Hybrid Ventilation Strategies Research Articles

Indoor PM2.5 and building energy consumption in nine typical residential neighborhoods in Nanjing under different ventilation strategies caused by traffic-related PM2.5 dispersion

Traffic-related PM2.5 seriously endangers human health and affects the energy consumption of building ventilation systems. This study investigates the impact of different ventilation strategies caused by traffic-related PM2.5 dispersion on indoor PM2.5 concentration and building energy consumption of nine typical residential neighborhoods in Nanjing using EnergyPlus software. Results of a third-floor apartment in a six-story slab-type parallel layout residential neighborhood (6F-Sp) show that strategy 1 (window opening, OW) and strategy 7 (natural and mechanical ventilation, NV&MV-TC) can maintain indoor PM2.5 concentration below 25 μg/m3. The NV&MV-TC strategy is chosen to simulate indoor PM2.5 concentrations and cooling/heating energy consumption in nine neighborhoods. The building cooling energy consumption range is 21.2–41.5 kW•h/m2, while the heating energy consumption is 14.9–74.7 kW•h/m2. In the cooling season, the hybrid ventilation strategy shows the lowest cooling energy consumption, followed by window closure with operating indoor air purifiers. Apartments employing window closure with mechanical ventilation have the highest cooling energy consumption. In the heating season, the most energy-efficient strategy is window closure with operating indoor air purifiers, followed by the hybrid ventilation strategy. The indoor PM2.5 concentration negatively correlates with the frontal area index (λf). This study provides valuable information for residential ventilation strategies and guides residents' behaviors in cooling/heating seasons.

Removal efficiency of restroom ventilation revisited for short-term evaluation

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.

Deep clustering of Lagrangian trajectory for multi-task learning to energy saving in intelligent buildings using cooperative multi-agent

The intelligent buildings provided various incentives to get highly inefficient energy-saving caused by the non-stationary building environments. In the presence of such dynamic excitation with higher levels of nonlinearity and coupling effect of temperature and humidity, the HVAC system transitions from underdamped to overdamped indoor conditions. This led to the promotion of highly inefficient energy use and fluctuating indoor thermal comfort. To address these concerns, this study develops a novel framework based on deep clustering of lagrangian trajectories for multi-task learning (DCLTML) and adding a pre-cooling coil in the air handling unit (AHU) to alleviate a coupling issue. The proposed DCLTML exhibits great overall control and is suitable for multi-objective optimisation based on cooperative multi-agent systems (CMAS). The framework of DCLTML is used greedy iterative training to get an optimal set of weights and tabulated as a layer for each clustering structure. Such layers can deal with the challenges of large space and its massive data. Then the layer weights of each cluster are tuned by the Quasi-Newton (QN) algorithm to make the action sequence of CMAS optimal. Such a policy of CMAS effectively manipulates the inputs of the AHU, where the agents of the AHU activate the natural ventilation and set chillers into an idle state when the outdoor temperature crosses the recommended value. So, it is reasonable to assess the impact potential of thermal mass and hybrid ventilation strategy in reducing cooling energy; accordingly, the assigning results of the proposed DCLTML show that its main cooling coil saves >40% compared to the conventional benchmarks. Besides significant energy savings and improving environmental comfort, the DCLTML exhibits superior high-speed response and robustness performance and eliminates fatigue and wear due to shuttering valves. The results show that the DCLTML algorithm is a promising new approach for controlling HVAC systems. It is more robust to environmental variations than traditional controllers, and it can learn to control the HVAC system in a way that minimises energy consumption. The DCLTML algorithm is still under development, but it can potentially revolutionise how HVAC systems are controlled.

Optimal Hybrid Ventilation Strategy to Assure Adequate Indoor Thermal Comfort and Air Quality in Educational Spaces under a Tropical Climate

Air quality, specifically in indoor environments, has become a growing concern. In general, people tend to spend most of their lives indoors due to the growing urbanization. Indoor air quality is associated with ventilation rates, academic performance, and occupant’s health due to the presence of indoor pollutants. Exposure to these contaminants is a risk factor for people to develop the sick building syndrome. The objective of this study was to determine an optimal hybrid ventilation strategy in a tropical climate, favoring natural ventilation with different proposed strategies, varying the opening of doors and windows, the opening time, and the occupancy, among other aspects and strategies using dynamic simulation. The results were compared with in-situ measurements and surveys conducted on students in the case study. Of the proposed strategies, it was decided as optimal hybrid strategy to increase the fresh air intake from 5 L/s*person to 10 L/s*person with the use of mechanical ventilation and reduction of occupancy, this way, in addition to improving indoor air quality, the thermal comfort of the students was ensured.

The efficiency of hybrid ventilation on cooling energy savings in NZEBs

Proper design of the ventilation system is strategic to achieve nearly zero energy building (NZEB) target while providing high IAQ standards. This paper investigates a multi-family complex of eight dwellings NZEB in Italy built on a former industrial shed. The planned HVAC system foresees the combined use of primary ventilation with fan-coil units fed by ground source heat pumps. Three hybrid ventilation strategies are compared to evaluate the potential cooling energy saving: the first one explores the use of an earth-to-air heat exchanger (EAHX), the second one proposes night hybrid ventilation from 10 p.m. to 6 a.m., and the last one analyzes the implementation of free cooling mode in mechanical ventilation. Cooling energy saving, thermal comfort, CO2 reduction and cost-effectiveness of three approaches comparing with the base case were evaluated. EAHX generatesa cooling energy saving of 20.7%. Combined use of night ventilation with mechanical ventilation system reduces the cooling energy demand by 14.4%, while free cooling produces a less effective decrease in the electricity consumption of 7.7% only. Moreover, the influence of climatic conditions on hybrid ventilation strategies efficiency is assessed in three cities. This analysis shows that EAHX is the hybrid ventilation strategy which produces the greatest energy saving in all Italian climatic zones showing an energy saving from 33.7% in Milan to 9.8% in Palermo. Free cooling and night ventilation generate more benefits in the middle-season when lower minimum outdoor temperatures occur.

Impact of Hybrid Ventilation Strategies in Energy Savings of Buildings: In Regard to Mixed-Humid Climate Regions

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.

ОБОСНОВАНИЕ ГРАНИЦ РЕЖИМОВ РАБОТЫ СИСТЕМ ГИБРИДНОЙ ВЕНТИЛЯЦИИ

The paper presents the results of a theoretical study of existing terms of hybrid ventilation. A classification of hybrid ventilation strategies has been drawn up: concurrent and changeover operations. Concurrent operation includes the sharing of mechanical and natural ventilation systems, for example, in the case of natural inlet and the removal of contaminated air from the room by axial roof fans; mechanical systems, equipped with low-pressure fans, used in conjunction with technologies aimed at increasing natural pressure (heat and wind inducement). Changeover operation includes seasonal work, night cooling and local alternating work. The analysis of climatic characteristics based on data from meteorological station 27612 (Moscow, VDNH) shows that the average temperature of outdoor air exceeds the requirement temperature for natural ventilation calculations for most of the year. Annual average air exchange factors for the period 2016-2020 are less than 50 %, which proves the need for a seasonal hybrid ventilation system. Based on the calculation of average monthly air exchange factors, the mechanical inducement is recommended from March to November.

Evaluation of mixed mode ventilation cooling energy saving potential in nZEB: A case study in Southern Italy

In recent decades, reducing the energy demand of the building sector has become a major goal of global policies. Proper design of the building-plant system is hence strategic to achieve nearly zero energy building (NZEB) target. This paper reports the results of modeling the building-plant system of an NZEB in Southern Italy. The case study is a multi-family complex of eight dwellings located in Bari, in the Apulia region. The building project originates from the energy refurbishment of a former industrial shed that was demolished and rebuilt for residential use. The planned HVAC system foresees the combined use of primary ventilation with fan-coil units fed by two ground source heat pumps (GSHP) supplied by eight vertical probes. Three hybrid ventilation strategies have been compared to evaluate the potential cooling energy saving: the first one examines an earth-to-air heat exchanger (EAHX), the second one proposes night hybrid ventilation from 10 pm to 6 am, and the last considers the adoption of free cooling in mechanical ventilation. Economic and energy comparisons among these three approaches are reported. Using EAHX, the cooling consumption saving reached about 20.7% The use of night ventilation combined with MVS can reduce the cooling energy demand for 14.4%, while free cooling in MVS produces a less effective decrease in the electricity consumption for cooling of about 7.7%. All three strategies generate major benefits in the middle-season.

Influence of environmental variables on thermal comfort and air quality perception in office buildings in the humid subtropical climate zone of Brazil

This study evaluates the influence of environmental variables on users’ thermal comfort and air quality perception in the humid subtropical climate of Florianópolis, southern Brazil. A building with central air-conditioning system and three mixed-mode buildings, which alternated between natural ventilation and air-conditioning modes, were investigated. Statistical analyses were performed considering environmental data collected in situ between 2014 and 2016 – using microclimate stations, a portable thermo-anemometer and a CO2 analyser – and users’ subjective responses obtained by means of an electronic questionnaire. Results showed a direct influence of air temperature and humidity ratio and indirect influence of air movement on thermal comfort. In addition, thermal, air movement and humidity sensation, preference and acceptability affected thermal comfort and air quality perception, highlighting the importance of carrying out a complete assessment of users’ perception of the thermal environment. This work supports the use of the ASHRAE 55 adaptive thermal comfort model for mixed-mode buildings under natural ventilation operation. Based on the results obtained in this study, the use of hybrid ventilation strategy is recommended for energy savings due to reducing the use of air-conditioning and improving indoor air quality as there is a decrease in air pollutants level.

Optimizing Hybrid Ventilation Control Strategies Toward Zero-Cooling Energy Building

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 predicated percentage of dissatisfied (PPD) for assessing the indoor comfort and CO2 level for assessing the indoor air quality). 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 the 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 space heating demand. Moreover, it ensures higher thermal comfort and indoor air quality levels compared to the first and second proposals.

Stressing the passive behavior of a Passivhaus: An evidence-based scenario analysis for a Mediterranean case study

This paper first reports the outcomes of a one-year measurement campaign of a passive house built in the Mediterranean climate of Cesena (Italy) in terms of thermal comfort parameters temperature and relative humidity and Indoor Environmental Quality (IEQ) parameter CO2 concentrations. The design carried out with the help of the steady state Passive House Planning Package (PHPP) was able to guarantee good comfort conditions during the heating period, but on the other hand, overheating occurrences during the cooling season have been recorded for almost 50% time according to EN 15251 Standard. Further analyses conducted with the help of dynamic simulations in EnergyPlus allowed identifying the insulation levels and ventilation mode as the key design factors to change in order to reduce overheating to less than 20% of time while keeping a comfortable indoor environment in winter.The simplifications that can be made by reducing the insulation material thickness (up to a third of the original value) on the roof and on the walls, replacing triple-glazed windows with double-glazed windows and implementing a hybrid ventilation strategy instead of using Mechanical Ventilation with Heat Recovery (MVHR) alone could also lead to economic savings. These savings, due to both lower construction costs and operational energy savings, amount to 8755 euros in terms of Net Present Value (NPV) over 30 years' time.The Passivhaus Standard can still be regarded as a good reference for designing low-energy and comfortable houses in a Mediterranean climate if some simplifications are made according to detailed building performance simulations.

Responsive Student Dormitory Design with Hybrid Ventilation Strategy in Education Region of Malang City

Responsive Student Dormitory Design with Hybrid Ventilation Strategy in Education Region of Malang City - written by Guruh Pratama Zulkarnaen , Sri Nastiti Nugrahani Ekasiwi , Ima Defiana published on 2018/01/18 download full article with reference data and citations

A multi-stage optimization of passively designed high-rise residential buildings in multiple building operation scenarios

This article proposes a two-stage design optimization approach which is applied to a prototype passively designed high-rise residential building under different ventilation modes and thermal load requirements. Machine learning methods are employed to develop surrogate models for improving the computation efficiency of the multi-objective optimization process. The surrogate model is trained by modeling experiments with EnergyPlus and R, which can provide reliable energy performance indicators of generic building models featuring passive design parameters including the building layout, envelope thermophysics, building geometry and infiltration & air-tightness. The lighting, cooling and heating demands of the generic building model are determined by the hybrid ventilation and light diming control strategies in compliance with local green building assessment criteria in Hong Kong. The multiple linear regression (MLR), multivariate adaptive regression splines (MARS), and support vector machines (SVM) are examined by the statistical modelling. SVM is capable of fitting a surrogate model with the best prediction performance based on the coefficient of determination and root mean square error. In addition, both single-sided ventilation and cross-ventilation models under varied thermal load requirements are investigated to compare the preferable design solutions for each scenario. The multi-stage optimization approach is also applied to a Mediterranean climate to explore optimal design solutions in more diverse external environmental conditions. This research can provide a highly efficient design optimization tool to appropriately deploy passive architectural strategies in a green building project.

Performance validation of a hybrid ventilation strategy comprising longitudinal and point ventilation by a fire experiment using a model-scale tunnel

We examined the exhaust performance of a hybrid ventilation strategy for maintaining a safe evacuation environment for tunnel users in a tunnel fire. The hybrid ventilation strategy combines the longitudinal ventilation strategy with the point ventilation strategy which is a type of transverse ventilation strategy. The model tunnel developed by this study was scaled to 1/5 the size of a full-scale tunnel. The model-scale experiment was performed taking into consideration Froude's law of similarity. Measurement items were the distribution of temperature and concentration of smoke inside the tunnel, longitudinal wind velocity, mass flow of smoke in the point ventilation duct, and the heat release rate of the fire source. The following main conclusions were obtained. The smoke height was constant even when varying the extraction rate of smoke from the ceiling vent. The backlayering length and critical velocity of the smoke flow in the hybrid strategy could be predicted by the methodology developed by using the longitudinal strategy. The hybrid strategy maintained a safe evacuation environment on both sides of the tunnel fire.

Performance of hospital spaces in summer: A case study of a ‘Nucleus’-type hospital in the UK Midlands

Nucleus-type Hospital in Glenfield comprises connected cruciform blocks with numerous small courtyards between. The hospital has mechanical ventilation and perimeter heating. The wards have a hybrid ventilation strategy with a low rate of mechanical ventilation. Ventilation through windows is the main source of summer time cooling. This paper investigates the summer time performance of spaces that are mechanically ventilated but passively cooled. The paper presents the measured indoor temperatures in selected hospital spaces and compares them with thermal comfort criteria. Finally, future summer conditions for the ward space are predicted using a calibrated multi zone dynamic thermal model.During June to September 2010, the maximum indoor temperatures in the case study spaces varied between 27.3°C and 29.3°C. The nurse station was found to be the hottest area. During this period the performance of most of the monitored spaces was reasonably within the thermal comfort threshold as defined by HTM03-01. The simulation results demonstrate that light-touch low carbon interventions could produce comfortable conditions in bedrooms into the 2050s in UK Midlands.

Potencial de economia de energia elétrica em edificações comerciais híbridas localizadas em Florianópolis, SC

A ventilação natural baseada em aberturas nas fachadas tem sua aplicabilidade limitada pelas características do clima, local e tipo de edificação, mas pode ser potencializada por meio da ventilação híbrida (ventilação natural e mecânica). O objetivo deste artigo é estimar o potencial de economia de energia elétrica com a utilização da ventilação híbrida em edifícios comerciais localizados em Florianópolis, SC. Como modelos de ambiente foram utilizadas salas com diferentes geometrias e tamanhos, em quatro orientações e com dez dimensões de janela por ambiente. Cada modelo foi estudado por dois casos: um caso-base em que se operou somente com sistema de ar condicionado; e um caso em que se aplicou a ventilação híbrida. As simulações termoenergéticas foram realizadas no programa EnergyPlus, utilizando-se do arquivo climático de Florianópolis TRY. A partir dos resultados das simulações obteve-se o consumo anual de eletricidade de cada ambiente. Os consumos do caso-base foram comparados com os do caso com ventilação híbrida. Desse modo, calcularam-se as porcentagens de economia de energia geradas pelo uso da ventilação híbrida. Além disso, foi realizada uma análise de alternativas de comportamento do usuário com relação aos padrões de uso da ventilação híbrida. A estratégia híbrida de ventilação apresentou uma significativa economia de energia, chegando-se a uma redução de consumo total de energia de até 31,9%. Porém, em que pese este potencial de economia de energia, é provável que os usuários possam se sentir insatisfeitos em determinados dias quentes, nos quais o sistema de ar condicionado é desligado em algum momento.

Optimizing hybrid ventilation in public spaces of complex buildings – A case study of the Wisconsin Institutes for Discovery

Complex buildings such as hospitals and laboratories require intensive ventilation and cooling loads in order to meet operational demands. One way to reduce energy use while meeting these demanding requirements in complex buildings is the incorporation of hybrid ventilation in areas that do not require high and continuous loads such as public spaces. This research establishes an experimental approach to test and analyze various hybrid ventilation strategies in an occupied, complex building utilizing hybrid ventilation in public spaces. To optimize the use of hybrid ventilation, this research focuses on tracking three performance criteria: energy savings, occupant comfort and indoor-air quality. The framework establishes a variety of hybrid ventilation strategies to test, and outlines how to analyze results graphically and through linear regression modeling. This experimental approach is illustrated through a case study example of a laboratory building located in Madison–Wisconsin. The selection of the ideal hybrid ventilation strategy for the public space studied resulted in 56 percent average savings in ventilation and cooling load when HV is in use, and established a potential to use hybrid ventilation for 28 percent of the 111 day cooling season (20 percent savings in mechanical cooling over the summer).

Comparison of natural and hybrid ventilation strategies used in classrooms in terms of indoor environmental quality, comfort and energy savings

Numerous studies have shown that ventilation in classrooms is often insufficient or inadequate, leading to health risks, discomfort and a decrease in student learning performances. The aim of this study was to compare the performances of four ventilation modes used in identical and adjacent classrooms at the University of La Rochelle in terms of indoor environmental quality, overall comfort perception by the occupants and energy consumption. The different ventilation strategies included the use of balanced mechanical ventilation and natural ventilation by manual or automated window opening. Parameters related to air quality as well as thermal, visual and acoustic comfort were measured, and questionnaires were filled out by the occupants during the courses. The monitoring approach was conducted during summer and winter 2010 in order to classify the tested strategies during both seasons with reference to the requirements of standards and French regulations. The results showed that the automated window opening system controlled by air temperature and lighting level was really efficient in summer. In winter, none of the ventilation modes was clearly more adaptable for classrooms than the other. Thus, a good use of natural ventilation, controlled by well chosen parameters can provide a satisfactory solution for the academic environment.

Thermal comfort standards, measured internal temperatures and thermal resilience to climate change of free-running buildings: A case-study of hospital wards

In view of the warming climate, there is increasing concern about the likelihood of overheating inside UK buildings that are not mechanically cooled. A number of studies are examining this matter, of which the DeDeRHECC project is one. The recent availability of the UKCP09 future climate data projections has acted as a stimulus to such work. This paper illustrates how field measurement, thermal modelling and the generation of current and future typical and extreme weather years, can be used to provide a picture of the resilience of buildings to climate change. The unified framework for assessing both measurements and current and future predictions that is offered by the BSEN15251 thermal comfort standard is a crucial component. The paper focuses on internal temperatures during the day and at night in wards within the tower building at Addenbrooke’s hospital, which has a hybrid ventilation strategy. The maintenance of thermal comfort in such spaces is critically important and installing air-conditioning in response to climate change is expensive and potentially energy intensive. Fans appear to be a simple retrofit measure that may substantially improve the wards’ resilience to climate change even in extreme years. Whilst healthcare provides the back cloth, the methodology developed has a much wider utility for assessing thermal comfort in buildings in the current and future climate of the UK.

Hybrid Ventilation for Multi-Zone Buildings - Development of Optimal Control Strategies through Experiments and Dynamic Modelling

Hybrid ventilation represents an interesting option both to guarantee good air quality for indoor environments and to reduce the energy consumption related to the mechanical motivation of the air.In order to join these objectives it is crucial to adopt an efficient ventilation management system. With this purpose, this paper focuses on the optimisation of control strategies for a multi-zone building equipped with a specific hybrid ventilation system, in which mechanical ventilation is provided by a forced flow system while natural ventilation is managed by properly motorized windows.An experimental platform was built in a real building. Also, a previously validated numerical model for the dynamic simulation of the environment was employed to compare three ventilation strategies in terms of the efficiency in removing carbon dioxide. The first strategy consisted of simple natural ventilation, while the remainder were hybrid strategies based on ON/OFF logic and on fuzzy logic respectively. Since the hybrid ventilation technique was found to be more efficient in maintaining good IAQ, the last step consisted in developing and testing an optimised multi-criteria hybrid ventilation strategy aimed at guaranteeing good IAQ with the minimum period of mechanical ventilation. The optimised strategy showed improved control of the CO2 concentration and a further reduction by 5% of the mechanical ventilation load.