Reduce Temperature Fluctuations Research Articles

Experimental study on road deicing using circulated heating produced from geothermal fluid

In this study, a ground source heat pump was employed as an energy source to perform preheating and deicing tests on asphalt pavement using hydraulic heating.The influence of different water temperature and ambient temperature on the temperature distribution of road system, energy consumption of heat pump system, energy consumption ratio between road system and heat pump system (COPsys) in preheating test was studied, and the influence of road temperature and deicing performance (qice) in deicing test was studied. The results show that during the preheating phase, increasing the water temperature from 40 °C to 50 °C resulted in COPsys drop of 46 %, and when the ambient temperature is reduced from −5 °C to −10 °C, resulted in a COPsys increase of 26 %. In the de-icing experimental, a higher critical temperature for de-icing indicates more energy stored at the surface, and greater temperature fluctuations during the melting phase indicate better ice melting effects. Lowering the ambient temperature increases the critical de-icing temperature and reduces temperature fluctuations during the melting phase. Increasing the water temperature increases the critical de-icing temperature and temperature fluctuations during the melting phase.

High reflectivity and latent heat synergetic TiO2/Cs0.33WO3-PU double-layer materials with zero transmittance

Passive Cooling Technology, as a method of achieving long-term refrigeration without the need for external energy input, has emerged as an alternative to traditional energy-intensive cooling, garnering increasing attention from academia and industry. However, current passive cooling technology faces challenges such as incomplete solar energy reflection, overcooling, and inevitable absorption of solar radiation and surrounding environmental heat. This paper presents a passive cooling bilayer film with latent heat storage capability, composed of a solid–solid phase change polyurethane (PU) matrix with added TiO2 and Cs0.33WO3.TiO2/Cs0.33WO3-PU exhibits minimal solar transmittance, with reflectance and emissivity rates of 84.46 % and 93.08 %, respectively. The solid–solid phase change matrix effectively mitigates overcooling and heat input issues, reducing temperature fluctuations and peaks, and thereby enhancing passive cooling performance. At the phase transition temperature (306 K), TiO2/Cs0.33WO3-PU achieves cooling powers of 113.77 W/m2(day time) and 173.19 W/m2(night time), the temperature can be reduced by 14.3 °C under 100 mW/cm2sunlight. Additionally, TiO2/Cs0.33WO3-PU demonstrates outstanding thermal stability and reliabitity, hydrophobicity, as well as resistance to UV aging. Moreover, it offers the flexibility to adjust the phase transition temperature and latent heat of the solid–solid phase change matrix according to specific environmental conditions. TiO2/Cs0.33WO3-PU combines passive cooling materials with phase change materials, and complements each other’s advantages. TiO2/Cs0.33WO3-PU not only improves the cooling power, but also provides a new solution to the problem of heat input and supercooling of passive cooling materials. TiO2/Cs0.33WO3-PU also provides new possibilities for the application of passive cooling materials in the fields of long-term outdoor building cooling, human heat management, food preservation and electrical equipment cooling.

Advanced thermal energy storage made of a ternary CPCM with two phase change temperatures in building walls

This paper introduces a ternary composite phase change material (CPCM) comprising three phase change materials, with a eutectic mixture as the low phase change temperature (PCT) component. The thermal performance and stability of the CPCM are rigorously evaluated through simulations and experiments including step cooling curves, differential scanning calorimetry (DSC), thermal cycling, and Fourier-transform infrared (FTIR) spectroscopy. The ternary CPCM CA/C18-TD (2.0:8.0) exhibits superior latent heat storage—224.53 J/g compared to 143.83 J/g for the binary CA-TD (3.0:7.0)—and maintains stability without supercooling after 300 thermal cycles. It also proves cost-effective compared to its components. In building applications, walls integrated with the CPCM CA/C18-TD (2.0:8.0) exhibited significantly enhanced thermal regulation properties, including longer thermal delay times and reduced attenuation factors across both winter and summer conditions. Specifically, the CPCM wall reduced temperature fluctuations by up to 31.91 % in comparison to ordinary wall and 21.63 % against single PCM wall in winter, 54.51 % and 44.22 % lower than the ordinary and single PCM walls respectively in summer. These walls also showed a remarkable reduction in heat flow density by up to 17.49 W/m2 and 5.41 W/m2 compared to ordinary wall under summer and winter conditions, respectively. This means that the CPCM has superior insulation performance and reduces susceptibility to external environmental changes. These findings confirm CA/C18-TD (2.0:8.0) as an optimal CPCM for seasonal thermal energy storage in energy-efficient PCM wall.

Parameter identification framework of thermal network model for ventilated heating floor

Due to system complexity and the inherent disturbances of building environment, identification of key parameters of thermal model of building with air-based thermally activated heating floor is challenging. In this study, a two-stage framework for identifying unknown parameters in the thermal network model of building with ventilated heating floor is proposed. Besides, two estimation methods are compared, including least square method and Bayesian inference, and the impact of input data quantity and parameter bound is also analyzed. Results show that floor ventilation can significantly reduce temperature fluctuation due to the increased space heating rate. Compared to least square method, Bayesian inference fully considers uncertainties, and can improve the accuracy. In addition, it is found that 9 days' data is accurate enough for parameter identification of this heating system.

Influence of coupling air conditioner with hybrid PCMs on building interior conditions and consumed power: Experimental investigation

Air conditioning systems are vital for modern comfort but consume a substantial portion of global energy, contributing to environmental concerns and rising energy costs. PCMs can store and release energy during phase transitions, making them promise to reduce cooling loads. This study endeavors to empirically investigate the influence of integrating hybrid Phase Change Materials (PCMs), specifically PCMSP24E and PCMSP26E, with a real vapor compression refrigeration system. The primary focus is on assessing the consequential effects on the energy consumption of the refrigeration system and the interior environmental conditions within a building, including temperature and relative humidity. The energy usage of the split air conditioner wherein the outdoor unit is attached to PCMs tube heat exchanger for precooling the incoming air is investigated. Experiments reveal that PCM precooling effectively reduces the ambient air temperature entering the air conditioning condenser, leading to substantial energy savings. Increasing the PCM quantity enhances the system performance and refrigeration unit power saving. With 11 kg of PCMs, energy consumption by the air conditioning system decreases by 10.4 %, and indoor air temperature and relative humidity reduce by 0.5° and 5 %, respectively. Hence, PCM integration ensures a more consistent indoor temperature profile, enhancing occupant comfort and reducing temperature fluctuations.

Real-world implementation of a cloud-based MPC for HVAC control in educational buildings

In their quest to enhance energy efficiency and carbon footprint management, many enterprises are turning their attention towards optimizing their facilities through amplified data monitoring and innovative control methods. In this context, this research highlights a practical solution in a commercial building located in the United States. It explains the creation, implementation, and costs of a universally applicable model predictive control (MPC) framework for the building’s heating, ventilation, and air conditioning (HVAC) system. The paper elaborates on both the hardware and software used to accumulate pertinent data and the formulation of the MPC system. This approach leverages cloud-based microservices and can be seamlessly integrated into current building management systems. In this regard, this paper presents three innovative strategies: Proportional–integral (PI)+Preheating, MPC, and occupancy-based control. These scenarios were designed to improve energy efficiency and thermal comfort significantly by reducing temperature fluctuations and adhering more closely to the setpoint temperature. The implementation of these strategies resulted in substantial energy savings, with reductions in energy consumption of 12.83%, 19.21%, and 14.98%, respectively.

Microclimate modulation: An overlooked mechanism influencing the impact of plant diversity on ecosystem functioning.

Changes in climate and biodiversity are widely recognized as primary global change drivers of ecosystem structure and functioning, also affecting ecosystem services provided to human populations. Increasing plant diversity not only enhances ecosystem functioning and stability but also mitigates climate change effects and buffers extreme weather conditions, yet the underlying mechanisms remain largely unclear. Recent studies have shown that plant diversity can mitigate climate change (e.g. reduce temperature fluctuations or drought through microclimatic effects) in different compartments of the focal ecosystem, which as such may contribute to the effect of plant diversity on ecosystem properties and functioning. However, these potential plant diversity-induced microclimate effects are not sufficiently understood. Here, we explored the consequences of climate modulation through microclimate modification by plant diversity for ecosystem functioning as a potential mechanism contributing to the widely documented biodiversity-ecosystem functioning (BEF) relationships, using a combination of theoretical and simulation approaches. We focused on a diverse set of response variables at various levels of integration ranging from ecosystem-level carbon exchange to soil enzyme activity, including population dynamics and the activity of specific organisms. Here, we demonstrated that a vegetation layer composed of many plant species has the potential to influence ecosystem functioning and stability through the modification of microclimatic conditions, thus mitigating the negative impacts of climate extremes on ecosystem functioning. Integrating microclimatic processes (e.g. temperature, humidity and light modulation) as a mechanism contributing to the BEF relationships is a promising avenue to improve our understanding of the effects of climate change on ecosystem functioning and to better predict future ecosystem structure, functioning and services. In addition, microclimate management and monitoring should be seen as a potential tool by practitioners to adapt ecosystems to climate change.

Intelligent control of electric vehicle air conditioning system based on deep reinforcement learning

The existing AC system of EVs consumes a lot of energy in summer, resulting in reduced range. Additionally, the cabin temperature (Tcabin) fluctuates due to varying driving conditions. In this paper, an innovative cooling strategy is designed to address the above drawbacks using deep reinforcement learning algorithms. The primary objective of this strategy is to achieve high-precision temperature control while concurrently minimizing the energy consumption of the AC system. The strategy combines compressor speed (Ncompressor) and blower airflow (Bairflow) control to optimize the AC system's performance. The RL controller minimizes energy consumption by reducing Ncompressor while increasing Bairflow, thus ensuring a constant cooling capacity (Q). And it effectively reduces temperature fluctuations within the cabin. Finally, the RL control strategy was compared with on/off control and proportional integral differential (PID) control. The results showed that RL control performed well in the multi-objective optimization of the AC system. In terms of temperature control, it effectively reduces the amount of overshooting, and the minimum temperature fluctuation achieved through RL control is merely 0.07 °C, exhibiting an 84.4 % and 86.5 % decrease compared to traditional control methods. The average absolute temperature error stands at 0.06–0.07℃, maintaining a remarkable precision in preserving the target temperature. Furthermore, RL control not only ensures superior energy efficiency but also reduces energy consumption by up to 5.98 % and 7.65 % compared with traditional control methods.

Enhanced Gypsum Boards with Activated Carbon Composites and Phase Change Materials for Advanced Thermal Energy Storage and Electromagnetic Interference Shielding Properties

This work presents the development of novel gypsum board composites for advanced thermal energy storage (TES) and electromagnetic interference (EMI) shielding applications. Activated carbon (AC) derived from spent coffee with a high surface area (SBET = 1372 m2/g) was used as a shape stabilizer, while the commercial paraffin, RT18HC, was used as organic encapsulant phase change material (PCM). The AC showed a remarkable encapsulation efficiency as a shape stabilizer for PCM, with ~120.9 wt% (RT18HC), while the melting enthalpy (ΔHm) of the shape-stabilized PCM was 117.3 J/g. The performance of this PCM/carbon nanocomposite as a thermal energy storage material was examined by incorporating it into building components, such as gypsum wallboards. The microstructure of these advanced panels, their density, and their dispersion of additives were examined using X-ray microtomography. Their thermal-regulated performance was measured through a self-designed room model with a similar homemade environmental chamber that was able to create a uniform temperature environment, surrounding the test room during heating and cooling. The measurements showed that the advanced panels reduce temperature fluctuations and the indoor temperature of the room model, in comparison with normal gypsum panels, by a range of 2–5%. The investigated gypsum board composite samples showed efficient electromagnetic shielding performance in a frequency range of 3.5–7.0 GHz, reaching an EMI value of ~12.5 dB, which is adequate and required for commercial applications, when filled with PCMs.

Thermal regulation capacity of a green roof in the Mediterranean climate of Istanbul

Green roofs are considered sustainable practices in the urban environment as they provide several benefits to the city and to the building such as mitigating the urban heat island effect and optimizing the energy performance of buildings. The impact of green roofs on the energy balance of urban building surfaces in warmer climates, such as the Mediterranean, is still under investigation. In this study, 5 years of experimental data recorded between 2015 and 2020 were analyzed in comparison between a non-insulated flat roof and a green roof. The aim of this study is to investigate the thermal regulation capacity of green roofs on the energy balance of buildings and their efficiency as potential UHI mitigation strategies to make cities more resilient. Results of the study demonstrated that despite the limited depth of the substrate and plant diversity, the green roof provided thermal regulation to the building by reducing temperature fluctuations and moderating temperatures for both the building and its surrounding environment. Practical application This study provides evidence that the implementation of a green roof could effectively moderate roof temperatures and reduce fluctuations, especially during the summer season. Furthermore, the study demonstrated that even a simple and shallow extensive green roof could provide thermal benefits in a Mediterranean climate. Therefore, due to its structural lower weight, this type of green roofs could be installed on existing buildings and could provide thermal benefits to the building and the city.

Characterisation of the COMFORTBOARD gypsum board for thermal energy storage in buildings

Currently, the construction sector contributes considerably to the total energy consumption and greenhouse gas emissions into the atmosphere. Thermal energy storage (TES) systems are alternatives to increase the thermal inertia of buildings, aiming to use less energy, improve thermal comfort and reduce temperature fluctuations of interior spaces. One of the possible applications in buildings is to increase their thermal mass by impregnating phase change materials (PCM) in porous construction materials, e.g., gypsum boards. In this investigation, a commercial gypsum board impregnated with PCM (Knauf Comfortboard – BASF) was investigated by carrying out a structural and thermal characterisation. The thermal response obtained agrees with the product's technical data sheet provided by the supplier. The results of the thermal characterisation show that the inclusion of PCM in the gypsum board decreased the U-value by 2 % compared to the control sample (no PCM), increased the heat storage capacity by around 45 %, improved the thermal dynamic characteristics of the material by decreasing the thermal stability coefficient from 0.92 to 0.76 and increasing the thermal lag from 0.27 to 0.49 h. Our results sustain the potential application of commercial gypsum boards with PCM under environmental conditions across a wide range of daily temperature fluctuations (e.g., The North of Chile).

Phase change materials integrated buildings: A short review

Buildings account for one-third of global energy consumption and 38% of greenhouse gas emissions. Improving a building’s energy efficiency is vital in minimizing climate change. As an alternative to active cooling systems, passive cooling methods are promising. Thermal energy storage employing latent heat is an effective passive cooling strategy for increasing a building’s thermal inertia and, in turn, reducing temperature fluctuations and improving thermal comfort for building occupants. To do this, high-density phase change materials (PCMs) for thermal energy storage (TES) can be put to good use. Recent developments in TES techniques using PCMs have gained much research focus, primarily to improve energy efficiency and promote clean energy sources. PCMs are regarded as the most promising materials due to their high energy storage density for developing high-performance and energy-efficient buildings. The primary disadvantage of PCM is its low thermal conductivity, limiting its practical usage, which could be resolved by loading nano or micro-sized conductive fillers. The investigated system’s initial findings show that they effectively lower indoor temperature changes and energy demand during winter seasons and can cause load reduction or shifting.

Experimental study on thermal performance of high absorption latent heat storage plate (LHSP) in greenhouse

Phase change material (PCM) can effectively reduce temperature fluctuations in greenhouses and increase crop yields. Plastic greenhouses are a major form of facility agriculture in southern China, and there are no walls in it. Therefore, how to combine plastic greenhouses with PCM has become research hotspot. A new type of high absorption latent heat storage plate (LHSP) was proposed. That is to lay PCM plates on the north side of the plastic greenhouse vertically. To enhance solar energy utilization and reduce heat loss, solar high absorption and thermal insulation layer were respectively placed on the sunny side and shady side. Two greenhouses were constructed and LHSP was placed in one greenhouse as Case 1. After that, a solar high absorption film and thermal insulation layer were attached to the sunny side and the shady side as Case 2 and Case 3. The average air temperature of two greenhouses and the thermal performance of LHSP were compared under three cases. Results showed that, in Case 1, the LHSP can raise the average air temperature inside the greenhouse by 1.8–2.9 °C during the night. in Case 2 and 3, the average air temperature had a stable improvement of 1.6–2.2 °C and 1.8–2.1 °C respectively at night. Besides, in Case 2, the heat storage of LHSP on sunny side had increased by 26.2%. In Case 3, the total average heat loss of LHSP was reduced by 21.5% and the average heat release from sunny side had risen by up to 39.7%. The high absorption latent heat storage plate showed excellent thermal performance.

Characteristics of photothermal transfer and biochemical reaction in up-flow direct absorption hydrogen reactor with embedded ribs

The anaerobic fermentation process of microbial community is a promising method to treat wastewater with high ammonia nitrogen, but it needs to provide suitable temperature. An innovative direct absorption anaerobic reactor was established to reduce the temperature fluctuation of biogas slurry by adding ribs to ensure the high efficiency and stability of anaerobic fermentation process. The effects of flow rate and number of ribs on gas production in the process of photothermal conversion and anaerobic fermentation were analyzed by numerical simulation. The results show that the addition of ribs can effectively reduce temperature fluctuation and increase gas production. Compared with 2269.7 mL/L gas production and temperature fluctuation of up to 8 K without ribs, the gas production increased by 863.1 mL/L and decreased to 0.1624 K when the number of ribs was 9, respectively. Simultaneously, a curve was fitted according to gas production to predict the best working conditions.

Peltier Cell Integration in Packaging Design for Minimizing Energy Consumption and Temperature Variation during Refrigerated Transport

This study proposes an innovative approach to reduce temperature fluctuations in refrigerated transport during loading and unloading, aiming to minimize food waste and optimize energy consumption in the food supply chain. The solution involves integrating Peltier cells into secondary and tertiary packaging to improve system efficiency and minimize temperature variations. Four distinct tests were conducted: a reference test, continuous Peltier system operation, and two intermittent cooling tests for the hot side of the cells. The results highlight the effectiveness of this approach, particularly in the fourth test where the average final food temperature decreased from 3.2 °C (reference test) to 2.8 °C. Integrating Peltier cells into packaging shows potential benefits in minimizing food waste, reducing energy consumption, and associated emissions during refrigerated transport. This research contributes to the sustainable design and manufacturing of packaging systems, specifically in the context of refrigerated transport. By maintaining a consistent temperature environment during the critical loading and unloading phases, incorporating Peltier cells enhances the overall performance and efficiency of refrigerated transport system. These results point out the significance of exploring innovative solutions for sustainable food preservation and the decrease of waste all along the food supply chain.

Research trends in phase change materials (PCM) for high-performance sustainable construction

In the face of escalating environmental perils driven by climate change and global warming, there is an urgent call for innovative and sustainable energy solutions, especially within the construction sector, which is a major consumer of energy and emitter of greenhouse gases. Among various energy-efficient interventions, Phase Change Materials (PCMs) have emerged as a promising technology for passive thermal regulation in buildings. This review paper delves into recent advancements in integrating PCMs within building envelopes, which serve to store thermal energy, thus reducing temperature fluctuations and enhancing indoor comfort levels. The study also underscores the increasing global demand for energy storage systems in pursuit of a low-carbon economy and how PCMs can address this imperative. A special focus is given to applications of PCMs in diverse climatic zones, and the paper offers insights into the thermo-physical properties that make them amenable for building integration. Furthermore, the paper reveals that paraffin wax is the most extensively used PCM and discusses the relevance of selecting PCMs based on their melting points, which is pivotal for optimizing heat transfer efficiency. This study also highlights the need for extensive real-world, full-scale evaluations of PCMs, and the importance of scrutinizing their impact on the mechanical properties of building materials. The lifecycle and cost analyses of PCM integration, which are often overlooked, are identified as crucial areas for further research. Through a comprehensive review of global applications and experimental findings, this paper accentuates the potential of PCMs in revolutionizing building energy efficiency, cooling-heating systems, and integration in concrete, mortar, walls, and solar energy applications while also calling for continued research into performance enhancement and understanding potential drawbacks. This underscores the pivotal role of PCMs in steering the construction industry towards sustainability and energy conservation.

Measurement performance evaluation and noise compensation for a Fourier transform infrared–based pyrometer

The Fourier transform infrared (FTIR) spectrometer is widely used for spectrum analysis and radiation intensity measurement. In this work, a pyrometer with the temperature measurement range of 800°C to 1200°C is developed based on the FTIR spectrometer, and the calibration of the instrument coefficients using a standard radiation source is performed. On this basis, the readout noise and shot noise in the spectral signal are analyzed, and a detailed quantitative evaluation of the influences of two kinds of noise on the temperature measurement accuracy is also carried out in this work. Experimental results show that the temperature deviation caused by the two kinds of noise is less than 1°C when the wavelength is within the range of 2.0 to 5.4 μm. However, when the wavelength is greater than 5.4 μm, the maximum temperature deviation caused by the readout noise and shot noise can reach about 12°C and 18°C, respectively. In view of this, a Kalman filter method is introduced in this work to reduce temperature fluctuations caused by these noises, where the maximum fluctuation can be reduced from 83.9°C to 6.1°C with this filter method. These experimental results can provide a valuable guidance for the general-purpose calibration and assessment of the FTIR-based pyrometer.

Cooling characteristics of a nitrogen micromachined Joule-Thomson cooler operating from 88.5 K to 295 K

Thermal management is critical in keeping electronic devices operating below their reliable temperature limits. One promising approach is to use vibration-free micromachined Joule-Thomson (JT) coolers that reduce temperature fluctuations in electronic devices. In this study, we systematically examine the cooling power provided by a micromachined JT cooler with dimensions of 60.0 × 9.5 × 1.3 mm3 using nitrogen. A heated silicon chip was attached to the JT cooler to simulate a microelectronic device producing heat load. The cooling power depending on cooling temperature with different insulation conditions and high pressures have been measured. Applying a high pressure of 11.1 MPa and a low pressure of 0.24 MPa, the cooler could cool down from a room temperature of 295 K to 88.5 K in 30 min. A general method is introduced to evaluate the cooling performance of a micromachined JT cooler. The relationship between the cooling performance and the allowed heat load is discussed. It is shown that the potential applications of micromachined JT coolers can be greatly expanded by increasing the high pressure of nitrogen and improving insulation conditions.

Improving LEED-certified building loads on borehole heat exchangers by coupling subsurface variables

To evaluate the performance of a ground source heat pump (GSHP) system, it is necessary to assess the subsurface thermal regimen around the borehole heat exchanger (BHE). This paper presented the preliminary results of an analysis of a newly constructed GSHP system for the Campus Instructional Facility at the University of Illinois at Urbana-Champaign, which will be a Platinum-level Leadership in Energy and Environmental Design (LEED)-certified building. Energy modeling of the entire building was performed in DesignBuilder software by considering all the high-efficiency thermal-insulated building subsystems. A numerical model for a single BHE constructed in a heterogeneous interlayered geology was first validated with data from a distributed thermal response test. The numerical model was then used to simulate the ground thermal response over both the short term (1 to 3 months) and long term (1 year). The geological and hydrological impacts and the benefits of the LEED-certified building load were evaluated. The results showed that under the fixed length of the BHE, the modest heating and cooling demand of the Campus Instructional Facility would result in reduced temperature fluctuations in the U-bend pipe at the outflow, by a maximum 8.91 °C, and would raise the coefficient of performance of the heat pump by 26.8 % when operating in extreme weather conditions and 7.4 % during July. The presence of an external heat source underground—a segment of the campus steam tunnel—raised the local ground temperature by 1.99 °C, providing slightly improvement in the performance of the BHE during the heating season and a similar drop in performance during the cooling season. This study validated the insignificance of the local groundwater velocity (2.07 × 10-7 m/s) on the thermal behavior of the BHE. The proposed model setup and simplifications could be applied to a large-scale borefield analysis at any site within a similar geological context. The proven enhanced efficiency of the BHE may also facilitate future implementation of GSHPs in green buildings.

Effect of water content in the composition of an extensive green roof on the temperature regime

Green roofs are becoming an increasingly fast-growing technology in the construction industry to eliminate the manifestations of massive urban development. Bringing natural vegetation back to cities has beneficial effects not only on natural biodiversity and the inhabitants themselves. It also has a beneficial effect on the surrounding climate and affects the building itself. Due to its evapotranspiration capacity, vegetation mitigates temperature fluctuations and eliminates the urban heat island phenomenon. To function properly, vegetated structures must have an optimum water supply, especially during summer. Several studies have shown that the absence of water, especially for extensive roofs, significantly impacts the proper functioning of such structures. The presence of water in the substrate promotes the formation of evaporation, cools the surrounding air and reduces temperature fluctuations at the waterproofing level. This article highlights the impact of irrigation of extensive vegetated roofs during summer days.