RESIDENTIAL FILTRATION FOR CONTROLLING BIOAEROSOLS T J Ptak
RESIDENTIAL FILTRATION FOR CONTROLLING BIOAEROSOLS T. J. Ptak • December 2 -3. 2020
SCOPE ØIntroduction ØBioaerosols, size distribution ØResidential HVAC systems and portable air cleaners ØPerformance for large particles ØSummary
INDOOR AIR QUALITY - CHALLENGES INDOOR AIR POLLUTANTS Bioaerosols TARGET POLLUTANTS VOC PM Formaldehy de Ø Indoor air is a mixture of more than 200 -300 pollutants Ø What is concentration level Ø Which can affect occupants’ health Ø Our focus - Bioaerosols HEALTH COMFORT
BIOAEROSOLS ØBioaerosols are aerosols of biological origin ØViruses, viable organisms such as bacteria and fungi, and products of organisms (spores, pollen) ØAllergens from dogs, cats, insects ØSources - plants, animals, humans, soil and water ØAerosolization ØParticle size Viruses 0. 02 – 0. 3 µm Bacteria 0. 3 – 10 µm Fungal spores 0. 5 – 10 µm Pollen 10 – 100 µm
BIOAEROSOLS ØExample of measured size distribution of bioaerosols Outdoor bacteria Indoor bioaerosols (Gram+, Gram-, Fungi) 70 0, 6 Location 1 0, 5 Location 2 Mean concentration [cfu/m 3] d. N/d. Log(da) 0, 7 0, 4 0, 3 0, 2 0, 1 0 0, 65 1, 1 2, 1 3, 3 4, 7 7 Aerodynamic diameter, [µm] AAQR 2012 Gram + 60 Gram- 50 Fungi 40 30 20 10 0 0, 65 1, 1 2, 1 3, 3 Particle size, [µm] AAEM 1999 Ø Outdoor bacteria average size 3 - 4 µm Ø Indoor bioaerosols average size 2 - 7 µm 4, 7 7
BIOAEROSOLS ØExample of measured size distribution of bioaerosols Influenza aerosol particle size Size distribution of cough aerosol from patient with tuberculosis 45 90 Cough 80 Breath 70 60 50 40 30 20 40 Total aerosol CFU, [%] Influenza aerosol particles, [%] 100 35 30 25 20 15 10 0 0 <1 1 -4 Particle size, [µm] thelancet 2020 >4 0, 65 1, 1 2, 1 3, 3 4, 7 7 Particle size, [µm] thelancet 2020
INDOOR AIR POLLUTANTS - STRATEGIES ØWhole house system Flow rate, cfm Ø Fan curve for PSC fan (1/2 hp) – majority of US homes Ø If pressure drop ΔP , flow rate Q Ø Flow rate decrease depends on the fan and the system Ø Current HVAC systems are not designed for higher ΔP Ø Current residential filters are designed to remove particulate matter 1500 1000 Cooling 500 Heating Pressure drop 1 Pressure drop 2 0 0 0, 2 0, 4 0, 6 0, 8 Pressure drop, in. H 2 O ØPortable air cleaners Ø Typical flow range 100 -400 (600) cfm Ø Valid option for removal gas-phase Ø Treatment of specific spaces Ø For occupants with allergies 1
RESIDENTIAL SYSTEM ØMajor components Ø Return and supply ducts Ø Blowers Ø Permanent Split Capacitor (PSC) Ø Brushless Permanent Magnet (BPM) Ø Rated at Total External Static Pressure ΔP = 0. 5 in. H 2 O Ø System resistance: Ø Filters Ø Heaters Ideal filter Ideal coil Ø Typical issues: Ø Filter by-pass Ø Filter not fully utilized Ø Uniformity of flow ΔP < 20% TESP ΔP < 40% TESP
RESIDENTIAL SYSTEM – CLEANING EFFECTIVENESS Ø Tests house Ø Volume ~20, 000 ft 3 Ø Fan PSC; continuous flow Ø Filters 20 x 25 x 5 in. , different MERV Ø Measured decay of large particles corresponding to the size of bioaerosols (NC – normalized concentration) Decay of 0. 85 µm KCl particles 0, 90 0, 80 0, 7 0, 6 0, 5 0, 4 MERV 13 - M MERV 13 - N MERV 10 - S MERV 13 - G MERV 7 0, 3 0, 2 0, 1 Decay of 3. 5 µm KCl particles 1, 00 NC (3. 5 micrometer) NC (0. 85 micrometer) 1, 0 MERV 13 -M MERV 13 -S MERV 10 -G 0, 70 MERV 10 -S 0, 60 MERV 7 0, 50 0, 40 0, 30 0, 20 0, 10 0, 0 0 5 10 15 20 25 30 35 Time, [min] 40 45 50 55 60 0 10 20 30 Time, [min] 40 50 60
RESIDENTIAL SYSTEM – CLEANING EFFECTIVENESS Ø Performance of the “used” filter made of electrostatically enhanced media Ø Fan PCS; continuous flow Ø Filter 20 x 25 x 5 in. , MERV 13 new and with reduced performance Ø E 2 90 and 58% Decay of 0. 85 µm KCl particles 1, 00 NC (0. 85 micrometer) 0, 90 MERV 13 S 0, 80 MERV 13 S-T 0, 70 0, 60 0, 50 0, 40 0, 30 0, 20 0, 10 0, 00 0 10 20 30 Time, [min] 40 50 60
PARTICULATE FILTERS - EFFICIENCY ØEfficiency of filters used in the experiment ØTest method ASHRAE 52. 2 ØFlow rate 1200 cfm ØE 2(1 -3µm) efficiency 14; 62; 67; 90 and 98% respectively ASHRAE 52. 2 requirements E 2 > 50% MERV 11 E 2 > 65% MERV 12 E 2 > 80% MERV 13 E 2 > 85% 3. 5 100, 0 90, 0 MERV 13 M 80, 0 MERV 13 S 70, 0 Efficiency, [%] MERV 10 0. 85 60, 0 50, 0 MERV 10 S MERV 10 G MERV 7 40, 0 30, 0 20, 0 10, 0 0, 100 1, 000 Particle size, [µm] 10, 000
PORTABLE AIR CLEANERS ØValid option to control indoor concentration of air pollutants (small area) ØCurrent technologies utilized in portable air cleaners: Ø Particulate filtration - high efficiency filters (HEPA filters) Ø Gas-phase - relatively low efficiency formaldehyde and VOC removal Ø Activated carbon, photocatalyst, catalyst Ø High emission of gaseous pollutants ØTest method: Ø Based on “Pull-down” concept (decay of pollutant) Ø Test chamber, V~ 30 m 3 Concentration ØChallenges: 1, 0 0, 9 0, 8 0, 7 0, 6 0, 5 0, 4 0, 3 0, 2 0, 1 0, 0 CADR=350 cfm CADR=150 0 Ø Challenge contaminants ; cigarette smoke, dust, pollens, formaldehyde, VOC Ø Standards: AHAM AC-1, GB/T 18801, Japan, France, Canada 5 10 15 Time, [minutes] 20
PORTABLE AIR CLEANERS ØFactors affecting the effectiveness of air purifiers inside the room Ø CADR – clean air delivery rate [cfm] Ø Location Ø Inlet/outlet Ø Flow rate – highest flow settings correlate to the highest noise level Room with HVAC supply and return registers Not well mixed area AP located next to wall Outlet position horizontally
PORTABLE AIR CLEANERS ØImpact of portable air cleaner (AP) Ø Test house Ø Air purifier CADR = 250 cfm and optical particle counter (OPC) placed in one room Ø HVAC fan ON; Filter = NO, brings particle to the test room through supply inlets Test setup Particle (KCl) decay in the test room with AP = ON Source AP OPC NC (0. 85 micrometer) 1 FAN=OFF 0, 8 0, 6 0, 4 AP=ON 0, 2 0 0 10 20 30 40 Time, [min] 50 60 70
POTENTIAL CONCERNS ØRelated to the portable air cleaner Ø Location inside the room in relation to the supply/return registers Ø Not operating continuously and at lower flow setting ØRelated to the HVAC system Ø System (fan) not operating continuously Ø Filter by-pass and system leaks Ø House not well mixed – insufficient number of registers and wrong location Ø Low efficiency filter, or filter with reduced efficiency due to charge “degradation” Ø HVAC system could potentially distribute pollutants through the house
CONSLUSIONS ØSize distribution of indoor bioaerosols is generally in the range of 1 – 7 micrometers. ØEffectiveness of residential MERV 10 filters (E 2 > 50%) for 0. 85 µm particles is significantly lower than the effectiveness of MERV 13 filters (E 2 > 85%). E 2 (13µm) efficiency is a good indicator of filter performance against indoor bioaerosols. ØProperly maintained residential HVAC systems with MERV 12/13 filters (E 2> 80/85%) and operating in the continuous mode can significantly reduce concentration of indoor bioaerosols. Performance could be enhanced by adding portable air cleaners in specific areas.
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