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Coil Protection in Fumigation Systems
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Coil Protection in Fumigation Systems

1. Introduction

 

In our previous post HVAC Fumigation design in pharmaceutical facilities, we discussed the design of decontamination in pharmaceutical HVAC systems. We talked about one of the possible designs, mostly used in the pharmaceutical industry, where only the cleanroom is decontaminated. In other words, the HVAC system is only used for ventilating the decontaminating agent. Taking a step further in ensuring quality and safety involves the disinfection of the entire AHU + ducts + room assembly. However, this can pose a series of additional challenges, which is what we’re going to discuss in this post: coil protection in fumigation systems.

2. System Description

 

This whole-system fumigation system involves the passage of the disinfectant agent throughout the entire HVAC assembly. That is, the AHU (including coils, filters, fans), ductwork, dampers, HEPA filters, silencers, etc. It is particularly suitable when dealing with biological agents, both in recirculating and non-recirculating systems. Unlike the system described for fumigating only the room, here the HVAC system is continuously in circulation with the disinfectant agent. Through the dampers system, once the exposure time is completed, the ventilation phase is responsible for purging the agent into the atmosphere.

3. Challenges

 

Common disinfecting agents often have a series of incompatibilities with different construction materials they may come into contact with. For example, a commonly used disinfectant, Actril, has a list of compatible materials:

As we can see, the list is not very extensive, and the manufacturer recommends testing for each material not included in the list. If the manufacturer does not provide data, to ensure proper behaviour, we must conduct the corresponding tests.

However, we can already anticipate that the weak point lies in the coils. Whether they are for hot water, chilled water, heat recovery, etc., these coils are typically constructed with copper tubes and aluminium fins. This combination provides very efficient heat transfer between the fluid circulating through the tubes and the air passing through the coil.

Nevertheless, over time, aggressive disinfection products can lead to corrosion. Corrosion causes the release of metallic particles, which can impact the filters at high speed, potentially causing damage. Consequently, there is a risk of particles entering the space, and this is a risk that must be eliminated.

Effect of corrosion of unprotected coil

4. Coil Protection

 

Traditionally, corrosion has been a problem in various applications, such as marine environments. To address this issue, there is the possibility of applying a coating system to the coils.

There are various types of coatings available: phenolic immersion, elastomeric, anodic or cathodic deposition, or epoxy polymer.

For saline-marine applications, all these options can be valid, but of all of them, the one that has shown the best results in my experience is the latter, under the brand name Electrofin.

Through Electrofin process, the coil is coated with flexible epoxy polymer applied uniformly to all areas of the coil surface without material bridging between the fins. The coating process ensures complete encapsulation of the coil and a uniform dry film thickness of 0.6 to 1.2 mil on all surfaces (including fin edges). Corrosion durability is confirmed through testing of no less than 10,000 hours of resistance to salt spray according to ASTM B117 or traced aluminium as test coupons.

4. Conclusion

 

Fumigation is a critical part of the process, and therefore their necessity must first be justified. Subsequently, the scope must be established: either just cleanrooms or the entire system, along with obtaining a list of the decontamination agents used. Material specifications for components in contact with the agents should then be established to ensure they are not affected.

Not considering coil protection in fumigation systems could lead to catastrophic outcomes for our pharmaceutical HVAC system.

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