Indoor Air Quality Monitoring

Specific Considerations For System Components As Detailed In Hvca Document Tr19

Air Handling Units and Other System Components

To obtain satisfactory conditions of cleanliness all the components associated with the ventilation system should be included in specific cleaning and maintenance procedures.

Fresh Air Inlet

Inlets should be protected by weather louvers backed by maximum 12mm mesh and situated away from potential sources of contamination. Heavy contamination within inlets prior to filters is common and may include insects, feathers, bird droppings, nesting, materials, wind blown leaves, grass, soil and paper. Inlets near roads may suffer carbon based deposits.

Water entry as droplets or condensation can support mould growth in inlets and make dirt deposits difficult to remove, as well as causing rust and permanent water marking.

The provision of extra access panels may be required to give operator entry to remove deposits by scraping, vacuuming, brushing or wet methods and to repair louvres, mesh and corrosion damage.

Where significant bird contamination or mould problems are encountered a preliminary disinfection before starting work may be required and appropriate protection provided for cleaning operatives.

Access to Air Handling Units

Access to all sections of the air handling unit is required for adequate cleaning. Occasionally there is no usable access door to the space between sections, for example heating and cooling coils. In this event extra access panels may have to be installed subject to the design of the unit. Defective door seals are a common and significant source of inward dirt leakage.

Filters

All filters should be correctly installed and maintained. Incorrectly fitted and collapsed filters are a common cause of ductwork system contamination.

Linings

Air handling units, ductwork and other system components may be lined with Man-Made Mineral Fibre (MMMF) which may or may not be protected by a coating, foil or fabric. Damaged linings releasing particles into the air system are common. Foam may also be used as a lining. This can break down with age to release fine particles.

Many linings are porous and have the capacity to absorb dirt. They require thorough but careful vacuum cleaning with a soft brush head to remove dirt without causing damage. Complete dirt removal is unlikely to be achieved.

Where moisture is present significant microbiological growth within the lining is possible. Biocidal treatment is an option, but may not be fully effective due to the porous surface. It would be difficult to assess the full extent of the damage/reaction caused by moisture or cleaning/biocidal chemicals.

The existing condition of the lining, or potential damage caused by cleaning activities, may necessitate the removal, repair or coating of the ductwork lining interior.

Moisture

Humidification and condensation on chilled surfaces and leakage can cause dampness or in extreme cases standing water resulting in corrosion or excessive microbial growth. Similar problems can occur at droplet eliminators. Poor drainage of condensate from chilled coil drip trays may require cleaning of drain lines and traps. Treatments to prevent microbiological growth contaminating and blocking trays and drain lines are a possible option.

Design and maintenance considerations to protect against proliferation of Legionella species are dealt with in HS(G)70 and NHS Guidance.

Heating and Cooling Coils

Those with very closely spaced fins and/or which are very deep, can suffer blockage due to accumulated dirt, corrosion and hardness deposits. They are prone to severe deterioration of the fins. Coils located before filters are particularly vulnerable.

Vacuum brushing, compressed air blast, washing, water jetting and the application of chemical cleaning methods, singly or in combination, may be required. Care must be taken to avoid damage to fins.

Fans

Fans, motors and drives may be heavily contaminated especially if oil or grease has leaked. Impellers may have heavy deposits on the blades. For full insitu cleaning, partial dismantling and, possible, the creation of extra access panels in fan casings, subject to manufacturer approval, may be required.

Sound Attenuators

Sound attenuators (also called silencers) may be located within air handling plant or situated remotely in ducts. These usually have linings covered with woven fabric or perforated sheet metal. Dirt readily accumulates in silencers and their porous nature makes complete cleaning impossible. Careful vacuum brushing with a soft brush head or gently application of compressed air are possible methods.

Where damage has occurred which may allow the release of MMMFs, consideration should be given to repair or replacement.

Turning Vanes, Volume Control Dampers, Fire Dampers

These tend to accumulate dirt which can affect their operation and may require access panels added to one or both sides to allow full cleaning and surface restoration.

Manually set volume control dampers should have the ‘as found’ setting marked indelibly to aid resetting.

Fire dampers should be physically cleaned, but inspection and functional testing of smoke/fire dampers should be separately specified.

In-Duct Heat Exchanger Coils

Lack of access for inspection and routine cleaning can result in these being blocked with dirt, restricting air flow through them (methods as used for air handling units apply). Additional access panels to give access to both sides of the coil will usually be required.

Flexible Ducts

Flexible ducts trap dirt in the corrugations. This dirt can be difficult to completely remove if the corrugations are deep and/or compressed together. Light weight foil, plastic flexible or aged flexible are liable to damage. Cleaning methods must be adjusted to account for the type of flexible duct. Brush methods require soft bristle brushes and gentle application. Compressed air methods may require a pressure reduction to avoid tearing the duct material.

It may be necessary to remove and extend flexible ducts to release dirt from folds.

Decay of the material of construction, or difficulties in releasing flexible ducts from their connection spigots without causing damage may make replacement a better option that cleaning.

Diffusers and Grilles

Where possible these should be removed for cleaning. Washing to remove grease and tobacco staining may be required.

Diffuser/grille locations and orientation should be marked or recorded if they are to be taken away for washing, so that they can be returned to the correct location. Opposed blade dampers should have the ‘as found’ setting marked to aid resetting.

Certain grille and diffuser arrangements may be installed such that they cannot be practicably removed for cleaning, e.g. linear diffusers or those trapped by partition walls. Insitu cleaning by air line and extraction to capture dislodged deposits may be used. Diffusers may have plenum boxes, possibly containing dampers behind them, which also require cleaning. Access will be required to permit cleaning or air jetting and extraction methods.

Terminal Equipment

Equipment such as fan coils, mixing boxes, CAV, VAV, induction units and unit air conditioners may be included in a cleaning programme.

Wall and sill mounted equipment is frequently obstructed by difficult to move furniture and fittings, preventing or hindering access for cleaning. Responsibility for moving obstructions should be defined by the Specifier.

Ceiling mounted equipment may be obstructed be services and structures preventing the opening of service hatches and withdrawal of internal components. Some terminal units have filters which may require cleaning or which are disposable. Contractual responsibility for supplying replacement filters will require definition by the Specifier.

Terminal units may be lined or included attenuator sections. Maintenance activity, ageing and erosion by air flow may have resulted in damage to the lining allowing fibre escape. If damage to the lining occurs remedial action should be taken immediately. The lining may have accumulated dirt within its matrix. The limited access to all air passages, especially labyrinth passages in attenuators within terminal units and the presence of delicate porous linings can prevent total dirt removal.

Gentle vacuum brushing or air jetting, plus high volume extraction may be required. Some units have air jet nozzles or small air passages which become blocked with dirt. This dirt can form a hard deposit which requires mechanical removal with suitable tools to chip or ream it away. Jet nozzles may also require washing.

It is important for the Specifier to define the extent of cleaning for Induction Units, e.g. whether secondary and mixed air surfaces only are included or whether typically less accessible primary air surfaces (plenum box) are also included.

Plenum Void

Ceiling and floor void plenums may be used as an integral part of the air distribution system and should therefore be subject to the same hygiene consideration as other system components. Regard should be given to the selection of cleaning technique(s) in view of the different construction materials used.