Application of the Standard 62.1-2007 indoor air quality procedure to retail stores.
Ventilation requirements for commercial buildings in the United States must satisfy building codes in the jurisdictions in which the buildings are located. The requirements in most codes can be traced to a model ventilation standard prepared by the American Society of Heating, Ventilating, and Air Conditioning Engineers (ASHRAE). This standard, ASHRAE 62.1, contains requirements that are intended achieve acceptable indoor air quality. The standard consists of two major compliance paths for ventilation rates. The first, called the ventilation rate procedure (Section 6.2), defines ventilation requirements for various types of buildings depending on their use. If the ventilation rates specified in this prescriptive procedure are provided, acceptable air quality is presumed to result. The second path is called the indoor air quality procedure (Section 6.3). This performance-based procedure involves the determination of ventilation rates, filter efficiencies and other design parameters based on the designers' use of concentration limits of key indoor contaminants. If sufficient ventilation is provided to maintain concentrations below these limits, acceptable indoor air quality is demonstrated.
This study is a follow-up and expansion of an investigation of air quality and ventilation rates in a Target store located in Stillwater, Minnesota in 1995-96 (Bridges et al. 1997, Grimsrud et al. 1999). The conclusion of that study indicated that a ventilation rate of 0.15 cfm/[ft.sup.2] (2.7 [m.sup.3]/h x [m.sup.2]) gave acceptable indoor air quality in this building design. For comparison, the Standard 62.1 Ventilation Rate requirement is 0.23cfm/[ft.sup.2] (4.2 [m.sup.3]/h x [m.sup.2]). The results of the Stillwater study have been applied to the subsequent construction of approximately 800 stores throughout the United States operated by Target Corporation. Since the Stillwater study was completed, ASHRAE has revised their IAQ procedure for determining the appropriate ventilation rates and other design parameters for selected buildings. The objective of this study was to apply a modification of the ASHRAE 62.1 IAQ procedure that is included in ASHRAE Standard 62.1-2007 in three Target stores located in three different climates zones of the United States. This study explores the idea that acceptable air quality, using the performance-based indoor air quality procedure, can be obtained in retail stores with ventilation rates less than those specified in the ventilation rate procedure of Standard 62.1.
This is not the path a designer would follow in starting the design process from the beginning. Rather it should be considered a field practical test of the performance of existing buildings. These results will inform the future design and construction of similar buildings. The major elements of the IAQ procedure are included. Contaminants of concern were identified in the field tests, emission rates of major pollutants are measured under different weather conditions with different seasonal merchandise in the stores. Weather conditions were varied by making measurements in different seasons and in different climate regions of the U.S. Subjective evaluation of air quality in the stores was tested using untrained observers.
Identification of contaminants of concern is an important issue. They were initially based on contaminants suggested by ASHRAE 62.1 and expectations related to products that were sold in the store (pressed board and plasticized packaging suggested formaldehyde). As contaminants were detected selection was focused on those with high enough concentrations that could be measured in a 48-hour collection period. In some of the samples a double aliquot was used to obtain a readable value. The contaminant list also changed in the FL and MD buildings from experience gained in the MN test (the first building investigated in this study).
This study has three primary elements:
Pollutants: Sources of pollutants, typical pollutant types, and critical pollutants that need to be controlled for compliance with the indoor air quality procedure of the ASHRAE 62.1 Ventilation Standard are identified. Appropriate monitoring to determine critical contaminant concentrations is demonstrated.
Concentrations: Concentrations of important contaminants are compared when different ventilation rates are used in order to obtain an estimate of the source strengths of important contaminant groups.
Ventilation: Ventilation rates that are sufficient to prevent concentrations of key pollutants observed in the stores from exceeding pollutant limits applied in this application of the ASHRAE 62.1 IAQ Procedure are recommended.
The project consists of two major measurement efforts: examining pollutant concentrations in each of three Target stores, and measuring the store's ventilation rate during the same time period. Together, these quantities are used to estimate the source strengths of the pollutant sources within the store. These source strengths, in turn, are used to predict concentrations that will result with other ventilation rates. Volatile organic compounds and formaldehyde were measured as 48-hour averages, while other pollutants were measured continuously over intervals ranging from one to five minutes. Even though all contaminants were not measured continuously, the examination of some provides a sense of short-term exposure for all.
Measurements were made in three Target stores located in three different climate zones of the country. The first, located in Roseville, MN, is a Super Target design located in a heating-dominated climate. It will be referred to as the Minnesota store throughout the report. The second, located in Mt Dora, FL is a standard design located in a cooling-dominated climate and will be labeled as the Florida store, while the third (Maryland), located in Rockville, MD, is a two-storey design located in a mixed heating/cooling climate.
The study was performed over three years. Each building was monitored for one year (four one-week periods, separated by three months to sample seasonal variations in each store). Each measurement week contained two 48-hour intervals separated by a day using different ventilation rates.
Measurement periods were typically one week at three-month intervals for a year. The measurement teams arrived on a Sunday and set up specialized monitoring equipment. The ventilation rates were typically fixed for a 48-hour period that would begin Monday at 8am. Continuous measurements of pollutant concentrations would continue until 8am Wed. morning. On Wednesdays the ventilation would be changed to a different value that would be fixed until Saturday. Pollutant measurements would begin again Thursday at 8 am and continue until Sat at 8 am. No specific statistical analysis of this schedule was made. Our goal was to sample 4 times in the year to obtain information about pollutant concentrations associated with seasonal variations of merchandise in the store and weather variations in the different climate zones that were sampled.
Non-symmetric operation of the HVAC systems was limited. The RTU/AHU schedule of operation and minimum damper position was fixed at the beginning of a ventilation rate cycle. This schedule superseded any alternate schedules of operation that might have been used. Thursday was no different in its HVAC operation than Friday or Saturday even though actual client traffic, work schedules and product deliveries may have varied. (If the kitchen exhaust fans ran on Friday morning because of the demand for baked goods, the same exhaust fans ran were run on Thursday and Saturday.) Daily cycles of client traffic and staffing were accounted through sales receipts to normalize these potential impacts. The procedures evolved as the project developed.
Major pollutants monitored for 48-hour periods were formaldehyde (HCHO), fine particles ([PM.sub.2.5]), carbon monoxide (CO), and total volatile organic compounds (TVOC). Limiting pollutant concentration limits are listed in Table 2.
The PureTrac[R] C[O.sub.2] monitors that are key to the ventilation measurements were calibrated daily using TSI QTrak[R] sensors as discussed on page 6. CO measurements were also obtained using four TSI QTrak[R] monitors dispersed throughout the store (cf. p.5). [PM.sub.2.5] and PM10 measurements were obtained using TSI DustTrak[R] monitors. The TSI instruments were factory calibrated and had their calibration certifications within a year of our application. VOC samplers used were 3M 3520 passive organic vapor badges. These were analyzed at the Wisconsin State Laboratory of Hygiene. Aldehyde samplers were Assay Technology #571 aldehyde samplers that were analyzed by AT Laboratories in Boardman, Ohio.
Formaldehyde was sampled at 8, (5, 11) locations spaced in a regular pattern in the Minnesota, (Florida, Maryland) stores. One outdoor sample and one blank were also measured giving a total of 10, (7, 13) samples per measurement cycle. Measurements were made for 48-hour using formaldehyde passive badge samplers. The samplers were mounted just above the breathing zone (6-7 feet) so they were neither located in product-display areas nor at a height subject to tampering. Samplers were analyzed at an outside laboratory (AT Laboratories, Boardman, Ohio) that also supplied the measurement protocols. Storewide uncertainties in the formaldehyde concentrations were [+ or -] 35%. The sampler concentration measurement has an uncertainty of [+ or -] 25%; the remainder represents averaging over the 8, (5,11) locations in each store to calculate a storewide average.
Measurements of individual organic compounds commonly found in the store were obtained at 8, (5, 11) locations in the Minnesota, (Florida, Maryland) stores using two-stage 3M model 3520 passive organic vapor badges. A check for total volatile organic compounds (TVOCs) as toluene and TVOCs as petroleum distillates was also included. Each badge was placed at an interior site for 48-hour. A blank and an outdoor sample were also obtained for each measurement sequence. The Wisconsin State Laboratory of Hygiene, in Madison, supplied the measurement protocols and analyzed the badges. The individual VOCs that were quantified changed during the course of the study as different source concerns were identified. Storewide uncertainties in the TVOC concentrations were [+ or -] 30%. The sampler concentration measurement has an uncertainty of [+ or -] 25%; the remainder represents averaging over the 8, (5, 11) locations in each store to calculate a storewide average. Table 1 lists the individual VOCs that were quantified in each store.
Table 2 describes our use of the TVOC information. We used it as a one-sided test--i.e., as an indicator of a possible problem issue. A value less than 1000 [mu]g/[m.sup.3] concentration is not an indication of the lack of a VOC problem while a value greater than 1000 [mu]g/[m.sup.3] clearly is.
The measurement strategy used in this study assumes that the retail space is a single, well-mixed zone. This assumption was tested repeatedly in the study in the course of attempting to associate various pollutant classes with particular sources in the store. A concentrated source, called a hot-spot was examined qualitatively using our sense of smell and semi-quantitatively using the RAE photo-ionization detector that measures VOCs in real time.
Few product hot-spots were observed in the store, i.e., areas where the RAE detector or the investigators' sense of smell indicated large off gassing of pollutants. Some areas, for example, the Shoes, Automotive, and Sporting Goods areas had stronger odors than others. The RAE photo ionization detector typically would read 140 [+ or -] 40 ppb in sampling the ten (4,10) areas where the C[O.sub.2] sensors were located. Hot-spots for the RAE were often the Automotive, Boys, and Shoes areas. Note that the concentrations differed by [+ or -] 15% throughout each store. The locations of the maxima shifted throughout the year as merchandise changed.
There were few differences in major seasonal changes of products and the typical daily contribution from restocking. Even at the lowest levels of ventilation, rate of contaminant introduction was slow enough to be mixed well throughout the store. To summarize, the research team observed few hot-spots in time, or in location, in the stores.
Measurements of [PM.sub.2.5] and [PM.sub.10] were made at two locations in each store using two TSI DustTrak[R] Monitors with data measured and recorded at 5-minute intervals continuously during the study. These devices have their own internal data loggers. These monitors sampled storewide average particle concentrations. Resolution of these devices is 1%, standard deviations of storewide averages ranged from 20% to 87% for the three stores investigated.
Carbon monoxide was measured in real-time and logged at five-minute intervals using a four TSI QTrak[R] IAQ Monitors spaced uniformly throughout the store. Their uncertainties were the larger of [+ or -] 3% or 3 ppm. Storewide average concentrations from four sensors ranged from 0 to 1.3 ppm with an outlier at 8.7 ppm. The outlier was due to a failure of a cleaning device during one of the measurement periods in Minnesota.
Perceived Air Quality
An important subjective test of indoor quality is the first impression that a visitor experiences of the indoor air quality in a building upon entering. The protocols for administering these tests were developed in Denmark by Professor P. Ole Fanger and colleagues at the Danish Technical University (Gunnarsson and Fanger, 1992). Following procedures outlined in the thesis of Wargocki, (1999) we assembled teams of untrained visitors and brought them to the stores. Prior to their evaluations, the teams, (approximately 30 students) received a brief introduction to the evaluation procedure and then used the procedure to evaluate the air quality in the bus where they were sitting. Then they rode to the store in the bus, entered the store, and quickly made their evaluation of the indoor quality in the store.
The primary technique used to determine the ventilation rates in each store was provided using a continuous measurement of the concentration of carbon dioxide (C[O.sub.2]) in the store. The dominant sources of C[O.sub.2] are the people in the store (staff and customers) who emit C[O.sub.2] by breathing, the propanefueled floor burnisher used to clean and polish the floor tiles at various times when the store is closed (typically 22:00 until 08:00 the following morning) and the C[O.sub.2] contained in the outside air. Knowing the concentration of C[O.sub.2] in the outside air, the use pattern of the floor burnisher, and the number of persons in the store as a function of time, one can use a mass balance equation to calculate the concentration of C[O.sub.2] as a function of tim efor different ventilation rates. These estimates are compared with the measured C[O.sub.2] concentration history to determine the ventilation rate present in the store.
Instrumentation in the store, (the 10 [4, 10] NOSE samplers [PureTrac[R] continuous IAQ monitoring systems] in the Minnesota [Florida, Maryland] stores), give real-time information about the average concentration of C[O.sub.2] at five-minute intervals. The sensors are calibrated daily against a TSI QTrak[R] C[O.sub.2] sensor calibrated to [+ or -] 3% of the reading or 50 ppm, which ever is larger. Carbon dioxide (C[O.sub.2]) is introduced into the space by the flow of outdoor C[O.sub.2] in ventilation and infiltration air, the emission of C[O.sub.2] by occupants and the emissions from floor burnishers that are used to that are used to clean and polish the floor during the re-stocking hours when the store is closed for business. C[O.sub.2] is removed from the space by the flow to the outdoors of exhaust and exfiltration air containing indoor C[O.sub.2].
Knowledge of the indoor concentration at a particular time, the number of guests and staff as a function of time, and the outdoor concentration of C[O.sub.2] permits a model (a mass balance equation) of C[O.sub.2] in the store to be constructed. The ventilation rate is estimated by comparing the model predictions of C[O.sub.2] concentrations in the store with the measured values and varying the ventilation rate to minimize the sum of the square of the discrepancies between the model predictions and the measured values.
C(t + [DELTA]t) = C(t) + [DELTA]t/V([C.sub.in] - [C.sub.out]) + [C.sub.B]
[C.sub.in] = [N.sub.c] x [E.sub.c] + [N.sub.s] x [E.sub.s] + Q x [C.sub.o]
[C.sub.out] = Q x C(t)
The symbols used are:
C(t + [DELTA]t) = the C[O.sub.2] concentration at time t + [DELTA]t(ppm)
C(t) = the C[O.sub.2] concentration at time t (ppm)
[DELTA]t = the time step (5 minutes)
V = the volume of the store
[N.sub.c] = the number of customers in the store
[E.sub.c] = the average C[O.sub.2] emission rate of each customer
[N.sub.s] = the number of staff in the store
[E.sub.s] = the average C[O.sub.2] emission rate of each staff member
Q = the ventilation rate in the store
[C.sub.o] = the outdoor C[O.sub.2] concentration
[C.sub.B] = the C[O.sub.2] added to the store from floor polishing (burnishing)
In practice the ventilation rate is adjusted to minimize the root-mean-square of the discrepancies between the measured time history of the C[O.sub.2] concentrations and the concentrations modeled using the equation above.
The ventilation rate is estimated by comparing the model predictions of C[O.sub.2] concentrations in the store at 5 min. intervals with the measured values (also recorded at 10, [4,10] locations) and varying the estimated ventilation rate to minimize the sum of the squares of the discrepancies between the model predictions and the measured values. Storewide ventilation rates over two-hour intervals are produced by the analysis. Further information about these procedures are found in the papers of Scheff et al., (2000), Schell andInthout, (2001), and Grimsrud, Bridges, and Schulte, (2006).
The best way to estimate the ventilation uncertainty is a direct comparison with simultaneous tracer decays and with Test and Balance (TAB) measurements for these pressurized buildings. (The Minnesota store was commissioned prior to the tests. It was positively pressurized to 0.04 in. [H.sub.2]O. The buildings actually varied from 0.04 to 0.08 in. [H.sub.2]O. Target engineers typically have less than 5000 cfm of exhaust airflow and more than 8000 cfm of ventilation airflow. The air balance minimum of +3000 cfm is generally recognized in grocery store design to provide positive building pressure.)
Specific local effects of wind, simultaneous position of loading and main entry doors, large differences of ambient to indoor temperatures (OAT < -20[degrees]F) would have created variations where a given envelope region at different comparative times would be specifically negative, even while the overall average was positive. Measurements were attempted but the expected 0.05 in. [H.sub.2]O (12.5 Pa) was difficult to confirm. When outdoor temperatures are appropriate (i.e., large differences of indoor and outdoor temperatures) the ventilation measurements were corroborated using a temperature-based mixed air fraction.)
The calculated ventilation was further supported with the fan status and damper positions related to TAB measurements using a TAB flow station and a differential pressure logger on the fans during the day to measure total ventilation flow. The ratio between the ventilation rates measured by the TAB contractor and the mass-balance model used in this study for three samples in the Minnesota building were 1.09 [+ or -] 0.23. Four separate 4-hour tracer decay comparisons were made with the C[O.sub.2]-based measurements, also in the Minnesota store. The ratio of the tracer gas decay ventilation determinations to the mass-balance model ventilation rates was 0.94 [+ or -] 0.13.
Ventilation and Pollutant Concentrations
Measurements of the average ventilation rates and average pollutant concentrations during 48-hour monitoring periods were used to calculate the source strength of different pollutant groups for that time period. Knowing the pollutant source strength allows us to calculate the ventilation rate required to dilute that pollutant group to values that are smaller than recognized limiting concentrations for the pollutant group. The repeated measurement of the pollutant source strength gives a distribution of results for each pollutant group. Assuming that these are normally distributed, the value given by the mean plus 1.65 standard deviations about the mean will include 95% of the values that will be seen if the experimental conditions are repeated. Therefore, the ventilation rates required to maintain pollutant concentrations below the limit values shown in Table 2, below, give the ventilation requirements for each store for each pollutant group. The ventilation rates in the final column of Table 2 are the values of the mean plus 1.65 standard deviations about the mean of the experimental measurements.
[FIGURE 1 OMITTED]
[FIGURE 2 OMITTED]
Analysis of 25 different 48-hour measurement series in the three stores yields the concentrations shown in Figures 1-3. Each of the data points in the data points in the figures shows a 48-hour average concentration measured in one of the three stores plotted as a function of the average ventilation rate present in the store during the measurement. These data are combined in Table 2 to yield normalized source strength, i.e., source strength per unit area, for that pollutant.
[FIGURE 3 OMITTED]
We also note that [PM.sub.2.5] particle concentrations were measured in the study. A total of 23 48-hour measurements of these concentrations were made. The average indoor concentrations from the three stores were 9 [+ or -] 4, 10 [+ or -] 2, and 8 [+ or -] 2 [micro]/[m.sup.3] for the MN, FL, and MD sites. However, we also observed that the dominant source for this pollutant was the outdoor air. Thus the reduction in [PM.sub.2.5] concentrations requires better filtration rather than the control of indoor sources, the topic of this study.
Perceived Air Quality Results
The first team of subjective observers evaluated the MN store at 6:45 p.m. Monday, September 24; the second made their evaluation at approximately the same time on Monday, October 1. The ventilation rate calculated for the 22 hours prior to the perceived air quality test September 24 was 8000 cfm (0.061 cfm/[ft.sup.2]; 1.15 [m.sup.3]/h x [m.sup.2]). The ventilation rate for the 22 hours prior to the perceived air quality test October 1 was 9600 cfm (0.073 cfm/[ft.sup.2]; 1.37 [m.sup.3]/h x [m.sup.2]).
The modest increase in the ventilation rate was not reflected in the perceived air quality tests in the store. On the first night (September 24) 80% (24 of 30) found the air quality in the Target store acceptable. On the second night (October 1), following the same procedures, 79% (26 of 33) found air quality in the Target store acceptable.
An additional assessment of perceived air quality with two different ventilation rates was conducted during measurement series 3 and series 4 in the Maryland store. Following the same procedures as those described above 84% of 26 participants in the tests judged that the air in the Target store was acceptable in the first test. After moving into a new series of measurements with the new ventilation rate, 75% of 28 untrained observers judged that the air quality was acceptable. In the 24 hours before the test in July 29 to ventilation rate for the store was 9700 cfm or 0.088 cfm/[ft.sup.2]; 1.65 [m.sup.3]/h x [m.sup.2]); in the same time prior to the second test July 31 the ventilation rate was 7700 cfm or (0.070 cfm/[ft.sup.2], 1.32 [m.sup.3]/h x [m.sup.2]) a decrease of 21%. The perceived air quality results are consistent with the change observed. Table 2 summarizes the results of the perceived air quality tests. The aggregate result of the four tests is 80 [+ or -] 4% of the untrained observers judged that the air quality was acceptable in these stores. This is consistent with the 80% goal of acceptability as note in ASHRAE Standard 62.1 (2007).
This study uses the IAQ Procedure (Section 6.3) of Standard 62.1-2007 to investigate the ventilation requirements for large retail stores in the United States. The approach was empirical, i.e., completed buildings in use in different climate regions of the United States provided full-scale test cases of the designs that were investigated. Changes in ventilation rates were implemented to investigate the response of the pollutant sources to these new ventilation rates. This approach allows us to specify a 95% confidence interval that will maintain pollutant concentrations below limits that were chosen for the study.
The total volatile organic concentrations are larger in the MN store than in stores in FL or MD. This is likely the result of bakery activity (ethanol generation) in the MN store that is not present in the other stores. The formaldehyde concentrations listed in Table 2 are remarkably consistent among the stores while the carbon monoxide values are quite low with the exception of the MN store. (A failure of a cleaning device released the CO in one measurement sequence). The consistency among the three stores is remarkable considering differences in climate and building sizes. Perhaps it supports the idea that similar operation strategies and merchandise are important for establishing good air quality in buildings.
Table 2 does not include results for fine particles ([PM.sub.2.5]). As the study proceeded we realized that concentrations of [PM.sub.2.5] in the store are dominated by outdoor concentrations in the ventilation air supplied to the store. We observed particle increases that could be associated with cleaning processes (the use of a floor burnisher during re-stocking when the store was closed) but the particle concentrations were dominated by the outdoor concentrations. Thus the control strategy for fine particles is dominated by the need to filter the outside ventilation air rather than dilute indoor [PM.sub.2.5] sources. Table 4 summarizes the ventilation requirements when the measurements in the three stores are grouped together.
The results of this study depend on the choices of pollutant concentration limits that are used as concentration goals. If the new CA EPA limit of 7 ppb (9 [micro]g/[m.sup.3]) were used, the ventilation requirement using this type of analysis would rise from 0.068 cfm/[ft.sup.2] to 0.76 cfm/[ft.sup.2]. Clearly that type of change would drive the owner to follow the Ventilation Rate Procedure of 0.23 cfm/[ft.sup.2] and increase the building's energy use. On the other hand, if one adopts the Health Canada guideline of 100 ppb (123 [micro]g/[m.sup.3]) the ventilation rate requirement would drop to 0.055 cfm/[ft.sup.2].
We note that not all pollutants that are present in the building were measured and quantified. We did measure the ones that are closest to pollutant concentration limits determined by cognizant authorities and quantified these to determine the appropriate ventilation rate for the space.
Other studies have begun to be reported that investigate pollutant concentrations in retail stores (Eklund et al., 2008; Loh et al., 2006; Wargocki et al., 2004; Wu, et al. 2011; for example). These report pollutant concentrations comparable to those reported in this work but do not apply the results to the ASHRAE 62.1 Indoor Air Quality procedure for design and operation.
It is important to note that the use of C[O.sub.2] as a tracer gas in the studies is physically similar to using perfluorocarbon (PFT) tracers in residential studies. Both measure the harmonic mean of the ventilation rate, i.e., [[1/Q].sup.-1] rather than the mean of the ventilation rate [Q]. The distinction is important because the energy cost of ventilation is proportional to the average ventilation rate while the ability of ventilation to reduce pollutant concentrations is proportional to the harmonic mean (Sherman and Wilson, 1986; Nazaroff, 2009). An important property of the harmonic mean is that it is always less than or equal to the mean value (or simple average). The two measures are equal when the ventilation is constant. This suggests that the most efficient strategy for ventilating spaces containing sources that are emitting at a constant rate and are occupied continuously is to use constant ventilation over the complete 24-hour cycle. Efficiency here means the least amount of ventilation air that produces the pollutant dilution desired.
It is useful to consider the perspective of the building owners exploring the results of the project. Target has an internal store design group responsible for building designs that meet codes and standards, provide a safe and inviting environment to our guests and team members, and are economical to build and operate. As noted above this project is an expansion and update of an earlier test performed in 1996-1997 to investigate ventilation rates and indoor air quality in a newly competed store in Stillwater, MN. The results showed that a ventilation rate of 0.15 cfm/[ft.sup.2] during occupied hours controlled contaminant levels and provided acceptable indoor air quality. The current 2006-2008 study expanded those results by investigating three newly completed stores in various formats built in three different climate zones of the United States. The results of the current study suggest that providing 0.068 cfm/[ft.sup.2] continuously 24 h/day provides acceptable indoor air quality.
As a result of these studies most jurisdictions have allowed the use of the ASHRAE 62.1 IAQ Procedure for determining the Sales area ventilation rate in Target Stores. Savings to date using this procedure have exceeded 100,000,000 kWh and 20,000,000 therms gas based on energy modeling validated by actual building energy use. Cutting energy use in well-designed buildings is difficult--optimized ventilation provides a good opportunity for sustainable design and a reduced carbon footprint. As an owner and operator of our buildings, the IAQ Procedure has provided an opportunity for research into design alternatives that yield lower energy use while maintaining good indoor air quality. Understanding the contaminants in our buildings allows us to control and reduce the source of indoor contaminants that enter through building materials, merchandize, or equipment. ASHRAE 62.1 IAQ Procedure provides an important tool to owners and designers in understanding how to optimize ventilation rates as we strive for healthy, low carbon buildings.
a. The three Target stores located in different regions of the United States perform well using the design assumptions of the 1997 Stillwater study. All showed pollutant concentrations below recognized standards when ventilated at the rates recommended in that study.
b. The ventilation requirements in the three stores examined in this study using the 2007 IAQ Procedure of Standard 62.1 (Section 6.3) are each lower than those recommended in the 1997 Stillwater study for each pollutant group.
c. The data in Table 2 shows that acceptable indoor air quality occurs in these stores supplied with continuous (24 hour/day) ventilation rates of 1.25 [m.sup.3]/h x [m.sup.2] (0.068 cfm/[ft.sup.2]) in the retail and supermarket spaces. Note that this result applies to this store brand and cannot be extrapolated to other stores unless these also undergo field monitoring.
Hoy Bohanon, Director of Energy Programs, Working Buildings, Winston-Salem, NC: What was the HERV rating of filters in stores? Will mixtures requirement being added to 62.1 change your conclusions?
Barry Bridges: The filters used in the stores are MERV-8 filters. Possible new requirements will affect the method of future testing. The conclusions based on the standard active at the time of the study do not change.
Michael Deru, Sr. Engineer, NREL, Golden, CO: Did you consider optimizing the ventilation rate based on the time averaged dilution of pollutants and on the energy impact? What is the optimal economizer operation to minimize energy consumption while maintaining acceptable IAQ?
Barry Bridges: We used the assumption that pollutant sources are continuous. The continuous steady-state ventilation rate minimizes average exposure to occupants in the store. (See the discussion section of the paper where the "harmonic mean" of the ventilation rate is discussed.) A performance-based ventilation approach does provide information on contaminants that could be used to further optimize timing of ventilation to take advantage of electrical demand response and other time of day energy opportunities. Daily variations in weather, occupancy, real time energy cost and contaminant concentration could be used for ongoing optimization.
Dennis Stanke, Staff Applications Engineer, Trane, La
Crosse, WI: If you measured OA flow rate indirectly (by measuring C[O.sub.2] for instance), then you can't really deduce how much OA flow the intake requires or contributes. Barry Bridges: We have observed that the building is pressurized to about 0.02 in. except for short durations at neutral pressure. In this case, determining the ventilation rate from C[O.sub.2] concentrations (when all sources are accounted for) is appropriate. In addition, test and balance reports and on-site verification of outside airflow taken during the test period were used to validate ventilation airflow.
Marwa Zaatari, Student, University of Texas at Austin, Austin, TX: Filtration will not solve the problem of high indoor [PM.sub.2.5] concentration if we have high infiltration and high outdoor [PM.sub.2.5] concentration.
Barry Bridges: We agree. Infiltration is unfiltered air. Our experience in this group of stores found in three different regions of the country (MN, FL, MD) that outdoor [PM.sub.2.5] concentrations are the dominant source of the [PM.sub.2.5] that is measured in the stores. As noted in the response to Stanke, the mechanical ventilation is operated to provide a neutral to slight positive pressure-mitigating infiltration.
Target Stores supported this project under contract EGMSi Award # 10092413-A01 to the University of Minnesota. We note the splendid support of Jason Whittymore, and Bill George of Target Corporation's Industrial Hygiene Group and University of Minnesota students Sui Cheung, Joshua Miller, Corinne Wichser, and Angela Vreeland.
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Barry Bridges, PE
Life Member ASHRAE
David Grimsrud, PhD
Fellow/Life Member ASHRAE
Tony Springman, PE
Scott Williams, PE
Barry Bridges is a professional engineer with Sebesta Blomberg & Associates, Roseville, MN, Neil Carlson is a public health specialist with Environmental Health and Safety and David Grimsrud is an emeritus professor at the University of Minnesota, St. Paul, MN, Tony Springman is a professional engineer and principal of Building Efficiency Services, and Scott Williams is group manager of mechanical engineering with Target Property Development of Target Corporation, Minneapolis, MN.
Table 1. VOCs Sampled at Each Site VOCs Sampled MN FL MD Acetone X X X Butoxyethanol X X X Butyl Alcohol X Cyclohexanone X X Ethanol X X X Ethyl Acetate X Ethyl Benzene X X X Formaldehyde X X X Isoproponal X X Limonene X X X Methyl Ethyl Ketone X X Methylcyclopentane X Naptha X X Napthalene X Pentane X Petroleum distillates X X X Pinene (alpha) X Styrene X X X Toluene X X X Total VOC X X X Xylene X X Table 2. Pollutant source strengths and ventilation rates required to maintain pollutant concentration standards in all stores and in individual stores that were studied Store Pollutant Retail Area Source Strength Group [m.sup.2] mg/h x [m.sup.2] ([ft.sup.2]) FL CO 9100 (98,000) 0.11 MD CO 10,200 (110,000) 0.40 MN CO 12,200 (131,000) 1.70 All CO 0.790 (0.34) FL HCHO 9100 (98,000) 0.096 MD HCHO 10,200 (110,000) 0.077 MN HCHO 12,200 (131,000) 0.059 All HCHO 0.074 FL TVOC 9100 (98,000) 0.34 MD TVOC 10,200 (110,000) 0.55 MN TVOC 12,200 (131,000) 0.75 All TVOC 0.54 Store Standard Deviation Pollutant Continuous Ventilation mg/h x [m.sup.2] Limit Required [m.sup.3]/h mg/[m.sup.3] x [m.sup.2] (cfm/[ft.sup.2]) FL 0.09 10 0.026 (0.001) MD 0.32 10 0.093 (0.005) MN 3.4 10 0.73 (0.040) All 2.1 (0.40) 10 0.43 (0.023) FL 0.030 0.10 1.46 (0.080) MD 0.028 0.10 1.23 (0.067) MN 0.028 0.10 1.05 (0.057) All 0.031 0.10 1.25 (0.068) FL 0.14 1.0 0.57 (0.031) MD 0.10 1.0 0.72 (0.039) MN 0.45 1.0 1.49 (0.081) All 0.33 1.0 1.08 (0.059) (CO) The carbon monoxide limit is based on the National Ambient Air Quality Standard (NAAQS) for an eight-hour exposure. This is not to be exceeded more than once per year. The MN value includes an outlier due to a failure of maintenance equipment. If this value is excluded the MN averages would be 0.61 [+ or -] 0.54 mg/h x [m.sup.3]. This changes the required ventilation rate to control CO for the entire sample to be 0.10 [m.sup.3]/h x [m.sup.2]. (HCHO) The WHO limit for a 30-min. exposure for formaldehyde is 100 [micro]g/[m.sup.3]. This applies to guests in the store. The occupational limit for workers is much higher. The OSHA eight-hour limit is 0.75 ppm (920 [micro]g/ [m.sup.3]). A provision of the OSHA regulation demands compliance at 100 ppb (123 [micro]g/[m.sup.3] or their workforce if a challenge is brought forward (OSHA 1910.1048[l][ii]). (TVOC) A guideline of 1000 [micro]g/[m.sup.3] was used in the 1997 study (Bridges et al., 1997). Since some VOCs in the mix of VOCs that could be found inside a building are highly irritating at very low concentrations, having a low TVOC concentration is not a guarantee Table 3. Summary of Perceived Air Quality Tests in Target Stores Trial Ventilation Rate Number of Percent [m.sup.3]/h- Participants Judging [m.sup.2] Acceptable (cfm/[ft.sup.2]) MN-1 1.15 (0.061) 30 80% (24/30) MN-2 1.37 (0.073) 33 79% (26/33) MD-1 1.65 (0.088) 25 84% (21/25) MD-2 1.32 (0.070) 28 75% (21/28) Table 4. Ventilation requirements for the stores investigated in this study (1) Pollutant Required Required Group Ventilation Ventilation Rate Rate (cfm/ ([m.ssup.3]/h [ft.sup.2]) x [m.sup.2]) CO 0.43 0.023 HCHO 1.25 0.068 TVOC 1.08 0.059 (1) For comparison, the requirement for ventilation required by the Ventilation Rate Procedure (Section 6.2) of ASHRAE Standard 62. for a retail space containing a mix of retail and supermarket space is 4.2 [m.sup.3]/h-[m.sup.2] (0.23 cfm/ [ft.sup.2]).
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|Author:||Bridges, Barry; Carlson, Neil; Grimsrud, David; Springman, Tony; Williams, Scott|
|Date:||Jul 1, 2013|
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