Search Results (37)

The new eco-friendly flammable refrigerant in air conditioners has resulted in an annual increase in fire incidents associated with these units. Fire investigators face significant challenges in identifying the causes of these fires. In this study, copper tube samples were extracted from various locations of air conditioner condenser debris post fire. The morphology characteristics of the ruptured copper tubes formed by a high-temperature flame in fire and that formed by corrosion were analyzed, respectively. The findings indicate that the ruptures in the copper tubes of air conditioners may be classified into two types based on their origins: ruptures resulting from fire and ruptures resulting from corrosion. The ruptures in the copper tubes resulting from fire are associated with the presence of aluminum alloy fins. At elevated temperatures, the copper and aluminum atoms persist in diffusing and fracturing. A significant quantity of silver-white aluminum is present surrounding the ruptures, and distinct elemental layers may be seen in the cross-section. The corrosion-induced ruptures in the copper tubes are associated with ant nest corrosion. Despite the influence of high-temperature flame melting on surface corrosion pits, they will not entirely obscure the pits and the cross-section continues to exhibit the bifurcated structure characteristic of ant nest corrosion. This investigation demonstrates that corrosion of ant nests is the root cause of copper tube breakage obscured by flames. An investigation method for the refrigerant leakage air conditioning fire is proposed. The above findings can provide proof and method for air conditioning fire investigation. Full article

This paper presents an enhanced fault prediction framework for synchronous condensers in UHVDC transmission systems, integrating Large Language Models (LLMs) with optimized Wavelet Packet Transform (WPT) for improved diagnostic accuracy. The framework innovatively employs LLMs to automatically optimize WPT parameters, addressing the limitations of traditional manual parameter selection methods. By incorporating a Multi-Head Attention Gated Recurrent Unit (MHA-GRU) network, the system achieves superior temporal feature learning and fault pattern recognition. Through intelligent parameter optimization and advanced feature extraction, the LLM component intelligently selects optimal wavelet decomposition levels and frequency bands, while the MHA-GRU network processes the extracted features for accurate fault classification. Experimental results on a high-capacity synchronous condenser demonstrate the framework’s effectiveness in detecting rotor, air-gap, and stator faults across diverse operational conditions. The system maintains efficient real-time processing capabilities while significantly reducing false alarm rates compared to conventional methods. This comprehensive approach to fault prediction and diagnosis represents a significant advancement in synchronous condenser fault prediction, offering improved accuracy, reduced processing time, and enhanced reliability for UHVDC transmission system maintenance. 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

To achieve the goals of carbon peaking and carbon neutrality, the retrofitting of existing coal-fired power plants is crucial to achieving energy-saving and emission reduction goals. A conventional recovery system of waste heat typically occurs downstream of the air preheater, where the energy quality in flue gas is low, resulting in limited coal-saving benefits. This study proposes a scheme involving a flue gas exchanger bypassing the air preheater and low-temperature economizers, which is used to transfer the waste heat from flue gas to primary and secondary air (System I). Additionally, a heat pump can be introduced to provide supplementary energy for primary and secondary air, as well as the condensate from the steam turbine (System II). The coal consumption rate and exergy efficiency are used to evaluate the two schemes. The results show that both waste heat recovery systems can increase the power output of the coal-fired unit by recovering waste heat. System II can boost power output by approximately 13.98 MW. The power increase in both waste heat recovery systems show a declining trend as the unit load decreases. This increased power is primarily attributed to the medium- and low-pressure cylinders, while the contributions from ultra-high-pressure and high-pressure cylinders are negligible. The increased power output for the medium-pressure cylinder ranges from approximately 3.49 to 3.58 MW, while the low-pressure cylinder has an increased power output of around 10.10 to 10.19 MW. The coal consumption rate is decreased from 250.3 g/(kW·h) to 247.5 g/(kW·h) under a full load condition for both systems, which can be augmented at lower load conditions. System II outperforms System I at 30% load condition, achieving a reduced coal consumption rate of 3.36 g/(kW·h). System I has an exergy efficiency of 40%, while System II shows a higher efficiency of 44%. Full article

The implementation of energy-saving measures has a substantial and beneficial impact on the preservation of energy resources as well as the reduction of carbon dioxide emissions. This study focuses on the design and experimental analysis of a water-to-air heat recovery system aimed at capturing waste heat from wastewater and transferring it to a fresh cold air stream using heat pipe technology. The research problem addressed in this study is the efficient recovery of low-grade thermal energy from wastewater, which is often underutilized. The prototype heat recovery unit was designed, manufactured, and tested in the laboratory to assess its performance across various operating conditions. The experimental setup included a system where the primary agent, hot water, was heated to 60 °C and circulated through the evaporator section of the heat recovery unit, while the secondary agent, fresh air, was forced through the condenser section. The system’s performance was evaluated under different air velocities, ranging from 3.5 m/s to 4.5 m/s, corresponding to airflow rates of 207.1 m³/h and 268.6 m³/h, respectively. The study employed analytical methods alongside empirical testing to determine the effectiveness of the heat recovery system, with the global heat transfer coefficient calculated for different scenarios. The efficiency of the system varied between 25% and 51.6%, depending on the temperature and speed of the fresh air stream. The most significant temperature difference observed between the inflow and outflow of the fresh air stream was 16.8 °C, resulting in a thermal output of 1553 W. Additionally, the average (mean) overall heat transfer coefficient of the unit was calculated to be 49 W/m² K, which aligns with values reported in the literature for similar systems. The results demonstrate the potential of the designed system for practical applications in energy conservation and carbon emission reduction. Full article

Indirect evaporative coolers (IECs) use the latent heat of water evaporation to cool air. This system has the advantage of operating at low power without a compressor and does not increase the absolute humidity of the air. However, an IEC is difficult to use on its own because its cooling capacity is limited by the theoretical constraint of the wet-bulb temperature of the ambient air. Therefore, an air conditioning unit (ACU) was integrated with an IEC and experimentally evaluated in this study. The dry and wet channels of the IEC were integrated with an ACU evaporator and a condenser, unlike previous studies where IECs were integrated solely with either an evaporator or a condenser. This reduced the cooling load on the evaporator and helped the condenser to dissipate heat to improve the performance of the existing ACU. In addition, the IEC was equipped with baffles to improve its performance. To assess the extent of the performance improvement due to integration with the IEC, comparisons were also performed under the same experimental conditions with an ACU only. The results showed that under conditions with an indoor temperature of 32 °C, integrating the IEC with the ACU increased the average cooling capacity by 13.1% and decreased the average power consumption by 8.60% during the test period, compared to using only the ACU. Consequently, the average coefficient of performance (COP) increased by 19.5% compared to using only the ACU under the same conditions. Full article

Mist spraying is a technique for locally lowering air temperature by spraying fine mist into the air and using the latent heat of evaporation immediately after spraying. This study focuses on the conditions under which mist spraying contributes to the increase in sensible heat release from the human body, using the ratio of air temperature decrease and humidity increase in the space where mist is sprayed. From the measurement results in front of the air-conditioning condenser unit, humidity increased by about 10 g/kg(DA), while air temperature decreased by about 10 °C. From the measurement results in an open space in a park, air temperature decreased by about 0.5 to 1 °C within 2 m of the mist spray and humidity increased by about 0.5 to 1 g/kg(DA) at the height of the mist spray, regardless of the distance from the mist spray. From the measurement results at semi-open bus stops, air temperature decreased slightly to 1 °C and humidity increased slightly to 1 g/kg(DA) under low-wind conditions. Unfortunately, the measured results of air temperature decrease in relation to humidity increase, which the human body perceives as cooler, were not available. Full article

This study documents results from a series of field experiments on the creation of artificial updrafts and convective clouds at a test site in the United Arab Emirates (UAE). The proposed method incorporates a vertically directed jet from an aircraft turbojet engine saturated with active hygroscopic aerosols for the purpose of energetically feeding the jet with water vapor condensation heat below cloud base level. This paper presents the description and main characteristics of the experimental equipment, methodology of experiments and atmospheric conditions, analysis of the obtained results, and prospects for further development of the proposed method. On the whole, the experiments showed that under the conditions of low air humidity, typical for the UAE, and the slowness of the condensation process, the replenishment of the jet energy by the heat of condensation is too small, and the power of the used jet engine in the experiments is insufficient to overcome surface temperature inversions, horizontal winds, and initiation of deep convection. Nevertheless, the results of field experiments and numerical simulation made it possible to outline promising directions for further research on improving the considered method for creating artificial clouds and precipitation. Full article

The paper focuses on water losses in the turbine condenser cooling system of the 905 MW power unit in Opole Power Plant (Opole Poland). The evaporative and drift losses are determined for various operating and atmospheric conditions. The drift loss is found to be 0.125–0.375% of the cooling water flux and some increase in this loss is noticed with increase in unit power and ambient temperature. The studies have shown that the presence of wind increases the total water loss related to the power generated by the power unit. This effect is analysed for selected constant air temperature values T_amb. The increase of the cooling water loss stream, related to the power of the unit, is at the level of 14.8% for T_amb equal to 7 °C, 23% for 15 °C, and approximately 10% at 22 °C. These increases are related to the level of losses in almost no wind conditions. It is investigated how the change in the cooling water flux affects the power unit operation and the amount of water loss. For the power unit under consideration, the reduction of the cooling water flux from 80,000 to 60,000 ton/h raises the temperature of water behind the condenser and lowers the temperature of the cooled water t_w2 within the range of 0.75–1.5 °C, depending on the unit power and the ambient temperature. Reducing the cooling water flux in the analysed range results in an increase in condenser vapour pressure, within 0.5 kPa at T_amb = 25 °C. This increase is lower at lower ambient temperatures. Within the range of variations analysed, the effect of cooling water flux on evaporative losses is negligibly small. The increase in condenser steam pressure significantly affects the power generated by the turbine generator unit. The calculations show that it is possible to optimize the size of the cooling water flux for the analysed power unit and condenser cooling system. This optimization would allow (within a limited range of load variability) an increase in the net power generated by the power unit. Full article

In view of the main problems of the condensing heat discharge modes of the existing underground air-conditioning system, the technical scheme of using phase change heat storage modules to improve the heat storage capacity of the reservoir is proposed. By establishing a 3D flow and transient heat transfer model of the phase change reservoir, the effects of thermal property parameters, package size and arrangement of the phase change heat storage modules on the heat storage performance of the phase change reservoir were quantitatively analyzed based on three indexes: heat storage capacity per volume Δq, guaranteed efficiency coefficient η and slope of temperature rise per unit load ε. The results show that when the phase change temperature is 29 °C (23 °C increased to 33 °C) and the latent heat value is 250 kJ/kg (100 kJ/kg increased to 250 kJ/kg), Δq (110.92 MJ/m³, 112.83 MJ/m³) and η (1.22, 1.24) under both conditions are at their most, respectively, indicating that the phase change temperature should be less than 4 °C at the outlet temperature of the reservoir, and phase change materials with a high latent heat should be selected in engineering design whenever possible. When the size of the phase change module is 150 mm × 20 mm and the phase change reservoir adopts four intakes, ε (0.259, 0.244) under both conditions is the smallest, indicating that increasing the area of the phase change heat storage module and the fluid and increasing the inlet disturbance of the reservoir can enhance its heat storage capacity. Full article

This paper discusses recycled non-potable water (NPW) quality test results from an existing, decentralized, treated air handling unit (AHU) air conditioning (A/C) condensate water (CW) system in a medical facility case study (MFCS) in Abu Dhabi (AD), the capital city of the United Arab Emirates (UAE). The MFCS, a 364-bed hospital that opened in 2015 with 50% landscaping, is targeting 100% non-clinical/non-potable water use for landscape irrigation (LI) from 179,700 m³/year treated CW, which is a by-product of AHU A/C. For seven months per year, however, a deficit of 14,340 m³ AHU A/C CW occurs, so costly and non-sustainable, desalinated potable water is required. The proposed change project, using a mixed methodology, develops a sustainable NPW strategy, including a protocol to extract water from recycled, onsite, organic food waste, fire sprinkler pump test water (FSPTW), and reverse osmosis reject water (RORW) to meet the AHU A/C CW shortfall by adapting, enhancing, and monitoring the medical facility’s NPW treatment system. The hospital’s sustainability strategy implemented by the author could be legislated and mandated by the relevant authority for regional medical facilities, taking the form of a water conservation protocol including the classification and characterization of different types of NPW to understand their impact on LI, human health, and building water systems. The outcome is a novel change in practice to reuse 25,141 m³/year RORW and 1136 m³/year FSPTW as makeup water for the A/C CW shortfall in winter. The results identify key considerations to be addressed by the target audience (building owners, landscape contractors, and facility managers) when reusing NPW to protect the environment against soil degradation—a major aspect of decarbonization. Full article

The indirect evaporative cooler (IEC) has excellent potential to replace or improve conventional vapor compression equipment in HVAC and refrigeration applications. This could be achieved by using the M-cycle (dew-point evaporative cooling technology). This thermodynamic concept makes it possible to derive a large amount of energy from the air stream (as latent heat released during water evaporation into the working air stream) and use it for another air stream (product). Its application has also spread to other sectors, such as water desalination and distillation, power plants, or NOx reduction. This paper provides an overview of the M-cycle mainly in air conditioning (MAC, D-MAC, H-MAC) and refrigeration (MCT, M-condenser). Various integrated solutions are described, showing improved effectiveness in terms of the wet-bulb temperature and the dew point. The design features of consolidated solutions are better In terms of the flow distribution, geometry, or volume. Most of the improvements confirm the great potential of the M-cycle to increase the unit or the system efficiency due to lower energy and water consumption. Full article

A fork-type heat pipe (FHP) is a passive heat-transport and air-cooling device used to remove the decay heat of spent nuclear fuels stored in a liquid pool during a station blackout. FHPs have a unique geometrical design to resolve the significant mismatch between the convective heat transfer coefficients of the evaporator and condenser parts. The evaporator at the bottom is a single heat-exchanger tube, whereas the condenser at the top consists of multiple finned tubes to maximize the heat transfer area. In this study, the heat transfer characteristics and operating limits of an FHP device were investigated experimentally. A laboratory-scale model of an FHP was manufactured, and a series of tests were conducted while the temperature was varied to simulate a spent fuel pool. As an index of the average heat transfer performance, the loop conductance was computed from the measurement data. The results show that the loop conductance of the FHP increased with the heat transfer rate but deteriorated significantly at the operating limit. The maximum attainable heat transfer rate of the unit FHP model was accurately predicted by the existing correlations of the counter-current flow limit for a single-rod-type heat pipe. In addition, the instant heat transfer behaviors of the FHP model under different temperature conditions were examined to interpret the measured loop conductance variation and operating limit. Full article

The paper presents the results of measurements and calculations concerning the influence of weather conditions on the operation of wet cooling towers of 905 MWe units of the Opole Power Plant (Poland). The research concerned the influence of temperature and relative humidity of air, wind and power unit load on the water temperature at the outlet from the cooling tower, the level of water cooling, cooling efficiency and cooling water losses. In the cooling water loss, the evaporation loss stream and the drift loss stream were distinguished. In the analyzed operating conditions of the power unit, for example, an increase in $T_{amb}$ air by 5 °C (from $20–22°\mathrm{C}$ to $25–27°\mathrm{C}$) causes an increase in temperature at the outlet of the cooling tower by $3–4°\mathrm{C}$. The influence of air temperature and humidity on the level of water cooling $\mathsf{\Delta }{T}_w$ and cooling efficiency $\epsilon$ were also found. In the case of $\mathsf{\Delta }{T}_w$, the effect is in the order of $0.1–0.2°\mathrm{C}$ and results from the change in cooling water temperature and the heat exchange in the condenser. The ε value is influenced by air temperature and humidity, which determine the wet bulb temperature value. Within the range of power changes of the unit from $400$ to $900\mathrm{MWe}$, the evaporated water stream ${\dot{m}}_{ev}$, depending on the environmental conditions, increases from $400–600\mathrm{tons}/\mathrm{h}$ to the value of $1000–1400\mathrm{tons}/\mathrm{h}$. It was determined that in the case of the average power of the unit at the level of $576.6\mathrm{MWe}$, the average values of the evaporation and drift streams were respectively $0.78\%$ and $0.15\%$ of the cooling water stream. Using statistical methods, it was found that the influence of wind on the level of water cooling, cooling efficiency and cooling water losses was statistically significant. Full article

Heat pump systems can simultaneously produce cooling energy for space cooling in hotels, office and residential buildings and heat for desalination using membrane distillation (MD). The MD technique uses a heat input at a temperature compatible with the levels of heat pump condensers (<60 °C). A heat pump prototype coupled with an air-gap membrane distillation unit was constructed and tested. This paper presents the experimental study on a lab-scale prototype and details the two operating modes “continuous” and “controlled” simulating an air conditioning system and a food storage, respectively. The experimental results enable to analyze the performance of the prototype and the physical phenomena involved. Finally, the study shows that this system could be a promising solution to help supplying freshwater to people in hot regions of the world. Full article