A Discussion Regarding the Measurement of Ventilation Rates Using Tracer Gas and Decay Technique
Abstract
:1. Introduction
- Assess the variability that can be found in the measurement of ventilation rates with tracer gas;
- Discuss the use of tracer gases other than sulfur hexafluoride (SF6) as its use is nowadays limited by environmental constrains;
- Compare the use of SF6 and occupant generated carbon dioxide (CO2) as tracer gases, stressing the importance of controlling cross-contamination of CO2;
- Evaluate the importance of the outdoor climate conditions on the results by tackling a relationship between the attained ventilation rates and the corresponding wind speed and indoor–outdoor temperature difference.
2. Literature Review
3. Materials and Methods
3.1. Framework
3.2. Tracer Gas Measurements
3.3. Equipment
4. Case Study
4.1. Description
4.2. Characterisation of the Indoor and Outdoor Environment
5. Results
5.1. Sulfur Hexafluoride (SF6) Measurements
5.2. Carbon Dioxide (CO2) Measurements
6. Discussion
6.1. Sulfur Hexafluoride (SF6) Versus Carbon Dioxide (CO2)
6.2. Air Change Rate Versus Outdoor Conditions
7. Conclusions
- If one intends to assess ventilation rates using tracer gas and the decay technique, one-time measurements are not enough. A large variability was found among the results with the coefficient of variation ranging from 20% (CO2_LR_C) to 64% (CO2_BR_O and SF6_BR_O). The variability was slightly higher in the BR, both for closed and open door scenarios, probably because it is located on the first floor. No large differences in variability were identified between open and closed door scenarios;
- Using occupant generated CO2 as tracer gas requires guaranteeing that no users are inside the dwelling when the decay starts. The results showed large differences in the air change rate attained using CO2 and SF6 in the LR, for the open door scenario, when the occupants left the space but were in the upper floor. These results confirm the impact of occupancy as a source of cross-contamination issues;
- The effect of wind speed was confirmed as the main trigger mechanism in this case study in the mid-season period, where the indoor–outdoor temperature difference is not so significant;
- Concerning the indoor–outdoor temperature gradient, the low values found in the majority of the measurements constrained the conclusions. However, the results indicated that a minimum difference of 3 °C was required to observe the effect of the temperature;
- Additional research is required as the effect of the wind direction was not considered. Future works include increasing the sample size and establishing the importance of wind direction and indoor–outdoor temperature gradient. The new results will also allow extending and validating the key achievements of the present work.
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
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Living Room | Bedroom | |
---|---|---|
Floor | Ground floor | First floor |
Orientation | North | South |
Area (m2) | 35 | 33 |
Volume (m3) | 84.5 | 72.2 |
Window area (m2) | 3.8 | 3.8 |
Door area (m2) | 4.4 | 1.9 |
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Almeida, R.M.S.F.; Barreira, E.; Moreira, P. A Discussion Regarding the Measurement of Ventilation Rates Using Tracer Gas and Decay Technique. Infrastructures 2020, 5, 85. https://doi.org/10.3390/infrastructures5100085
Almeida RMSF, Barreira E, Moreira P. A Discussion Regarding the Measurement of Ventilation Rates Using Tracer Gas and Decay Technique. Infrastructures. 2020; 5(10):85. https://doi.org/10.3390/infrastructures5100085
Chicago/Turabian StyleAlmeida, Ricardo M. S. F., Eva Barreira, and Pedro Moreira. 2020. "A Discussion Regarding the Measurement of Ventilation Rates Using Tracer Gas and Decay Technique" Infrastructures 5, no. 10: 85. https://doi.org/10.3390/infrastructures5100085