| Tubes-embedded building envelope cooling system is also called thermally activated building system(TABS),where the pipes are embedded in the central concrete core of a building construction.The cooling components(such as cooling coils)and the building structure(concrete roof or wall)are coupled to each other,so that the building envelope can be directly involved in the indoor air conditioning as a part of the end of the air conditioning system.At present,the systems are increasingly being in practical applications due to their high energy efficiency and good thermal comfort.The cooling load calculation is a critical step in designing any HVAC system.In the current standard,cooling load is defined and calculated independent of HVAC system type.This paper is based on the existing research and software simulation to show that the surface side cooling load of the radiant system is different from the hydronic cooling load.In this paper,EnergyPlus is used to simulate the load,and discuss the load forming process and the load characteristics when radiant cooling system is intermittent operation or continuous operation and the difference between the two operations.Because of the higher heat storage capacity of the system components,the radiant surface side load are delayed and attenuated compared with the hydronic side.In this study,the typical office building model is built by using the tubes-embedded building envelope cooling system to study the relationship and the difference between the surface cooling load and the hydronic side cooling load in the summer design day.The effects of heat storage performance and system operation strategy on the relationship between the two cooling load also were studied.In summary,the works of this paper are:(1)Provided clear evidence to demonstrate the feasibility of intermittent operation of the radiant system and the difference in heat transfer between the hydronic side and the surface side.This finding have an important influence for accurate and reliable designing methods and energy simulation tools using.(2)Introduced the tubes-embedded building envelope cooling system,and summarized the calculation method of hydronic side cooling load and surface side cooling load of radiant system and the relationship between cooling load and heat.(3)The practical designing method and guidance were put forward,the office building was used as the research object,and using Energyplus simulation as the research means to simulate and calculate to study cooling load formation process,peak characteristics and dynamic characteristics during the intermittent operation of the cooling system.(4)Sensitivity analysis of the influencing factors of the intermittent cooling load of the radiant system was carried out,such as radiant heat gain(different shading coefficient),cooling time distribution,cooling capacity of the cooling components,insulation method and performance of building envelope and so on.(5)Comparing with the cooling load coefficient method,the correction coefficient is proposed.The results show that:(1)There is a difference between the surface cooling load with hydronic cooling load,due to the thermal storage effect of the tube-embedded envelope.There is a shift and a clipping characteristics of peak cooling load compared surface cooling load and hrdronic cooling load when the cooling system is intermittent running.The peak cooling load of water side is higher 70.62% than surface side.The difference of continuous operation between the surface cooling load and hydronic cooling load is much smaller than intermittent operation.(2)During 20:00-24:00 of intermittent operative system,there can form additional cooling load because the residual cooling capacity of cooling structure is less than the residual heat of non-cooling structure.And this is the main difference between intermittent cooling and continuous cooling.(3)The total length of the cooling time,the location of the radiation surface(ceiling,floor),the cooling performance of the cooling component and room orientation have a great influence on the intermittent cooling load characteristics.However,Cooling time distribution,the type of internal heat source,different solar radiation heat(different shading coefficient),insulation method,performance of building envelope,thermal performance and amount of furniture,amount of exterior wall and the ratio between window and wall have a little influence on the intermittent cooling load characteristics.(4)Comparing with the air system,a large portion of the heat was removed during the occupied period for the radiant case,and the radiant systems peak cooling rates were higher than the air system.(5)Comparing with the load calculated by Tianzheng,the coefficient of the continuous operation of the tube-embedded envelope is 1.32,and the coefficient of different intermittent operation scheme is different. |
PDF Full Text Request