FOCUS HVAC
LIMIT THE SPREAD
With airborne transmission accounting
for over a third of all hospital-acquired
infections, it is important to explore methods
of limiting the spread of contagious viruses and
respiratory tract infections. Airborne infections
are transmitted from an individual to another
through droplets of moisture released from the
upper respiratory tract through coughing and
sneezing. Some virus droplets, like COVID-19,
remain in the air for up to three hours and can
be carried by the airflow due to their size. This is
why, if maintained and optimised correctly, HVAC
systems play a pivotal role in preventing hospitalacquired
infections.
Studies have consistently shown that ventilation
is one of the key factors that influence airborne
transmission, highlighting the importance of
HVAC systems in reducing the risk of healthcare
sta‘ and patients catching infectious viruses. As
a result, maintaining good air quality is a critical
strategy in decreasing infection rates in healthcare
environments. But what actions can be taken to
help HVAC systems control the spread of infection in
healthcare environments?
CIRCULATE FRESH AIR
With the World Health Organisation(i) reporting that
poor ventilation increases the risk of transmitting
COVID-19, the safest indoor space is one that is
constantly receiving fresh air which replaces the
stale indoor air. Replacing stagnant air with fresh air
from outside dilutes the contaminants that linger
in the indoor air and reduces the risk of airborne
transmission.
The air exchange rate represents the number
32 FEBRUARY 2021
of times fresh outdoor air replaces indoor air in
an hour. A study(ii) into a hospital in Hong Kong
suggested that during a pandemic, the air exchange
rate should be nine times in an hour. These findings
highlight the importance of adjusting the HVAC
system’s settings to circulate more fresh air around
the hospital every hour.
CHANGE THE AIR FILTER
Air filtration plays a crucial role in preventing the
spread of infection, with studies showing a positive
correlation between higher quality filters and
reduced airborne transmission risks. Designed to
filter 99.97% of particles with a diameter of 0.3
microns, High E‘ iciency Particulate Air (HEPA) filters
are commonly used in healthcare environments
and have demonstrated good performance filtering
COVID-19 droplets and other airborne contaminants.
Healthcare guidelines around air filtration suggest
that HEPA filters are e‘ ective in most patient care
areas, lowering the risk of infection.
To sustain the performance of the HVAC system,
air filters should be regularly cleaned or changed
to ensure that they do not become clogged and
less e‘ ective. The type of filter and its MERV rating
will indicate how o
en it should be changed, but
in a healthcare setting, filters should be changed
more frequently due to the higher risk of infection
presented by the medical environment.
DEEP CLEAN THE HVAC SYSTEM
With industry specialists arguing that dirty HVAC
systems are o
en less e‘ icient, cleaning the entire
HVAC system is another strategy implemented to
reduce the risk of airborne infection within hospitals.
A thorough HVAC clean can enhance indoor air
quality, lower the risk of airborne infection, extend
the longevity of the unit, and provide energy
savings.
To enhance the performance of an HVAC system, the
following must be cleaned:
Condensate drain
Evaporator coils
AC ducts
Air filters
The exterior of the unit
When it comes to infection control, cleaning the
evaporator coils is particularly important because
dirty coils are the perfect place for mould, bacteria,
and other contaminants to build up. The air
passing through the coils has already been filtered,
meaning any bacteria in the coils may be dispersed
throughout the hospital. Unclean AC ducts carry
a similar risk and should be routinely cleaned to
mitigate the risk of infectious droplets being carried
by airflow through the system and into hospital
wards.
PPM WILL ENHANCE INFECTION CONTROL
In healthcare environments, planned preventative
maintenance (PPM) is crucial because it ensures that
HVAC systems are compliant with health and safety
legislation while improving infection control. A strict
PPM schedule reduces the frequency of unplanned
repairs and ensures the system is operating at peak
e‘ iciency, thereby reducing the transmission of
airborne droplets.
According to the Department of Energy(iii), 25 to 40
per cent of air flowing through HVAC systems is lost
due to leaky ductwork, making checking the duct
system highly important. To further support the
circulation of fresh air around the hospital, some
form of manual intervention may be required to
increase the air exchange rate, fully open dampers,
and close recirculation paths to improve airflow.
Other PPM tasks that improve the performance of
an HVAC system include:
Recharge refrigerant and repair refrigerant leaks
Check and lubricate belts, bearings, and other
moving parts
Check and calibrate system controls and
thermostats
Inspect heat exchanger and operation of the fan
Paul Lucas, MD at Artic Building Services discusses how HVAC systems
can promote infection control within a healthcare environment
REFERENCE NOTES
www.articbuildingservices.com
(i) www.who.int/news-room/q-a-detail/coronavirus-disease-covid-19-
ventilation-and-air-conditioning-in-public-spaces-and-buildings
(ii) https://journals.sagepub.com doi/10.1177/1420326X16631596
(iii) www1.eere.energy.gov/buildings/publications/pdfs/building_
america/27630.pdf
/1420326X16631596
/coronavirus-disease-covid-19-ventilation-and-air-conditioning-in-public-spaces-and-buildings
/www.articbuildingservices.com
/27630.pdf
