Acceptable Thermal Environment Research Articles

The impact of IEQ in the university lecture theatres on students’ concentration levels in London

PurposeUniversity students’ lecture theatre concentration levels are significantly related to indoor environmental quality (IEQ). The purpose of this study is to investigate the relationship between indoor environmental quality (IEQ) and the self-reported concentration levels of university students during the winter at University College London (UCL), UK.Design/methodology/approachA questionnaire survey and physical measurements were used to assess the IEQ factors affecting students’ concentration levels.FindingsThe lecture theatre design factor was the most significant factor influencing students’ concentration levels, and the facility environment was more important than the thermal environment, indoor air quality, and acoustic environment in influencing students’ concentration levels in this winter investigation at UCL, UK. Additionally, students prefer a colder thermal environment. The concentration level of students was positively correlated with the indoor air quality and negatively correlated with the acoustic environment.Practical implicationsBased on model application, this research could provide lecture theatre IEQ design. This research additionally provides an acceptable indoor thermal environment temperature range based on a large sample, which can be used to calibrate a student performance benchmark.Originality/valueAs this study evaluates the IEQ factors that influence the concentration levels of university students, interior designers and engineers should consider the rational layout of these factors. Therefore, this study may provide a reference for the interior environmental design of lecture theatres in educational buildings.

The influence of perceived control on outdoor thermal comfort: A case study in a hot summer and warm winter climate

Perceived control is a psychological state experienced by individuals in their environment and is considered a critical factor in adaptive thermal comfort models. A longitudinal study lasting two and a half years was conducted in Xiamen, China, to investigate the impact of perceived control on outdoor thermal comfort. The study, carried out in an outdoor living laboratory with 56 participants, explored conditions with and without perceived control. Subjective thermal perception and thermal environment parameters were collected. Differences in outdoor thermal comfort across summer, transition seasons, and winter between participants with and without perceived control were established, and conversion formulas for thermal sensation votes were obtained. The study results indicate that: (1) The neutral mPET of participants with perceived control were 26.4 °C, 24.9 °C, and 22.3 °C in summer, transition seasons, and winter respectively, while those without perceived control were 25.2 °C, 24.6 °C, and 22.8 °C respectively. (2) Participants without perceived control tend to prefer different thermal environment (either cooler or warmer). (3) Perceived control expanded the range of acceptable thermal environment for participants in all seasons. (4) Perceived control can reduce outdoor thermal sensitivity and make participants more likely to achieve a comfortable thermal experience, but the effect varies under different thermal conditions. (5) Regardless of perceived control, global radiation and air temperature are the most crucial environmental factors affecting thermal sensation, while the impact of clothing thermal resistance and duration of stay on thermal sensation is enhanced under conditions without perceived control.

Comparative assessment of night ventilation performance in a nearly zero-energy office building during heat waves in Brussels

With increasing urbanization, overheating intensifies, resulting in a greater risk of indoor overheating in commercial buildings, which already have high internal gains. The impact of urban climate on the cooling energy needs of buildings has been extensively researched. However, the building performance during extreme heat events needs further investigation to reduce the energy demand from the grid during critical events and to ensure an acceptable indoor thermal environment. Here, a comparative assessment approach for natural and mechanical night ventilation performance to reduce indoor overheating and energy needs of a nearly zero-energy office building in Brussels, Belgium, was evaluated for the heat wave and non-heat wave periods in urban and rural microclimates, using calibrated thermal-energy simulations. The analysis indicated that active cooling with natural night ventilation was more effective during heat waves than other cooling strategies. In addition, natural night ventilation was also effective in maintaining safer levels of heat index values in the reference office compared to other strategies. Natural night ventilation reduced overheating by 0.39 °C in the urban microclimate and 0.50 °C in the rural microclimate relative to the Baseline. Considering the cooling energy use, natural night ventilation had no significant impact. In contrast, mechanical night ventilation increased energy use by 0.54 kWh/m2 in urban microclimate and 0.40 kWh/m2 in rural microclimate due to prolonged ventilation fan operation in the reference office building. The presented findings in the paper lead to the formulation of design guidelines, recommendations for future practices and identifying needs for further research.

Wind tunnel experiment of wind-induced single-sided ventilation under generic sheltered urban area

Natural ventilation is an important ventilation method due to its potential to improve indoor air quality and provide an acceptable thermal environment without energy consumption. In the urban area, the ventilation performance of the natural ventilation is very sensitive to surrounding building density. This paper presents a wind tunnel experiment to assess the influence of urban density on the ventilation rate of single-sided ventilation. Spacing density, wind direction, and the number of openings were factors that were investigated in this experiment. The ventilation rate is evaluated by a continuous dose method of the tracer gas technique. The wind pressure coefficient at openings of the sealed model without openings was measured by pressure transducers. The streamwise velocity at the street canyon was measured by a split-film probe with a constant temperature anemometer unit. The ventilation rate, wind pressure coefficient fluctuations and velocity of an isolated building are compared to those of a building with two layers of surrounding buildings with the spacing of 0.5H (H is building height), 1H and 1.5H. A higher building density decreases the ventilation performance of windward opening cases and increases the ventilation performance of the leeward opening cases. The simplified ventilation rate prediction methods for wind-induced ventilation are presented.

Thermal Performance Investigation at Different Temperature and Airflow Settings in a Conference Hall of Expo Building

The airflow distribution for a large space, such as a conference hall, is quite challenging to achieve a good and uniform thermal distribution. In the recent study, insufficient quantitative knowledge has been provided, notably for the appropriate supply air temperature and air velocity for the conference hall environment. In this study, a full-scale conference hall was simulated extensively for an expo building in Taiwan. A total of nine experiment numbers were carried out with various supply air temperature and air velocity settings. Through the use of a CFD approach, this study seeks to identify the ideal parameters for a comfortable and acceptable airflow distribution and temperature, with an eye toward potential compromises with an energy-efficient approach. The results demonstrate that the temperature distribution ranges from 18 to 26 °C, indicating an acceptable indoor thermal environment, depending on the parameter settings. The best settings for providing a pleasant indoor thermal environment are with a supply air temperature and air velocity of 15 °C and 1 m/s, which can keep the PMV index between −0.5 and 0.5. Utilizing a greater temperature setting may save energy, but sufficient air velocity must be addressed in order to meet the indoor thermal conditions. Furthermore, a greater air velocity may generate more noise and disrupt the situation in the conference hall, so it must be selected specifically.

Energy consumption, thermal comfort, and indoor air quality in mosques: Impact of Covid-19 measures

Restrictions have been imposed on the number of people, the duration of their stay and air conditioning operation in temples to limit the spread of the SARS-CoV-2 pandemic. This work studied how restrictions affected energy consumption, thermal comfort, and indoor air quality (IAQ) in mosques. Energy consumption data on lighting, heating and cooling before and during the pandemic were analyzed in six mosques of various sizes located in Yalova city, Turkey. The annual energy consumption for lighting was reduced during the pandemic in all mosques due to less usage, while the annual heating and cooling costs were raised in one mosque despite their restricted use. Besides, experiments were conducted to assess the effect of pandemic measures on thermal comfort and IAQ by measuring indoor temperature, relative humidity, air velocity, CO2 and PM concentrations in a typical mosque. Keeping the windows open and limiting occupancy improved the IAQ. This was evidenced by the lower average CO2 concentration during the pandemic (428 ± 40 ppm) than before the pandemic (661 ± 201 ppm). An acceptable thermal environment was achieved under pandemic measures at night during the summer period. Creating excellent conditions can be difficult without air conditioning even with open windows and prayers performed at night.

Exploring the thermal behaviour of building materials: Terracotta, concrete hollow block and hollow brick, under the arid climate, case study of Biskra-Algeria

Over time, the need for acceptable indoor thermal environment is inevitable, this need become more alluded in spaces that staying indoor is remarkably more than others (e.g. residential buildings). Also, saving natural resources through adapting the appropriate materials in buildings’ envelopes is an important up-to-date issue. The purpose of this paper is to explore the thermal behaviour of different houses’ envelopes of several materials (terracotta, hollow concrete block and hollow brick walls). In order to understand their performance, three different cases study in Biskra (South of Algeria) have been analysed through in-situ measurements of: outdoor air temperature, external and internal wall radiant temperature. The results show that the terracotta wall has a good thermal behaviour compared to the other walls in term of providing constant and reduced values between external and internal surfaces. This study can be useful for further investigations of classifying materials according to their thermal behaviour and encouraging the use of local materials in hot-dry regions.

Investigation of thermal comfort on innovative personalized ventilation systems for aircraft cabins: A numerical study with computational fluid dynamics

Airliner passengers are more and demanding in terms of thermal comfort. But it is not yet easy for crew to control the environment control system (ECS) that satisfies the thermal comfort for most travelers due to a number of reasons. It is, therefore, essential to develop the existing design of air circulation system for aircraft cabins. This work proposed six innovative personalized ventilation systems (PVSs) that would maintain thermal comfort to improve the cabin micro-environment. This study first validated a Computational Fluid Dynamics (CFD) program with the experimental data of airflow and air temperature from an environmental chamber. Then the validated CFD program was used to calculate the air velocity, air temperature, relative humidity (RH) and examined the thermal comfort in a section of Boeing 767 aircraft cabin with the six innovative PVSs. By comparing the six PVSs in terms of relative humidity, velocity, temperature, predicted mean vote (PMV), predicted percentage dissatisfaction (PPD) and age of air (AoA), this study found that the proposed systems provided an acceptable thermal environment aircraft cabin. The personal outlets configuration at both sides of the passenger head (PVS-1) was the best; it can improve the RH by 12% without the risk of air drafts, and it also has a standard PMV (0.2) and PPD (<15%) range.

A simulation of the thermal environment of a plastic body of a new type of launch vehicle at the atmospheric phase of the trajectory

PurposeLeading developers and providers in the modern space launch market note a splash in the development of ultralight launch vehicle (LV), driven by the growing demand for small satellites for large constellations in low Earth orbits. One of the promising ways to solve the problem of the quick launch of such satellites is to use a new type of ultralight launch vehicle with a plastic body. The project of such a launch vehicle was proposed by Oles Honchar Dnipro National University (Ukraine). Along with that, there is a need for appropriate research studies on the thermal resistance of the plastic shell, as the physical, mechanical and thermophysical characteristics of polymers significantly differ from traditional aerospace materials. The purpose of this study is to validate the design and ballistic parameters of such a launch vehicle in terms of providing an acceptable thermal environment at the atmospheric phase of the trajectory.Design/methodology/approachThe workability of a new type of propulsion system is being investigated experimentally in bench conditions. To study the process of aerodynamic heating of a plastic shell, numerical modeling based on the integration of the flight dynamics and heat transfer equations is used.FindingsBrief information about the design of a new type of ultra-light autophage launch vehicle with a plastic body is presented. A mathematical model for the movement of the launch vehicle at the atmospheric phase of the trajectory, and for the heating of the polyethylene body of the launch vehicle, taking into account the dynamic change in the atmospheric parameters is proposed. The influence of the motion trajectory on the thermal environment of the rocket body is investigated, rational motion trajectories and corresponding permissible g-loads are determined.Originality/valueThe fundamental possibility of using plastic (polyethylene) as a structural material and fuel for bodies of a new type of ultralight launch vehicles has been substantiated. It is shown that to ensure acceptable thermal conditions of a plastic body, it is necessary to use thermal insulation. It is proposed to use a polymeric Teflon coating as such thermal insulation. The results are important for the development of technologies for launching small satellites into orbit, as the use of plastic as the main structural material of the rocket body will significantly reduce the launch cost.

Performance Evaluation of Particulate Matter and Indoor Microclimate Monitors in University Classrooms under COVID-19 Restrictions.

Optical monitors have proven their versatility into the studies of air quality in the workplace and indoor environments. The current study aimed to perform a screening of the indoor environment regarding the presence of various fractions of particulate matter (PM) and the specific thermal microclimate in a classroom occupied with students in March 2019 (before COVID-19 pandemic) and in March 2021 (during pandemic) at Valahia University Campus, Targoviste, Romania. The objectives were to assess the potential exposure of students and academic personnel to PM and to observe the performances of various sensors and monitors (particle counter, PM monitors, and indoor microclimate sensors). PM1 ranged between 29 and 41 μg m−3 and PM10 ranged between 30 and 42 μg m−3. It was observed that the particles belonged mostly to fine and submicrometric fractions in acceptable thermal environments according to the PPD and PMV indices. The particle counter recorded preponderantly 0.3, 0.5, and 1.0 micron categories. The average acute dose rate was estimated as 6.58 × 10−4 mg/kg-day (CV = 14.3%) for the 20–40 years range. Wearing masks may influence the indoor microclimate and PM levels but additional experiments should be performed at a finer scale.

A numerical study on evaluating the thermal environment in a space served by a bed-based air source heat pump (B-ASHP) system

Both air source heat pumps (ASHPs) and traditional Chinese-Kangs heating systems are widely used. However, they have their pros and cons. By combining the merits from both an ASHP and a Chinese-Kang heating system, a prototype bed-based ASHP (B-ASHP) system has been proposed, and its operating characteristics experimentally obtained under a fix set of design/operating parameters for the bed-based heating terminal. Therefore, a follow-up numerical study was carried out to numerically evaluate the impacts of optimizing these design/operating parameters, including the location, dimension, surface temperature and surface emissivity of the bed-based heating terminal, on the indoor thermal environment and the operating efficiency of the B-ASHP system. The numerical study results suggested that the variation in these parameters did impact both indoor thermal environment and the operating efficiency of the B-ASHP system, in terms of the uniformity of indoor thermal environment, indoor air velocity distribution and the output heating capacity, as well as the installation space requirement and cost implication. Therefore, care must be exercised in properly balancing all influencing parameters. Also, to both maintain an acceptable indoor thermal environment that can meet the Chinese National Standard, and achieve the best possible operating efficiency of the B-ASHP system, the bed surface temperature of its bed-based heating terminal may be set at around 35 °C. Furthermore, although the changes in surface emissivity did not significantly impact on indoor thermal environment, a higher surface emissivity should be preferred when a lower bed surface temperature was used, so as to further improve potentially the operating efficiency of the B-ASHP system.

COMPARISON OF INDOOR AIR TEMPERATURE AND OPERATIVE TEMPERATURE -DRIVEN HVAC SYSTEMS BY MEANS OF THERMAL COMFORT AND ENERGY CONSUMPTION

The main purpose of Heating, Ventilating and Air-Conditioning (HVAC) systems is to satisfy thermal comfort for the occupants. Conventionally, HVAC systems adjust set-temperature to achieve thermal comfort by continuously measuring indoor air temperature of the environment. However, ASHRAE 55, a standard of acceptable thermal environments, offers to use acceptable ranges of operative temperatures in air-conditioned buildings. Considering operative temperature is a function of indoor air temperature and mean radiant temperature, set-temperature of HVAC system can be controlled by using operative temperature to satisfy neutral thermal comfort for the occupants. This study compares thermal comfort and energy consumption of two exactly same HVAC systems which are operated based on indoor air temperature and operative temperature, respectively. Two office rooms with same architectural configurations -which are located in a university-Ankara-Turkey- were selected as a case study. The HVAC systems were operated based on indoor air temperature and operative temperature, respectively, at the same time and occupancy schedules. The results showed that operative temperature driven controlled HVAC system achieves better thermal comfort while slightly increasing energy consumption. The main findings of this study would be useful not only to design energy-efficient HVAC systems but also create more comfortable environments.

Experimental evaluation of a capillary heating bed driven by an air source heat pump and solar energy

The traditional Chinese kang is a widely used domestic heating system in rural areas in northern China. However, such system could cause serious air pollution due to burning of biomass materials or coal. An improved bed heating system is introduced in this study to reform the traditional kang, using a capillary mat as a heating terminal, an air source heat pump (ASHP) and a solar energy as the heat source. An experimental prototype was built in a residential house in Xi’an, China, and tests were conducted to evaluate the system’s feasibility and performance under different operational modes. Results showed that the system could effectively provide an acceptable thermal environment for a separately heated room and with a reduced consumption of carbon-based fuel. When the system was completely driven by the ASHP, the daily electricity consumption of the ASHP is only 5.5 kWh with a supply water temperature of 40°C. When coupling the ASHP with the solar energy, the daily hours of solar energy utilization ranged from 3.5 to 4.5 h per day when the ratio of the solar thermal collector area to the floor area was approximately 1.0. The available ratio (days of utilized solar energy to the days comprising the full heating season) exceeded 66.0% over three heating seasons. The system was shown to be a feasible and energy-efficient heating strategy for rural buildings.

Daylight affects human thermal perception

Understanding the factors that affect human thermal responses is necessary to properly design and operate low-energy buildings. It has been suggested that factors not related to the thermal environment can affect thermal responses of occupants, but these factors have not been integrated in thermal comfort models due to a lack of knowledge of indoor factor interactions. While some studies have investigated the effect of electric light on thermal responses, no study exists on the effect of daylight. This study presents the first controlled experimental investigation on the effect of daylight quantity on thermal responses, combining three levels of daylight illuminance (low ~130 lx, medium ~600 lx, and high ~1400 lx) with three temperature levels (19, 23, 27 °C). Subjective and objective thermal responses of 84 participants were collected through subjective ratings on thermal perception and physiological measurements, respectively. Results indicate that the quantity of daylight influences the thermal perception of people specifically resulting in a cross-modal effect, with a low daylight illuminance leading to a less comfortable and less acceptable thermal environment in cold conditions and to a more comfortable one in warm conditions. No effect on their physiological responses was observed. Moreover, it is hypothesised that a warm thermal environment could be tolerated more whenever daylight is present in the room, as compared to the same thermal condition in a room lit with electric lights. Findings further the understanding of factors affecting human thermal responses and thermal adaptation processes in indoor environments and are relevant for both research and practice. The findings suggest that daylight should be considered as a factor in thermal comfort models and in all thermal comfort investigations, as well as that thermal and daylight illuminance conditions should be tuned and changed through the operation and design strategy of the building to guarantee its occupants’ thermal comfort in existing and future structures.

Fast Heating Model for the Aircraft Cabin Air

Maintaining a suitable cabin air temperature distribution is essential for providing an acceptable thermal environment for passengers and crew. However, cabin air may be very cold for the first flight in winter morning. It could be difficult to heat quickly the cabin air and to maintain an acceptable temperature gradient before boarding with the existing environmental control system. This study developed numerical model for predicting the heating process that coupled airflow and heat transfer in a cabin. The model was validated by using the experimental data obtained from an MD-82 airliner. With the validated numerical model, this investigation proposed to use an electric blanket to heat cabin air quickly and to reduce the air temperature gradient.

Study of the Thermal Comfort of a Building that does not Comply with Construction Standards in Madagascar: Experimentation and Simulation with OMEdit

A very large number of buildings in developing countries are far from complying with the standards of housing. This paper presents the subjective study of the thermal comfort of a building that does not comply with construction standards or thermal regulations, located in Madagascar. Modeling was done using the Modelica tool, especially its BuildSysPro library. In order to minimize the inaccuracies, a step of an experimental adjustment of the developed numerical model was also carried out usingexperimental reference data that were obtained from the temperaturemeasurementsof the studied building elements as well as the wind speed and the received solar radiation flux. It was found that despite the obvious non-compliance with building standards and thermal regulations, the building has an acceptable thermal environment vis-à-vis its occupant.

Study of the Thermal Comfort of a Building that does not Comply with Construction Standards in Madagascar: Experimentation and Simulation with OMEdit

A very large number of buildings in developing countries are far from complying with the standards of housing. This paper presents the subjective study of the thermal comfort of a building that does not comply with construction standards or thermal regulations, located in Madagascar. Modeling was done using the Modelica tool, especially its BuildSysPro library. In order to minimize the inaccuracies, a step of an experimental adjustment of the developed numerical model was also carried out usingexperimental reference data that were obtained from the temperaturemeasurementsof the studied building elements as well as the wind speed and the received solar radiation flux. It was found that despite the obvious non-compliance with building standards and thermal regulations, the building has an acceptable thermal environment vis-à-vis its occupant.

An innovative personalized displacement ventilation system for airliner cabins

In airliner cabins, mixing ventilation systems with gaspers are not efficient in controlling contaminant transport. To improve the cabin environment, this investigation proposed an innovative ventilation system that would reduce contaminant transport and maintain thermal comfort. We manufactured and installed the proposed ventilation system in an occupied seven-row, single-aisle aircraft cabin mockup. Air velocity, air temperature, and contaminant distribution in the cabin mockup were obtained by experimental measurements. The investigation used the experimental data to validate the results of CFD simulation. The validated CFD program was then used to study the impact of the locations and number of exhausts on contaminant removal and thermal comfort in a one-row section of a fully occupied Boeing-737 cabin. Although the diffusers in the proposed system were close to the passengers' legs, the air velocity magnitude was acceptable in the lower part of the cabin and the leg area. The proposed system provided an acceptable thermal environment in the cabin, although passengers could feel cold when placing their legs directly in front of the diffusers. The four-exhaust configuration of the new ventilation system was the best, and it decreased the average exposure in the cabin by 57% and 53%, respectively, when compared with the mixing and displacement ventilation systems.

Assessment of thermal comfort in high-occupancy spaces with relevance to air distribution schemes: A case study of mosques

In high-occupancy intermittently operated buildings such as mosques and auditoriums, maintaining an acceptable thermal environment may present a challenging task. Variations in the operation and the thermal loads can result in variable and non-uniform thermal comfort conditions when the HVAC system is not properly designed. Non-uniformity of the thermal environment is greatly influenced by the design and scheme of the air distribution system. Mosques, with their distinctive five intermittent short occupancies and the non-fixed posture of occupants, present a unique case for investigation. In this study, the effect of air distribution of various schemes of a ceiling-based system on the thermal comfort in mosques is investigated. Air diffusion performance index and Fanger’s PMV method are used to assess thermal comfort. Three air distribution schemes at four diffuser terminal velocities were studied using the EnergyPlus and computational fluid dynamics techniques. Results indicate major variations in air diffusion performance index with each air distribution scheme type and diffuser terminal velocity. The uniformity of the PMV was entirely dependent on the air diffusion performance index value and exhibited large variations when the air diffusion performance index value was low. In most cases, the space was overcooled with an average PMV of −0.66 or below. Practical application: The effect of air distribution system design on human thermal comfort has been very complex to understand, as it involves different schemes and different diffuser discharge velocities. This study will help engineers and designers in designing better thermal environment for the occupants.

Effects of indoor temperature and background noise on floor impact noise perception

This study investigates effects of room air temperature and background noise on the perception of floor impact noises in a room. Floor impact noises were recorded in apartment buildings and were presented in an indoor climate chamber with background noise for subjective evaluation. Thirty-two participants were subjected to all combinations of three thermal conditions (20%C, 25%C, 30%C and relative humidity 50%), four background noise types (Babble, Fan, Traffic and Water), three background noise levels (35 dBA, 40 dBA and 45 dBA) and four floor impact noises (Man Jumping, Children Running, Man Running and Chair Scraping). After a 1-h thermal adaptation period for each thermal condition, the participants were asked to evaluate their thermal and acoustic perceptions. Statistically significant effects were found for the room air temperature and background noise level on the perception of the floor impact noises. Noisiness, loudness and complaints of floor impact noise increased with increasing room temperature and background noise level. Annoyance of floor impact noise showed a peak in acceptable thermal environment for general comfort. Room air temperature was a dominant non-auditory factor contributing to floor impact noise annoyance, while the floor impact noise level influenced the floor impact noise loudness and the floor impact noisiness was almost equally affected by the room temperature, background noise level and floor impact noise level. Further investigation is needed to fully understand the combined perception of floor impact noise under various indoor environmental conditions.