• Energy Research

Abstract The time-varying nature of the heating loads of public buildings creates scope for exploring strategies to improve the energy system efficiency and to reduce the energy consumption and system operating costs. A well-researched and refined energy system operation strategy based on time-varying heating load demands is proposed in this paper. The proposed strategy is more effective and efficient than the existing experience-based operation strategies used to run energy systems. With full consideration of the factors affecting building heating loads under various scenarios, a multi-objective particle swarm optimisation algorithm combined with a scenario analysis is presented in this paper. The system efficiency and operation cost are set as two basic objectives to generate a Pareto frontier, and the occupant thermal comfort level is the dominant consideration while selecting an optimal state point for the final operation strategy. Using this simplified decision-making process, this approach can simultaneously calculate both the starting sequence and parameter settings for an optimised operation of the heat supply units. An energy plant on a university campus in Tianjin was selected to implement and evaluate this optimisation strategy. The case study results show that, without compromising the requirements of the thermal comfort of the building occupants, the energy system operating cost can be reduced by 38.9%, with an increase by a factor of 2.24 in the system coefficient of performance when compared with the current experience-based operation strategies.

Abstract During the past 5 years, the Chinese government has organized and implemented a large-scale energy-efficiency retrofit program for existing residential buildings in China׳s northern heating region. However, many obstacles, especially lack of successful financing arrangements, have limited the implementation of retrofits under the program. This paper analyzes the key financing challenges that have faced the program, using case studies of the different financing arrangements that have been used. Some of the key issues influencing the program׳s success to date are differing retrofit and other priorities of various stakeholders, timing and methods of payback on investments, potential investors׳ lack of access to risk analysis, uncertainty about benefit sharing, and the need for revisions in policies governing retrofits and energy contracts. We make recommendations to address these issues and improve the success of the north China energy-efficiency retrofit program.

The nature of the exergy consumption of district heating (DH) systems can not be explained clearly using the first law of thermodynamics. Exergy analysis method was used. A case study based on a DH system in Inner Mongolia, China, was carried out. The impact of operating parameters and design parameters on the energy quality of circulating water and exergy losses of DH systems during heat distribution was revealed. Results show that the energy quality of circulating water and exergy losses of DH systems during heat distribution could be reduced by decreasing the indoor temperature or increasing radiator areas. Compared with other factors, the outdoor temperature and indoor temperature have a greater impact on the energy quality of circulating water, exergy losses of circulating water, and total exergy losses during heat distribution. When the outdoor temperature varied by 10.00%, the average variation rates of such parameters were 85.12%, 90.02%, and 64.60%, respectively. When the outdoor temperature was 273.00 K and indoor temperature varied by 50.00%, the average variation rates of such parameters were 83.88%, 99.34% and 32.87%, respectively. It can be observed that the energy quality and exergy losses of DH systems can be reduced in the operation process.

Architectural shade is an effective method for improving building energy efficiency. A new shade combined with the double skin facade (DSF) system, called middle shade (MS), was introduced and developed for buildings. In this paper, a 3D dynamic simulation was conducted to analyze the influence of MS combined with DSF on the indoor thermal characteristics. The research on MS for DSF involves the temperature, the ventilation rate, the velocity distribution of the air flow duct, and the indoor temperature. The results show that the angle and position of the shade in the three seasons are different, and different conditions effectively enhance the indoor thermal characteristics. In summer, the appearance of MS in DSF makes the indoor temperature significantly lower. The indoor temperature is obviously lower than that of the air flow duct, and the temperature of the air flow duct is less affected by MS. The influence of the position of blinds on indoor temperature and ventilation rate is greater than the influence of the angle of blinds. According to the climate characteristics of winter and transition season, in winter, early spring, and late autumn, the indoor temperature decreases with the increase of the position of blinds at daytime, but the opposite is true at night. The results found in this paper can provide reference for the design and use of MS combined with DSF in hot summer and cold winter zone.

Abstract In this study, a novel hybrid composite PCM was manufactured by adsorbing octadecane into the porous supporting material based on the aluminum nitride (AlN) material, which owned high thermal conductivity. Meanwhile, a layer of nanocapsule PCM was coated on its surface for increasing the latent heat and achieving the PCM encapsulation. The results showed that the AlN efficiently enhanced the thermal conductivity of the composite PCM, and the addition of nanocapsule PCM further improved the stability and latent heat of the composite PCM. The composite PCM melted at 26.12 °C with a latent heat of 116.26 kJ/kg and solidified at 25.02 °C with a latent heat of 115.96 kJ/kg. In addition, the leakage problem of pure PCM was solved, and the thermal conductivity of composite PCM was 3.5 W/(m·K), which was 17.5 times of pure PCM. More importantly, the dynamic thermal performance exhibited the composite PCM as an energy storage material for buildings was able to lower the fluctuation of building temperature in winter. Therefore, the as-prepared composite PCM is a desirable candidate for building energy storage systems.

Abstract Phase change materials (PCM) and cool materials used in construction field cannot only effectively reduce buildings energy consumption, but also improve indoor thermal comfort and mitigate the urban heat island (UHI) condition. A novel energy efficiency roof coupled with PCM and cool materials has been conducted a field test in Tianjin of China. A kind of PCM-eutectic mixture was prepared, which was encapsulated in the polyethylene of raised temperature resistance (PE-RT) pipe, for using in building roofs. Thermal performances such as the roof surface temperatures and heat fluxes have been studied. The results indicated that, compared with reference rooms, the novel energy efficiency roof has shown good effect on decreasing the peaks of temperature and heat flux, which means that the influence of the outdoor circumstance on indoor environment has been weakened. In conclusion, it has been proved that the novel roof has good thermal insulation effect and energy efficiency potential.