© Professor Alan Hedge, Cornell University, January 2006
Ventilation standards
Past, Present, Future?
Why ventilate a building?
Comfort ventilation
reduces odors
improves thermal comfort
Health ventilation
dilutes air contaminants
provides “fresh” air
Structural cooling
maintains integrity of building envelope and building contents
Ventilation: Human issues
Comfort ventilation
Perceived indoor air quality
Odors
Olfs, decipols
Health ventilation
Toxicity, illness
Exposure guidelines:
Threshold limit values (TLVs)
Permissible exposure limits (PELs)
Time weighted average (TWA)
Short-term exposure limit (STEL)
Ceiling limit (CLG)
Biological Exposure Indices (BEIs)
Ventilation rate and SBS symptoms
(Menzies et al., 1990)
Air flow principles
Air flows from areas of high pressure to areas of low pressure.
Air flows from areas of positive pressure to areas of negative
pressure.
Blowing is easier than sucking!
Evolving Ventilation standards
Evolving Ventilation standards
Evolving Ventilation standards
Evolving Ventilation standards
Evolving Ventilation standards
Evolving Ventilation standards
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© Professor Alan Hedge, Cornell University, January 2006
Evolving Ventilation standards
Evolving Ventilation standards
Evolving Ventilation standards
Ventilation and IAQ
Increasing the outdoor air ventilation rate (assuming unpolluted
outdoor air) should have the greatest effect on pollutants from
indoor sources, such as body odor and tobacco smoke, rather than
ambient gases (O2, CO2 etc.).
Improving IAQ will improve occupant perceptions of their
environment and health.
Ventilation Requirements (Yaglou, 1937)
Ventilation Requirements (Yaglou, 1937)
Ventilation Requirements (Yaglou, 1937)
Ventilation Requirements (Yaglou, 1937)
Carbon Dioxide as an Indicator of Adequate
Ventilation
CO2 is a normal constituent of exhaled breath.
Outdoor CO2 is usually 300-400 ppm.
If indoor CO2 > 1000 ppm, sick building complaints begin to
prevail; mild physiological strain may occur.
High CO2 reading is indicative of poor ventilation, which can allow
other contaminants to accumulate.
CO2 levels can serve as a guideline for occupant comfort.
Carbon Dioxide (CO2) Generation
Indoor CO2 is directly proportional to the number of people in a
building and the ability of the ventilation system to dilute occupant
generated CO2.
ASHRAE 62-2001 assumes an average CO2 generation rate of
0.31 L min-1 (0.0106 cfm), which is the average generation rate for
1.2 met activity.
CO2 levels change as a function of activity and diet.
Approximate CO2 generation rates
ASHRAE 62-2001 ventilation standard
Specifies minimum ventilation rates and IAQ that will be acceptable and
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© Professor Alan Hedge, Cornell University, January 2006
minimize potential adverse health effects.
Applies to all enclosed spaces that people occupy.
Considers, chemical, physical and biological contaminants.
Excludes thermal comfort.
ASHRAE 62-2001
Defines acceptable indoor air quality as:
“Air in which there are no known contaminants at harmful
concentrations, as determined by cognizant authorities, and with
which a substantial majority (80% or more) of the people exposed
do not express dissatisfaction.”
ASHRAE 62-2001 Minimum Outdoor Air Ventilation
Rate
ASHRAE 62-2001 Ventilation Standard
ASHRAE 62- 2001 minimum recommendations:
20 cfm/Person for nonsmoking offices
15 cfm/Person for lobbies/reception areas
60 cfm/Person for smoking lounges
15 cfm/Person for classrooms
20 cfm/Person for laboratories
Standard assumes the following maximum density of people /1000 ft2 :
Offices = 7
Lobbies = 30
Smoking lounges = 70
Classrooms = 50
Laboratories = 30
Ventilation rate
Estimating % Outdoor Air Quantities
Thermal Mass Balance Equation:
Temperature (°F) can be used to estimate ventilation rate:
Outdoor air (%)=((Treturn air -Tmixed air)/(Treturn air -Toutdoor air))x100
Carbon dioxide concentration (C ppm) can be used to estimate
ventilation rate:
Outdoor air (%)=((Csupply air - Creturn air )/(Coutdoor air -Creturn air))x100
Converting Outdoor air % to ventilation rate (cfm):
Outdoor air (cfm)= (Outdoor air (%)/100) x total HVAC airflow (cfm)
Ventilation and IAQ:
common assumptions
Increasing the ventilation rate will reduce the concentration of
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© Professor Alan Hedge, Cornell University, January 2006
indoor air pollutants.
Increasing the ventilation rate will improve occupant perceptions of
IAQ.
Increasing the ventilation rate will decrease complaints of odors.
Increasing the ventilation rate will decrease complaints of the sick
building syndrome.
Comfort ventilation: odor control
Ventilation is needed to control indoor odors.
People are a source of indoor odors (body odor).
Body odor (sweaty armpit smell) is caused by 3-methyl-2-hexenoic acid, a
metabolic byproduct of bacteria that live in the armpit (lipophilic diptheroids)
and feed on apocrine secretions.
~90% of men and 67% of women have these bacteria resident in the armpit,
and women produce a milder odor than men.
~5% of people cannot smell body odor.
Perceived Air Quality
Perceived air quality depends on:
general chemical sense (all mucus membranes, eyes, nose, throat) irritation
olfaction (nose, tongue) - odor (smell)
2 aspects of odor perception:
Intensity (quantitative measure)
Offensiveness (qualitative measure)
Odor perception follows Weber-Fechner Law (S=Klog10I, where I is
the concentration and K (constant of proportionality) varies with odor
offensiveness)
Odor Perception
Olfaction can be extremely sensitive with some odor thresholds in the ppb
range.
Odor adaptation occurs rapidly, and ratings usually include:
Instantaneous impressions (higher odor ratings at first)
Residual impressions (lower odor ratings after adaptation)
Odor masking occurs with competing chemicals.
Odor perception can be influenced by air temperature (~10°C decrease from
30°C-20°C ~= 10-fold increase in ventilation rate from 0.5 - 5 m3min-1)
Odors: olfs and decipols (Fanger, 1988)
decipol - air pollution from 1 standard person (0.7 baths/day, 1.8m2, clean
underwear daily, 80% use deodorant) ventilated by 10l/s unpolluted air.
olf - relative measure of bioeffluents from standard person.
1 decipol = 0.1 olf/l/s.
olfs can be added.
Odors and perceived IAQ
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© Professor Alan Hedge, Cornell University, January 2006
(Fanger, 1988)
Olf values for humans
Sedentary person (1 met)
Active person (4 met)
Active person (6 met)
Smoker (not smoking)
Smoker smoking
1 olf
5 olf
11 olf
6 olf
25 olf
Olfs and interiors
Olf values can be determined for any interior furniture, finish or material.
For example, if a table is determined to have a source strength of 3 olf, then that level of
emissions will cause the same degree of disatisfaction as the pollution from 3 standard
persons (3 olf).
Decipol scale and Perceived Air Pollution
Outdoor air (Mountain)
Outdoor air (Town)
Indoor air (Healthy building)
Indoor air (Sick building)
0.01decipol
0.1 decipol
1.0 decipol
10.0 decipol
Comfort Ventilation Equation
Fanger proposes the following comfort ventilation equation:
Qc = 10 x (G/(Ci - Co)) x (1/Ev)
where Qc = ventilation rate for comfort (L sec-1)
G = sensory pollution load (olf)
Ci = desired perceived IAQ (decipol)
Co = perceived outdoor air quality at air
intake (decipol)
Ev = ventilation effectiveness(usually
assumed as 1)
Ventilation Standards
Proposed European approach is to calculate ventilation
requirements based on CO2 levels (occupancy) and odors (olfs).
The higher ventilation rate from both calculations is the one to be
applied.
Assumption is that ‘olfs’ are predictive of IAQ, which in turn is
predictive of SBS.
Heating, ventilating and
air-conditioning (HVAC) systems
Decentralized HVAC Systems
Individual unit ventilators dispersed around perimeter of a building.
Perimeter Fan coil - perimeter conditioning, no ducts.
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© Professor Alan Hedge, Cornell University, January 2006
Commonly found in schools, hotels, smaller office buildings.
CO2 and Occupant density
CO2 and Air changes per hour (ACH)
Centralized HVAC Systems
Building is subdivided into ventilation zones.
Each ventilation zone is served by an air handler unit (AHU).
Supply/exhaust air is ducted to/ from space from central AHUs.
Commonest systems in large buildings.
Centralized HVAC Systems
Ceiling heat pumps - air is ducted from a mechanical supply and
tempered locally at the point of supply to the space.
Constant air volume (CAV) - HVAC delivers a constant volume of air and
responds to changing thermal loads by varying air temperature.
Variable air volume (VAV) - HVAC delivers a constant temperature of air
and responds to changing thermal loads by varying the quantity of supply air.
ASHRAE Filter Ratings
(Kay et al., 1991)
ASHRAE 62-2001 Ventilation Standard
Ventilation rates specified in ASHRAE 62-2001 BUT...
if the ventilation system is contaminated a higher ventilation rate will
accelerate building contamination.
Ventilation standard focuses on HVAC design, operation, contamination and
maintenance issues, not merely ventilation rate. BUT ...
The standard does not directly address health issues.
ASHRAE Ventilation Standard
62-2001
Buildings that meet the ventilation requirements in ASHRAE 622001 should protect occupants with hazardous or unsatisfactory
indoor air quality.
Buildings that meet the ventilation requirements in ASHRAE 622001 should be free from occupant complaints.
No evidence that, above 20 cfmpp, changes in ventilation rate have
any beneficial effect on either perceived IAQ or SBS.
Strategies for Improving Indoor Air Quality
DEA 350 Human Factors - Ambient Environment
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© Professor Alan Hedge, Cornell University, January 2006
Ways to improve IAQ
Ensure a clean HVAC system
Dilution ventilation
Source control
Air cleaning
Space cleaning
Ensure a Clean HVAC System
Ensure optimum functioning of HVAC components:
Coils and Drain Pans
Humidification and Dehumidification Equipment
Outdoor Air Dampers
Air Filters
Ducts
Exhaust Systems
Return Air Plenum
VAV Boxes
Cooling Towers
Boilers
Dilution Ventilation
The commonest approach to improving IAQ
Outside air is introduced into a building in controlled quantities (cfm) to dilute
the concentration of indoor pollutants
To conserve energy, outdoor and indoor air usually mixed (20%:80%)
Indoor air gradually replaced by outdoor air (air changes per hour - ACH).
Assumes that indoor air is more polluted than outdoor air.,
Effects of outdoor air mix
(Jaakkola et al., 1990)
Compared SBS complaints in an office building ventilated by either
25% or 100% outdoor air.
No difference in the % SBS complaints with either 100% or 25%
outdoor air.
Ventilation rate, IAQ and comfort (Nagda et al. 1990)
Compared effects of 2 ventilation rates (16.5 cfmpp vs. 38 cfmpp)
on IAQ and comfort in a 20-story office building.
No effects of increased ventilation rate on IAQ - formaldehyde,
nicotine, RSP, CO, CO2.
slightly higher % occupants reporting dissatisfaction with thermal
comfort, odors and dust at the higher ventilation rate.
Dilution Ventilation Limitations
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© Professor Alan Hedge, Cornell University, January 2006
Dilution ventilation doesn’t work well when outdoor air is more polluted than
indoor air (e.g. pollen, fungi, smoke, smog, traffic fumes)
Dilution ventilation doesn’t work well when the ventilation system itself is
contaminated (e.g. biological contaminants in the air handler, ducts,
fiberglass)
Dilution ventilation is slow to respond to acute exposure situations (e.g. ETS)
Dilution ventilation rates are normally tied to thermal comfort issues
Pollution pathways
How might a pollutant move from source to occupant?
What pressure differentials exist?
HVAC systems
furnaces, fires
stack effect, wind effects
Are contaminant sources under negative pressure?
Are occupied areas under positive pressure?
Source Control - Identification
Outside sources
Equipment (dirty HVAC, stove)
Building components (dust, fibers, water damage, product
emissions, condensation)
Furnishings (emissions, dust mites)
Human activities (smoking, cooking, cleaning, painting)
Pesticides
Pollutants source control solutions
Remove or reduce the pollutant source
Seal or cover the pollutant source
Isolate the pollutant source
Modify the building
Air Cleaning - options
Ozone emitting air cleaners - not to be used in occupied spaces!
Mechanical filters (remove large particles)
HEPA filters (remove small particles)
Electrostatic filters, negative ionizers
Sorbent filters (remove VOCs, selective gases)
UV duct cleaning systems
Air Cleaning Solutions
Match air cleaning method to the suspected contaminant(s)
Match HVAC system and spatially localized (e.g. room based) air
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© Professor Alan Hedge, Cornell University, January 2006
cleaning and filtering technologies
Maintain equipment regularly
Monitor effect on suspected pollutant(s) and symptoms
Space Cleaning
Keeping a space clean for good IAQ requires:
Keeping dirt out
Using Maximum Extraction, Minimum Polluting equipment and methods
Choosing low polluting products
After spills or cleaning thoroughly dry wet carpet or other porous material
Properly mix and store housekeeping products in a ventilated room or closet
Train Housekeeping Personnel
Scrutinize contractors
Monitor results
Perceived IAQ:
What can we sense?
CO, CO2
Biologicals - fungal spores, viruses, bacteria, mites, etc.
VOCs - some
Ozone - mucosal irritation
Humidity - poorly
Temperature (skin)
Smoke - sight, smell
Occupant characteristics
Who is being affected?
What are the symptoms?
How long have symptoms been experienced?
When do they occur?
What susceptibilities exist (e.g. allergies)
Common factors in
IAQ problems
(after Davis & Brooks, 1992)
Situation characteristics
When did problems start?
What has recently changed?
Have obvious problems been fixed?
What interventions have been tried and which have worked?
Ventilation rate and SBS symptoms (Menzies
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© Professor Alan Hedge, Cornell University, January 2006
et al., 1990)
Ventilation rate and SBS symptoms (Menzies
et al., 1993)
Outdoor air ventilation rates were manipulated between 20 and 50
cfmpp within each of 4 office buildings for a 1 week period within 3
consecutive 2 week blocks.
Each week participants rated their environment and reported SBS
symptoms.
Increases in ventilation rate did not affect workers’ perceived IAQ
or SBS.
Ventilation, IAQ,Perception:
Have we been studying the appropriate relationships?
Effects of outdoor air mix
(Sterling & Sterling, 1983)
Compared the effects of 25% outdoor air and 87% outdoor air on %
SBS complaints.
No significant decreases in SBS symptoms by increasing the %
outdoor air ventilation.
IAQ and SBS in US Offices
(Hedge et al. 1989-1996)
Over 50 US office buildings and ~10,000 workers have been
studied.
No correlations between measured IAQ and SBS.
Some correlations between measured IAQ and perceived IAQ
(mainly thermal variables).
Perceived IAQ correlates with SBS.
Gender, occupational and psychosocial factors correlate with SBS.
Odors, IAQ and SBS
(Bluyssen et al. 1996)
Studied 55 office buildings from 9 European countries.
IAQ, SBS and ‘olfs’ (rated by a panel of ‘olfbusters’!) data were
collected.
No correlations between ‘olfs’ and perceived IAQ, measured IAQ,
or SBS.
No correlations between objective IAQ and SBS.
Perceived IAQ correlated with SBS.
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© Professor Alan Hedge, Cornell University, January 2006
Indoor Air Quality Concerns
Combustion gases (CO, CO2, NOx, SOx, O3)
Volatile organic compounds (VOCs - paints, adhesives, caulking,
cleaners)
Pesticides
Soil gases (Radon)
Biologicals (bacteria, fungi, mites, insects, pollens, pet dander
etc.)
Particles (ETS, lead, diesel)
Fibers (fiberglass, asbestos)
Ventilation, IAQ and SBS
“...the solution to SBS will only come from an inclusion of a wider
collection of disciplines from outside the natural sciences, such as
those involved in labor-management mediation and experimental
psychologists.”
David Grimsrud
Alternative Heating, Ventilating and
Air-conditioning (HVAC) System Designs
Conventional Dilution ventilation
Heating, Ventilation and Air Conditioning (HVAC)
Systems
Modern HVAC systems are mostly VAV designs
HVAC systems often the source of thermal discomfort
HVAC systems can be a source of contaminants(dirt, particulates, fibers,
microorganisms etc.)
Indoor Air Quality (IAQ)
and
Task Area Ventilation (TAV)
Inadequate Air Mixing
High office partitions can create zones of stagnant air in an office.
Inadequate Air Mixing
Why Task Area Ventilation?
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© Professor Alan Hedge, Cornell University, January 2006
System Lag - HVAC systems respond too slowly to transient environment
changes in pollutants.
Filtration - HVAC system cannot easily achieve high filtration efficiency.
Why Task Area Ventilation?
Energy efficiency - not all office air needs to be treated, only that in the breathing zone.
Thermal comfort - eliminating 'dead zones' improves thermal comfort conditions.
Personal control - most HVAC systems have only crude control mechanisms.
Task Air Systems
Under Floor Air Delivery
UC Berkeley Laboratory
(Faulkner et al., 1995)
Testing laboratory (5 m x 5 m x 2.5 m)
Two units directed towards occupant reduced age of air in the breathing zone
by up to 40%
Air travels from floor to ceiling in a piston-like way
Ventilation Layout Flexibility
Easily relocated, the TAM/MIT provides flexibility to deliver individualized
control
Personal Comfort Control
Adjusting the flow of air from the task air module allows the
individual better control over personal working environment
FUNDI
Functional Diagnostic Unit (FUNDI)
Collapsible, mobile modular workstation (1m x 1m x 1.75m collapsed and locked) with power,
data and phone
Personal controls for flexible position task light, radiant heat panel, air circulation fan, speech
privacy, visual privacy and spatial layout
Window with roller blind
White board, pin board
Height adjustable surfaces for computer screen, keyboard, document holder, printer
Overhead shelf and mobile pedestal storage
FUNDI Research
(Kaplan, 1987)
16 FUNDI units tested for 15 months
Environmental and subjective data collected from knowledge workers and office staff
Environmental controls perceived to significantly enhance the quality of the work setting
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© Professor Alan Hedge, Cornell University, January 2006
Better privacy that open-office cubicles
Perceived ability to control environment conditions decreased stress,and improved
satisfaction and performance.
Climadesk
Climadesk
Climadesk - developed by the Swedish National Board of Public Buildings
Individual temperature control
Individual filtered air supply
Low installation and annual running costs
Discreet and inaudible
Climadesk - Thermal Comfort
Two adjustable outlets under the desk cool the body
Fresh air above it reduces complaints of draughts and dry air
Heating from the adjustable surface temperature of a radiant panel under the
desk
Temperature range controllable from 2 °C above room temperature to 4 °C
below
Rapid response to adjustment
Climadesk - Air Quality
The Climadesk air filter combines electro-statically charged fibers and active
charcoal. It retains particles smaller than smoke, and absorbs most gases.
Climadesk supplies filtered air directly to the breathing zone.
An outdoor-air version suits allergic or hyper-sensitive users.
Air Filter/Task Light
Air Purification
Overhead task light and electronic air filter:
Carbon impregnated, non-woven polyester filter.
(Odor and particulate removal to .01 microns)
Passive electrostatic media (does not produce ozone - particulate
removal to .01 microns)
Antimicrobial treated non-woven polyester.
(Particulate removal to .01 microns. Inhibits mold, fungi and bacteria)
Breathing Zone Filtration
BZF Filter System
Pre-filter
(20% polyester filter for large particulates)
Charcoal filter (Polysorb for VOC removal)
HEPA
(99.97% efficient, for fine particles, biologicals, etc.)
BZF: Airflow system
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© Professor Alan Hedge, Cornell University, January 2006
BZF: Airflow Workstation
BZF Layouts
BZF Controls
Hudson County, NJ
(Hedge et al., 1991)
Study Design
(Hedge et al., 1991)
Pre-installation survey (4 floors)
BZF installation (2 floors)
1st post-installation survey (2 BZF floors, 2 control floors)
BZF installation on all floors
Final post-installation survey
Hudson County, NJ
BZF Effects
(Hedge et al., 1991)
on Particulates (Hedge et al., 1991:
Test floors)
BZF Effects on Employees
(Hedge et al., 1991)
Cornell Study:
Statistics Canada
(Hedge et al., 1993)
Statistics Canada
(Hedge et al., Indoor Air, 1993)
Statistics Canada
- IAQ Monitoring
BZF and VOCs
BZF and Particulates
BZF and PIAQ
BZF and SBS symptoms
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© Professor Alan Hedge, Cornell University, January 2006
BZF and SBS Effects on Productivity
Personal Environments
Personal Environments
Desktop control unit allows individual control for:
air temperature
air flow
radiant heat
lighting
background noise masking
Integrated occupancy sensor shuts the system down when the workstation is
empty, saving energy
Personal Environments
User control unit for:
Task light
Radiant heat panel
Diffusers
Fan & electronics unit
Particle filter
Air temperature
Supplies conditioned air to the desktop
Personal Environments
PEM unit interfaces with underfloor ventilation system
Personal Environments
The fan and electronics unit contains filters, an air mixing box and generates
background noise.
Two adjustable diffusers distribute the air.
A radiant heat panel provides extra warmth for feet and legs and fits
conveniently under the desk.
Personal Environments
Wide individual variations in preferred temperature
average for women = 24 °C (range 21.7 °C – 26.0 °C)
average for men = 22 °C (range 18.0 °C – 24.2 °C)
West Bend Study
(Kroner et al., 1993)
In a recent study, the West Bend Mutual Insurance Company attributed a 6 8% productivity gain to the installation of Personal Environments
In less than 18 months, the system paid for itself
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© Professor Alan Hedge, Cornell University, January 2006
West Bend Study
(Kroner et al., 1993)
West Bend Mutual Insurance Company, West Bend, Wisconsin
14,000 m2 company headquarters houses with >500 employees in
open-plan offices
>375 PEMs installed, access floor and indirect uplighting
16% total increased employee productivity
2.8 % increase attributed to Personal Environments
West Bend Study: Cost savings
(Kroner et al., 1993)
Thermal condition complaints virtually eliminated. Calls
plummeted from >40 per day (at a conservatively estimated cost of
$25 per call plus $300 in maintenance) to only 2 per week
(>US$6,500 decrease per week)
Reduced building construction costs from the market average of
$125 to $90 per square foot
Utility costs decreased >US$ 10,000 per month (~US$0.75 per m2
per month) in the new building
Personal Environments
Environmental comfort impacts employee productivity in open offices
~1% of the salaries in an average 46,500 m2 office building > US $975,000
~3% productivity gain when employees use Personal Environments
Productivity increase for average 46,500 m2 office building ~US $2,925,000
per year
Rapid payback for PEMs
Aura
Aura
Personal environmental control
Customized comfort zone
Small footprint with the usable space of a much larger standard office furniture
cubicle
Eliminates the cramped, claustrophobic feeling of a cubicle?
Aura Workstation
Compact footprint is only <3.2 m2
(actually 2.3m long x 1.8m wide x 2.4m high = 4.1m2 effective rectangular footprint)
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© Professor Alan Hedge, Cornell University, January 2006
Aura Workstation
Personal control of:
Air flow
Seating
Lighting
Sight lines
Aura's Rotation Feature
Pre-programmed to rotate
120° over 8 hours
Allows user to take advantage of natural sunlight cycle, avoid external glare,
vary sight lines, and change position for conferencing
Offers an optional quick
rotation adjustment
(120° in 15 seconds)
Can be adjusted manually
Airstream
Airstream Ventilation System (2000)
Personally controllable air delivery from HVAC system
Airstream Ventilation System (2000)
Energy efficiency
Not all office air needs to be treated, only that in the breathing zone
Thermal comfort
Eliminates 'dead zones' and improves thermal comfort conditions
Reconfigurable
Reconfigures with furniture
Airstream Ventilation
Personal control
most HVAC systems have only crude control mechanisms
Task area ventilation (TAV)
gives optimal local control
Benefits of Task Area Ventilation (TAV)
TAV can continuously provide clean air to employees.
TAV can augment HVAC performance and improve air mixing.
TAV can reconfigure with "office churn".
TAV can eliminate dead air spaces.
TAV can protects employees against transient air pollutants.
TAV may improve IAQ and reduces SBS.
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