03 - air quality

8/9/2019 03 - Air Quality

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Indoor Air Quality (IAQ)

Qualidade do Ar Interior QAI

Sources of pollutants

Effect on health and limits

Pollutant emission from persons

olf and decipol units

Mass balance to pollutantsUse of recirculation with filters

RSECE‐QAI Flow rates and limits

Internal Air Quality (IAQ)

• For comfort, indoor air quality may be said to be acceptable

if not more than

– 50% of the occupants can detect any odour

– 20% experience discomfort

– 10% suffer from mucosal irritation

– 5% experience annoyance

for less than 2% of the time.

• To guarantee air quality

– Maximum concentration of certain pollutants are defined

– Minimum flow rate of fresh air are defined per occupant

Values depend on human activity and building materials


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Sick Buildings

• sick building defined as a building in which a significant number (more than 20 percent) of occupants report illness perceived as being building related.

, , , , and throat irritation, dryness of mucous membranes and skin, nose bleeds, skin rash, mental fatigue, headache, cough, hoarseness, wheezing, nausea, and dizziness.

• Identification of main causes of sick buildings in 80s (why?):

Table from S. Wang – Handbook of Air Conditioning

Reference ventilation rate

• Due to oil shock crisis the reference values were

lowered leading in the 80’s to health problems

Since 1989

Untill when? w

r a t e ( m 3 / h /

p e r s o n )

How is the ventilation rate

related to energy consumption?

F r e s h a i r f l o

From José Luís Alexandre, FEUP


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Sources of pollutants

• Occupants (CO2, moisture, particles, odours)

• Smoking (CO2, CO, particles, PAHs, VOC, odours)

• Building materials (furniture coatings, adhesives,

carpets, dusts, house mites) ácaros

• Equipments (printers, copiers, computers, burners

and boilers) (gas and solid emissions and odours)

, • HVAC equipment (VOC (Refrig.), dust, legionella)

• Land and water (Radon, Chlorine)

Particulate Classification

• Dusts, fumes and smokes – Mainly solid

• Mists fo s and smo s – Mainl li uid smaller

• Bioaerosols – Viruses, bacteria, fungal spores

• Acording to the size can be:

– Visible or invisible

– Macroscopic, microscopic or submicroscopic or

– .

– Nowadays classified by mean diameter: PM10; PM2.5; etc.

• Accoding to the interaction with persons:

– Inhalable (


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Limits and Health Effects• Particulates – Limit of 50 μg/m3 (1 year) and 150

μg/m3 (1 day). Main problem with diameters from 1

to 10 μm retained on body.

• CO (Carbon Monoxide) – Colorless and odorless

affects O2 distribution in body (35/9 ppm @ 8/1h)

• VOC (Volatile Organic Compounds) – Irritation of

. • Radon ‐ colorless, odorless, inert radiative gas widely

found in soil, rocks, and water, created by the decay of

the radium and uranium. Fix in lung and give cancer.

Legislation for air quality

• There are several sources of information for limits of

pollutants for human occupation:

• Laboral legislation: NP 1796‐1988 Higiene e segurança no trabalho: valores limites de exposição para substâncias nocivas

existentes no ar dos locais de trabalho• World Health Organization

• HVAC regulations/Regulations

e.g. CO limits are established in ppm for short (1h)

and long (8h) exposure.

Values in ppm can be converted to mg/m3 (@25oC) by:

5.24)()/( 3 iii M

ppm X mmgC


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CO/CO2 Limits (From José Luis Alexandre, FEUP)

WHO(mg/m3)

NP

(mg/m3)

ASHRAE 62‐2001


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r i s o n

A E C o m p

A S H

ASHRAE Fundamentals 2009; Ch. 10

RSECE ‐ QAI

Indicado em tabela que é PM10

UFC – Unidades Formadoras

de Colónias

Pesquisa obrigatória apenas em edifícios construídos em zonas

graníticas, nomeadamente nos

distritos de Braga, Vila Real, Porto,

Guarda, Viseu e Castelo Branco

Bq ‐ Becquerel corresponde

a uma desintegração de um

núcleo por segundo

9—Em edifícios com sistemas de climatização em que haja produção de aerossóis,

nomeadamente onde haja torres de arrefecimento ou humidificadores por água líquida,

ou com sistemas de água quente para chuveiros onde a temperatura de armazenamento

seja inferior a 60oC as auditorias da QAI incluem também a pesquisa da presença de

colónias de Legionella em amostras de água recolhidas nos locais de maior risco,

nomeadamente tanques das torres de arrefecimento, depósitos de água quente e

tabuleiros de condensação, não devendo ser excedido um número superior a 100 UFC.


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Emissions from occupants I

• CO2 and H2O release depend on person and activity

Tabela extraída de José Luis Alexandre, FEUP

Emissions from occupants II

ASHRAE A08: Ch. 45 – Control of Gaseous Indoor Air Contaminants


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Mass balance to pollutant• Volumetric flows ( ) for new air (n), insuflation (i ),

infiltration from outside (o), extracted by ventilation (e)

•

V

.

• Pollutant concentration (C ) with values in the room space (s), outside environment (o) and in the insuflation (i ) inlet.

• For a room of volume V and air recirculation R:

oso C C V onC V

iiC V seC V

s

se C RV )1( se RC V

The insulation and extraction are not always similar and in that case the

infiltration is not a direct exchange with the outside ambient.

If there is no balance between all the streams the concentration in the room

may change along time (accumulation or decrease along time).

Dilution with new air

sC V

sC V G

as C C V

sC V G

oC V

• Considering a global ventilation flow rate ( ) either forced or natural the concentration in the room may be obtained as:

so C V GC V V GC C os

• Based on the person production of 19 L/h CO2 and with the limit of 1800 m m3 or 1000 m and with 400 m in the

V

environment we can define the required new air flow rate:

persson/3166710)4001000(

196 h L

X X

GV

os

Volumetric

m3

h pers.32The Oxygen requirement is lower and therefore is satisfied.CO2 limits from other sources are in general >2500 ppm !

For CO limit with 40% smokers (calculate the value) + 2 m3/h pers.


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Odours• Outdoor – Automotive exhaust, waste or sewage plants .

• Indoor – tobacco, bathrooms, building materials, consumer products, humans.

• There are two important limits of concentration:

– Threshold limit value (TLV) – Value with adverse health consequences for exposure for 8h periods.

– Odor detection threshold (ODT) – Concentration detected by olfact

When the ratio between the two (TLV/ODT) is low there is higher risk.

• Other properties of odours are:

–

– Character (e.g. fishy, ,flowery). Level of unpleasant or pleasant

• The detailed characterisation of odour sources can only be done by mass spectrometry and gas chromatography but in general is not necessary and only a global relative value is used.

Pollutants quantification• The olf unit is defined as the emission of air pollutants (bio‐

effluents) generated by a standard person in thermal comfort

• The decipol is the resultant erceived oluttion level when the emission is ventilated with 10 L/s of unpolluted air.

• The percentage of dissatisfied persons is related with the

ventilation rate q

in (L/s)/olf by:

• The ventilation rate for a given value of sources and pollution

25.085.1exp395 qPPDO PPDo=100 % for q 14000 ppm (1,4%)

][

10/ DecipolC C

s LV OS

][/ olf Gs LV q


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OLF Emission sources

Emission (olf)

olf emissions per occupant Aditional olf emissions

from room type

Offices 0.3 0 – 1

Class rooms 0.3 0.1 – 0.6

Auditory 0.5 0.1 – 1.3

Room with carpets 1.5 0.1 – 4

House 0.1 0 – 1

Ventilation 0.2 0 – 0.4

Outside polutant level in Decipol

Pure Air (Mountain) 0 DecipolAir in city 0.05 to 0.3 Decipol

If the volume of air per person decreases from 10

m3 to 1 m3 the emissoin in olf is almost the double.

Table and values from José Luis Alexandre, FEUP

Definition of new air flow rate• For Cs=1.4 Decipol the PPDO for IAQ is 20%.

• Based on this value of decipol and from outside 0.3: – .

– Office as before with + 20% smokers: 23 L/s pers.

– Office as before with + carpet: 36 L/s pers.

Recomended values from W.P. Jones – Air Conditioning Engineering


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ASHRAE 62‐2001

Exigências de

caudais de ar

novo (RSECE)

RPH

nexo

Legislação anterior (98) exprimia valores em renovações por hora (2ª coluna) e duplicava valores na presença de fumadores.

Nova legislação exige valores superiores a 60 m3/h ocupante com extracção directa para exterior e pressão na zona de fumo inferior à restante Art 29 RSECE.


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Pollutant Removal• The removal of most pollutants is made by air renewal.

• The removal or articulates includin bioaerosols ma

also be achieved by filtering recirculated air.

• Microorganisms can also be removed by UV radiation

or using biocides or antimicrobials.

• VOCs and non‐organic gases (CO2, CO, etc) can also

be adsorbed in activated carbon or otassium

permanganate‐impregnated alumina and VOCs can be

converted in a catalytic surface using UV radiation.

Mass Balance to Pollutant

Scheme from ASHRAE

• The use of local

filters or collection

of pollutants is just

deduced from the

generation term.

Figura de ASHRAE HVAC Applications 07: Ch 45


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ASHRAE 62‐2001

• Air renewal may start some

• This norm includes the possibility of treating transient cases.

.

• After utilization air renewal

should also operate to lower

pollutants.

• For transient situations:

V

t V

V

o

V Initialss

eV GC

eC C

1

,

Mass Balance with Recirculation

iC V

sC

V

se C RV )1(

G

mC V

• The new air and extraction can be expressed as a fraction of the

insuflation flow rate and the recirculation ratio R as indicated.

•

seC V on

se RC V

o

C RV 1 s RC V

m

so

som RC C R

V

RC V C RV C

1

1

naasV

GC

RV

GC C

1

Without filters C i =C m

The balance is the same as considering only the new air supply


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Mass balance with filters

• Filters can be installed in the recirculation line or in

the insuflation line after the mixture.

• Considering the efficiencies of these filters as εr ; εm:

• Or expressing the total flow:

r mmo

s R

V G RC C

111

11

• The new air flow rate is

RC RC V

mar ms 11111

RV V n 1

Impingement panel filters

• Made of coarse highly porous fibers coated with a viscous substance to stick particles. Thickness from 13 to 100 mm and section up to 610x610 mm. Design at velocity from 1 to 4 m/s low De taP up to 125 Pa in operation , Low cost goo e iciency use before higher efficiency filters.

• Renewable‐media filters are panels where the medium is replaced

from a roll and they may be viscous or dry panel.• Dry extended‐surface filters (mangas) are supported by a wire

frame forming pocket. Media velocities range from 0.03 to 0.5 m/s, although approach velocities run to 4 m/s. Depth indirection of a r ow var es rom o mm. ommerc a es gns yp ca y have an initial resistance from 25 to 250 Pa. It is customary to replace the media when the final resistance of 125 Pa is reached for low‐resistance units and 500 Pa for the highest‐resistance units.


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Electrostatic filters• Electret filters are composed of electrostatically charged fibers.

The electrical charges are loaded during the filter production. The

chages on the fibers augment collection of smaller particles by

interception and diffusion (Brownian motion) with Coulomb forces

caused by the charges. There are three types of these filters: resin

wool, electret, and an electrostatically sprayed polymer.

• Electronic air cleaners can be highly efficient filters using

electrostatic precipitation to remove and collect particulate

, , .

air cleaner denotes a precipitator for HVAC air filtration. The filter

consists of an ionization section and a collecting plate section.

Charges of 6 to 25 kV are given to the dust and the particles are

later collected in grounded plates.

High efficiency filters

• Very high‐efficiency dry filters, HEPA (high‐efficiency particulate air) filters, and ULPA (ultralow‐penetration air) i ters exten e ‐sur ace con gurat on o eep space o s

of submicrometre glass fiber paper. These filters operate at duct velocities near 1.3 m/s, with resistance rising from 120

to more than 500 Pa over their service life. These filters are the standard for cleanroom

• Membrane filters are used mainly for air sampling and specialized small‐scale applications where their particular

, resistance, and high cost. They are available in many pore diameters and resistances and in flatsheet and pleated forms.


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Efficiencies for different sizes• Arrestance test – Measures the mass that

is retained in the filter but it does not

show any influence of the smaller dust.

• Dust spot – Is a test that measures the

opacity of a sample in a filter that

characterises the retention of finer

particles.

• DOP Penetration Test – For high efficiency filters is based on

the measuerement of the rate of droplets passing the filter

compared with upstream, with mean particle diamenter 0.3

μm !

Typical filter efficiencies

• Panel‐type or automatic roll (70 to 85% arrestance)

•

arrestance and 25 to 50% dust spot

• Extended surface, cartridge, bag, or electronic

(manually cleaned or replaceable media) 50 to 65% dust spot

• Use of prefilter (75 to 85% and 25 to 40%) and e ectron c ter or ot er w t to ust spot.

• Higher quality has second filter with 80 to 95% and further a high efficiency filter with DOP from 95 to 99.97% with a disposable cell.

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