Every year, millions of people in offices, schools, hospitals and homes across the UK rely on ventilation and air conditioning systems to provide them with a supply of clean fresh air.
Where mechanical ventilation is provided, the system needs to be maintained in efficient working order, this includes cleaning as appropriate.
When undertaking cleaning work, it is important to ensure that the tools and processes used are appropriate for the ventilation system to be cleaned. To support all the professionals involved, including maintenance managers and cleaning contractors, we recently asked the National Association of Air Duct Specialists UK (NAAD UK) to carry out an independent assessment of how best to clean and maintain ductwork fabricated from the pre-insulated Kingspan KoolDuct System. In this blog, we’ll take a look at their recommendations and how to determine when a ventilation system needs cleaning.
What risks does a poorly maintained ventilation system pose?
Ventilation and air conditioning systems feature a wide range of components such as air handling units (AHU), filters, dampers, ductwork, grilles and diffusers. All these need regular checks as dust and debris within the system can affect the quality of the indoor environment served by the system.
For example, dust can collect in all components, inside return air/intake ductwork, and even in supply air ductwork if filters are not maintained correctly. With neglect these deposits may eventually contaminate the air supply with odours and provide a breeding ground for mould, mildew and microorganisms, particularly if the air within is humid. All these factors can contribute to so called ‘sick building syndrome’ and cause health problems. Deposits in the ventilation system can also represent a fire risk, so it is important to keep them in check.
It is generally recommended that, rather than setting a cleaning schedule for ductwork and ventilation equipment, facilities managers instead create an inspection schedule so they can determine when cleaning is necessary.
How can you tell when a ventilation system needs to be cleaned?
The best place to start when assessing a system is with a simple visual check of the various components looking for any significant build-ups of dust, microbial or other contamination.
A visual inspection from a suitably trained individual may be all that is required in some cases, however, if there is any uncertainty about the cleanliness of the system then it will be necessary to undertake some more in-depth, objective testing (such as the vacuum test discussed below). Objective measurements may be defined in advance as part of the inspection plan .
The point at which cleaning is required will depend on the type of ventilation system and the purpose of the rooms it services. To assist facilities managers, clear guidance is set out in BS EN 15780 (Ventilation for Buildings. Ductwork. Cleanliness of Ventilation Systems).
This standard identifies three cleanliness quality categories for ventilation systems shown in the table below:
||Offices, hotels, schools, restaurants, general hospital areas
||Laboratories, treatment areas in hospitals
Table 1 – Cleanliness quality categories within BS EN 15780
The standard goes on to set clear criteria to determine whether ductwork servicing the different cleanliness quality classifications require cleaning.
Its preferred objective assessment method for post-clean verification uses a dust vacuum test. For this, a 100 cm2
template is secured with duct tape within a section of the ductwork. The open area of the template is then carefully vacuumed using a calibrated air pump with a pre-weighed cassette filter that is slid twice, once in each direction along the template slot. Once the surface has been vacuumed , the cassette is closed off. By measuring the weight of the cassette before and after this process, an independent laboratory can calculate how much dirt has been collected in grams per the sample area. Using this test, ductwork should meet the following requirements:
||Recirculation or secondary air ductwork
||< 4.5 g/m2
||< 6.0 g/m2
||< 3.0 g/m2
||< 4,5 g/m2
||< 0.6 g/m2
||< 3.0 g/m2
Table 2 – Acceptable cleanliness levels in existing ductwork within BS EN 15780
For ductwork serving a sterile or sensitive area, a quantitative method for micro-organisms verification is possible: swab samples can be taken from the surface of the ductwork and sent to an independent laboratory so that cultures can be verified.
How often should ductwork be inspected?
BS EN 15780 recommends that High cleanliness quality class ductwork is inspected every 12 months to ensure it is functioning effectively. Ductwork for Medium and Low cleanliness quality class areas should be inspected at 24 month and 48 month intervals respectively.
Bear in mind, that other parts of the ventilation system (such as the air-handling unit, filters and humidifiers) will need to be checked more regularly. See Table A.2 of BS EN 15780 for guidance.
Any inspection schedule should be adapted to the circumstances based on the results of previous inspections or on changes in the operation of that particular system. This may mean that certain systems or components need to be checked at more regular intervals than mentioned above.
How should I clean ductwork fabricated from The Kingspan KoolDuct System?
In order to determine the most suitable cleaning approach through mechanical brushing, NAAD UK carried out up to 100 passes on different sections of ductwork fabricated from The Kingspan KoolDuct System including 90 degree angles and t-sections.