Search Results (70)

Improving outdoor thermal comfort is a critical objective in urban design, particularly in densely built urban environments. Elevated semi-open spaces—outdoor areas located beneath raised building structures—have been recognized for enhancing pedestrian comfort by improving airflow and shading. However, previous studies primarily focused on warm or temperate climates, leaving a significant research gap regarding their thermal performance in cold climate zones characterized by extreme seasonal variations. Specifically, few studies have investigated how these spaces perform under conditions typical of northern Chinese cities like Xi’an, which is explicitly classified within the Cold Climate Zone according to China’s national standard GB 50176-2016 and experiences both severe summer heat and cold winter conditions. To address this gap, we conducted field measurements and numerical simulations using the ENVI-met model (v5.0) to systematically evaluate the microclimatic performance of elevated ground-floor spaces in Xi’an. Key microclimatic parameters—including air temperature, mean radiant temperature, relative humidity, and wind velocity—were assessed during representative summer and winter conditions. Our findings indicate that the height of the elevated structure significantly affects outdoor thermal comfort, identifying an optimal elevated height range of 3.6–4.3 m to effectively balance summer cooling and winter sheltering needs. These results provide valuable design guidance for architects and planners aiming to enhance outdoor thermal environments in cold climate regions facing distinct seasonal extremes. Full article

In northern China, radiant floor heating is widely used in multi-apartment residential buildings, with indoor temperature being a key factor in evaluating a user’s heating demands. However, due to variations in building structure, room orientation, and the outdoor environment, identifying the optimal placement of temperature sensors across multiple zones remains challenging. In this study, we propose a data-driven methodology to identify the optimal placement of temperature sensors for a typical apartment with multiple zones. The proposed methodology is based on computational fluid dynamics (CFD) simulations of several typical scenarios and quantifies the relationship between the temperature field and the volume-averaged operating temperature to determine the optimal locations for temperature sensors. Results indicate that the temperature sensors need to be placed on planes ranging from 1.0 m to 1.7 m, with each plane featuring a distinct optimal area. The RMSE analysis reveals that, despite obvious temperature variations across the residence, the root mean square errors (RMSEs) at the designated sensor locations remain consistently low, with a maximum of 0.35 °C and most values below 0.3 °C. The above results indicate that the optimal sensor placement can significantly reduce potential errors between recorded temperatures and volume-averaged operating temperatures, which can be used as input parameters for personal indoor temperature control. Full article

This paper proposes an innovative system that integrates two thermoelectric heat pumps (one air–water and the other water–water) with two thermal storage tanks at different temperatures to provide heating and domestic hot water to a 73.3 m² passive-house-certified dwelling in Pamplona (Spain). The air–water thermoelectric heat pump extracts heat from the ambient air and provides heat to a tank at intermediate temperature, which supplies water to a radiant floor. The water–water heat pump takes heat from this tank and provides heat to the other tank, at higher temperature, which supplies domestic hot water. The system performance and comfort conditions are computationally analyzed during the month of January under the climate of Pamplona and under different European climates. The COP of the system lays between 1.3 and 1.7, depending on the climate, because of the low COP of the air–water thermoelectric heat pump. However, it is able to provide water for the radiant floor and to maintain the temperature of the dwelling above 20 °C 99.8% of the time. Moreover, it provides domestic hot water at a temperature above 43 °C 99.9% of the time. Noteworthy is the fact that the water–water heat pump presents a COP close to 4, which opens up the possibilities of working in combination with more efficient heat pumps for the first stage. Full article

According to extant Italian legislation implementing the Renewable Energy Directive, the mandatory renewable quota for a new building is 60% referring to a single service (e.g., heating during winter) or to multiple services (e.g., heating during winter and air conditioning during summer), depending on which services are actually present. The obligation to satisfy this minimum value often leads heating and ventilation plant designers to provide heat pump systems in industrial buildings, typically air/water or direct expansion type coupled with air terminals (air heaters or ventilation units) or radiant floors. The question is: Is this always the most advantageous option for industrial buildings? A typical industrial building was modeled by Trnsys^® in two different climates. Based on the calculated thermal heating loads, the condensing radiant tubes and heat pump coupled with the air heaters systems were analyzed through dynamic simulation, evaluating their performance from an energy, environmental impact, and economic point of view. The analysis carried out revealed that a heat pump system is not always the most advantageous solution depending on the climate, the characteristics of the building (less or more thermal insulation, which corresponds to existing buildings rather than new ones), and the size of the photovoltaics system eventually installed on the roof. Full article

The flashover mechanism in an aircraft cargo compartment under low pressure was investigated in this study. A series of fire experiments were conducted in a scale model of a one-quarter volume FAA standard aircraft cargo compartment at 96 kPa and 60 kPa. The ignition of single-walled corrugated cardboard was chosen as the criterion of the flashover. The influence of different fire sizes and fuel types on the flashover was studied by comparing the average temperature of the smoke layer, the radiation heat flux at the floor level, and the heat release rate of the fire source. The critical condition and behavior of the flashover were analyzed. The results show that under low pressure, the flashover occurs at a higher temperature and radiation heat flux. Increasing the fire source size brings the flashover forward. At 60 kPa and 96 kPa, the cardboard ignites under a flashover when the average temperature of the smoke layer reaches 551 °C and 450 °C, and the average radiant heat flux at the floor level reaches 19.6 kW/m² and 14 kW/m², respectively. In addition, the minimum fire size for a flashover is directly proportional to the heat of evaporation and inversely proportional to the heat of combustion. Full article

While forced-air convective systems remain the predominant method for heating and cooling worldwide, radiant cooling and heating systems are emerging as a more efficient alternative. Current radiant cooling systems primarily rely on hydronic chilled water systems. This study introduces direct-expansion radiant cooling as a novel technique that could enhance the efficiency of radiant cooling and reduce its environmental impact. Water (R-718) has been tested as a refrigerant due to its favorable thermodynamic properties and environmental advantages; however, to the author’s knowledge, it has yet to be tested in direct-expansion radiant cooling. This research investigated several refrigerants, including water (R-718), ammonia (R-717), R-410a, R-32, R-134a, and R-1234yf, for this application. The findings indicate that water demonstrates efficiency comparable to other non-natural refrigerants, making it a promising candidate, given its favorable thermodynamic properties and substantial environmental benefits. Despite challenges such as a high compression ratio necessitating multi-stage compression, a high compressor discharge temperature exceeding 300 °C and requiring specialized blade materials, and a high suction volume flow rate, direct-expansion radiant cooling operates within a different temperature range. Consequently, the compressor discharge temperature can be reduced to 176 °C, and the compression ratio can be lowered to approximately 3.5, making water a more viable refrigerant option for this application. Full article

In this study, the heating capacity of a new prefabricated assembled hot water radiant modular heating system made from a recycled waste building masonry structure is investigated through experimental and numerical simulation methods. The heating capacity of the system in different working conditions (a water supply temperature of 48 °C, 51 °C, 56 °C, and 61 °C; a flow rate of 0.49 m³/h, 0.35 m³/h, and 0.21 m³/h) is analyzed and verified. A three-dimensional steady-state heat transfer numerical model of the floor heat transfer of the module is established, and the accuracy of the model is verified through the measured results to investigate the heating capacity of this system under different water supply temperatures, flow rates and coil spacings. The results show that the new prefabricated hot water radiant module heating system has a 0.9 °C higher air temperature and 2.1 °C higher average floor surface temperature than the traditional wet floor radiant heating system under the same experimental conditions, and the response time is 44% shorter. The water supply temperature can significantly change the heating capacity of the system, while the water supply flow rate has little effect on the system. The established three-dimensional steady-state numerical model can be in good agreement with the measured results. This study can provide an experimental and theoretical basis for the design and application of such systems. Full article

Coal-fired power plants generate power by rotating turbines (TBNs). According to the high-temperature work exposure standard (KOSHA CODE 02), the turbine (TBN) building, where essential power-generation components, turbines (TBNs), are installed, contains various types of high-temperature equipment, creating a hazardous working environment for onsite employees. In addition, malfunctions from lubricant leaks occur at the moving parts of such power-generation equipment in the building, due to the high-temperature environment. In this study, we analyzed the heat concentration phenomenon in the turbine (TBN) building using computational fluid dynamics (CFD) software and made recommendations for its improvement. We examined options for installing automatic ventilation windows and additional heat exhaust fans on turbine (TBN) floors. We discovered that installing an automatic ventilation window and a heat exhaust fan on the deaerator floor can reduce the average temperature by 1.2 °C and 6.6 °C, respectively. In addition, the mezzanine floor, where the core heat-generating equipment is installed, is significantly affected by radiant heat. To mitigate the heat concentration phenomenon, we recommend installing additional radiant heat shields. Full article

Radiant cooling floors combined with ventilation systems have been widely applied in large space buildings. However, there has been a lack of research on system control strategies for their adaptation to weather changes. This study aimed to find control strategies for radiant cooling floors combined with displacement ventilation systems used in large space buildings in order to achieve energy conservation and environmental improvement. Supply air temperature and cooling surface temperature were determined to be the control variables. It was found that cooling capacity of the combined system and the comfort index, PMV (predicted mean vote), were linear in relation to the supply air temperature and cooling surface temperature. The linear equations regarding cooling capacity and PMV were established separately using environment data, and then the optimal region was determined. A case study on Terminal 3 of Xi’an Xianyang International Airport was conducted. The thermal environment was investigated through on-site measurements, questionnaires, and numerical simulations with CFD (computational fluid dynamics). It was found that supply air temperature and cooling surface temperature had a significant impact on PMV, and less impact on the cooling capacity. Therefore, it was determined that the supply air temperature should be altered first when the indoor temperature exceeds the upper limit, and then the cooling surface temperature should be changed if the indoor environment continues to overheat with the supply air temperature set to 18 °C. Thus, the supply air temperature was kept at 18 °C, and the floor surface temperature was set to be 22 °C on a high-temperature day. The average PMV was 0.87, and the cooling capacity of the combined system was 200 W/(m²·K), according to the CFD simulation. In addition, the surface heat transfer coefficient of the cooling floor was found to be 10.26 W/(m²·K). This research provides important references for the design and operational management of radiant cooling floors in large space buildings. Full article

This paper investigates the microclimate in a conference room with thermal stratification, taking as a case study the chapel of Villa San Saverio, now the seat of the “Scuola Superiore” of the University of Catania (Italy). Surveys of the former chapel were conducted to monitor air temperature and relative humidity. Subsequently, the investigation relied on numerical simulations of a simplified computational fluid dynamics (CFD) model built with the DesignBuilder v7.0 software and validated by comparison with measured values. Simulations were then carried out considering three different scenarios: the current state without any HVAC system and two possible HVAC system configurations providing both air conditioning and ventilation. The results show that, from a comfort perspective, a lightweight radiant floor heating system, assisted by an appropriate ventilation system for air renewal placed at the floor level near the occupants, is preferable to floor-level fan coils and high ventilation channels. Furthermore, this was also confirmed by a preliminary energy analysis of the two HVAC options, where the ventilation effectiveness of the winter period, the temperature of the water the emitters are fed, the consequent COP value of the heat pump, and the electricity consumption were taken into consideration. Full article

Phase-change materials (PCMs) are commonly employed in building service equipment to regulate indoor temperatures and reduce energy consumption. This study conducted multi-scale finite element modeling to analyze the steady-state and dynamic thermal behavior of a hydronic radiant floor heating system integrated with macro-encapsulated PCMs. It predicted performance values for hydronic floor heating with and without macro-encapsulated PCMs. The study assessed the impact of the PCM volume fraction, heating water temperature, capsule thermal conductivity, and shape on the thermal performance of hydronic floor heating through various finite element models. The predictive capability of the finite element model was validated using experimental data, showing good agreement. Although the inclusion of PCMs lowered the floor temperature, it improved temperature distribution and retained heat when the system was inactive. The PCM volume fraction significantly influenced the performance of the hydronic floor. However, the shape of the macro-encapsulated PCM and thermal conductivity of the shell had minimal effects in the studied case. For instance, increasing the thermal conductivity of the shell of the PCM capsule fifty times from 0.3 to 15 W m⁻¹ K⁻¹ resulted in an increase in surface temperature by 1.2 °C. Full article

With the growing interest in radiant heating and cooling systems, driven by their improved efficiency and enhanced thermal comfort compared to air systems, there is an increasing need to develop a more accessible method for designers to understand the implications of radiation heat exchange between the human body and radiant panels. To address this, a novel angle factor calculation model, named the HNU Angle Factor Model, was developed, taking into account the spatial arrangement and geometric relationship between the human body and radiant panels. The angle factors obtained using the HNU Angle Factor Model exhibited good agreement with the results obtained with Fanger diagrams and the contour integral method, with average relative differences of 8.1% and 10.0% for 140 cases, respectively. Furthermore, placing a radiant panel on the floor while maintaining its fixed size can contribute to the creation of an even and efficient thermal environment for individuals in both seated and standing positions. By implementing the HNU Angle Factor Model in practical engineering applications, more effective utilization of radiant systems can be achieved, as it provides an evaluation of the heat transfer between the human body and radiant panels. Full article

Forced convection is the most effective way to improve the thermal efficiency of a radiator under low-temperature conditions. This technical method differs significantly from the heating effects of general radiation and natural convection. Few studies have applied the objective evaluation method based on quantitative calculation to evaluate the effectiveness of indoor heating or optimize the technical parameters (air flow rate, air supply method, etc.) of heating systems. This article couples human metabolic factors with heating environmental factors and uses a 57-node human thermal physiological model to evaluate the effectiveness of forced convection radiator heating from the perspective of the local thermal comfort of the human body and demonstrates the feasibility of this scheme by comparing it with floor radiation heating. The research shows that the air supply speed of a radiator affects human thermal comfort. Continuing to increase the wind speed, at a speed of 3 m/s, the surface temperature of the human body reaches a high value and will then decrease, leading to a decrease in thermal comfort. Research on indoor air distribution shows that the use of bottom-side air supply provides better thermal comfort compared to top air supply. The local skin temperature distribution of the human body indicates that when the indoor average temperature is higher than 20 °C, the overall thermal comfort of convective radiator heating and floor radiant heating is comparable. The article provides a way of objectively calculating and directly quantifying the effect of heating equipment on human thermal physiological parameters. Full article

The increasing incidence of aircraft cargo compartment fires in recent years has caused heavy losses and drawn attention to understanding the combustion process, especially under low pressure. The present paper aims at exploring the conditions of flashover at different pressures. Experiments were conducted in Guanghan (96 kPa) and Kangding (60 kPa), which are located at different altitudes. Five different sizes of pool fires were tested and smoke temperature and heat flux were measured for flashover criteria analysis. Corresponding simulations were performed using a commercial software FDS to examine the pressure effect on the flashover phenomenon and to validate the simulation results. The critical conditions for the onset of flashover in a 1/4 MPS compartment were found to be (1) an average upper layer temperature of about 450 °C at 96 kPa or about 550 °C at 60 kPa, and (2) radiant heat flux at floor level of about 10 to 15 kW/m² at 96 kPa or 20 to 25 kW/m² at 60 kPa. By using the average upper layer temperature as a criterion in modeling, a relatively accurate prediction of flashover onset time could be obtained at 96 kPa and a delay of about 25 s was found at 60 kPa. Full article

The use of slag silicate cement mortar as a thermal mass layer for radiant floor heating systems holds significant potential for active thermal energy storage systems in buildings. The main objective of this article is to experimentally test the thermal performance of slag silicate cement mortar thermal storage blocks after the addition of phase change materials. The present study focuses on investigating the thermal performance of thermal storage blocks made of slag silicate cement mortar that incorporates a microencapsulated phase change material (mPCM). The mPCM consists of particles of paraffin-coated resin, which are uniformly distributed in the mortar. The analysis revealed that the introduction of mPCM particles into the mortar decreases the bulk density by approximately 9.4% for every 5% increase in mPCM particles ranging from 0% to 20%. The results obtained utilizing the Hot Disk characterization method demonstrate that the mPCM particles significantly affect the thermal properties of the mortar. Particularly, the thermal conductivity and thermal diffusion coefficient of the SSC30 mortar with a 17.31 wt.% mass of mPCM particles decreased by 59% and 69%, respectively. The results of this study provide a basis for the application of RFHS end-use thermal storage layers. Full article