Precise control of temperature, humidity, and ventilation is essential to ensure the performance and efficiency of paint booths. In addition to traditional climate control systems, advanced technologies now exist that allow for optimizing the internal environment and reducing energy consumption without compromising process quality.

In this article, we focus on three solutions that take environmental control to another level: adiabatic humidification , evaporative cooling , and heat recovery . When integrated into a well-tuned control logic, these technologies can improve the stability of operating conditions and generate significant savings, especially in intensive industrial environments.

In this second part, I analyze in more detail adiabatic humidification , evaporative cooling , and heat recovery , explaining how their correct integration into the control logic can generate significant energy savings without compromising process quality.

Adiabatic humidification

Adiabatic humidification reduces air temperature, meaning that temperature and humidity control needs to consider the relationship between these two variables. To maintain the desired temperature in the paint booth, as the amount of moisture transferred to the airflow increases, preheating also needs to be adjusted.

To limit temperature fluctuations caused by humidification, the most effective control method is based on absolute humidity (the amount of water vapor per kg of dry air). Unlike relative humidity, absolute humidity does not vary with temperature .

Furthermore, the control must consider that the effectiveness of humidification depends on the conditions of the incoming air. Cold air does not have enough energy to evaporate and absorb water, requiring the use of large quantities of water to generate small amounts of humidity.

Therefore, the air needs to be preheated, not only to compensate for the temperature drop, but also to ensure a high absorption capacity. A typical system uses a temperature probe after the heating coil (“saturation probe”), which ensures that the air reaches the ideal temperature before humidification.

In medium evaporative systems, additional heating downstream of the humidification process may be necessary due to the inertia of the evaporative matrix, in order to avoid temperature fluctuations.

The use of variable-speed adiabatic atomizers allows for very precise control of conditions after the humidifier, based on readings of the saturation temperature or, even more effectively, on measuring the temperature and humidity after the preheating coil, adjusting the system to achieve the desired enthalpy.

Example of enthalpy-based preheating control with preheating only.

With modulating actuators and the controller correctly configured, preheating can be regulated based on the temperature probe after the humidifier: a greater need for humidification generates a temperature drop that the heating must compensate for.

However, the response speed of the devices is crucial. If the coil valve takes two minutes to complete its cycle, but the humidifier responds in seconds, there will be a sudden increase in relative humidity and a drop in temperature before the heating can react. In this case, it is essential to correctly adjust the PID values, using a smaller proportional constant for the humidifier and adjusting the integral to ensure stability.

Evaporative cooling

Direct evaporative cooling (DEC) can be applied to the paint booth's inlet air, provided that the relative humidity does not exceed the process limit , typically around 80% RH.

The control system uses a temperature probe, along with a humidity limit probe, to prevent excessive values ​​that could cause condensation in the ducts or paint defects. With modulating humidifiers, the operation adjusts to cooling needs and humidity limits.

It is essential to ensure that the cooling device does not dehumidify the air —otherwise, the energy used for humidification would be wasted. Whenever dehumidification occurs, evaporative cooling should be stopped.

In temperate climates, where latent loads are significant, evaporative cooling can be advantageous, raising humidity to the acceptable limit and benefiting from "free cooling".

It can also be used to cool the exhaust air entering the heat recovery unit, reducing the temperature of the blown air without altering the humidity — a process known as indirect evaporative cooling (IEC) .

(Adiabatic humidification and evaporative cooling system (DEC + IEC) with a single pumping station)

Heat recovery

Different heat recovery technologies vary in their modulation capabilities and the type of heat recovered (sensible or sensible + latent).

From a control standpoint, a recovery unit behaves like a heating or cooling device, and can also dehumidify. Control is achieved through ON/OFF or modulating outputs, which operate bypass dampers, control the rotation of thermal wheels, or adjust the fluid flow rate in a recirculation coil.

The activation of heat recovery is typically based on the temperature difference between the outside air and the extracted air . If this difference is low, the recovered energy may not compensate for the energy expended by the fans to overcome the additional pressure drop in the exchanger. In such cases, it is more efficient to divert the air through the bypass.

Typically, the minimum temperature difference to activate heat recovery is between 1°C and 2°C .

The bypass is especially useful in winter, when ice and condensation can form on the heat exchangers. Warm cabin air helps melt the ice when diverted through the unit.

Additional probes — for temperature, humidity, or differential pressure — allow for more precise control strategies, depending on the available inputs.

Thermal wheels

Thermal wheels require additional functions, usually managed by a dedicated controller, including:

• Rotation check (detect belt faults),

• defrosting functions,

• Periodic rotation while inactive , to prevent deformation from remaining in the same position.

Heat recovery with indirect evaporative cooling

When indirect evaporative cooling is used, the activation threshold for heat recovery may be different. Conditions that were previously not economically advantageous can become efficient when combined with evaporative cooling.

The decision to activate heat recovery and evaporative cooling should consider several cost-benefit factors, especially energy and water costs .