Thermal Capacity Research Articles

In-situ construction of chitosan@tannin structure on bamboo fiber for green and convenient reinforcement of poly(3-hydroxybutyrate) biocomposite

Fiber-reinforced biocomposites were widely considered as the optimal sustainable alternative to traditional petroleum-based polymers due to their renewable, degradable, and environmentally friendly characteristics, along with economic benefits. However, the poor interfacial bonding between the matrix and natural fiber reinforcement remained a key issue limiting their mechanical and thermal properties. Focusing on cost-effective, convenient, and low-pollution chemical methods, this work proposed a strategy for in-situ synthesis of composite structures on bamboo fiber (BF) surfaces. Crude chitosan (CS) and reclaimed tannic acid (TA) were utilized as the raw materials, to construct stereo-netlike chitosan @ tannin structures (CS@TA) via a one-pot method facilitated by hydrogen bonding and complexation. The influence of reactant concentration and pH value on the process was further investigated and optimized. The CS@TA structure improved the interfacial bonding between the BF reinforcement and matrix poly(3-hydroxybutyrate) (PHB), and this non-amino-driven construction provided a potential reaction platform for functionalizing the interfacial layer. The modified biocomposite showed improvements in tensile and impact strengths (51.58 %, 41.18 %), also in tensile and flexural moduli (13.59 %, 26.88 %). Enhancements were also observed in thermal properties and heat capacity. This work presents a simple and promising approach to increase biocomposite interface bonding.

Design of an injera baking system using parabolic trough solar collectors at Mekelle University cafeteria

Injera baking poses a significant energy demand and strain on the national grid, requiring temperatures of 180–220 °C with traditional clay Mitads. This study aimed to design a solar thermal system to replace electrical baking energy at the Mekelle University student cafeteria. The system, designed for baking 11,000 Injera within a 6-h daily operation, comprises 92 Anodized aluminum plate Mitads heated by hot oil from an oil gallery, stored in a hot oil storage unit, and recharged via a parabolic trough solar collector. A heat exchanger and thermal storage system ensure efficient heat transfer and storage. Computational Fluid Dynamics (CFD) and Soltrace analyses were conducted to assess temperature distribution on the baking pan and oil gallery surfaces, as well as solar thermal heat flux. Results revealed a heating capacity of 2.11 kW per Mitad, meeting the required capacity, and a system energy consumption of 1216.5 MJ per hour, achieving a thermal efficiency of 57.4 %. Baking Injera at higher temperatures, enabled by a uniform temperature distribution, yielded uniformly textured Injera with an optimal number of eye bubbles and prevented sticking to the Mitad. Consequently, this design offers a viable alternative for the energy-intensive application at the Mekelle University student cafeteria, providing valuable insights for future solar thermal Injera baking system designers.

Thermal regulation potential of urban green spaces in a changing climate: Winter insights

Global warming affects both summer and winter temperatures, altering the ecological and social dynamics of urban green spaces not only during the summer months but also during the winter. Strategies to mitigate climate change impacts often emphasize increasing urban vegetation cover, but the effectiveness of these green spaces in regulating the local microclimate depends on various factors, including the vegetation structure. These effects remain largely underexplored during the winter season. To investigate the thermal regulation capacity of urban green spaces we measured air temperature and humidity in 36 parks with different sizes and vegetation structures in Munich, Germany, in their non-green surroundings, as well as in a nearby forest during the 2022–23 winter. We then analyzed the relationship between the local microclimatic differences and the vegetation structure derived from mobile laser scans. In comparison with the nearby forest, we measured a winter urban heat island effect of 1.8 °C in Munich. The urban microclimates in winter were mainly influenced by the urban landscape of Munich, namely the distance to the city center with increasing air temperature closer to the center. Urban green spaces in Munich provided small but consistent local cooling and humidifying effects throughout the winter. These cooling effects largely depended on the green space size but partially also on the vegetation structure. We found a significant relationship between the microclimatic difference, the vegetation density, and the vertical homogeneity of vegetation. The canopy cover, however, could not significantly predict the cooling effect in winter. We conclude that increasing the structural complexity of urban green spaces through management decisions could improve their cooling effect and ecological value, even during winter months. To maximize the ecological and climatic benefits of urban green spaces, a nuanced understanding and management of urban microclimates is needed across all seasons.

Dynamic modeling and defrost optimization for air source heat pumps: A deep learning and autoregression approach

Air source heat pumps (ASHPs) are celebrated for their exceptional energy efficiency and their capacity to curtail greenhouse gas emissions. However, a critical challenge in ASHPs research is the effective and accurate management of the defrosting process to preserve peak performance. The development of robust and precise simulation models is crucial yet complex for formulating and assessing defrosting strategies. To address this, our study investigates the integration of deep learning models with feature encoding to establish dynamic models for ASHPs. We evaluated various deep learning architectures, achieving a Mean Absolute Percentage Error (MAPE) of 3.5% in heating capacity predictions. Moreover, our analysis reveals that feature encoding substantially lowers the MAPE by 12%, thereby enhancing model accuracy. We employed a comprehensive suite of evaluation metrics to benchmark the performance across models, finding that the Temporal Convolutional Network (TCN) marginally surpasses others, including Transformer, LSTM, and LightGBM models. Additionally, we utilized transfer learning to boost the generalization capabilities models across different outdoor conditions (temperature and humidity), facilitating effective few-shot training. Finally, our study introduces a novel defrosting control strategy based on Heating Capacity Degradation (HCD). Using dynamic modeling, we determined optimal control thresholds (89%-94%) that ensure maximum heating efficiency during frosting conditions. This strategy improves the average heating capacity by 101-278 W compared to conventional defrosting methods. The insights from this research not only advance defrosting control but also serve as a valuable reference for dynamic modeling and control optimization in the heat pump sector. The proposed control method enhances ASHPs performance and energy efficiency, supporting efforts towards achieving carbon neutrality.

Synthesis and characterization of octahedron and cube shape Mn0.5Zn0.5Fe2O4 particle dispersion for magnetic fluid hyperthermia

The present work reports a synthesis of octahedron (A55NO) and cube-shaped (A55NC) Mn0.5Zn0.5Fe2O4 ferrite nanoparticle dispersion in distilled water. The crystal structure analyzed using powder X-ray diffraction (XRD) shows the crystallite sizes of 17.7 ± 0.4 nm and 11.9 ± 1.0 nm, respectively, for the A55NO and A55NC particles. The morphology as seen from transmission electron microscopy (TEM) confirms 17.8 ± 0.3 nm (σ = 0.27) and 8.7 ± 0.3 nm (σ = 0.33) edge lengths, respectively, for octahedron and cube-shaped particles. The thermogravimetric analyzer (TGA) and Fourier transform infrared (FTIR) spectroscopy are used to confirm the chemical binding of the surfactant with a sharp transition at 208.67 °C and 218.32 °C, respectively, for octahedron and cube-shaped particles, indicating the removal of the surfactant due to its decomposition from the particle surface. Both the particles are highly magnetic and have 75.32 Am2/kg and 72.93 Am2/kg saturation magnetization, as revealed by their M − H loops using a vibrating sample magnetometer (VSM). The stability of the sample is confirmed using the particle size analyzer (DLS) and the Zeta potential analyzer. The induction heating capacity of the fluid was investigated using the Embrell Easy Heat model LA6310 at 330 kHz. The heating response shows that even a minimum concentration of 1 mg/mL is sufficient to achieve the hyperthermic window temperature of 42 °C for both samples, which, unlike the same composition prepared by other routes, makes it impossible to go beyond 38 °C. Moreover, octahedron particle dispersion can reach this window temperature within 10 min, whereas cube particle dispersion requires only 15 min. The findings of this study hold significant practical value since it confirms that Mn0.5Zn0.5Fe2O4 composition with tuneable shape has the potential to work as a temperature-controlled magnetic switch for magnetic fluid hyperthermia under the defined safety limit with the minimum concentration.

Thermally enhanced flexible phase change materials for thermal energy conversion and management of wearable electronics

The developing trend of miniaturization and integration for electronics imposes challenges of efficient heat dissipation technology, where novel materials with advanced thermal energy conversion and management are urgently needed. In this work, we propose an emerging phase change material (PCM) system with polyvinyl alcohol/expanded graphite network loading paraffin wax (PE-PW), which exhibits superb flexibility, thermal energy storage capacity and thermal conductivity. The phase change enthalpy is from 115.61 J/g to 168.93 J/g without any leakage, which can be maintained even after 500 thermal cycles. The thermal conductivity can reach 1.46 W/mK, 484% enhanced compared with that of pure PCM. Meanwhile, the thermal management test indicates that the PE-PW composites can quickly absorb and store the generated heat to achieve temperature control, thus protecting the system from overheating and indicating excellent thermal management capacity. This flexible PE-PW system has broad application prospects in the field of thermal energy conversion and management for wearable electronics.

Enhancing structural strength and water retention of crosslinked polyacrylamide gel with the T-ZnOw

Crosslinked polyacrylamide gel serves as an effective plugging material, crucial for preventing water/gas channeling in reservoirs and enhancing the swept volume and oil recovery. However, its practical application encounters a significant challenge in maintaining long-term stability of strength and volume, particularly under high temperatures. This study investigates the reinforcement of polyacrylamide gel with three-dimensional (3D) nanomaterials, specifically tetra-needle-like zinc oxide whiskers (T-ZnOw), to enhance its structural stability and bound water content. The stress sweep tests showed that the addition of 0.15 wt% T-ZnOw increased the maximum elastic modulus of the gel to 28.5 Pa, representing a 51.2 % improvement compared to before the addition. After 60 days of high-temperature aging at 130 °C, the T-ZnOw strengthened gel still maintained an elastic modulus of 21.8 Pa. With increasing T-ZnOw concentration, the yield point of the gel increased from 4.74 Pa to 9.57 Pa, the anti-deformation of the gel has significantly increased. The stability test results in high salinity water indicate that at a salinity of 150,000 mg/L, the dehydration rate of the strengthened gel is less than 5 %, with an elastic modulus retention rate exceeding 88 %. Furthermore, thermodynamic testing confirms the enhanced thermal degradation resistance and water retention capacity of the gel. Under reservoir temperature conditions, the T-ZnOw strengthened gel exhibits a weight loss of less than 3 %. Additionally, the inclusion of T-ZnOw results in an increase in the bound water capacity index from 4.65 to 12.28. In conclusion, the integration of T-ZnOw into the polyacrylamide gel network not only enhances its mechanical performance and water retention under high-temperature conditions but also demonstrates superior stability in high-salinity environments. This innovative material shows significant potential for improving oil recovery rates in high-temperature reservoirs and can be applied to other high-temperature underground scenarios such as geothermal development and CO2 utilization and storage.

Structural-phase state and properties of heat and wear resistant cast irons of Cr–Mn–Ni–Ti system additionally alloyed with Al and Nb

The paper presents the data on phase composition and structure forming for the alloys, on distribution of elements among the alloy structural components, on variation of wear resistance, scale resistance, growing stability and mechanical properties of cast iron of Cr–Mn–Ni–Ti–Al–Nb system depending on different aluminium and niobium content and thermal ac-cumulating capacity of a casting mould. Complex carbides (Nb, Ti)C are forming in white cast iron during niobium alloying. Quantitative metallographic analysis of (Nb, Ti)C carbides and (Cr, Fe, Mn)7C3 complex carbides was carried out on the samples with examined composition. Aluminium provides favourable influence on forming of the thin protective spinel-type films with minimal amount of defects; diffusion through such oxide film is very difficult. Joint alloying by aluminium and niobium leads to simultaneous increase of heat resistance and wear resistance. Wear resistance increased as a result of enlargement of the part of primary carbides (Nb, Ti)C with high hardness in the structure of cast iron. Composition of oxide films includes aluminium, which strengthens their protective properties and rises of the alloy scale resistance. It is found for the first time that niobium doping leads to secondary solidification during cooling in the casting mold. Dispersion particles of М7С3 carbides are forming in solid state, thereby no structure degradation occurs during testing at increased temperatures, and growing stability rises. On the basis of the complex of the conducted researches the rational composition of heat and wear resistant cast iron is offered at the following ratio of components, wt. %: 2.1–2.2 C; 4.5–5.0 Mn; 18.0–19.0 Cr; 1.0–1.2 Ni; 0.4–0.6 Ti, 2.0 Nb; 2.0 Al. Wear resistance increased 1.2 times compared to cast irons before the introduction of aluminum and niobium, and scale resistance – 2.4–4.5 times depending on the type of casting mold, the index of growth resistance is equal to zero for cast irons cast in dry SLM

Comprehensive performance analysis and optimization for PEMFC-heat pump combined system considering dual heat source

Traditional proton exchange membrane fuel cell (PEMFC) systems face the challenges of strong thermal–electrical coupling and insufficient heating capacity. This study proposes a PEMFC–heat pump combined system considering dual heat source, which effectively utilizes fuel cell waste heat and environmental heat to achieve significant improvements in thermal–electrical decoupling and heating capacity. Energy, economic, and environmental analysis models were established, and the effects of key parameters on the combined system were systematically analyzed, followed by multi-objective optimization. Results show that the PEMFC current density has the largest effect on the heating capacity, while the heat flow ratio exerts the strongest influence on economic performance. The minimum pollutant emissions are achieved when wind power is adopted for hydrogen production. Under an ambient temperature of 248.15 K, the combined system increases the heating capacity by 12.8 % and reduces the levelized cost of energy and greenhouse gas emissions by 7.85 % and 15.9 %, respectively. The optimal solution presents a strong nonlinear relationship with the PEMFC current density and condenser undercooling, the heat flow ratio is close to the upper limit (0.99), and the operating temperature is close to the lower limit (333.4 K). These findings provide innovative thermoelectric decoupling and efficient energy supply solutions for PEMFC systems and have important implications for accelerating the low-carbon transition of regional energy systems.

A study of capacity demands for heat pumps intermittent heating of China’s residences

Heat pump heating is one of the most promising solutions for transitioning residential heating in China’s cold regions, as well as hot summer and cold winter regions from centralized, continuous heating to decentralized, intermittent heating, promoting low-carbon transformation. However, the fundamental issue of the actual capacity requirements for heat pumps in intermittent heating has not yet been addressed. In view of this, this study developed a numerical model that considers the dynamic coupling characteristics between the heat pump and the building environment. Using the model, the worst startup conditions for heat pumps in intermittent heating, actual heat pump capacity demands, and the differences in capacity compared to continuous heating mode for residential buildings in 230 Chinese cities are analyzed. The findings revealed an exponential relationship between intermittent heating capacity demands and time constraints, as well as a linear relationship with heating temperature. Specifically, the impact of the set temperature on capacity demands in cold regions and hot summer and cold winter regions is 22.8 W/(m2·°C) and 32 W/(m2·°C), respectively. These findings provide insights into the planning and design of future intermittent heating renovation projects in China.

Thermal Behaviour of Hydrofugated Plaster Block Masonry with Variation of Coating Thickness

The objective of this research is to analyze the influence of ceramic coating, simulating the external side, and plaster with different thicknesses, simulating the internal side of a prototype of solid water-repellent gypsum block masonry, aiming to improve the thermal performance mainly in the settlement joints of the block. For this purpose, two specific test methods were used: thermal camera and infrared thermography. The temperature differences between the internal and external faces were analyzed by means of thermocouples connected in the middle of the prototype and the mapping of the temperature profile on the surface of the cladding. It was found that the addition of gypsum sheathing plus ceramic improves the thermal performance of the masonry system, observing that the variation of the thickness of the gypsum mortar provides a gain in thermal resistance, a reduction in thermal transmittance and an increase in thermal capacity.

Investigation on saturated vapor and two-phase refrigerant injection in the rotary compressor for the extreme hot and cold conditions

Vapor injection has been widely applied in the rotary compressor to improve the heating capacity and reduce the discharge temperature in the cold condition. However, under the evaporation temperature below −20 °C or the condensation temperature above 60 °C, the discharge temperature is still relatively high, which limits compressor performance and its continuous operation time. To keep the optimal performance and further reduce discharge temperature, this paper focuses on the two-phase refrigerant injection and proposes a mathematical method to investigate the effect of injection vapor quality on the compressor performance. Based on the proposed method, some performance parameters including cooling capacity, heating capacity, EER(COP), power, discharge mass flow rate and discharge temperature have been calculated and an experiment is conducted to test these performance parameters. The calculation errors between calculated and tested results are within 4% and it indicates that the proposed method is accurate to investigate saturated vapor and two-phase refrigerant injection characteristics. The simulated results show that the use of two-phase refrigerant injection results in the trade of a slight drop in cooling capacity, heating capacity and EER(COP) for a large drop in discharge temperature, which is valuable and meaningful for engineering application under the extreme hot and cold conditions.

A comparison of the physicochemical properties, allergenicity, and stability of recombinant β-lactoglobulin: Development of standard bovine milk allergens

Bovine milk is one of the eight major allergenic foods identified by WHO/FAO, and β-lactoglobulin (BLG) is the primary allergen. Allergen standardization is very important for the diagnosis of milk allergy, and recombinant protein preparation is a promising method. In this study, BLG with high soluble expression was prepared by a method based on Escherichia coli. To verify the feasibility of recombinant BLG, the difference in physicochemical properties, allergenicity, and stability were investigated. Recombinant and natural BLG both had a size of approximately 230 nm with a zeta potential of −50 mV, indicating that they share the similar solubility and colloidal properties. Additionally, allergic mice model results confirmed that recombinant BLG showed comparable ability in stimulating antibody production, Th2 cytokine release, and cellular immunity compared with natural BLG. Then, the thermal stability of BLG was studied using spectrum analysis within the range of 25–85 °C. Recombinant BLG showed satisfactory thermal stability, the concentration, protein structure and IgG binding capacity changed obviously until temperature reached at 55 °C, although natural BLG is more heat resistant. After 28 days storage at 4 °C in the form of lyophilized powder, there was no significant change in the content of recombinant and natural BLG. In summary, the physicochemical properties, allergenicity, and stability of recombinant BLG were comparable to those of natural BLG. This study provides theoretical reference for the development of standard bovine allergen, and it is expected that recombinant allergen can be used in the research and diagnosis of bovine milk allergy.

Flexibility exploitation in Net-Zero Energy Factories. A technical and economic study case for dairy systems located in Central and South Europe

The decarbonization of energy systems (electric, thermal, gas, and transportation) requires flexibility to integrate power generated by volatile and renewable energy sources (vRES). Industrial systems can contribute to exploiting the flexibility needed to integrate the electricity generated by vRES into energy systems. Designing industrial systems as Net-Zero Energy Factories (NZEF) offers the possibility of exploiting the flexibility that could be used internally to integrate the power generated by renewable energy sources. This study addresses, on one hand, the presentation of a methodology to identify and quantify the flexibility potential of continuous processes typical in dairy systems. On the other hand, it aims to demonstrate a methodology for designing additional flexibility options to operate dairy systems as NZEF. A model has been developed in which the energetic and material flows of conventional diary systems are simulated. The model allows for the design of conventional dairy systems as NZEF and the evaluation of their potential to exploit flexibility. Two different European climate zones have been investigated: Bari (Italy) and Magdeburg (Germany). This study is relevant for designers and facility managers who are following their decarbonization plans, aiming to operate their industrial facility as Net-Zero Energy. The results of this study show that for dairy systems designed as Net-Zero Energy Factories and located in southern Europe (Bari, Italy), the operational costs are much lower than those operating in central Europe (Magdeburg, Germany). Specifically, integrating an 800 kW PV system reduced operational costs by 16.3 % in Bari, compared to 3.8 % in Magdeburg. Additionally, achieving 97 % vRES integration in Bari requires a 1000 kWh thermal storage capacity, whereas in Magdeburg, a 500 kWh capacity is sufficient. These findings suggest that NZEF designs can be optimized based on regional climatic conditions to maximize cost efficiency and vRES integration. The analysis indicates that sensible heat storage systems should be preferred over electrochemical batteries when designing additional flexibility options, considering both technical and economic criteria.

Study on performance of a multi-heat source heat pump coupled energy storage system for plant factory heating system

CO2 air source heat pump (CASHP) faces challenges of performance degradation caused by the high return water temperature and the low ambient temperature for building heating. This study proposed a novel multi-heat source heat pump system (MHSHP) that combined with a CO2 air source heat pumps (CASHP) and ground source heat pumps (GSHP) with the implementation of a thermal storage tank. The performance and CO2 emissions of both CASHP and MHSHP systems were investigated by applying a plant factory located in Beijing, China. The effects of user-side parameters and ambient temperature were explored with the storage water temperatures ranging from 20 °C to 40 °C. The results demonstrated that the heating performance of the CASHP improved with an increase of user water flow rate and ambient temperatures, while it decreased as the storage water temperature increased. At the flow rate of 1.1 m3/h, the increase of the compressor frequency from 40 Hz to 60 Hz led to a significant improvement in heating capacity by 53.3 %, and a reduction in COP by 23.3 %. When the user-side water flow ratio decreased or the total flow rate increased, the COP of the MHSHP system showed improvement and outperformed that of the CASHP system, with an increase ranging from 46.9 % to 61.5 %. Additionally, it exhibits reduced sensitivity to ambient temperature fluctuations, resulting in a decrease in COP variability from 33.3 % to 20.6 %. Moreover, the CO2 emissions of the system decrease as the COP increases, with significant reduction of 69.2 %.

Structural effects on heat capacity, moisture absorption and thermal expansion of epoxy-novolac polymers

Today epoxy novolac resins are of great interest for the aerospace industry. Thermal properties of the polymer matrix, as well as the effect of moisture on the characteristics of polymer composite materials (PCM) under thermomechanical impacts, are critical tasks in creating dimensionally stable structures operating in a wide temperature range. Particularly, thermal and moisture expansion as well as heat capacity are important parameters for evaluating of polymer matrices and modeling their properties. In this work, polymers based on a number of epoxy novolac resins with aromatic amine hardener were studied. The values of the crosslink density were experimentally determined, and a comparative analysis of thermal expansion and heat capacity for epoxy polymers with different crosslink density was carried out. The dependence of thermophysical properties on polymer crosslinking density is shown, both in glass and highly elastic states. Additionally, this study analyzes the process of water sorption by polymers and the coefficient of moisture expansion. The most significant dependence of the diffusion coefficient was observed with coefficient of moisture expansion.

The Effect of Zn2(BDC)2 Metal Organic Framework on the Miscibility and Properties of Poly(Lactic Acid)/Poly(Butylene Adipate-co-Terephthalate) Biodegradable Blends

In our research described in this paper, the metal-organic framework MOF-2 [Zn2(BDC)2] was used to enhance the properties of a biodegradable blend based on poly(lactic acid) (PLA) and poly(butylene adipate-co-terephthalate) (PBAT). PLA/PBAT/(1, 3, 5, and 7 wt%) MOF-2 blends were prepared using a melt blending technology with a twin-screw extruder. The phase morphology, rheological behavior and barrier properties of the blends were studied. X-ray diffraction (XRD) showed a slight increase in the crystalline content of the PLA/PBAT matrix with increasing MOF-2 content. Scanning electron microscopy (SEM) revealed that the PLA/PBAT blend was immiscible, and the phase morphology improved with MOF-2 by enhancing the interfacial compatibility, reducing the size of micro-domains and cavities, and promoting a transition to a co-continuous morphology, indicating better miscibility. The ternary nanocomposites with 5 and 7 wt% MOF-2 showed increased complex viscosity (η*) and storage modulus (G′) compared to those with 1 and 3% MOF-2, indicating stronger percolated networks. The thermal and barrier properties and water absorption capacity were also improved, confirming the rheological measurements. All the results showed that the PLA/PBAT/MOF-2 nanocomposites could be used in the field of packaging.

A multi-valve flexible heat pump system with latent thermal energy storage for defrosting operation

There has been growing interest in using air-source heat pumps as an alternative to potentially replace fossil-fuel-based heating technologies for heat decarbonisation. One of the technical issues that hinders the wide uptake of air source heat pumps is the decreasing energy efficiency caused by frequent defrosting operations under low ambient temperatures. Currently, the most widely used defrosting method is the reverse-cycle defrosting but this operation would have to interrupt the heating supply during the defrosting process. The authors recently proposed, developed, and demonstrated a flexible heat pump concept that recovers partial of the subcooled heat from the hot refrigerant exiting the condenser and stores it in an integrated thermal storage. The stored heat could later be used to save compressor power and defrosting applications. In this paper, we proposed an innovative method by using a multi-valve design of the flexible heat pump to achieve the defrosting function. In this new concept, defrosting is achieved by condensing the refrigerant inside the evaporator and simultaneously ensuring uninterrupted heating during the heat storage discharge process. A model has been established to study the heat pump performance during a full charge/discharge cycle of the storage. Results indicated that with R410a, R134a and R1234yf, the proposed flexible heat pump has the potential to respectively save up to 11.2%, 10.8% and 13.2% of compressor power, in comparison with a heat pump using the conventional reverse cycle defrosting method. Concurrently with the defrosting operation, the same heating capacity is ensured without interruption by the flexible heat pump.

Performance analysis of a fresh air and indoor air co-treatment parallel-loop exhaust air heat pump for buildings

To reduce building energy consumption and solve the problem that the power of traditional exhaust air heat pump is limited by exhaust air volume, an innovative fresh air and indoor air co-treatment parallel-loop exhaust air heat pump (CPEAHP) was proposed, and three operating modes of the CPEAHP were studied. The results showed that the co-treatment mode not only increased the flexibility of system regulation, but also improved the heating performance of the system at low temperature in winter. When the winter outdoor temperature was higher than 0 °C, the temperature efficiency of the co-treatment mode was higher than 100 %, and that efficiency was higher than 100 % under all outdoor temperature conditions in summer. At a winter outdoor temperature of −15 °C, the co-treatment mode could increase the temperature of fresh air by 20.4 °C and increase the temperature of indoor air by 3.1 °C, the heating capacity of the system was 6.3 kW and the COP was 8.7 at this time. At an outdoor temperature of 42 °C in summer, the co-treatment mode could decrease the temperature of fresh air by 22.8 °C and decrease the temperature of indoor air by 3.1 °C, the cooling capacity of the system was 7.3 kW and the COP was 4.5 at this time. These results demonstrated the excellent performance of CPEAHP system, and the application of CPEAHP system was expected to reduce building energy consumption and promote carbon neutrality in the construction industry.

Thermal resilience of buildings: The role of partition walls and slabs in the optimization of the building external envelope

Nowadays it is advisable for buildings to be thermally resilient, so as to passively resist to the daily external air temperature fluctuations, reducing the interventions of air conditioning systems to a minimum. The decrement factor and time lag are parameters notoriously used to evaluate the responses of the building envelope to periodic oscillations in external air temperature. However, in their traditional definition, these parameters do not consider the effects of internal elements, such as partition walls and slabs, which instead influence the passive thermal behaviour of the building. For this reason, a choice of the external wall stratigraphy, made exclusively on the basis of the traditional decrement factor and time lag, seems to be simplistic. In this paper, problems concerning the passive behaviour of buildings, in case of sinusoidal outdoor air temperature variations, are investigated. Within a lumped-capacitance scheme and using the heat transfer matrix method, the problem of the determination of a wall stratigraphy minimizing the decrement factor for given values of the overall thermal resistance and capacity, usable for the realization of both external and internal walls of a given room, is solved. After developing an analysis on the influence of the internal walls and slabs on the room thermal balance, the resistance-capacity distribution, within the external wall, minimizing the decrement factor is determined, for assigned thermal resistances and capacities of internal elements and the external wall. Results indicate that there is no resistance-capacity distribution that is absolutely better than the others, but it is dependent on the thermo-physical characteristics of the internal elements. The optimized external wall stratigraphy can be composed of an even number of resistive and capacitive layers, alternating with each other, or of an odd number of layers (with one more resistive layer than the capacitive ones). Even the number of layers that makes optimized the passive behaviour of the external wall varies with the characteristics of the internal elements, the results show that already with a number of layers varying from 2 to 5 high performances can be obtained.