Thermal Comfort & Health

8/6/2019 Thermal Comfort & Health

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HVAC for Comfort, Health

& Safety



Comfort

- “ASHRAE Std 55 the condition of mind which expresses satisfaction

.”with the environment•It is a cognitive process

• ,Influence by physical inputs physiology and personalpreference

’ - - :Engineer s practical rule of thumb.1 (Absence of discomfort no

)complaint.2 neutrality



Perception of Comfort

• ASHRAE attempts todefine objectively“what is comfortconditions?”

•

ASHRAE thermalsensation scale:• +3 hot• +2 warm• +1 slightly warm• 0 neutral• -1 slightly cool• -2 cool• -3 cold

0 1-1

20

P e r c e n

t a

g e

o f

p e o p

l e

d i

s s a

t i s

f i

e d



Comfort Conditions

• Human comfort occurs when thehealthy person can maintain thermal

balance with the surrounding.

• The physical factors for humancomfort are:

• DB temperature

• Humidity

• Relative velocity of air

• Temperature of nearby surfaces(radiative exchange)



Thermal environment forcomfort

Condition Value

Air Temperature 19-24 C

Relative humidity 40-70%

Air speed 0.1-0.2 m/s (no draught)

Radiant heat No direct exposure to

radiant heat source

Clothing Light clothing (personal)

Activity Sedentary (personal)

.Most people are not discomforted by the following



Comfort Zone According toASHRAE



Health

-“ WHO A state of complete ,hysical- ,ental and social well being not

merely the absence of diseases and”infirmity

Indoor Environmental Health is related( ).to indoor air quality IAQ-Building related illnesses due to poor

IAQ as a result of•Tight enclosure

•Pollutants•Long exposure duration



Poor IAQ

• Inadequate ventilation (50% of allcases)

• Poor intake/exhaust location

• Inadequate filtration or dirty filter

• Poor air distribution

•

Inadequate operation & maintenance



The Concerns of IAQ

• To protect equipment from

– Corrosion

– Dirt

– Reduce energy cost

• To protect occupants

– Clean air is important

• (Everyday, we breath in 20-30 kg of air.

Compare to just about 1 kg of foodand 3 kg of liquid.)



What is this?

“ , W e d o n o t filte r a ir w e b re a th o u tsid e

”w h y b o th e r w ith H V A C filtra tio n ?



Airborne Pollutants

•Particulates

• Nonbiological -Dusts, fumes, smokes , mists

• Bio-aerosols – viruses, bacteria, fungal spores•Gases & Vapors

• Organic (VOC, methane, benzene)

• Inorganic (CO2, SO2, H2S, NO2)•Units of measurement:•Particulates : mg/m3•Gases : ppm• To convert: ppm = (mg/m3) x 24.45• molecular weight•

•



Sources of Contamination

Category Sources Examples

Outside air Contaminated air Industrial emissionMoistureDust

Equipment HVACOffice Refrigerant leak VOCHuman Personal

CookingSmoking

Carbon dioxideOdor VOC

Processes LaboratoryBattery ChemicalsGasesAccidental Fire

SpillsCombustion productsFlue gases



Health Effect of Exposure

• Health effects depends on dose, size,toxicity

• A particulate must first be inhale to

be hazardous• Respirable particulates from <1 to

10μm

•

Particles smaller than 3μm is of primary concern as it is most likelyto be retained in the lung

• Particles larger than 10μm are

separated by the respiratory tract



Common Air ContaminantSizes

:Source ASHRAE Report



What to Filter?

Particulate Size (μm)Viruses 0.003-0.1

Bacteria 0.4-5

Fungal spores 2-10

Pollen 10-100Dust <100

Human hair 100-150

Respirable particles <10

• Typical 1 ft3 air contains 2.5 billionparticles

– 99% is smaller than 1μm

– 70% by weight comes from particles



Hazard Control

• The principles for controlling theindoor environment are:

• Substitution, Isolation ( but

sometimes not possible)• Ventilation

• Air cleaning (i.e. filtering)

V e n tila tio n a n d a ir cle a n in g a re

E n g in e e rin g co n tro l co m m o n ly u se d

.in H V A C sy ste m s



Control by Air Cleaning

• Two Types of air filters

• Particulate filter

•

Gas phase filter• Basic questions

• What are available?•

How are they rated?• How to select?

•

•



Particulate Air Filter

Pa n e l Filte r

P le a te d Filte r

B a g Filte r



Air Filter Selection

• Filter selection depends on the degree of aircleanliness required. The factors to consider:

1.Efficiency• Ability to remove particulates from air

stream•2. Air-flow resistance• Loss of total pressure• Increase energy

3.Dust holding capacity• Amount of particulates it can hold before

becoming inefficient•4. Space and cost required• •



ASHRAE 52.1 Filter Tests

• Two methods of testing filter efficiency

• By weight fraction that filter removesfrom air stream

– Weight arrestance efficiency• By particulate size that filter removes

from the air stream – Dust spot efficiency

•

• The filter efficiency required depends onthe indoor

• air quality that one would like to achieve.



Air Filter Rating (ASHRAE 52.1-1992)

1.% Arrestance efficiency• Measures how much dirt the filter

can hold. Captures larger particles(>10 micron)

2.% Dust spot Efficiency• Measures how well the filter captures

smaller particles (0.3 -10 micron)•

Problems are: – average efficiency – Test result is not reliable due to in

consistent dust size – confusion



ASHRAE 52.2-1999

• ASHRAE 52.2 –1999 specifiesefficiency byMERV rating

• Ranges fromlevel 1-20

• 1-6 for low efficiency

filter (prefilter)• 7-12 medium efficiency

(main filter)

• 13-20 higher efficiency

Media MERV

Throw-awayfiberglass media

1-4

30% pleated media 8

65% pleated media 13

95% pleated media 15



52.1 OR 52.2

•52.1

• Expressesefficiency as

overallpercentage

• Suitable for low

efficiency filter• Many local

standards still

refer to this

.5 2 2

• E x p re sse s

e fficie n cy a s a

fu n ctio n o f

sp e cific p a rticle

size s

• G a in in g p o p u la rity

• S o m e

m a n u fa ctu re rs

te st n e w p ro d u cts



DEP: HVAC Filter Requirements

DEP 31.76.10.10 AREA STANDARD (% dust

spot efficiency)

Control Room Fresh air intake/returnair

95/65

Electrical Aux Room Fresh air intake/returnair

95/65

Analyzer house Fresh air intake 85

Office/Meeting /Mess Fresh air intake 65

DEP 34.17.00.32 AREA STANDARD (% dustspot)

Office Fresh air intake 65Kitchen/canteen Fresh air intake 65

Laboratory Fresh air intake 65

Computer room Fresh air intake/return

65/65



ASHRAE 62.1- 2004

• Ventilation with outdoor air of acceptable quality

• The minimum of MERV 6 filter must

be used and it should be locatedupstream of cooling coils andwetted surfaces.

•

A t bl O td Ai Q lit



Acceptable Outdoor Air Quality



Applying the Right Filter forOffshore

• Minimum MERV 6 before cooling coil

• Minimum 65% dust spot efficiencyfor indoor environment which are

occupied on regular basis



One More Thing

10mm gap between filters can make MERV rating drop by 2 lev



What filter static pressureshould be used?

• Filter manufacturers provide bothclean and dirty filter pressure drops

• Example: a 30% DS filter is 0.5”/

1.0” wg

• Use the mean value for fancalculation

• Choose a fan with very steep fancurve so changes in static pressureresult only in small changes in air

volume



Gas Phase Contaminants

• Organic & inorganic gases of industrialorigin

• Harmful effects – toxicity, odor,irritation, corrosion

• ACGIH publishes Threshold Limit Values(TLV)

– FEV (Fatal Exposure Value) – STEL (short term exposure level) – TWA8 (Time weighted average 8-h) – Example, for H2S, FEV= 302 ppmSTEL=

50; TWA8= 22

• ASHRAE 62 “ concentration values of

toxic gases be kept below one-tenth”



How should gases and vaporbe removed?

• HEPA filter can remove down to 0.3μm range

• Gases and vapor is smaller than

0.1μm

• Particulate filter cannot removegases & vapor

• In HVAC when gas concentration low,gas adsorption by activated carbonis the most effective method



Gas Filter

: (M e d ia A ctiva te d ca rb o n g ra n u la r).o r p e lle tize d U su a lly p re ce d e d b y

-a p re filte r

What is activated carbon?



Activated Carbon

• Coconut shell, charcoal, coalheat treated to increase

internal pores

• Gas molecules attach to thesurface i.e. adsorbed by

activated carbon• Has large capacity for

organic molecules

• Can be impregnated withpotassium permanganate

•

Adsorbs and retain a widevariety of chemicals

• Adsorbs odor

• Inert and safe

•

•



Gas Filter TypicalConfiguration

-ter sized media are held between perforated retaining sheets or fibrous

.efficiency depends on filter and housing effectiveness



Moisture Coalescer

1st –stage vane to

remove droplets

2nd -stage filter to remove mist



Using moisture coalescer toremove salt-laden mist

• Protects ventilation system againstweather elements such as rain,spray, splash containing sea-salt

• Usually design in 2 or 3-stages

• DEP required salt aerosols reduced to5 ppm



Any Question?

Thermal Comfort & Health

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