Airflow Pattern And Performance Of Wall Confluent Jets Ventilation For Heating In A Typical Office Space

In the rapid progress of urbanization in China,people are demanding more comfortable thermal environment indoors.The energy consumption for establishing thermal environment in buildings is about two thirds of total energy consumptions for buildings,which account for one third of total energy consumption.The indoor airflow distribution plays a great role in the indoor thermal environment,indoor air quality and building energy consumption.Poor airflow distribution indoors would cause thermal discomfort for the occupants,such as the draught sensation,warm head and cold feet.Moreover,the indoor airflow distribution has strong correlation with the transport and infection of respiratory disease.People in major cities spend 90%of their time indoors?homes,schools,vehicles,etc?.As the building space and structure are becoming more compact,the global epidemic respiratory diseases break out more often than ever.Meanwhile,the deterioration of indoor environment leads to great economic loss.Therefore,the airflow distribution indoors needs to be improved to satisfy the people's growing appetite for healthier and more comfortable life.Traditional mixing ventilation?MV?would cause airflow short-circuit when applied for heating,and displacement ventilation?DV?is not suitable for heating condition.The wall confluent jets ventilation?WCJV?combining the characteristics of both MV and DV systems has the potential to establish good thermal environment and indoor air quality indoors when applied for heating.In present study,the air velocity,temperature and turbulence of wall confluent jets and the air temperature field in a typical office was measured.The Coanda effect was confirmed by the jets contour based on the experimental results.Before the case study by FLUENT,the jets characteristic and the thermal distribution predicted by the RNG k-?model,realizable k-?model and SST k-?model were compared with the experimental data.The SST k-?model was chosen for case study of wall confluent jets ventilation under heating mode.Then the airflow distribution,indoor thermal environment and air quality and energy consumption of WCJV were compared with those of MV by simulation.The results indicate that the wall fluent jets entrained less ambient airflow thus could maintain its momentum and energy to occupied zone.Therefore,compared with MV,the thermal environment and air quality in occupied zone of WCJV room was more comfortable.The theoretic calculation of energy consumption indicated that the energy consumption of the MV was a bit higher than that of WCJV because the temperature of recirculated air of MV was lower.In order to study the effect of supply airflow velocity?2.00-8.50m/s?and supply air temperature?2.00-7.79??on the jets characteristic,thermal environment,air quality and theoretical energy consumption,the constant volume system?CAV?and variable volume system were adopted.The superimposing model was introduced to analyze the jets characteristic.The correlation coefficients of all WCJV cases indicated that the superimposing model has the potential to predict the velocity decay of wall confluent jets.It could be deduced that the decay rate of non-dimensional jets velocity was more allergic to the change of supply air velocity than to the change of supply air temperature difference.The jets velocity spreading rate was almost independent of supply air velocity and supply air temperature difference.The jets temperature spreading rate was hardly affected by the supply air temperature difference,whereas the jets temperature spread faster as the supply air velocity decreased.These are in accordance with previous experimental study.According the thermal comfort indices including predicted mean thermal sensation vote?PMV?and draught sensation?DR?,the thermal environments of all CAV cases were rather similar.While the decrease of supply air velocity would render that the confluent jets could not reach the occupied zone and reduce the thermal comfort indoors.Based on the indoor air quality indices including mean air age and concentration of CO₂,the indoor air quality was worse as the supply airflow rate decreased.In the range of the supply temperature difference concerned in present study,the change of supply air temperature difference had little influence on the indoor air quality.The theoretical calculation indicated that the energy consumption of CAV system and VAV system were rather similar.To conclude,for the WCJV,the energy consumption of VAV and CAV were rather close.However,the reduction of supply airflow rate would render the jets momentum insufficient to the occupied zone thus the indoor thermal environment and air quality became worse.It is necessary to derive appropriate supply air velocity by the decay regulation of jets velocity so that the supply warm jets could reach the occupied zone when applying the WCJV for heating.