Ventilation for Acceptable Indoor Air Quality

1-ASHRAE STANDARD
ASHRAE stands for American Society of Heating, Refrigerating and
Air-Conditioning Engineers. The purpose of this standard is to improve
indoor air quality with the minimum ventilation rates .

This standard is applied to all places intended for human occupancy

except : Aircrafts, vehicles , multifamily structures of three stories or
fewer above grade. In the case of hospitals , laboratories or any industrial
health care , there are more requirements to take into account .

Just to mention that this standard does not subscribe a specific ventilation
rates requirements for ETS area and ETS free area . ( A no-smoking area is
not necessarily an ETS-free area : it still may be contaminated by tobacco
smoke from other spaces due to infiltration ,poor separation ,or
inadequate ventilation ).

2-OUTDOOR AIR QUALITY

Outdoor air quality should be investigated in accordance with two sections
:

1) Regional air quality : It is imperative to determine the status of

compliance with national ambient air quality standards for the
geographic area of the building site .

2) Local air quality : during the hours of the construction , an

observational survey of the building side should be conducted to
identify local contaminants from surrounding facilities that may be
of concern if allowed to enter the building .

The result of investigation should be documented in accordance with the

following section :

3) Documentation : the result should be reviewed by the owners of

the building or its representatives and should contain all
informations (date and time , area surveyed ,description of nearby
facilities ,…) and a conclusions regarding the acceptability of
outdoor air quality based on the informations provided )
3- AIR REQUIREMENTS AND EQUIPEMENTS

1- Natural Ventilation : the natural ventilation systems designed

according to the requirements of the area are allowed either instead
of mechanical ventilation or together with mechanical ventilation .

Requirements :
-Naturally ventilated spaces must be within 8 meters
-The openable area (the area that can be opened to allow airflow)
should be at least 4% of the net occupiable floor area of the room or
space.
-If openings are covered by louvers or other obstructions, the
openable area should be calculated based on the unobstructed area
through the opening.
-If an interior space doesn’t have direct openings to the outdoors
and is ventilated through adjacent rooms, the opening between the
rooms must be permanently unobstructed.
-The free area of the opening between rooms should be at least 8%
of the interior room's area or 25 ft², whatever its larger .
- The operable openings should be accessible to building occupants
whenever the wspace is occupied .

2-Ventilation Air Distribution : these systems should take in

consideration the following :

-The ventilation air distribution system should be ajusted ( manually or

automatically ) in a way that allows to achieve the minimum
ventilation airflow required regardless of the occupancy or the loading
conditions of the building .

-Plenum Systems : these systems are designed to distribute ventilation air

and to recirculate return air to the ceiling- mounted terminal units .

-Exhaust Duct Location : When it comes to harmful contaminants the

system should be maintained at a lower pressure than its surrounding
environment , the purpose is to ensure that the air cannot leak out of the
duct and contaminate other areas .

-Ventilation System Controls : Mechanical ventilation systems shall include

controls, manual or automatic, that enable the fan system to operate
whenever the spaces served are occupied

“VAV” : Variable Air Volume are systems that adjust the volume of air they
supply on demand of cooling or heating in the space . In case the outdoor
air damper which is na valve that controls the intake of fresh air is fixed
and doesn’t change position , then the VAV system must still comply with
ventilation requirements even when operating at minimum airflow .

Exemple :

an office with a VAV system:

At noon, when many people are present, the system supplies a high
volume of air.

At 6 PM, when fewer people are there, the system reduces the airflow.

Problem: If the outdoor air damper is fixed, we need to make sure that at
6 PM, it still brings in enough fresh air.

-Resistance to Mold Growth :Material surfaces shall be determined to be

resistant to mold growth, Resistance to Erosion aswell

-Outdoor Air Intakes. Ventilation system outdoor intakes shall be designed

in accordance with the following :

Location : Outdoor air intakes ,windows , doors , vents … must be

positioned far enough from potential sources of outdoor pollution.

Outdoor contaminants can include:

 Exhaust from vehicles or generators

 Industrial emissions

 Kitchen or bathroom exhausts

 Waste disposal areas

-Combustion Air : Fuel-burning appliances, both vented and unvented,
shall be provided with sufficient air for combustion and adequate removal
of combustion products

-Particulate Matter Removal : filters

-Dehumidification Systems. : Mechanical air-conditioning systems with

dehumidification capability

-Relative Humidity : Relative humidity in occupied spaces should be 65%

or less

-Exfiltration. For a building, the design minimum outdoor air intake shall
be greater than the design maximum exhaust airflow when the
mechanical air-conditioning systems are dehumidifying

-Building Envelope and Interior Surfaces : The building envelope and

interior surfaces within the building envelope shall be designed in
accordance with the following :

The building envelope, including roofs, walls, fenestration systems, and

foundations, shall comply with the following:

- A weather barrier or other means shall be provided to prevent liquid

water penetration into the envelope.
- An appropriately placed vapor retarder
- Exterior joints, seams, or penetrations in the building envelope that
are pathways for air leakage shall be caulked.

-Condensation on Interior Surfaces : When a surface’s temperature falls

below the dew point of the surrounding air, moisture in the air
condenses into water droplets which can ccause moisture , mold ,
corrosion , …
So . Pipes, ducts, and other surfaces within the building whose surface
temperatures are expected to fall below the surrounding dew-point
temperature shall be insulated .
- Air Classification and Recirculation :

Class 1 Air : air may be recirculated or transferred to any space.

EXEMPLE : Office spaces or conference rooms with no pollutants or

hazardous materials.

Class 2 Air : air may be recirculated within the space of origin . Class 2
air may be transferred or recirculated to other Class 2 or Class 3
spaces utilized for the same or similar purpose or task and involving
the same or similar pollutant sources. Class 2 air may be recirculated
or transferred to Class 4 spaces. Class 2 air shall not be recirculated or
transferred to Class 1 spaces.

EXEMPLE : chemistry lab , Kitchens or restaurants

Class 3 Air : air may be recirculated within the space of origin. Class 3
air shall not be recirculated or transferred to any other space

EXEMPLE : factory floor or a welding area

Class 4 Air. Class 4 air shall not be recirculated or transferred to any

space nor recirculated within the space of origin.

EXEMPLE : biohazard lab, a containment area for dangerous

pathogens, or spaces handling hazardous waste

- Requirements for Buildings Containing ETS Areas and ETS-Free

Areas :

-Classification : All spaces shall be classified as either ETS-free

areas or ETS areas.

-Pressurization. ETS-free areas shall be at a positive pressure with

respect to any adjacent or connected ETS areas.
ETS-free areas (areas that are free from environmental
tobacco smoke) should always be at a positive pressure
compared to any adjacent or connected ETS areas (areas where
smoking is allowed or where tobacco smoke may be present). This
ensures that smoke and contaminants from the ETS areas don't
flow into the ETS-free areas, maintaining a clean air environment
and protecting occupants from harmful tobacco smoke.
 -Separation: Solid walls, floors, ceilings, and doors equipped with
automatic closing mechanisms shall separate ETS areas from ETS-
free areas

-Transfer Air. When air is transferred from ETSfree areas to ETS

areas, the transfer airflow rate shall be maintained regardless of
whether operable doors or windows between ETS-free and ETS
areas are opened or closed.

EXEMPLE : In a building, there is a non-smoking office (ETS-free

area) and a smoking lounge (ETS area).
To maintain a consistent airflow rate, air from the non-smoking
office must be transferred to the smoking lounge, regardless of
whether the door between them is open or closed.
This could be done through transfer ducts or fixed grilles in the
walls to ensure that the air flow remains the same and tobacco
smoke is kept contained.

-Recirculation : Air-handling and natural ventilation systems shall

not recirculate or transfer air from an ETS area to an ETS-free area.

-Exhaust Systems : This requirement ensures that exhaust or relief

air from an ETS area (an area where smoking is allowed or where
tobacco smoke is present) is properly ventilated to prevent smoke
and contaminants from being recirculated into any ETS-free area (an
area where smoking is not allowed).

-Signage : A sign shall be posted outside each entrance to each ETS

area. The sign shall state, as a minimum, “This Area May Contain
Environmental Tobacco Smoke”

4- PROCEDURES
This section is not required for natural ventilation
systems;

-Ventilation Rate Procedure :This is a prescriptive procedure in which

outdoor air intake rates are determined based on space type/application,
occupancy level, and floor area.
-The IAQ (Indoor Air Quality) Procedure is a design methodology
used in building systems to manage indoor air quality by analyzing
various factors that affect air cleanliness. This procedure focuses on
controlling the sources of contaminants, achieving target
contaminant levels, and ensuring acceptable air quality for building
occupants.

Breathing Zone Outdoor Airflow : =R .P +R . A

v bz p z a z

Where :
A z : zone floor area

PZ : zone population

R p: outdoor airflow rate required per person

Ra :outdoor airflow rate required per unit area

This equation is used to calculate the amount of outdoor air required to be

supplied to a breathing zone in a building by considering:

People-related sources: Contaminants produced by people in the space

(CO2 exhalation, body odors).

Area-related sources: Contaminants originating from other sources

within the space (furniture, materials, equipment).

Zone Outdoor Airflow : The design zone outdoor airflow v oz

refers to the amount of outdoor air that must be supplied to a given zone
of a building through the supply air distribution system .

vo z =v bz {E ¿z

Where :

Ez : Zone Air Distribution Effectiveness

v bz : Breathing Zone Outdoor Airflow

Single-Zone Systems : When there is a mixture between
the outdoor air and recirculated air to a single zone , the outdoor air
intake flow is determined by :

vo t =v oz

100% outdoor air Systems : the air handler only

supplies outdoor air to one or more zones, with no recirculated air. This
means the system is designed to provide fresh air from the outside to
maintain indoor air quality and meet ventilation requirements. The
outdoor intake flow v ot is determined by :

v ot =∑all zones
v oz

Primary Outdoor Air Fraction : The Primary

Outdoor Air Fraction (Zp) is a measure used to assess the efficiency of
an HVAC system in terms of how much of the air supplied to a zone is
outdoor air. This means the system is designed to provide fresh air from
the outside to maintain indoor air quality and meet ventilation
requirements. The outdoor intake flow v ot is determined by :

zp =v oz {v ¿ p z

Where :
v pz : the total airflow supplied to the zone, which includes both outdoor air

(Voz) and any recirculated air from the indoor environment.

Uncorrected Outdoor Air Intake: v ourepresents the

total amount of outdoor air that the system needs to supply to the
building or zones

This value is calculated based on two things:

1. The number of people in each zone.

2. The floor area of each zone.

However, Vou doesn't consider the efficiency of the ventilation system. It
assumes the system is working at a standard, normal efficiency and
doesn't adjust for how well it actually delivers air.

=D ∑
vou
all zones .
¿ ¿ P z ¿+ ∑
all zones .
¿¿ A ¿
z

Where :

D=P s / ∑ Pz
all zones

D is the occupant diversity

Ps : the total population in the area served by the system.

Outdoor Air Intake: the outdoor air intake flow is

determined by :

v ot =v ou { E ¿v

where :
E v : The system ventilation efficiency

If it is known that peak occupancy will be of short duration and/or

ventilation will be varied or interrupted for a short period of time, the
design may be based on the average conditions over a time period T
determined by :

T =3 v {v ¿ bz

Where :
T = averaging time, min

v = the volume of the zone for which averaging is being applied, (m3 )
v bz= the breathing zone outdoor airflow calculated

Average Outdoor Air Fraction: is a value that tells us

what percentage of the air that is being circulated in a building comes
from outdoor air versus recycled indoor air .

Xs =v ou {v ¿ ps

Where :

System Primary Airflow: v ps The total primary airflow supplied

to all zones served by the system from the airhandling unit at which the
outdoor air intake is located,

v ps =∑ v pz

Discharge Outdoor Air Fraction: represents the

proportion of outdoor air in the total air discharged to the occupied zone.
It indicates how much fresh air is actually reaching the zone compared to
the total air supplied by the ventilation system

Zd =v oz {v ¿ dz

Where :

Zone Discharge Airflow: v dzThe expected discharge (supply) airflow to the

zone that includes primary airflow and locally recirculated airflow
5 - CONSTRUCTION AND SYSTEM START-UP
This section is about the requirements that we ca apply in both new and
exesting buildings .

First of all , the systems designed with filters should not be operated
without them .

Materials should be protected from any form of mold , moisture , rain ,…

To prevent the migration of constraction generated contaminants liske

dust , fume , we should be sealing the construction area for exemple by
using temporary walls , or plastic sheeting . We can also exhaust the
construction area by using ventilation systems to remove and reduce
contaminants .

For the system strat up : we should make sure that the ventilation
systems are balanced in accordance with ashrae standard , we should test
the ventilation air distribution systems and clean them up and finally
make sure that each ventilation system operate properly .

6 - INFORMATIVE APPENDIX C RATIONALE FOR

MINIMUM PHYSIOLOGICAL REQUIREMENTS FOR
RESPIRATION AIR BASED ON CO2 CONCENTRATION

-Mass Balance Equation for Ventilation or Steady-

State CO₂ Ventilation Equation :
v0 = N /C s-C 0

Where :
v 0 : outdoor airflow rate per person

N : CO2 generation rate per person

C s: CO2 concentration in the space

C 0:CO2 concentration in outdoor air

7 -SEPARATION OF EXHAUST OUTLETS AND OUTDOOR
AIR INTAKES

This section describes the minimum separation distance (L) required

between exhaust air outlets (such as vents and ducts) and outdoor air
intakes, operable windows, skylights, and doors.

Purpose: To prevent contaminated exhaust air from being drawn back

into the building or into neighboring properties.

Measurement Method:

 The distance L is the shortest possible "stretched string" distance

between the exhaust outlet and the intake/opening.

 This means if you were to physically stretch a string between the

two points, the length of that string would represent L.