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Indoor air quality and energy efficiency are instrumental aspects of school facility design and construction, as they directly affect the physical well-being, comfort, and academic output of both pupils and staff. The challenge of balancing the need for adequate ventilation to enhance indoor air quality with the goal of reducing energy consumption has long been a topic of debate. The implementation of mixed-mode ventilation systems with automated controls presents a promising solution to address this issue. However, a comprehensive literature review on this subject is still missing. To address this gap, this review examines the potential application of mixed-mode ventilation systems as a solution to attaining improved energy savings without compromising indoor air quality and thermal comfort in educational environments. Mixed-mode ventilation systems, which combine natural ventilation and mechanical ventilation, provide the versatility to alternate between or merge both methods based on real-time indoor and outdoor environmental conditions. By analyzing empirical studies, case studies, and theoretical models, this review investigates the efficacy of mixed-mode ventilation systems in minimizing energy use and enhancing indoor air quality. Essential elements such as operable windows, sensors, and sophisticated control technologies are evaluated to illustrate how mixed-mode ventilation systems dynamically optimize ventilation to sustain comfortable and healthy indoor climates. This paper further addresses the challenges linked to the design and implementation of mixed-mode ventilation systems, including complexities in control and the necessity for climate-adaptive strategies. The findings suggest that mixed-mode ventilation systems can considerably lower heating, ventilation, and air conditioning energy usage, with energy savings ranging from 20% to 60% across various climate zones, while also enhancing indoor air quality with advanced control systems and data-driven control strategies. In conclusion, mixed-mode ventilation systems offer a promising approach for school buildings to achieve energy efficiency and effective ventilation without sacrificing indoor environment quality. [ABSTRACT FROM AUTHOR]

This study evaluates thermal sensitivity, expectations, and adaptability in mixed-mode ventilated buildings by subjective and objective assessments. A field study of simultaneous measurements of physical environmental parameters and right-here-right-now surveys was conducted in three office buildings from summer to winter in humid subtropical climates. The study confirmed previous findings that thermal adaptability and preferences changes as the ventilation system switches between natural ventilation (NV) and air-conditioning (AC). Occupants in this study showed more sensitivity to temperature changes than previously reported by ASHRAE Standards, yet thermal sensitivity was the same under different modes of operation. The neutral temperature was 0.5 oC higher than the predicted neutral temperature by ASHRAE 55 under both modes of operation. Thermal expectations were 1.5 oC warmer than the neutral temperature estimated by ASHRAE 55 when the building was operated by AC, while thermal expectations were almost the same as predicted by ASHRAE 55 under NV mode. Thermal comfort range was 0.75 oC wider than those predicted by ASHRAE 55 under NV operation, and the same as ASHRAE 55 under AC operation. The findings of this research provide a better understanding of mixed-mode building operations and perspectives from occupants, important for building designers and building operation managers. [ABSTRACT FROM AUTHOR]

Energy efficiency and air quality in residential buildings have aroused intensive interest. Generally speaking, the heating, ventilation and air conditioning (HVAC) system is widely used to regulate indoor environmental spaces. Meanwhile, mixed-mode ventilation has been proven to reduce energy consumption and introduce fresh air effectively. This study aims to discuss the correlations between air velocity, temperature and indoor thermal comfort and establish corresponding statistical models based on the ASHRAE_db II database and the Predicted Mean Vote (PMV). On this basis, the air-velocity adjustment strategy, including determining adjustability and establishing adjustable intervals, is optimized based on support vector machine and envelope curve methods. The results show that the recognition accuracy of the adjustability determination model is over 98%, and the air-velocity adjustable interval in the envelope is increased, facilitating control of mixed-mode ventilation. The case shows that interval adjustment increases the sample points by 18.6% (18.1% above 20 °C and 4.5% above 28 °C). Therefore, further research can be supported on improving thermal comfort by air-velocity adjustment to take advantage of the mixed-mode ventilation mode, which is beneficial to building energy efficiency. [ABSTRACT FROM AUTHOR]

Buildings are responsible for one‐third of the UK's greenhouse gas (GHG) emissions. The move to reduce emissions has resulted in recent stringent building regulations primarily aimed at reducing heating and associated energy use, often by improving the building fabric's airtightness. However, internal gains dominated, highly–insulated and airtight non‐domestic buildings will likely overheat in the projected warming climate, requiring energy‐intensive cooling, thus diminishing the effectiveness of heating efficiency focused regulations. This research investigated the effects of the warming climate on overheating and energy use and resulting emissions in representative urban office spaces in London in the present‐day and projected future climates using hourly dynamic thermal simulations. Findings suggest that airtight and highly–insulated office buildings in the temperate UK will overheat in the 2050s. Heating demand reduces by at least 36% in the 2050s but electricity consumption and summertime space conditioning will increase by at least 13% and 55% respectively when hybrid cooling is adopted to ameliorate overheating. Despite the increase, a mixed‐mode ventilation strategy is one of the ways of achieving overall energy efficiency while meeting benchmark overheating and emissions targets. Current heating‐focused legislation needs to be re‐evaluated to account for the effects of the warming climate and overheating risks. [ABSTRACT FROM AUTHOR]

Abstract Buildings are responsible for one‐third of the UK's greenhouse gas (GHG) emissions. The move to reduce emissions has resulted in recent stringent building regulations primarily aimed at reducing heating and associated energy use, often by improving the building fabric's airtightness. However, internal gains dominated, highly–insulated and airtight non‐domestic buildings will likely overheat in the projected warming climate, requiring energy‐intensive cooling, thus diminishing the effectiveness of heating efficiency focused regulations. This research investigated the effects of the warming climate on overheating and energy use and resulting emissions in representative urban office spaces in London in the present‐day and projected future climates using hourly dynamic thermal simulations. Findings suggest that airtight and highly–insulated office buildings in the temperate UK will overheat in the 2050s. Heating demand reduces by at least 36% in the 2050s but electricity consumption and summertime space conditioning will increase by at least 13% and 55% respectively when hybrid cooling is adopted to ameliorate overheating. Despite the increase, a mixed‐mode ventilation strategy is one of the ways of achieving overall energy efficiency while meeting benchmark overheating and emissions targets. Current heating‐focused legislation needs to be re‐evaluated to account for the effects of the warming climate and overheating risks.

• Assessment of the energy performance of mixed-mode ventilation in office buildings. • Evaluation of energy performance in archetypes according to climate change impacts. • Natural ventilation reduces energy consumption in office buildings over time. • Adaptive strategies needed in office buildings to mitigate climate change impacts. • Belo Horizonte is more vulnerable city to an increased in energy consumption. With the projected increase in temperature, coupled with the rise in intensity and frequency of heatwaves caused by climate change, it has become essential to investigate the impact of climate change on building energy consumption and thermal comfort. This study focuses on office buildings with mixed-mode ventilation in Brazil as a case study. Using a typical 15-story office building archetype for various Brazilian cities, considering current and predicted scenarios (2050 and 2080), the potential for energy savings through natural ventilation was assessed. It was observed that the average increase in temperature and wind speed in the predicted climate varied in each city and showed significant variations over the years. Predicted projections under high-emission scenarios (SSP5-8.5-2080) reveal significant increases in energy consumption, highlighting the vulnerability of cities like Belo Horizonte, which could face a 77% increase in total energy consumption. Additionally, the analysis of HVAC hours of use over time indicates a progressive increase, suggesting a potential reduction in natural ventilation as a mitigation strategy. Mitigation measures, especially in the SSP1-2.6 scenario, are crucial to stabilize HVAC consumption and preserve the use of natural ventilation, emphasizing the importance of sustainable approaches to address the energy challenges arising from climate change. [ABSTRACT FROM AUTHOR]

In the U.S., approximately 47% of the total electricity use comes from residential buildings. Most of the residential buildings use HVAC system to ventilate, cool, or heat the indoor environmental spaces mechanically, rather than using natural outdoor air in transition seasons, even though the outdoor environmental conditions are favorable for indoor thermal comfort. In this case, an HVAC system using mixed-mode ventilation with an appropriate ratio of using indoor air and outdoor air could decrease the energy use in residential buildings. This research uses high-granular HVAC electricity use data with indoor thermostat data and outdoor weather data from residential buildings in Austin, Texas, to evaluate the benefits of energy and economics when using HVAC mixed-mode ventilation in spring and fall transition seasons. The results demonstrate that the household owners could save approximately 150.79 kWh of total HVAC energy use and 24.41% of HVAC cost in spring transition months (April/May), and similarly, 143.86 kWh of energy use and 27.2% cost savings in fall transition months (October/November). The results could support further study to use automatically operated windows for natural ventilation to reduce energy use in residential buildings toward sustainable development. [ABSTRACT FROM AUTHOR]

Mixed-mode ventilation is a design feature to improve building energy efficiency and indoor air quality. However, in practice, it does not always achieve better performance, largely due to inappropriate window operations. The research effort is also limited when exploring approaches to regulate manually operable windows. The present study found that the unregulated window operations could increase the heating load up to 21% and cooling load by 22% relative to identical buildings with fixed windows in a cold climate. To regulate the manually operable windows, we investigated the effectiveness of employing HVAC terminal devices' by improving the control sequences. The control sequences could apply setbacks on thermostat setpoints to nudge occupants to undertake window opening and closing actions. The control sequences were tested by the building performance simulation (BPS), and 3-16% of energy reductions could be achieved when control sequences encouraged occupants to undertake energy-efficient window use behaviours. [ABSTRACT FROM AUTHOR]

Effective mitigation of greenhouse gas (GHG) emissions in the buildings sector requires a full understanding of the factors influencing emissions over the life-cycle of buildings, particularly in places where large additions to the building stock are expected. Currently, little is known about what affects the GHG emissions of buildings located in warmer climates, a typical situation for many emerging economies. This paper presents a study of emissions from Brazilian office buildings using building archetypes. A sensitivity analysis explores possible parameter ranges, various contributions to life-cycle impacts and their key drivers. For each of the 1000 building variations in the sample, the emissions were calculated using a life-cycle assessment. Multivariate regression analysis enabled the study of the results’ sensitivity to 10 parameters, influencing building operation, design and others. The emissions ranged from 20 to 106 kg CO2-eq/m2 gross floor area and year. Electricity mix, climate and cooling efficiency were the most impactful parameters, but building component service time was also significant. 'Policy relevance' Emerging economies are expected to rapidly increase their building stock and energy use, particularly for cooling in the coming decades. The findings show the key factors influencing the GHG emissions of office buildings in warm climates, typical for many emerging economies, such as Brazil. For effective mitigation, priority should be placed on reducing the carbon intensity of electricity and encouraging highly efficient heating, ventilation and air-conditioning systems. Policymakers may want to offer incentives for office buildings with a combination of natural ventilation and mechanical cooling, because they were less emission-intensive in every investigated city. The benefits are the biggest for buildings in which a high proportion of windows can be opened for natural ventilation.

Effective mitigation of greenhouse gas (GHG) emissions in the buildings sector requires a full understanding of the factors influencing emissions over the life-cycle of buildings, particularly in places where large additions to the building stock are expected. Currently, little is known about what affects the GHG emissions of buildings located in warmer climates, a typical situation for many emerging economies. This paper presents a study of emissions from Brazilian office buildings using building archetypes. A sensitivity analysis explores possible parameter ranges, various contributions to life-cycle impacts and their key drivers. For each of the 1000 building variations in the sample, the emissions were calculated using a life-cycle assessment. Multivariate regression analysis enabled the study of the results' sensitivity to 10 parameters, influencing building operation, design and others. The emissions ranged from 20 to 106 kg CO2-eq/m² gross floor area and year. Electricity mix, climate and cooling efficiency were the most impactful parameters, but building component service time was also significant. [ABSTRACT FROM AUTHOR]

Modern buildings are operationally classified as fully naturally ventilated (free running, FR), fully mechanically ventilated and conditioned (air-conditioned, AC) or intermediary (mixed mode, MM). Each strategy implies (i) the selection of different internal comfort models and controls, e.g. adaptive thermal comfort + operable windows in FR and static thermal comfort (Predicted Mean Vote - PMV) + non-operable windows in AC, and (ii) different energy consumption and carbon emissions with FR being the least (zero) and AC being the most. In each instance, the choice of strategy is dictated by the designer with little choice for the occupants. Here we ask the question: what operational mode would occupants select, given complete freedom? We examine this question using real concurrent data from three offices of similar size and use. In each, occupants have complete freedom in adopting FR, AC or a series of intervening MM strategies. We use monitored data on window and air-conditioning operation combined with internal and external thermal conditions to create validated computer models for each office. We discover the true operational mode of each office by comparing the computer model against 23 different scenarios using Dynamic Time Warping for binary (window open/close, AC on/off) and Euclidean distance for continuous operative temperature time series. Strikingly, results demonstrate that while each office used divergent strategies across the seasons, the indoor conditions were very similar and attainable through NV alone. This suggests that while a purely NV strategy is likely to deliver indoor thermal comfort, understanding occupant motivation and educating them on the impact of AC operation is needed to minimise energy use. • We evaluate the energy performance of mixed-mode office buildings. • We investigate what operational mode occupants would select in a mixed-mode office. • We evaluate multiple behavioural patterns for the AC an NV systems. • We show that occupant priority could change how buildings are being designed. [ABSTRACT FROM AUTHOR]

However, the availability in the 1950s of large-scale mechanical cooling, along with other technologies such as curtain walls and fluorescent lighting, led to the more common building forms we see today in North America—typically all-glass, flush-skin buildings with large floor plates and no operable windows.Our technological capabilities allow architects greater design freedom while they can relinquish responsibility for environmental control to the engineers, who use their ingenuity to design mechanical systems that will ensure (ideally) thermal comfort regardless of the loads that are imposed. In air-conditioned buildings, thermal conditions generally are perceived to be predictable and controllable, with the goal of maintaining consistent indoor thermal conditions uniformly across space and throughout the day, regardless of the outdoor climate.

Studies have demonstrated the energy savings potential of mixed-mode ventilated office buildings. Yet, it is important to widen the knowledge about how those buildings have been designed and built in practice, and which design parameters have greater influence on its energy performance. The aim of this paper was to evaluate how building envelope design parameters influence the energy performance of cellular mixed-mode office buildings, in order to identify key design variables. The analysis presents a comparison among literature research studies and typical construction practices from a sample of buildings located in the city of Sao Paulo, Brazil. According to a base case model, established based on the real buildings sample, three sensitivity analysis techniques were performed to obtain relative parameter sensitivity to thermal loads: OFAT, Morris and Monte Carlo. Results showed the importance of the window opening effective area and the reduced impact of the window-to-wall ratio on the energy performance of mixed-mode office buildings. By applying a multivariate regression model, it showed significant in predicting 78.1% of the variance in annual thermal loads. The accurate determination of annual thermal loads into mixed-mode office buildings can be used to optimize the envelope characteristics based on a combination of input data and the building geometry. Findings from this study could also be applied to other locations, provided that similar climatic environment and urban context are taken into account. • We evaluate the energy performance of mixed-mode office buildings. • A base case and its characteristics were defined based on a sample. • Typical construction practices versus theoretical studies were compared. • Three sensitivity analysis methods were applied and compared. • Multivariate regression model predicted 78% of the variance in annual thermal loads. [ABSTRACT FROM AUTHOR]

• A pilot study in three mixed-mode change-over buildings in subtropical climate was performed. • A new definition for mixed-mode classification was proposed particularly relevant to thermal comfort studies. • Occupant thermal expectation and satisfactions was different across the three change-over mixed-mode buildings with different control strategies. • Mixed-mode change-over control strategy seemed to be an important influencing factor in thermal comfort sensations. Change-over mixed-mode buildings prevent the concurrent use of air-conditioners and operable windows, thus are energy-efficient. Based on automation levels for mixed-mode control, change-over mixed-mode buildings can be classified into three types: automated, semi-manual, and manual. The objective of this research was to conduct a pilot study on the effects of different change-over mixed-mode control strategies on building occupants' thermal perception and comfort, as well as develop adaptive comfort models for mixed-mode buildings with different change-over control strategies in subtropical climates. Occupants from three types of mixed-mode control buildings were surveyed about their real-time thermal perception, while indoor environmental conditions were recorded simultaneously for a period from summer to winter. Although an overlooked factor in previous studies, this pilot study suggests that change-over control strategy may significantly affect thermal perceptions in mixed-mode buildings. Occupants who had limited control over thermal environments showed less sensitivity to outdoor conditions regardless of operation modes. In buildings where, users had a full control, a clear distinction in thermal sensation was observed when the system switched between air conditioning and natural ventilation modes. The adaptive thermal comfort model seems to be more suitable and applicable for semi-manually and manually controlled mixed-mode buildings rather than for automatically controlled mixed-mode buildings. [ABSTRACT FROM AUTHOR]

Abstract Designing, optimizing and testing ventilation systems and their control strategies calls for dedicated simulation tools. Because building occupants are important influence factors for thermal comfort and indoor air quality (IAQ) and active actors by opening doors and windows, these tools must allow both an adequate modelling of air flows and of occupant behaviour. While the state of the art in software applications offers sufficient possibilities to model everyday ventilation systems, several authors indicate a need for dedicated simulation tools that enable modelling of complex mixed-mode (MMV) systems. These systems are characterised by their ability to switch between natural and (partly) mechanical operating modes according to demand and opportunity. In addition, deterministic occupant models that are often used in IAQ simulations offer room for improvement. VCVTB (Ventilation Controls Virtual Test Bed) is a new opensource EnergyPlus based test bed for single- and mixed-mode ventilation simulations, which provides a streamlined workflow for accelerated modelling, optimizing and testing of ventilation strategies and their control systems using an airflow network approach. It includes an integrated semi-probabilistic occupant model for IAQ simulation and facilitates a quick and effective comparison between systems by means of standard report sheets, comparative tables and 3D airflow output. To showcase some of the possibilities of VCVTB and to demonstrate the potential of MMV, VCVTB is used to implement a generic MMV system in a case study building. The performance of this setup is compared to several reference systems. First and foremost, the case study demonstrates the potential of VCVTB in designing and comparing ventilation strategies and their controller, facilitating further application-oriented research. Second, it shows that MMV can be a promising residential ventilation solution in regions with mild winters and cool summer. In these regions MMV can exploit the freely available natural ventilation potential to balance IAQ and adaptive user comfort with energy efficiency. Highlights • VCVTB enables accelerated modelling and testing of advanced ventilation strategies and their control systems. • VCVTB facilitates application-oriented ventilation research and allows large-scale comparative studies. • VCVTB avoids co-simulation by offering an integrated platform. • VCVTB includes a unique semi-probabilistic model to take into account occupant behaviour in IAQ studies. • Mixed-mode ventilation can be an energy friendly alternative to mechanical ventilation, but a robust control system is key. [ABSTRACT FROM AUTHOR]

Mixed-mode ventilation offers a promising solution for achieving comfortable indoor environments in an energy-efficient manner. However, in the tropics, characterized by a year-round hot and humid climate, opportunities for natural ventilation (NV) are typically limited to specific hours, necessitating operational mode switches on an intraday basis. Much of the thermal comfort research on mixed-mode ventilation relies either on cross-sectional data collected from different subjects or longitudinal data spanning a few seasons. This raises an open question: Can occupants thermally adapt when switching between NV and air-conditioning (AC) modes within a single day? To address the gap, our experimental study engaged 57 tropically acclimatized subjects, exposing them to combinations of five operational modes and four ceiling fan speeds (0.15-1.15 m/s) over an eight-hour timeframe. The results revealed that the subjects preferred a Standard Effective Temperature (SET*) that was 2-3 °C higher when operating in the NV mode compared to the AC modes, indicating thermal adaptation within the same day and in the same space. Specifically, the adaptation process was observed to stabilize between 35 to 45 mins following a mode switch. These findings contribute to the optimization of thermal comfort in mixed-mode controls, considering the dynamic characteristics of thermal adaptation. • Thermal comfort experiment in tropical mixed-mode ventilation with ceiling fans. • Same-day and same-space thermal adaptation was observed when switching modes. • Thermal perceptions took 35 to 45 mins to adapt and stabilize after a mode switch. • NV in the tropics achieved 90% acceptability at a ceiling fan speed of 1.15 m/s. • Significant divergence between thermal preference and acceptability was identified. [Display omitted] [ABSTRACT FROM AUTHOR]

Studies have revealed important roles quality indoor environment plays on human health and productivity; consequently, its influence on certain shopping behavior has also been well spelt out. In other to keep up with the demand for quality indoor environment, new trend has been evolving in the design of Malaysian shopping malls. From fully air-conditioned to newly designed ones that integrate passive ventilation strategies; and as such operating under mixed-mode ventilation system. These passive ventilation strategies are implemented to reduce energy consumption and also to improve the indoor environment within the mall’s indoor space. However, the potentials of these designs in terms of their indoor environmental quality (IEQ) performance have not been studied nor have their advantages been revealed. In this study, occupants’ thermal perception and IEQ performance was investigated in two mixed-mode ventilated malls selected based on their design concept (‘open’ and ‘enclosed’). Both subjective and objective measurements were carried out in accordance with the ASHRAE performance measurement protocol for commercial buildings. Five IEQ factors (indoor air temperature, operative temperature, relative humidity, air speed, and carbon dioxide concentration level) were evaluated in the two malls. The results revealed that both malls fell below the ASHRAE comfort requirement but majority of the occupants still found the indoor thermal performance acceptable despite the high indoor air temperature recorded. For both malls, high air speed and low humidity level were recorded. However, higher air movement was still preferred by the occupants while the recorded mean carbon dioxide (CO2) concentration was within the recommended level. The ‘open’ concept mixed-mode ventilated mall proved superior compared to the ‘enclosed’ concept by providing a more thermally tolerance indoor environment for its occupants. Generally, results from this study contribute to the knowledge on the advantages of adopting sustainable designs in commercial buildings for improving the indoor environment as well as the health and general well-being of the occupants. The study will open more opportunities for future IEQ studies to be carried out in hot-humid climatic regions.

• Evaluating the energy performance of mixed-mode ventilation in office buildings. • A methodology for deriving archetypes based on empirical and literature data. • Assessing energy performance in archetypes and comparing to local benchmarks. • Favoring natural ventilation in mild temperate climates can reduce energy consumption in office buildings. The growing concern regarding environmental issues and energy efficiency has led to an increased interest in natural ventilation as a cost-effective alternative to reduce energy consumption in buildings. In a mild temperate climate, promoting natural ventilation using operable windows can significantly improve indoor thermal comfort in office buildings for a significant part of the year. However, archetypes for office buildings that include operable windows and use mixed-mode ventilation in this climate are not common in the literature. Typically, these buildings feature individual offices where the installation of an air conditioning system is a decision made by the owner or tenant, as window or split systems used in such spaces are not pre-installed. Thus, there is a gap in investigating how these buildings are designed, used, and operated. Therefore, this study aims to develop archetypes for office buildings with mixed-mode ventilation and compare their estimated energy consumption with a local energy benchmark developed for a mild temperate climate. The archetypes were defined based on three different floor plans: rectangular, triangular, and square-shaped. The archetypes were simulated, and their electric energy consumption ranged from 53.4 to 60.2 kWh/m2.year. These values were higher than the average consumption of the local benchmarking. The difference is believed to be due to the overestimation of the use hours of building systems, as air conditioning usage was predicted based on temperatures for window opening and closure. Nonetheless, these archetypes can be applied in other locations with mild temperate climates to analyze their potential in reducing energy consumption, as they consume significantly less energy than fully conditioned buildings. [ABSTRACT FROM AUTHOR]

The aim of this work is to assess the use of mixed-mode ventilation for a typical office building in Lebanon and consequently reduce Heating Ventilation and Air Conditioning (HVAC) energy consumption in the observed current and under the future projected climatic conditions. Mixed-mode cooling is considered a compromise between the insufficient natural ventilation and the expensive year round-operated HVAC. A control algorithm is set for windows and HVAC system to ensure mixed-mode operation. Dynamic simulations are performed on a typical office building in Beirut City under the mixed-mode operation in the present and the future using commercial IES-VE software. The results of the software were validated against measured HVAC and total energy consumption of the typical office base case with conventional mechanical system. The results of the simulations are evaluated in terms of potential reduction in energy consumption under the present and the future weather data. Finally, a lifecycle cost analysis is performed for the proposed system, and its payback period is computed. Under present construction practices and weather data, 31% annual energy savings were achieved using mixed-mode system. Under future 2050s projected weather data, annual energy savings of 21% was attained with a payback period of 3.8 years. [ABSTRACT FROM AUTHOR]

The paper presents an energy simulation-based study to investigate the impacts of climate change on energy consumptions of an office building located in five different cities, United States. Annual energy consumption of a medium-size office building was predicted by building energy simulation software—EnergyPlus using TMY3 weather data and future climate data. In this study, we have used two sets of further climate data with different climate models including (1) Hadley Centre Coupled Model, version 3 (HadCM3), and (2) NCAR Community Earth System Model version 1 (CESM1) with the Community Atmosphere Model version 5 (CAM5). A morphing method was applied to downscale the monthly weather forecast to hourly forecast for use in building energy simulation for the two General Circulation Models (GCMs): HadCM3 and CESM1. Using the generated future weather files, HVAC operation related mitigation measures including adjustment of thermostat setpoints, reduced HVAC operation hours, reduced VAV box minimum flow setting, and mixed-mode ventilation were simulated to compare with ASHRAE Standard 90.1 baseline simulated using TMY3 weather data. Simulation results on predicted whole building, heating and cooling energy consumptions were examined. The paper highlighted the importance of efficiently operating mechanical systems in buildings to ensure a more sustainable future. [ABSTRACT FROM AUTHOR]

Natural ventilation (NV) that reduces building energy consumption and improves indoor environment has become a key solution to achieving sustainability in the building industry. The potential for utilizing NV strategies depends greatly on the local climate, which varies widely from region to region in the world. In this study, we estimated the NV potentials of 1854 locations around the world by calculating the NV hour. Energy saving potentials of the world's 60 largest cities were calculated with Building Energy Simulation (BES). We demonstrated that NV hour derived from outdoor meteorological data can measure maximum energy saving potential of NV without conducting detailed BES. Our analysis shows the subtropical highland climate, found in South-Central Mexico, Ethiopian Highland, and Southwest China, is most favorable for NV, because spring-like weather occurs all year with little variation in temperature and almost no snowfall. Another climate where NV can be beneficial is the Mediterranean climate, which occurs not only near the Mediterranean Sea, but also in California, Western Australia, Portugal, and Central Chile. In certain regions with desert climate and large diurnal temperature range such as the Middle East and Central Australia, greater-than-expected NV hours are observed due to significant potential of night-purge ventilation. Countries in Southeast Asia, e.g., Singapore and Malaysia, are shown to have little to no NV potential as a result of hot and humid weather all year. These findings provide valuable guidelines for architects and policy makers around the world to effectively utilize NV designs that meet local climatic conditions. [ABSTRACT FROM AUTHOR]

The design of energy conservative buildings that incorporates natural ventilation (NV) strategy has become increasingly popular around the world. Natural ventilation is a key solution for reducing energy consumption of buildings and for maintaining a healthy indoor environment. However, the adoption of natural ventilation in high-rise buildings is less common. As rapid population growth and urbanization take place in cities, it is important to explore the substantial energy saving potential of high rises by utilizing natural ventilation. In this study, we have provided the early effort to estimate quantitatively the vertical profiles of NV potential for high rises at major cities from six climate zones in the U.S. (i.e., Miami, Houston, Los Angeles, New York City, Chicago, and Minneapolis), using an in-house boundary layer meteorology model. The diurnal cycle of atmospheric boundary layer (ABL) and local climate characteristics are found to have a great effect on the vertical structure of NV potential. In general, negative vertical gradients of NV hours are observed for all cities except Miami where the vertical distribution is nearly uniform. For example, the annual NV hour decreases from 7258 at ground level to 4866 at 300 m above the ground in Los Angeles. Our analysis shows that outdoor temperature is a key meteorological parameter that determines vertical profiles of NV hours in New York City, Los Angeles, Chicago, and Minneapolis. In contrast, humidity plays a greater role in cities like Miami and Houston where the outdoor temperature is often favorable for using natural ventilation except in the summer. Among studied cities, Los Angeles provides the ideal climate (warm and dry) for utilizing natural ventilation, displaying the greatest NV potential (7258 NV hours or 83% time of the year at ground level), followed by New York City with 3360 NV hours. The remainder of the four studied cities display comparable numbers of NV hours of approximately 2500 at ground level. The methodology and findings from this study are intended to assist architects and policy makers in quantifying the potential energy savings of natural ventilation, and illustrating the importance of considering the vertical variations of elevated thermal environment in high-rise buildings across different climate zones in the U.S. [ABSTRACT FROM AUTHOR]

This study uses field monitoring and post occupancy evaluation (POE) surveys to investigate the indoor thermal comfort of an office building that is located in subtropical zone. The building is special as it combines advanced natural ventilation (ANV) strategies and underfloor air distribution (UFAD) systems. A comparison between a static thermal comfort model and a dynamic thermal comfort model is also conducted. The results show that the thermal comfort conditions in the case study building are satisfactory in summer while in winter there is evidence of thermal discomfort. For the case study building, the static thermal comfort model gives outputs that matched well with the responses of the occupants during the POE survey in winter while the dynamic model is more representative of the sensation of the occupants in summer, [ABSTRACT FROM AUTHOR]

Thermal comfort studies are necessary in the early stage of building design, especially in tropical climates where buildings are exposed to solar radiation throughout the year. In this study, we aimed to determine the summer comfort temperatures in offices in Malaysia, Indonesia, Singapore, and Japan. Through field surveys during 2015, we collected 2049 responses from 325 occupants in 13 office buildings employing various ventilation modes, namely, free running (FR), mixed mode (MM), and mechanical cooling (CL). The results showed that the comfort range differed for each group of occupants under the different ventilation modes. The comfort operative temperatures in tropical climates are 25.7 °C, 24.9 °C, and 27.5 °C for the CL, FR, and MM ventilation modes respectively, whereas in Japan it is 25.8 °C for both CL and MM. The survey revealed that 97% of the responses in Japan were within the central three points of the TSV scale, but lower percentages were recorded in the other countries. In Singapore, 92.9% of the respondents were feeling either cold, cool, or slightly cool in their offices. In terms of adaptive behaviour, most of the occupants in Malaysia frequently used air-conditioning systems to maintain thermal comfort, while drinking cold beverages was more common in Indonesia and Japan. The high comfort temperature with MM ventilation could be influenced by the strong air movement and a wide range of adaptive options, such as opening windows and utilising air-conditioning systems. [ABSTRACT FROM AUTHOR]

Mixed-mode ventilation can effectively reduce energy consumption in buildings, as well as improve thermal comfort and productivity of occupants. This study predicts thermal and energy performance of mixed-mode ventilation by integrating computational fluid dynamics (CFD) with energy simulation. In the simulation of change-over mixed-mode ventilation, it is critical to determine whether outdoor conditions are suitable for natural ventilation at each time step. This study uses CFD simulations to search for the outdoor temperature thresholds when natural ventilation alone is adequate for thermal comfort. The temperature thresholds for wind-driven natural ventilation are identified by a heat balance model, in which air change rate (ACH) is explicitly computed by CFD considering the influence of the surrounding buildings. In buoyancy-driven natural ventilation, the outdoor temperature thresholds are obtained directly from CFD-based parametric analysis. The integrated approach takes advantage of both the CFD algorithm and energy simulation while maintaining low levels of complexity, enabling building designers to utilize this method for early-stage decisionmaking. This paper first describes the workflow of the proposed integrated approach, followed by two case studies, which are presented using a three-floor office building in an urban context. The results are compared with those using an energy simulation program with built-in multizone modules for natural ventilation. Additionally, adaptive thermal comfort models are applied in these case studies, which shows the possibility of further reducing the electricity used for cooling. [ABSTRACT FROM AUTHOR]

[Display omitted] • Reinforcement learning saves energy by 52% for mixed-mode ventilation buildings. • Explainable AI can prompt new insights in mixed-mode ventilation building control. • Optimizing window opening area and cooling setpoint can increase energy saving. • Reinforcement learning utilizes internal thermal mass to increase cooling efficiency. The application of mixed-mode ventilation (MMV) in the tropics is challenging, given its hot and humid climate. Consequently, there are limited periods when operating in natural ventilation (NV) is desirable. Furthermore, the potential to use NV diminishes at locations characterized by generally light winds. Given the complex interactions in MMV, this study aims to use reinforcement learning (RL) to identify relationships that can further reduce cooling energy use while maintaining occupant thermal comfort. The control variable variables considered include the percentage of window opening area and dynamic cooling setpoint temperature. Results show that RL can achieve a 52% reduction in cooling energy while maintaining good thermal comfort and indoor air quality compared to the existing baselines that typically involve switching between NV and air-conditioning based on outdoor conditions. We then developed an Explainable AI (XAI) framework to prompt building scientists toward new insights into MMV control in the tropics, which consists of shapley additive explanations (SHAP) and decision tree. The SHAP is able to improve the transparency of RL strategy by revealing the impact of each input on the final decision and the decision tree can extract the key control rules from RL. Using the XAI framework, this study also identified that the RL algorithm was taking advantage of the internal thermal mass to increase cooling efficiency. The extracted rules are further applied to the actual testbed, showing the feasibility of the rules extracted by XAI approach. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive SA (sensitivity analysis) of the typical PRH (public rental housing) development in Hong Kong based on a combined building energy, daylight and AFN (airflow network) simulation. A generic building model is constructed with a proposed MM (mixed-mode) ventilation control strategy to fulfill the thermal comfort requirement in the local green building guidance. The numerical modeling results are used to conduct both local and global sensitivity analyses to determine the relative importance of major passive design parameters, which comprehensively cover design aspects of the building layout, envelop thermophysics, building geometry and infiltration & air-tightness. The calculated global and local sensitivity indices on the cooling energy prove that the window solar heat gain coefficient, window to ground ratio, external obstruction and overhang projection fraction are the four most influential passive design factors. Similar results are also obtained when the lighting energy is specified as the output of the sensitivity analysis. The optimized building model derived from the sensitivity analysis is anticipated to achieve an energy saving of 41.6% compared to the baseline model as stipulated by the local building regulation. It is believed that sensitivity analysis is useful for identifying crucial design parameters to facilitate further optimization of the building performance in early architectural design stages. [ABSTRACT FROM AUTHOR]

The quest for building sustainability and reduction in building energy consumption has called for alternative means to cooling in buildings. Natural ventilation has been considered in this regard. However, due to its limitations, buildings are now shifting towards mixed-mode ventilation, which is a combination of the best features in natural and mechanical ventilation also offering huge advantages for reducing energy consumption. This shift will be a gratifying advantage in retail buildings since retail buildings account for the largest energy consumption in the commercial sector in Malaysia. Unfortunately, in Malaysia, mixed-mode ventilation has not been largely employed in retail buildings, particularly shopping malls. Furthermore, little information is available on malls with mixed-mode ventilation. Therefore, this study aims to explore and classify different application modes of mixedmode ventilation strategy adopted in Malaysia's existing malls. Relevant literature was reviewed and site visitations and observations were conducted. Out of 105 malls identified in Selangor, Kuala Lumpur and Putrajaya, only six included passive strategies in their ventilation approach. These malls were identified as operating under mixed-mode ventilation and were further grouped under different categories of mixed-mode ventilation strategy. This taxonomy study provides the basis for classifying mixed-mode ventilation in retail buildings and will potentially create awareness among designers and building owners on the growing effort of improving and encouraging energy efficiency in the commercial building sector. [ABSTRACT FROM AUTHOR]

To clarify the controversy about whether the adaptive comfort model is applicable in buildings with mechanical cooling systems operating in natural ventilation (NV) mode, we designed a longitudinal study in a mixed-mode (MM) building where mechanical air conditioning and natural passive cooling coexist in the same case building. Through statistical analysis of occupants' thermal responses during air conditioning (AC) and NV periods, considerable differences in occupants' perceived comfort were observed. The results show that occupants' actual thermal sensation and acceptance of thermal conditions both varied when the building changed from AC to NV mode, or vice versa. Compared to the steady-state comfort model (i.e., PMV), the adaptive model was found to be more applicable to MM buildings, especially when NV was being utilized. These findings provide support for a more flexible applicability of the adaptive comfort model in the real world, and can serve as a valuable reference for the design and operation of MM buildings. [ABSTRACT FROM AUTHOR]

The way buildings are operated highly influences energy consumption, and occupants play a significant role in it. However, challenges related to the prediction of occupants' behavior decrease the potential to accurately predict a building's energy consumption. Such inaccuracy presents one reason for the gap between measured and simulated energy data. In an effort to bridge this gap, this work aims at creating statistical models to predict occupant behavior, in relation to window and air conditioning operation in mixed-mode office buildings in a humid subtropical climate. The statistical behavioral models developed were based on data collected in an 18-month monitoring campaign conducted in São Carlos, Brazil. Two types of statistical methods were applied: generalized linear mixed and Markov chain models. Model results showed high probabilities of status change in both controls upon arrival and departure. Indoor temperature approximately at 24 °C and outdoor temperature around 23 °C show the lowest probability of either control being activated. In addition, the behavioral patterns presented by the models show an alternating use of the controls, indicating a conscious use of the available equipment. • Stochastic models to predict occupant behavior in mixed-mode office buildings. • Prediction of air-conditioning and window operation entirely controlled by users. • Analysis of occupant behavior data in a humid subtropical climate for all seasons. • Novel observations about activation time and alternating use of AC and windows. • Innovative contributions on occupant behavior in mixed-mode office buildings. [ABSTRACT FROM AUTHOR]

Indian residences are vulnerable to heat-driven discomfort amid the mounting prevalence of weather extremes, residential design and construction practices, and densifying urbanscapes. Therefore, it is vital to understand the thermal comfort characteristics of nationwide residences. This study proposes an adaptive thermal comfort model based on yearlong field surveys in eight cities located across five climate zones of India – the India Model for Adaptive Comfort - Residential (IMAC-R). The model prescribes the operative temperature bands for 80% and 90% thermal acceptability in correlation with the outdoor reference temperature, applicable to mixed-mode (MM) and naturally ventilated (NV) residences. More than 80% of the Indian residential occupants experienced a neutral thermal sensation in the indoor operative range of 16.3–35 °C in response to a 5.5–33 °C variation in the 30-day outdoor running mean temperature. Comparing the proposed model with the PMV model revealed that the latter underpredicts the thermal adaptivity of Indian occupants. The model was also compared against its predecessor – India Model for Adaptive Comfort for Commercial Buildings (IMAC MM and NV), along with relevant global and regional thermal comfort models. On average, the neutral temperature prescribed by IMAC-R was warmer than the temperatures prescribed by IMAC MM and NV by 2.9 °C and 2.1 °C, respectively; it was also warmer than the temperature prescribed by the recent ASHRAE-55 and EN 16798-1 models by 2 °C and 0.3 °C, respectively. IMAC-R reserves the prospect of addressing the thermal comfort needs of the national population while paving the way for long-term energy savings and climate action. • An adaptive model is proposed for mixed-mode and naturally ventilated residences across the Indian climates. • Indian residential occupants are more adaptive than as predicted by ASHRAE-55, EN 15251, and PMV models. • Fan/window operation and change in clothing insulation were the key adaptive responses. • Comfort modelling is explored in correlation with Universal Thermal Climate Index. [ABSTRACT FROM AUTHOR]

The aim of this paper is to identify which method to assess thermal comfort is the most appropriate to be used in hybrid commercial buildings located in hot and humid summer climate. Three methods to assess thermal comfort were analysed: (1) ASHRAE 55 for determining acceptable thermal conditions in occupied spaces, (2) ASHRAE 55 for determining acceptable thermal conditions in naturally ventilated spaces and (3) Givoni's chart for hot and humid climates. Models with two geometries, two room sizes per geometry, two solar orientations and three window areas per model were analysed. Simulations were performed using the EnergyPlus programme, with the TRY climate file of Florianópolis. Thermal comfort was evaluated applying the simulations output data into the three methods. Thus, the amount of time (number of hours per year) in which the use of air-conditioning is necessary to bring thermal comfort for the users throughout the year was determined using each method. Such number of hours of use of air-conditioning was also compared with the pattern of use of air-conditioning observed in Florianópolis. The main conclusion is that the most suitable method for use in hot and humid summer climates is the method proposed by Givoni. [ABSTRACT FROM AUTHOR]

Highlights: [•] We simulated mixed-mode ventilation for various office buildings using EnergyPlus. [•] Increasing thermal mass will increase energy savings by mixed-mode ventilation. [•] We developed an accurate semi-empirical model to predict the impact of thermal mass. [•] We conducted a cost-return analysis to find optimal amount of thermal mass. [ABSTRACT FROM AUTHOR]

Highlights: [•] Mixed-mode or hybrid cooling of office buildings has great energy saving potential. [•] Application in a range of arid sub-climates has been simulated. [•] Operating air conditioning in a mixed mode strategy has significant energy benefits. [•] Up to 90% plant energy savings were shown using low energy cooling technologies. [•] Evaporative, radiant and ground-cooling technologies were particularly effective. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigates how mixed-mode (MM) ventilation affects occupant comfort by presenting results from a longitudinal field study within an academic office building from a tertiary educational institution in sub-tropical Sydney, Australia. The building automatically switches into air-conditioned (AC) mode whenever indoor temperatures exceed 25 °C. Coincident indoor and outdoor climate measurements along with 1359 subjective comfort questionnaires were collected. Thermal sensations during natural ventilation did not conform to those predicted using Fanger’s PMV-PPD . Differences in thermal perception were also apparent between these two modes. Within AC mode, a PMV = +1 environment elicited much ‘warmer-than-neutral’ thermal sensations than the same PMV = +1 environment within naturally-ventilated (NV) mode, suggesting thermal subjective perceptions were affected by the building’s mode of operation over and above the objective indoor climatic conditions. These discrepancies emphasize the complexity of thermal perception and the inadequacy of using PMV models to describe occupant comfort in MM buildings. ASHRAE’s Standard 55 currently classifies MM buildings as AC buildings, and as such, limits the operation of these buildings to the more restrictive PMV-PPD range of indoor thermal conditions. In contrast, EN15251 permits the more flexible adaptive comfort standard to be applied to buildings operating under NV mode. Results from this study favour EN15251’s application of the adaptive comfort model instead of PMV-PPD to MM buildings when they are operating in NV mode. [Copyright &y& Elsevier]

The thermal environment in offices affects the productivity of workers; thus, it is important to adjust the thermal environment appropriately with heating, ventilation, and air conditioning. However, there is an urgent need to reduce the amount of energy used in the building sector for cooling, which has been rising. Mixed-mode ventilation has attracted attention as a means of decreasing air conditioning power consumption and improving the satisfaction of office workers. In the present study, a measurement survey and a questionnaire survey were conducted during springtime to investigate air conditioning power consumption during mixed-mode ventilation and to elucidate the relationship between the use of mixed-mode ventilation and productivity. The power consumption on the mixed-mode ventilation floors was less than that on the mechanical ventilation floors in the measurement period when the average outdoor air temperature was 21 °C, with savings ranging from 3.1% to 70.6%, although it varied widely with the weather conditions. The relationship between the use of mixed-mode ventilation and productivity was analyzed using multilevel analysis (hierarchical linear model), a method that considers the data hierarchy. Mixed-mode ventilation improved the productivity of male participants by about 9.1%, suggesting that mixed-mode ventilation could both decrease air conditioning power consumption and improve productivity during springtime. However, the increase in productivity of female participants was about 0.5%, indicating that there may be differences depending on gender. The present study has practical implications for promoting mixed-mode ventilation as a means to reduce air conditioning power consumption in offices and improve productivity. • Mixed-mode ventilation in springtime was studied by measurements and questionnaire. • The effects of mixed-mode ventilation were analyzed by multilevel analysis. • Mixed-mode ventilation reduced air conditioner power consumption by 3.1%–70.6%. • Mixed-mode ventilation improved productivity by about 9.1% in male participants. • The effects of mixed-mode ventilation on productivity may differ by gender. [ABSTRACT FROM AUTHOR]