The block solves for
*(U _{MA}A)_{nom}*
with

$${\left({U}_{MA}A\right)}_{nom}={C}_{mi{n}_{nom}}{\overline{c}}_{{p}_{MA,nom}}NT{U}_{nom}.$$

The block calculates
*NTU _{nom}* by inverting the applicable
effectiveness equation.

When **Flow arrangement** is ```
Counter
flow
```

,

$$NT{U}_{nom}=\frac{1}{1-C{R}_{nom}}\mathrm{ln}\left(\frac{1-{\u03f5}_{nom}C{R}_{nom}}{1-{\u03f5}_{nom}}\right),$$

where *CR _{nom}* is the
capacity ratio and $${\u03f5}_{nom}=\frac{{Q}_{combine{d}_{nom}}}{{Q}_{combined,ma{x}_{nom}}}$$ with

*Q*,

_{combined}*Q*, and

_{combined,max}*CR*evaluated at the nominal operating conditions.

_{nom}When **Flow arrangement** is ```
Cross
flow
```

and the fluid with the lower value for *C*
is mixed

$$NT{U}_{nom}=-\frac{\mathrm{ln}\left[1+C{R}_{nom}\mathrm{ln}\left(1-{\u03f5}_{nom}\right)\right]}{C{R}_{nom}}.$$

If the fluid with the lower value for *C* is unmixed,

$$NT{U}_{nom}=-\mathrm{ln}\left[1+\frac{\mathrm{ln}\left(1-{\u03f5}_{nom}C{R}_{nom}\right)}{C{R}_{nom}}\right].$$

### Thermal Liquid Equations

The pressure of the thermal liquid when it enters the cooling tower at port
**A1** is

$${p}_{T{L}_{A1}}={p}_{MA},$$

where *p _{MA}* is the moist
air pressure inside the cooling tower. Because the block assumes that water loss due
to evaporation is small, the thermal liquid mass flow rate is equal to the port

**A1**inflow rate, $${\dot{m}}_{TL}={\dot{m}}_{T{L}_{A1}}$$.

The steady state mass balance equation for the thermal liquid is

$${\dot{m}}_{T{L}_{A1}}-{\dot{m}}_{e}-\lambda {\dot{m}}_{T{L}_{A1}}={\dot{m}}_{T{L}_{fill,out}},$$

where:

*λ*is the value of the**Drift rate as fraction of water flow**parameter. The drift accounts for liquid droplets that blow out of the cooling tower without evaporating.*ṁ*is the mass flow rate of the thermal liquid at the exit point of the fill material._{TLfill,out}

The steady state mass balance equation for the thermal liquid is

$${\Phi}_{T{L}_{A1}}-{Q}_{combined}-\lambda {\Phi}_{T{L}_{A1}}={\Phi}_{T{L}_{fill,out}},$$

where:

*Φ*is the energy flow rate at port_{TLA1}**A1**.*Φ*is the energy flow rate out of the fill material._{TLfill,out}

If you select **Model cold-water basin**, the block models an
internal tank with the tank outlet at the bottom of the tank. Because the water in
the tank must be replenished, the thermal liquid mass and energy conservation
equations have two additional source terms,
*ṁ _{TLmakeup}*
and

*Φ*.

_{TLmakeup}When you select **Automatically replenish lost water**,

$$\begin{array}{l}{\dot{m}}_{T{L}_{makeup}}={\dot{m}}_{e}+\lambda {\dot{m}}_{T{L}_{A1}}\\ {\Phi}_{T{L}_{makeup}}={\dot{m}}_{T{L}_{makeup}}{h}_{T{L}_{makeup}}\end{array}$$

where *h _{TLmakeup}*
is the thermal liquid specific enthalpy specified by the

**Temperature of make-up water**parameter.

If you clear the **Automatically replenish lost water** check
box, you can specify the volumetric flow rate and temperature of the tank make-up
water with ports **Vm** and **Tm**, respectively.
Port **L** outputs the liquid level in the basin. The make-up water
terms are

$$\begin{array}{l}{\dot{m}}_{T{L}_{makeup}}={\rho}_{TL}\left({p}_{MA},{T}_{mu}\right){V}_{mu}\\ {\Phi}_{T{L}_{makeup}}={\dot{m}}_{T{L}_{makeup}}{h}_{TL}\left({p}_{MA},{T}_{mu}\right)\end{array}$$

where:

*p*is the moist air pressure in the cooling tower._{MA}*T*is the temperature of the make-up water, which is the value of the signal at port_{mu}**Tm**.*ρ*is the thermal liquid density evaluated at the moist air pressure and make-up water temperature._{TL}(p_{MA},T_{mu})*h*is the thermal liquid specific enthalpy evaluated at the moist air pressure and make-up water temperature._{TL}(p_{MA},T_{mu})

If you select **Model cold-water basin**, the block models an
internal tank.
*ṁ _{TLfill,out}* and

*Φ*define the input flows of the internal tank. Port

_{TLA1}**B1**is the outlet of the internal tank.

If you clear the **Model cold-water basin** check box,

$$\begin{array}{l}{\dot{m}}_{T{L}_{B1}}=-{\dot{m}}_{T{L}_{fill,out}}\\ {\Phi}_{T{L}_{B1}}=-{\Phi}_{T{L}_{fill,out}}\end{array}$$

Port **B1** acts as a flow rate source for any downstream
components. Connect a Tank
(TL) block to port **B1** to model the cold
water basin. The **Inlet height** parameter of the
Tank (TL) block must be larger than the liquid
level in the tank.

### Moist Air Equations

The behavior of the moist air side of the block depends on the **Moist air
operating conditions** parameter.

**Physical Signals**

When you set **Moist air operating conditions** to
`Provided by input signals`

, the block enables
physical signal ports that you can use to specify the moist air attributes:

Port

**P**is the input signal for the moist air inlet pressure. The moist air pressure,*p*, is equal to the value of this signal._{MA}Port

**T**is the input signal for the moist air dry-bulb temperature.The flow rate input port depends on the

**Flow rate input signal specification**parameter:Value of **Flow rate input signal specification**Enabled Port Port Meaning `Mass flow rate`

**M**Moist air mixture mass flow rate `Volumetric flow rate`

**V**Moist air mixture volumetric flow rate `Fan power`

**Pwr**Moist air fan power The humidity level input port depends on the

**Humidity input signal specification**parameter:Value of **Humidity input signal specification**Enabled Port Port Meaning `Relative humidity`

**W**Moist air inlet relative humidity `Specific humidity`

**W**Moist air inlet specific humidity `Mole fraction`

**W**Moist air inlet water vapor mole fraction `Humidity ratio`

**W**Moist air inlet humidity ratio `Wet-bulb temperature`

**Tw**Moist air inlet wet-bulb temperature When

**Flow rate input signal specification**is`Mass flow rate`

or`Volumetric flow rate`

, the block uses the signal at port**M**or**V**to calculate the moist air mixture mass flow rate that enters the cooling tower,*ṁ*. The dry air and trace gas flow rate is_{MAin}$${\dot{m}}_{a{g}_{MA}}=\frac{{\dot{m}}_{M{A}_{in}}}{1+{W}_{M{A}_{in}}}.$$

The block calculates the humidity ratio,

*W*, from the input signals at ports_{MAin}**P**,**T**, and**W**or**Tw**.When

**Flow rate input signal specification**is`Fan power`

, the fan power,*Φ*, is proportional to the cube of the volumetric flow rate,_{fan}*q*, and pressure gain across the fan,*Δp*.The moist air mixture volumetric flow rate is

$${\text{q}}_{MA}={\left(\frac{Pwr}{{\Phi}_{fa{n}_{nom}}}\right)}^{1/3}{q}_{M{A}_{nom}},$$

where:

*Pwr*is the value of the signal at port**Pwr**.*Φ*is the value of the_{fannom}**Nominal fan power**parameter.*q*is the nominal volumetric flow rate. If you select_{MAnom}**Specify full moist air nominal condition**,*q*is the value of the_{MAnom}**Nominal moist air volumetric flow rate**parameter. If you clear**Specify full moist air nominal condition**, the block calculates*q*from the nominal water flow rate so that the capacity ratio is one._{MAnom}

When **Moist air operating conditions** is
`Provided by input signals`

, the block does not
model trace gas.

**Moist Air Domain Ports**

When you set **Moist air operating conditions** to
`Moist air domain ports`

, the block enables the
moist air ports **A2** and **B2**, which you
can connect to a moist air network. Because the direction of the moist air flow
does not matter in this block, either port **A2** or
**B2** can be the inlet. The dry air and trace gas flow
rate is

$${\dot{m}}_{a{g}_{MA}}=\frac{{\dot{m}}_{M{A}_{in}}}{1+{W}_{M{A}_{in}}},$$

where:

*ṁ*is the moist air mixture mass flow rate at port_{MAin}**A2**or**B2**.*W*is the moist air mixture humidity ratio at port_{MAin}**A2**or**B2**.

The moist air mixture mass conservation equation is

$$\frac{d{M}_{MA}}{dt}={\dot{m}}_{M{A}_{A2}}+{\dot{m}}_{M{A}_{B2}}+{\dot{m}}_{e},$$

where:

*ṁ*and_{MAA2}*ṁ*are the mass flow rates at ports_{MAB2}**A2**and**B2**.*M*is the total mixture mass of the moist air volume._{MA}

The water vapor mass conservation equation is

$${M}_{MA}\frac{d{x}_{{w}_{MA}}}{dt}+{x}_{{w}_{MA}}\left({\dot{m}}_{M{A}_{A2}}+{\dot{m}}_{M{A}_{B2}}+{\dot{m}}_{e}\right)={\dot{m}}_{{w}_{M{A}_{A2}}}+{\dot{m}}_{{w}_{M{A}_{B2}}}+{\dot{m}}_{e},$$

where
*x _{wMA}* is
the specific humidity of the moist air volume and

*ṁ*and

_{wMAA2}*ṁ*are the water vapor mass flow rates at ports

_{wMAB2}**A2**and

**B2**.

The trace gas mass conservation equation is

$${M}_{MA}\frac{d{x}_{{g}_{MA}}}{dt}+{x}_{{g}_{MA}}\left({\dot{m}}_{M{A}_{A2}}+{\dot{m}}_{M{A}_{B2}}+{\dot{m}}_{e}\right)={\dot{m}}_{{g}_{M{A}_{A2}}}+{\dot{m}}_{{g}_{M{A}_{B2}}},$$

where
*x _{gMA}* is
the trace gas mass fraction of the moist air volume and

*ṁ*and

_{gMAA2}*ṁ*are the trace gas mass flow rates at ports

_{gMAB2}**A2**and

**B2**.

The water droplet mass conservation equation is

$${\text{M}}_{MA}\frac{d{r}_{{d}_{MA}}}{dt}+{r}_{{d}_{MA}}\left({\dot{m}}_{M{A}_{A2}}+{\dot{m}}_{M{A}_{B2}}+{\dot{m}}_{e}\right)={\dot{m}}_{{d}_{M{A}_{A2}}}+{\dot{m}}_{{d}_{M{A}_{B2}}},$$

where:

*r*is the mass ratio of the water droplets to the moist air._{dMA}*ṁ*and_{dMAA2}*ṁ*are the water droplet mass flow rates at ports_{dMAB2}**A2**and**B2**.

The moist air mixture energy conservation equation is

$${M}_{MA}\frac{d{u}_{MA}}{dt}+{u}_{MA}\left({\dot{m}}_{M{A}_{A2}}+{\dot{m}}_{M{A}_{B2}}+{\dot{m}}_{e}\right)={\Phi}_{M{A}_{A2}}+{\Phi}_{M{A}_{B2}}+{Q}_{combined},$$

where *u _{MA}* is the
mixture specific internal energy of the moist air volume and

*Φ*and

_{MAA2}*Φ*are the moist air mixture energy flow rates at ports

_{MAB2}**A2**and

**B2**.

The pressure loss of the moist air in the cooling tower is

$$\Delta {p}_{MA}={\left(\frac{{q}_{MA}}{{q}_{M{A}_{nom}}}\right)}^{2}\Delta {p}_{M{A}_{nom}},$$

where:

*Δp*is the value of the_{MAnom}**Nominal moist air pressure loss**parameter.*q*is the value of the_{MAnom}**Nominal moist air volumetric flow rate**parameter.*q*is the volumetric flow rate of moist air through the cooling tower._{MA}

### Using the Cooling Tower in a Model

When using the Cooling Tower (TL-MA), follow these guidelines:

If you clear the

**Model cold-water basin**check box, you must connect the cooling tower port**B1**to a Tank (TL) block.When modeling transient situations such as startup or shutdown, connect the cooling tower port

**A1**to port**A**of a Partially Filled Pipe (TL) block to avoid a possible nonphysical situation of liquid flowing out of port**A1**. During startup and shutdown, port**A1**may be exposed to the environment, which means there is no liquid present. The partially-filled pipe handles this scenario by allowing the liquid level to fall along the pipe while port**A1**is exposed, if necessary.Some cooling towers may use a pressure source to force water out of the spray nozzles and spread the water over a wider area, which causes a pressure drop at the inlet. To model pressure drop through the spray nozzles, connect a block that models pressure loss, such as an Orifice (TL), Local Resistance (TL), or Flow Resistance (TL) block, to port

**A1**of the cooling tower.The Cooling Tower (TL-MA) block models a direct-contact cooling tower. To model an indirect-contact cooling tower, connect the thermal liquid side of the Cooling Tower (TL-MA) block to one side of a Heat Exchanger (TL-TL) block. In this configuration, the other side of the heat exchanger block represents the thermal liquid flowing into and out of the cooling tower, and the block models the heat transfer from the coil inside the cooling tower.

If you set

**Moist air operating conditions**to`Moist air domain ports`

, you can model a mechanical forced-draft or an induced-draft cooling tower. To model a forced-draft cooling tower, connect a Fan (MA) block to the moist air inlet side of the tower. To model an induced-draft cooling tower, connect a Fan (MA) block to the moist air outlet side. If you set**Moist air operating conditions**to`Provided by input signals`

, the block does not distinguish between forced-draft or induced-draft cooling towers.

### Assumptions and Limitations

The block only models a mechanical-draft cooling tower, which means a fan moves the moist air through the tower.

The block only models a direct-contact cooling tower, which means the thermal liquid is in direct contact with the moist air.

## Examples

## Ports

### Input

### Output

### Conserving

## Parameters

## References

[1] Mitchell JW, Braun JE.
*Principles of heating, ventilation, and air conditioning in
buildings*. Hoboken: Wiley, 2013.

[2] ASHRAE Standard Committee.
*2012 ASHRAE Handbook—HVAC Systems and Equipment (SI).*
2012.

[3] ASHRAE Standard Committee.
*2013 ASHRAE Handbook—Fundamentals (SI).* 2013.

## Extended Capabilities

## Version History

**Introduced in R2023b**