Mechanical Exhaust Ventilation Research Articles

Ventilation's role in adaptable school buildings: Comparing traditional and adaptable strategies through life cycle assessment

Adaptable buildings are a promising enabler in the transition towards a more circular economy, with the ambition of using materials as efficiently as possible. To exploit adaptable buildings to their full potential, HVAC designers should critically rethink how to design technical services and ventilation systems in particular. This case study illustrates how five ventilation strategies perform from an environmental point of view in a school building where the configuration of the floorplan changes every five years, each of the changes reflecting a pedagogical vision. Consequential LCA is used to assess the environmental impact. A decentralized balanced mechanical ventilation system, which requires almost no adaptations when the configuration changes, has the lowest environmental impact while mechanical exhaust ventilation has the highest. However, when the configuration of the floorplan layout alters more rapidly, the relative environmental impact of the latter decreases substantially. The main conclusion is that, in a flexible context, the material-related environmental impact gains importance over the energy-related impact. With respect to this conclusion, a key finding is that minimizing the material use of ductwork (rather than oversizing ductwork dimensions to decrease the energy consumption of the fan) is more sustainable from an environmental point of view. Finally, distributing the ductwork over two shafts offers more flexibility and results in a lower environmental impact as this allows for the use of smaller dimensions of ductwork.

Ventilation Strategies for Mitigating Indoor Air Pollutants in High-Rise Residential Buildings: A Case Study in Dubai

This study investigates the effectiveness of different ventilation methods in reducing indoor air pollutants in newly constructed residential buildings, focusing on indoor air quality (IAQ) in Dubai. The paper highlights the growing concern for IAQ in response to residents’ increasing awareness of their well-being and environmental sustainability. The study examines the concentrations of formaldehyde (HCHO), volatile organic compounds (VOCs), and total volatile organic compounds (TVOC) in bedrooms and living rooms before and after implementing various ventilation methods during the construction phase. The findings indicate that mechanical exhaust ventilation, mainly through bathroom and kitchen exhaust fans, was highly effective in reducing HCHO levels. Combining kitchen and bathroom exhaust fans demonstrated the most significant reduction in HCHO concentrations. Similarly, reductions in VOCs, such as ethylbenzene, toluene, and xylene, were observed with different ventilation methods. Natural ventilation also proved effective in reducing pollutant concentrations. The results emphasize the importance of implementing appropriate ventilation strategies to improve IAQ in residential buildings. However, the study acknowledges the limitations of a single-location measurement and recommends further research to validate the findings across different building types and locations. Additionally, long-term studies are necessary to assess the sustained effects of ventilation methods on IAQ. The study highlights the significance of addressing IAQ concerns in residential buildings and suggests potential research directions to explore other ventilation strategies and their energy efficiency implications. Ultimately, this research contributes to developing healthier and sustainable living environments by promoting effective ventilation strategies to mitigate indoor air pollutants.

Evaluation of the Primary Energy and Carbon Dioxide Emissions of a Passive Ventilation System with a Solar Air Heater

Improvements in envelope performance have reduced heat loss from insulation, and the ratio of heat loss through ventilation load has become relatively large. In recent years, the use of heat recovery ventilation systems (HRV) has particularly increased. However, ventilation generates not only ventilation load but also air conveying fan power, such that conserving energy for both is important. Therefore, this paper focuses on a passive ventilation system with a solar air heater (PVSAH), which is a passive ventilation system that does not use air conveying fan power and uses a solar air heater that uses solar energy. The total energy consumption of the PVSAH, the widely used mechanical exhaust ventilation system (EV), and the HRV, which has high energy efficiency, was compared with the ventilation load plus air conveying fan power. The primary energy evaluation and carbon dioxide (CO2) emissions were compared by region, and the optimal system was proposed according to regional characteristics. In warmer zones, the PVSAH saved the most energy, while the HRV increased energy consumption. The comparison of CO2 emissions by ventilation systems when using heat pumps for cooling and heating showed that PVSAH > MEV > HRV for Heating Degree-Day (HDD) 1500 and below, PVSAH > HRV > MEV for HDD 1500 to 2750, and HRV > PVSAH > MEV for HDD 2750 and above. MEV were favored in that order. As the CO2 emission factor decreases, the difference in CO2 emissions between systems decreases. If the difference in emissions becomes smaller, then considering the initial and running costs and the risk of failure of the system is crucial. A simple system configuration with low risks of failure and maintenance, such as PVSAH, may prove advantageous in the future.

A CFD based methodology to design an explosion prevention system for Li-ion based battery energy storage system

This work developed a performance-based methodology to design a mechanical exhaust ventilation system for explosion prevention in Li-Ion-based stationary battery energy storage systems (BESS). The design methodology consists of identifying the hazard, developing failure scenarios, and providing mitigation measures to detect the battery gas and maintain its global concentration lower than 25% of the lower flammability limit (LFL) to meet the prescriptive performance criterion of NFPA 69 – Standard on Explosion Prevention Systems. Representative UL 9540A test data is used to define the battery gas composition, release rate, and release duration to describe the failure scenario involving thermal runaway propagation. In addition, an exemplar BESS enclosure geometry is defined to model the failure scenarios using a computational fluid dynamics (CFD) solver. A grid convergence study is performed to estimate the grid resolution required to perform the CFD analysis. In addition, sensitivity studies for different input parameters are performed to understand the impact of inputs on the detection times and ventilation performance. The approach used in this work provides a systematic procedure for the fire protection engineering community to understand the explosion prevention requirement for a BESS installation. The explosion prevention system functionality presented in this work is limited to removing flammable battery gas generated due to the non-flaring decomposition of batteries.

The indoor environmental quality and energy savings potential of room ventilation units compared to exhaust-only ventilation systems in France

Humidity-controlled mechanical exhaust ventilation (RH-MEV) has been widely used in France for over 35 years, demonstrating high durability and robustness. This exhaust-only ventilation strategy is widely used as an energy-saving measure, replacing constant mechanical exhaust ventilation (Constant-MEV) systems in residential buildings. It demonstrates energy savings due to the restricted airflows, but as a downside, the building’s indoor air quality (IAQ) often deteriorates. Moreover, it is impossible to recover heat with exhaust-only ventilation systems, which means that energy consumption for space heating is still quite significant and cold supply air temperatures are frequently introduced to the heated spaces. Room ventilation units (RVUs) with heat recovery represent an alternative ventilation solution allowing simple installation through the façade and providing fresh outdoor air and exhaust ventilation to each room. This study investigates these units’ energy saving potential and indoor environmental quality performance as an alternative solution to centralized exhaust-only ventilation systems. The dynamic simulations were performed for a reference residential building under various French climatic conditions for a heating season. The three ventilation strategies investigated were Constant-MEV, RH-MEV and room-based ventilation with RVUs. The results demonstrated 61–85% savings in space heating demand with the RVUs, compared to Constant-MEV under all climatic conditions. Compared to RH-MEV, the RVUs saved 44–75% energy for space heating while the CO2 concentration and relative humidity levels were decreased due to RVUs’ constant air exchange rate. In all cases, RVUs provided considerably higher supply air temperatures due to the implemented heat recovery, which can potentially improve indoor thermal comfort.

Special aspects of calculation of infiltration in residential and public buildings

In the current paper, the methods of calculating infiltration for different ways of the ventilation system operation have been reviewed. The calculation of infiltration losses of buildings in cases of organizing natural and mechanical supply and exhaust ventilation, as well as recent scientific research in this area, has been considered. The calculation of natural ventilation with the values of air exchange given in Set of Rules 54.13330.2016 “Residential multi-apartment buildings” has been compared with the calculation of mechanical ventilation taking into account different glazing of the building facade. The influence of gravitational and wind components of pressure on various facades of the building has been analyzed. The gravitational and wind effects on the building are illustrated as a pressure diagram. The calculation of the specific heat flux for heating the infiltrated outdoor air on each floor is presented. The scientific studies of infiltration losses with a mechanical balanced supply and exhaust ventilation system proposed by A.S. Kubenin in his scientific work have been considered. The method of calculating the amount of infiltrated air for residential and public buildings has been thoroughly researched. Studies of heat consumption for one or more windward facades are presented. Criteria conditions of different schemes of filtration air exchange at different wind directions are formulated.

Waste heat recovery potential in residential apartment buildings in Finland's Kymenlaakso region by using mechanical exhaust air ventilation and heat pumps

With the growing share of ventilation heat loads, the heat recovery over the mechanical ventilation systems appears as one of the key solutions to reduce heat loss and generate energy savings. Finland's long-term renovation strategy aims for a highly energy-efficient and almost carbon-free building stock by 2050. One of the greatest potentials for energy savings relates to those built between the 1960s and 1980s where no heat recovery exists. This study addresses the wasted heat potential of apartment buildings in the Kymenlaakso region in Finland and how EAHPs can utilize it. The wasted heat potential was mapped by selecting buildings of different ages in Kotka from the 1950s to 2010 and for which the thermal energy balance was determined. The apartment buildings with mechanical exhaust ventilation in Kymenlaakso were surveyed. If all the mapped exhaust air waste energy could be utilized by EAHPs, it could produce the thermal energy combined from different decades up to 18.7 GWh/a in Kotka and 36.8 GWh/a in Kouvola. The calculated annual reduction in CO 2 emissions might be about 590 and 944 tCO 2 in Kotka and Kouvola, respectively. The calculated payback periods varied from 7 to 13 years for the selected buildings.

Design of residential ventilation systems using performance-based evaluation of Indoor Air Quality: application to a Danish study case

A Demand-controlled ventilation (DCV) has been recognized as a promising solution for decreasing energy consumption while ensuring good Indoor Air Quality (IAQ) in buildings. However, its application in the residential sector has increased first recently. Implementation of DCV systems brings the problem related to assessing their performance, not only in the view of energy savings but also in the ability to ensure IAQ. The objectives of this paper were to introduce a multicriteria performance-based approach for the evaluation of residential ventilation systems with CONTAM airflows simulations; illustrate its applicability to three DCV strategies in the context of renovated apartment buildings in Denmark and challenge the minimal background airflow requirements anchored in the Danish building code. Our performance-based approach allows assessing ventilation performance regarding IAQ (CO2, humidity, PM2.5, and formaldehyde-based indicators), energy consumption, and ventilation heat loss. Our results show that DCV strategies can improve IAQ while decreasing airflows. For example, application of DCV reduced the cumulative indicator of occupant exposure to formaldehyde, IHCHO by 6 to 28 %, compared to the constant-airflow system. For humidity controlled mechanical exhaust ventilation, the heat loss can be reduced up 51%.

The impact of the technical requirements of the renovation grant on the ventilation and indoor air quality in apartment buildings

In this study, the impact of ventilation requirements set in the conditions of a renovation grant was analysed with field measurements. Effects of renovation measures applied in two grant periods on the air change rate (ACR) and indoor air quality (IAQ) of apartments were examined. CO2 levels and airflow rates were measured in 21 buildings during the first renovation grant period and in 15 buildings in the second grant period. During the first grant period, the average ACR studied apartments was as low as 0.17 h−1, and in the second grant period ACR had improved to 0.57 h−1, complying with requirements. Room-based ventilation requirements as well as heat recovery and preheating of intake air, mandatory airflow rate and sound pressure level measurement protocols, and third party inspection of design documentation assured adequate ventilation and IAQ in the second grant period. Centralized mechanical supply and exhaust ventilation with heat recovery resulted in best performance but an alternative system with exhaust heat pump and ventilation radiators may also be recommended. We concluded, that the installation of proper ventilation system is a key issue in renovation. The results of the study are a valuable input in designing technical conditions of the renovation grant.

Effect of energy renovation and occupants' activities on airborne particle concentrations in Swedish rental apartments

Exposure to airborne particles causes detrimental health effects, hence their assessment in indoor environments, where people spend most of the time, is important. The influence of energy renovation and occupants' activities on airborne particle concentrations was assessed in seven occupied Swedish residences. Ultrafine particle (UFP, <100 nm) number concentrations, PM2.5 (<2.5 μm) and black carbon (BC, <900 nm) mass concentrations were simultaneously measured inside and outside before, after renovation, and during follow-up.The average indoor UFP number concentrations increased from 6200 (±4070) cm-3 before renovation to 12,700 (±6040) cm-3 during the follow up, as the number of indoor activities doubled. Indoor UFP number concentrations depended mainly on frequency and type of occupants' activities in studied residences (e.g., cooking, candle burning). The average indoor PM2.5 concentration decreased from 8.6 (±5.8) μg m-3 before renovation to 2.5 (±1.3) μg m-3 during follow up, as the activities that generated PM2.5 decreased, and infiltration of outdoor particles could have been decreased due to renovation measures. However, the indication of infiltration decrease during the follow up, assessed on the basis of indoor to outdoor ratios during non-activity times (with no influence of occupants' activities), was not observed after the renovation and should be treated with caution. In this study indoor PM2.5 and BC were influenced by activities and outdoor concentrations. Reduction of exposure to indoor UFP, might be obtained by optimization of kitchen exhaust flows. An improved design of supply air inlets in mechanical exhaust ventilation systems may reduce PM2.5 infiltration.Occupants' logbook records, needed for identification of sources contributing to particle exposure, proved useful but not always accurate compared to technical measurements of activities and UFP concentrations. Development of simple and reliable activity detection systems is needed to complement logbooks and allow accurate assessment of source contribution to particle exposure in homes and associated health effects.

Air exchange calculation in traditional buildings of orthodox churches in Russia

The paper devoted to indoor air quality providing in orthodox churches in Russia. Using the results of theoretical and experimental research made some practical recommendations for design and installation of ventilation systems in orthodox churches. Significant part of research deals with air and constructions humidity controls by reverse osmosis. It is reaffirmed that the rate of dehumidification is directly connected with the air exchange rates and operation of space heating devises in premises. It is very common to use natural ventilation in old churches. It is very easy to install and maintain, but still this way of indoor air conditions providing is absolutely not sustainable. And to avoid the leak of ventilation efficiency for different rooms it is recommended to provide mechanical supply and exhaust ventilation. Another significant issue for providing rapid wall dehumidification is properly operating space heating. It is noted that heating should be combined with an action of ventilation and electroosmotic drying.

Theoretical and experimental substantiation of the system of local removal of harmful substances during the combustion of candles in the worship hall of Orthodox churches and cathedrals

The analysis of the features of Orthodox churches, temples and cathedrals, elements of the design of the halls of worship, and their preservation. The types of hazards generated during the burning of candles and the parishioners and staff present are systematized. Thermal imaging surveys of convective flows formed during candle combustion were carried out. A technique for conducting experiments and a diagram of an experimental setup for measuring the temperature and air velocity in a convective jet have been developed. The diagram of the convective flow structure is presented, which consists of individual jets from each candle. The results of the study have been obtained, which make it possible to determine the area of stable convective flow and the place of installation of the exhaust hood above the candlestick, as well as the distance between the burning candles and the edge of the bottom of the umbrella. A local mechanical exhaust ventilation system with umbrellas has been developed to trap and remove harmful substances from the worship hall and provide comfortable conditions for parishioners and preserve the decoration elements of the halls. The characteristics and conditions for the efficient operation of the hoods in the local exhaust ventilation system and the factors influencing their operation are given.

Measured performance of exhaust air heat pumps in Finnish apartment buildings

The energy efficiency of existing apartment buildings is playing an important role in energy and climate targets. In Finland, mechanical exhaust ventilation system is commonly used in older apartment buildings. Hence, there could be an energy saving potential by an exhaust air heat pump system (EAHP). In this work two cases have been studied. Buildings were built in 1960’s and 1970’s and in renovation equipped with hybrid heating system: district heating and exhaust air heat pump system. Two years measurement data, 2018 and 2019, was collected to evaluate the performance of exhaust air heat pump systems. According to measurement data the monthly coefficient of performance (COP) was calculated as well as seasonal coefficient of performance (SCOP) was defined. The monthly COP values varied from 3,1 to 4,6 and SCOP values were about 3,7. Heating energy cost savings were 23-31 %. Energy performance class before and after EAHP installation was calculated. If at least 50 % of heating energy consumption was covered by EAHP then also energy performance class was improved.

Comprehensive survey on radon mitigation and indoor air quality in energy efficient buildings from Romania

Over the last 10 years applied scientific research has been carried out in Romania to tacked the residential radon issues. The increased interest to reduce the carbon footprint of buildings has lead to the implementation and use of new architectural solutions aimed to save energy in houses and other buildings. As a consequence, the degree of retrofit in existing buildings and energy efficiency of new buildings promoted the need to not only mitigate indoor radon, but improve indoor air quality overall. The present study found that the while the best performance in radon reduction was confirmed to be based on sub-slab depressurization (61% - 95% reduction), centralized and decentralized mechanical supply and exhaust ventilation with heat recovery yielded a good efficiency in overall improvement of indoor air quality (CO2, VOC, RH, temperature). The outcome of our research, as well as future perspectives, take into account the recommended harmonization of energy efficiency programs with those of public health by finding and applying the best technologies in compliance with energy saving and indoor environmental quality.

Furry pet-related wheeze and rhinitis in pre-school children across China: Associations with early life dampness and mould, furry pet keeping, outdoor temperature, PM10 and PM2.5

BackgroundFew Chinese population studies exist on early life risk factors for furry pet allergy. ObjectivesWe studied childhood respiratory symptoms when in contact with furry pets in relation to early life exposure. Moreover, we studied similar environmental associations for rhinitis not related to furry pets. MethodsChildren aged 3–6 y from day care centres in seven Chinese cities participated (N = 39,782). Parents answered a questionnaire on home environment and children’s health, including rhinoconjunctivitis and wheeze when in contact with furry pets, and diagnosed rhinitis. Prenatal and postnatal outdoor temperature, PM2.5, PM10, and NO2 were calculated using data from monitoring stations. Associations were estimated by multilevel logistic regression. ResultsTotally 2% had cats, 4% dogs, and 3.2% had rhinoconjunctivitis or wheeze when in contact with furry pets (FP symptoms). Moreover, 1.1% had furry pet related diagnosed rhinitis and 7.5% had diagnosed rhinitis not related to furry pets (other diagnosed rhinitis). Prenatal PM2.5 and PM10, especially in second trimester, and a colder climate were risk factors for FP symptoms. ETS, dampness and mould, condensation on windows in wintertime, and cats and dog keeping were associated with FP symptoms. Breast feeding and frequent window opening were protective. Similar indoor associations were found for furry pet related diagnosed rhinitis. ETS, dampness and mould, window condensation, urbanization and mechanical exhaust ventilation were risk factors for other diagnosed rhinitis. Cooking with an electric stove and early life exposure to animals (cats, dogs, farm environment during pregnancy) were protective for diagnosed rhinitis not related to furry pets. ConclusionsPrenatal outdoor PM10 and PM2.5 can be risk factors for symptoms suggestive of furry pet allergy. Early life dampness and mould can be risk factors for rhinitis related and not related to furry pets. Exposure to animals (cats, dogs, farm environment) may reduce diagnosed rhinitis not related to furry pets.

Ventilation in low energy residences – a survey on code requirements, implementation barriers and operational challenges from seven European countries

This paper reports the results of an interview survey conducted among different stakeholders involved in design, installation and operation of residential ventilation in seven European countries. In total 44 interviews were performed. The results provide a valuable snapshot of current practices and insights into potential barriers and challenges regarding installation of mechanical ventilation in low-energy residences to maintain high indoor air quality (IAQ). The results show that mechanical ventilation with heat recovery is becoming a common choice in new low energy residences in Europe. However, there are countries that apply airing or other types of ventilation such as mechanical exhaust or natural ventilation due to tradition, national legislation, climatic conditions and/or cost reasons. Demand-controlled ventilation (DCV) is often allowed or even recommended in standards, but rarely implemented in practice, except for exhaust-only humidity-based DCV in France and Belgium. The main barriers against mechanical ventilation seem to be high capital cost, space requirements and duct routing. The respondents commonly reported problems resulting from poor construction, lack of commissioning and/or maintenance. The main needs to be identified in the survey were more legislative pushes including more flexibility in legislation, a coordinated approach to energy efficiency and IAQ, and control mechanisms to ensure good implementation and operation.

Highly insulated crawl spaces with controlled minimal ventilation – proof of concept by field measurements

In current practices crawl spaces are typically ventilated with outdoor air. This leads very often to high relative humidity especially in the beginning of the summer, which can be problematic if the excess humidity cannot be ventilated efficiently enough. This paper introduces a crawl space concept where the crawl space is highly insulated and traditional ventilation openings are replaced by minimal mechanical exhaust ventilation set by pressure difference with the aim to prevent potential pollutants to penetrate indoors through the base floor. The concept that has been developed based on the simulation study is tested in this study with field measurements in four single family houses. Continuous measurements of relative humidity and temperature in crawl spaces and outdoor air were running more than one year in each building. The results revealed that all the crawl spaces had very low relative humidity, mostly below 75% and for very short periods close to 80% even though some of the buildings were new and construction phase moisture was drying out. The results revealed that the crawl space concept studied provided an ultimate moisture safety and can be recommended for all buildings with wooden floor.

ОСОБЕННОСТИ ФОРМИРОВАНИЯ ВОЗДУШНОЙ СРЕДЫ В СОВРЕМЕННЫХ ЖИЛЫХ ЗДАНИЯХ

Air quality in residential premises equipped with modern airtight windows and entrance doors causes public complaints. We discussed peculiarities of air quality changes in residential buildings resulting from large-scale use of window glass units, which are characterized by increased thermal resistance and high-quality insulation, used in modern residential construction. Regulatory and law documentation are analyzed. Advisability of using mechanical supply and exhaust ventilation in residential premises, as well as special inlet devices – ventilation valves, which ensure sufficient air exchange in the apartment, unlike currently used exhaust ventilation system with natural inducement, are substantiated. It is suggested to coordinate the requirements of current sanitary standards and rules for residential premises with the requirements of engineering regulatory documents.

Indoor air temperatures, CO2 concentrations and ventilation rates: Long-term measurements in newly built low-energy schools in Sweden

Within a period of ten years a large number of schools need to be built in Sweden and these new schools need to be nearly zero energy buildings. School classrooms are required to provide healthy learning environments to help children perceive and process information. This means that classrooms must provide adequate levels of indoor air quality and thermal comfort. This article investigates CO2 concentration levels and indoor air temperatures in several recently built, low-energy schools in Sweden, and compares them with design criteria stipulated in specific international standards and Swedish regulations to provide feedback to the building construction industry. Field measurements of CO2 concentrations, indoor air temperatures and ventilation rates in seven low-energy schools, with a total of 145 classrooms, taken during several months spanning both summer and winter periods, are analysed in this article. All the schools in the study have mechanical supply and exhaust ventilation systems with demand control devices in the classrooms.The study shows that all the classrooms, in general, comply with the design criteria regarding indoor air temperatures and CO2 concentrations in EN15251, ASHRAE 62.1 and the Swedish national regulations and recommendations. Median values of indoor air temperatures were between 19 and 23.5 °C in all classrooms during school hours. The 90-percentile levels of CO2 concentrations were below 1000 ppm in 60 of 61 classrooms in which these measurements could take place. It is concluded that during this long-term measurements in the studied seven low-energy schools, modern HVAC systems with demand control and heat recovery, in general, provided satisfactory indoor climates in terms of CO2 levels and indoor air temperatures.

Effect of ceiling centralized mechanical smoke exhaust on the critical velocity that inhibits the reverse flow of thermal plume in a longitudinal ventilated tunnel

Toxic fire smoke in a tunnel fire is an important factor causing casualties. The critical ventilation velocity that inhibits reverse transportation of toxic thermal smoke in a longitudinal ventilated tunnel is an important design parameter. The evolution characteristics of the critical velocity in a tunnel with the coupling effect between ceiling centralized mechanical smoke exhaust and longitudinal ventilation have never been studied before. A series of small scale tunnel experiments were conducted, ten different ceiling mechanical exhaust rates (0–2.7 m/s) and twelve fire heat release rates (1.5–18 kW) are considered. It is found that, the ceiling centralized mechanical smoke exhaust will affect the critical velocity that inhibits the reverse flow of smoke in a tunnel. Due to the effect of ceiling mechanical smoke exhaust, the critical velocity decreases with increasing mass flow rates of mechanical smoke exhaust. The critical Froude number increases with increasing exhaust mass flow rate for a given dimensionless fire heat release rate. A new empirical model for predicting the critical ventilation velocity with the coupling effect between ceiling centralized mechanical smoke exhaust and longitudinal ventilation is proposed, which agree well with the measurement.