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Ventilation efficiency or contaminant removal efficiency is often evaluated using the ratio between the concentrations in the exhaust air and the room air. This ratio does not truly represent the expectation of ventilation in restrooms, where dynamic airflow fields and sources are more typical. This study focuses on a short-term (10 min) pollutant removal percentage in a residential restroom featuring a dynamic airflow field, particularly with the onset of window-induced stack ventilation during toilet uses. Thirteen ventilation scenarios of a residential restroom were studied using the numerical method that was validated by a mock-up experiment. The scenarios differed in the operation of the exhaust fan and window. Results show that the 10-min pollutant removal percentage of a typical exhaust ventilation system at 10 h-1 air change rate (ACH) is only 68.5%. Under exhaust ventilation, opening the window can introduce both adverse short circuit and favorable stack ventilation depending on the difference between the indoor and outdoor temperatures. As the temperature difference increases from 0 to 12.5 °C, the removal percentage increases from below 50%, a drop due to short circuit, to above 98% thanks to a tripled ventilation rate. The human thermal plume has notable effect on the removal percentage, but its effect can be neglected with the presence of stack ventilation. The hybrid ventilation strategy has impact on perceived air quality and thermal comfort. When the outdoor air is colder, opening the window under exhaust ventilation may increase the current sitting user's exposure to the self-produced pollutants but can reduce the exposure of the next immediate standing user. In addition, opening the window in cold days will make the toilet user thermally uncomfortable with reduced local temperatures and increased airflow velocities. The study highlights the importance of using the short-term removal percentage to evaluate the performance of restroom ventilation. [ABSTRACT FROM AUTHOR]

Enclosed-space ventilation plays a pivotal role in enhancing indoor air quality (IAQ). Various regulations and guidelines determine minimum fresh air requirements, varying by the application, country, etc. The present study employs real-time indoor CO2 measurements to calculate the actual air change rate (ACH) and models the building's compliance with Chartered Institution of Building Services Engineers (CIBSE) guidelines to assess its impact on IAQ. The contaminant considered is the SARS-CoV-2 virus with multiple infectors, and the study calculates the virus's transmission risk under different scenarios. Fresh air is assumed to be provided by mechanical or hybrid ventilation. The results reveal that the current building conditions are unacceptable, showing a significant gap from the recommended guideline rates. Meeting CIBSE recommendations ensures indoor air safety in terms of CO2 concentration. However, in extreme conditions with five infectors, findings show a 14% reduction in mechanical ventilation efficacy. Among the hybrid ventilation scenarios, combining CIBSE rates with natural ventilation, with a 30% door and window opening from the class outset, proves most effective in reducing the virus's transmission risk, with a 58–70% reduction from the building's current condition. Furthermore, implementing supplementary measures like air cleaners resulted in an additional 28–50% reduction in transmission risk. [ABSTRACT FROM AUTHOR]

Excessive solar radiation negatively affects classroom occupants' perfor­mance and thermal comfort, especially in buildings with West and East-facing glazed openings. This study utilises fixed external shading devices and triple-glazed low-emissivity windows to optimise a classroom building in Nigeria. Employing hybrid ventilation mode in EnergyPlus simulations, the optimised model shows a 44% reduction in discomfort hours, a 23% decrease in cooling load, and a 16% drop in energy demand compared to the original design. Comparative analysis of the optimised model with the as-built and West-East oriented classroom reveals a 16% and 10% reduction in energy consumption per conditioned area, along with 56 KWh/m² and 32 KWh/m² savings in cooling demand, respectively. Despite the effectiveness of fixed shading in curbing solar gains, occasional glare persists. This research underscores that shading alone may not fully meet thermal comfort requirements, emphasising the importance of building fabrics, building orientation and climate-sensitive design.

This paper delves into the examination of indoor comfort in classroom environments and its interplay with ventilation on human wellbeing in scenarios of varying indoor carbon dioxide concentrations. The assessment of these parameters was done according to the provisions outlined in the Spanish national Regulation of Thermal Installations in Buildings (RITE). This study also compares various ventilation strategies, namely natural, mechanical and hybrid ventilation, commenting the pros and cons of each method in the climate of the Basque Country, Spain. To do so, a classroom in the School of Architecture in the Basque Country was modelled in thermal simulation software. Simulations were carried out for full days in 10-minute intervals using Design Builder and considered three different exterior scenarios (a cold day, temperate day, and a warm one) and three different ventilation systems (natural, mechanical with simple flux, and hybrid). Two additional scenarios where added for control, one with no ventilation at all and another with a partial, constant, natural ventilation, like was done during the COVID-19 pandemic. Thus, the natural ventilation option was evaluated under four conditions (windows always closed, windows constantly open 15 %, COVID-19 mode, and windows operated by thermal sensation of the user). The mechanical system evaluated consisted of a constant flux ventilation for IDA 2 IAQ with an air flux of 12.5 L/s per person. The modelled hybrid system consisted in a combination of simple flux mechanical ventilation and open windows and doors under some particular conditions. An occupancy rate of 50 % of the theoretical maximum occupancy of the classroom and a scheduled heating operation were considered. This article presents the CO2 concentration, energetic balance and thermal comfort results obtained in the simulation and compares between the different scenarios. The results showed that the hybrid ventilation system was able to effectively control indoor air quality, providing a healthy and comfortable environment for occupants. The hybrid system demonstrated improved energy efficiency compared to the natural ventilation system, while maintaining an acceptable indoor air quality. Overall, the results of this study highlight the importance of considering hybrid ventilation in educational spaces in the northern Basque Country climate. The study provides valuable insights for building design and operation, especially for renovation of existing schools and educational facilities that lack any means of mechanical ventilation, showing some of the potential for hybrid ventilation to improve indoor air quality and energy efficiency.

This study aimed to determine the relation between airflow pattern characteristics and indoor air quality of a hybrid personalized ventilation (PV) with under-floor air distribution (UFAD) system in a standard office. Actually, it was tried to introduce a practical design consideration for a suitable airflow division between inlet diffusers based on streamline analysis. In each scenario, the total airflow rate was 47.5 L/s. When each PV unit was set at 1.25 and 2.5 L/s, the cold/dense consequent airstreams of PV and occupants' exhalations were returned to the inhaled zones after losing the required momentum in penetrating the background airflows to reach the ceiling level. The density differences between airflows formed steady vortexes at the occupants' micro-environments. These negative interactions acted like obstacles in contaminant transference and could decrease the micro-environment air quality between 21 and 62% compared to the standalone UFAD. At high or dominant PV flow rates (equal to 7 L/s), the air change efficiency reduced to 0.50 which meant the PV flow quickly escaped through the exhaust, and the weak UFAD couldn't remove the heat and particles at ambient areas as well as the standalone UFAD. When each PV diffuser had the minimum required flow rate which was necessary to prevent any formation of steady vortexes, the micro-environment air quality improved between 19 and 25%. The corresponding ventilation effectiveness and air change efficiency indexes were 1.4 and 0.55, respectively which showed acceptable conditions at ambient areas. The balancing PV flow rate was 5 L/s for each PV diffuser. [ABSTRACT FROM AUTHOR]

The article presents the results of measurements of temperature, relative humidity and CO2 concentration in six single-family houses' bedrooms located in Poland, in Wrocław and vicinity, during two climatic seasons: summer–autumn and winter. Two buildings with natural ventilation (NV) were tested, three with mechanical ventilation with heat recovery (MV) and one with hybrid ventilation (HV)—mixed mode natural and mechanical. The behavior of residents regarding opening windows was analyzed and the influence of the changing internal and external conditions on their active reactions was examined. The analysis confirms and adds to the global discourse on the key impact of user behavior on securing healthy indoor air quality in housing, regardless of ventilation system or building energy standard. A disconnect exists between the observed window opening practices and typical design principles, assuming adjustment to a given ventilation system or changing weather conditions. The observations showed that in both analyzed seasons it was possible to obtain a good quality internal environment, in terms of CO2 level, regardless of the ventilation system used in the building. However, unfavorable results were observed for one bedroom, in which the inhabitants do not adapt their behavior to local technical conditions. Taking into account the level of relative humidity (RH), much higher values were observed in the NV bedrooms in both analyzed periods. The obtained results were divided into IAQ classes in accordance with the EN 16798-1. The recorded values of the internal temperature confirm the significant influence of the location of the room in the building and the actions taken by the residents. [ABSTRACT FROM AUTHOR]

Studying the effect of adding a ventilation system consisting of two devices, impinging and personal ventilation, and knowing the extent of their impact on the presence of different thermal loads represented by humans, computers, and light inside a thermally isolated office room by using sandwich panels. In addition, examining the air distribution inside a room also found the required thermal comfort for two people who were represented in the form of the thermal manikin and inside them a heat source close to 80 watts, which is close to the heat emitted by the human being according to the global A share. The most important results that were obtained first when adding the personal ventilation system to the impinging ventilation showed a clear improvement in heat levels close to the thermal manikin at a level of 1.1 meters and above. Second, the homogeneity of temperatures within the space, where the difference between the main source of ventilation (impinging) and the heat at the level of 1.8 meters is relatively small, compared to the use of the impinging ventilation system alone. The aim of the research is to prove the efficiency of such a system within the Iraqi summer weather between march to June month, under the conditions studied during this project, energy savings can be achieved using this strategy. Providing respiratory and thermal comfort inside the air-conditioned space, especially in the people’s seating area at 1.1 meters, and achieving two goals of sustainable development (an industry with innovation and clean with affordable energy). [ABSTRACT FROM AUTHOR]

Engineers have integrated general ventilation systems with personalized ventilation (PV) to achieve energy efficiency while providing good indoor air quality (IAQ) and thermal comfort. Previous studies conducted parametric analyses of PV by varying its flow rate and temperature, analyzing energy, IAQ, and thermal comfort while keeping main ventilation settings constant, even though the latter significantly affect the general flow field. Therefore, computational fluid dynamics simulation is performed to simultaneously optimize the above-mentioned three outputs in an office with displacement ventilation (DV) and PV by varying the DV supply flow rate and temperature, the fraction of outlet air being resupplied to inlet or DV recirculation, and PV supply flow rate and temperature. We utilize the Taguchi design to minimize the number of simulations as well as use the "technique for order preference by similarity to ideal solution" (TOPSIS) coupled with Taguchi's signal-to-noise ratio analysis for optimization. Four optimization cases are investigated by varying the thermal comfort and IAQ parameters from volume-averaged to occupant-centric values, such as the skin temperature and inhaled concentration. Results show that occupant-centric optimization presents low energy requirements with acceptable IAQ and thermal comfort compared with volume-averaged optimization, which can be attributed to imperfect mixing conditions. Furthermore, the DV settings and thermal plumes significantly affect the direction of jet released by the PV, which does not improve the IAQ. This underscores the importance of considering the aforementioned effects in maximizing the PV potential. Nevertheless, the PV system functions as intended under a flow rate of 6 L/s. • Multicriteria optimization of energy, indoor air quality, and thermal comfort. • Main-ventilation supply temperature and flow rate significantly affect PV jet. • Thermal plumes or buoyancy significantly affect PV jet. • Room average and occupant-skin average temperatures depend on DV settings. • Occupant-centric system reduces input energy with acceptable IAQ and thermal comfort. [ABSTRACT FROM AUTHOR]

Owing to the impact of global warming, the weather becomes hotter than the past. Responding to the hot–humid climate, the Taiwan government intends to install air-conditioning in classrooms to provide comfort study environment. The thermal management of school buildings is separated into naturally ventilated and air-conditioning seasons based on the strategies of reducing energy use while maintaining thermal comfort. In this paper, the school buildings located in northern and southern Taiwan (Taipei and Kaohsiung) are selected as study objectives to simulate cooling load, thermal comfort, and the natural ventilation potential to discuss the parameters related to building envelope design. Through regression analysis of the 360 simulation cases, the Overall Thermal Transfer Value (OTTV) for Taipei and Kaohsiung are established. Besides, the coefficient of azimuth correction factor and area ratio correction factor are clarified for equivalent ventilation area. Through coupled analysis, the Pareto ranking method is used to obtain numerical solution sets corresponding to the index including OTTV and equivalent ventilation area.Consequently, a school building envelope design criteria for balancing the energy use and thermal comfort is proposed. According to the analysis results and the intersection of OTTV and equivalent ventilation area at Pareto front, it is confirmed that the restriction of the OTTV index is 20 W/m2 in Taipei and Kaohsiung; the equivalent ventilation area which guarantees no overheating risk during natural ventilation season is determined as 9.5 m2 in Taipei and 14.3 m2 in Kaohsiung. Furthermore, the influence level of the parameters is clarified that the area and shading performance of windows make a major influence on sensible cooling load; comparing to external shading, the window insulation performance is considerably less important. Overall, this study seeks the balance between energy use and thermal comfort then provide the efficient strategies at the initial design stage through the proposed criteria.

Hybrid ventilation systems present many advantages compared to the natural or mechanical ventilation systems. In the case of buildings with significant heat gains, they seem to be the proper solution, if correctly analyzed and designed. The paper presents the calculations and study of the natural ventilation parameters with the possibility of including roof fans in the model glasswork in Kielce, Poland. The calculations for the optimization process were conducted using Ventos software. The limitations of the method include maximal values of air temperature at the top of the building, air velocity at the inlets and outlets, and negative pressure. Conclusions for the summer season arise that the most optimal solution ensuring the minimum internal temperature and air velocity conditions for the glassworks building is the use of wall inlets located on two levels. On the other hand, in winter conditions not all wall intakes should be open. Further analyses and simulations were performed for hybrid ventilation. Assessments confirm the accuracy and efficiency of using natural ventilation in facilities with significant heat gains, including glassworks. [ABSTRACT FROM AUTHOR]

It has been identified that improving building energy efficiency is an effective method to reduce greenhouse gas (GHG) emissions. Although standards have been established to satisfy a building's minimum energy demand while ensuring the comfort of its residents, they are difficult to implement in mixed-humid regions. This study proposes a hybrid ventilation strategy that can comprehensively reduce cooling, heating, and ventilation energy in mixed-humid climate regions to significantly decrease the primary energy demand and reduce the impact of buildings on the environment. This study evaluated the changes in energy saving potential and thermal comfort according to the extension of the natural ventilation period and passive strategies, such as decentralized ventilation. Changes in indoor air temperature, operative temperature, and PMV for each strategy were analyzed. As a result, extending the natural ventilation and the decentralized ventilation strategies can save 32% and 34% of the building's energy, respectively. Considering that electricity is the main energy source for cooling in Korea, the extension of the natural ventilation period was judged to be the best approach from the perspective of primary energy demand. The results can be used to predict changes in building energy demand and thermal comfort and select an appropriate ventilation strategy based on occupant information obtained using Internet of Things. [ABSTRACT FROM AUTHOR]

A hybrid ventilation system combining both natural and mechanical ventilation has proven very promising in moderating indoor climate, based on its ability to ensure indoor air quality with low energy consumption. The system maintains indoor thermal comfort conditions by switching to mechanical mode whenever natural ventilation is not possible. However, the application of such a system in severe arid climates is still very limited and challenging, and almost half the urban peak load for energy demand is used to supply cooling and air-conditioning in summer. This paper assessed the application of the hybrid ventilation mode for an educational building in a hot, arid climate, with the aim of reducing the building's energy consumption without compromising the occupants' thermal comfort. A dynamic simulation was conducted using Integrated Environmental Simulation in a Virtual Environment building energy software, and the outcomes were validated against actual consumption data over one year. The results were then evaluated for indoor thermal comfort and energy reduction and showed the potential of the hybrid system to provide energy savings of 23% across the year. Better energy performance was achieved during the cooler seasons (33.5%) compared to hot (17.1%). When photovoltaic systems were incorporated, by examining different inclination angles and locations for energy savings and carbon emissions (CO2) reductions, the outcomes proved that photovoltaic south and a 25° tilt angle recorded the maximum energy and minimum CO2 emissions annually. This integration of hybrid ventilation and photovoltaics reduced the building's energy consumption from 106.1 MWh to 36.6 MWh, saving almost 85% in total annual energy and cut down the carbon emissions from 55,227 kgCO2 to 6390 kgCO2. [ABSTRACT FROM AUTHOR]

Air pollution is detrimental to human health, causing several human illnesses. The industrial microenvironment generates high levels of indoor airborne pollutants, becoming a pervasive issue for workers. It is essential to improve the indoor air quality in this workplace by applying enhanced ventilation systems to minimize inhalation risk. Displacement ventilation is used in industrial buildings because of its stratified air distribution and low cost. However, in case of accidental pollutant release, an enhancement is needed to minimize inhalation exposure. This study proposes a hybrid emergency ventilation system using localized push-pull ventilation to improve the installed displacement ventilation system of a representative workshop. Computational fluid dynamics was applied to calculate steady-state indoor air flow and volume-averaged pollutant concentration. System performance was evaluated in terms of source position; a computer simulated person was integrated to the building to confirm effectiveness against personal inhalation. Results showed marked improvement in performance when push-pull technique was used: room-averaged concentration diminished up to 91% while ventilation rate only increased 4%. Inhaled pollutant mitigation was achieved but performance dependence against leakage source and personal position was confirmed.

The development of an accurate control of hybrid ventilation which combines the strengths of natural ventilation and mechanical ventilation relies on better energy efficiency and healthy Indoor Air Quality (IAQ) in buildings. This paper focuses on development of mathematical models for natural ventilation and mechanical ventilation through the use of temperature differences, and on design of a control strategy for hybrid ventilation that switches between control actions for both ventilation modes to optimize energy consumption while maintaining IAQ and thermal comfort at the desired setpoints. These control actions are developed to automatically adjust the position of motorized dampers at the button of the cavity, the position of the motorized windows of the test-cell, and turn on the air-supply fan only when needed. The paper ends with a demonstration and discussion of real experiments on the flexibility and effectiveness of the proposed control strategy for hybrid ventilation in the test-cell building case study.

The article presents the results of measurements of temperature, relative humidity and CO2 concentration in six single-family houses’ bedrooms located in Poland, in Wrocław and vicinity, during two climatic seasons: summer–autumn and winter. Two buildings with natural ventilation (NV) were tested, three with mechanical ventilation with heat recovery (MV) and one with hybrid ventilation (HV)—mixed mode natural and mechanical. The behavior of residents regarding opening windows was analyzed and the influence of the changing internal and external conditions on their active reactions was examined. The analysis confirms and adds to the global discourse on the key impact of user behavior on securing healthy indoor air quality in housing, regardless of ventilation system or building energy standard. A disconnect exists between the observed window opening practices and typical design principles, assuming adjustment to a given ventilation system or changing weather conditions. The observations showed that in both analyzed seasons it was possible to obtain a good quality internal environment, in terms of CO2 level, regardless of the ventilation system used in the building. However, unfavorable results were observed for one bedroom, in which the inhabitants do not adapt their behavior to local technical conditions. Taking into account the level of relative humidity (RH), much higher values were observed in the NV bedrooms in both analyzed periods. The obtained results were divided into IAQ classes in accordance with the EN 16798-1. The recorded values of the internal temperature confirm the significant influence of the location of the room in the building and the actions taken by the residents.

Among the various strategies for the prevention of airborne transmission, engineering measures are placed high in the hierarchy of control. Modern hospitals in high-income countries have mechanical systems of building ventilation also called HVAC (heating, ventilation, and airconditioning) but installation and maintenance of such systems is a challenging and resource-intensive task. Even when the state-of-the-art technology was used to build airborne infection isolation rooms (AIIRs), recommended standards were often not met in field studies. The current coronavirus disease-2019 pandemic has highlighted the need to find cost-effective and less resource-intensive engineering solutions. Moreover, there is a need for the involvement of interdisciplinary teams to find innovative infection control solutions and doctors are frequently lacking in their understanding of building ventilation-related problems as well as their possible solutions. The current article describes building ventilation strategies (natural ventilation and hybrid ventilation) for hospitals where HVAC systems are either lacking or do not meet the recommended standards. Other measures like the use of portable air cleaning technologies and temporary negative-pressure rooms can be used as supplementary strategies in situations of demand surge. It can be easily understood that thermal comfort is compromised in buildings that are not mechanically fitted with HVAC systems, therefore the given building ventilation strategies are more helpful when climatic conditions are moderate or other measures are combined to maintain thermal comfort. [ABSTRACT FROM AUTHOR]

In the post-pandemic era, Signaled Manual Airing (SMA, i.e. windows opening driven by alarms and real-time IAQ measurements) is still expected to play a role in schools, either independently or in support of mechanical ventilation (MV) systems, as a cost-effective solution to meet more stringent regulatory requirements for indoor CO 2 levels. The present study in-depth evaluates the impact of SMA on improved levels of CO 2 but also its thermal downside in winter via a dedicated IoT-IAQ monitoring platform equipped with fully tuneable multi-threshold alarm schemes. An aged middle-school building, representative of a large amount of old existing school buildings in Italy (and Europe) and a Northern Italy location, were selected to investigate cold and high humidity winter conditions as the most critical for SMA. The mean indoor CO 2 difference with reference classrooms without alarms ranged from 20% to an impressive nearly 70% reduction. We demonstrate a clear dependence on signalling mode and level of system usage learning. The best results were in fact attained with acoustically enhanced signalling (acu-SMA). As a downside effect, operating SMA at even moderately cold latitudes caused also thermal discomfort during the coldest days, with worsened response to the alarms. The observed mean CO 2 levels maintained by classroom groups appear to be correlated with the average indoor temperature and its inverse product [CO 2 *T indoor ]-1 to a cumulative fatigue function with memory effect, referred as "thermal behavioural fatigue". Bounds of generalization, further developments towards hybrid ventilation solutions and most suitable Italian regions for operating SMA in schools are finally discussed. [ABSTRACT FROM AUTHOR]

It has been identified that improving building energy efficiency is an effective method to reduce greenhouse gas (GHG) emissions. Although standards have been established to satisfy a building’s minimum energy demand while ensuring the comfort of its residents, they are difficult to implement in mixed-humid regions. This study proposes a hybrid ventilation strategy that can comprehensively reduce cooling, heating, and ventilation energy in mixed-humid climate regions to significantly decrease the primary energy demand and reduce the impact of buildings on the environment. This study evaluated the changes in energy saving potential and thermal comfort according to the extension of the natural ventilation period and passive strategies, such as decentralized ventilation. Changes in indoor air temperature, operative temperature, and PMV for each strategy were analyzed. As a result, extending the natural ventilation and the decentralized ventilation strategies can save 32% and 34% of the building’s energy, respectively. Considering that electricity is the main energy source for cooling in Korea, the extension of the natural ventilation period was judged to be the best approach from the perspective of primary energy demand. The results can be used to predict changes in building energy demand and thermal comfort and select an appropriate ventilation strategy based on occupant information obtained using Internet of Things.

The differences between temperatures in the animal occupied zone (AOZ) and temperatures measured by control system sensors are rarely explored. This experimental study quantifies the dry-bulb air temperature [hereinafter temperature] distribution inside a finisher pig building that combines natural ventilation through automatically controlled openings with a mechanical ventilation system. Year-long temperature data from 28 sensors located at 3 different heights in the building was analysed to help understand the temperature distributions and indicate the temperatures below or above an assumed optimal temperature range, defined as between 14 °C and 24 °C. Relatively large variations in the spatial temperature distribution were found, and they were higher in the vertical direction than in the longitudinal direction. The temperatures measured in the AOZ at 0.25 m height, were on average, 7 °C warmer than that at 1.5 m height. The AOZ temperature correlated better with temperatures measured at 0.7 m or 1.5 m height in the same pen than with temperatures measured in the AOZ at other pens. The analyses show that a proportional–integral based control system effectively counteracts the effects of outdoor wind conditions, and the control system is capable of maintaining the defined optimal temperature at the measurement height. However, the optimum temperatures at the measurement heights above AOZ do not correspond to the measured temperatures in the AOZ. • Temperature gradients exist in both vertical and horizontal direction. • Average temperatures at 0.25 m were 7 °C warmer than at 1.5 m for 50% of time. • Temperature gradients were worst during the winter and periods with no wind. • Maintaining optimal temperature at control sensors alone is not sufficient for pigs. • Temperatures experienced by pigs are not reflected by control temperatures. [ABSTRACT FROM AUTHOR]

Combining natural and mechanical ventilation, hybrid ventilation is an effective approach to reduce cooling energy consumption. Although most existing control strategies for HVAC systems with hybrid ventilation provide acceptable operation results, there still often exists a mismatch of demand and response from sensing, decision making, and operating. Especially when using renewable energy sources, such as solar and thermal storage, many energy-saving decisions need to be made before the actual events may happen. As a result, predictive-based controls are preferred, and the future energy loads and saving potentials from renewable measures should be evaluated in a forecasted manner. Typical prediction simulation methods are developed for designs and analysis, which may not ensure the required accuracy for modeling future events. In this study, a novel data assimilation method originating from numerical weather prediction, Ensemble Kalman Filter (EnKF), was proposed and applied for the forecasting simulations of high-rise building cooling load and energy-saving potential from its hybrid ventilation system. Similar to an accurate short-term weather prediction process, the proposed EnKF method can ensure the simulation accuracy by combining numerical simulations and measured data for short-term forecasting of future events. In the EnKF algorithm, a simulation model is adjusted according to the measuring data to output more accurate predictive results of the cooling load reduction from a hybrid ventilation system. Based on these predictions, the supply air temperature can be adjusted, and the duration of applying natural ventilation in real-time to maintain the desired comfort of building occupants with less energy consumption than existing strategies. The proposed forecasting model can be used in real life when combined with smart building controls. The results show that the proposed EnKF method improves the accuracy of the predicted velocities. The key EnKF parameters, Kalman filter gain, and the number of ensemble members are discussed as well. With the localized Kalman filter, the average RMSE and CVRMSE decrease by 46.4% and 53.5%, respectively. [ABSTRACT FROM AUTHOR]

Countries around the world develop and use software based on the monthly calculation method of DIN V 18599:2007 and EN ISO13790 for building energy performance evaluations. The purpose of this study is to propose a method that can consider the effect of reducing cooling energy demand by hybrid ventilation outdoor air cooling in monthly calculation method-based software. For ventilation simulation, some representative floor plans and area types of Korean residential buildings were established through literature research. A number of dynamic energy simulations were performed for various building orientations, heights, and opening factors. Based on the simulation results, a nomograph that can calculate the cooling energy demand reduction factor according to hybrid ventilation that can be applied to the ventilation heat transfer coefficient is proposed.

Hybrid ventilation is an effective approach to reduce cooling energy consumption by combining natural and mechanical ventilation. Previous studies of full-scale whole-building measurements of high-rise hybrid ventilation are quite limited due to the complexities of buildings and variable ambient conditions. As a result, validated and accurate whole-building simulations of hybrid ventilation often cannot be found in the literature. This paper reports a series of full-scale measurements of hybrid ventilation in a 17-storey high-rise building and associated whole-building simulations by 15-zone detailed and a 5-zone simplified multizone models. The paper is one of the first studies of using multizone models and real-world full-scale data and sharing key operational and performance experience and case studies of high-rise hybrid ventilation. Both the test data and the validated simulation models can be used for the comparison and validation of simulation models. The 5-zone simplified model developed from this study was able to model such a complex high-rise building by only a few zones, making possible the on-line model predictive control of a high-rise building. This was illustrated in this paper by an example of optimizing the uniformity of the hybrid ventilation on different floors by modifying inlet areas. [ABSTRACT FROM AUTHOR]

Current thermal comfort standards and the models underpinning them purport to be equally applicable across all types of building, ventilation, occupancy pattern and climate zone. A recent research project sponsored by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE, RP-884) critically evaluated these assumptions by statistically analysing a large database of research results in building comfort studies from all over the world (n=22,346). The results reported in this paper indicated a clear dependence of indoor comfort temperatures on outdoor air temperatures (instead of outdoor effective temperature ET* used in RP-884), especially in buildings that were free-running or naturally ventilated. These findings encourage significant revisions of ASHRAE’s comfort standard in terms of climatically relevant prescriptions. The paper highlights the potential for reduced cooling energy requirements by designing for natural or hybrid ventilation in many moderate climate zones of the world.

Optimal ventilation strategies are fundamental to achieve net/nearly-zero energy buildings. In this study, three hybrid ventilation control strategies are proposed to minimize the cooling need in an open-plan office building, located in the center of Glasgow (Scotland). The performance of the three proposals is assessed by IDA ICE (a whole building performance simulation tool) and compared to a traditional fully mechanical ventilation system. The performance comparison includes different criteria, i.e., indoor temperature and predicted percentage of dissatisfied (PPD) for assessing the indoor comfort, and CO2 level for assessing the indoor air quality (IAQ). The results show that the three proposed hybrid ventilation strategies are able to minimize the cooling need to zero. They can also imply a drastic reduction of AHU heating power, compared with a mechanical ventilation system without heat recovery (or with low efficiency heat recovery). In addition, they significantly save the fan energy. The only drawback of the proposed strategies is that they might increase space heating demand. For instance, the first and second strategies save about 75 and 50% of AHU (air handling unit) fan energy; however, the space heating increases by about 4.2 and 2.2 kWh/m2a, respectively. The third strategy features as the best proposal because it saves around 68% of fan energy with less increase (1.3 kWh/m2a) in heating demand. Moreover, it ensures higher thermal comfort and IAQ levels compared to the first and second proposals.

Mixed-mode buildings (MM), which use both natural ventilation and mechanical cooling to provide thermal comfort and energy savings, have a high potential in climates where it is favorable to use natural ventilation (e.g., Brazil). In these buildings, operable windows are the source of natural ventilation, lighting and heat gains, and their characteristics can influence energy consumption. This work aims to evaluate the energy and luminous performance of mixed-mode office buildings with operable windows in a high-altitude tropical climate in Brazil. The performance is evaluated concerning energy savings, air-conditioning operation hours, the period of use of natural ventilation and balance between energy demand and illuminance levels. It is considered variations in envelope parameters (window-to-wall ratio and solar orientation). The method is composed of computer simulations on Daysim and EnergyPlus programs. The results showed that the mixed-mode strategy has great potential to reduce air-conditioning energy consumption. The most significant reductions occurred with larger WWRs, reaching 39.4% of energy savings (north facade, WWR = 80%). Nevertheless, while the larger WWR provided more natural ventilation availability, it increased the discomfort by high illuminance, which reached about 90% of the office’s area. Therefore, when the mixed-mode system was used, the cases with a better balance between adequate illuminance levels and low energy consumption were the south facade with all WWRs and the east and west facades with WWR of 30%. It is important to emphasize that the adoption of these solutions depends on the building's design requirements.

Abstract To reduce energy consumption and improve the safety and reliability of ventilation systems in underground subway depots, a hybrid ventilation (HV) system composed of natural ventilation, mechanical fans, and flow deflectors was proposed and tested. A reduced-scale (1:50) experiment and a full-scale numerical simulation were conducted, wherein four heat release rates (HRRs; 281 W, 380 W, 531 W, and 866 W) of the fire source and five ventilation velocities (0.7 m/s, 1.0 m/s, 1.4 m/s, 1.9 m/s, and 2.4 m/s) were tested. The temperature distributions under the ceiling were measured. Smoke movement and smoke layer stability were visualized using a laser sheet. The smoke layer height, gas flux of shafts, and smoke movement route were recorded from the simulation. Under HV, the ceiling temperature decreased significantly with increasing ventilation velocity; however, changes in temperature were different at different locations. With appropriate ventilation velocity (1.4 m/s), HV effectively controlled the smoke temperature of the bottom layer and ensured the stability of the smoke layer in the interlayer. However, the stability of the smoke layer was disrupted at higher ventilation velocities, which caused the smoke to sink, whereas a lower velocity could not slow the rise in temperature. The relationship among ventilation velocity, HRR, ceiling temperature, and smoke layer stability was analysed. A new criterion, N (N = 0.62), was proposed to determine the critical ventilation velocity associated with a lower ceiling temperature and improved smoke layer stability. [ABSTRACT FROM AUTHOR]

Abstract In this study, the thermal comfort of the occupants of learning spaces using three different ventilation strategies (i.e. air-conditioning [AC], hybrid [HB], and natural ventilations [NV]) was investigated at a tropical university campus. Data were collected from 1043 survey questionnaires; concurrently, on-site measurements in three consecutive years were analysed. Findings indicated that HB spaces have significant advantages over AC and NV spaces in terms of a higher rate of neutral thermal sensation votes, temperature satisfaction levels, and overall thermal comfort levels. It was also found that, as compared to those in AC spaces, occupants in HB and NV spaces maintained higher comfort temperature and they could tolerate a wider range of acceptable temperatures. They were also less sensitive to changes in temperature. A significant correlation between the neutral operative temperature and latitude, as identified in existing studies, supports the observation regarding acclimatisation of occupants in warmer climates. The PMV/PPD thermal comfort model predicted warmer thermal sensations than those actually felt by the occupants. The comfort rate estimated according to the PMV/PPD model was consistently lower than that according to the adaptive comfort model in HB and NV spaces, raising concerns about the effectiveness of the PMV/PPD model in predicting thermal comfort in NV spaces in a warm environment. The findings provide convincing evidence to promote the design of HB and NV learning spaces in hot and humid climates. Such ventilation strategies can provide comfortable thermal conditions and, potentially, reduce energy use for cooling and associated CO 2 emissions significantly. Highlights • Hybrid (HB) and naturally ventilated (NV) spaces outperform air-conditioned (AC) spaces in various aspects. • Occupants in HB and NV spaces experience higher neutral and comfortable operative temperatures. They can tolerate a wider range of acceptable temperatures, and they are are less sensitive to changes in temperature. • Neutral temperature is significantly and negatively correlated with latitude. • The PMV/PPD model underestimates the ratio of occupants predicted to be comfortable. • The adaptive thermal comfort model is a better predictor than the PMV/PPD model. [ABSTRACT FROM AUTHOR]

Abstract The potential of mixed-mode office buildings with varying design and control parameters is examined by using an uncertainty analysis in the three climate zones of India. The analysis is in terms of cooling energy consumption, thermal comfort conditions, and natural ventilation hours. Furthermore, influential parameters are identified using sensitivity analysis. In this study, opening the windows enables natural ventilation. Night-time ventilation through the windows is not enabled because these are mostly closed at night. A maximum natural ventilation of 10% of the total building occupancy hours are observed in warm and humid, and hot and dry climates; however, they are slightly higher in the composite climate. A further increase in the number of natural ventilation hours leads to an increase in the occupancy hours outside the Indian Model for Adaptive Comfort model for mixed-mode buildings with at least 90% of occupants are satisfied. There are no occupancy hours outside of 80% of occupants are satisfied. The choice of thermal comfort band is crucial for determining the potential of mixed-mode buildings. The cooling setpoint temperature, building size, window solar heat gain coefficient, and surface properties of exterior surfaces are identified as the more influential parameters than the thermophysical properties of building envelope constructions. Although the building envelope which is in compliance with the Energy Efficient Building Code of India increases energy efficiency during air-conditioning periods, whether it reduces natural ventilation hours, because of overheating during such period remains to be determined. Highlights • The potential of diurnal mixed-mode office buildings in India is found to be low. • Increase in the natural ventilation hours increases thermal discomfort. • Efficient air-conditioned buildings are not inevitably efficient mixed-mode buildings. • Few design strategies contradict between air-conditioned and mixed-mode buildings. [ABSTRACT FROM AUTHOR]

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Highlights • One-dimensional analysis is used for UTLTs smoke control design. • Diverse driving forces are combined for smoke control of UTLTs. • Jet fans, axial fans and natural smoke exhaust are well cooperated. • One-dimensional analysis results agree well with CFD simulations. Abstract Urban traffic link tunnels (UTLTs) could become increasingly more complex because they incorporate both looped main tunnels and multiple branch tunnels. In such a complex tunnel structure, smoke control in the event of fire becomes more difficult than that in conventional simple tunnels due to the enhanced flow interactions among various branches. Moreover, there are still no specific smoke control guidelines for such complex tunnels. Furthermore, the use of a single smoke control method could be inapplicable or even unaffordable in UTLTs because the complicity of the configuration and the interaction between the flow of different branches. In this paper, hybrid ventilation modes which combine diverse flow driving forces are proposed for smoke control in UTLTs. The hybrid modes could exploit the advantages of each of the constitutive modes. Three-dimensional numerical simulations are performed to show the benefits of combining diverse driving forces. Then, a one-dimensional flow modelling approach was employed to investigate the efficiency of three hybrid modes. The results demonstrate that proper matching of various driving forces is crucial for effective application of the hybrid modes. This paper provides a new route for UTLT smoke control and also demonstrates the advantages of one-dimensional flow modelling in such designs. [ABSTRACT FROM AUTHOR]

Humidity-sensitive, demand-controlled ventilation systems have been in use for many years in regions with oceanic climates. Some attempts have been made to apply this technology in Poland, which has a continental climate. This article evaluates the performance and energy consumption of such a system when applied in an eight-floor, multiunit, residential building, i.e., the virtual reference building described by the National Energy Conservation Agency (NAPE), Poland. Simulations using the computer program CONTAM were performed for the whole heating season based upon the climate in Warsaw. Besides passive stack ventilation, that served as a reference, two ventilation systems were studied: one standard and one “hybrid” system with additional roof fans. This study confirmed that the application of humidity-sensitive, demand-controlled ventilation in multiunit residential buildings in a continental climate (Dfb) led to significant energy savings (up to 11.64 kWh/m2 of primary energy). However, the operation of the system on higher floors was found to be ineffective. Ensuring consistent operation of the system on all floors required supplementary fans. The introduction of a hybrid mode reduced carbon dioxide concentrations by approximately 32% in the units located in the upper part of the building. The energetic effect in such cases depends strongly on the electricity source. In the case of the national energy grid, savings of primary energy would be relatively low, i.e., 1.07 kWh/m2, but in the case of locally produced renewable energy, the energy savings would be equal to 5.18 kWh/m2.

Maintaining both indoor air quality (IAQ) and thermal comfort in buildings along with optimized energy consumption is a challenging problem. This investigation presents a novel design for hybrid ventilation system enabled by predictive control and soft-sensors to achieve both IAQ and thermal comfort by combining predictive control with demand controlled ventilation (DCV). First, we show that the problem of maintaining IAQ, thermal comfort and optimal energy is a multi-objective optimization problem with competing objectives, and a predictive control approach is required to smartly control the system. This leads to many implementation challenges which are addressed by designing a hybrid ventilation scheme supported by predictive control and soft-sensors. The main idea of the hybrid ventilation system is to achieve thermal comfort by varying the ON/OFF times of the air conditioners to maintain the temperature within user-defined bands using a predictive control and IAQ is maintained using Healthbox 3.0, a DCV device. Furthermore, this study also designs soft-sensors by combining the Internet of Things (IoT)-based sensors with deep-learning tools. The hardware realization of the control and IoT prototype is also discussed. The proposed novel hybrid ventilation system and the soft-sensors are demonstrated in a real research laboratory, i.e., Center for Research in Automatic Control Engineering (C-RACE) located at Kalasalingam University, India. Our results show the perceived benefits of hybrid ventilation, predictive control, and soft-sensors.

This paper deals with a large single space building for smoke control when a fire happens. Two hybrid ventilations are investigated, i.e. natural ventilation through a roof opening combined with mechanical suction flow, and with mechanical jet flow. Pure natural ventilation is used as a benchmark. An experimental model was reproduced as 1/10 of the prototype. Under pure natural ventilation, the roof opening played an important role in exhausting but the smoke layer height descended rapidly. Influences of mechanical flows from sidewalls on the smoke distributions were found to be evident. Large eddy full-scale simulations were performed in which grid size of the fire-domain was determined to be 0.125 m being one half of the non-fire domain. The simulation results agreed well with the experimental ones. A total of 63 ventilation cases are further simulated, and it reveals that mass flow rates of the roof opening increase with the increase of opening area ratio or discharge velocity of inlets or heat release rate but with the decrease of exhaust velocity of outlets; under hybrid ventilation of mode 4, back-flow occurs under the roof opening when the exhaust velocity reaches up to 6 m/s, and the maximum smoke temperature and the CO concentration near the door is of the lowest indicating its best advantage in controlling the fire smoke; the smoke plume is more easily disrupted by jet flow than by suction flow. This study helps to promote the design and operation of ventilation system for large and high spaces when firing. [ABSTRACT FROM AUTHOR]

A “hybrid ventilation system that uses both natural and mechanical ventilation has drawn attention with its low operation cost and constant ventilation rate”. This study is to advance the use of hybrid ventilation concepts in building design by assessment of opening air supply with an operation of ceiling fan-assisted ventilation system. Airflow characteristics of ceiling fan and its effect on the thermal comfort was investigated numerically. Thermal comfort criteria namely; predicted mean vote has been used to predict the thermal comfort zone inside the room. After validation of the model, effect of supply air velocity and blade pitch on the flow and thermal field is investigated. The response surface methodology based on 5 factorial central composite design (CCD) was employed to investigate the optimum parameters of thermal comfort. The response factor PMV was set to be in slightly cool zone to slightly warm zone (−0.5–0.5). A mathematical model of the relationship between the environmental and operational factors considered was then derived from the data. One of the predicted optimal values for the warm-humid climate zones (maximum temperature of 36 °C and humidity of 80%) were as follows: blade pitch = 5.75°, fan speed = 99 rpm, inlet air temperature = 36 °C and inlet air humidity = 73.3%, which led to keep PMV within recommended comfort range (slightly cool) defined by ISO and ASHRAE. [ABSTRACT FROM AUTHOR]

Hybrid ventilation can be employed to precool thermally massive buildings, reducing energy consumption for cooling the following day, particularly at night when the outdoor temperature is lower, and especially when its operation is done in a predictive manner by incorporating weather forecasts. An important requirement is defining the temperature low limit for admitting exterior cool air into a building through transition spaces, to ensure thermal comfort. This paper uses a case study of a 17-story high institutional building with a hybrid ventilation system. To develop a strategy for the admission of outside air into the building, this study focuses on the corridors as generic transition zones/buffer spaces with flexible thermal comfort limits and with the motorized façade openings to determine how the air temperature evolves with distance from the inlets. A developed thermal model, calibrated from a full-scale test, calculates the amount of heat removed from the 0.4 m thick concrete floor. Through 4 h of night cooling with an average local exterior temperature of 8.3 °C, the air temperature rises to about 12 °C in the transition corridor region at a time when occupancy in that area is expected to be nearly zero. Taking into consideration the flexibility in thermal comfort in the corridor transition spaces, control strategies are developed, based on exterior temperature and humidity. Using humidity ratio instead of relative humidity as criterion for admitting outdoor air potentially results in the system being active for 49% - 180% more hours during the year. [ABSTRACT FROM AUTHOR]

Coupling natural ventilation with mechanical ventilation, hybrid ventilated buildings have the potential to minimize the energy bills for owners without compromising the thermal comfort of building occupants. The thermal performance of this type of building is much more robust compared to naturally ventilated buildings due to the supplementary cooling provided by the mechanical system when the outdoor environment is not favorable. With benefits of both energy saving and health improvement, the hybrid ventilation is promising to make buildings more sustainable and occupants healthier. The first step to popularize this type of building is to clearly realize its benefits across different climates. To fully map out the potential of utilizing hybrid ventilation, in our study, we applied general uncertainties and different intelligence levels of building control to an illustrative small to medium commercial building to investigate potential benefits of hybrid ventilation across different climate zones in US with respect to energy saving. The research is composed of two phases – the first phase for a preliminary investigation and the second phase for a thorough investigation. The results show that the hybrid ventilation could help save 10%–50% of energy across different climates. In US, Climate 3B Coast – Los Angeles and Climate 3C – San Francisco are the most suitable climate zones for the hybrid ventilation based on our investigation while the other zones share similar potentials (window opening hour percentage). Lastly, improving the hybrid ventilation operation intelligence turns out to be significant in enhancing the performance of hybrid ventilation buildings. Large discrepancy of energy saving (up to 15%) is observed when the hybrid ventilation building is controlled using different building intelligence. [ABSTRACT FROM AUTHOR]

In the last years, multi-objective optimization techniques became into one of the main challenges of the building energy efficiency area. The objective of this paper is to develop and validate a computational code for multi-objective building performance optimization by linking an evolutionary algorithm and a building simulation software in a powerful cluster. A sophisticated version of the multi-objective Non-dominated Sorting Genetic Algorithm-II (NSGA-II) was implemented in Python code to determine the optimal building design, which allows working with categorical and discrete variables, and the objectives were evaluated using the building energy simulation software EnergyPlus. NSGA-II was implemented to run in a high-performance cluster for the parallel computing of the fitness of each population (set of possible designs). In this work, the strengths of the proposed method were demonstrated by its application to the optimal design of a typical single-family house, located in the Argentine Littoral region. This house has some rooms conditioned only by natural ventilation, and other rooms with natural ventilation supplemented by mechanical air-conditioning (hybrid ventilation). The most influential design variables like roof types, external and internal wall types, solar orientation, solar absorptance, size, type, and windows shading of this house among others were studied in two complex cases of 10 8 and 10 16 possibilities to obtain the best trade-off (Pareto front) between heating and cooling performance. Finally, a decision-making method was applied to select one configuration of the Pareto front. Optimal simulation results for the study cases indicated that is possible to improve up to 95% the thermal comfort in naturally ventilated rooms and up to 82% energy performance in air-conditioned rooms of the building with respect to the original configuration by using a design that takes simultaneous advantage of passive strategies like thermal inertia and natural ventilation. The methodology was proved to give a robust and powerful tool to design efficient dwellings reducing the optimization time from almost 12 days to 4.4 h. [ABSTRACT FROM AUTHOR]

The aim of this study is to develop a method to assess window area based on electricity consumption in office buildings in southern Brazil. The method may be used in the preliminary building design process in order to help choose an adequate window area to minimize its impact on energy consumption, depending on climate, building size, solar orientation, and mode of operation. The method also considered thermal comfort and daylighting performance. Four cases were investigated: Case 1, building operating with artificial lighting and air-conditioning; Case 2, considering integration of daylight and artificial light with air-conditioning; Case 3, building operating with hybrid ventilation and artificial lighting; and Case 4, considering integration of daylight and artificial light with hybrid ventilation. EnergyPlus and Daysim simulation programs were used to estimate the electricity consumption for each model. The integration of daylighting with artificial light (Case 2) generates more potential for energy savings (PES) than hybrid ventilation (Case 3). Case 4 showed PES ranging from 4.2% to 64.9%, allowing larger window areas with lower consumption, resulting in the highest PES. [ABSTRACT FROM AUTHOR]

Reducing the energy demand for residential cooling systems is crucial in order to limit CO 2 emissions, consistently with the EU climate change policy. Within this context, solar DEC (Desiccant, Evaporative Cooling) technologies can represent a valid answer to the energy saving targets. This experimental analysis aims to present the last results of a scientific campaign on a solar DEC prototype, named NAC-wall (Natural Air Conditioning), operating with a hybrid ventilation mode. Heat and mass transfer happens in an innovative dehumidification component, a finned coil coated with a layer of Zeolite SAPO-34, presenting very low pressure drops. Different tests have been performed in the flow regime Reynolds 750–3500 to analyze dehumidification effectiveness. For a better comparison between each test, a preliminary complete regeneration of the adsorbent mean have been always carried out with hot water circulation, produced by a solar thermal system. A theoretical optimized working cycle, i.e. one regeneration stage followed by one adsorption stage, has been studied starting from the experimental results and its performance has been compared with the optimized natural ventilation operating case, reported in a previous work. [ABSTRACT FROM AUTHOR]