Reducing energy consumption and creating a comfortable thermal indoor environment in rural residential buildings can play a key role in fighting global warming in China. As a result of economic development, rural residents are building new houses and modernizing existing buildings. This paper investigated and analyzed a typical rural residential building in the Ningxia Hui Autonomous Region in Northwest China through field measurements and numerical simulation. The results showed that making full use of solar energy resources is an important way to improve the indoor temperature. Reasonable building layout and good thermal performance of the building envelope can reduce wind velocities and convective heat loss. Insulation materials and double-glazed windows should be used to reduce energy loss in new buildings, although it is an evolution process in creating thermally efficient buildings in rural China. This research provides a reference for the design and construction of rural residential buildings in Northwest China and similar areas for addressing energy poverty.

Sodium sulfate (Na₂SO₄) and sodium carbonate (Na₂CO₃) are weakly alkaline activators. Alkali-activated slag (AAS) cement prepared with them shows the special advantages of long setting time and low shrinkage, but it shows slow development of mechanical properties. In the paper, Na₂SO₄ and Na₂CO₃ were used as activators and compounded with reactive magnesium oxide (MgO) and calcium hydroxide (Ca(OH)₂) to optimize the setting time and mechanical properties. The hydration products and microscopic morphology were also studied using XRD, SEM, and EDS. Furthermore, the production cost and environmental benefits were compared and analyzed. The results show that Ca(OH)₂ is the main influencing factor for setting time. It reacts preferentially with Na₂CO₃ to form CaCO₃, which makes AAS paste lose plasticity rapidly and shortens the setting time, and then produces strength. Na₂SO₄ and Na₂CO₃ are the main influencing factors for flexural and compressive strength, respectively. Suitably high content is beneficial to promote the development of mechanical strength. The interaction of Na₂CO₃ and Ca(OH)₂ shows a great effect on the initial setting time. High content of reactive MgO can shorten the setting time and increase the mechanical strength at 28 days. There are more crystal phases in hydration products. Considering the setting time and mechanical properties, the composition of activators are: 7% Na₂SO₄, 4% Na₂CO₃, 3–5% Ca(OH)₂, and 2–4% reactive MgO. Compared with ordinary Portland cement (OPC) and AAS cement activated by sodium hydroxide (NaOH, NH) and water glass (WG) with the same alkali equivalent, the production cost and energy consumption are greatly reduced. Compared with P·O 42.5 of OPC, CO₂ emission is reduced by 78.1%. AAS cement activated by weakly alkaline activators shows excellent environmental and economic benefits and good mechanical properties.

To analyze the effect of summer ventilation on the thermal performance and energy efficiency of buildings utilizing phase change materials (PCMs), this paper simulated the indoor temperature variation and energy saving performance of buildings constructed with PCM under different ventilation conditions from June to September. With EnergyPlus and degree-day method, 48 ventilation schemes, including eight ventilation periods (3 h per period) and six ventilation quantities (0.5 ac/h to 3 ac/h), were modeled and simulated in five cities located in different climate regions in China. According to the results, it is believed that the simultaneous use of PCM and ventilation can significantly improve the indoor thermal comfort and offer a good energy saving performance in summer. Considering the economic benefits, different optimal ventilation schemes (including ventilation periods and ventilation quantities) were suggested for different climate regions.

In areas where solar energy is abundant, such as the Tibetan plateau, passive solar buildings are attracting more and more attention and becoming a popular form of rural building. However, it is often difficult to achieve the satisfactory indoor thermal environment in a local rural passive solar single-family house. In order to improve the indoor thermal environment of passive solar buildings through building design, a systematic study of rural single-family buildings in Tibet was conducted. The basic parameters were investigated on the outdoor thermal environment, space-arrangement, envelope structure, and the indoor thermal environment. The building model considering space-arrangement modes was developed based on the survey data in multi-space passive solar buildings. The general physical and mathematical analysis models of multi-space passive solar buildings were established based on the heat transfer theory. Furthermore, the effects of space-arrangement and exterior wall thermal resistance on indoor air temperature were analyzed by numerical simulation. Results show that the indoor air temperature of the passive solar building is influenced by space-arrangement and wall thermal resistance together. When the space-arrangement of the building model was changed from “north-south through type” (mode a) to “through and separation combination” (mode b) and “north-south separation” (mode c), the indoor air temperature of the living room increased from 8.8 °C to 10.6 °C and 11.6 °C, with increases of 20.5% and 31.8%, respectively. In addition, equally increasing the thermal resistance of exterior walls in different orientations has different effects on the indoor air temperature. In the space-arrangement mode c, comparing with the temperature increment of the living room and bedroom caused by increasing thermal resistance of the south wall and north wall, the temperature increment of the living room caused by increasing thermal resistance of the east/west wall increased by 151.7% and 32.7%, and that of the bedroom increased by 609.1% and 239.1% respectively. This study can provide a reference for the optimal design of passive solar buildings in solar energy abundant areas.

Efficient use of solar energy by thermal energy storage composites and utilizing environmentally friendly cementitious materials are important trends for sustainable building composite materials. In this study, a paraffin/low density polyethylene (LDPE) composite shape-stabilized phase change material (SSPCM) was prepared and incorporated into a sulphoaluminate cement (SAC) mortar to prepare thermal energy storage mortar. The thermal and mechanical properties of SSPCM and a SAC-based thermal energy storage material (SCTESM) were investigated. The result of differential scanning calorimeter (DSC) analysis indicates that the latent heat of SCTESM is as high as 99.99 J/g. Thermogravimetric analysis demonstrates that the SCTESM does not show significant decomposition below 145 °C. The volume stability test shows the volume shrinkage percentage of the SCTESM is less than that of pure SAC mortar and far less than that of ordinary Portland cement mortar. The SCTESM has high early strength so that the compressive strength at 1-, 3-, and 7-day curing age is up to that at 28-day curing age of 67.5%, 78.3%, and 86.7%, respectively. Furthermore, a mathematical prediction model of the SCTESM compressive strength was proposed. The investigation of latent heat storage characteristics and the thermoregulating performance reveals that SCTESMs have the excellent capacity of heat storage and thermoregulating.

Phase change material (PCM) embedded in the building contributes to enhancing indoor thermal comfort and reducing the heating load in winter by absorbing/releasing solar energy. The application effects of PCM incorporated into a single-space passive solar building with the auxiliary heating system (AHS) were investigated numerically in the six representative regions of western China. In the calculation and analysis by the enthalpy model, it was found that the effectiveness of PCM greatly depended on local climate conditions, thickness, and location of PCM. The results indicated that it was necessary to adopt the AHS for winter heating of the passive solar building. On this basis of using AHS, it showed a favorable thermal energy storage effect after the application of PCM resulting in the minimum indoor air temperature being maintained above 15°C within the comfort range stably. The integrated discomfort degree in each region was decreased by more than 96% compared to the original building, and the average temperature in Lhasa was 2°C higher than that in Urumqi. Furthermore, the highest rate of energy saving and carbon dioxide emission saving in the six regions was 19.7% and 17.4% in Lhasa, and the lowest were 4.3% and 4.2% in Urumqi, while other regions were relatively close, respectively. As a result, it can be stated that for a passive solar building using the AHS during the heating period, PCM was the most suitable for application in Lhasa, unsuitable in Urumqi, and generally suitable in other regions.