Dry Cooler

Create Controlled Function

pandaprosumer.create_controlled_dry_cooler(prosumer, n_nom_rpm, p_fan_nom_kw, qair_nom_m3_per_h, t_air_in_nom_c=15, t_air_out_nom_c=35, t_fluid_in_nom_c=65, t_fluid_out_nom_c=40, fans_number=1, adiabatic_mode=False, phi_adiabatic_sat_percent=99, min_delta_t_air_c=0, name=None, index=None, in_service=True, period=0, level=0, order=0, **kwargs)[source]

Creates a dry cooler element in prosumer[“dry_cooler”] and a dry cooler controller

INPUT:

prosumer - The prosumer within this dry_cooler should be created

n_nom_rpm (float) - Nominal rotational speed of the fans [rpm]

p_fan_nom_kw (float) - Nominal electric power of each fan [kW]

qair_nom_m3_per_h (float) - Nominal air flow [m3/h]

t_air_in_nom_c (float, default 15) - Air nominal input temperature [C]

t_air_out_nom_c (float, default 35) - Air nominal output temperature [C]

t_fluid_in_nom_c (float, default 60) - Water nominal input temperature [C]

t_fluid_out_nom_c (float, default 40) - Water nominal output temperature [C]

OPTIONAL:

fans_number (integer, default 1) - Number of fans in the dry cooler

adiabatic_mode (boolean, default False) - Whether to use the air adiabatic pre-cooling mode.: If False, apply dry cooling only

phi_adiabatic_sat_percent (float, default 99) - Adiabatic Pre-Cooling saturation level [%]

min_delta_t_air_c (float, default 0) - Minimum air temperature difference [C]

name (string, default None) - The name for this dry cooler

index (int, default None) - Force a specified ID if it is available. If None, the index one higher than the highest already existing index is selected.

in_service (boolean, default True) - True for in_service or False for out of service

level (int, default 0) - The level of the controller

order (int, default 0) - The order of the controller

period (int, default 0) - Index of the period, default is 0

OUTPUT:

index (int) - The unique ID of the created dry cooler

EXAMPLE:

create_controlled_dry_cooler(prosumer, “dry_cooler_1”)

Controller

Input Static Data

Parameter	Description	Unit
name	A custom name for this heat pump	N/A
n_nom_rpm	Nominal rotational speed of the fans	rpm
p_fan_nom_kw	Nominal electric power of each fan	kw
qair_nom_m3_per_h	Nominal air flow	m3/h
t_air_in_nom_c	Air nominal input temperature	Degree Celsius
t_air_out_nom_c	Air nominal output temperature	Degree Celsius
t_fluid_in_nom_c	Water nominal input temperature	Degree Celsius
t_fluid_out_nom_c	Water nominal output temperature	Degree Celsius
fans_number	Number of fans in the dry cooler	int
adiabatic_mode	Whether to use the air adiabatic pre-cooling	boolean
phi_adiabatic_sat_percent	Adiabatic Pre-Cooling saturation level	%
min_delta_t_air_c	Minimum air temperature difference	Degree Celsius

Input Time Series

Parameter	Description	Unit
mdot_fluid_kg_per_s	Water required mass flow rate	kg/s
t_in_c	Water input required temperature	Degree Celsius
t_out_c	Water output expected temperature	Degree Celsius
t_air_in_c	Input dry bulb temperature of the ambient air	Degree Celsius
phi_air_in_percent	Input relative humidity of the ambient air.	Degree Celsius

Output Time Series

Parameter	Description	Unit
q_exchanged_kw	Extracted heat power	kW
p_fans_kw	Electrical power consumed by the fans	kW
n_rpm	Fans rotational speed	rpm
mdot_air_m3_per_h	Air mass flow through the cooler	m3/h

Mapping

The Dry Cooler Controller can be mapped using FluidMixMapping.

The dry cooler can be used as responder for a FluidMix mapping, taking the output from another controller as its input
No output are mapped, as the dry cooler does not act as an initiator.

Model

class pandaprosumer.controller.models.DryCoolerController(prosumer, dry_cooler_object, order=-1, level=-1, in_service=True, index=None, name=None, **kwargs)[source]

Controller for dry coolers.

First implementation of the dry cooler that do not model the heat exchange between the water the air

Parameters:

prosumer – The prosumer object
dry_cooler_object – The heat pump object
order – The order of the controller
level – The level of the controller
in_service – The in-service status of the controller
index – The index of the controller
kwargs – Additional keyword arguments

control_step(prosumer)[source]

Executes the control step for the controller.

Parameters:: prosumer – The prosumer object

The dry cooler model is based on a combination of the heat demand controller and of the heat_exchanger_element.

The dry cooler is a heat exchanger that uses air to cool down a fluid.

On the secondary side, the cooling demand is given from the input \(Q\), \(\dot{m}\), \(T_\text{feed}\) and \(T_\text{return}\) that may come from a timeseries data through a ConstProfile controller.

The ambient air temperature on the primary side is also an input that may be mapped from timeseries data.

Schematic representation of a dry cooler — Schematic representation of an air-cooled heat exchanger (source: [RTH23])

The heat exchanger will then calculate the air flow rate needed to cool down the fluid to the desired temperature. This air flow rate will be used to calculate the power consumption of the fans of the dry cooler, who are needed to apply a forced convection on the air and ensure cooling. The power consumption of the fans is assumed to be proportional to the air flow rate.

The air mass flow rate is calculated similarly to the heat exchanger model based on the logarithmic mean temperature difference (LMTD) calculation. However as known temperature is the cold input air temperature, the model is adapted.

The equation to solve is in this case:

\begin{align*} a * X - \ln{(1+X)} &= 0 \\ \end{align*}

With

\begin{align*} a &= \Delta T_\text{cold} * \frac{Q_{r_n}}{Q_r} * \frac{1}{LMTD_n} \\ X &= \frac{\Delta T_\text{hot}}{\Delta T_\text{cold}} - 1 \end{align*}

This equation is solved by dichotomy to find \(X\), then \(\Delta T_\text{hot}\), then \(T_{\text{air}_\text{out}}\).

Assuming no heat losses, we then derive \(\dot{m}_\text{air}\) given that

\begin{align*} Q_r = Q_\text{air} = Q_\text{water} = \dot{m}_\text{air} * Cp_\text{air} * \Delta T_\text{air} = \dot{m}_\text{water} * Cp_\text{water} * \Delta T_\text{water} \end{align*}

Note

\(a = 1\) means that \(X = 0\) so \(\Delta T_\text{hot} = \Delta T_\text{cold}\)

\(0 < a < 1\) means that \(X > 0\) so \(\Delta T_\text{hot} > \Delta T_\text{cold}\)

\(a > 1\) means that \(-1 < X < 0\) so \(\Delta T_\text{hot} < \Delta T_\text{cold}\)

Note

\(X < -1\) would mean \(\Delta T_\text{hot} < 0\), so \(T_{2_\text{out}} > T_{1_\text{in}}\), which is not possible for the heat exchange

\(a << 1\) would mean \(\Delta T_\text{hot} >> \Delta T_\text{cold}\), so \(T_{2_\text{out}} < T_{2_\text{in}}\) which is not possible for a countercurrent flows

The power consumption of the fans is then calculated from the “Fan Affinity Laws”:

With impeller diameter \(D\) constant, the power consumption of the fans is proportional to the cube of the air flow rate, which is proportional to the shaft speed:

\begin{align*} \frac{Q_{\text{fan}_n}}{Q_{\text{fan}}} &= \left(\frac{\dot{m}_\text{air}}{\dot{m}_{\text{air}_n}}\right) \\ \frac{P_{\text{fan}_n}}{P_{\text{fan}}} &= \left(\frac{\dot{m}_\text{air}}{\dot{m}_{\text{air}_n}}\right)^3 \\ P_\text{fan} &= \frac{P_{\text{fan}_n} * \dot{m}_\text{air}^3}{\dot{m}_{\text{air}_n}^3} \\ \end{align*}

Schematic representation of an adiabatic cooler system and process (source: [RTH23])

The adiabatic feature consists in spraying water on the air to cool it down and increase the efficiency of the dry cooler.

For a given input air dry bulb temperature \(T_{db}\) and relative humidity \(\phi\), the wet bulb temperature \(T_{wb}\) can be calculated using the formula from [RTH23]:

\begin{align*} T_\text{wb} &= T_\text{db} * \arctan{(0.151977 * (\phi + 8.313659)^{0.5})} \\ &+ \arctan{(T_{db} + \phi)} - \arctan{(\phi - 1.676331)} \\ &+ 0.00391838 * \phi^{3/2} * \arctan{(0.023101 \phi)} - 4.686035 \\ \end{align*}

with temperature in °C and in % as input arguments.

We assume that the air is saturated with water at the wet bulb temperature after going through the adiabatic pre-cooling system when it is activated, and that the air is then cooled down to this temperature.