This document discusses HVAC systems and indoor air quality in relation to the COVID-19 pandemic. It provides information on various types of isolation rooms used in hospitals, including negative pressure isolation rooms which are designed to contain airborne contaminants and protect others. The document discusses factors like air changes per hour, pressure differentials, air filtration levels, and exhaust requirements that HVAC systems must meet for isolation rooms. It also defines key terms related to indoor air quality and ventilation.

2. COVID-19 PANADEMIC
HVAC SYSTEMS &
INDOOR AIR QUALITY
TECHNICAL ARTICLE
Mr. Zeeshan is a professional
mechanical engineer graduated
from NED University. He has
worked in many position from
Project Engineers to Sales
Engineers. Mr. Ahmed is
associated with Carrier for last
11 years and has spend most of
the 18 years in Dubai managing
the Pakistani market. He has
vast know how of major air
conditioning equipment and
has presented many technical
papers.
Recently he has volunteered
his time to assist Pakistan
HVACR Society and its member
in writing a basic understanding
of Covid 19 and HVAC design.
His study is preliminary about
Covid 19, type of isolation
rooms related to HVAC Design
and System.
We as a Society is very much
obliged with Mr. Zeeshan
Ahmed P.E who has taken his
timeout to give something in
brief writeup to help society
members to understand the
basic Air Conditioning design.
Should anyone have any
suggestion, feedback please
feel free to give so we can issue
an addendum.
PHVACR Society
ABOUT THE AUTHOR
Coronavirus disease
(COVID-19) is an infectious
disease caused by a new virus.
The COVID-19 virus spreads
primarily through droplets of
saliva or discharge from the
nose when an infected person
coughs or sneezes.
The COVID-19 virus is
approximately 0.125 Micron or
125 nanometers in diameter.
(Source: National Library of
M e d i c i n e )
However, it often travels in
biological aerosols from
coughing and sneezing which
range in size from 0.5 – 3.0
Micron.
INTRODUCTION
1.Restrict Air movement.
2.Dilute concentration.
3.Temperature.
4.Humidity.
5.Minimize risk of
Transmission of airborne
SAFTEY & PREVENTION
TIP
1.STAY home as much as
you can
2.KEEP a safe distance
3.WASH hands often
4.COVER your cough
5.SICK? Call ahead

3. HVAC SYSTEMS & INDOOR AIR QUALITY
COVID-19-PANADEMIC
The main ways of virus
transformation are as follows:
1.Direct Contact Less than 1
meter.
2.Droplets – when the
droplet particles are < 5μm in
diameter, they are referred to
as droplet nuclei according to
World Health Organization
(WHO).
i)Mouth
ii)Nasal
iii)Eyes
iv)Through air at short
distance – talk.
v)Indirect – Surfaces such as
metal or floor etc.
3.Airborne Transmission
i)Airborne droplet Nuclei
(Small droplet). These
droplets rapidly evaporate in
the air leaving.
ii)Dust particles in the
environment.
MODES OF INFECTION TRANSIMISSION OF VIRUS
NOTE
When the droplet particles are >5 -10 μm in diameter they are
referred to as respiratory droplets according to World Health
Organization (WHO).
A Suspension of fine solid or liquid particles in gas smoke, fog, and
mist are named Aerosols.

4. virus is primarily transmitted between people
through respiratory droplets and contact
routes.In an analysis of 75,465 COVID-19 cases in China,
airborne transmission was not reported – WHO Website.
Droplet transmission occurs when a person is in in close
contact (within 1 m) with someone who has respiratory
symptoms(e.g., coughing or sneezing) and is therefore at
risk of having his/her mucosae (mouth and nose) or
conjunctiva (eyes) exposedto potentially infective
respiratory droplets.
Therefore, transmission of the COVID-19 virus can occur by
direct contact with infected people and indirect contact
withsurfaces in the immediate environment or with objects
used on the infected person (e.g., stethoscope or
thermometer).In the context of COVID-19, airborne
transmission may be possible in specific circumstances
and settings in which proceduresor support treatments
that generate aerosols are performed; i.e. open suctioning,
administration of nebulized treatment,disconnecting the
patient from the ventilator etc.
.
HVAC SYSTEMS & INDOOR AIR QUALITY
COVID-19-PANADEMIC
MODES OF INFECTION
TRANSIMISSION OF VIRUS
COVID-19
CONCLUSION
NOTE
Based on the available evidence,
including the recent publications
mentioned above, WHO continues to
recommenddroplet and contact
precautions for those people caring
for COVID-19 patients. WHO
continues to recommend airborne
precautions for circumstances and
settings in which aerosol generating
procedures and support treatment
are performed, according to risk
assessment.
WHO is aware of other studies which
have evaluated the presence of
COVID-19 RNA in air samples, but
which are not yet published in
peer-reviewed journals.

5. HVAC SYSTEMS & INDOOR AIR QUALITY
COVID-19-PANADEMIC
Protective Environment
named as – PE rooms are
hospital rooms designed to
protect a high-risk
i m m u n o c o m p r o m i s e d
patient from human and
environmental airborne
pathogens. These are positive
pressure rooms intended to
keep patients safe during
recovery from cancer
treatment or stem-cell
transplant.
CLASSIFICATION OF
ISOLATION ROOMS
In hospitals, the risk of airborne virus diffusion mainly depends on airflow
behavior and changes in direction caused by supply air and exhaust air locations.
An improved isolation room ventilation strategy has been developed and is found
to be the most efficient in removing contaminants based on observations and
simulation results. There are different classification of rooms in hospital:
a)Class S – Standard Pressure Room. A Standard room with normal
air-conditioning is appropriate.
b)Class P – Positive room air pressure where an immune-compromised patient is
protected from airborne transmission of any infection.
c)Class N – Negative Pressure Room. These rooms are used for patients requiring
airborne nuclei isolation. Negative room air pressure, where others are protected
from any airborne transmission from a patient who may be an infection risk.
d)Class Q – Negative room air pressure with additional barriers including an
Anteroom for quarantine isolation.
Protective Environment Rooms

6. HVAC SYSTEMS & INDOOR AIR QUALITY
COVID-19-PANADEMIC
AIIR rooms are a specialized application of a
hospital's HVAC system for Messel, COVID -19,
where the airflow supplied into the room is
balanced with exhaust airflow to create at least
-0.01” Water of gauges negative differential
pressure with respect to an adjacent space, usually
the hallway or an anteroom.
Air-conditioning systems for negative pressure
Isolation Rooms should be connected to an
emergency power supply to maintain air
pressurization in the event of a power failure. The
room requires labelling as a negative pressure
Isolation Room.
An Anteroom or airlock lobby, when attached to an
Isolation room, functions as:
A controlled area in which the transfer of supplies,
equipment and persons can occur without
contamination impacting on the surrounding
health care areas.A barrier against the potential
loss of pressurization.Controls the entry or exit of
contaminated air when the anteroom door is
opened.The Anteroom will require sufficient space
to allow for storage of Personal Protective
Equipment (PPE) i.e. gowns and gloves for
protective isolation. Anterooms should not be
shared between Isolation rooms.
A clinical handwash basin with ‘hands
free’ operation in the Isolation Room and
the Anteroom, if provided:
An Ensuite shower and toilet
A self-closing door
100% outside air ventilation (i.e. no
return air permitted), with low level
exhaust ducts.
Airborne Infectious Isolation Rooms short form (AIIR)
Ante Rooms
Air-conditioning systems for negative pressure Isolation Rooms should be connected to an emergency power
supply to maintain air pressurization in the event of a power failure. The room requires labelling as a negative
pressure Isolation Room.
A negative pressure Isolation Room
requires the following:
Type of Pressurization * Isolation Room Anteroom Ensuite
Class S (Standard pressure) Not required
Class N (Negative Pressure) - 30 Pa - 15 Pa - 30 Pa
Class P (Positive Pressure) + 30 Pa + 15 Pa + 30 Pa
Class P with negative
pressure Anteroom + 15 Pa - 15 Pa + 30 Pa

7. HVAC SYSTEMS & INDOOR AIR QUALITY
COVID-19-PANADEMIC
ROLE OF HVAC SYSTEM
EQUIPMENT SYSTEM
When designing the mechanical systems to support isolation rooms, the designer
must consider not only the airflow required to maintain the proper pressure
differential, but also the location of the equipment, the serviceability of the equipment
and equipment redundancy. Depending on the number and type of isolation rooms in
the facility, it is generally more economical to provide a single larger system to serve
multiple rooms than multiple smaller systems.
The same air-handling
system that serves other
standard patient rooms
may be used for isolation
rooms. The air-handling unit
serving the isolation rooms
r e q u i r e s
m i n i m u m - e f fi c i e n c y
reporting value (MERV) 7
pre-filters, with either MERV
14 or high-efficiency
particulate air (HEPA) final
filters. MERV 14 filters are
adequate for AII negative
pressure rooms and for PE
positive pressure rooms
when terminal HEPA filtration
is used at the supply
diffusers serving the PE
room.
For the exhaust system
serving AII rooms, the
exhaust fan should be
located outdoors, if possible,
and be placed as far away
from intakes and public
areas as practical, but no
less than 25 feet with
discharge above the roof.
For outdoor fans, all exhaust
from AII rooms should be
exhausted by means of a
vertical exhaust stack or
exhaust fan with a vertical
discharge arrangement.If
the fan must be located
inside, welded ductwork
should be used downstream
of the exhaust fan, and a
bag-in/bag-out filter
housing with pre-filters and
HEPA filters should be
installed upstream of the
exhaust fan. The exhaust
fans shall be served by
emergency power, and the
fans should be labeled as
contaminated air to meet
the recommendations of
the Centers for Disease
Control (CDC) and
Prevention.Redundancy of
the equipment also needs
to be considered and will
depend on the facility’s
typical census of infectious
patients. On larger systems
serving multiple rooms,
redundant fans are
recommended so the failure
of a single fan does not
compromise the safety of
patients.
A. PRESSURE RELATIONSHIP. B. AIR CHANGE (SUPPLY / EXHAUST AIR).
C. AIR FILTRATION. D. TEMPERATURE.
E. HUMIDITY. F. AIR MOVEMENT (Supply & Exhaust).

8. A negative pressure room in a hospital is used to contain airborne contaminants within the
room. Viruses, bacteria, fungi, yeasts, molds, pollens, gases etc.
A negative pressure isolation room is commonly used for patients with airborne infections like
COVID-19.According to the CDC, a patient known to have contracted the coronavirus can
spread it person-to-person.The negative-pressure isolation room therefore is designed to help
prevent the spread of a disease from an infected patient to others in the
hospital.Negative-pressure isolation rooms require a minimum of 12 air changes of exhaust
per hour and must maintain a minimum -0.01-inch Water gauges negative-pressure
differential to the adjacent corridor whether an anteroom is utilized.
When an anteroom is provided, airflow should be from the corridor into the anteroom, and
from the anteroom into the patient isolation room.
To maintain the required pressure differential, the exhaust air quantity must always be higher
than the supply airflow. Depending on such factors as room size and the room’s heating and
cooling loads, more than 12 air changes per hour may be necessary.
These individual control and equipment decisions come together in the designs of the
positive-pressure and negative-pressure rooms. These include:
Positive Isolation Rooms
A positive-pressure isolation room is designed to keep contagious diseases away from patients
with compromised immune systems, such as those with cancer or transplants. These rooms
require a minimum of
a) 12 air changes per hour of supply air and
b) Must maintain a minimum 0.01 inch WC positive-pressure differential, ensuring that the
patient is protected from airborne contamination regardless of whether an anteroom is used.
HVAC SYSTEMS & INDOOR AIR QUALITY
COVID-19-PANADEMIC
A. DESIGN REQUIREMENTS FOR PRESSURIZATION:
B. COVID -19 NEGATIVE PRESSURE ROOMS:

9. Typically, a minimum airflow difference of 150 to 200 cubic feet per minute (CFM) is
adequate to maintain pressure differential in a well-sealed room.
Temperature of room may be 21 to 24 C depends on the requirement. Humidity should be
around 40% to 60%.Exhaust from negative-pressure isolation rooms, associated
anterooms and associated toilet rooms must be discharged directly to the outdoors
without mixing with exhaust from any non-AII rooms.
However, multiple AII isolation rooms may be connected to the same exhaust system. The
exhaust ductwork serving AII negative isolation rooms also should be permanently labeled
as contaminated air within the facility.
An air change is how many times the air enters and exits a room from the HVAC system in one
hour.
Room CFM Formula
Let’s look at this engineering formula differently. For example, what if the airflow is unknown and
you need to calculate the required CFM for a room?
Here is a four-step process on how to calculate the room CFM:
Step One – Use the above Air Changes per Hour Table to identify the required air changes
needed for the use of the room. Let’s say it’s a conference room requiring 10 air changes per
hour.
Step Two - Calculate the volume of the room (L’ x W’ x H’).
Step Three - Multiply the volume of the room by the required room air changes.
Step Four - Divide the answer by 60 minutes per Hour to find the required room CFM:
Here’s an example of how to work the formula:
HVAC SYSTEMS & INDOOR AIR QUALITY
COVID-19-PANADEMIC
Typical Negative Pressure Isolation Room with Anteroom & Ensuite, showing airflows and
relative pressure gradients
AIR CHANGE

10. a)acceptable indoor air quality (IAQ): air in which
there are no known contaminants at harmful
concentrations,
b)determined by cognizant authorities, and with
which a substantial majority (80% or more) of
the people exposed do not express
dissatisfaction.
c)air
d)ambient air: the air surrounding a building;
the source of outdoor air brought into a
building.
e)cool air: air whose temperature is less than
the average space temperature.
f)exhaust air: air removed from a space and
discharged to outside the building by means of
mechanical or natural ventilation systems.
g)indoor air: the air in an enclosed occupiable
space.
h)makeup air: any combination of outdoor and
transfer air intended to replace exhaust air and
exfiltration.
i)outdoor air: ambient air and ambient air
that enters a building through a ventilation
sys- tem, through intentional openings for
natural ventilation, or by infiltration.
j)primary air: air supplied to the ventilation
zone prior to mixing with any locally
recirculated air.
k)recirculated air: air removed from a space
and reused as supply air.
l)return air: air removed from a space to be
recirculated or exhausted.
m)supply air: air delivered by mechanical or
natural ventilation to a space and composed
of any combination of outdoor air,
recirculated air, or transfer air.
n)transfer air: air moved from one indoor
space to another. ceiling supply: air supplied
to the space more than 4.5 ft (1.4 m) above
the floor.
HVAC SYSTEMS & INDOOR AIR QUALITY
COVID-19-PANADEMIC
CFM CALCULATION:
Length of Room 12 Feet
Width of Room 12 Feet
Height of Room 08 Feet
Air Change Requirement12 Minimum (ACH)
Area of Room 144 Sq. Feet
Volume of Room1,152 Cubic Feet
Air Flow 230 CFM
CFM = ACH X Room volume in Cubic Ft / 60
(Min / Hr)
Where
ACH = Air Change Rate per Hour
CFM = Air Flow Rate (Cubic Feet per Minute)
Room volume = Space Volume (Cubic Feet)
DEFINITIONS AS PER ANSI / ASHRAE STANDARD 62.1 - 2019
CFM

11. HEPA stands for High Efficiency
Particulate Air and is a filtration rating
that captures microbes, dust, and
particulates down to 0.3 Micron. But
what does that really mean and how
do they work?
The U.S. Department of Energy first
termed HEPA as a filtering
specification for suppliers of filtration
products based on how effective they
were at particle removal.
HEPA filters consist of a complicated
mix of filaments and fibers that carry
a static charge which lures various
microbes and particles like a magnet.
HEPA filters should be mandatory in
all healthcare-sensitive environments
such as hospitals, clinics, quarantine
facilities etc.
An interesting study performed by
NASA indicated that HEPA filters were
able to capture sub-micron
particulate down to 0.1 micron!
You can view the study here: NASA
HEPA Study
The chart (next slide) shows the MERV ratings. It shows particle
size ranges. It also shows air filter efficiency levels. Efficiency is
measured by the percentage of particles captured.
A MERV rating chart shows a numerical value. The range is from
1 (lowest efficiency) to 20 (highest efficiency).
HVAC SYSTEMS & INDOOR AIR QUALITY
COVID-19-PANADEMIC
AIR FILTRATION

12. ASHRAE Standard 170 2008/ 2013 or CDC defines for
airborne infectious isolation room to supply and
return grilles for air flow to protect the infectious
particles.
Doors should design as per isolation standard
room.Windows should be proper sealed.Air Change
Per Hour should check coz low means starve and high
means turbulence.In clinic and open grocery room –
they can use plastic or glass at different points in order
to restrict the cough & sneeze and then clean it.
Require more study.
Please see the video shown for isolation room COVID
19 recently.
Temperature of the room should be design. Normally
design 21 C to 24 C.Humidity should be between 40%
to 60%.
HVAC SYSTEMS & INDOOR AIR QUALITY
COVID-19-PANADEMIC
TEMPERATURE & HUMIDITY
COMMISSIONING & MAINTENANCE
AIR RESTICTION AND SUPPLY &
RETURN AIR FLOW DIRECTIONS
https://www.youtube.com/watch?v=qBR-s-a6IaU
1. After construction is completed, but prior
to occupancy, the mechanical or balancing
contractor typically will adjust the airflow
quantities as directed by the design engineer to
ensure that the isolation room is operating as
Pressure Difference between the rooms. Air Flow
directions between the corridor and anteroom,
anteroom and patient room.
2. Air Flow patterns within the patient room
should be tested to ensure that there are no
stagnant areas.
3. In addition, isolation rooms should be
commissioned to prove correct pressure
relationships, proper operation of room controls
and the functionality of the pressure monitor and
alarms.
4. Most manufacturers of pressure monitor
also recommend that the pressure monitor be
recalibrated annually. The results of this periodic
testing should be recorded because the authority
having jurisdiction may request the data during a
survey.
5. The tightness of the room should be
checked and documented. The containment of
the isolation room should be checked and
documented.
6. In addition to routine testing of the
isolation room, the hospital staff who will be
utilizing or maintaining the room should be
trained on the proper use of the room, including
how the pressure monitor works.
7. It also can be used to alert hospital staff, if
the room is not performing as designed.
8. HEPA Filter pressure drop should be
checked and documented.
9. The maintenance should be checked as
per the guidelines for the classification and design
of isolation rooms in healthcare facilities:
10. The planned maintenance should be
scheduled at an interval not greater than 13
weeks and the following items should be checked.
11. Air Change Rate.
12. Supply Air & Exhaust Air Quantities.
13. Terminal HEPA Filters.
14. Exhaust Register.
15. Room Pressure Gauges.
16. Damage to the room interior.
17. Supply & Exhaust Fans.
18. Room seals and Door closer.
19. BMS System, if applicable.

13. HVAC SYSTEMS & INDOOR AIR QUALITY
COVID-19-PANADEMIC
CONCLUSION REFERENCES
1.World Health Organization
Web Site.
2.NASA Website Link.
3.CDC – The Centers for
Disease Control.
4.Guidelines for the
Classification & design of
Positive / Negative Pressure
Rooms.
5.OSHA - Occupational Safety
and Health Administration
6.CHT Healthcare
7.BSD Solutions
8.HVAC-ENG Website
9.ASHRAE Handbook 2019 –
HVAC Applications
10.ASHRAE Standard 2016 For
Location of Filters.
11.MERV Table – ASHRAE
12.ANSI / ASHRAE Standards
62.1 – 2019
1.Calculate the load and match the equipment as per
the design requirement.
2.Use HEPA Filters - 99.97% effective of 0.3 Microns.
3.Dehumidification.
4.Fresh Air as per the requirement of application.
5.Minimum 12 ACH requires.
6.Humidification, if require.
7.Heating, if require.
8.Room Temp. 70 F to 75 F (21 – 24 C) and RH 40% to
60%.
9.Positive Pressure Room or Negative Pressure Room
at least 0.01 inches of water gauge.
10.Exhaust Air should require HEPA filters most of the
cases and velocity should be above 10 m/sec.
11.Labelling on entrance of room.
12.Proper Commissioning.
13.Operation & Maintenance as per the guide-lines.
.
DISCLAIMER
This article is a preliminary finding and guideline all comments and suggestion are
welcome to fine tune. Pakistan HVACR Society and the author may be indemnified on
any implementation. It is suggested to further investigate before any final execution.