Post on 18-Nov-2014
description
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
Introduction Indoor air quality
Airborne contaminantsFilter performance test methodResidential HVAC systemImpact of filter efficiency on indoor airEnergy cost Conclusions
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
Size Efficiency (PSE) 1.0 - 3.0 Microns
E3 Average Particle
Size Efficiency (PSE) 3.0 - 10.0 Microns
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"
2 MERV 5 MERV 6 MERV 7 MERV 8
20 - 34.9% 35 - 49.9% 50 - 69.9% 70 - 84.9%
0.6" 0.6" 0.6" 0.6"
3 MERV 9 MERV 10 MERV 11 MERV 12
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"
4 MERV 13 MERV 14 MERV 15 MERV 16
Less than 75% 75% - 84.9% 85% - 94.9%
95% or greater
90% or greater 90% or greater 90% or greater 95% or greater
90% or greater 90% or greater 90% or greater 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
Performance of Selected FiltersFilters tested according to ASHRAE 52.2
Filter dimensions 20 x 25 x5 in.
Filter efficiency at 2000 cfm
Performance of Selected FiltersFilters tested according to ASHRAE 52.2
Filter dimensions 20 x 25 x5 in.
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
Introduction Indoor air quality
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
Particle decay for 0.3 – 0.5 micron particles
Cleaning Effectiveness – Filter Size Impact
Particle decay for 1 – 3 micron particles
Cleaning Effectiveness – Filter ΔP impact
Particle decay for 0.3 – 0.5 micron particles
ΔP = 0.15 and ΔP = 0.49 in. H2O @ 1200 cfm
Cleaning Effectiveness – Filter ΔP impact
Particle decay for 1 – 3 micron particles
ΔP = 0.15 and ΔP = 0.49 in. H2O @ 1200 cfm
Scope
Introduction Indoor air quality
Airborne contaminantsFilter performance test methodResidential HVAC systemImpact of filter efficiency on indoor airEnergy cost Conclusions
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
Impact on Heating Time
Average heating time for each filter was measured
Heating time for high ΔP filterRatio = --------------------------------------- Heating time for low ΔP filter
Impact on Heating Time
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