Energy-saving Renovation Of Existing Office Buildings In Hot Summer And Cold Winter Areas Combined With Radiant Ceiling Cooling And Heating And Overhead Air Distribution Systems

With the pressure of energy use increases,China has proposed the timing for carbon plan,indicating that it will strive to reach the peak of carbon dioxide emissions by 2030 and strive to achieve carbon neutrality by 2060.In order to achieve this goal,as the energy use field with the greatest energy-saving potential,building industry not only needs to promote the energy-saving of new buildings,but also needs to improve the energy efficiency and indoor environment of existing buildings.Existing office buildings have large stocks and high energy use.Therefore,reducing the energy use of existing office buildings and improving indoor environmental quality have become a crucial research topic.This research selected an existing office building(constructed in the 1990s)in Suzhou which is equipped with a radiant ceiling cooling/heating and overhead air distribution(RCF)system as the study case.Through theoretical analysis,field investigation,energy/thermal simulation and data statistics,the indoor thermal comfort conditions and energy performances were studied.The study then analyzed comprehensive energy-saving renovation measures improving existing office buildings to meet the energy performance of ultra-low energy buildings standards.On-site thermal comfort conditions of the existing office building combined with the RCF system for cooling and heating was studied in summer and winter,respectively,with on-site measurement,questionnaire survey and data statistics.Under cooling conditions,at the operative temperature(OPT)range of 23.6-28.6℃,the actual thermal sensation from occupants with the RCF system has deviated from the PMV model.Within the same OPT,the main advantage of the RCF system is less complained than that of traditional convective air conditioning systems.Under cooling conditions,the thermal neutral temperature is about 26℃,and the thermal preference temperature is about 25.3℃.Under heating conditions,the PMV model can accurately predict the actual thermal sensation of occupants surveyed with RCF system at the OPT range of 20-24.5℃.Under this condition,the thermal neutral temperature is about 21.1℃,and the thermal preference temperature is 22.7℃.Under cooling and heating conditions,the local thermal sensations and the whole thermal sensations have high and medium correlation,and the local thermal sensations and the whole thermal comfort levels have medium and weak correlation,respectively.The energy-saving possibility of existing office buildings with RCF system was studied.The study adopted DesignBuilder and EnergyPlus software to simulate the existing office building in Suzhou as the study case,and combined the actual measurement of building energy use and indoor thermal environment to carry out model calibration and comparison verification.The energy-saving scenarios of the building envelope improvement and the replacement the original variable refrigerant flow air conditioning system(VRF)with the RCF system were analyzed.For the existing office buildings in Suzhou,improving the performance of the envelope,the annual heating,cooling,fan and pump(HVAC)energy use may be reduced 19.5%;replacing the original VRF system with the RCF system is expected to reduce annual HVAC energy use may reach 30%,of which the cooling related energysaving rate is 34%in summer and heating related energy of 15%in winter.On this basis,a comprehensive energy-saving measure for existing office building combined with RCF systems(as the design building)was analyzed for meeting the ultra-low energy building standard requirements.The main measures include optimizing the air conditioning system,reducing and lighting power density and improve the performance of the envelope.With the optimizing the air-conditioning system of the existing office buildings,the annual HVAC related energy-saving rate may reach 40.8%,and the building energy efficiency improvement rate is about 23%,which can meet the requirement of the ultra-low energy building standard(greater than or equal to 20%).With further optimization of lighting system and envelope design,the comprehensive energy-saving measures for the study case existing office building with RCF system may have an annual HVAC energy-saving rate of up to 49%,and the whole building energy-saving potential may reach 33%.It is predicted that this research could provide a reference prototype for energy-saving renovations of existing office buildings in the hot summer and cold winter climate zones,as well as at the hot summer and warm winter climate zones.