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Heating, ventilation, and air-conditioning (HVAC) are among the major energy demand in the buildings sector globally. Improving the energy efficiency of such systems is a critical objective for mitigating greenhouse gas emissions and transitioning towards renewable sources of energy supply. The interest of this paper is to explore means to increase the efficiency of HVAC systems in accommodating occupants’ behavior in real time. For instance, rooms in office buildings are not always occupied by occupants during scheduled HVAC service periods. This offers an opportunity to reduce unnecessary energy demands of HVAC systems associated with occupants’ behavior. An in-depth analysis of occupants’ stochastic behavior within an office building is conducted in this paper. A demand-driven control strategy is proposed that automatically responds to occupants’ energy-related behavior for reducing energy consumption and maintains room temperature for occupants with similar performances as a static cooling. In this control strategy, two types of machine learning methods – unsupervised and supervised learning – are applied to learn occupants’ behavior in two learning processes. The occupancy-related information learned by the algorithms is used by a set of specified rules to infer real-time room setpoints for controlling the office's space cooling system. This learning-based approach intends to reduce the need for human intervention in the cooling system’s control. The proposed strategy was applied to control the cooling system of the office building under real-world conditions. Eleven case study office spaces were selected, representing three typical office uses: single person offices, multi-person offices, and meeting rooms. The experimental results report between 7% and 52% energy savings as compared to the conventionally-scheduled cooling systems. [ABSTRACT FROM AUTHOR]

This paper presents an in-depth numerical and thermodynamic study of a two-stage, 2-bed silica gel/water adsorption system for simultaneous generation of cooling power and potable water. The system is air cooled where the ambient temperature remains constant at 36 °C. The first part of this paper investigates the effect of cycle time, chilled water inlet and heat source temperature on system performance viz. specific cooling capacity (SCC), specific daily water production (SDWP) and coefficient of performance (COP). A significant outcome of this study is to show that decrease in heat source temperature not only reduces the specific throughput but also increases the optimum cycle time, whereas COP is relatively insensitive to such alterations. The second part of this paper discusses the estimation of the minimum desorption temperature from the simulated system throughput results as well as from fundamental thermodynamic analysis of a two-stage adsorption cycle. This thermodynamic analysis provides a theoretical limit for minimum desorption temperature and optimal inter-stage pressure for a two-stage adsorption cycle. [ABSTRACT FROM AUTHOR]

The building sector is one of the main consumers of energy. Therefore, heating and cooling concepts for renewable energy sources become increasingly important. For this purpose, low-temperature systems such as thermo-active building systems (TABS) are particularly suitable. This paper presents results of the use of a novel adaptive and predictive computation method, based on multiple linear regression (AMLR) for the control of TABS in a passive seminar building. Detailed comparisons are shown between the standard TABS and AMLR strategies over a period of nine months each. In addition to the reduction of thermal energy use by approx. 26% and a significant reduction of the TABS pump operation time, this paper focuses on investment savings in a passive seminar building through the use of the AMLR strategy. This includes the reduction of peak power of the chilled beams (auxiliary system) as well as a simplification of the TABS hydronic circuit and the saving of an external temperature sensor. The AMLR proves its practicality by learning from the historical building operation, by dealing with forecasting errors and it is easy to integrate into a building automation system. [ABSTRACT FROM AUTHOR]

This paper presents new metrics to measure the effect of thermal mass on the energy required to heat and cool buildings. Previous studies have been flawed as they have not considered the interaction between intermittent occupancy and thermal mass, which has a significant impact on overall energy use. However, existing parameters do not adequately capture these effects, so the new metrics developed in this paper are used to analyse the impact of thermal mass in hot climates with active cooling, and cold climates with active heating. The results agree with existing literature that high thermal mass structures are likely to be effective in hot climates; however, in cold climates the drawbacks of high thermal mass likely outweigh the advantages, and high thermal mass can cause an increase in energy use. This finding has implications for the design of buildings in cold climates, and contradicts the commonly-held assumption that high thermal mass is correlated with low energy use. The new metrics (transient energy ratio and effective U -value) provide a generalisable method to quantify these effects. They are further used here to analyse the dynamic performance of heavily insulated buildings and show that high thermal mass often leads to higher energy use in cold climates. [ABSTRACT FROM AUTHOR]

The research on the crystallization process is a fundamental task for the investigation of freezing properties of ice slurry. This paper presents an experimental study on the influence of concentration on essential parameters of the crystallization process for the ice slurry produced from sodium chloride solution using a scraped surface heat exchanger. It was found that the liquid temperature experiences four different segments during the whole crystallization process. This trend keeps accordance with the result from literature and it was used to verify the accuracy of the experiment test. It was also observed that the concentrations of sodium chloride solution have significant effects on several freezing properties of the ice slurry generation. The curves obtained in this paper are useful to predict the freezing point and the solidification time in practice. Additionally, a mathematical correlation between the latent heat and concentration was developed eventually by polynomial fitting the curve gained from experiments. The error between the fitting curves and original experimental data was no more than 5%. Totally, during the ice generation process, it is of great significance that the concentration of brine solution can be adjusted to meet the cooling capacity requirement according to the fitting curves and mathematical correlations obtained in this paper. [ABSTRACT FROM AUTHOR]

In this paper, the cooling feasibility of air flow via a novel air-water based TEC system (as an alternative air cooling unit) is experimentally investigated for different climate conditions. Contrary to previous studies, thermoelectric hot side temperature was adjusted by a low constant water flow rate (and not by an air fan) which significantly increased the cold side performance of TEM. Ten parameters including T a,inlet , T w,inlet , T a,outlet , T w,outlet , T c , T a , m ̇ a , m ̇ w and DC voltage and DC current were directly recorded by measurement instruments during the experiments. Six other parameters including q c , q h , COP c , COP max , COP c /COP max and q air were evaluated by formulas and correlations using of aforesaid measured data. Five numbers of aforementioned parameters were variant parameters. Indeed, the effect of m ̇ a , m ̇ w , DC voltage/current and T a,inlet (variant parameters) on other impressionable parameters were investigated in present study. Optimum working condition was evaluated from a new point of view. Indeed, in this paper, it was accidently found out that, despite the descending behavior of both COP c and COP max (due to changing of variants), the ratio of said parameters (COP c /COP max ) creates a peak point (ascending and then descending) in all cases. Said peak point can be considered as an appropriate working condition of thermoelectric units. Findings showed that, the cold side of thermoelectric system can act as an applicable air cooling system especially when the hot side of thermoelectric is cooled by a current liquid such as water. [ABSTRACT FROM AUTHOR]

In this paper, the cooling, thermal and electrical energy storages are integrated into the combined cooling, heating, and power (CCHP) system to improve its energy utilization efficiency. Eight scenarios with or without electrical energy storage (EES) are investigated for the CCHP system. Furthermore, a non-dominated sorting genetic approach using elite crossover is presented for the eight scenarios. The elite crossover enables the individuals with non-domination rank 1 to converge towards the Pareto front of each scenario, and the other crossover helps the individuals with larger ranks to search in wide regions. In addition, an elimination strategy is used to exclude the individuals in crowded regions, which is beneficial for obtaining diversified solutions for each scenario instead of similar ones. For the four scenarios where selling electricity to grid is allowed, their energy, economy and environment function values are higher than those of the separate production scenarios, and the two scenarios with EES are 1.5997% and 2.6495%, respectively, higher than the two scenarios without EES. For the four scenarios where selling electricity to grid is forbidden, the two scenarios with EES can provide feasible solutions while the others fail. The two scenarios with EES achieve 72.1202% and 80.5804% total growths, respectively, for the separate production scenarios. • This paper studies dispatch of combined cooling, heating, and power (CCHP) system. • The cooling, thermal and electrical energy storages are integrated into the CCHP system. • Eight scenarios are investigated to improve the energy utilization efficiency of CCHP. • A non-dominated sorting genetic approach using elite crossover is presented for CCHP. • The scenarios with electrical energy storages achieve relatively high total growths. [ABSTRACT FROM AUTHOR]

Thermoelectric generators (TEGs) present good potential applications for the conversion of low level thermal energy into electrical power, especially applied to waste heat recovery systems. This paper presents an advanced mathematical model that uses multi-element thermoelectric components connected in series, and considers internal and external irreversibility and also the temperature gradients along the flow direction. A Fortran computation program was used for the numerical calculations. This paper focusses mainly on the thermoelectric performance study under four different types of cooling methods with temperature gradient modeling. The results showed that it is important in TEG system design to choose an optimal module area that is appropriate to the mass flow rate of the fluids, but this is not affected by the intake temperature of fluids. With the water cooling method, the coflow and counterflow methods did not need to be distinguished because of their small difference, but they should be distinguished for the air cooling method. The counterflow arrangement generally produced a small higher maximum power output, but needed a much larger module area compared to the coflow method. [ABSTRACT FROM AUTHOR]

Insulation is one of the most effective methods intended for reducing energy consumption in both heating and cooling of buildings. Selecting the right materials and determining the optimum insulation thickness in building insulation application is an important issue. Moreover it is important to use green insulating materials in order to limit the environmental impact in the use of these solutions. A growing interest is focused on the incorporation of low cost recycled materials in building products and their potential use as insulating panels for both new buildings and refurbishments. In this paper two panels were investigated, composed by waste paper and textile fibres, joined by glue, with a total thickness of 12 mm and 20 mm respectively. The study is focused on the thermal and acoustic characterisation of the panels, in order to provide accurate data for a reliable building integration. Thermal performance was evaluated by using the hot-box apparatus, according to UNI EN ISO 8990. A good thermal behaviour was found for all the investigated panels: k -values vary in the 0.034–0.039 W/m K range. The investigated panels could be a valid solution in place of classic insulation systems, even though thermal resistance is strongly influenced by the environmental humidity, the rate of the compression, and the presence of air between the layers. Therefore a thermal infrared camera was also used during the measurements, aiming to investigate the weak points of the assembled panels and to select the positions of the sensors. The acoustic absorption coefficient was determined by means of a Kundt’s tube, in compliance with ISO 10534-2. The Noise Reduction Coefficient (NRC – the arithmetic value of the absorption coefficient at the frequencies 250, 500, 1000 and 2000 Hz) of the samples varies in 0.23–0.38 range, depending on the layer thickness. Finally an initial Life Cycle Assessment of the proposed solutions was considered and compared to the performance of other replaceable insulating materials. Results showed that the panel composed by recycled papers and textile fibres causes relative large energy consumptions and a high global warming potential. The importance of this kind of insulation system is due to the use of recycled materials: both the waste paper and the TNT fibres should be disposed by means of a large use of energy. This way they will be re-used and the cost for the production of the panels is very low. A disadvantage of these panels could be their high density (about 433 kg/m 3 ): the future step for this work will be the improvement of this new insulating type in order to obtain a competitive solution on the market. The manufacturing of lighter solutions will allow the panels to be more competitive on the market in terms of embodied energy and GHG emissions. [ABSTRACT FROM AUTHOR]

Dynamic optimization of adsorbent-heat exchangers (Ad-HExs) represents a key issue for the broader diffusion of adsorption cooling and heating (ACH) technologies. This paper is a sequel to an earlier one (Sapienza et al., 2014) that described the study of an ideal Ad-HEx configuration (loose adsorbent grains placed on a flat metal plate) by a new gravimetric version of the large temperature jump method. In the present paper, the study is extended to analyse the dynamic behaviour of HExs with much more complex geometry, namely, small but representative pieces of a finned flat-tube HEx. The Ad-HEx configuration tested is obtained by filling these small HExs with loose grains of AQSOA FAM Z02. The aim of the study is to evaluate the effect of the HEx geometry, grain size and flow rate of heat transfer liquid. The results obtained are compared with a reference flat Ad-HEx configuration. The ad-/desorption dynamics is found to be nearly exponential that proves the applicability of a modified Linear Driving Force model to characterize the water ad-/desorption rate. The majority of the tests have revealed the existence of the “grain size insensitive” regime for grains of 0.3–0.7 mm size. Under this mode, the dynamic behaviour is only function of the ratio ( S / m ) = 〈heat transfer surface〉/〈absorbent mass〉. This leads to a practically important conclusion that it is not necessary to precisely select the adsorbent grain size. When the grain size becomes too small or too large the rate reduction was found that is due to inter- or intra-grain mass transfer resistances. The tested Ad-HEx configuration is proved to be quite efficient: the specific cooling power amounts to 50–66% of that obtained with the reference (ideal) one, and the average specific cooling power W 80% can reach 2.3 kW kg −1 . This power is 6–8 times higher than those reported in the literature for full scale Ad-HExs with similar cell geometry. Thus, the study showed that there is still a big room for significant dynamical improvement of real ACH units. [ABSTRACT FROM AUTHOR]

In the traditional combined cooling, heating, and power (CCHP) systems, the frequently changed user loads result in unfavorable supply-demand matching characteristics, which weakens the practical operational regulation performance. In this work, the thermochemical recuperation (TCR) with syngas storage method is proposed to optimize the system regulation characteristics and enhance the waste heat recovery. Various building energy load scenarios are also adopted to comprehensively evaluate the modified CCHP system operation characterizes. Meanwhile, with the consideration of reasonable operation regulation of syngas storage and multi-energy demands supplementary between different buildings, the coordinated system energy scheduling capacity are deeply explored to investigate the practical system application feasibility. The results indicate that under the designated operating conditions, the cooling/heating-to-power output ratios have been adjusted from 2.45 and 2.73 to 0.24–2.55 and 0.64–2.85, respectively. Additionally, with the efficient operation regulation process of TCR and syngas storage, the annual average energy utilization efficiency of the hotel, hospital, office and shopping center will be increased by 3.88%, 3.85%, 4.50% and 3.98%. Besides, through the synergistic complementary of syngas storage and adjustment between shopping center and hospital, the annual average syngas storage utilization rate of the shopping center can be increased from 16.99% to 97.41%, with the annual fuel consumption reduction of 5.78% in hospital scenario. This paper provides a combined TCR and syngas storage regulation method for the CCHP system, which enhances the system energy output flexibility and waste heat recovery capabilities in the distributed energy system application. • A coupling method of thermochemical recuperation and syngas storage is proposed. • The off-design condition thermodynamic model of the system is established. • The dynamic operation of the system in the long-term regulation process are analyzed. • The characteristics of syngas storage complementary coordination capability is explored. [ABSTRACT FROM AUTHOR]

To better make use of the waste heat in distributed data centers, a new design of integrated waste heat recovery system that can meet different needs including heating for users and data center cooling is introduced. The system can switch among different operation modes including waste heat recovery mode, natural cooling mode, composite cooling mode and refrigeration mode based on the ambient temperature. The integrated waste heat recovery system is experimented in the enthalpy-difference laboratory, and the experimental results show well consistency compared with the modeling results. The operation strategies to switch among different modes are determined based on the experimental and modeling results. The paper introduced PUE (Power Usage Effectiveness) and ERE (Energy Reuse effectiveness) to comprehensively evaluate the cooling and energy reutilization effectiveness of the system. According to the evaluation result, the integrated waste heat recovery system has well performed energy effectiveness, environmental and economic effect. The ERE values of using the integrated waste heat recovery system in Chinese typical climate cities including Harbin, Beijing, Xi'an, Shanghai and Guangzhou are 0.87, 1.02, 1.04, 1.17 and 1.29 respectively. Using this system at 96 kW distributed data center instead of CRAC (computer room air conditioning) system can save 152.7 MWh electricity, 56.4 tons of standard coal, and 244.7 tons of CO 2 emission in Beijing annually. The payback periods of this new system in different climate regions in China are all within 3 years. • An integrated data center cooling and waste heat recovery system is proposed. • Operation performance of the system is verified by experiment and modeling. • Energy Reuse Factor in Beijing is 1.02, and payback period is within 3 years. [ABSTRACT FROM AUTHOR]

Abstract: Air conditioning is essential for maintaining thermal comfort in indoor environments, particularly for hot and humid climates. Today, air conditioning, comprising cooling and dehumidification, has become a necessity in commercial and residential buildings and industrial processes. It accounts for a major share of the energy consumption of a building or facility. In tropical climates, the energy consumed by heating, ventilation and air-conditioning (HVAC) can exceed 50% of the total energy consumption of a building. This significant figure is primarily due to the heavy duty placed on cooling technologies to remove both sensible and latent heat loads. Therefore, there is tremendous potential to improve the overall efficiency of the air-conditioning systems in buildings. Based on today’s practical technology for cooling, the major components of a chiller plant are (1) compressors, (2) cooling towers, (3) pumps (chilled and cooling water) and (4) fans in air handling units. They all consume mainly electricity to operate. When specifying the kW/Rton of a plant, there are two levels of monitoring cooling efficiency: (1) at the efficiency of the chiller machines or the compressors which consume a major amount of electricity; and (2) at the overall efficiency of cooling plants which include the cooling towers, pumps for moving coolant (chilled and cooling water) to all air-handling units. Pragmatically, a holistic approach is necessary towards achieving a low energy input per cooling achieved such as 0.6kW/Rton cooling or lower by considering all aspects of the cooling plant. In this paper, we present a review of recent innovative cooling technology and strategies that could potentially lower the kW/Rton of cooling systems – from the existing mean of 0.9kW/Rton towards 0.6kW/Rton or lower. The paper, broadly divided into three key sections (see Fig. 2), begins with a review of the recent novel devices that enhances the energy efficiency of cooling systems at the component level. This is followed by a review of innovative cooling systems designs that reduces energy use for air conditioning. Lastly, the paper presents recent developments in intelligent air-control strategies and smart chiller sequencing methodologies that reduce the primary energy utilization for cooling. The energy efficient cooling technology, innovative systems designs, and intelligent control strategies described in the paper have been recently researched or are on-going studies. Several have been implemented on a larger scale and, therefore, are examples of practical solutions that can be readily applied to suit specific needs. [Copyright &y& Elsevier]

• Internal methanation effectively promoted by high pressure and reactant utilization. • Stack outlet CH 4 fraction up to 30 vol.% at 0.3 A/cm2 and large stack cooling. • Stack outlet CH 4 fraction only up to 15 vol.% to achieve high system efficiency. • Internal methanation as internal heat source preferred by endothermic operation. This paper presents a model-based investigation to handle the fundamental issues for the design of co-electrolysis based power-to-methane at the levels of both the stack and system : the role of CO 2 in co-electrolysis, the benefits of employing pressurized stack operation and the conditions of promoting internal methanation. Results show that the electrochemical reaction of co-electrolysis is dominated by H 2 O splitting while CO 2 is converted via reverse water-gas shift reaction. Increasing CO 2 feed fraction mainly enlarges the concentration and cathode-activation overpotentials. Internal methanation in the stack can be effectively promoted by pressurized operation under high reactant utilization with low current density and large stack cooling. For the operation of a single stack, methane fraction of dry gas at the cathode outlet can reach as high as 30 vol.% (at 30 bar and high flowrate of sweep gas), which is, unfortunately, not preferred for enhancing system efficiency due to the penalty from the pressurization of sweep gas. The number drops down to 15 vol.% (at 15 bar) to achieve the highest system efficiency (at 0.27 A/cm2). The internal methanation can serve as an effective internal heat source to maintain stack temperature (thus enhancing electrochemistry), particularly at a small current density. This enables the co-electrolysis based power-to-methane to achieve higher efficiency than the steam-electrolysis based (90% vs 86% on higher heating value, or 83% vs 79% on lower heating value without heat and converter losses). [ABSTRACT FROM AUTHOR]

• Advanced LCOS method to compare electricity and thermal energy storage. • Parametric storage sizing to analyse self-sufficiency and LCOS. • Evaluation of an office, a hotel and a warehouse scenario in Singapore. • Thermal energy storage offers lower LCOS, but achieves low self-sufficiency. • Battery storage needs to be well-sized. In this paper, we propose an advanced Levelised Cost of Storage (LCOS) model to compare electricity and thermal energy storage for cooling applications. The proposed model is applied to evaluate the LCOS for Lithium-Ion (Li-Ion) battery, chilled water and ice storage for Photovoltaic (PV) powered cooling for an office, a hotel, and a refrigerated warehouse scenario in Singapore. Parametric energy simulations varying the storage size were carried out to analyse the optimal storage size for different applications and technologies. The thermal energy storages were found to cause a lower chiller plant Coefficient of Performance (COP), which leads to an increased energy consumption. As a result, the battery can achieve a better performance in terms of self-sufficiency. The LCOS for the thermal energy storages are generally lower than that of the battery, at 23–47 USD ct / kWh el for all the analysed storage sizes. However, a well-sized battery can only achieve LCOS of 55 USD ct / kWh el for the office scenario, 71 USD ct / kWh el for the hotel scenario, and 55 USD ct / kWh el for the refrigerated warehouse, due to high investment cost. This work also highlights that thermal energy storage has a better potential for applications that require a larger shift of energy, such as in the investigated hotel and refrigerated warehouse scenario. [ABSTRACT FROM AUTHOR]

Highlights • Numerical proof of concept is provided for a novel dynamic PCM building system. • The system is able to modify the position of PCM with respect to the insulation. • The system can not only be used as thermal barrier but as a cooling supplier system. • Activations of the system and melting PCM temperature were optimized. Abstract A novel concept based on the dynamic use of phase change materials (PCM) in building envelopes is presented in this paper. The concept aims at breaking the main technical barriers that PCM have been dealing with in its application as passive cooling system: (i) solidification process of PCM is limited and (ii) peak cooling load is delayed but mainly discharged indoors. The concept relies on the ability of the system to modify the position of the PCM layer inside the building envelope with respect to the insulation layer. A proof of concept evaluation based on a numerical tool demonstrates the cooling load reduction potential of this technology when implemented in different construction systems. PCM peak melting temperature as well as the daily activations of the system were optimized using a Particle Swarm Optimization (PSO) algorithm. The numerical results indicate that the dynamic system facilitates dramatically the solidification process of PCM, allowing the system to be designed with lower PCM peak melting temperatures. The potential of the system to charge PCM which solidifies at temperatures lower than indoor set point, allows the technology to be used not only as a thermal barrier but as a cooling supplier system. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a classification of green vertical systems for buildings. The aim of this classification is to facilitate the identification and differentiation between systems. This classification is also essential to compare future research results relating to their operation. In addition, the mechanisms by which green facades can be used as passive energy savings systems are reviewed: shadow produced by the vegetation, insulation provided by vegetation and substrate, evaporative cooling by evapotranspiration, and the barrier effect to the wind. Finally, the paper describes the first results about the behaviour of a double-skin green facade or green curtain in Dry Mediterranean Continental conditions. It is verified that a microclimate between the wall of the building and the green curtain is created, and it is characterized by slightly lower temperatures and higher relative humidity. This means that the green screen acts as a wind barrier and confirms the evapotranspiration effect of the plants. [Copyright &y& Elsevier]

Highlights • A methodology to offer frequency regulation with complementary resources is presented. • Their aggregated flexibility is formally computed. • An experimental campaign is conducted on an office building and an electrical battery. • Results reveal that combining such resources increases the offerable flexibility. • Excellent tracking performance can be achieved while respecting all local constraints. Abstract This paper presents a predictive control scheme for coordinating a set of heterogeneous and complementary resources at different timescales for the provision of ancillary services. In particular, we combine building thermodynamics (slow), and energy storage systems (fast resources) to augment the flexibility that can be provided to the grid compared to the flexibility that any of these resources can provide individually. A multi-level control scheme based on data-based robust optimization methods is developed that enables heterogeneous resources at different time scales (slow and fast) to provide fast regulation services, especially a secondary frequency control service. A data-based predictor is developed to forecast the future regulation signal and is used to improve the performance of the controller in real-time operation. The proposed control method is used to conduct experiments, for nine consecutive days, demonstrating the provision of secondary frequency control fully complying to the Swiss regulations, using a controllable building cooling system on the EPFL campus and an emulated grid-connected energy storage system. The experimental results show that optimally combining such slow and fast resources can significantly augment the flexibility that can be provided to the grid. To the best of author's knowledge, this work is the first experimental demonstration of coordinating heterogeneous demand-response to provide secondary frequency control service. [ABSTRACT FROM AUTHOR]

Highlights • A continuous-instant running water cooler by thermoelectric is proposed. • A novel thermoelectric pack is designed and no water reservoir is required. • The effects of water flow rates on heating/cooling characteristics are evaluated. • The effects of DC voltage and inlet temperatures are discussed. • Present system was found as a novel promising water cooler. Abstract Current water coolers contain a water reservoir which always deal with hygienic problems because of accumulation of bacteria, etc. Furthermore, based on sanitary laws, the tubes contained CFC (in current water coolers) cannot be placed inside the water fluid and must be welded on the outer surface of the reservoir which causes reduction of the performance of cooling process. Besides, the limit capacity of reservoirs does not allow them to provide continues chilled water. Hence, this paper hopes to clarify the fabrication feasibility of a water cooler which provides continuous-instant chilled water (without requirement of any reservoir) by thermoelectric power and find its appropriate working condition. In other words, such cooler does not use electrical power while nobody requires chilled water. Once the valve of the cooler is opened, the running water fluid is directly and instantaneously cooled after passing through a thermoelectric pack which overcomes all aforesaid issues. For this aim, two water flows are injected into the two sides of a novel thermoelectric unit and a comprehensive experimental analysis of the system is performed under different operating conditions. The amounts of outlet temperatures, surfaces-temperature, COP, heat transfer rate, etc. are evaluated and discussed to find the suitable working condition. It was concluded that the feasibility of instant water cooler is possible with a compatible value of COP if the value of effective parameters are selected appropriately. [ABSTRACT FROM AUTHOR]

Abstract: Optimization of combined cooling, heating, and power (CCHP) systems operation commonly focuses only on energy cost. Different algorithms have been developed to attain optimal utilization of CCHP units by minimizing the energy cost in CCHP systems operation. However, other outcomes resulting from CCHP operation such as primary energy consumption and emission of pollutants should also be considered during CCHP systems evaluation as one would expect these outcomes can be subject to regulation. This paper presents an optimization of the operation of CCHP systems for different climate conditions based on operational cost, primary energy consumption (PEC), and carbon dioxide emissions (CDE) using an optimal energy dispatch algorithm. The results for the selected cities demonstrate that in general there is not a common trend among the three optimization modes presented in this paper since optimizing one parameter may reduce or increase the other two parameters. The only cities that show reduction of PEC while also reducing the CDE are Columbus, MS; Minneapolis, MN; and Miami, FL. For these cities the operational cost always increases when compared to the reference case consisting of using a vapor/compression cycle for cooling and natural gas for heating. On the other hand, for San Francisco and Boston, CCHP systems increase the CDE. In general, if CCHP systems increase the cost of operation, as long as energy savings and reduction of emissions are guaranteed, the implementation of these systems should be considered. [Copyright &y& Elsevier]

Abstract: Integrating the building structure to act as an energy-storage, thermally-activated building system (TABS) has proved to be energy efficient and economically viable for cooling and heating of buildings. However control has remained an issue to be improved. In this paper, a method is outlined allowing both for dimensioning and for automated control of TABS, with automatic switching between cooling/heating modes for variable comfort criteria. The method integrally considers both HVAC and building automation design aspects, as well as the fact that during design and operation heat-gains are unknown, but that bounds of them normally can be specified. This integral method is termed the Unknown-But-Bounded or UBB method. Applying the method guarantees that comfort can be maintained, as long as the actual heat-gains stay within the predefined range between the lower and upper bounds. The UBB method can also handle non-predictable day-to-day variations as well as room-to-room variations of the heat gains. The paper outlines the underlying thermal models and assumptions, and gives the procedure and an example for the application of the method. [Copyright &y& Elsevier]

In this paper, one MOEA/D variant using two crossover strategies (MOEA/D-TCS) and two constraint handling methods are proposed to deal with four combined cooling, heating, and power (CCHP) scenarios in summer and winter. MOEA/D-TCS maintains a balance between global search and local search by combining a modified spiral updating position of whale optimization algorithm and the simulated binary crossover of genetic algorithm, and it is able to obtain a wide and even Pareto set for each CCHP scenario. The two constraint handling methods enable infeasible solutions to get rid of infeasible regions over a short period of time, guaranteeing that the reserved solutions of MOEA/D-TCS satisfy all constraints. Experimental results show that each CCHP scenario with the battery has lower energy consumption, operation cost and carbon dioxide emission than the corresponding CCHP scenario without the battery, and hence the battery is helpful to the improvements of the flexibilities and efficiencies of energy cascade utilization for the CCHP systems in summer and winter. Also, MOEA/D-TCS performs better than the other seven multi-objective evolutionary algorithms and achieves larger hypervolumes and coverage rates for four CCHP scenarios. • The optimal dispatch of combined cooling, heating, and power is studied. • The battery is added to the combined cooling, heating, and power system. • A MOEA/D with two crossover strategies is presented for OD-CCHP. • The scenarios with the battery achieve small objective function values. • The improved MOEA/D outperforms the other methods for four OD-CCHPs. [ABSTRACT FROM AUTHOR]

Schematic illustration of the double-layer PDRC coating. [Display omitted] • The idea of introducing masking layer for double-layer PDRC coating is proposed. • PDRC coating achieves high solar reflectivity (94.0%) at a thin thickness. • The PDRC coating reduces the indoor temperature of container room by 5.0 °C. • The prepared PDRC coating can realize large-scale long-time outdoor applications. The realization of spontaneous sub-ambient cooling in daytime typically requires the solar reflectance and thermal emittance of passive daytime radiative cooling (PDRC) material to be > 90%. Toward real-world applications, however, to achieve high optical performance and excellent durability, PDRC coating is often cost-prohibitive due to its high thickness (500 μm or higher). To solve the contradiction between high optical performance and thin thickness of PDRC coating, the idea of introducing masking layer for PDRC coating is proposed in this paper to prepare the water-based double-layer PDRC coating and explore its long-term outdoor application potential. The PDRC coating can achieve high solar reflectance (94.0%) and "atmospheric transparent spectrum window" emittance (93.0%), while the thickness and cost are only 40% and 60% of existing water-based PDRC coating. The PDRC coating shows efficient cooling performance when applied as the external coating of large temporary buildings, with maximum temperature reduction of 20.8 °C and 5.0 °C on the roof/indoor, which are equal to or greater than recorded values. The 150-day large-scale outdoor application shows that the coating has excellent durability, which offers a reference for the long-term outdoor application of PDRC coating. The application of the PDRC coating on rooftops of containers can achieve a cooling energy savings of up to 15.3% compared to conventional steel roofs, translating to an annual energy savings of 413.2 MJ and a reduction of approximately 114 kg in carbon dioxide emissions, which provide compelling evidence for the ability of PDRC coating to mitigate carbon emissions and address global climate change. [ABSTRACT FROM AUTHOR]

• Building integrated earth-to-air heat exchanger for global footprint reduction. • Offering similar energy gains than traditional earth-to-air heat exchanger. • Two time-dependent 3-dimensional finite volume models are developed and coupled. • Coupled heat and moisture transfers and complex boundary conditions are considered. • Successful validation against in-situ temperature and water content measurements. This paper investigates an innovative earth-to-air heat exchanger (EAHE), namely the geothermal foundation Fondatherm®. This system solves numerous technical problems inherent to a traditional EAHE. However, an accurate understanding of its thermal behavior is crucial to ensure the best energy gain and its economic viability. This current paper focuses on a numerical study of the ventilated foundation. A time-dependent three-dimensional finite volume numerical model is developed. This model considers coupled heat and moisture transfers as well as complex boundary conditions such as the weather, the building and the water table simultaneous influences. A matric-head based system of equations is used to represent the heat, vapor and liquid transfers within the soil. It is combined to a capillary pressure-based formulation of the heat and vapor balance equation for the concrete foundation. Furthermore, a numerical method built on a switching from a potential- to a flux-based system of equations is proposed. It is added to a variable time-step method of resolution and allow to handle the greatest hygric loads variations at the ground surface. The numerical code is successfully validated against analytical solutions for simple cases, and against experimental and in situ measurements. [ABSTRACT FROM AUTHOR]

Highlights • Developing building cooling forecasting model for energy saving of HVAC system. • Forecasting step-ahead building cooling load by time series prediction. • Forecasting step-ahead building cooling load by Fourier’s law-based analysis. • Improving performance of building cooling load forecasting by ensemble technique. Abstract Short-term load prediction, which forecasts a building’s thermal load with a lead time ranging from seconds to a few days, is essential for not only monitoring and controlling the system operation, but also on-line scheduling. Dynamic cooling load forecasting, which belongs to short-term load prediction, is both meaningful for monitoring the system or fuzzy on-line scheduling and crucial for solving the time-lag problem to meet the heating, ventilation and air-conditioning system’s time-varying cooling loads. Numerous studies have been carried out to develop dynamic load-forecasting models, and great achievements have been made. However, limitations in their applicability persist because most previous models are calendar- and time-based data-driven models that may fail when unexpected issues occur or special schedules are adopted. What’s more, the inputs that were selected passively from the source data pools at hand rather than via active exploration may be insufficient and impair the accuracy of forecasting models. This paper proposes a novel dynamic forecasting model for building cooling loads that combines an artificial neural network with an ensemble approach. Based on physical principles other than the available data source, the inputs are explored actively and are independent from both calendar and time indicators, which make the forecasting model being capable of dealing with irregular occasions and unexpected schedules with high accuracy. A benchmark is proposed that uses the current load Q (t) as a forecasted cooling load Q ^ (t + i) and gives the minimum accuracy requirement for a dynamic forecasting model. The benchmark not only can be used to evaluate dynamic forecasting models that are validated by various case studies, but also ensures that the proposed forecasting model can be applied immediately to heating, ventilation and air-conditioning systems to tackle the time-lag problem. [ABSTRACT FROM AUTHOR]

Highlights • The infiltration is responsible for more than half of the total cooling load. • A direct method is developed for measuring the transient infiltration airflow rates. • The method is validated by the experiments of tracer gas decay technique. • The measurement errors of infiltration airflow rates are distributed between ±10%. • The practical application of the proposed method is discussed. Abstract The measurement of the infiltration airflow rates can support the calculation of the infiltration cooling load for the better understanding and optimizing the energy consumption of cold stores. However, the large temperature difference and the intense transient features make it difficult and complex to measure the airflow rates accurately. In this paper, a simple and practical method to measure the transient infiltration airflow rates is developed by using the local air velocity linear fitting. The proposed method is validated by the measurement results of the tracer gas decay method. It is concluded that the proposed method shows a good performance on the transient infiltration airflow rates measurement. The measurement errors are between ±10%. To enhance the application of this method, the layout of the measuring points of the air velocities are analyzed. The results show that, along the vertical layout direction, air velocity measuring points around the neutral level (where the cold and the warm air separate, about the middle height of the door) are not preferred when using this method. What’s more, the calculation of the infiltration cooling load by using this measuring method is also discussed. [ABSTRACT FROM AUTHOR]

Latent heat thermal energy storage is an attractive technique as it can provide higher energy storage density than conventional heat energy storage systems and has the capability to store heat of fusion at a constant (or a near constant) temperature corresponding to the phase transition temperature of the phase change material (PCM). This paper provides a state-of-the-art review on phase change materials (PCMs) and their applications for heating, cooling and electricity generation according to their working temperature ranges from (−20 °C to +200 °C). Four working temperature ranges are considered in this review: (1) the low temperature range from (−20 °C to +5 °C) where the PCMs are typically used for domestic and commercial refrigeration; (2) the medium low temperature range from (+5 °C to +40 °C) where the PCMs are typically applied for heating and cooling applications in buildings; (3) the medium temperature range for solar based heating, hot water and electronic applications from (+40 °C to +80 °C); and (4) the high temperature range from (+80 °C to +200 °C) for absorption cooling, waste heat recovery and electricity generation. Different types of phase change materials applied to each temperature range are reviewed and discussed, in terms of the performance, heat transfer enhancement technique, environmental impact and economic analysis. The review shows that, energy saving of up to 12% can be achieved and a reduction of cooling load of up to 80% can be obtained by PCMs in the low to medium–low temperature range. PCM storage for heating applications can improve operation efficiency from 26% to 66%, depending on specific applications. Solar thermal direct steam generation (DSG) is the most common electricity generation application coupled with PCM storage systems in the high temperature range, due to the capability of PCMs to store and deliver energy at a given constant temperature. The recommendations for future research are also presented which provide insights about where the current research is heading and highlights the challenges that remain to be resolved. [ABSTRACT FROM AUTHOR]

The melting process and the solidifying process of phase change material (PCM) are usually considered symmetrical in the traditional PCM heat transfer models, but there are inevitable calculation errors using these models. In this paper, a new heat transfer model of PCM based on the energy asymmetry was built, and it was validated by experimental data. It was found that the two main reasons for the energy asymmetry of the PCM were the melting temperature range and the solidifying temperature range were not the same and the supercooling problem during the cooling process. No matter for only one thermal cycle or for the multiple thermal cycles, the results from the asymmetrical model and the symmetrical model were different. Apparently, compared with the symmetrical model, the asymmetrical model had higher accuracy, and the heating/cooling process in the asymmetrical model was more consistent with the real heating/cooling process of the PCM. [ABSTRACT FROM AUTHOR]

The application of ground source heat pumps (GSHP) for heating and cooling of buildings is currently increasing in popularity in the UK and globally. Traditional GSHP systems use the naturally available geothermal gradient of earth for heating and cooling purposes using open loop or closed loop systems. In this paper, the use of mine water from a flooded coal mine for heating of buildings is presented using a GSHP system with an open loop configuration. The novelty of this approach is that a single shaft is used to extract the warm water and inject the cooler water back into the same shaft, thereby minimising the area needed, initial capital costs in constructing a doublet system and also potentially overcome the time consuming process to address related environmental agencies regulation regarding the discharging of the mine water. The relatively stable temperature low enthalpy of mine water contained in the abandoned and flooded coal mines are ideal to be used for both heating and cooling of buildings when used in conjunction with heat pumps. The GSHP is considered to be an effective means of reducing the carbon emission as it gives more output in the form of thermal energy in comparison to the electrical energy it consumes as input. This research work reports on the performance of the system over the winter season and its long term potential in converting the mine water from an environmental liability to a sustainable energy resource and offers a means to regenerate the former coal mining areas. [ABSTRACT FROM AUTHOR]

This paper is focused on the development of a model for achieving optimal control of the cooling system of a polymer electrolyte membrane fuel cell (PEMFC)-based cogeneration system. This model is developed to help facilitate the development and application of control strategies to maximize the energy efficiencies of PEMFCs, so that the costs associated with electric and thermal generation can be reduced. The results of experimental analysis conducted using an actual PEMFC-based combined heat and power system that can produce 600 W of electrical power are presented. Then, the development and validation of a simulation model of the experimental system are discussed. This model is based on a combination of an artificial neural network (ANN) with a non-linear autoregressive exogenous configuration and a 3D lookup table (LUT) that updates the data input into the ANN as a function of the electrical power demand and the flow rate and input temperature of the coolant fluid. Due to the nonlinearity of the data contained in the 3D LUT, an algorithm based on linear interpolation and shape-preserving piecewise cubic Hermite dynamic functions is implemented to interpolate the data in 3D. As a result, the model can predict the outlet temperature of the coolant fluid and hydrogen consumption rate of the PEMFC as functions of the inlet temperature and flow rate of the coolant fluid and the electrical power demand. The proposed model exhibits high accuracy and can be used as a black box for the development of new optimization strategies. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel game model based on the hierarchical Stackelberg game for analyzing the multiple energies trading (MET) problem in integrated energy systems (IESs). In the proposed game model, a number of distributed energy stations (DESs) lead the game deciding the unit prices of electricity and cooling energies they generated, while multiple energy users (EUs) perform as followers determining the amounts of energies to consume. In addition to maximizing the profit of each DES, the proposed hierarchical game model also considers the benefit of each EU, who actively participates in the MET. We prove that, for the first time, there exists a unique Stackelberg Equilibrium (SE) in the MET, so that the existence of an equilibrium strategy optimizing the objectives of all participants can be guaranteed. Moreover, we found that the price setting game played by DESs is a submodular game when energy dispatching is performed during their generation process, which indicates that the behaviors of DESs are strategic substitutes. Furthermore, the SE is obtained in a closed-form, by which the effects of coupling generation of multiple energies are analyzed. Finally, a best response algorithm is provided to obtain the SE in an iterative way. Numerical studies demonstrate the convergency of the proposed best response algorithm, corroborate the jointly effects of market scale and exogenous parameter on the SE and verify the practicability of the proposed game-theoretic approach. [ABSTRACT FROM AUTHOR]

As the greenhouse effect becomes increasingly serious, cooling a vehicle cabin parked under the blazing sun without running the engine or using an electric vehicle’s power has received considerable attention. In this paper, we develop a novel portable, renewable, solar energy-powered cooling system with wireless power transfer (WPT) and supercapacitors to cool the vehicle cabin. The proposed system consists of a solar collector mechanism, an energy conduit, and a temperature control and cooling module. First, consisting of folding solar photovoltaic (PV) panels, the solar collector mechanism making the proposed system portable. Once collected, the solar energy is converted into electricity and stored in the supercapacitors through wireless power transfer without breaching the vehicle body. Automatic temperature regulation is achieved with the cooling device via the temperature control and cooling module. The experimental results indicate that a maximum output power of 2.181 W and a maximum WPT efficiency of 60.3% are achieved when the prototype loaded with 3 Ω and 5 Ω respectively. Meanwhile, the simulation shows the temperature inside the cabin is reduced by as much as 4.2 °C in average, demonstrating that the proposed solar energy-powered cooling system is effective and feasible in cooling a hot vehicle cabin. [ABSTRACT FROM AUTHOR]

Building-integrated photovoltaic (BIPV) windows provide the benefits of generating electricity, reducing building cooling and heating energy consumption, and efficiently utilizing daylight simultaneously. In this paper, the overall energy performance of a PV double skin façade (PV-DSF) and a PV insulating glass unit (PV-IGU) is studied through comparative experiments on a test rig in Hong Kong. The PV-DSF means ventilated PV-DSF by default, if not special mentioned. It is found that the average solar heat gain coefficients (SHGCs) of the PV-DSF and the PV-IGU are 0.152 and 0.238, while the U-values are 2.535 W/m 2 K and 2.281 W/m 2 K. The results indicate that the PV-DSF has better performance than PV-IGU in reducing solar heat gains, while it has worse performance regarding thermal insulation. With a lower PV module temperature, the energy conversion efficiency of PV-DSF is 1.8% better than PV-IGU. Simulation models for the PV-DSF and the PV-IGU are developed and validated against experimental data. Using the validated models, the overall energy performances of PV-DSF and PV-IGU in five different climates of China are investigated. The results show that the average energy saving potential of the PV-DSF and the PV-IGU are 28.4% and 30%, respectively, compared to the commonly used insulating glass window in five different climates. On average, the performance of PV-IGU was 2% better performance than the ventilated PV-DSF in the five representative cities. However, if an appropriate ventilation control scheme was adopted, PV-DSF can have a much better performance than the PV-IGU. The models developed in this study can be used for selecting suitable PV windows in the design process, and the results achieved can be used as a guideline for utilizing PV windows in different climates. [ABSTRACT FROM AUTHOR]

This paper proposes a gravity heat pipe exchanger used for cooling the communication base station to replace the traditional air conditioning system during winter and transition seasons. Tests were conducted on a commercial available gravity heat pipe exchanger. The experiment was performed to study the effects of the air flow rate and temperature on the cooling capacity, the heat transfer unit number (NTU) and cooling efficiency of the heat pipe exchanger. The results showed that the larger the air flow rate, the smaller the NTU and the larger the cooling capacity. Based on the analysis of the experimental data, it proved that the gravity heat pipe exchanger could reduce running time and operating cost of air conditioning system. According to the practical applications, the yearly cooling loads of a typical communication base station were further calculated for five typical cities which represent the five climatic zones of China. The results validated that the energy saving by using the gravity heat pipe exchanger is significant. The highest annual electricity-saving rate is achieved by Kunming, about 48.6%, while the lowest annual electricity-saving rate is obtained in Guangzhou, about 18.7% among the five climatic zones. The fitted correlation of cooling capacity in term of outdoor temperature is generic to evaluate approximately the performance of applying the gravity heat pipe exchanger in the actual applications subject to various outdoor temperatures. [ABSTRACT FROM AUTHOR]

This paper presents a new methodology for the estimation of power capacity profiles for smart buildings. The capacity profile can be used within a demand-side management system in order to guide the building temperature operation. It provides a trade-off between the quality of service perceived by the end user and the requirements from the grid in a demand-response context. We use a data-fitting approach and a multiclass classifier to compute the required profile to run a set of electric heating and cooling units via an admission control module. Simulation results validate the performance of the proposed methodology under various conditions, and we compare our approach with neural networks in a real-world-based scenario. [ABSTRACT FROM AUTHOR]

Solar still is a cheap and convenient device for producing freshwater, but it’s not popular due to its low productivity. In this paper, we modified the conventional solar still. The outdoor performance of modified solar stills was studied to assess its potential for real application. The modifications include using flake graphite nanoparticles (FGN), phase change material (PCM), and film cooling. In the presence of the three previous modifications, the productivity was enhanced as high as 73.8% compared with that of the conventional still. The effect of water depth on the enhancement was also investigated. It shows that the enhancement of productivity increases by around 13% when the water depth decreases from 2 cm to 0.5 cm. Besides, an indoor experiment was carried out to analyze the enhancement mechanism by FGN. It shows that the increase in both temperature and saturated vapor pressure contributed to the enhancement. [ABSTRACT FROM AUTHOR]

This paper examines naturally ventilated buildings in hot and humid summer zones and proposes an air enthalpy-based energy conservation rating method with an emphasis on the combined thermal comfort-ventilation parameters, particularly the impact of humidity and human adaptations on thermal comfort. The new method starts with energy flow analysis to a naturally ventilated room and assessment of thermal comfort accounting for the humidity of the naturally ventilated room as well as the occupants’ adaptability, differing from the PMV models and widely-used adaptive models adopted in existing rating methods. It contributes to designing a well-performed naturally ventilated building by analysing the interplay of climate elements, design features, indoor thermal comfort, and energy consumption for cooling in hot-humid climates. It also gives the access to rate the influence of an estimated energy saving due to natural ventilation on the energy system at a district or national scale. The proposed method is then applied to a naturally ventilated office located in three cities within this particular climatic region of China. The results indicate that natural ventilation is an effective way to improve thermal comfort while maintaining a low cooling energy consumption in hot-humid summer zones. Using natural ventilation could help reduce cooling energy demand by 10–30% compared to not using natural ventilation. Its energy saving potential is strongly affected by the enthalpy of outdoor air, followed by airflow rate. Then, a contrast comparison between the new method based on energy balance and Chinese indoor thermal comfort standard and the conventional method coupling adaptive ASHRAE standard-55 thermal comfort model with sensible heat balance model is carried out. The contrast results validate the considerable impacts of humidity on energy balance analysis and thermal comfort rating. It points out the new method makes improvement of the maximum energy saving potential of naturally ventilated buildings prediction. [ABSTRACT FROM AUTHOR]

Metal–organic framework (MOF) materials are new adsorbent materials that have high surface area and pore volume and hence high adsorption uptake. The previous exceptional properties make this class of materials have a great potential in many applications like cooling, gas separation and energy storage. However, there is very limited information on the performance of metal–organic framework materials in energy storage applications and their performance compared to conventional adsorbents. This paper aims to present an experimental characterisation of CPO-27(Ni) MOF material for water adsorption and to investigate its viability for energy storage. CPO-27(Ni) (known as MOF-74(Ni)), which is a MOF material that has high water adsorption capabilities of 0.47 g H2O gads −1 and hydrothermally stable and can be supplied in large quantities. Firstly, the material water adsorption isotherms were predicated using Materials Studio software via the material structure information and then compared to the experimentally measured isotherms. The experimentally measured isotherms and kinetics were used to model a double bed adsorption system for energy storage application using Simulink–Matlab software coupled with Nist RefProp thermophysical routines. Finally, the performance of CPO-27(Ni) was then compared with silica gel. The CPO-27(Ni) was found to outperform silica gel at long half cycle time (more than 30 min) at low evaporating temperature making it suitable for energy storage applications. The energy stored in the condenser and the adsorption bed was found to be dependent mostly on the regeneration and the cooling temperatures. The potential of the energy recovered from the adsorption bed can be double the one recovered from the condenser. Also, the energy recovery during condensation and adsorption was found to be independent of the reactor conductance except at small conductance ratio. Finally, the adsorption unit cooling water flow strategy was found to affect the amount of the energy recovered as recirculating the cooling water through the adsorption bed and then condenser was found to decrease the recovered energy from the condenser by 4%. [ABSTRACT FROM AUTHOR]

Buildings worldwide consume approximately 45% of primary energy sources, making it the single largest energy consumption sector. The importance of improving a building’s energy performance was emphasized by the government with the enforcement of sustainable building policies. Article 9 of the Directive 2010/31/EU of the European Parliament and the Council (19th May 2010) on the energy performance of buildings states the importance of stimulating refurbishment of existing buildings into near zero-energy buildings. However, the effectiveness of the process depends on the basic building structure and the refurbishment designs. Hence, methods to find the effective strategies for retrofitting and modelling to predict energy reduction is vital. Unlike the previous studies, this paper presents a method for a deep building retrofit based on the whole building’s thermal analysis specifically for cooling demand countries. This work set against recommended best practice office building energy benchmarks in Malaysia, and following a comprehensive building audit, a retrofit strategy was proposed based on target building’s thermal analysis with cooling demand reduction in particular focus. It was found that 71% of the building’s heat gain emanated from its lighting system and solar heat gain through windows. A 40.2% reduction in the building’s cooling load is estimated to reduce 47% of the total energy consumption. A comparison of the actual and simulated energy results suggested that the simulation made under predicted the energy reduction by 4.3%. [ABSTRACT FROM AUTHOR]

An effective quantification of the energy absorbed and supplied by latent heat thermal energy storage (LHTES) units is critical to maximise their use within thermal systems. An effective control of the charging and discharging processes of these units demands an accurate estimation of the state-of-charge (SoC). However, a direct and reliable SoC estimation requires incorporating internal sensors to monitor the temperature gradient of the phase change material (i.e. the storage medium), resulting in higher instrumentation costs and technical specifications. These issues may be relieved by adopting state observers for SoC estimation to drastically reduce the number of measurements. This paper bridges this gap by presenting a novel and direct method for estimating the SoC of LHTES units, both for heating and cooling applications, based on a non-linear state observer. The observer is based on a simple one-dimensional dynamic model of the thermal store and the thermophysical properties of the storage medium and the heat transfer fluid, which are usually provided by manufacturers. This enables the estimation of the internal temperatures of the LHTES unit and, in turn, SoC calculation. The observer implementation is simple as it requires three measurements only as input variables (i.e. the mass flow rate and the input and output temperatures of the heat transfer fluid). The SoC estimation approach is assessed through dynamic simulations of two LHTES units: one for a heating application and one for a cooling application. The results show that the SoC can be estimated with root mean square and mean absolute errors of less than 4.6% and 3.62%, respectively, compared with experimental measurements. • The specific latent heat value of phase change materials is dynamically modelled using probability density functions. • A non-linear observer estimates the temperature of a phase change material in thermal energy storage units. • The state-of-charge of latent heat thermal energy storage units is calculated using the observer outputs. • A calculation method of the state-of-charge is proposed to reduce the computation time. • Implementation and verification of non-linear observers and state-of-charge calculation method is performed using MATLAB. [ABSTRACT FROM AUTHOR]

• The principle of spectrally selective approaches for cooling solar cells is analyzed. • Radiative cooling is a significant method for solar cells to dissipate waste heat. • Full-spectrum thermal management of solar cells is a novel way to cool solar cells passively. • The cooling effect of full-spectrum thermal management is better than radiative cooling. • Appropriate material is the biggest challenge for this new cooling technology. Waste heat is generated in solar cells during the daytime because they operate with a limited electrical efficiency. Moreover, the generated heat increases the solar cells' operating temperature, and this has an adverse effect on their electrical efficiency. Therefore, numerous cooling methods have been developed to cool solar cells, such as forced air/water flow, hybrid photovoltaic/thermal system, and phase change material based photovoltaic application. Recently, a novel concept of changing the solar cells' spectral response to both sunlight and thermal radiation has been proposed and developed to provide a passive cooling method for solar cells, which has drawn much attention from materials science to engineering fields. In this paper, the recent advancements of such a spectrally selective approach to passively cool solar cells, including radiative cooling of solar cells and full-spectrum thermal management of solar cells are reviewed, analyzed, and discussed from fundamental principles to detailed demonstration. Furthermore, the technical challenges involved in developing this new cooling technology are discussed. This paper is devoted to give a systematic introduction to a new passive cooling technology for solar cells by controlling the spectral property of solar cells, aiming to open a new opportunity for solar cells' cooling. [ABSTRACT FROM AUTHOR]

Quality of indoor environment as well as energy consumption in buildings are a growing concern in the context of overheating of buildings, as the EU legislation is primarily focused on heating season. The statistical data of EU have shown that there is already a large amount of buildings not comfortably cool during summer and the trend is increasing. Therefore, the main goal of this paper is to evaluate the influence of high intensity passive cooling as one of the passive solutions for overheating of buildings on the overall thermal response of building envelope systems. Specifically, a variety of multi-layer external walls during realistic summer time conditions of Central European climate were considered. For this purpose, a finite element method was used to simulate the non-stationary thermal response of several heavy weight and light weight external wall constructions. The results have shown that indoor air change intensity as well as internal heat gains have a significant impact on heat flow through the building envelope. Clear difference in thermal behaviour was detected between light weight and heavy weight envelope systems, as a consequence of different thermal mass and thermal insulation position. While the results of the conducted study represent guidelines to architects, designers, investors and other stakeholders in building industry, the growing popularity of light weight constructions, especially in residential buildings, dictates further research of building envelope configurations and passive cooling system impact on the thermal response of constructions. [ABSTRACT FROM AUTHOR]

Carbon dioxide emission reduction is the most important challenge concerning on the road transportation. Stringent quantitative commitments have been set, both for automotive and for light and heavy duty vehicles. Future engine (and vehicle) technologies will consider a portfolio of new components, engine layouts, control strategies, integrated functions which will match also new comfort standards and fun to drive options, and complying fuel consumption savings. Engine thermal management is an area of intervention aimed at reducing the warm up time: in most part of the homologation cycle, both in passenger cars and in light duty vehicles, engines do not reach a stabilized thermal state. This produces a significant pollutants and fuel consumption increase. Engine thermal management can match also more effective cabin heating requirements, improving comfort, which is an important market advantage. Basic idea of engine thermal management is to reduce or make nil the cooling fluid circulation inside the engine. In this paper, the oil warm up is considered as the main focus: a faster temperature grow up decreases oil viscosity and improves mechanical efficiency and organic efficiency, during engine cold state. An experimental activity has been conducted on a dynamic test bench, testing the cooling fluid and oil dynamics of a widely known commercial engine, in fixed engine points and during the New European Driving Cycle (NEDC). A comprehensive mathematical model reproducing both the integrated circuits has been developed and validated: this required an overall engine and vehicle modeling whose input data was determined by the vehicle mission profile. By means of such model, three new technologies have been proposed and verified in terms of warm up time. They are: (a) by pass of the oil cooling, (b) oil heating using exhaust gases, and (c) a partial reduction of the oil quantity inside the sump. All of them were applied during transients, which revealed they are able to reduce warm up time of about 65–70% with a significant benefit in terms of CO 2 reduction. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to assess the economic impact following as a result of the conversion of conventional stations to cogeneration plants connected to a system for distributing heat and refrigeration. The analysis will be carried out through a financial evaluation in order to assess yearly variations of the whole scheme expenditure. In particular, yearly capital and operating costs of supplying cold and heat to urban areas that represent weather conditions in northern, central, and southern Europe (Oldenburg–Wilhelmshaven, Bristol, and Cartagena, respectively) were studied. In the base case scenario, today conditions are represented; they will be compared with alternative scenarios in which existing conventional thermal power stations will be converted into cogeneration plants. [ABSTRACT FROM AUTHOR]

Appropriate design provides the cooling system to achieve good performance with low energy consumption and cost. Conventional design method in heating, ventilation and air-conditioning (HVAC) field usually selects the cooling system based on certain cooling load and experiences. The performance of the selected cooling system may deviate from the expectations due to cooling load uncertainty. This paper proposes a novel design method to obtain the robust optimal cooling systems for buildings by quantifying the uncertainty in cooling load calculation and equipment reliability in operation comprehensively. By quantifying the cooling load uncertainty with Monte Carlo method and chiller reliability using Markov method, the robust optimal cooling system is obtained with minimum annual total cost. By applying the new method in the design of the cooling system for a building, its function and performance as well as potential benefits are demonstrated and evaluated. Results show that the proposed method can obtain the optimal cooling systems with low cost and high robustness and provides a promising means for designers to make their best design decisions based on quantitative assessment according to their priority. [ABSTRACT FROM AUTHOR]

• A resonance tube-coupled FPS-CCP system is proposed. • A novel time-domain unsteady model of the FPS-CCP system is developed and verified. • Evolvement of onset process is successfully achieved. • A cooling capacity of 1000 W at 110 K and electric power of 800 W with a global exergy efficiency of 29.4% is obtained. This paper proposes a novel resonance tube-coupled free-piston Stirling engine-based combined cooling and power (FPS-CCP) system for future application in scavenging unconventional natural gas from coal mines and oil fields. Unlike the traditional duplex Stirling system, the proposed system employs a resonance tube to couple an engine and a cryocooler. In addition, a linear alternator is introduced to facilitate startup and meet multiple demands, resulting in flexible adjustments and even higher exergy efficiency. A novel time-domain unsteady model based on thermoacoustic theory was developed to investigate the onset behavior of the (FPS-CCP) system. The proposed model successfully predicted the onset temperature and onset frequency. Results indicated that within the calculation range, the resonance tube with either a larger diameter or a shorter length leads to a lower onset temperature. Furthermore, the system performance under the steady-oscillating state was studied in terms of the typical operation characteristics and energy flow distribution. When the heating temperature is 833 Kand the mean pressure of helium gas is 5 MPa, the proposed system can provide a cooling capacity of 1000 W at 110 K and an electric power of 800 W with a global exergy efficiency of 29.4%, demonstrating an efficient power matching among the subsystems. [ABSTRACT FROM AUTHOR]

In this paper, the potential of industrial waste heat for heating and cooling applications is investigated. Therefore, heat transformation technologies are presented and their technical and economic potential are discussed. First, different industrial processes and their operating temperatures are presented as possible waste heat sources as well as low temperature processes, which can be supplied with waste heat. Then, a general economic analysis is performed for three different cases of waste heat use: an absorption chiller producing cold and heat production with a compression and an absorption heat pump. The maximum acceptable investment cost for each technology is estimated and compared with the current investment cost depending on the operating hours of the system. For this, three different consumer types, Enthusiast, Real Estate and Industry, are defined to represent different expectations in interest rate, payback period and the resulting annuity factor. Instead of judging if a technology is profitable or not, it is calculated how much the system is allowed to cost in order to be competitive for certain operating hours. Combined with present day cost of the technology, this serves as a rough judgment of the market deployment process. Finally, a sensitivity analysis of the initial assumptions for the economic analysis is performed, revealing a strong influence of the annuity factor. For the present day technology cost, absorption chillers were found to be profitable for two of the three consumer types when operated for at least 2500 h per year. Electric heat pumps are profitable for all consumer types when exceeding 4000 operating hours per year while absorption heat pumps start at 3000 h of operation per year to be profitable for all consumer types. [ABSTRACT FROM AUTHOR]

A great portion of the primary energy is consumed by space heating and cooling in buildings. The need for utilizing more renewable energy in the building sector remains critical for ensuring the energy and environment sustainability. Geothermal energy is one of the renewable energy sources that we have an easy access to for supplying low-grade thermal energy with a low impact on the environment. The methods of utilizing geothermal energy for buildings include such as ground source heat pumps and earth to air heat exchangers (EAHEs). In this paper we presented the comprehensive performance analysis and deduced an easy-to-apply regression model for predicting the cooling capacity of an EAHE. A one-dimensional steady-state control volume model was developed and applied to simulate the performance of the EAHE. It couples both heat and mass transfer between the air and the tube. The model was calibrated by comparing against the experimental data from an existing renewable energy testing facility. After the calibration, six factors, namely the air temperature, the air relative humidity, the air velocity at the inlet of EAHE, the tube surface temperature, and the tube length and diameter on the performance were analyzed using the calibrated model. The polynomial regression models for predicting the cooling capacities including total, sensible and latent cooling capacity with high accuracy were obtained. The easy-to-apply formulas can be of great use in the design and application of EAHEs. [ABSTRACT FROM AUTHOR]

In a modern greenhouse there are a number of alternative systems that can be deployed to control the climate, and the choice what to use and when is not easy for the grower. A novel management system is proposed, consisting of an energy input minimizing module, and a module to realise the determined input with the available equipment. The current paper describes the energy minimization part. A dynamic optimization tool based on optimal control theory was used to obtain time trajectories of the energy flux that minimizes total external energy input over the year, while maintaining greenhouse air temperature and humidity between grower defined bounds. By giving the grower the lead in defining the bounds, the method stays as closely as possible to the grower’s daily practice and experience, and no crop production models and market prices are needed. The underlying dynamic model of temperature and humidity, based on known physical principles and parameters, compared very well with unique, year round high frequent data from a commercial rose greenhouse. A relatively simple crop transpiration model was validated separately, with very good results. It was shown that over twelve selected days, distributed over the entire year, the energy saving potential as compared to the actual grower’s practice is substantial. This potential was related to the definition of lower and upper bounds, less natural ventilation at colder days, and more natural ventilation and less heating at warmer days. The prominent role of the bounds was clearly demonstrated. Relaxing the temperature and humidity bounds decreases the energy input to the greenhouse. While this is obvious, the quantification of the effect as demonstrated here is of great interest to growers, and is essential for the development of the second part of the system. [ABSTRACT FROM AUTHOR]

Comparative study on flat photovoltaic (PV) string and symmetric compound parabolic concentrator (CPC) photovoltaic system has been presented in this paper. Two flat PV strings and two unglazed PV–CPC systems are considered. The cells of each of the flat PV and PV–CPC strings are subjected to cooling to reduce temperature. The performance of the two configurations with and without cooling is evaluated numerically and experimentally. The numerical models for the flat PV string and the PV–CPC systems are solved using Engineering Equation Solver (EES) software and the concentration ratio of the CPC system is considered as 2.3X. Absorbed energy is calculated with and without cooling for the PV–CPC and flat PV systems. The absorbed energy is used to solve the energy balance equations on different nodes of the system from which the cell temperature was determined. The results showed that the maximum power output of the flat PV string with cooling was approximately 21 W which gives about 49% more than the power obtained without cooling. The maximum power output of the PV–CPC system with cooling was approximately 34 W which is about twice of the power obtained in the absence of cooling. It was found that the power output of the PV–CPC system is higher than that of the flat PV string with and without cooling by 39% and 23% respectively. Comparison of the numerical results with experimental data showed good agreement for the two configurations. The maximum percentage differences between the numerical and experimental power output for the flat PV with and without cooling are 5% and 7%, respectively. While those of the PV–CPC system with and without cooling are 9% and 11%, respectively. [ABSTRACT FROM AUTHOR]