Ventilation system cleaning: from air handling unit to grille

Ventilation system cleaning: which components are involved?

A central system in a commercial building has more parts than a residential unit, and each part needs its own approach. Use this overview for your scope of work.

If you mainly work in homes or small buildings with a ventilation box, the approach is simpler. That is covered in the guide on cleaning MEV systems. For balanced ventilation with a heat exchanger, see the guide on cleaning a heat recovery system.

Air handling unit cleaning: the heart of the system

The AHU draws in outside air, filters it, heats or cools it and blows it into the building. Anything left behind here travels along with the air. That is why a good inspection starts at the unit.

• Filter section: check that filters seal properly in their frames. A poorly fitting filter lets dust pass alongside it, straight into the ducts.
• Fan section: dust on the blades and the floor is a sign that dirt has been passing through for some time.
• Cooling and humidification section: moisture plus dust is a breeding ground. The RIVM (Dutch National Institute for Public Health) names humidifiers and central air humidification as possible sources in its legionellosis guideline. Employers using air humidification must take measures under article 4.87b of the Working Conditions Decree (Arbobesluit), with a risk analysis and a management plan.
• Heat recovery: a wheel or coil with dense fins holds on to dust. Follow the cleaning instructions of the installation manufacturer.

Milieu Centraal (Dutch public information centre) points out that dirty filters can let moulds and bacteria be blown into the building and that a dirty filter creates more resistance. The biggest risk is underventilation: less fresh air than the system was designed for.

Inspection hatches: no access means no clean ventilation system

You can only clean what you can reach. The Eurovent recommendation REC 6/7 (1999) gives useful dimensions that many professionals still use as a reference:

• inspection openings no more than 10 metres apart, or no more than two bends of 45 degrees or more between two openings;
• for ducts larger than 500 mm, a hatch of at least 500 x 400 mm;
• openings on both sides of dampers, coils, heat recovery, silencers, filters and fans.

If those hatches are missing, fitting extra resealable inspection hatches is often the first step. Danduct Clean supplies resealable inspection hatches and small access doors as accessories. A practical tip: on the first round, mark the position of each hatch on the drawing. On every later cleaning you will save search time.

The number of hatches also determines your choice of equipment. With a 30 metre shaft, DC4 duct cleaner bridges a long stretch of duct between two openings, including vertical sections and 90 degree bends, in ducts from 100 to 600 mm.

In which order do you clean a complete ventilation system?

Practical advice, not a requirement of any standard. No standard prescribes a fixed order. The method below is a logical sequence that stops loose dirt ending up in sections you have already cleaned. Always adapt it to the system in front of you.

1. Survey: record the drawing, hatch positions, duct sizes, duct material and the number of grilles and valves.
2. Baseline and photos: camera footage or photos per section, so you can compare afterwards.
3. Switch off and lock out the installation: and note the grille settings before you remove anything.
4. Seal and create negative pressure: seal off the section to be cleaned and keep it under continuous negative pressure with an extraction unit, using duct sealing balloon to protect the rest of the system.
5. Clean ducts section by section: work towards your extraction point, so loose dirt moves to the extraction and not back into clean sections.
6. AHU, dampers and silencers: finish by hand, including the floor and the fan section.
7. Grilles and valves: clean them and refit them in the recorded setting.
8. Replace filters last: a new filter that catches all the dust from the cleaning is money thrown away.
9. Final check and report: after measurement, photos and job sheet.

More background on permitted methods and measuring methods can be found under duct cleaning standards.

Which equipment suits each part of the ventilation system?

A system in a commercial building often has main ducts, branches and small end ducts leading to valves. No single machine fits all of these perfectly. So look at the full range of air duct cleaning tools and choose per duct type.

For short end ducts, duct cleaning with a power drill is often faster than setting up a large machine. In narrow ducts with many bends, the Intelligent Airnozzle shows you on camera straight away whether a corner is clean. Take care with fibreglass duct board: the EPA recommends soft brushes there.

How often do you inspect a ventilation system in a commercial building?

There is no statutory cleaning interval for offices and commercial buildings in the Netherlands. Article 6.2 of the Working Conditions Decree (Arbobesluit) does require ventilation installations to be in working order at all times and the workplace to have enough uncontaminated air. For planning, you therefore rely on references:

Inspection is not the same as cleaning: you only clean when the inspection shows it is needed. A practical route is a fixed inspection cycle with camera and measurement, and cleaning per section based on the outcome. More on intervals can be found under the interval for ventilation duct cleaning. For the situation in offices there is a separate guide on ventilation in commercial buildings.

Suppliers of air handling units or of cleaning equipment?

Anyone searching for suppliers of air handling units will find manufacturers and wholesalers who make and sell the AHU itself. That is a different market from cleaning equipment. The AHU manufacturer supplies the unit, the maintenance instructions and often the filters. A supplier of cleaning equipment supplies the brushing machines, compressed air nozzles, sealing products and extraction units you use to clean the unit and the ducts.

• Questions about replacement parts, filter sizes or the maintenance instructions for the unit go to the installation manufacturer.
• Questions about which machine fits which duct diameter go to a duct cleaning equipment supplier.
• Questions about the cleaning instructions for a heat recovery wheel or coil: consult the AHU manufacturer's documentation first.

Lamers Reinigingstechniek belongs to the second group: the family business has supplied professional cleaning equipment for more than 50 years, including the Danduct Clean machines for air ducts.

Cleaning ventilation systems alongside workshop extraction

Many commercial buildings have a separate process or dust extraction installation next to the comfort ventilation. These are two different systems with different risks: with dust extraction, combustible dust plays a role; with comfort ventilation, the main issues are hygiene and air volume. List them separately in your scope of work. For the second group there is the guide on cleaning workshop extraction systems.

Fictional example: the facilities team of a three storey office building plans the cleaning floor by floor, each time on a Friday afternoon. Per section the valves are closed with foam caps, the section is put under negative pressure and the main ducts are done with a rotating brush. The short branches are handled with a drill driven cleaner. Only after the last floor does the AHU get new filters.

A short checklist before you start a job like this:

• Is the drawing up to date and are all hatches marked?
• Do you know the diameter and material of every duct type?
• Have you agreed with the client when the installation may be switched off?
• Are the filters for the final replacement ready on site?

Want to know which set suits your work? Use the form to duct cleaner quotation or advice on the right machine.