The effect of positive pressure on indoor air quality in a deeply renovated school building – a case study

Moisture excess in buildings constitutes a complex problem affecting indoor air quality, energy consumption and the lifetime of the building envelope. We investigate the effect on moisture transfer in structures as a positive pressure is applied inside the enclosure. It is found that, contrary to established belief, the positive pressure does not induce any negative effects on the structures’ moisture content in normally ventilated classrooms, even with high occupancy. Our case study consists of a school building in Finland, subject to temperature and relative humidity measurements after a small (5–7 Pa) positive pressure was realized through ventilation control. We first address analytically the moisture excess generated inside the classrooms for 14 days, using dynamical balance equations that account for both ventilation effects and occupants’ moisture release in the environment. It is found that the average moisture excess is very small, largely below 1 g/m3, even for ventilation rates that are half the design value. We also examine the moisture performance of the envelope, by addressing the moisture migration at upper and lower joints of the external walls for both measured and design values of the indoor absolute humidity (AH). A coupled numerical model of diffusion and convection shows that moisture accumulation in the envelope and the according stresses are negligible for any realistic AH values. This result is in agreement with field measurements at the school. In conclusion, it seems that applying a small overpressure in a well-ventilated school building during a standard service period resulted in no accumulation inside the external walls, even at high occupancy and with low ventilation. Remarkably, it slightly dried out the moisture content in structures under actual occupancy conditions. The positive pressure has accordingly no negative effects on moisture performance, and is capable to guarantee a good indoor air quality as well.

Download Full-text

Ventilation Positive Pressure Intervention Effect on Indoor Air Quality in a School Building with Moisture Problems

International Journal of Environmental Research and Public Health ◽

10.3390/ijerph15020230 ◽

2018 ◽

Vol 15 (2) ◽

pp. 230 ◽

Cited By ~ 12

Author(s):

Camilla Vornanen-Winqvist ◽

Kati Järvi ◽

Sander Toomla ◽

Kaiser Ahmed ◽

Maria Andersson ◽

...

Keyword(s):

Air Quality ◽

Indoor Air Quality ◽

Indoor Air ◽

Positive Pressure ◽

School Building ◽

Intervention Effect

Download Full-text

84. Ergonomic Solutions for an Indoor Air Quality Investigation: A Case Study

10.3320/1.2757984 ◽

2003 ◽

Author(s):

P. Prendergast

Keyword(s):

Air Quality ◽

Indoor Air Quality ◽

Indoor Air

Download Full-text

Assessing ventilation strategies in a school with observed indoor air problems

Facilities ◽

10.1108/f-03-2021-0019 ◽

2021 ◽

Vol ahead-of-print (ahead-of-print) ◽

Author(s):

Ulrika Uotila ◽

Arto Saari ◽

Juha-Matti Kalevi Junnonen ◽

Lari Eskola

Keyword(s):

Decision Making ◽

Air Quality ◽

Indoor Air Quality ◽

Indoor Air ◽

Final Decision ◽

Target Number ◽

Content Type ◽

Existing Building ◽

Ventilation Strategies

Purpose Poor indoor air quality in schools is a worldwide challenge that poses health risks to pupils and teachers. A possible response to this problem is to modify ventilation. Therefore, the purpose of this paper is to pilot a process of generating alternatives for ventilation redesign, in an early project phase, for a school to be refurbished. Here, severe problems in indoor air quality have been found in the school. Design/methodology/approach Ventilation redesign is investigated in a case study of a school, in which four alternative ventilation strategies are generated and evaluated. The analysis is mainly based on the data gathered from project meetings, site visits and the documents provided by ventilation and condition assessment consultants. Findings Four potential strategies to redesign ventilation in the case school are provided for decision-making in refurbishment in the early project phase. Moreover, the research presents several features to be considered when planning the ventilation strategy of an existing school, including the risk of alterations in air pressure through structures; the target number of pupils in classrooms; implementing and operating costs; and the size of the space that ventilation equipment requires. Research limitations/implications As this study focusses on the early project phase, it provides viewpoints to assist decision-making, but the final decision requires still more accurate calculations and simulations. Originality/value This study demonstrates the decision-making process of ventilation redesign of a school with indoor air problems and provides a set of features to be considered. Hence, it may be beneficial for building owners and municipal authorities who are engaged in planning a refurbishment of an existing building.

Download Full-text