Analysis of Building Retrofit, Ventilation, and Filtration Measures for Indoor Air Quality in a Real School Context: A Case Study in Korea
Abstract
:1. Introduction
1.1. Relevant Literature Concerning School Energy Retrofit
1.2. Relevant Literature Concerning School Operation and Maintenance Issues
- Many ventilation systems are turned on only when heating and cooling is needed;
- OA dampers are intentionally closed even though the ventilation system is operating (i.e., only to recirculate the indoor air).
- Portable air cleaners can generate noticeable or uncomfortable noise levels at maximum fan speed. So, ASHRAE has suggested selecting air cleaners based on reduced fan speed if noise is a concern [28];
- Controls that rely on human behavior, such as opening windows or manually controlled mechanical ventilation or filtration systems, may not be implemented reliably or as intended. In some situations, heuristic operations may jeopardize or diverge the built environment that has converged to the optimum.
- Teachers were not educated regarding mechanical ventilation. Errors in HVAC system installation and programming may have contributed to misunderstandings and even occasionally made it possible for teachers to turn off the HVAC fan to reduce noise;
- Occupants in classrooms with poorer ventilation may momentarily perceive more comfort because room temperatures fluctuated more when ventilation rates were higher, such that teachers in the classroom were not likely to accurately perceive insufficient ventilation or turn on the ventilation.
1.3. Typical Building Measures for Domestic School Retrofit and Operation Issues
1.4. Typical System Measures for Domestic School Retrofit and Operation Issues
1.5. Study Objectives and Steps
2. Selected Building Retrofit, Ventilation, and Filtration Measures
3. Case Studies
3.1. Observation and Measurement of Airflow and Contaminant Transport Characteristics of Test Classrooms
- (i).
- Infiltration and exfiltration flowrates by measuring CO2 concentration decay;
- (ii).
- Penetration coefficient and deposition rate of PM2.5 by measuring PM2.5 concentration decay through infiltration and exfiltration;
- (iii).
- Supply flowrate and filter efficiency of the existing ERV by measuring decreasing PM2.5 concentration;
- (iv).
- Supply flowrate and filter efficiency of the existing AP by measuring decreasing PM2.5 concentration;
- (v).
- Incoming and outgoing flowrates when windows were open by measuring decreasing PM2.5. concentration;
- (vi).
- Incoming and outgoing flowrates when both windows and doors were open by measuring decreasing PM2.5 concentration.
3.2. Preparation of Calibrated CONTAM Models
- (i).
- r (Correlation coefficient) ≥ 0.9;
- (ii).
- 0.75 ≤ a (Regression slope) ≤ 1.25;
- (iii).
- b (Regression intercept) ≤ 0.25 × Average concentration;
- (iv).
- NMSE (Normalized mean square error) ≤ 0.25;
- (v).
- FB (Fractional bias) ≤ 0.25;
- (vi).
- FS (Similar index of bias) ≤ 0.5;
3.3. Annual PM2.5 I/O Ratio by Building Retrofit, Ventilation, and Filtration Measures
3.4. Daily PM2.5 and CO2 Profiles by Building Retrofit, Ventilation, and Filtration Measures in the Worst-Case Situation
3.5. Summary of Case Studies
4. Discussion and Conclusions
4.1. Discussion
4.2. Limitations and Future Studies
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
Appendix A. PM2.5 and CO2 Profiles when Measures are Applied to Each Case
References
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Building Measures | Major Advantages | Major Weaknesses |
---|---|---|
Insulation added to exterior walls (form-board, loose-fill, sprayed-form insulation) |
|
|
Exterior performance windows |
|
|
Exterior performance doors |
|
|
Heated micro-cement, or hardwood floors with insulation |
|
|
Acoustic ceiling tiles |
|
|
System Measures | Major Advantages | Major Weaknesses |
---|---|---|
VRF system |
|
|
Package air conditioner (PAC) |
|
|
Electric heater |
|
|
ERV system |
|
|
Air purifier (AP) |
|
|
Building Measures | Actions | Description and Remark | |
---|---|---|---|
B1 | To replace external windows | To reduce air leakage and penetration of the outdoor contaminants through the window perimeter | System window set with the first-grade airtight (infiltration ≤ 1.0 m3/hm2 at dP 10 Pa [34]; effective leakage area (ELA) ≤ 0.593 cm2 per unit window area) |
B2 | To replace classroom doors | To reduce air leakage and penetration of the hallway contaminants through the door perimeter | (a) Economy rail sliding door (the airtight 30th-grade [37]; infiltration ≤ 30.0 m3/hm2 at dP 10 Pa [34]; ELA ≤ 17.791 cm2 per unit door area) (b) System door set with the airtight first-grade (infiltration ≤ 1 m3/hm2 at dP 10 Pa [34]; ELA ≤ 0.593 cm2 per unit door area) |
B3 | To replace hallway-side windows in the classroom | To reduce air leakage and penetration of the hallway contaminants through the window perimeter | (a) PVC double-pane window set (the airtight sixth-grade [38]; infiltration ≤ 6.0 m3/hm2 at dP 10 Pa [34]; ELA ≤ 3.439 cm2 per unit window area) (b) System window set with the first-grade airtight (infiltration ≤ 1.0 m3/hm2 at dP 10 Pa [34]; ELA ≤ 0.593 cm2 per unit window area) |
B4 | To increase the airtightness of the classroom enclosure | To reduce air leakage and penetration of the ambient contaminants by caulking/sealing/gasketing/taping the cracks and gaps of brick/masonry walls, slab, penetrating wires/ducts, power inlet, vent, drains, etc. | 3.0 ACH50 that corresponds to the airtightness of a high-energy-performance residential building [39]; ELA ≤ 0.091 cm2 per unit room air volume |
System Measures | Actions | Description and Remark | |
---|---|---|---|
S1 | To install new ERVs | To provide the required ventilation rate of OA (typically 800 CMH for 25 occupants) with 80% filter efficiency | (a) Silent operation at 600 CMH (b) Normal operation at the rated 800 CMH |
S2 | To replace the existing ERV filter | To replace the existing filter with MERV 15 [40] | 95% filter efficiency |
S3 | To install new APs | To provide the air filtration using HEPA filters for at least 150% of the standard classroom area [35] | (a) Single AP: 900 CMH with 99% filter efficiency (for 170% of the standard classroom area) (b) Dual APs: 600 CMH*2EA with 99% filter efficiency (for 220% of the standard classroom area) |
Natural Ventilation | Actions | Description and Remark | |
---|---|---|---|
Nwin | Natural ventilation by opening windows | To introduce the outdoor air by opening windows | Average daily PM2.5 concentration ≤ 35 μg/m3; 22 °C ≤ outdoor temperature ≤ 28 °C |
Ncv | Cross-ventilation | To introduce a through outdoor airflow by opening windows and doors | (The same as above) |
Variables | Case D | Case I | Case M |
---|---|---|---|
λinf (1/h) | 0.2 | 0.1 | 0.47 |
λexf (1/h) | 0.3 | 0.1 | 0.47 |
PPM2.5 | 1 | 0.4 | 0.9 |
kPM2.5 | 0 | 0.25 | 0.2 |
Qerv (m3/h) | - | 641.2 (Rated: 800 CMH) | 690.4 (Rated: 800 CMH) |
ηerv | - | 0.60 (Rated: 0.80) | 0.75 (Rated: 0.80) |
Qap (m3/h) | 414 (Rated: 650 CMH) | 405 (Rated: 650 CMH) | 622 (Rated: 650 CMH) |
ηap | 0.70 (Rated: 0.85) | 0.70 (Rated: 0.85) | 0.80 (Rated: 0.85) |
ELA of south windows | 155.3 cm2 (69.330 cm2/m2) | - | 3.6 cm2 (1.667 cm2/m2) |
ELA of east windows | 230.6 cm2 (102.946 cm2/m2) | 383.1 cm2 (85.513 cm2/m2) | - |
ELA of hallway-side windows | - | 36.6 cm2 (10.007 cm2/m2) | - |
ELA of door | 150 cm2 (46.875 cm2/m2) | 676.2 cm2 (160.904 cm2/m2) | 169.8 cm2 (35.375 cm2/m2) |
ELA of holes/cracks/gaps | 968.6 cm2 (6.726 cm2/m3; 32 ACH50) | 347.8 cm2 (2.058 cm2/m3; 9.8 ACH50) | 432.1 cm2 (2.223 cm2/m3; 10.6 ACH50) |
Variables | Corresponding CONTAM Parameters |
---|---|
ELA of window, door, and hole/cracks/gaps | Airflow path element → One-way flow using power law type → Leakage area data |
P | Airflow path element → One-way flow using power law type → Filter → Constant efficiency filtration model → Filter efficiency |
k | Source/sink element → Deposition rate sink model → Deposition rate |
Opened window, opened door | Airflow path element → Two-way flow type → One-opening → Height and width |
Simple air handling system → Minimum OA flow | |
Simple air handling system → Outdoor air filter → Constant efficiency filtration model → Filter efficiency | |
Duct Segment Properties → Duct flow element → Constant volume flow → Design maximum flow rate | |
Simple air handling system → Recirculation air filter → Constant efficiency filtration model → Filter efficiency |
Scenario | R | a | b | NMSE | FB | FS |
---|---|---|---|---|---|---|
CO2 decay | 0.992 | 1.16 | 131.65 | 0.01 | 0.04 | 0.30 |
PM2.5 decay | 0.981 | 0.99 | 3.36 | 0.02 | 0.27 * | 0.15 |
Door open | 0.92 | 0.49 ** | 11.4 ** | 0.43 ** | 0.12 | 1.12 ** |
Window open | 0.81 * | 0.73 * | 9.6 | 0.01 | 0.07 | 0.01 |
Cross-ventilation | 0.97 | 0.57 ** | 22.6 ** | 0.07 | 0.11 | 0.96 ** |
Scenario | R | a | b | NMSE | FB | FS |
---|---|---|---|---|---|---|
CO2 decay | 0.97 | 1.29 ** | 535.4 * | 0.01 | 0.01 | 0.54 |
PM2.5 decay | 0.99 | 1.37 ** | 26.3 ** | 0.01 | 0.07 | 0.62 * |
ERV operation | 0.97 | 0.98 | 11.7 | 0.20 | 0.41 ** | 0.01 |
AP operation | 0.97 | 0.95 | 3.1 | 0.01 | 0.00 | 0.03 |
Door open | 0.89 * | 0.89 | 25.2 ** | 0.42 ** | 0.63 ** | 0.80 ** |
Window open | 0.99 | 0.86 | 8.4 | 0.02 | 0.09 | 0.29 |
Cross-ventilation | 0.98 | 0.84 | 3.5 | 0.03 | 0.04 | 0.32 |
Scenario | R | a | b | NMSE | FB | FS |
---|---|---|---|---|---|---|
CO2 decay | 0.98 | 1.09 | 128.5 | 0.06 | 0.20 | 0.15 |
PM2.5 decay | 0.99 | 1.21 | 7.3 | 0.03 | 0.07 | 0.39 |
ERV operation | 0.99 | 1.03 | 5.5 | 0.04 | 0.18 | 0.07 |
AP operation | 0.99 | 1.01 | 2.6 | 0.01 | 0.09 | 0.03 |
Door open | 0.98 | 0.78 | 3.8 | 0.05 | 0.10 | 0.47 |
Window open | 0.99 | 0.83 | 8.2 | 0.02 | 0.07 | 0.37 |
Cross-ventilation | 0.9748 | 0.57 ** | 21.0 | 0.23 | 0.29 * | 0.98 ** |
Winter Vacation | Spring#1 | Spring#2 | Spring#3 | Summer Vacation | Fall#1 | Fall#2 | Fall#3 | |||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1/1–2/28 | 3/1–4/25 | 4/26–5/26 | 5/27–6/30 | 7/1–8/31 | 9/1–10/5 | 10/6–11/13 | 11/14–12/31 | |||||||||||||||||
Hour | 0–9 | 9–15 | 15–24 | 0–9 | 9–15 | 15–24 | 0–9 | 9–15 | 15–24 | 0–9 | 9–15 | 15–24 | 0–9 | 9–15 | 15–24 | 0–9 | 9–15 | 15–24 | 0–9 | 9–15 | 15–24 | 0–9 | 9–15 | 15–24 |
Set point temperature | - | 16 | 20 | 16 | 16 | 20 | 16 | 30 | 26 | 30 | - | 30 | 26 | 30 | 16 | 20 | 16 | 12 | 20 | 12 | ||||
Classes? * | No | Yes | No | Yes | No | Yes | No | Yes | No | Yes | No | Yes | No | |||||||||||
Natural ventilation? ** | No | No | No | Yes | No | No | No | No | No | Yes | No | No | No | |||||||||||
Heating or cooling? | No | Heating | No | No | No | Cooling | No | Cooling | No | No | No | Heating | No |
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Sung, H.J.; Kim, S.H.; Kim, H. Analysis of Building Retrofit, Ventilation, and Filtration Measures for Indoor Air Quality in a Real School Context: A Case Study in Korea. Buildings 2023, 13, 1033. https://doi.org/10.3390/buildings13041033
Sung HJ, Kim SH, Kim H. Analysis of Building Retrofit, Ventilation, and Filtration Measures for Indoor Air Quality in a Real School Context: A Case Study in Korea. Buildings. 2023; 13(4):1033. https://doi.org/10.3390/buildings13041033
Chicago/Turabian StyleSung, Ho Jin, Sean Hay Kim, and Hyunsuk Kim. 2023. "Analysis of Building Retrofit, Ventilation, and Filtration Measures for Indoor Air Quality in a Real School Context: A Case Study in Korea" Buildings 13, no. 4: 1033. https://doi.org/10.3390/buildings13041033