Indoor air quality has received increased attention. Surveying human thermal comfort and evaluating indoor airflow and ventilation can improve the integrity assessment of the indoor environment. In this study, indoor air quality measurements and spatial assessments were performed in a convenience store on a campus. The computational fluid dynamics model was used to simulate the indoor airflow and explore the spatial distribution of the CO 2 concentration. The results showed the CO 2 concentration easily surpassed the standard value during the weekdays and accumulated in short flows and dead zones. In the condition of no-building alterations, the preferred improvement strategy is to modify the air supply angle to 30°.
The Taiwan Environmental Protection Agency (TEPA) enacted the “Indoor Air Quality (IAQ) Management Act” on November 8, 2011, and implemented the act on November 23, 2012. The IAQ standard documents standard concentrations for nine indoor air pollutants, including carbon dioxide (CO2), carbon monoxide (CO), formaldehyde (HCHO), total volatile organic compounds (TVOC), bacteria, fungi, suspended particulates (PM2.5 and PM10), and ozone (O3). Man-made combustion and occupant breathing are primary sources of indoor CO2. Occupant breathing is regarded as one of the major source in general public spaces. CO2 is generally used as an indicator to assess appropriate indoor occupant density and ventilation rate. The outdoor concentration of CO2 generally varies from 350 to 450 ppm, however, the standard IAQ concentration of CO2 is 1000 ppm. High indoor CO2 concentrations in an office environment may increase the transcutaneous CO2 level and lead to sleepiness during cognitive work [
Average persons spend 80% - 90% of their time daily in the indoor environment. Thus, IAQ is of increasing concern in research on human health. Factors that affect indoor airflow and distribution mainly include: 1) the size, location, and form of air conditioning outlets and return air inlets; 2) air velocity and air volume from supply air outlets; 3) temperature differences between outlet airflow and indoor air; 4) type of ventilation equipment; 5) intensity and location of the heat source; 6) the size and geometric shape of the indoor space; and 7) the layout of furniture or equipment. Previous studies have noted that providing a good indoor airflow and ventilation can improve IAQ and meet the specification standard for human thermal comfort (HTC) [
The main purpose of this study was to investigate factors associated with indoor CO2 concentration in a convenience store. We also discussed the relationship between indoor airflow and spatial distribution of CO2 concentration. Strategies and recommendations for improvements were provided.
This study was conducted in a convenience store on the campus of a medical university in Central Taiwan. The spatial dimensions of the indoor environment were 17.3 m × 6.8 m × 3.0 m (length × width × height), with a floor area of 117.6 m2. The ventilation equipment was a central air conditioning system. Five sampling points in the indoor environment and one sampling point in the outdoor space were set for IAQ measurements.
The measurements included three items: chemical pollutant, physical environment, and occupants. The chemical pollutant was chosen according to the characteristics of the indoor environment. The CO2 concentration in the convenience store tends to increase in the crowd rush hour when customers go shopping. Thus, we chose CO2 as the chemical pollutant to measure. Temperature, relative humidity and air velocity were physical environment factors measured to investigate HTC and indoor airflow pattern. These items were used not only to calculate HTC but also to simulate indoor airflow patterns and to verify the simulation results. We used the number of invoices to assess the number of customers in the store during different time periods.
The commercial computational fluid dynamic software (Solidwork 2013) was used to evaluate the performance of different improved suggestions. The indoor air fluid was simulated by changing the number, type and position of air supply outlets, return air inlets, and vans. The CFD analysis parameters of different air conditioners are shown in
During December 29 - 31, 2013, IAQ measurements and HTC surveys were conducted in the convenience store on campus. Each day was divided into five periods from 07:30 to 17:30.
Airconditioner | Boundary condition |
---|---|
Supply air outlet | Velocity: 0.7 m/s, Temperature: 299 K |
Return air inlet | Velocity: 0.4 m/s, Temperature: 299 K |
Fan | Static pressure, Temperature: 303 K |
Point | Relative humidity (%) | Temperature (˚C) |
---|---|---|
A | 48.2 ± 3.5 | 21.9 ± 1.4 |
B | 48.3 ± 3.3 | 21.0 ± 1.3 |
C | 46.3 ± 2.9 | 21.2 ± 1.3 |
D | 47.5 ± 3.6 | 20.9 ± 1.3 |
E | 47.7 ± 3.7 | 21.5 ± 1.5 |
F | 45.5 ± 3.6 | 22.4 ± 1.3 |
G | 47.8 ± 4.4 | 21.6 ± 1.5 |
H | 47.2 ± 2.9 | 19.5 ± 2.1 |
Thermal comfort sensation | Survey number (percentage) |
---|---|
Hot | 2 (1.8%) |
Warm | 5 (4.4%) |
Slightly warm | 23 (20.4%) |
Neutral | 54 (47.8%) |
Slightly cool | 19 (16.8%) |
Cool | 9 (8.0%) |
Cold | 1 (0.9%) |
revealed that with regard to the subjects’ sensation of temperature, a neutral state accounted for the highest proportion. The indoor environment complied with international normative standards as specified by ASHARAE Standard 55. However, the CO2 concentration surpassed the standard IAQ value.
In fact, four measurements points (B, C, D, F) with higher CO2 concentrations corresponded to dead zones in the indoor airflow distribution. Because the indoor ventilation design and indoor airflow were affected by the arrangement of interior furnishings, leading to low air velocity in local areas and thus became dead zones. As a consequence, CO2 easily accumulated in these areas and surpassed the standard value. Moreover, a short circuit was caused due to the close proximity of the supply air outlet to the return air inlet.
Appropriate strategies were needed to improve the indoor distributions of CO2 concentrations, especially in the dead zone and low velocity area. In this study, improvement strategies were to modify the indoor airflow distributions to reduce CO2 accumulations in the indoor environment. Here, Solid Works 2013 software was used to perform CFD simulation analysis of indoor airflow distribution to assess indoor ventilation in the indoor environment. The improvement strategies include door opening, increased return air inlets, modifying the air supply angle for the ventilation opening, horizontal ventilation, and displacement ventilation (
・ Door opening:
・ Increasing and modifying return air inlets:
The strategy for increasing the number and modifying the location of the return air inlets was to use three return air inlets and modify the location to an appropriate distance to the ventilation opening and fan as well as the areas prone to forming dead zones.
The next strategy was modifying the air supply angle of the ventilation opening from 45˚ to 30˚. When the air supply angle was adjusted upwards to 30˚, the magnitude of air supply became wider, and the dead zone areas were markedly reduced compared to those in the original space (
・ Horizontal ventilation supplies air from both sides:
Horizontal ventilation supplies air from both sides, with a return air inlet set on the central pillar at the same height as the supply air outlet.
environment. There are few dead zone areas and no short circuits.
・ Displacement ventilation:
The displacement ventilation strategy is to set up an exhaust vent in the corner of the space, install a supply air outlet at the door and on both sides of the door, and leave the door open. This strategy used air supply from the outlet and natural ventilation to bring fresh air into all of the corners of the space and to discharge air pollutants from the space via the exhaust vent, thereby achieving displacement ventilation. This design enables airflow to easily move around the entire space. There were rarely any dead zone areas, and the short-circuit phenomenon did not occur (
Finally, we compared the indoor airflow distributions of all proposed strategies by considering the results of airflow improvement and the cost. The preferred ventilation methods include displacement ventilation, horizontal ventilation, and modifying the air supply angle to 30˚. The second-best strategies include opening the door and increasing the number/changing the position of ventilation openings. If not considering interior decoration work and given the limit of expenditure, modifying the air supply angle to 30˚ is the optimal improvement strategy.
In this study, we discussed the difference between indoor airflow and spatial distribution of CO2 concentration in a convenience store on campus. We found that the areas that easily accumulate CO2 in the indoor environment were corresponded to dead zone areas. There was also a similarity between the concentration distribution and indoor airflow trajectory. Thus, the model field established in this study was in line with the actual spatial distribution of airflow and the distribution of pollutant. This model can be used to estimate the spatial distribution of CO2 in the indoor environment. Dead zones were formed in some areas associating with not only indoor ventilation design and indoor airflow but also interior furnishings. Low air velocity increased the risk of dead zones. As a consequence, CO2 accumulated in these areas and the pollutant concentration surpassed the standard value. Additionally, there was a short circuit due to the close distance between the supply air outlet and the return air inlet. The preferred improvement strategies include displacement ventilation, horizontal ventilation, and modifying the air supply angle to 30˚. The second-best strategies include opening the entrance door and increasing ventilation openings. Taking expenditure into consideration, the optimal improvement strategy is to modify the air supply angle to 30˚.
Chen, Y.-C., Chang, S.-Y., Cheng, C.-H. and Wu, C.-C. (2018) Influencing Factors and Improvement Strategies for Indoor Air Quality and Human Thermal Comfort in a Convenience Store. Health, 10, 215-227. https://doi.org/10.4236/health.2018.102018