Residential HVAC Filtration What Does it Do? T.J. Ptak and Chrystal Gillilan Presented at National Air Filtration Association, TECH 2009

Filter performance test method Residential HVAC system Scope Introduction Indoor air quality Airborne contaminants Filter performance test method Residential HVAC system Impact of filter efficiency on indoor air Energy cost Conclusions

Indoor and outdoor air pollutants Indoor Air Quality Air pollution Unwanted substances Particulate matter including bioaerosols Gaseous pollutants, radon, noise U.S. residents spend* 87% of time indoors 7.2% in transit and 5.6% outdoors Indoor and outdoor air pollutants Indoor 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 monitored Baseline 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 outdoor PM2.5 Personal and outdoor PM10 Personal and Ambient Personal 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

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

Tobacco smoke 0.01 – 1 µm Household dust 0.05 – 100 Pollen 5 – 100 Particle Size Tobacco smoke 0.01 – 1 µm Household 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 – 100 Bacteria 0.2 – 20 Viruses 0.005 – 0.1 Biological agents 0.5 – 5 Molecules < 0.001 Settling velocity of 10 µm particle V = 1.5 fpm

PARTICLE SIZE, MICROMETERS 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

Particle deposition in lungs Lung Deposition Particle deposition in lungs Source; J. Heyder, GSF

Particle deposition in respiratory tract: Lung Deposition Particle deposition in respiratory tract: Upper, upper bronchial, lower bronchial, alveolar Source; J. Heyder, GSF

Filter performance test method Residential HVAC system Scope Introduction Indoor air quality Airborne contaminants Filter performance test method Residential HVAC system Impact of filter efficiency on indoor air Energy cost Conclusions

Filtration efficiency for particle sizes 0.3 to 10 m 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 and residential HVAC 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 loading Greater 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

Building as protection against outdoor contaminants Residential HVAC Building as protection against outdoor contaminants Residential HVAC systems Indoor sources of particulate matter Re-circulating air Portable air cleaners Infiltration Recommended < 0.06 cfm/ft2 of outside area at ΔP = 0.30” H2O Typical commercial and residential infiltration is higher

Major components Residential HVAC Return and supply ducts Blowers Permanent Split Capacitor (PSC) Brushless Permanent Magnet (BPM) Rated at Total External Static Pressure ΔP = 0.5 in. H2O Filters Ideal filter ΔP < 20% TESP Heaters Ideal coil ΔP < 40% TESP

Typical Residential HVAC ΔPS (+) ΔPR (-) SUPPLY RETURN HEATING F

Fan curve for PSC blower 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 furnace filters – typical issues Residential HVAC Residential furnace filters – typical issues Filter bypass Lack of seal, gaskets Filter size does not match size of specific housing Undersized filters for given flow rate Filter area not fully utilized Non-uniform air velocity Inefficient filters Large number of MERV 7-8 filters Majority filters MERV 10

Practical industry standards Undersized Filters Practical industry standards One ton of cooling 12,000 Btu Cooling airflow 400 cfm/ton Heating airflow 100 – 150 cfm/10,000 Btu Undersized filters for given flow rate Filter Face area, [ft2] Flow rate @ 295 fpm 16 x 25 2.47 820 20 x 20 2.47 820 20 x 25 3.47 1,024

Filter Area Utilization Change in cross section area of a return duct Smaller inlet to the blower

Selection of residential furnace filters Test Overview Selection of residential furnace filters Dimensions 20 x 25 x 5 in. Efficiency MERV 4 – 16 Filter testing according to ASHRAE 52.2 Laboratory testing Filter efficiency measurement using test set up simulating a typical residential furnace Impact of seal and filter bypass Test house Concentration of particulates inside test house Power consumption – test house

Blower Test set up Measurements Air velocity Laboratory Test 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 Filters Filters tested according to ASHRAE 52.2 Filter dimensions 20 x 25 x5 in. Filter efficiency at 1200 cfm

Performance of Selected Filters Filters tested according to ASHRAE 52.2 Filter dimensions 20 x 25 x5 in. Filter efficiency at 2000 cfm

Performance of Selected Filters Filters tested according to ASHRAE 52.2 Filter dimensions 20 x 25 x5 in. Filter pressure drop

Filter penetration, P with bypass flow, QB Bypass flow through gaps Filter Bypass Filter penetration, P with bypass flow, QB Bypass flow through gaps     Efficiency decrease depends on: Bypass flow Filter efficiency without bypass U-shaped 10 mm gap at ΔP = 50 Pa QB/Q ~20%

Filter initial efficiency at the flow rate of 2000 cfm Filter Efficiency Filter initial efficiency at the flow rate of 2000 cfm E1 efficiency for submicron particles (0.3 – 1) Ambient aerosol Optical particle counter Filter MERV 8 MERV 13 MERV 16 ASHRAE 52.2 23.0 64.3 95.0 Test set up 20.0 59.7 91.2 NOTE: MERV 13 filter ΔP = 0.48 in. H2O at 2000 cfm MERV 16 filter ΔP = 0.32 in. H2O at 2000 cfm

Filter initial efficiency at the flow rate of 2000 cfm Impact of Bypass Filter initial efficiency at the flow rate of 2000 cfm E1 efficiency for submicron particles (0.3 – 1) Ambient aerosol Optical particle counter Filter MERV 8 MERV 13 MERV 16 Test set up 20.0 59.7 91.2 With 5 mm gap* n/a 58.1 89.1 NOTE: *Bypass gap 250 x 5 mm (10 x 0.25 in.)

Filter performance test method Residential HVAC system Scope Introduction Indoor air quality Airborne contaminants Filter performance test method Residential HVAC system Impact of filter efficiency on indoor air Energy 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

Filter performance test method Residential HVAC system Scope Introduction Indoor air quality Airborne contaminants Filter performance test method Residential HVAC system Impact of filter efficiency on indoor air Energy cost Conclusions

LCC = Initial Investment + Energy Cost + Maintenance Cost + 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 life Flow rate, average filter pressure drop and energy cost

Typical Residential HVAC ΔPS (+) ΔPR (-) SUPPLY RETURN HEATING F

Fan curve for PSC blower Flow Rate Fan curve for PSC blower Typical, small residential PSC blowers ⅓ HP

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

HVAC System Measurements Test House 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

Filter Filter ΔP Flow Power ΔPR ΔPS [in. H2O] [cfm] [W] [in. H2O] Test Results Filter Filter ΔP Flow Power ΔPR ΔPS [in. H2O] [cfm] [W] [in. H2O] NO FILTER 1232 636 -0.23 0.11 MERV 8 0.13 1172 606 -0.22 0.10 MERV 16 0.17 1117 600 -0.19 0.10 MERV 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

Test results Impact on Heating Time Test house 2300 Ft2 Mode Heating Test time 1-1.5 hr per filter Outside temperature 30 – 35oF During 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 Impact on Heating Time Average heating time for each filter was measured Heating time for high ΔP filter Ratio = --------------------------------------- Heating time for low ΔP filter

Blower electrical energy High ΔP filter Low ΔP filter Impact on Heating Time Blower electrical energy High ΔP filter Low ΔP filter Power usage, [W] 552 606 Corrected for time 592 606 Annual heating 2080 hrs 1231 kWh 1260 kWh Cost @ $0.10/kWh, [$] 123 126 Furnace – natural gas Annual energy, [therm] 790 Corrected for time 848 790 Cost @ $1.30/therm, [$] 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