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Passive daytime radiative cooling (PRDC) is a promising technology providing a cooling strategy that radiates heat directly into outer space without additional energy consumption, a crucial consideration in controlling construction energy consumption. However, the preparation of PRDC materials with controlled radiative properties is still challenging because the radiative interface must be maintained in a clean environment. Herein, a densely distributed porous hybrid aerogel with controlled radiative properties was fabricated using the wollastonite and cellulose as building blocks for building energy-saving applications. To do this, the cellulose pulp was obtained by using waste paper as raw material. Then, the hybrid aerogels, comprising paper cellulose and wollastonite particles, were fabricated by combining the acrylic acid polymers (PAA) bonding, freeze drying and vapor deposition modification. The radiative cooling hybrid aerogel exhibits high solar reflectivity (94.6%) and high atmospheric emissivity (95.1%), due to the laminated design of wollastonite randomly dispersed in the radiative hybrid aerogel. The excellent PRDC capability is also proven by outdoor tests where practical temperature difference is ~ 6.3 ℃ and the maximum cooling power of 147.4 Wm−2 under direct sun irradiance. Wettability test infers that the hybrid aerogel has a static water contact angle of 144.07° ± 2°, thereby indicating its hydrophobicity. In addition, based on the Energyplus simulation, the hybrid aerogel exhibits an average annual cooling energy saving of 8% in buildings across China. The excellent radiative cooling and self-cleaning properties of hybrid aerogel make it durable for long-term outdoor PRDC applications. [ABSTRACT FROM AUTHOR]

This paper proposes a temperature-adaptive radiative cooling (TARC) coating with simple preparation, cost effectiveness, and large-scale application based on a thermochromic powder. To determine the energy efficiency of the proposed TARC coating, the heat transfer on the surface of the TARC coating was analyzed. Then, a typical two-story residential building with a roof area of 258.43 m2 was modeled using EnergyPlus. Finally, the energy-saving potential and carbon emission reduction resulting from the application of the proposed TARC roof in buildings under different climates in China were discussed. The results showed that the average solar reflectivity under visible light wavelengths (0.38–0.78 μm) decreases from 0.71 to 0.37 when the TARC coating changes from cooling mode to heating mode. Furthermore, energy consumption can be reduced by approximately 17.8–43.0 MJ/m2 and 2.0–32.6 MJ/m2 for buildings with TARC roofs compared to those with asphalt shingle roofs and passive daytime radiative cooling (PDRC) roofs, respectively. This also leads to reductions in carbon emissions of 9.4–38.0 kgCO2/m2 and 1.0–28.9 kgCO2/m2 for the buildings located in the selected cities. To enhance building energy efficiency, TARC roofs and PDRC roofs are more suitable for use on buildings located in zones with high heating demands and high cooling demands, respectively. [ABSTRACT FROM AUTHOR]

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Building climatic zoning is a prerequisite for implementing building energy efficiency technology, which can help code makers and architects have an accurate understanding of the local climatic conditions. It takes the extreme monthly average temperature as the zoning index in the existing climatic zoning of rural areas in China. There will be unreasonable design phenomena of insufficient or excessive thermal insulation for a building envelope in rural areas. Aiming at the above problems, this paper modifies the current zoning. This research established the cooling and heating degree-day indexes HDD14 and CDD30 based on the thermal comfort characteristics of rural occupants and used the threshold method to subdivide rural areas into eight sub-zones. The results show that the problem of insufficient or excessive thermal insulation in rural areas can be effectively solved by replacing the extreme monthly average temperature index with the degree day index and the annual cumulative building load can be reduced by 6.4% on average without increasing the insulation cost. After more detailed zoning, the variance within the group is reduced and it accurately describes climate diversity, which is conducive to implementing climate-responsive energy-saving design in each subzone. Practical application : The major purpose of this paper is to solve the problem of unreasonable climate zone boundaries specified in the existing Design Standard for Energy Efficiency of Rural Residential Buildings. The existing zoning has led to conflicts between the actual heating demand and the building envelope thermal parameter limits specified in the standard. This work redefines the boundaries of the existing map using more up-to-date weather data to provide the right guidance for architectural designers. [ABSTRACT FROM AUTHOR]

Passive houses have strong thermal insulation and airtightness of doors and windows, and they are generally used in cold climates. This case study aims to evaluate the energy-saving potential of this technology in the hot-summer and cold-winter areas (Cf in Köppen climate classification) of China. The results show that after enhancing the thermal insulation and airtightness, the energy consumption in winter significantly decreased by 62% overall. However, the energy consumption of cooling in the transition season and summer increased, which is caused by overheating. Hybrid ventilative cooling and shading can solve this problem. In particular, when the indoor temperature range is set to the adaptive thermal comfort of natural ventilation, the energy consumption from air conditioner cooling can be greatly reduced by 81% overall. Passive houses combined with ventilative cooling has significant application value in this climate zone. [ABSTRACT FROM AUTHOR]

Climate is a key element in building design. The determination of adequate climate zoning is crucial for achieving building energy efficiency and reduced carbon emissions. In this study, a cluster analysis method was applied to develop new thermal climate zones for building envelope thermal design in China. In total, three different cluster analysis methods, including k-means, average-linkage, and Ward's clustering, were considered. The analysis indicated that the average-linkage clustering was more appropriate for this study, and the elbow method could not accurately determine the best number of categories of average-linkage clustering. Further analysis showed that the unsupervised cluster processes may generate an unavoidable redundancy category and, to obtain precise results, supervision may be necessary in some contexts. Finally, China was classified into 10 climate zones. The North China plain and Qinghai–Tibet plateau are classified into two independent climate zones, and Turpan and Bayanbulak were classified into two newly defined climate zones different from their surrounding area in the new definition. Quantitative analysis indicated that the new zones were more precise when compared to the current ones, which can provide more precise climate information and contribute to formulating more precise standards and policies related to the thermal design of building envelopes in the future. [ABSTRACT FROM AUTHOR]

Building integrated photovoltaic (BIPV) glazing is currently regarded as a promising building material with a wide range of benefits. Photovoltaic combined vacuum glazing is a relatively new innovative concept in BIPV glazing. On the other hand, photovoltaic combined hybrid vacuum glazing (PVCHVG) is a rarely studied topic in which an air gap exists between vacuum glazing and photovoltaic glazing to form an insulated glazing unit. This paper investigates the overall energy-saving performance of a CdTe-based semi-transparent PVCHVG. A dynamic simulation model was developed and validated with an outdoor experiment to explore the energy-saving performance of the PVCHVG under five different climate conditions in China, and the results were compared with commonly used window systems. The results indicated good insulation properties against both heat loss and heat gain due to the combined action of vacuum glazing and semi-transparent photovoltaic glazing. Compared to clear single-glazing and double-glazing window systems, PVCHVG can save overall energy consumption up to 59.39% and 39.97% in heating-dominated region, and 76.33% and 73.766% in cooling-dominated region, respectively. Furthermore, the PVCHVG window system generated electricity with a good performance ratio and total system efficiency ranging from 85.7% to 85.78% and 7.45%–7.55%, respectively, considering five climate conditions. • A CdTe-based STPV glazing combined hybrid vacuum glazing is investigated. • A dynamic simulation model is developed and validated with an outdoor experiment. • It poses inferior heat loss and heat gain in 5 distinct climate conditions in China. • The energy-saving potential is better in cooling than heating-dominated regions. • Key performance parameters for the window PV system are discussed. [ABSTRACT FROM AUTHOR]