residential hvac filtration - what does it do?

Residential HVAC Filtration What Does it Do?

T.J. Ptak and Chrystal Gillilan

Presented at National Air Filtration Association, TECH

2009

Scope

Introduction Indoor air quality

Airborne contaminantsFilter performance test methodResidential HVAC systemImpact of filter efficiency on indoor airEnergy cost Conclusions

Indoor Air Quality

Air pollutionUnwanted substances

Particulate matter including bioaerosolsGaseous pollutants, radon, noise

U.S. residents spend* 87% of time indoors 7.2% in transit and 5.6% outdoors

Indoor and outdoor air pollutantsIndoor concentration >outdoor concentration

*R. Wilson and J. Spengler – Particles in Our Air

Indoor Air Quality – Commercial Buildings

Sick Building Syndrome (SBS)30% office buildings suffer from SBS (64 million

workers)

Indoor Air Pollution costs employees $150 billion in employee productivity 5 -7 % productivity loses

Productivity loss $22.67/Ft2

Indoor Air Quality – Residential Buildings

Over 50% of homes have at least 6 detectable allergens present

Allergic diseases affect as many as 40 -50 mln

Asthma (chronic disease) affects about :20 mln adult Americans

9 mln children

Allergic asthma – allergens (dust mites, mold, animal dander, pollen) make their symptoms worse

Asthma costs USA $18 billion Source: American Academy of Allergy Asthma & Immunology

Indoor Air Quality – Health Impact

Short term and chronic exposure to particulate matter (PM) is associated with:

Relationship between mortality rate and PM2.5 concentration

Increased morbidity and mortality Respiratory and cardiovascular disease

Pulmonary inflammation, oxidative stress, endothelial dysfunction,

Combustion PM associated with mortality

Ultrafine particles induce reactive oxygen species, oxidative stress and inflammation

Source: American Journal of Respiratory and Critical Care Medicine

Indoor Air Quality – Impact of Filtration

Filtration impact on microvascular function (MVF):21 couples, nonsmokers

During test ( 48 hrs) participant stayed home

Concentration of particles (0.1 – 0.7 µm) was monitoredBaseline concentration 10,016 #/cm3

Filtered 3,206 #/cm3

MVF was measured

Results: Indoor air filtration significantly improved MVP by 8.1%

Source: American Journal of Respiratory and Critical Care Medicine

Personal and AmbientPersonal and outdoor PM2.5

Good correlation (impact of ETS)

Personal and outdoor PM10 CPersonal = 55 + 0.6 COutdoor [µg/m3]Weak correlation

*R. Wilson and J. Spengler – Particles in Our Air

Indoor Air Particle size - 0.005 to 500 micrometers Sources:

Outdoor Infiltration

Tobacco smoke, stoves, fireplaces Occupant activities Carpets, curtains, furniture Emission by humans

100,000 to 10,000,000 particles per minute

Relationship between indoor/outdoor concentrationResidence with smokers 4.4Residence without smokers 1.1 - 1.4Indoor sources – cooking 5 - 10

Particle Size

Tobacco smoke 0.01 – 1 µmHousehold dust 0.05 – 100

– Pet dander 0.5 – 100– Dust mite debris 0.5 – 50– Skin flakes 0.4 – 10– Cooking smoke/grease 0.02 – 2

Pollen 5 – 100Bacteria 0.2 – 20Viruses 0.005 – 0.1Biological agents 0.5 – 5 Molecules < 0.001

Settling velocity of 10 µm particle V = 1.5 fpm

Household Aerosols

PARTICLE SIZE, MICROMETERS

0.01 0.1 1 10 100

Pet Dander

Dust Mite Debris

Skin Flakes

Can

Tobacco Smoke

Cooking smoke

Pollens

Bacteria

Hair

Lung Deposition

Particle deposition in lungs

Source; J. Heyder, GSF

Lung Deposition

Particle deposition in respiratory tract: Upper, upper bronchial, lower bronchial, alveolar

Source; J. Heyder, GSF

Scope



ASHRAE 52.2 Test Method

Filtration efficiency for particle sizes 0.3 to 10 m Challenge aerosol KCl

Test dust ASHRAE

Initial efficiency and efficiency after dust loading

Efficiency for three particle size ranges:E1 0.3 – 1.0 m

E2 1.0 – 3.0 m

E3 3.0 – 10 m

Minimum Efficiency Reporting Value (MERV)

ASHRAE 52.2 Test Method

Air flow rate (face velocity) for testing 118 – 246 – 295 – 374 - 492 – 630 – 748 fpm

Concept of the face velocity strongly influenced by commercial HVAC

Residential HVAC – filter tested at 295 and 492 fpm

Final resistance of filter after dust loadingGreater than twice the initial resistance

Minimum final resistance depends on MERV

Does not reflect conditions for residential HVAC

ASHRAE 52.2 and residential HVAC

MERV

GROUP NUMBER

MERV RATING

E1 Average Particle

Size Efficiency (PSE) 0.3 - 1.0 Microns

E2 Average Particle


E3 Average Particle


Average Arrestance

(ASHRAE 52.1

Minimum Final

Resistance (In W.G.)

1 MERV 1 MERV 2 MERV 3 MERV 4

Less than 20 % Less than 20% Less than 20% Less than 20%

Less than 65% 65 - 69.9% 70 - 74.9%

75% or greater

0.3" 0.3" 0.3" 0.3"


20 - 34.9% 35 - 49.9% 50 - 69.9% 70 - 84.9%

0.6" 0.6" 0.6" 0.6"


Less than 50% 50% - 64/9% 65% - 79.9% 80% - 89.9%

85% or greater 85% or greater 85% or greater 90% or greater

1.0" 1.0" 1.0" 1.0"


Less than 75% 75% - 84.9% 85% - 94.9%

95% or greater



1.4" 1.4" 1.4" 1.4"

Residential HVAC

Building as protection against outdoor contaminants

Residential HVAC systemsIndoor sources of particulate matter

Re-circulating air

Portable air cleaners

InfiltrationRecommended < 0.06 cfm/ft2 of outside area at ΔP = 0.30”

H2OTypical commercial and residential infiltration is higher

Residential HVAC

Major componentsReturn and supply ducts

BlowersPermanent Split Capacitor (PSC) Brushless Permanent Magnet (BPM)Rated at Total External Static Pressure ΔP = 0.5 in. H2O

FiltersIdeal filter ΔP < 20% TESP

HeatersIdeal coil ΔP < 40% TESP

Typical Residential HVAC

ΔPS (+) ΔPR (-)

SUPPLY RETURN

HEATING

F

Flow Rate

Fan curve for PSC blower Typical, small residential PSC blowers ⅓

HP

Types of Residential Filters

Pleated and flat panel – 1 and 4” deep

Residential HVAC

Residential furnace filters – typical issuesFilter bypass

Lack of seal, gasketsFilter size does not match size of specific housing

Undersized filters for given flow rate

Filter area not fully utilized

Non-uniform air velocity

Inefficient filtersLarge number of MERV 7-8 filtersMajority filters MERV 10

Undersized Filters

Practical industry standardsOne ton of cooling 12,000 BtuCooling airflow 400 cfm/tonHeating airflow 100 – 150

cfm/10,000 Btu

Undersized filters for given flow rate

Filter Face area, [ft2] Flow rate @ 295 fpm

16 x 25 2.47 82020 x 20 2.47 82020 x 25 3.47 1,024

Filter Area Utilization

Change in cross section area of a return ductSmaller inlet to the blower

Test Overview

Selection of residential furnace filtersDimensions20 x 25 x 5 in.Efficiency MERV 4 – 16

Filter testing according to ASHRAE 52.2

Laboratory testingFilter efficiency measurement using test set up

simulating a typical residential furnace Impact of seal and filter bypass

Test houseConcentration of particulates inside test housePower consumption – test house

Laboratory Test

Blower Permanent Split Capacitor (PSC)

¾ HP

Test set up Duct dimensions 28 x 12 in.

28 x 21 in.

Filter housing 21 x 28 x 7 in. Filter dimensions 20 x 25 x 5 in.

Measurements Air velocity Filter efficiency

Air Velocity

Air velocity across MERV 8 filter Measurements 2 in. from the test filter Theoretical air velocity V = 576 fpm Turbulent flow due to sharp turns

Performance of Selected FiltersFilters tested according to ASHRAE 52.2

Filter dimensions 20 x 25 x5 in.

Filter efficiency at 1200 cfm



Filter efficiency at 2000 cfm



Filter pressure drop

Filter Bypass

Filter penetration, P with bypass flow, QB

Bypass flow through gaps

Efficiency decrease depends on:Bypass flowFilter efficiency without bypassU-shaped 10 mm gap at ΔP = 50 Pa QB/Q

~20%

𝛥𝑃= 12𝜇𝐿𝑊𝐻3 𝑄𝐵 + ሺ1.5+𝑛ሻ𝜌2𝑊2 𝐻2 𝑄𝐵2

Q

QPQPP BBFF

Filter Efficiency

Filter initial efficiency at the flow rate of 2000 cfmE1 efficiency for submicron particles (0.3 – 1)Ambient aerosolOptical particle counter

Filter MERV 8 MERV 13 MERV 16ASHRAE 52.2 23.0 64.3 95.0Test set up 20.0 59.7 91.2

NOTE: MERV 13 filter ΔP = 0.48 in. H2O at 2000 cfmMERV 16 filter ΔP = 0.32 in. H2O at 2000 cfm

Impact of Bypass

Filter initial efficiency at the flow rate of 2000 cfmE1 efficiency for submicron particles (0.3 – 1)Ambient aerosolOptical particle counter

Filter MERV 8 MERV 13 MERV 16Test set up 20.0 59.7 91.2With 5 mm gap* n/a 58.1 89.1

NOTE: *Bypass gap 250 x 5 mm (10 x 0.25 in.)

Scope


Airborne contaminantsFilter performance test methodResidential HVAC systemImpact of filter efficiency on indoor

airEnergy cost Conclusions

Cleaning Effectiveness – Particle Decay

Concentration of particles Submicron 0.3 – 0.5 micron

E2 range 1 – 3 micron

Instrument optical particle counter

Location 36 in. above the floor

Test house House size 2300 ft2

Blower PSC, heating mode

Test filters Dimensions 20 x 25 x 5 and 20 x 25 x 1 in.

Seal gasket around filters

Cleaning Effectiveness – Impact of MERV

Particle decay for 0.3 – 0.5 micron particles

Cleaning Effectiveness – Impact of MERV

Particle decay for 1 – 3 micron particles

Cleaning Effectiveness – Filter Size Impact


Cleaning Effectiveness – Filter ΔP impact


ΔP = 0.15 and ΔP = 0.49 in. H2O @ 1200 cfm

Scope



Life Cycle Costs

Life Cycle Costs (LCC) widely used to design energy efficient commercial HVAC systems

LCC = Initial Investment + Energy Cost +

Maintenance Cost +

Cost of Disposal

Cost of energy during filter service lifeFlow rate, average filter pressure drop and

energy cost PTPQ

tEnergy8515

[$]cos

Typical Residential HVAC

ΔPS (+) ΔPR (-)

SUPPLY RETURN

HEATING

F

Flow Rate

Fan curve for PSC blower Typical, small residential PSC blowers ⅓

HP

Power Consumption

Power consumption for PSC blower Typical, small residential PSC blowers ⅓

HP

Test House

HVAC System Duct dimensions 24 x 10 in. Blower PSC – 1/3 HP

Rated at TESP 0.50 in. H2O

Furnace 88,000Btu Filter dimensions 20 x 25 x 5 in.

Measurements Flow rate

Air velocity in the return duct Filter pressure drop

Power consumption

Test Results

Filter Filter ΔP Flow Power ΔPR ΔPS [in. H2O] [cfm] [W] [in. H2O]

NO FILTER 1232 636 -0.23 0.11MERV 8 0.13 1172 606 -0.22 0.10MERV 16 0.17 1117 600 -0.19 0.10MERV 16 – H 0.42 950 552 -0.13 0.07

COMMENTS:• Flow rate without filter is comparable to the fan curve•Power usage is comparable the fan curve•Pressure drop in the return and supply ducts is significant•Filter pressure drop inside the system

Impact on Heating Time

Test results

Test house 2300 Ft2

Mode Heating

Test time 1-1.5 hr per filter

Outside temperature 30 – 35oFDuring test temperature within 2oF

Test filters MERV 8

MERV16 – High

MERV 8 filter ΔP = 0.10 in. H2O @ 1200 cfm

MERV 16 – H filter ΔP = 0.49 in. H2O @ 1200 cfm


Average heating time for each filter was measured

Heating time for high ΔP filterRatio = --------------------------------------- Heating time for low ΔP filter


Blower electrical energyHigh ΔP filter Low

ΔP filterPower usage, [W] 552 606Corrected for time 592 606Annual heating 2080 hrs 1231 kWh 1260 kWhCost @ $0.10/kWh, [$] 123 126

Furnace – natural gasHigh ΔP filter Low

ΔP filterAnnual energy, [therm] 790Corrected for time 848 790Cost @ $1.30/therm, [$] 1102 1027

TOTAL COST, [$] 1225 1153

Summary

Literature data support link between exposure to submicron particles and health issues

Performance of residential filters in real life conditions does not correlate well with the laboratory testing according to ASHRAE 52.2 due to lower test face velocity (295 fpm), flow conditions, leaks, duct construction

Low grade residential HVAC filters (MERV ≤ 10) do not provide sufficient protection against airborne particles

In order to decrease cardiovascular risk and other health hazards associated with exposure to air pollution, high efficiency residential filters such as MERV 14 – 16 should be used

Summary

Energy cost to operate residential HVAC system during heating mode is higher for high resistance filters

Residential HVAC systems with PSC blowers and installed high pressure drop filters require: Longer time to heat specific space resulting in higher

operational cost

Longer time to reduce concentration of airborne particles due to reduced flow rate

residential hvac filtration - what does it do?

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