Study On Building Fresh Air Handling Using Radiative Sky Cooling

Catering to the alleviation of the global warming trend,full use of renewable energy is crucial to saving energy,reducing carbon emissions,and realizing sustainability,especially under the Chinese policy of“carbon peaking”and“carbon neutrality”.In recent years,radiative（sky）cooling has become a focused area due to its exploitation of renewable energy,i.e.,deep space cold source.Radiative sky cooling is a phenomenon that terrestrial objects exchange heat with outer space,whose temperature is 2.7K,through what we called the atmospheric window and cool themselves by radiation.In this work,building fresh air handling using radiative sky cooling and its energy-saving potential under different climate conditions is discussed by means of experiment and simulation.First of all,radiative sky cooling is innovatively used for building fresh air pre-cooling.A fresh air pre-cooling system is designed as an active application of radiative cooling in buildings and applied in cities with high fresh air cooling loads in low latitude.A mathematical model of radiative cooling air panel was built using MATLAB with specified working area and fresh air flow rate to simulate the performance of the system under different climates and analyze the effects of different weather parameters.Furthermore,a typical medium office building model based on relevant energy-saving standards was developed in Energy Plus to analyze the energy-saving potential of the proposed system.Results show that the system can offer an energy-saving ratio of around 10%in tropical and subtropical cities.Further,to break the limit of static radiative cooling,an electrochromism-inspired dynamic radiative cooling system was proposed and designed based on the theory that silver electrochromic cell can switch between high transmittance state and high reflectance state.The system can be driven by voltage and switch between solar heating mode and radiative cooling mode adaptively,of which experiments were conducted to validate the feasibility.From bleached state to colored state,transmittance of the electrochromic glass reduces from 70%to1%,while reflectance goes up from 17%to 89%within the visible light and near infrared range（0.3～2.5 microns）.In addition,an energy-consumption-analysis model was developed to investigate the energy-saving performance of the proposed system in typical public buildings,industrial buildings,and residential buildings.Climate-adaptability of the system was validated by analyzing the performance in representative cities with various climate conditions in different climate zones of China.Finally,large-scale passive building application of radiative cooling and its prospective carbon emission reduction was studied since there lacks relevant research.Data from yearbooks was fetched and counted to estimate the total building stock.Nine typical building types were selected accordingly and modeled to estimate carbon emission reduction ratios,with which ratio maps were drawn to demonstrate the spatial distribution across China.Results show that the current building stock in China is 61.79 billion square meters,and the total annual carbon emission reduction is 184 million t CO₂,accounting for 8.72%of the carbon emissions from building operations and 1.91%of the total energy carbon emissions.By 2030,based on the estimated building stock,the annual carbon emission reduction can reach up to 253 million t CO₂.It is concluded that the passive application of radiative cooling has great prospective contributions toward the“dual carbon”goals of China.