Indoor Thermal Conditions Research Articles

Simulation and Machine Learning Investigation on Thermoregulation Performance of Phase Change Walls

The outdoor thermal environment can be regarded as a significant factor influencing indoor thermal conditions. The application of phase change materials (PCMs) to the building envelope has the potential to improve the heat storage performance of building walls and, therefore, effectively regulate the temperature variations of the inner surfaces of walls. COMSOL Multiphysics software was adopted firstly to perform the simulations on the thermoregulation performance of phase change wall; the time duration of the temperature at the internal side maintained within the thermal comfort range was used as a quantitative evaluation index of the thermoregulation effects. It was revealed from the simulation results that the time durations of thermal comfort were extended to 5021 s and 4102 s, respectively, when the brick walls were filled with two types of composite PCMs, namely eutectic hydrate (EHS, Na2CO3·10H2O and Na2HPO4·12H2O with the ratio of 4∶6)/5 wt.% BN and EHS/5 wt.% BN/7.5 wt.% expanded graphite (EG), under the conditions of 18 °C ambient temperature and 60 °C heating temperature at the charging stage. Both of them were longer than 3011 s, which corresponds to a pure brick wall. EHS/5 wt.% BN/7.5 wt.% EG exhibited better leakage prevention performance and, therefore, was a candidate for actual application, in comparison with EHS/5 wt.% BN. Then, a machine learning training process focused on the temperature control effects of phase change wall was carried out using a BP neural network, where the heating surface and ambient temperature were used as input variables and the time duration of indoor thermal comfort was the output variable. Finally, the learning deviation between the raw data and the results obtained from machine learning was within 5%, indicating that machine learning can accurately predict the temperature control effects of the phase change wall. The results of the simulations and machine learning can provide information and guidance for the advantages and potentials of PCMs of hydrate salts when being applied to the building envelope. In addition, the accurate prediction of machine learning demonstrated its application prospects to the research of phase change walls.

Modelling urban dwellers’ indoor heat stress to enhance heat-health warning and planning

Due to climate change, the intensity, duration and frequency of heatwaves are likely to increase in the coming years. Excessive heat events can increase local urban heat island intensity affecting the health and wellbeing of urban dwellers vulnerable to heat stress. Heat-Health Warning Systems (HHWSs) have been developed to warn the public of impending heat events and to advise on preventable negative health outcomes. However, metrics upon which action triggers are made in HHWSs rely on reported critical outcomes, such as heat-related excess death. Thus, human exposure to heat is underestimated in current metrics and consequently, their capacity to prevent heat-related health risks remains uncertain, particularly indoors. This study investigates how indoor heat stress in urban dwellings at a city-scale can be modelled to enhance Heat-Health Warning and Planning. First, the effects of housing typologies on indoor thermal conditions are quantified in a local urban microclimate context. We then model the dynamic relationships between outdoor climate and indoor heat exposure to identify specific outdoor climatic thresholds as action triggers for alerting urban dwellers’ indoor heat stress. Based on urban microclimate data available for a city of Birmingham UK, a proof-of-principle study is presented. The result shows the presence of large variances in the heat-health action triggers across different housing typologies. This is further extended to consider the Birmingham climate projection scenarios provided by the UKCP18. Compared to the current UK Heat-Health Alert Service, we show how indoor heat stress warnings may look like and the implications for long-term heat-health planning.

Effect of ventilation strategy on performance of upper-room ultraviolet germicidal irradiation (UVGI) system in a learning environment

Upper-room ultraviolet germicidal irradiation (UVGI) system is recently in the limelight as a potentially effective method to mitigate the risk of airborne virus infection in indoor environments. However, few studies quantitatively evaluated the relationship between ventilation effectiveness and virus disinfection performance of a UVGI system. The objective of this study is to investigate the effects of ventilation strategy on detailed airflow distributions and UVGI disinfection performance in an occupied classroom. Three-dimensional computational fluid dynamics (CFD) simulations were performed for representative cooling, heating, and ventilation scenarios. The results show that when the ventilation rate is 1.1 h−1 (the minimum ventilation rate based on ASHRAE 62.1), enhancing indoor air circulation with the mixing fan notably improves the UVGI disinfection performance, especially for cooling with displacement ventilation and all-air-heating conditions. However, increasing indoor air mixing yields negligible effect on the disinfection performance for forced-convection cooling condition. The results also reveal that regardless of indoor thermal condition, disinfection effectiveness of a UVGI system increases as ventilation effectiveness is close to unity. Moreover, when the room average air speed is >0.1 m/s, upper-room UVGI system could yield about 90% disinfection effect for the aerosol size of 1 μm–10 μm. The findings of this study imply that upper-room UVGI systems in indoor environments (i.e., classrooms, hospitals) should be designed considering ventilation strategy and occupancy conditions, especially for occupied buildings with insufficient air mixing throughout the space.

Mejora del desempeño térmico de colegios en la Región Altoandina del Perú. El caso del “módulo prefabricado aula tipo heladas - PRONIED”

Faced with the qualitative and quantitative deficit of educational infrastructure in Peru’s rural high Andean areas, in recent years the Peruvian State has been investing in and supporting modular solutions, seeking efficiency in the construction processes. The specific proposal, with special emphasis on bioclimatic design, is the "Prefabricated Frost-type Modular Classroom". However, users have been expressing discomfort with these new facilities. This study shows the measurement process carried out on a built module, which allowed calibrating and validating the model using simulation software, to propose improvements in the design that may contribute to future constructions. Taking the adaptive thermal comfort model as a reference, it was confirmed that indoor temperatures were below thermal comfort limits in the early hours of the morning and well above them close to noon, by around 6 ºC and 7 ºC respectively. With the application of complementary bioclimatic strategies, it was possible to considerably improve indoor thermal conditions, although not enough to reach comfort early in the morning. This is because the night-time outdoor temperatures are very low, the building is uninhabited all night long, there is no thermal mass in the envelope, and there are no active solar systems or mechanical air conditioning.

A thermal response in architecture: Case study (Malaysian residential)

This study aims to create an awareness of the indoor and outdoor thermal conditions of a design and how design influences the outcome of as a responsive design. The desirable and undesirable thermal conditions are considered, and an analysis of the cause-and-effect is discussed. While thermal conditions, and its cause-and-effect considerations may be directed to any building, achieving an ideal solution requires careful integration of thermal comfort principles. Refinement through the understanding of thermal comfort principles can achieve significant energy saving without necessarily sacrificing functionality or aesthetics. Precedent studies are being discussed to see the benefits and usage of the materials based on the intention of the design and the function of the space that would impact the indoor quality environment. Based of field observation, data collection and result analysis, solutions are proposed to two different local residential buildings. Key finding shows different design factors, materials and operative conditions can influence the thermal performances of buildings. This analysis may help to improve energy efficiency in built environment and to be used for further study in thermal response in architecture while investigating new ways to design building walls that could possibly be modularized in the future with both external and internal design considerations. This intention is to be further explored with first the basic understandings of layering of materials before the simulations into the spaces.

Effects of natural ventilation on indoor thermal comfort in a residential house constructed with reinforced concrete wall

This study aims to investigate the effect of natural ventilation on the thermal performance of a double-story end-lot unit residential house constructed with reinforced concrete walls and structure in Kluang, Johor. Field measurement was conducted in the master bedroom of the house. Five ventilation cases were investigated which are night ventilation (case 1), no ventilation (case 2), day ventilation (case 3), day ventilation with fan (case 4), and night ventilation with fan (case 5). The measured data were indoor air temperature, outdoor air temperature, indoor relative humidity, outdoor relative humidity, and globe temperature. Then, the thermal comfort assessment was conducted based on the adaptive thermal comfort equation for hot-humid climate for all cases. The results show that the mean indoor temperature for all cases is in the range of 29°C to 31.5°C which indicates a high indoor air temperature. Furthermore, the analysis of air temperature difference between outdoor and indoor (out-in) for different natural ventilation modes showed that the indoor thermal conditions of the master bedroom were not significantly different when compared between cases. In the thermal comfort assessment, the night ventilation case (case 1) provided the most comfortable hours during the measurement with a range of 11 to 35.4 %, thanks to the lower outdoor climate conditions at night compared to the other cases. Overall, in this study, the effect of natural ventilation modes on the indoor thermal condition of a master bedroom in a residential house with concrete walls and structures was found not significantly different in the performance of air temperature reduction and comfort hour improvement when compared between cases.

Assessment of Indoor Thermal Condition on Traditional Vernacular Masjid: A Case Study on Masjid Kampung Laut, Malaysia

Traditional vernacular architectures in Malaysia include public buildings such as a masjid were designed with the tropical climate in mind and have proven to be an excellent example of providing indoor thermal comfort to the occupants. It is a naturally ventilated building being greatly influenced by the building designs. In traditional vernacular architecture, the roof is the main building enclosure that contributes to the total heat gain. Hence, the research aims to assess the indoor thermal condition of Masjid Kampung Laut, Kelantan, the first traditional vernacular masjid in Malaysia. Data were collected using the method of field measurement to evaluate the indoor comfort level of the masjid, in terms of indoor air temperature, air velocity, and relative humidity. The results demonstrate that the average indoor air temperature is acceptable and Masjid Kampung Laut responded favorably to the local climate. However, it is believed that with an increase of 0.4m/s to 1.2m/s of air movement, will further enhance indoor thermal comfort. Therefore, the findings can guide further thermal comfort prediction studies for other naturally ventilated buildings. Several other potential passive design strategies for roof design are proposed in this study to achieve acceptable indoor thermal comfort conditions for the masjid in Malaysia.

Evaluating the Impact of Natural Ventilation on Indoor Thermal Conditions in Hot and Arid Climate School Buildings

Evaluating the Impact of Natural Ventilation on Indoor Thermal Conditions in Hot and Arid Climate School Buildings

Experimental investigation of a solar-assisted absorption-compression system for heating and cooling

Decarbonizing the energy sector becomes a key topic to solving man-made climate change. For achieving indoor thermal comfort conditions, conventional heating, ventilating, and air-conditioning systems consume so much energy in both residential and public buildings. In this paper, a novel solar-assisted absorption-compression system for both heating and cooling is proposed to utilize solar thermal energy throughout the year for the heating/cooling supply. The experimental prototype was built and operational modes including solar-assisted heating/cooling mode and vapor compression individual heating/cooling mode. The performance enhanced by assisted heat input of the proposed system is evaluated by comparing it with air-source heat pumps operated under the same ambient conditions. Performance indices consisting of COPele increment, power-saving ratio (PSR) and energy-saving ratio (ESR) are presented. The results indicate that the combination of the absorption heat pump subsystem and the vapor compression subsystem lowers the heat-driven temperature to 60 °C and thus makes higher solar collection efficiency possible. The maximum of the COPele increment and the PSR under solar-assisted heating mode are achieved at conditions with 80 °C hot water temperature, of 45.8% and 31.4%, respectively, and the corresponding value for solar-assisted cooling mode are 18.9% and 16.0%. The speed of compressor as well as fan frequency of terminal has a greater influence on heating performance that on cooling performance due to the different coupling mechanisms.

Predictive Model of Clothing Insulation in Naturally Ventilated Educational Buildings

Providing suitable indoor thermal conditions in educational buildings is crucial to ensuring the performance and well-being of students. International standards and building codes state that thermal conditions should be considered during the indoor design process and sizing of heating, ventilation and air conditioning systems. Clothing insulation is one of the main factors influencing the occupants’ thermal perception. In this context, a field survey was conducted in higher education buildings to analyse and evaluate the clothing insulation of university students. The results showed that the mean clothing insulation values were 0.60 clo and 0.72 clo for male and female students, respectively. Significant differences were found between seasons. Correlations were found between indoor and outdoor air temperature, radiant temperature, the temperature measured at 6 a.m., and running mean temperature. Based on the collected data, a predictive clothing insulation model, based on an artificial neural network (ANN) algorithm, was developed using indoor and outdoor air temperature, radiant temperature, the temperature measured at 6 a.m. and running mean temperature, gender, and season as input parameters. The ANN model showed a performance of R2 = 0.60 and r = 0.80. Fifty percent of the predicted values differed by less than 0.1 clo from the actual value, whereas this percentage only amounted to 32% if the model defined in the ASHRAE-55 Standard was applied.

Cold Housing in Central Mexico: Environmental Dissatisfaction and Underheating Lowers Self-Perceived Health in Central Mexico

Despite being perceived as a warm country, winters in the Central Mexican Plateau frequently reach temperatures below zero Celsius. Prolonged exposures to low temperatures resulting in heart and respiratory morbidities are estimated to be responsible for 50% of the reported illness in the plateau, attributable primarily to the design of homes ill-suited to extreme temperatures. Consequently, there is a growing need to ensure that dwellings provide adequate indoor thermal conditions in the region. Hence, on-site sensors were used to collect temperature and relative humidity data every five minutes in 26 living rooms in the Plateau for 11 months. From these data, a subsample was determined, resulting in dwelling-level thermal comfort and health surveys on 15 homes. Computer simulations were used to investigate whether the building itself could provide thermal comfort under different retrofitting scenarios. Multiple linear regression relating the Predicted Percentage Dissatisfaction (PPD) index to self-perceived health was undertaken. Both monitored and simulated results were matched against our underheating model, finding that 92% of the homes had cold indoor environments, some even during summer. High PPD and intense levels of underheating were positive predictors of higher self-reported health problems. More self-reported health problems were correlated with both lower life satisfaction and self-worth, and with subjects’ use of more adaptive strategies against environmental dissatisfaction. Dynamic computer simulations suggested that indoor thermal environments could be improved by enforcing the non-utilised standard NOM-ENER-020, which recommends the addition of insulation on walls and roofs. These findings suggest that the cold environments within homes of the plateau influence the self-perceived physical and mental health of its population. Hence, the application of adequate measures, such as retrofitting homes with stronger standards than the existing NOM-ENER-020 are needed in place.

The adoption of pressure independent control valves (PICVs) for the simultaneous optimization of energy consumption and comfort in buildings

The optimization of energy consumption in buildings’ HVAC systems plays a crucial role in reducing greenhouse gas emissions worldwide. In new and deeply-renovated buildings, characterized by modulating terminal units and aiming at the maximum exploitation of renewables, an accurate hydraulic balance of the distribution network may become critical, resulting in a significant increase of pumping energy consumptions and a deterioration of indoor thermal comfort conditions. In the present paper, we compare the performance of traditional manual balancing valves and new pressure independent control valves (PICVs), used to balance the hydronic loop of HVAC systems. To perform this analysis, a new MATLAB-Simulink model has been specifically developed to simulate the behavior of PICVs and has been used in an application case study. The efficiency of manual and pressure independent control valves is evaluated numerically by simulating a multi-zone distribution network under variable operating conditions and considering different control strategies of the circulating pump. Results show that in off-design conditions, when some of the branches of the hydraulic network are closed, traditional manual balancing valves are not able to guarantee the nominal mass flow rate in the remaining loops. On the contrary, no significant variations of water mass flow rate are observed when PICVs are adopted, even in partial load conditions. Despite their additional cost, PICVs allow to ensure better indoor thermal comfort sensations for individuals, avoiding under/over-heating of rooms and, moreover, yield a decrease of the pump electric consumption with respect to traditional manual balancing valves. In addition, based on the obtained results, general rules concerning the adoption of PICVs are provided, depending on the extension of the hydraulic loop and the adopted pump control logic. The reported results highlight the role that PICVs can play to ensure energy savings in HVAC systems without penalizing users’ indoor comfort conditions.

A Review on Adaptive Thermal Comfort of Office Building for Energy-Saving Building Design

The thermal environment quality of office buildings has an important role because thermal comfort is directly related to human productivity. Thermal comfort conditions are influenced by climate, location, and the built environment; hence, comfort standards are required to assist building designers in creating a comfortable indoor environment for building occupants. In this context, the present study analyzes the adaptive thermal comfort studies conducted in office buildings from various countries. A large number of research articles selected from the Scopus database were considered for this study. Based on the analysis, outdoor climatic conditions have a greater influence on indoor thermal conditions in naturally ventilated than in air-conditioned office buildings. The temperature required for comfort is as low as 17.6 °C and as high as 31.2 °C in naturally ventilated buildings. An adaptive comfort equation for naturally ventilated and air-conditioned office buildings has also been proposed to predict the indoor comfort temperature. Various studies show that a substantial amount of energy can be saved by changing the set point and natural ventilation. Furthermore, this study successfully provides hearty evidence that there is a need for climate-specific standards on thermal comfort for energy-efficient design development because existing comfort standards might not be applicable to all climates.

Field studies on the energy consumption and thermal comfort of a nZEB using radiant ceiling panel and open-loop groundwater heat pump system in a cold region

Field studies were conducted in an office building in a cold region equipped with a radiant ceiling panel (RCP) and open-loop groundwater heat pump (GWHP) system. First, the indoor thermal comfort in a target office was evaluated based on the results obtained from the physical measurements and survey questionnaire. The results showed that the suspended RCP system could achieve comfortable indoor thermal conditions throughout the year. The indoor temperature was maintained within the range of 22–26 °C, the humidity was within 30–60%, and CO2 concentration was mostly below 1000 ppm. Second, the energy performance was tested simultaneously, and intermittent and continuous operation methods were compared. Under the continuous operation method, a stable indoor environment was maintained, and the COP of the GWHP system increased by 10%. The results showed the potential to further reduce energy consumption and maintain a high level of thermal comfort through the optimization of system operations. Finally, the annual energy consumption was calculated based on the recorded measurements. The results illustrate that this building can reach the ZEB-ready level in Japan. The primary energy consumption can be decreased by approximately 67% compared to the reference by applying the combined system.

An experimental study of thermal performance of the radiant ceiling cooling in office building in Thailand

This paper investigated the radiant ceiling cooling in office buildings in a tropical hot humid climate. Full-scale experiments were conducted in an outdoor laboratory chamber to observe the indoor thermal conditions and the envelope heat gain from the intermittent operation of the installed radiant chilled panels (RCP) coupled with an outdoor air unit (OAU). The radiant system was also modeled by using a simulation software namely Transient System Simulation Software (TRNSYS), and the calculation results from the model were compared to the experimental observations. In the simulation part, the validated TRNSYS model was adopted to assess the radiant system performance in a typical office environment under the four schemes of combinations of the technology options for the OAU and the building envelope. The perceived comfort from the radiant cooling was assessed based on the thermal sensation of the local subjects acclimatized to hot humid climate. The energy consumption of the radiant cooling was also apprised as opposed to the conventional mixed-air system. The simulation results presented an insight into the importance of the exhaust air heat recovery and the envelope insulation on energy saving and human comfort improvement for the radiant cooling.

Thermal regulation mechanism of air-drying shelter to indoor environment of earth buildings located in Turpan basin with extremely dry and hot climate conditions

This study investigates the thermal regulation mechanism of air-drying shelter of earth buildings located in Turpan basin to indoor thermal environment under the extremely dry and hot climate condition. Firstly, a field measurement lasting for three days was performed to investigate the thermal effect of air-drying shelter on indoor thermal condition. The measured results indicated that air-drying shelter provides the shaded space and natural ventilation to reduce the internal surface temperature of the roof and further improve the indoor thermal comfort in the hot summer. Then, a series of numerical studies on the effects of design parameters of air-drying shelter on indoor environment of earth building in Turpan basin were performed. The selected design parameters of air-drying shelter included air-drying shelter to room height ratio, thickness of carved walls, thickness of air-drying shelter's roof and hole to wall area ratio. The simulated results demonstrated that hole to wall area ratio of the carved walls is considered as an important design parameter of air-drying shelter, and increasing hole to wall area ratio of carved walls could increase solar radiation heat gain of roof, leading to increasing internal surface temperature of roof and indoor air temperature.

Monitoring summertime indoor overheating and pollutant risks and natural ventilation patterns of seniors in public housing

Indoor heat and air pollution pose concurrent threats to human health and wellbeing, and their effects are more pronounced for vulnerable individuals. This study investigates exposures to summertime indoor overheating and airborne particulate matter (PM2.5) experienced by low-income seniors and explores the potential of natural ventilation on maintaining good indoor thermal conditions and air quality (IAQ). Environmental and behavioural monitoring and a series of interviews were conducted during summer 2017 in 24 senior apartments on three public housing sites in NJ, USA (1930s’ low-rise, 1960s’ high-rise and LEED-certified 2010s’ mid-rise). All sites had high exposures to overheating and PM2.5 concentrations during heat waves and on regular summer days, but with substantial between-site and between-apartment variability. Overheating was higher in the 30s’ low-rise site, while pollutant levels were higher in the 60s’ high-rise. Mixed linear models indicated a thermal and air quality trade-off with window opening (WO), especially in some ‘smoking’ units from the older sites, but also improved both thermal and PM2.5 concentration conditions in 20% of the apartments. Findings suggest that with warmer future summers, greater focus is needed on the interdependencies among (1) thermal and IAQ outcomes and (2) technological and behavioural dimensions of efforts to improve comfort for vulnerable occupants.

Holistic Approach towards a Sustainable Urban Renewal: Thermal Comfort Perspective of Urban Housing in Kigali, Rwanda

Urban upgrading programs are implemented to enhance the living conditions in a city. However, the concept of to what extent the life of the targeted communities is improved remains contested and fluid. The purpose of this study was two-fold. First, it evaluated for the first time the indoor thermal conditions in the three main urban housing types in Kigali and analyzed whether the ongoing urban renewal takes into consideration occupant thermal comfort. Second, alternatives to improve thermal performance of urban housing were investigated and recommendations were given. Results indicate that modern urban housing performed significantly greater compared to other housing types, especially during daytime. Indoor thermal conditions in the planned low-income housing were no better—and, in fact, were slightly poorer—than in the informal settlement from which households were to be relocated. Through design parameter optimization, the indoor thermal conditions in the planned low-income housing were improved by 85.5% in the daytime hours and 71.2% in the nighttime hours. These findings are valuable to officials in resettlement programs by providing insights to improve urban dwellers’ living conditions from a wholistic prospective. This can assist related parties in mitigating project failure often caused by local resistance to resettlement.

Adaptive thermal comfort for energy saving office building design- A literature review

Office building thermal environment quality is essential since thermal comfort and worker productivity are closely related. As thermally comfortable condition is determined by the climate, geography, and surroundings, it is vital to have thermal comfort standards to guide the building designers to create a comfortable indoor thermal environment. The current paper reviews studies on adaptive approach of thermal comfort carried out in offices across the world. It has analyzed many research papers through Scopus. This study reveals that indoor thermal condition is impacted by outdoor climates and the impact is higher in naturally ventilated building. Building with natural ventilation has 17.6°C to 31.2°C rage of comfortable temperature. Adaptive comfort models have also been proposed to predict the comfortable indoor temperature in different modes. According to several studies, lowering the set point and using natural ventilation may result in considerable energy savings. The importance of developing climate specific thermal comfort guidelines in order to create energy efficient designs is also emphasized in this study, as present comfort standards may not be suitable for all climates.

Field Assessment of The Indoor Thermal Environment and Thermal Comfort Levels for Naturally Conditioned Residential Buildings in The Tropical Climate

As we spend most of our time in indoor spaces, half of the energy consumption in buildings is used to improve the indoor thermal environment to achieve thermally comfortable conditions. However, studies showed that people in naturally ventilated buildings have a broader thermal comfort zone. Additionally, people in hot areas can tolerate higher indoor temperatures. Therefore, this work investigates and evaluates the indoor thermal environment and the thermal comfort level in naturally conditioned buildings. Field measurements were conducted in various residential spaces in different buildings. The measurements were used to calculate the operative temperature (Tₒₚ), which was utilized to evaluate the thermal comfort level based on the adaptive models and taking into account the effect of the various orientations. The results showed that maximum Tₒₚ ranged between 27.70 ℃ and 35.50 ℃, depending mainly on the space’s orientation. Additionally, the thermal discomfort time ranged between 0% and 73%. The South & East, Southeast, South, and East orientation were more critical during the study period, while the North, Northeast, and Northwest orientations achieved better indoor thermal conditions. However, these results can vary throughout the year, depending on the sun’s path. This study revealed that the daily average heat gain to the building from the Southeast and South orientations is higher than that from the East and West orientations due to the longer exposure time to solar radiation.