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HVAC
Examples of different modular installation layouts.
About the Author
Luca Brotto is Application Manager at CAREL’ s HVAC Industrial Marketing Unit. He graduated in Energy Engineering from the University of Padova in 2016 and joined CAREL as Technical Sales before becoming Area Manager for the HVAC portfolio. Since 2022, he has focused on expanding CAREL Group’ s position in industrial markets and developing tailored solutions for industrial customers. allows easier installation in the duct and increases system flexibility. Maintenance is also simplified, as individual modules can be removed and cleaned more easily than one large single unit. Plate heat exchangers are often divided into parallelepiped-shaped modules, which can be easily adapted to the space available in the ventilation unit. The various units can be arranged in series, to increase system efficiency when limited space does not allow the installation of a single, larger device. However, for larger ducts, the heat recovery unit can also be split into several units in parallel, one next to the other, each of which manages a portion of the air stream. These modular structures offer the possibility to customise the heat recovery system, creating different configurations. Thermal wheels can also be installed side-by-side inside large air handling units, as in the case of the automotive sector, where it is not uncommon to have air flow-rates of 200,000-300,000 m3 / h processed by units more than 10 metres wide, with the wheels arranged in parallel alongside each other.
Bypass systems Heat exchangers are generally equipped with builtin bypass systems, comprising dampers capable of diverting the flow through an empty duct to the side of the heat exchanger. This means there is no longer any heat exchange between the two air streams. Motor-driven bypass dampers can have ON / OFF control, when the air parameters do not need to be managed with specific precision, or modular, with variable and gradual opening for more precise control. One of the main reasons why a bypass is used is to control the temperature, for example, when the incoming outside air is in conditions close to the set point, as can happen in the mid-seasons. The outgoing exhaust air could in fact be warmer than the supply set point, due to the thermal loads in the paint booth. Heat exchange between the two air streams would therefore lead to excessive heating of the incoming air, if it is already at the optimal conditions required by the process. Another benefit of using a bypass on the heat recovery unit is to prevent frosting on the fins
in winter. When the outside air is very cold, the outgoing exhaust air is cooled suddenly in the heat recovery unit. The very humid outgoing air can thus temperatures below dew point, causing condensation and ice to form on the heat exchanger fins. To prevent this from occurring, a portion of the cold outside air is bypassed to the side of the heat exchanger, preventing heat exchange with the outgoing air. If there is already ice on the surface of the heat exchanger, defrosting can be achieved by bypassing the entire flow of cold outside air and allowing only the warm outgoing air to pass through for a short period of time. The presence of ice on the heat exchanger reduces its efficiency and increases pressure drop: a bypass is therefore essential in colder climates.
Maintenance and cleaning Regular cleaning of heat exchangers inside paint booths is essential to ensure efficient operation. Build-up of dust and paint particles on the heat exchanger plates can in fact cause blockages, with a consequent increase in pressure drop and lower heat exchange efficiency. Furthermore, paint deposits, being flammable, increase the risk of fires inside the booth. Easy maintenance and cleaning are aspects that should never be underestimated when purchasing a heat recovery unit for a paint booth. Construction solutions that provide for easy dismantling of plate heat exchangers and automatic washing systems for thermal wheels can make maintenance operations easy and effective.
Resistance to high temperatures In addition to the actual painting phase, the paint curing phase is often carried out inside the same booths. This process normally requires a temperature of 60 °-80 ° C and at times even higher. Although not normal for painting applications, heat recovery for some surface coating or related processes can take place at much higher temperatures( e. g. catalytic oxidisers). Solutions are available that can recover large amounts of energy from very high temperature air streams, up to 600 °-650 ° C, using stainless steel heat recovery units, ceramic sealants and specific construction solutions.
56 Heat Exchanger World October 2026 www. heat-exchanger-world. com