Published Date 02/11/17 08:00
This is the third and final discussion on paint booth applications. If you haven’t read the previous ones yet, please don’t forget to check them out!
Today I’m going to talk about the best humidification solution for this specific application.
First of all, there is no one overall best solution, rather it depends on the requirements of each individual installation. A good guide is to find out which of the solutions meets the needs of the installation by focusing not only on initial investment costs, but also operating costs. Higher capital costs can be paid back by the savings achieved in the following months as a result of extensive use of the system.
There are many different aspects that must be taken into account when choosing the right humidification system, however the main drivers are performance, reliability and costs.
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This primarily represents the capability of the humidifier to keep the humidity level inside the right range. Paint manufacturers define precision requirements for environmental parameter control. A precision of ± 2 to 3% around the humidity set point is necessary to allow correct preparation of paints, particularly water-based products, which are among the most sensitive to variations in relative humidity. A humidifier with basic control logic, such as ON/OFF, is very imprecise. If the humidity load to be delivered is high, the required precision may not be able to be guaranteed. A humidification system with proportional or proportion+integral control, on the other hand, is certain to provide better performance.
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Humidification systems used in industrial processes require a high level of reliability. Indeed, the processes must be able to run continuously, without any stoppages due to sudden breakages or frequent maintenance. Humidifier rotation and redundancy are features that can avoid stoppages.
Rotation is implemented by splitting the total humidification load between two or more units. This feature allows the humidifiers to alternate operation, reducing the total number of operating hours and extending maintenance intervals. Redundancy, on the other hand, guarantees continuous operation: if one humidifier is off due to maintenance or a malfunction, humidity production is not interrupted, as the other humidifiers make up for the missing production capacity.
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Air conditioning is one of the most energy-consuming aspects of the entire painting process. A significant part of this can be attributed to relative humidity control.
Manufacturers aim to minimise system operating costs in order to limit the incidence of energy costs on the production of each piece.
The operating costs of a humidification system depend on a number of key factors:
- costs due to energy consumption for the production of humidity;
- costs due to indirect energy consumption, relating mainly to the pressure drop that the humidification system needs to overcome (distributor, droplet separator, turbulators, etc...). These energy costs are thus due to other mechanical components installed in the air handling unit, and are present not only when the humidifier is on, but whenever the AHU is operating;
- costs due to routine maintenance, relating to both functional and hygiene aspects, as well as possible replacement costs when it is not cost-effective to continue operation.
There are two main types of humidifiers: isothermal (electrode steam, heater steam, gas steam) and adiabatic (air washers, wetted media, pressure-based humidifiers). In the first case, steam is produced by heating water, at an energy cost of around 750 W/kg. With a pressure-based humidifier, pressurised water is sprayed into the air handling unit, at an energy cost of around 4 W/kg. Note that the latter value must not be confused with the energy needed to evaporate the water (690 W/kg); 4 W/kg is simply the energy consumed by the pump to spray 1 kg of water. On the other hand, adiabatic humidifiers have a higher investment cost than isothermal appliances.
Gas steam humidifiers, isothermal appliances, have a lower running cost than electrode steam and heater steam humidifiers, and may be a good choice when humidification load is quite high (around 45 kg/h) due to the price of gas, which is usually cheaper than electricity.
Humidifiers can be generally divided based on their costs, as shown in the image below:
In economic terms, isothermal humidifiers are most suitable for low humidification loads, whereas adiabatic appliances are used more with high humidification loads.
I have briefly explained how humidifiers are divided and some of their related features. For further details, please download the white paper by clicking the link below.
Relative humidity inside paint booths: what causes deviations from optimum conditions?
Why does air relative humidity affect the quality of coatings?