Organic phase change material (PCM) with macro-encapsulation is attractive in energy storage applications as it has relatively low cost. This study focuses on using PET plastic pipes to encapsulate paraffin and using low-cost float stones to increase the thermal conductivity of PCM modules as they have a special structure of high porosity. Float stones were immersed in the liquid PCM and an ultrasonic welding method used to prevent leakage of the PET plastic pipes. Scanning electron microscopy (SEM) was used to discover the appearance of the composite PCM. The thermal performance of the PCM cylinder module was analyzed through experimental tests of a constant-temperature water bath and numerical simulations. The result indicates that this PCM Ccylinder module is superior in thermal energy storage compared with the reference module even though fewer PCM was contained and the latent heat loss is considerable. The pipe diameter is an important parameter when using this kind of PCM cylinder module in water tanks.

A total of 8 mechanically ventilated residential buildings and 8 naturally ventilated residential buildings were selected to analyze the pollution characteristics of indoor VOCs under different ventilation modes in the severe cold area of northeast China. On typical meteorological days in each season, VOCs were detected on site, and ventilation modes were investigated by long-term online monitoring. The test results showed that the TVOC (total volatile organic compounds) concentrations varied greatly in different seasons or different functional rooms, and the TVOC concentration was the highest in winter, with a value of 0.994 mg/m³. The kitchen was the place with the most serious VOC pollution, and the TVOC concentration could reach 1.403 mg/m³. Benzene series and methylsiloxane had the highest detection rates, but the detected concentrations were low, and the average concentrations were 0.025 mg/m³ and 0.013 mg/m³ respectively. Among the VOC types with a detection rate greater than 50%, the average proportions of aldehydes, alkanes, and benzene series were 18.7%, 15.39%, and 14.38%, respectively. And their mass ratios were also high, which were 14.90%, 30.85%, and 15.70%, respectively. The annual daily average ventilation duration of mechanically ventilated residential buildings was 7.84 h longer than that of naturally ventilated residential buildings. The median TVOC concentrations of mechanically ventilated residential buildings and naturally ventilated residential buildings were 0.621 mg/m³ and 0.707 mg/m³, respectively. The fresh air system was applicable in the severe cold area of northeast China.

In this paper, the effects of night natural ventilation on indoor thermal environment of ultra-low energy consumption in a university in Shenyang were evaluated. The DeST software was used to establish the ultra-low energy consumption building model and the conventional building model, and the accuracy of the model is also verified experimentally. The indoor temperature, building power consumption of air conditioning system of the two models were calculated under the natural ventilation condition at night. The results show that under the optimal night natural ventilation conditions in July and August, the energy saving rate of ultra-low energy building refrigeration system is 15% and 46% respectively. The energy saving rate of conventional building refrigeration system is 14% and 44% respectively. The peak indoor temperature of the two types of buildings decreases with the increase of natural ventilation time at night. Both ultra-low energy consumption buildings and conventional energy consumption buildings adopt natural ventilation at night to help reduce indoor temperature, building power consumption of cooling system.

In order to study the fresh air load characteristics of low energy consumption buildings with different envelope structure parameters, combined with the law of fresh air load, energy saving measures were studied. Taking the ultra-low energy consumption building of Shenyang Jianzhu University as an example, the DeST simulation software was used to establish five groups of models with different envelope structure parameters for load simulation. The simulation results show that the fresh air heat load in model 1 to model 5 is 29.89%, 34.66%, 38.60%, 44.68% and 53.36% of the building heat load, respectively. The seasonal fresh air cooling load of air conditioning accounted for 13.78%, 13.85%, 13.88%, 13.99% and 14.05% of the building cooling load respectively. The thermal insulation performance of the envelope has great influence on the thermal load of the building, but little influence on the cooling load of the building. The better the insulation performance of building envelope, the greater the energy saving potential of fresh air load. Fresh air heat load is sensible heat load, and fresh air cooling load is mainly latent cooling load. From the theoretical point of view, the building adopts a heat recovery device with a heat recovery efficiency of 0.6, which can save 5989.91kW • h in the heating season and reduce the building heat load by 32.02%. In the air conditioning season sensible heat recovery device can save energy 131.45kW • h, reduce building cooling load by 1.56%; Total heat recovery device can save energy of 708.73kW • h and reduce cooling load of building by 8.43%.With the development of zero-energy building technology, the requirement of fresh air energy consumption is more strict, and the active all-heat fresh air heat recovery device is more suitable for this building. It also has more space for future development. This paper analyzes the change of energy saving potential of fresh air with the development of building envelope. The methods and ideas of reducing energy consumption of fresh air in low energy consumption buildings are discussed.

Frost formation is a common phenomenon observed across many different fields, including refrigeration, construction, and natural gas processing. However, due to its complex nature, developing an accurate and reliable numerical model remains a significant challenge. Despite previous efforts to tackle this issue, current models still have certain limitations. This paper introduces a modified numerical model for frost formation, developed based on the fundamental mechanisms underlying frost formation. The model utilizes an Eulerian multiphase flow approach coupled with the Lee phase change model. In addition, the approach for determining the maximum frost volume fraction is updated, enabling the model to consider density variations during the frosting process. The model is rigorously validated by comparing it with experimental data on thickness, density, and distribution from various studies. The results indicate that the mean absolute relative deviation (MARD) for frost thickness is 8.97%, while the MARD for density is 16.06%. Furthermore, the frost morphology predicted by the model closely matches the experimental observations reported in the reference.

Frost formation is a common phenomenon observed across many different fields, including refrigeration, construction, and natural gas processing. However, due to its complex nature, developing an accurate and reliable numerical model remains a significant challenge. Despite previous efforts to tackle this issue, current models still have certain limitations. This paper introduces a modified numerical model for frost formation, developed based on the fundamental mechanisms underlying frost formation. The model utilizes an Eulerian multiphase flow approach coupled with the Lee phase change model. In addition, the approach for determining the maximum frost volume fraction is updated, enabling the model to consider density variations during the frosting process. The model is rigorously validated by comparing it with experimental data on thickness, density, and distribution from various studies. The results indicate that the mean absolute relative deviation (MARD) for frost thickness is 8.97%, while the MARD for density is 16.06%. Furthermore, the frost morphology predicted by the model closely matches the experimental observations reported in the reference.