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Solar-based radiant heating systems represent a sustainable, and relatively low-cost, technology to raise the temperature of the interior thermal mass of our buildings. Through the use of direct absorption solar thermal collectors, the same working fluid which absorbs the solar energy can be used to transfer the energy for storage in the thermal mass of the structure using a network of pipes embedded in concrete floors. This study investigates a promising working fluid which can be used in such systems – one which is based on multi-walled carbon-nanotubes suspended in normal base fluids. A major stumbling block affecting the wide spread use of carbon-nanotube nanofluids is their low dispersion stability at elevated temperatures, which significantly reduces the absorption capabilities of the nanofluids and could lead to clogging of the pumps used to circulate the fluids. In this paper, we report on a scalable UV-ozone (UVO) treatment technique to produce highly stable dispersions for the elevated temperatures experienced by working fluids in radiant heating systems. To probe suitability of UVO treated multi-walled carbon-nanotube (MWCNTs) for solar-assisted radiant heating systems, this paper investigates the effects of exposure time and temperature on stability, optical absorbance properties, the extent of functionalisation, and the photothermal conversion performance of UVO-treated MWCNT nanofluids. No agglomeration or degradation of the MWCNTs was observed at elevated temperatures (up to 150   °C), highlighting the stability of proposed nanofluids. [ABSTRACT FROM AUTHOR]

HVAC systems in buildings are composed of many subcomponents which consume energy in huge amounts. In recent years, energy consumption becomes very important aspect due to the lack of energy resources and environmental reasons. In terms of energy consumption, the components of HVAC systems account for large portion of total energy used in buildings. Therefore optimization of energy consumption in HVAC applications is an essential requirement in terms of thermodynamic and economic point of views. Besides, the efforts for decreasing energy consumption turn into economic recovery. It also provides benefits for human health and cleaner environment. In this paper, as originality, thermodynamic and economic analyses of an existing social and cultural building which has a heating and cooling area of 8852 m 2 are presented by comparing of a conventional HVAC and a VRF system. A novel contribution is given to the open literature by comparing two systems with actual data measured from the existing system. The other originality is to apply and test a VRF system to a complex-structured building. This study is a rare one which contains insulation, heating and cooling accounts of a building together. In this paper, VRF system is modelled to the existing building for the comparison of the conventional HVAC system. Both systems have been compared in terms of heating and cooling capacity, initial, operation and maintenance costs. It is found that the VRF system is more economic and efficient such that the VRF system is found to have 44% cost profit when compared with the conventional HVAC system. [ABSTRACT FROM AUTHOR]

Abstract: The article described the dilatancy technology of district heating system with high-temperature heat pump (HTHP). For the exploitation of low-temperature return network sources, a high-temperature heat pump with a heat exchanger was planned. As the core technology of the dilatancy district heating system, HTHP units and heat exchanging systems had been described detailedly through theoretical and experimental analysis. The model was proved to be in good agreement with the experiment data. It could be used for engineering design. In this paper the district heating system in Datong was taken as a case study. The main characteristics of the dilatancy district heating system had been presented in the form of diagrams. The principal advantage of dilatancy technology in the district heating system lies in increasing the temperature difference, reducing the diameters and the initial investment of primary side network. This paper shows clearly the analysis of the dilatancy technology for characterising and improving the performance of district heating systems. [Copyright &y& Elsevier]

Abstract: This paper presents a review of studies on natural convection heat transfer in the triangular enclosure namely, in attic-shaped space. Much research activity has been devoted to this topic over the last three decades with a view to providing thermal comfort to the occupants in attic-shaped buildings and to minimising the energy costs associated with heating and air-conditioning. Two basic thermal boundary conditions of attic are considered to represent hot and cold climates or day and night time. This paper also reports on a significant number of studies which have been performed recently on other topics related to the attic space, for example, attics subject to localized heating and attics filled with porous media. [Copyright &y& Elsevier]

• A new enclosed melting system was built for deicing the bottom of a train. • A new method was used for simulating gravity shedding melting in complex models. • The effect of supply air properties on system performance was studied. In winter, a large amount of icing and snowing occurs in outdoor equipment and systems, which adversely affects their lifespan. The melting process is divided into two parts: convection melting and gravity shedding melting. This paper is based on an experiment with a real high-speed train unit, and it establishes a three-dimensional computational fluid dynamics model of the bogie area to validate the mathematical model of the winter ice melting experiment. A numerical simulation was used to calculate the airflow in the baffle-enclosed space and to predict the effects of interactions between air and the ice body on heat transfer and phase change. The influence of air velocity and temperature on the heat transfer was analyzed. The computational simulation effectively quantifies the amount of heat transfer and energy consumption under different conditions. This paper also presents a research method for the simulation of gravity shedding in complex models. These models provide information for the construction of similar ice melting models. This paper has suggested that for thin ice bodies, convection melting was the dominant strategy. For thick ice bodies, however, gravity shedding melting became dominant. The study also confirmed that enclosed hot-air ice-melting systems gave a better energy performance than unenclosed systems. [ABSTRACT FROM AUTHOR]

In continental climates heating accounts for a significant part of the total energy consumption of a residential building with average thermal characteristics of the envelope. Solar heat gains have to be used wisely in order to reduce the energy need for heating. Glazed ratio of the facades, orientation of the transparent area and thermal mass has to be properly chosen in order to obtain the desired utilization factor. In this paper the effects of window size, thermal mass and window orientation on the balance point temperature are analysed in case of a reference room. The calculation methodology given by EN ISO 13790 standard was used. Measurements were done in order to validate the model. Performing the calculus on 48 different cases it was shown, that differences of even 11% can appear between the energy demands for heating (for similar overall heat transfer coefficients of the external building elements). [ABSTRACT FROM AUTHOR]

• Simplified models for heat transfer and surface temperature were established. • Calculated heat transfer and surface temperature agreed well with experimental data. • Heat transfer and surface temperature linearly changed with mean water temperature. • The pipe space clearly affected the heat transfer and surface temperature. • Heat transfer and surface temperature varied greatly as the transition changed. Prefabricated radiant heating and cooling (RHC) system is a typical form of high efficiency and lightweight radiant terminal, which has been extensively used in the residential and non-residential buildings. Heat transfer and surface temperature are the key parameters for rational design of a prefabricated RHC system. Therefore, in this paper, based on the analysis of the heat transfer mechanism, simplified models and numerical models were established for calculating the heat transfer and surface temperature of the prefabricated floor or ceiling RHC system. Compared with experimental test results, when the supply water temperature increased from 35 °C to 50 °C under heating condition or from 13 °C to 19 °C under cooling condition, the relative errors calculated by the simplified models were between −10.8% and 3.7% and between −3.8% and 5.0% for the heat transfer and surface temperature of the prefabricated floor RHC system, and ranged from 0.8% to 6.9% and from −0.7% to 0.3% for the prefabricated ceiling RHC system. Moreover, the calculated heat transfer and surface temperature of the prefabricated ceiling or floor RHC system using the simplified models were highly consistent with the numerical simulation results. Hence, the calculation accuracy of the proposed simplified models for the heat transfer and surface temperature can meet the requirements of engineering application, which will provide the support for the rational design of a prefabricated floor or ceiling RHC system. [ABSTRACT FROM AUTHOR]

• Heat exchange performance optimization study of the coaxial deep borehole heat exchanger. • Optimal insulation backfill depth for deeply buried pipes. • Multi-factor orthogonal simulation experiment. • Multiple linear regression analysis for optimal insulation backfill depth. Coaxial deep borehole heat exchanger (DBHE) coupled with ground source heat pump (GSHP) system has been widely applied in building heating. Insulation backfill is essential for the heat transfer performance of DBHE in colder regions. However, few studies focus on the combined influence of multi-factors on the optimal insulation backfill depth. In this paper, an orthogonal experiment was designed to explore the influence of multi-factors on the optimal insulation backfill depth of DBHE by using a numerical heat transfer model. Sensitivity analysis concluded that heat transfer factors such as inlet flow rate (A), inner pipe thermal conductivity (B), inlet temperature (C), geothermal gradient (D), and pipe depth (E) all affected insulation backfill depth of DBHE, and the comparison order of significance are C > D > B > A > E. An optimal insulation backfill depth exists for different DBHE heat transfer conditions. Compared with no insulation backfill, the average heat extraction of buried pipe under optimal insulation backfill conditions increased by 6.09 kW, with an average growth rate of 8.78 %. In addition, multiple linear regression analysis was utilized to examine the relationship between affecting factors and the optimal insulation backfill depth, based on the findings of orthogonal tests. The outcomes revealed that inlet temperature, inner pipe thermal conductivity, and pipe depth were positively correlated, with the highest standardized positive correlation value of 0.755 for inlet temperature. In contrast, inlet flow and geothermal gradient were negatively correlated, with the highest standardized negative correlation coefficient of −0.420 for the geothermal gradient. The linear regression equation could predict the magnitude of optimal insulation backfill depth with diverse input parameters. The relative error between the predicted and simulated values of the equation was less than 5 %. The findings of this research can guide the popularization and application of the GSHP coupled with the DBHE system in colder regions. [ABSTRACT FROM AUTHOR]

• A new methodology to investigate the impact of thermal mass is defined. • The use of unrepresentative boundary conditions could lead to inaccurate conclusions. • High thermal mass helps to decrease and regulate the internal temperature. • High thermal mass could increase energy use in the summer and winter seasons. • Isolating thermal mass through internal insulation results in better energy performance than external insulation. Contradictory conclusions have been reported on whether thermal mass reduces or increases energy demand in hot and cold climates. A novel approach to measuring the impact of thermal mass on the building's energy consumption is presented. The method aims to better represent reality and applies two different control conditions simultaneously in a numerical model: the first condition, which has been used in past studies, adjusts the internal boundary condition based on the time duration of heating/cooling activation (simulating an occupancy pattern) and the second, which has not been used in past studies, adjusts the internal boundary condition based on both the time duration and the internal temperature (simulating an occupancy pattern and the thermostatic control system). When investigating the impact of thermal mass on the internal temperature in a scenario where no heat is transferred into the building, the high thermal mass outperforms the low thermal mass, showing a time-shifting effect, long time lag, and small decrement factor. However, when modelled using the method presented in this paper, high thermal mass results in greater energy consumption during summer and winter periods in Saudi Arabia. During transition seasons where temperature swings occur on either side of the indoor set-point temperatures, thermal mass reduces thermal transmission. The impact of thermal mass is also investigated for several climatic conditions in Saudi Arabia. Simulation results show that an internally exposed thermal massive wall section results in greater energy consumption when compared to a similar building with isolated thermal mass (i.e. insulated internally). This is due to the fact that even though the internal temperature inside the building is being cooled/warmed up to the set-point, the thermal mass continues to transfer heat that is absorbed by the building's fabric from/to the interior, placing a greater demand on the cooling/heating system. Over the course of a year, however, the impact of thermal mass is negligible when compared to other factors, such as the insulative properties of the building's fabric. [ABSTRACT FROM AUTHOR]

The paper examines implementation of heat saving measures in buildings in 2050, under the assumption that heat and power supply comes solely from renewable resources in Denmark. Balmorel – a linear optimisation model of heat and power sectors in Denmark is used for investigating economically viable levels of heat savings, which can be implemented by reducing heat transmission losses through building elements and by installing ventilation systems with heat recovery, in different future Danish heat and power system scenarios. Today almost 50% of heat demand in Denmark is covered by district heating. A further expansion of district heating network in Denmark is assessed and penetration of heat savings is analysed in this context. If all heat saving measures, included in the model, are implemented, heat demand in Danish buildings in 2050 could be reduced by around 40%. Results show that it is cost effective to reduce from approximately 12% to 17% of future heat demand in buildings depending on assumed lifetime and costs of heat saving measures. Individual heating areas have higher penetration of heat savings than district heating areas. When district heating systems are expanded, an overall penetration of heat savings slightly decreases along with lower capacity investments and system costs. [ABSTRACT FROM AUTHOR]

Abstract: Thermal mass can be effectively used for controlling temperature in buildings. Based on its location and function, building thermal mass can be classified as interior thermal mass and exterior (envelope) thermal mass. In this paper, the dynamic heat transfer performance of exterior Planar Thermal Mass (ePTM) subject to sinusoidal heating and cooling is investigated. When the mean value of outdoor air temperature is equal to indoor air temperature, solutions of temperature distribution and heat flux in ePTM are deduced analytically. Using the analytical solutions, heat exchange and thermal storage of ePTM are attained. Correspondingly, the time lag and the decrement factor are obtained; they show similarity characteristics—independent of environment temperatures. When the two temperatures are not equal, an approximated temperature distribution solution is developed based on the principle of superposition, which has been validated by numerical solutions. The approximated solution is then used to investigate the heat exchange between the ePTM and the environment. In contrast to the common belief that a large thermal mass has an apparent insulating effect, no “insulating effect of mass” under sinusoidal heating and cooling is found in this investigation. Another two rules of thumb based on common belief are corrected: a wood wall is better than a concrete wall of same thickness as exterior walls in terms of the time-lag effect and the decrement factor. The effect of the time lag is not the longer the time lag is the better its contribution to thermal comfort becomes. [Copyright &y& Elsevier]

Abstract: The use of groundwater for cooling and heating purposes is of interest from both the economical and the ecological perspective. The groundwater heat pump (GWHP) system utilizes groundwater as alternative renewable and clean energy source for space heating and/or cooling, withdraws water from a production well, passes it through a heat exchanger and discharges the water into an injection well. By utilizing the relatively stable temperature of groundwater, GWHP system can achieve a higher coefficient of performance. Due to the utilization of groundwater stored in the aquifer, the assessment of the hydraulic capacity of the aquifer based on numerical groundwater models is always needed for the optimum design and the efficient performance of GWHP. In this paper, numerical methods of underground heat-water transfer, energy balance method and thermal storage method were presented to calculate the capacity of unit area of shallow groundwater aquifer. The model results indicate that the numerical method, which is based on performance efficiency of GWHP, represents the behaviour of groundwater pumping/recharging processes, and serves better than energy balance method and thermal storage method, in addition it has been proven itself that this method has the advantages of energy saving and environmental protection. The calculated capacity is positively related to aquifer thickness. It is found that it is easy for ground water recharge in alluvial and pluvial fan located at the piedmont, while the calculated capacity is relatively smaller compared with that of south-east plain where it is not easy for groundwater recharge. [Copyright &y& Elsevier]

Abstract: New Zealand has a temperate maritime climate. Despite mild winters compared to nations with continental climates, New Zealand houses have been reported to often be at temperatures below internationally recommended levels. Sources of additional heating are therefore of interest to many New Zealand home occupants. Roof space solar gains have been identified as one possible source of heating. This paper investigates the energy gains available in New Zealand homes from ventilation systems drawing air from the roof cavity. Three New Zealand houses were monitored and a computer-based thermal building simulation developed to quantify the heating and cooling energy that might be transferred by home ventilation systems. The computer model simulating the temperature in the roof space and occupied spaces was constructed using MATLAB, and used publicly available weather station data as the inputs. A good match between measured and modelled results was obtained. Small heating and cooling benefits are possible at certain times from pumping roof space air into the living areas of some New Zealand houses. The magnitude of these benefits, however, is not significant compared with the space heating required to maintain reasonable indoor temperatures over the New Zealand winter. [Copyright &y& Elsevier]

• The cascaded PCMs charge–discharge processes and cycle entransy models are studied. • To run stably and efficiently, the charge–discharge cycle model is recommended. • The thermal performance of cascaded PCMs may be worse than that of single PCM. • The cascaded PCMs is suitable for scenes with large temperature differences. • In heating systems, the total NTU of cascaded PCMs is recommended between 4.5 and 6. Thermodynamic analysis can guide the application of the cascaded latent heat storage system (CLHSS) for space heating. However, in previous studies, the CLHSS charge–discharge process and the cycle are not distinguished, and the applicability of the corresponding models is not analyzed. In addition, the technical advantages of CLHSS in heat utilization are still unclear. This paper solved the above three problems to provide theoretical guidance of the CLHSS integrated into heating systems. First, the CLHSS charge–discharge cycle is the special charge–discharge processes in which the initial and final states of each PCM are consistent. The CLHSS charge–discharge processes and cycle models are established and optimized. Second, the optimization results of charge–discharge processes model cannot ensure the same initial and final states of each PCM, which leads to unstable operation and performance degradation of the CLHSS. Thus, the CLHSS charge–discharge cycle model is recommended. Third, when the total number of heat transfer unit (NTU) of CLHSS is less than that of single-stage latent heat storage system (SLHSS), the thermal performance of CLHSS may be worse than that of SLHSS. Besides, the use of CLHSS instead of SLHSS is suitable for scenes with large temperature differences between heating equipment and heating terminals. Finally, parameters effects on optimization results are analyzed. From the perspective of improving entransy efficiency, it is recommended that the total NTU of CLHSS during charge process and discharge process are between 4.5 and 6, and as close as possible. [ABSTRACT FROM AUTHOR]

Abstract: Energy performances and building quality can be achieved by high performance envelopes. In this paper the thermal and mechanical performances of external cladding, applied to a traditional wall, largely used in existing buildings, were investigated by a transient simulation. Result comparison with the thermal performances obtained by simulating the wall without the insulation system showed that external insulation is particularly effective in reducing cooling and heating loads and can also guarantee indoor thermal comfort. Fatigue stresses of the external cladding, investigated by ANSYS simulation, showed that continuous change of the loads over time with limited cyclic stress can cause deterioration of materials. [Copyright &y& Elsevier]

Abstract: An energy cost allocation system records the energy consumption of a building and divides the overall energy costs between the flats. Because the indoor temperatures of rooms are usually not equal, static heat flows between flats cannot be avoided. Hence, in order to ensure fair energy costs per flat the system should be able to determine the static heat flows, preferably without utilising in situ measurements. This paper presents a new method for estimating static heat flows between neighbouring rooms. The approach is theoretical, focusing only on heat transfer issues. Energy cost allocation is not considered. The approach is based on the parametric model describing thermal behaviour of an occupied space. The model is created for each room of a building. Parameter values are identified using real-time measurements collected by a building automation system from each room and its environment. The tuning of parameters takes a few days using a 15-min sampling time. A prerequisite for successful system identification is the overall control of the room temperatures. All test runs are performed in a simulated office hotel using the TRNSYS simulation program. The results are encouraging, but further research is needed, especially in a real building environment. [Copyright &y& Elsevier]