Study on the Effect of an Intermittent Ventilation Strategy on Controlling Formaldehyde Concentrations in Office Rooms

Material emission and ventilation are two aspects influencing indoor air quality. In this study, a model predictive control (MPC) strategy is proposed for intermittent ventilation system in office buildings, to achieve a healthy indoor environment. The strategy is based on a dynamic model for predicting emissions of volatile organic compounds (VOCs) from materials. The key parameters of formaldehyde from panel furniture in the model are obtained by an improved C-history method and large-scale chamber experiments. The effectiveness of the determined key parameters is validated, which are then used to predict the formaldehyde concentration variation and the pre-ventilation time in a typical office room. In addition, the influence of some main factors (i.e., vacant time, loading ratio, air change rate) on the pre-ventilation time is analyzed. Results indicate that the pre-ventilation time of the intermittent ventilation system ranges from several minutes to several hours. The pre-ventilation time decreases exponentially with the increase in the vacant time, the air change rate, and with the decrease in the loading ratio. When the loading ratio of the furniture is 0.30 m2/m3 and the vacant time is 100 days, the required pre-ventilation time approaches zero. Results further reveal that an air change rate of 2 h−1 is the most effective means for rapid removal of indoor formaldehyde for the cases studied. The proposed strategy should be helpful for achieving effective indoor pollution control.

Study on Self-Cleaning Time and Suspended Particle Distribution in Medical Clean Room

CFD numerical simulation of clean room in Class D medical factory was carried out and compared with the actual measurement to verify the feasibility of the simulation method. On this basis, four typical air flow organizations were simulated and compared by changing air change rate from two directions of self-cleaning time and suspended particle concentration field. According to the simulation results, in order to meet the self-cleaning time within 20 min, the best air change rate should be between 15/h and 25/h. Different air flow organizations have different self-cleaning capacity, and the value of air change rate can be relatively small in the form of single-side supply same-side down return. Different airflow organizations have different suspended particle distribution characteristics, and there are differences in the applicable scenarios, and the applicability of the top supply down return is the best.

Impact of Indoor-Outdoor Temperature Difference on Building Ventilation and Pollutant Dispersion within Urban Communities

Mechanical ventilation consumes a huge amount of global energy. Natural ventilation is a crucial solution for reducing energy consumption and enhancing the capacity of atmospheric self-purification. This paper evaluates the impacts of indoor-outdoor temperature differences on building ventilation and indoor-outdoor air pollutant dispersion in urban areas. The Computational Fluid Dynamics (CFD) method is employed to simulate the flow fields in the street canyon and indoor environment. Ventilation conditions of single-side ventilation mode and cross-ventilation mode are investigated. Air change rate, normalized concentration of traffic-related air pollutant (CO), intake fraction and exposure concentration are calculated to for ventilation efficiency investigation and exposure assessment. The results show that cross ventilation increases the air change rate for residential buildings under isothermal conditions. With the indoor-outdoor temperature difference, heating could increase the air change rate of the single-side ventilation mode but restrain the capability of the cross-ventilation mode in part of the floors. Heavier polluted areas appear in the upstream areas of single-side ventilation modes, and the pollutant can diffuse to middle-upper floors in cross-ventilation modes. Cross ventilation mitigates the environmental health stress for the indoor environment when indoor-outdoor temperature difference exits and the personal intake fraction is decreased by about 66% compared to the single-side ventilation. Moreover, the existence of indoor-outdoor temperature differences can clearly decrease the risk of indoor personal exposure under both two natural ventilation modes. The study numerically investigates the building ventilation and pollutant dispersion in the urban community with natural ventilation. The method and the results are helpful references for optimizing the building ventilation plan and improving indoor air quality.

Moisture Risk Analysis for Three Construction Variants of a Wooden Inverted Flat Roof

The paper presents an analysis of the hygrothermal performance of an inverted flat roof with a CLT (cross-laminated timber) structure in a building that meets the requirements of Passive House Standard (PHS) with regards to the potential risk of moisture. The calculations were made in the WUFI®Plus and WUFI®Bio software. The following variants were taken into account: three structure configurations, three different external climates and different scenarios of microclimate control and air change rate. The results of the calculations show that, especially in cooler climates, there is an actual moisture risk in the structure despite the excellent thermal insulation. The structure of the inverted flat roof, due to the use of a tight membrane on the outer side, allows for the partition to discharge the excess moisture only to the inside of the building. Ensuring the comfort of users may require periodic humidification of internal air, which translates directly into an increase in moisture content of the structure. The performed analysis clearly showed that there are no universal solutions. It is important to point out that for the proper performance of inverted wooden roofs, it is crucial to analyse moisture, not only thermal and energy parameters.

Indoor Air Pollution in Housing Units

Pollution and poor quality of the indoor environment is a common problem in today's residential buildings. These problems are reflected in the well-being and health of the users of these buildings. Targeted identification of the various harmful substances (pollutants) is essential for understanding the interactions of components of the internal environment for the welfare and health of building users. The Czech housing units were selected for screening investigation of indoor air quality. Measuring of indoor chemical factors was performed during the year 2019. The indoor levels of TVOC, nitrogen oxides, indoor radon, and particulate matters PM10 were measured. The results provide introduce data on indoor air quality concerning seasonal changes which were in correlation to air change rate. These results, introduced in this paper, help to understand the indoor pollutants occurrence and help to design next more focused studies.

ANALYSIS OF THE INFLUENCE OF AIR EXCHANGE DISTRIBUTION BETWEEN ROOMS ON THE APARTMENT ENERGY CONSUMPTION

Modern results of Ukrainian buildings energy analysis show that 30-50% of the energy for heating goes to heat the supply air, and that is the largest share in the building energy balance. In terms of energy consumption, efficiency of the air exchange mode largely depends on occupancy schedule and air distribution in time and space. The application of air exchange schedule approach makes more sense in case when individual heating control is carried out. Therefore, during occupied hours, the comfortable ventilation level can be ensured, and, during unoccupied hours, it can be reduced to a minimum. According to the results of the study, the use of intermittent air exchange mode in the studied apartment on weekdays, leads to decrease in energy consumption compared to constant air exchange at the level of upper values of the ventilation schedule. In terms of energy efficiency, the use of the constant air change rate from ASHRAE Std 62 is the most efficient approach. In terms of indoor air quality and concentration of CO2 and VOCs, the scheduled air exchange approach with increased air change rates (from EN 16798) during occupied hours is more efficient. Therefore, the use of required and experimental air change rate values to create the hourly schedules allows to define more precisely a building energy consumption and to choose an optimal operation schedule for building engineering systems to provide thermal comfort and indoor air quality during occupied hours.

Performance Improvement of a Negative-Pressurized Isolation Room for Infection Control

Negative-pressurized isolation rooms have been approved effectively and applied widely for infectious patients. However, the outbreak of COVID-19 has led to a huge demand for negative-pressurized isolation rooms. It is critical and essential to ensure infection control performance through best practice of ventilation systems and optimum airflow distribution within isolation rooms. This study investigates a retrofitting project of an isolation room to accommodate COVID-19 patients. The field measurement has been conducted to ensure the compliance with the design specification from the CDC of Taiwan. The pressure differentials between negative-pressurized isolation rooms and corridor areas should be at least 8 Pa, while the air change rate per hour (ACH) should be 8–12 times. Computational fluid dynamics (CFD) is applied to evaluate the ventilation performance and contamination control. Different layout arrangements of exhaust air have been proposed to enhance the ventilation performance for infection control. A simple projected air-jet curtain has been proposed in the simulation model to enhance extra protection of medical staff. The resulting ventilation control revealed that the contamination control can be improved through the minor adjustment of exhaust air arrangement and the application of an air-jet curtain.

Comparison of Downdraught and Up Draft Passive Air Conduction Systems (PACS) in a Winery Building

A huge portion of energy consumption in buildings comes from heating, ventilation, and air conditioning. Numerous previous works assessed the potential of natural ventilation compared to mechanical ventilation and proved their justification on the field. Nevertheless, it is a major difficulty to collect enough information from the literature to make decisions between different natural ventilation solutions with a given situation and boundary conditions. The current study tests the passive air conduction system (PACS) variations in the design phase of a medium-sized new winery’s cellar and production hall in Villány, Hungary. A computational fluid dynamics simulation based comparative analysis enabled to determine the differences in updraft (UD) and downdraught (DD) PACS, whereby the latter was found to be more efficient. While the DD PACS performed an air change range of 1.02 h−1 to 5.98 h−1, the UD PACS delivered −0.25 h−1 to 12.82 h−1 air change rate. The ventilation performance of the DD version possessed lower amplitudes, but the distribution was more balanced under different wind incident angles, thus this version was chosen for construction. It could be concluded that the DD PACS provides a more general applicability for natural ventilation in moderate climates and in small to medium scale industry hall domains with one in- and one outlet.

Improving Indoor Air Quality in Classrooms via Wind-Induced Natural Ventilation

Student performance in classrooms is related to the indoor environmental quality. High air change rates are necessary to secure an acceptable level of indoor air quality and provide fresh air, which require large amounts of energy and technical installations. Mostly, mechanically supplied air is partially mixed with the return air. In warm climates, the capacity for natural ventilation is not fully exploited in modern buildings. During periods of acceptable outdoor temperatures, buildings need to adapt and employ available free renewable resources, such as wind. In this context, the building form, orientation, and envelope openings are crucial to enable an increased air change rate, user satisfaction, and energy savings. Owing to the difficulty of providing cross-ventilation in buildings with double-loaded corridors, single-sided ventilation is the most common approach. This study investigates the methods to improve the wind-driven air exchange of classrooms in warm climates, where naturally ventilated corridors help increase air movement. This study examines the potential of a set of alternatives within the context of a generic model regarding the pressure distribution, thermal sensation, air velocity, and air change rate. The study suggests that no single opening scenario can be applied to all façades at any time. Each façade requires special treatment. Decisions on natural ventilation need to be made during the early design stages for each façade. It was found that with the aid of low-tech modifications, remarkable increases in air change rates, in some cases up to 14.5 times that of the typical single-sided ventilation case, could be achieved.