Study On Heating Performance Optimization Of Office Buildings With Attachment Ventilation In Winter

Indoor thermal environment and air quality in buildings directly affect the health and work efficiency of occupants.The air distribution systems can meet the requirements of two aspects.Traditional ventilation systems have poor performance in heating mode.Short-circuit is usual under the effect of buoyant force causing the supply warm air jet hardly reaching the lower part occupied zone,especially in deep underground spaces,and cause low ventilation efficiency and energy waste.Attachment ventilation has been studied in recent years.In winter cases,supplying warm air directly to the lower part of the occupied zone may solve the problem.For a space with large depth,there is still a problem with the upward rise of the heated air lake.The characteristics of airflow and indoor thermal environment of attachment ventilation in heating mode will be investigated.The basic model with the size of 7.0 m × 5.0 m × 2.7 m has seemed like a typical office with a long depth.Indoor temperature distribution,air velocity distribution created by different operation status of relayed fans and different dimensionless heights of exhausts are compared.The temperature difference between head and foot,the index of PMV-PPD,the percentage of dissatisfaction of unwanted local draught,the index of temperature efficiency,the index of ventilation efficiency,the index of ADI and so on are applied to show the change of the indoor thermal environment and air quality in a visual way.The indoor thermal environment created by attachment ventilation system can satisfy the thermal comfort requirement of most people in the occupied zone.High temperature efficiency(about 0.83)and ventilation efficiency(about 1.005)are reached by applying attachment ventilation for space heating.The application of relayed fans not only increases the attachment distance of warm air lake but also improves indoor PMV and temperature difference between head and foot.Besides,temperature efficiency and ventilation efficiency in the occupied zone are significantly increased by 9.7% and 13.5% respectively.The ventilation performance of attachment ventilation is highly related to the dimensionless height of exhausts located at external wall.The indoor thermal environment is inversely proportional to the height of exhausts i.e.,the lower height of exhausts,the greater indoor thermal environment.The temperature efficiency can increase by 32.5% at most by decreasing exhaust height.Ventilation efficiency reaches 1.08 while the exhausts are set at the height 0.5H.The ventilation performance of attachment ventilation under heating mode is optimized by applying relayed fans and low-level exhausts.The combined performance of attachment and relayed fans under heating mode are studied by considering the supply air parameters of attachment ventilation and the shape of relayed fans.The results show that the lower air supply temperature of attachment ventilation can help improve indoor thermal comfort,and reduce the temperature stratification in the height direction,and have high energy efficiency,which is suitable for the space considering thermal comfort.Increasing air supply temperature of attachment ventilation is helpful to improve the ventilation efficiency in the workspace,accelerating the elimination of indoor pollutants,and is suitable for the space considering indoor air quality.The shape of relayed fan outlet and the air velocity at fan outlet has little influence on local thermal comfort near the workstation.Finally,the heating and ventilation effects of attachment ventilation,mixing ventilation,and stratum ventilation in winter cases were compared and analyzed.Attachment ventilation creates the vertical temperature distribution of " low below and high above" in space,making full use of the warm supply air to heat the occupied zone and improving the uniformity of indoor temperature distribution.The temperature difference between head and foot is less than 3 ℃ at each position in the room,and the indoor thermal comfort is very close to the thermal neutral.Air short-circuit exists in mixing ventilation and stratum ventilation resulting in significant temperature difference in the vertical direction,causing energy waste and indoor thermal discomfort.By comparing the ventilation effects of three air distribution systems,attachment ventilation has better performance in diluting indoor pollutants whose ventilation efficiency is around 1.10 in the occupied zone.The ventilation efficiency of mixing ventilation and stratum ventilation reduces as the height increase,and the two systems have poor ventilation performance for space heating.