Multi-zone particulate, formaldehyde and VOC measurements in two lab houses under operation of different whole-building ventilation systems.
Airtightness of new homes is critical to achieving low-energy consumption, healthy and comfortable spaces, and durability. Airtight homes require rational and predictable ventilation. Over-ventilation unnecessarily consumes energy and raises the risk of comfort and indoor air quality complaint problems due to elevated indoor humidity in warm-humid climates (Rudd and Henderson 2007). Higher performing ventilation systems may be able to eliminate unnecessary overventilation, thereby providing equal or improved indoor air quality and comfort at lower cost and risk. A key gap and area of ongoing research is to allow ventilation rate credit for better performing ventilation systems, such as those with a known source and entry path of outside air, and systems with predictable filtration of outside air and recirculation filtration. This would yield energy savings and reduced moisture control risk in humid climates, without compromising indoor air quality relative to the least performing system allowed by ASHRAE Standard 62.2. ASHRAE Standard 62.2 currently assumes that:
a) all dwellings covered by the Standard act as a single well-mixed zone, thus, actual distribution of ventilation air to each occupiable space is not addressed;
b) all ventilation systems perform equally well in terms of the quality of outdoor air delivered the occupiable space;
c) there is no benefit from recirculation mixing and recirculation filtration of indoor air where that is an inherent part of a ventilation system; and
d) the only important performance metric is relative annual average exposure, which ignores the acceptability of shorter-term odor and sensory irritation dissatisfaction.
Building on previous research dealing with ventilation air distribution, this study added new elements of ventilation effectiveness research, accounting for source of outside air, particle contaminants, formaldehyde, and volatile organic compound (VOC) contaminants. The intended result is to provide a basis for specific guidance for understanding whole- building ventilation system effectiveness, which is critical to promoting the best low energy and high value ventilation solutions.
The ventilation rates set in ASHRAE Standard 62.2 are currently based on the collective engineering judgment of the committee members. They are based on committee member's notions of what they feel good about based on their own experience and judgment in view of information they are currently aware of. There is no published basis for the required ventilation rates in any health or medical study. Using engineering judgment based on new information, such as in this study, to make adjustments to numbers that are themselves based on engineering judgment is appropriate. These new data provide support for the development of a system of credit factors for better performing ventilation systems.
TEST AND ANALYSIS APPROACH
Description of the Test Houses
The project involved testing at two unoccupied, 1,475 [ft.sup.2] (137 [m.sup.2]) single-story, single-family, detached homes in Tyler, TX that were constructed as lab homes at the University of Texas--Tyler. Refer to Rudd and Bergey 2014 for a full report of the testing conducted in October 2012. The twin lab homes offered a unique opportunity for the direct comparison of nearly identical homes except for House 1(H1) having a vented attic, and House 2(H2) having an unvented attic assembly (also known as sealed cathedralized attic with spray foam insulation under the roof sheathing). House 1 had 3.5 inch (8.89 cm) wood frame walls with netted and blown fiberglass insulation, and loose blown fiberglass insulation on the floor of the attic. House 2 had 5.5 inch (13.97 cm) advanced-framed walls with open-cell spray foam insulation in the walls and under the attic roof deck. The homes were completely finished, with kitchen and bathroom cabinets, but were unfurnished and unoccupied. This allowed an evaluation focus on the building elements themselves, avoiding conflation with occupant activities and items that particular individuals bring into their homes. Zone designations for the testing were as follows:
* Main zone included the kitchen, dining area, living area, foyer, and family bathroom;
* Master zone included the master bedroom, master bathroom, and walk-in closet;
* Front zone was the bedroom on the front side of the house;
* Middle zone was the bedroom between the master bathroom and the family bathroom;
* Garage zone was the 2-car garage; and
* Attic zone was the vented attic for House 1 (including the vented attic over the garage) and the unvented attic for House 2 (the vented attic over the garage for House 2 was separate from the unvented attic and the garage but was not monitored as a separate zone).
The central space conditioning system return air filters were new, 1 inch (2.54 cm) thick filters with a Microparticle Performance Rating (MPR) of 700. The MPR measures a filter's ability to capture particles between 0.3 and 1.0 micron. The ASHRAE Minimum Efficiency Reporting Value (MERV) reports a filter's ability to capture particles between 0.3 and 10 microns. Available product literature roughly relates the MPR 700 filter to a MERV 9 filter.
Despite the greater volume and surface area, House 2, with the unvented attic house and spray foam under the roof sheathing, was more airtight, having 789 [ft.sup.3]/min (372 L/s) at 50 Pa (.0073 in w.c.) pressure differential (CFM50) leakage compared to 1048 CFM50 leakage for House 1 with a vented attic. House 2 had lower cooling and heating loads than House 1, and therefore lower space conditioning system airflow (707 cfm (334 L/s) versus 1137 cfm (537 L/s), measured). Duct leakage to outdoors was 56 [ft.sup.3]/min (26 L/s) at 25 Pa (.0036 in w.c.) pressure differential for House 1 and effectively zero for House 2 with all ducts being inside the building thermal enclosure.
The objective of the testing program was to compare the whole-building, multi-zone, indoor air quality performance between continuous exhaust ventilation both with and without central system recirculation mixing, central-fan- integrated supply ventilation, and energy recovery ventilation. The focus of the testing approach for this paper was multi-zone sampling of airborne particulates, formaldehyde, and VOCs to determine indoor air quality impacts as a function ventilation system operation. Another paper on this project focuses on per-fluorocarbon tracer (PFT) measurements to determine zone air change rates and inter-zonal airflows with the different ventilation systems operating.
Five tests were conducted in each house, including: Baseline, Exhaust, Exhaust with mixing; Central-fan-integrated supply (CFIS) (Rudd 2011); and Energy Recovery Ventilator (ERV). The test configurations were intended to represent normal limiting case conditions for most homes when space conditioning equipment may not operate for long periods (overnight or more) and bedroom doors are closed at night.
Baseline Test. The Baseline test was conducted with no ventilation system or space conditioning system operating as reference for comparison.
Exhaust Test. The exhaust test was conducted using the master bathroom fan because that fan is most often the larger and better of the bathroom and toilet room fans in new houses. The continuous exhaust airflow was adjusted to 45 cfm (21 L/s) to meet the ASHRAE Standard 62.2-2010 continuous fan flow rate for the 1475 [ft.sup.2] (137 [m.sup.2]), 3- bedroom house.
Exhaust With Mixing Test. The exhaust with mixing test was the same as the Exhaust test except with a central air distribution system fan cycle of 48 minutes Off and 12 minutes On. It was conducted to see the effects of trying to achieve better ventilation air distribution effectiveness and recirculation filtration via whole-house mixing of ventilation air drawn in by the exhaust fan through unknown locations in the building enclosure. The intent of the central system air mixing was to achieve a 0.7 recirculation turnover factor based on prior ventilation effectiveness research (Rudd and Lstiburek 2000, 2001, 2008; Hendron et al. 2007; Townsend et al. 2009b).
Central-Fan-Integrated Supply Test. The central-fan-integrated supply (CFIS) ventilation system test was conducted to evaluate the performance effects of drawing outside air from a planned outdoor air location, then filtering and fully distributing that air to each conditioned space zone. The outside air ventilation supply airflow was set at 135 cfm (64 L/s) by means of a calibrated flow station (Iris damper), and the central system fan was controlled to operate on a 33% duty cycle, 20 minutes Off / 10 minutes On.
Energy Recovery Ventilator Test. The energy recovery ventilator (ERV) test was conducted with a system independently ducted from the central air distribution system. The ERV ductwork in these houses was configured to exhaust from two locations in the main area and supply to all bedrooms. The ERV total supply airflow was measured to be 96 cfm (45 L/s) so the ERV timer control was set for 50% runtime. The ERV included a washable course filter at the inlet of the heat and moisture energy recovery core within the unit. That filter was cleaned before testing began.
A general note for all tests is that all closet doors were left open to allow that air volume to fully interact with the adjoining space, and all bedroom doors were configured to have the same 0.5 inch (1.27 cm) undercut above the decoratively stained concrete floors throughout the houses.
The first 12-hour period of each test was to approach steady-state for the particulate, formaldehyde, and VOC sampling in the second 12-hour period of each test. The test sequence was scheduled such that the 12-hour period for sampling would be overnight. Overnight occupancy with bedroom doors closed and mechanical ventilation is a normal and important limiting condition in homes. This testing approach would eliminate solar heating effects on air exchange and take advantage of generally lower and less-changing wind conditions at night, to limit those as potentially confounding factors in the interpretation of results.
Airborne Particulate Sampling
During the 12-hour quasi steady-state period of each test period (second half of each 24-hour test period), air sampling for airborne particulate matter (PM) was conducted in the Main (common area) and Master bedroom zones. During some tests, additional PM sampling was done outdoors, and in the garage and attic of each house. PM was monitored at six particle sizes (0.3, 0.5, 1.0, 2.0, 5.0, 10.0 micron) with a laser airborne particle counter. The meter had a counting efficiency of 50% @ 0.3 [micro]m (1.18E-05 inch) and 100% for particles > 0.45 [micro]m (1.77E-05). The sample flow rate was 0.1 cfm (2.83 L/min). The meter was programmed to complete 48 cycles of 15 minute samples over the second 12-hour period of each test, gathering a sample volume of 1.5 [ft.sup.3] (43 L) each cycle. Data was recorded electronically and imported into a worksheet for analysis. Only the last twenty-one 15-minute particle counting cycles (cycles 20 through 40), or the last 5.25 hours before researchers re-entered the houses were used for analysis. This was to analyze the data closest to steady-state and to isolate the particle load attributable to the operation of different ventilation systems from any occupant (researcher) disturbance.
Volatile Organic Compound Sampling
Ninety minutes before the end of the 12-hour steady-state period of each PFT test period, VOC sampling was conducted in the Main (common area) and Master bedroom zones. During some tests, additional VOC sampling was done in the Garage and Attic zones of each house. An 18 L (0.64 [ft.sup.3]) air sample was collected in each case. The solid sorbent samplers and the calibrated low-flow sample pumps (0.2 L/min (0.007 [ft.sup.3]/min)) were provided by a commercial laboratory service. Laboratory analysis of the samples was conducted by thermal desorption/mass spectrometry based on USEPA Compendium Method TO-17 and ASTM 6196. Individual compounds and total volatile organic compounds (TVOC) were calibrated relative to toluene. A report identifying the concentration of the "Top 20" VOCs typically found in buildings was provided.
Sixty minutes before the end of the 12-hour steady-state period of each 24-hour test period, formaldehyde sampling was conducted in the Main (common area) and Master bedroom zones. During some tests, additional VOC sampling was done in the Garage and Attic zones of each house. A 60 L (2.1 [ft.sup.3]) air sample was collected in each case. The DNPH samplers and the calibrated sample pumps (1.0 L/min (0.035 [ft.sup.3]/min)) were provided by a commercial laboratory service. Laboratory analysis of the samples was conducted by DNPH/HPLC based on ASTM Method D5197 and a laboratory report identified the formaldehyde concentrations.
DISCUSSION OF RESULTS
Particle disturbance by occupant interaction had a large impact on large particles (5-10 micron) but little to no impact on small particles (0.3-1.0 micron). This response appeared at the end of each test when researchers entered the houses to begin the formaldehyde and VOC sampling. Thus, only the particle counting cycles before researchers re- entered the houses were used for analysis.
This paper is not intended to address detailed human health concerns related to particle contaminants (Carl et al. 2004), but a little background is useful. Small particles are considered hazardous to human health. Particle sizes of 10 micrometer (micron or [micro]m) or less are generally not filtered by the nose and throat and reach the lungs. Particle sizes of 2.5 micron and less can enter into the gas exchange region of the lung. Particles sizes of 0.1 micron and less can pass through the lung to organs, including the heart and brain. In rough perspective, bacteria, mold spores, and dust mite allergens can all be 10 micron or less. Cat allergens, tobacco smoke, soot, and smog can all be 1 micron or less. Viruses, tobacco smoke, soot, and smog can all be 0.1 micron or less.
Figure 1 shows plots of the cumulative particle counts for the House 1 Main zone, for 1.0 micron particle size, for all the ventilation systems. The same result trends were found for the 0.3 and 2.0 micron particle sizes in the Main and Master zones of House 1 and House 2 but were not included here in chart form for brevity. There was not an important difference in particulate levels between the Main and Master zones, but there was an important and consistent difference found between the ventilation systems. The highest levels were found for the Exhaust system, followed by the Baseline or ERV, followed by the Exhaust with mixing and CFIS. CFIS always showed the lowest particle counts regardless of particle size. As would be expected, this indicated that the 700 MPR/roughly MERV 9 filters in the central air distribution system return air grilles were removing a significant amount of particle contaminant 0.3 micron and larger.
Differential particle counts were calculated from the cumulative particle counts for the Main and Master zones in the range of 0.3-2.0 micron. Compared to the Exhaust ventilation system, the other ventilation systems showed an average percent difference of 69-85% reduction in small particles in House 1, and a 52-73% reduction in House 2. The CFIS ventilation system showed the greatest reduction in small particles for both houses, attributable to recirculation air filtration by operation of the central air distribution system.
Particulate measurements were also taken in the Attic and Garage zones. The levels of particulate counts were reasonably close between the Attic and Garage of each house. The levels for House 1 were somewhat lower than for House 2 in the smallest particle sizes, they were nearly the same for the 1.0 micron size, and House 2 had lower levels in the 2.0 micron size and larger. The Attic and Garage in both houses had lower particulate levels than outside, particularly in the larger particle sizes.
Particulate was monitored outdoors during two Baseline tests, on test days 1 and 6. Indoor and outdoor temperature and relative humidity were similar during both tests. Wind speed was a little higher during the second test but the outside sample location was somewhat sheltered from wind. The particle count results of the two outside tests showed remarkable consistency, indicating good measurement repeatability. We did not have enough meters to measure outdoor particulate for each test, however, the measurements from these two tests, bracketing the entire testing period, were consistent with each other and were essentially unchanging for 12 hours at a time. There were no obvious sources nearby in this suburban location, or weather disturbances that would give particular reason to believe that outdoor particulate conditions would have changed much between test day 1 and test day 6 any more than they did on test day 1 and test day 6.
Coincident outside and inside particle count measurements taken during the Baseline test showed the particle counts to be nearly the same for the 0.3 and 0.5 micron particle sizes. For 1.0 micron particles, the inside counts were about five times lower than outside. That trend increased progressively to about 100 times lower for inside counts compared to outside counts at the 10.0 micron size.
The chart on the right side of Figure 1 graphically compares the formaldehyde concentrations for the Baseline test and the four ventilation system tests. Outside formaldehyde concentration was not measured at this specific location, but can generally be taken to be 2-3 ppb (2.5-3.7 [micro]g/[m.sup.3]) for this region of Texas (EPA 1991).
In House 1, all ventilation systems reduced the formaldehyde concentration over the indoor Baseline concentration, which was roughly 20 times higher than what would be expected outdoors. Exhaust-only ventilation reduced the indoor formaldehyde concentration the least, followed by Exhaust with mixing, CFIS, and ERV. Exhaust with mixing likely reduced the concentration over Exhaust-only because Exhaust-only interacted much more with the Main and Master zones than with the Front and Middle bedroom zones. Whole-house mixing averaged conditions such that concentrations in the Main and Master zones were lower.
In House 2, the Exhaust systems either increased or did not appreciably change the formaldehyde concentration in the Main and Master zones. The CFIS and ERV systems showed a significant reduction in formaldehyde concentration over the Baseline, and Exhaust tests. In general for both houses, the CFIS and ERV systems showed a 60% to 70% reduction in formaldehyde concentration over Exhaust.
Formaldehyde concentration was measured in the vented attic of House 1 and the unvented attic of House 2, as well as both garages during the Exhaust with mixing test. The Exhaust with mixing test was a period with higher wind than for the other test periods (4-8 mph (6-13 km/h) vs. 0-2 mph (0-3 km/h)). The vented attic formaldehyde concentration (9 [micro]g/[m.sup.3]) was about three times higher than what would be expected for outdoors (~3 [micro]g/[m.sup.3]), while the unvented attic concentration (23 [micro]g/[m.sup.3]) was about eight times higher. The garages of House 1 and House 2 showed formaldehyde concentrations of 25 [micro]g/[m.sup.3] and 35 [micro]g/[m.sup.3], respectively.
Volatile Organic Compounds
Concentrations of the Top 20 VOCs were reported by the testing lab. The predominant trend was that the Baseline test showed the highest VOC concentrations, followed by the Exhaust and Exhaust with mixing ventilation systems, then the CFIS and ERV ventilation systems.
A full listing of the concentrations and functional descriptions of the individual VOCs found in the living zones, attics, and garages is given in Appendix A of Rudd and Bergey (2014). The highest concentrations found in House 1 (and also in the House 1 attic) were from Xylene and Benzene--solvents used in sealer for sealing the decoratively stained concrete floors throughout both houses. The concrete floor sealer used in House 2 was advertised to be low-emitting, and, based on the relatively low concentrations of Xylene and Benzene in House 2, it apparently worked as advertised. House 2 also used a special gypsum board reported to absorb VOCs. Two of the top three compounds found in the House 2 unvented attic were related to the foam insulation used in the walls and roof.
Besides the solvents used in finishing the stained concrete floors, the predominant compounds found in both houses were seemingly low-risk fragrance and flavor products: Pinene--used as a fragrance chemical; Limonene--used in flavor, fragrance, cosmetics, and cleaning products; Hexanal--used in flavor products; Carene--used in flavor and fragrence products; occurs naturally in turpentine, rosemary, cedar, pine; and Phellandrene--used in fragrances. Some of the same compounds found in this study were also found in a prior study by Hodgson et al. 2000, where, in both manufactured and site-built houses, the predominant airborne compounds were a-pinene, formaldehyde, hexanal, and acetic acid. Similar to the living space, garage VOCs with the highest concentrations were those typically used in flavor, fragrance, cosmetics, and cleaning products. Neither of the garages housed any vehicles or other equipment with engines or fuel.
Total Volatile Organic Compound (TVOC) concentration is the sum of all of the individual VOC concentrations reported. Compared to the Exhaust system, the CFIS and ERV ventilation systems reduced TVOC concentration by 47% and 57%, respectively, averaged between the two houses. Compared to the Baseline tests, the Exhaust system increased TVOC concentration by 37% in the House 1 Main zone, and increased TVOC concentration by 18% in the House 2 Master zone. This highlights that the unknown source of outdoor air and air path for the Exhaust ventilation system can cause indoor air to be more contaminated depending on what contaminants are picked up on the way in. TVOC concentration in the unvented attic of House 2 was three times higher (602 [micro]g/[m.sup.3]) than in the vented attic of House 1.
This study of two nearly identical houses under baseline conditions and under operation of four different mechanical whole-building ventilation systems found that Exhaust ventilation operation showed higher concentrations of particulates, formaldehyde and other Top 20 VOCs than did the supply and balanced ventilation systems.
Exhaust ventilation showed 70% higher concentrations of particulates on average relative to ventilation systems that had direct outdoor air intake and filtered that air. The highest particulate levels were found for the Exhaust system, followed by either the Baseline or ERV, followed by the Exhaust with mixing system, and then CFIS. CFIS always showed the lowest particle counts regardless of particle size. This indicated that the MPR 700 (roughly MERV 9) filters in the central air distribution system were removing a significant amount of particle contaminant 0.3 micron and larger. The CFIS ventilation system showed an 85% and 73% reduction in 0.3-2.0 micron particles for House 1 and House 2, respectively, attributable to recirculation air filtration by operation of the central air distribution system.
The CFIS and ERV systems showed a significant reduction in formaldehyde concentration over the Baseline, and a large 60-70% reduction in formaldehyde concentration over Exhaust. The vented attic formaldehyde concentration was about three times higher than what would be expected for outdoors, while the unvented attic and both garages were about 8-10 times higher.
The predominant trend in individual VOC concentrations showed the Baseline with the highest VOC concentrations, followed by the Exhaust and Exhaust with mixing ventilation systems, then the CFIS and ERV ventilation systems. Besides the solvents used in finishing the stained concrete floors, the predominant compounds found in both houses were seemingly low-risk fragrance and flavor products: Pinene; Limonene; Hexanal; Carene; and Phellandrene.
Total Volatile Organic Compound data showed that, compared to the Exhaust system, the CFIS and ERV ventilation systems reduced TVOC by 47% and 57%, respectively, averaged between the two houses. Compared to the Baseline tests, the Exhaust system increased TVOC by 37% in the House 1 Main zone, and increased TVOC by 18% in the House 2 Master zone. This highlights that the unknown source of outside air and air path for the Exhaust ventilation system can cause indoor air to be more contaminated depending on what contaminants are picked up on the way in.
This project was supported by the U.S. Department of Energy, Building Technologies Office, Building America Program. The Texas Allergy, Indoor Environment, & Energy Institute (TxAIRE) at The University of Texas-Tyler, under direction of Roy Crawford, Ph.D. and John Vasselli, provided the two lab houses for this research. Daniel Bergey, formerly of Building Science Corporation assisted in the testing.
Carl-Gustaf Bornehag, Jan Sundell, Charles J. Weschler, Torben Sigsgaard, Bjorn Lundgren, Mikael Hasselgren, and Linda Hagerhed-Engman. 2004. The Association between Asthma and Allergic Symptoms in Children and Phthalates in House Dust: A Nested Case--Control Study. Environ Health Perspect. 2004 October; 112(14): 1393-1397.
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Hendron, R., A. Rudd, R. Anderson, D. Barley, A. Townsend 2007. Field Test of Room-to-Room Distribution of Outside Air with Two Residential Ventilation Systems. IAQ 2007: Healthy & Sustainable Buildings Conference Proceedings. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.
Hodgson, A.T., A. Rudd, D. Beal and S. Chandra, 2000. Volatile Organic Compound Concentrations and Emission Rates in New Manufactured and Site-Built Houses. Indoor Air 10: 178-192.
Rudd, Armin and Daniel Bergey (2014). "Ventilation System Effectiveness and Tested Indoor Air Quality Impacts." http://www.nrel.gov/docs/fy14osti/61128.pdf. Prepared for the National Renewable Energy Laboratory, Golden, CO, for the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Building America Program. February.
Rudd, Armin (2011). "Ventilation Guide--Fully Updated." Building Science Press, Somerville, MA. September. ISBN-10: 0-9755127-6-5.
Rudd, Armin, and Joseph Lstiburek 2008. Systems Research on Residential Ventilation. Proceedings of the 2008 ACEEE Summer Study on Energy Efficiency in Buildings, Pacific Grove, California, August. American Council for an Energy Efficient Economy, Washington, D.C.
Rudd, Armin, Hugh Henderson, Jr., 2007. Monitored Indoor Moisture and Temperature Conditions in Humid Climate U.S. Residences. ASHRAE Transactions (17, Dallas 2007). American Society of Heating Refrigeration and Air-Conditioning Engineers, Atlanta, GA.
Rudd, Armin, Joseph Lstiburek 2001. Clean Breathing in Production Homes. Home Energy Magazine, May/June, Energy Auditor & Retrofiter, Inc., Berkeley, CA.
Rudd, Armin, Joseph Lstiburek 2000. Measurement of Ventilation and Interzonal Distribution in Single-Family Homes. ASHRAE Transactions 106(2):709-18, MN-00-10-3, V.106, Pt.2., American Society of Heating Refrigeration and Air- Conditioning Engineers, Atlanta, GA.
Rudd, Armin, and Joseph Lstiburek 1999. Design methodology and economic evaluation of central-fan-integrated supply ventilation systems. Indoor Air 5:25-30. Air Infiltration and Ventilation Center, Coventry, United Kingdom.
Townsend, A., A. Rudd, and J. Lstiburek 2009a. Extension of Ventilation System Tracer Gas Testing Using a Calibrated Multi-Zone Airflow Model. ASHRAE Transactions 115(2).
Townsend, A., A. Rudd, and J. Lstiburek 2009b. A Method for Modifying Ventilation Airflow Rates to Achieve Equivalent Occupant Exposure. ASHRAE Transactions 115(2).
Armin Rudd is Principal at ABT Systems LLC, Annville, Pennsylvania, and formerly Principal at Building Science Corporation, Somerville, Massachusetts when this research was conducted.
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|Date:||Jul 1, 2014|
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