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Why a clean start makes perfect sense

A new standard for cleanliness in newly installed ventilation ductwork will end potentially damaging confusion in the industry, as Darren Ling explains
It is crucially important to clean ductwork in new buildings. It sounds simple, but for too long there has been confusion surrounding the issue of cleanliness in newly installed ductwork, with potentially harmful consequences.

The industry was quick to accept that regular cleaning of a building's ventilation system is essential for maintaining safe, comfortable and efficient working conditions. However, it has failed to agree on the required level of cleanliness for newly installed ductwork.

A popular myth within the industry was that protection of ductwork on a construction site would be sufficient for maintaining the internal cleanliness of the system in a new building. In 2009, the Heating and Ventilating Contractors' Association (HVCA) attempted to correct this assumption by publishing the TR/19 Guide to Good Practice, Internal Cleanliness of Ventilation Systems.

The guide stipulates that 'protection of ductwork on a construction site will not guarantee internal cleanliness of ductwork. Where specific verifiable levels of internal cleanliness are required it will be the responsibility of the designer to specify the inclusion of a specialist cleaning contractor on the outset of a contract to internally clean newly installed ductwork just prior to commissioning work commencing'.

Further confusion arose where the HVCA's TR/19 Table 5 was specified along with Deposit Thickness Tests as a means for determining if a new ductwork system needed to be cleaned. The problem was that this table was designed for existing ductwork, not newly installed ductwork. As a result, new buildings were being handed over with ductwork that did not meet sufficient levels of cleanliness.

The new British Standard EN 15780:2011 Ventilation for buildings - Ductwork - Cleanliness of ventilation systems was published in November 2011 and surpasses the HVCA's TR/19 guidance.

The standard has been produced by taking the great and the good from across Europe and has standardised levels of cleanliness in ductwork systems according to the building use, giving specifiers, installers and facilities managers clear guidance, a published set of standards and a new vacuum test that can apply to circular duct as well as rectangular ductwork.

It should bring to an end all the confusion regarding newly installed ductwork and what is considered acceptably clean, while helping the industry achieve safer, cleaner ductwork.

There are three different standards depending on the use of the supply duct system:
  • Low is for rooms with intermittent occupancy such as storage rooms and technical rooms.
  • Medium covers general offices, hotels, restaurants, schools, general working areas in industry and hospitals, sport and exhibition buildings, etc.
  • High is for high quality offices, treatment areas in hospitals, laboratories.

Before (top) and after ductwork cleaning

Defined standards
The BS EN 15780:2011 gives clearly defined standards for newly installed ductwork in these types of installations by means of a vacuum test. The values it recommends for supply, recirculation and secondary ductwork are Low <0.9g/m2, Medium <0.6g/m2 and High <0.3g/m2. For extract ductwork, the standard specifies Low <1.8g/m2, Medium <1.8g/m2 and High <0.9g/m2.

The post clean test to determine if an acceptable level has been achieved is now 0.3g/m2 to ensure optimum cleanliness of new ductwork prior to the handover.

The standard does not stop there. It has newly defined limits set against trigger levels for cleaning these types of systems for existing ductwork which differ from the current guidelines set out in the HVCA's TR/19.

Vacuum test modified
The values it recommends for existing ductwork are Low <4.5g/m2, Medium <3.0g/m2 and High <0.6g/m2, and for re-circulation and secondary ductwork it specifies Low <6.0g/m2, Medium <4.5g/m2 and High <3.0g/m2. In addition, the current HVCA TR/19 Vacuum Test has been modified to ensure that accurate readings are obtained both pre and post clean. The original vacuum test capsule remains the same, however the intake will now have an additional length of those attached with a 45-degree angle on the end to enable the template area to be sampled on flat or circular duct.

Plus, the vacuum pump capacity has been increased from 10 litres per minute up to 15 litres per minute, making the vacuum test more efficient at collecting dust.

The HVCA is revising its TR/19 to include the new British Standard. However, until then, the BS EN 15780:2011 will ensure that the ductwork cleaning industry raises its standards to ensure compliance and make our indoor environment safer and cleaner.

// The author is a director of System Hygienics //
1 February 2012


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