Advisory Note - Mould in Buildings and HVAC Systems

A Service to A.G. Coombs Group Clients
Mould in Buildings
and HVAC Systems
Mould plays an important role in the natural environment as a break-down mechanism for
dead organic matter. In the built environment, it is an unwanted presence and a particular
problem in the warm and humid conditions experienced in much of Australia. Unpleasant and
unsightly, it can damage fabric and equipment and is a threat to the health of occupants.
Causes of Mould in Buildings
Mould requires three factors to be simultaneously present to
germinate and propagate:
• Mould spores
• Moisture
• Organic matter.
In a similar fashion to extinguishing a fire, the existence of mould
indoors can be controlled by eliminating one or more of these factors.
In all but the cleanest of environments mould spores and organic
matter will be present to some degree, and moisture is often the
catalyst of many outbreaks. Once an outbreak is established it is
important to control all three elements to eradicate mould colonies
and prevent their re-occurrence.
Health Risks
When mould colonies form in a closed indoor environment, they
release millions of spores which can circulate through a building’s
ventilation system, causing indoor levels to reach concentrations that
are hundreds of times higher than ambient levels.
For most people the presence of mould will be a minor irritant, possibly
triggering sneezing, coughing or minor inflammation. For those with
allergies it may lead to more pronounced inflammation, eye irritation,
skin rashes or asthmatic breathing difficulties. In some circumstances,
mould can lead to more serious consequences – particularly with
immunocompromised individuals.
For this reason, the presence of mould in healthcare facilities, and in
particular acute care settings such as cancer wards, is a serious issue
which must be monitored and treated accordingly.
Controlling Mould in Buildings
Moisture
Managing moisture in buildings is typically the key factor in
preventing and controlling mould growth. Without moisture mould
reproduction cannot occur, and existing mould colonies will die.
Water leaks, condensation, groundwater, poor drainage and/or
elevated humidity are contributing factors towards starting
and sustaining a mould outbreak.
Organic Matter
Moulds are a type of fungus - living organisms which require
a source to grow and propagate. They feed on organic matter.
Building materials such as timber, paper, natural fabrics and leather
will be susceptible to mould growth under the right conditions.
A build-up of dust containing dead skin cells and other organic
matter can also lead to conditions suitable for mould to grow on
otherwise inorganic surfaces, such as air handling plant-cooling
coils. A regular cleaning regime is important to prevent these
conditions from occurring.
Mould Spores
Mould reproduces by forming microscopic spores that disperse into
the air and settle elsewhere as new potential host sites. Outdoor air
normally contains some level of these airborne spores and as such
they are introduced at low concentrations on a constant basis via
the air handling plant regardless of whether active mould colonies
already exist in the building.
This ingress of new mould spores can be reduced by ensuring that
the source location of outside air is not damp, dark or contaminated
with decaying organic matter.
Mould spores range from 1 to 100 microns in size with the majority
between 2 and 20 microns. High-efficiency particulate air (HEPA)
filtration can be used on the incoming outside air to remove mould
spores however this is often impractical.

Advisory Note: Mould in Buildings and HVAC System
Heating, Ventilation and Air Conditioning (HVAC)
Systems and Mould
HVAC systems play an important role in preventing, controlling and
remediating mould outbreaks in the built environment.
High humidity levels and low airflow create conditions where mould
spores may be more likely to germinate and propagate. Controlling
the HVAC system to maintain indoor conditions within a 40-60%
relative humidity range is an important factor in preventing this
from occurring.
For more critical environments such as hospitals, museums and
art galleries it is important to ensure HVAC systems are designed
to include active humidity control. This can be through the use of
additional cooling and heating coils for overcooling and reheating of
air to remove moisture.
4. Cooling Coils
Mould colonies can be removed from cooling coils by applying
a coil cleaner agent and washing down. This will remove active
mould colonies along with inactive spores and flush any trapped
organic matter from the coils, preventing the establishment of new
growth as well as freeing up airflow and improving the efficiency of
the coil.
Coil cleaning should be scheduled as a preventative maintenance
activity and not used only as a reactive step when outbreaks occur.
Typically, an annual coil cleaning regime should be appropriate.
Coils should be inspected during routine HVAC maintenance
inspections when air filters are checked, and cleaned more regularly
if any contamination is reported.
HVAC systems can also be a common cause of mould issues when
inadequately maintained. Cooling coils are a source of moisture from
condensation on the cold surface. It is important that coil condensation
is well drained to avoid moisture build up or leakage. Additionally,
air flow velocities through cooling coils should be kept within good
design limits to avoid condensate carry-over into downstream
ductwork – particularly when internally lined with porous insulation.
This is sometimes an issue in modified systems.
Air filters should be replaced at recommended intervals and cooling
coils kept clean as part of the maintenance schedule. For HVAC
systems serving critical environments the use of ultraviolet lamps
should be considered to constantly irradiate cooling coils to kill mould
spores and bacteria.
Correctly-designed and specified HVAC filter media will help trap both
mould spores and any airborne organic matter, preventing their travel
to a moist cooling coil where outbreaks can occur and spread. It is
important that air filter banks are well sealed.
Remediation of Mould Outbreaks
1. Remove all Active Mould Colonies
When the presence of mould is verified, it is important to ensure that
all contaminated sites are located and dealt with promptly to remove
the colonies and prevent further spread of spores.
2. Replace Filters
Following a mould outbreak, air filters will likely be contaminated with
mould spores and should all be replaced simultaneously to prevent
cross-contamination from occurring.
It is recommended that a full filter change be performed immediately
to remove the dirty filters already laden with spores from the facility,
and then a further filter change upon completion of the rest of the
remediation actions to dispose of any trapped spores which would
have been dislodged by the remedial works occurring.
3. Remove Contaminated HVAC Components
Once visible mould colonies have been removed, it may be necessary
to remove contaminated sections of ductwork insulation or other
porous elements such as attenuators which may have become loaded
with mould spores during the outbreak.
5. Plantroom Walls, Floors and Surfaces
General good housekeeping and cleanliness of plant room areas is
an important factor in avoiding and remediating a mould outbreak.
Keeping plant rooms tidy, clutter-free and clean of dust and grime
helps to prevent ingress of organic matter into the air handling plant
and eventually ending up the moist environment within the cooling
coil chambers and beyond.
As a priority all plant rooms should be cleaned out and left clutter
and dirt-free. Any signs of visible mould on walls, floors and surfaces
should be cleaned using a vinegar-based solution or hospital-grade
disinfectant and dried thoroughly.
For further guidance on mould in buildings and HVAC systems,
please contact:
Andrew Bagnall
Leader - Technical Advice (NSW/ACT)
A.G. Coombs Advisory
+61 431 238 654
abagnall@agcoombs.com.au
Published Jul 2024. While every effort has been made to ensure the accuracy of information in this publication, the A.G. Coombs Group assumes no responsibility for errors or omissions
for any consequence of reliance on this publication. Registered Electrical Contractor licence REC 17632. © 2024 A.G. Coombs Group and all related entities. All Rights Reserved.