Clean New HVAC Ductwork

• By: Craig Booth
• On: 13/11/2009 12:49:41
• In: Uncategorised
• Comments: 5 Add

An article by Peter Gregory, a surveyor with Triventek's sister company, System Hygienics, was published in the Heating and Ventilating News on 28/10/2009. See the news story on our website for a link to a pdf

This deals with the issue of new ductwork which is often installed dirty. Building sites are dusty, dirty places so it's not surprising that you often find brick, cement and plaster dusts in brand new duct systems, never mind mineral fibres, forgotten sandwiches and hard hats

This is no way to start off a system. The potential for adverse reaction from the new occupants (especially when combined with a cocktail of VOC's off-gassing from adhesives, coatings and other components) is immense, and experienced often enough. You can imagine the frustration of the Facility Manager who has just spent a fortune on building/renting/moving into new premises!

There are two problems which the British HVCA Guide to Good Practice TR19: 'Cleanliness of Ventilation Systems', tries to address.

Firstly, specifiers need to decide what they want and specify it clearly. There are 3 levels of protection listed in TR19. The third, highest level requires cleaning by a specialist contractor after installation. It is practically impossible to keep ductwork clean by "capping off"; partly because you have to have the system open in order to erect new duct sections, and that is during the busy, dusty, daytime site working periods. What is more: site people have a strange desire to 'pop' the covers! So if you do want to operate a clean system (and, really, who wouldn't?), the only way to go is to specify cleaning.

Secondly misunderstandings arise over what is the appropriate cleanliness level to measure new systems against. Should you measure using the Post-Clean verification level (0.075g/m2) or against the Surface Deposit Limits ( 6g/m2 for extracts and 1g/m2 for supply and recirculation ducts)? The latter (Surface Deposit Limit) is really a measure of dirtiness, i.e. a 'trigger' level designed to advise when an existing system in use, has become so dirty that it should be cleaned.

It really is wrong to use the Surface Deposit Limit as a decider as to whether to clean a new system. You wouldn't accept a dirty new car from the garage showroom ("Oh, don't worry: it'll get dirty like that after a couple of years use, anyway"), now would you?

There are a some more big advantages in having a new system professionally cleaned before being brought into use.

1. It means you can verify and fine-tune the access system for cleaning
2. It means you can save a fortune by dispensing with excessive capping off (which leads to many more truck miles to deliver ductwork since you can't 'nest' the ducts)
3. Most importantly in practice, it gives the project people certainty: if a specifier ducks the issue and simply says 'install the ductwork cleanly', without measurable post-clean verification limits to achieve, then who decides what is clean? It's a recipe for under-cutting at tender stage, and conflict throughout the construction and handover stages