Conference Agenda

Overview and details of the sessions of this conference. Please select a date or location to show only sessions at that day or location. Please select a single session for detailed view (with abstracts and downloads if available).

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Session Overview
Session
Session 18: Ventilation for IAQ
Time:
Tuesday, 22/June/2021:
10:30am - 12:00pm

Session Chair: Mads Mysen
Session Co-chair: Thomas Olofsson
Location: Zoom room #1
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Presentations
10:30am - 10:42am

Is the air change efficiency sufficient to assess the removal of airborne contamination in mixing ventilation?

Gerrid Brockmann, Anne Hartmann, Martin Kriegel

Technische Universität Berlin, Germany

There are two common methods to assess the ventilation effectiveness: the air change efficiency (ACE) and the contamination removal effectiveness (CRE). For known contamination sources in a room, it is easy to determine the CRE. Often this is not given. Especially, when the contamination is exhaled from a random position and get mixed up in the environment. Then the ACE, the ability of the ventilation to exchange the air in the room, will be chosen for IAQ assessment.

By determining the residual lifetime, the averaged time for air transport from a specific point in the room to the exhaust, it is possible to examine the resulting CRE if the point is the source position and the contamination is airborne. This data can be averaged for the whole room or a potential source zone. The present numerical investigation will focus on a simple mixing ventilation scenario with different conditions: air change rate, specific heat flux, supply air diffuser and exhaust position. It will analyze the correlation between an averaged CRE value based on the residual lifetime and the ACE to better understand their relationship and give a recommendation for the IAQ-assessment of ventilation designs.



10:42am - 10:54am

Demand-controlled ventilation in schools: Influence of base ventilation rates on subjective symptoms, perceived indoor environment and young adults' learning performance

Sverre B. Holøs1, Aileen X. Yang1,2, Kari Thunshelle1, Mads Mysen1,2

1SINTEF, Oslo, Norway; 2OsloMet - Oslo Metropolitan University, Oslo, Norway

Demand controlled ventilation may significantly reduce energy consumption by lowering the ventilation rate when spaces are unoccupied (base ventilation). Air quality in a room will be affected by the base ventilation rate for some time after occupancy, as even the higher ventilation rates used during occupancy will not be able to immediately reduce pollutant levels to new steady-state levels. Also, commonly used control-systems, like CO2-based control of the ventilation rate, will require some time to adjust to the number of people present.

Classrooms typically have relatively short but intense hours of occupancy, and a low base ventilation rate can result in high energy savings. Thus, it is of interest to examine how different base ventilation rates affect subjective symptoms, perceived indoor environment, and performance, to make recommendations for base ventilation rates in different situations.

In this study, we compared the effect of exposing 10-12 young adults to base ventilation rates of 1.1 vs. 2.0 l/s per m² in two small classrooms built from presumably low-emitting materials. Upon entry, the ventilation rates were increased to 5.7 l/s per m². The air temperature during the different tests varied in the range of 22.6 °C to 25.4 °C due to temperature rise during tests and room differences.

Symptom intensity and perceived environmental quality were recorded on a visual scale, and performance was examined by identifying three different letters in a nonsense text. Tests were done immediately after entering the classroom and after 75 minutes. A test of the operational memory span was performed at 75 minutes.

We observed no significant or consistent effects of increasing the base ventilation rate on the measured outcomes. These results indicate that decreasing the base ventilation from 2.0 to 1.1 l/s per m² does not influence the performance, symptoms, or the perceived indoor environmental quality.



10:54am - 10:59am

Can human CO2 emission rates staying awake be used staying asleep?

Xiaojun Fan1, Mitsuharu Sakamoto2, Huiqi Shao3, Kazuki Kuga2, Li Lan4, Kazuhide Ito2, Pawel Wargocki1

1International Centre for Indoor Environment and Energy, Technical University of Denmark; 2Interdisciplinary Graduate School of Engineering Sciences, Kyushu University; 3School of Chemistry and Biological Engineering, University of Science and Technology Beijing; 4Department of Architecture, School of Design, Shanghai Jiao Tong University, China

Carbon dioxide (CO2) as a product of human metabolism is the dominant pollutant from occupants. Its concentration indoors has been widely used as a surrogate of ventilation efficiency, hence indoor air quality (IAQ). When estimating ventilation rate (VR), the CO2 emission rate (CER) needs to be known. While CER till now is mainly obtained from people staying awake. There are few studies showing if it can be used for sleeping people, so the VR estimation in bedrooms. This study experimentally determined human CER during sleep and compared it with that of people staying awake. Recruited 11 participants slept in a specially designed capsule for four nights at three conditions combined by two temperatures (24 and 28 °C) and two levels of IAQ indicated by two CO2 concentrations (800 and 1700 ppm), the order of sleep was balanced, and the first night was for adaption. The CER was estimated using measured CO2 concentration with a mass-balance equation after the CO2 level reached steady-state during sleep. The measured CER was on average 11.04±1.43 L/h per person. This was similar to what predicted using the models provided by the standard and previous study. Measured CER from sleeping people is significantly lower compared with that of people staying awake. No significant differences in CER were observed across conditions. Present results suggest that CER from awake people can not be used for sleeping people. Otherwise, it will increase energy consumption due to overestimated VR in bedrooms.



10:59am - 11:11am

Local ventilation for general patient rooms

Zichan Xie, Mariya Petrova Bivolarova, Arsen Krikor Melikov

International Centre for Indoor Environment and Energy, Technical university of Denmark, Denmark

Numerous studies on ventilation of general patient rooms have been performed, while most of the studies have focused on total volume air distribution (mixing or displacement). This study presents results of local ventilation (LV) aimed to efficiently protect a lying person from cross-infection due to airborne respiratory viruses. Experiments performed in a climate chamber (4.7 m × 4.7 m × 2.6 m) included LV when used alone and when coupled with background mixing ventilation (MV). A thermal manikin and a heated standing dummy were used to simulate respectively a patient lying in bed and an infected doctor or nurse standing beside the bed. The LV was able to reduce substantially the exposure of the patient to the infected air exhaled by the doctor. The results show that the efficiency of the LV depended mostly on its supply air flow rate. An increase of the background ventilation's supply flow rate, i.e. increase of the air change rate in the room, was less important. At 15 L/s supplied by LV the concentration of a contaminant at the patient's mouth decreased by 76%. The findings of the paper give insights for researchers and designers in developing a novel ventilation system to be used during a pandemic in general patient rooms.



11:11am - 11:23am

Proposing a new tracer gas for future field applications of passive tracer gas tests for air change rate measurement

Sarah Lima Paralovo1,2, Marianne Stranger2, Borislav Lazarov2, Maarten Spruyt2, Jelle Laverge1

1Ghent University, Belgium; 2VITO, Belgium

Ventilation is critical in interpreting indoor air quality (IAQ), yet most IAQ assessments do not report ventilation adequately. The ultimate aim of this research is to encourage researchers, contractors and building owners to include ventilation measurements in their IAQ assessments, thus making them more comprehensive and representative. Most ventilation assessments use tracer gas tests (TGTs) to measure total air change rates (ACH), but currently applied TGTs present at least one of three major shortcomings: (1) limited comparability between ACH and IAQ data due to differing timescales, (2) inadequate substances employed as tracer gases, either from a health or environmental perspective, and (3) tendency to bias due to imperfect air mixing. Therefore, this paper proposes a new TGT approach, intended for use in large-scale IAQ assessments and based on constant tracer injection. The new proposed TGT employs an alternative and more adequate tracer gas that is captured and analyzed together with commonly assessed IAQ pollutants (VOCs) by means of commercially available passive IAQ samplers, thus simultaneously addressing (1) and (2). To address (3), the new TGT also proposes the inclusion of a careful simulation-based planning phase to help finding the optimal positioning of sources and samplers. The present paper is focused specifically in the developments aimed at addressing (1) and (2); developments regarding (3) will be dealt with in future publications. Via literature study and lab experiments, decane-D22 was found to be a suitable tracer substance. A passive source of decane-D22 was developed and optimized in lab, providing stable and repeatable emission rates under standard temperature, while unaffected by varying RH and ACH. The effect of the liquid solvent level over the source emission rate was only barely noticeable, but a range of adequate solvent level is suggested nevertheless. The selected tracer was also shown not to adhere/absorb significantly to surfaces. Additionally, a consistent exponential curve was derived for determining the source emission rate from the room temperature. Field applications of this new TGT method are ongoing and will be published elsewhere shortly.



11:23am - 11:28am

Measurement of current air exchange in homes. Method description and practical experience.

Johan Mattsson, Kolbjørn Mohn Jenssen

Mycoteam AS, Norway

An important factor for a good indoor climate in homes is adequate air change rate of the premises. It is not possible to feel how good the ventilation is and strikingly often there is significantly poorer air exchange than is desirable. The consequence of this is that there is no desired removal of, among other things, odors, water vapor and airborne dust that are naturally produced by the people staying in the home. In addition, inadequate ventilation can lead to undesirably high radon values ​​in parts of the homes.

The actual symptom of inadequate ventilation can be clarified by measuring relative humidity and radon as well as CO2. In addition, air sample analyzes with regard to quantities and types of airborne dust will provide a clarification of whether there are abnormally high values ​​in the home.

The ventilation requirements in Norwegian homes have both previously and are still an air change rate of at least 0.5 turnover / hour. It is not possible to feel how good the air exchange is, so it has to be a standardized method to measure and document the relevant air change rate. We have tested a practical method for how air change measurements can be carried out in an objective and accurate way.

The method is technically easy to perform, inexpensive and relatively quick to implement since it provides sufficient clarification during measurement during a day. A representative number of CO2 loggers is placed in different areas in the home before the rooms is filled with a sufficient amount of CO2 gas. Logging how fast the CO2 values ​​decrease down to the natural background levels due to the existing ventilation provides an accurate basis for calculating the actual air change rate.

This article describes with specific cases how the method is used in practice and how the results are interpreted and evaluated.



 
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