Influences Of Occupant Ventilation-Behavior During Off-periods On Heating Energy Consumption And Indoor Thermal Environment In Intermittently Heated Buildings

Most buildings in the Hot Summer and Cold Winter(HSCW) zone of China are not equipped with centralized heating systems,which have been installed in northern China,due to the provisions of winter heating policy and design standards.The winter in this region is typically characterized by cold and wet weather,thus the indoor thermal environment in civil buildings is usually poor in winter.To improve the poor indoor thermal environment,domestic heating is becoming popular for room heating during the past decade,while the heating systems are usually switched on or off intermittently depending on whether occupants are at home or not.Since the HSCW zone is hot in summer and has a rainy climate with monsoon,outdoor climate is usually hot and humid.Then natural ventilation through windows becaomes a traditional custom of local occupants for the improvement of indoor thermal environment during this season.Even in the winter when the weather is very cold,the occupants still prefer to open windows during the off-periods of IH system.Due to the invasion of cold outdoor air during the non-heating periods,the heating energy consumption caused by the heat storage of thermal mass(e.g.,interior walls and furniture)will be increased during the next heating period.In addition,the larger the air change rate during the non-heating periods,the lower the wall temperatures,the lower the mean radiant temperature at the beginning of the next heating,and the poorer the indoor thermal environment.On the other hand,urban land-scarcity has become a pressing problem with the rapid development of modern cities in recent years.Underground buildings,which can provide extra space with several functions,have gained more and more attentions for the alleviation of urban land-scarcity.Semi-underground rooms in residential buildings are thus gradually provided for occupants.For underground buildings,the heat transfer through building envelopes is a typical three-dimensional unsteady heat transfer process due to the coupling-effect between the wall temperatures and the surrounding soil temperature,which is significantly different from aboveground buildings.For aboveground and semi-underground rooms in an intermittently heated multi-storey residential building,this study quantitatively analyzes the influence of OVB during the off-periods on heating energy consumption and indoor thermal environment in the whole heating season.The quantitative study can provide a theoretical basis for reducing the heating energy consumption and improving the indoor thermal comfort of residential buildings in the HSCW zone of China.In order to quickly analyze the quantitative influence of OVB during the off-periods on heating energy consumption and indoor thermal environment with low computational cost,appropriate calculation models should be determined for aboveground and semi-underground rooms respectively.For aboveground buildings,an alternative analytical model,which is derived by means of Laplace-transform method and method of constant variation,is proposed for quick calculations of transient temperatures of building envelopes and indoor air.The analytical model is further validated against field test data.It is shown that the calculated values of the proposed analytical model are in good agreement with the measured data.Therefore,the proposed analytical model can be considered appropriate for the heat transfer analysis of aboveground buildings.With respect to underground buildings,four main ground coupled heat transfer models are comprehensively evaluated by means of inter-program comparison.The study reveals that the Ground Domain Xing model integrated into Energy Plus can be considered as the relatively accurate ground coupled heat transfer model with low computational cost.Evapotranspiration of ground surface is a critical factor that affects the ground coupled heat transfer,which can significantly influences the calculation accuracy of ground coupled heat transfer models for underground buildings.For intermittently heated buildings,the energy consumption caused by the heat storage of thermal mass during heating periods is the main difference between intermittent heating and continuous heating,and it can be affected by OVB during non-heating periods.In the present study,the influence of OVB during off-periods on heating energy consumption of aboveground and semi-underground rooms in the whole heating season for different heat capacities of internal building envelope and non-heating durations.The results indicate that the OVB during non-heating periods can significantly increase the heating energy consumption for both aboveground and semi-underground rooms,and has a minor effect for semi-underground room.The ventilation behavior has a more significant effect on heating energy consumption for lower outdoor air temperature during non-heating periods,higher non-heating durations,air change rates during non-heating periods and heat capacity of internal building envelope.In addition,the heating energy consumption components of the semi-underground room are different from that of the aboveground room.For the aboveground room,the internal building envelope consumes the largest amount of energy,followed by the infiltration of cold air,while the heat loss through the window and the external wall is smaller.With regard to the semi-underground room,the heating energy consumption of internal building envelope is also largest,but the semi-underground wall significantly consumes more energy than the cold air infiltration,window and external wall.To balance the preference for ventilation and the control of energy consumption,two predictive models are developed for aboveground and semi-underground rooms respectively by means of multiple nonlinear regression analysis.The predictive models present the mathematic relationship among heating energy consumption,air change rate during non-heating periods,non-heating durations,outdoor air temperature during non-heating periods and heat capacity of internal building envelope.The sensitivity of the allowed value of air change rate during non-heating periods at the increasing rate in heating energy consumption of 50% to outdoor air temperature is related to the heat capacity of internal building envelope and non-heating duration.When the heat capacity of internal building envelope or non-heating duration is relatively low,the allowed value of air change rate during non-heating periods is significantly increased with the increase of outdoor air temperature during non-heating periods.However,the outdoor air temperature during non-heating periods has little effects on the allowed value of air change rate during non-heating periods for a higher heat capacity of internal building envelope or non-heating duration.In intermittently heated buildings,the indoor thermal environment is significantly dynamic.When the IH system is switched on,the indoor air temperature can be quickly increased while the wall temperatures slowly increase due to the higher thermal capacity,which results in the poorer indoor thermal comfort.It should be noted that the poor indoor thermal comfort at the beginning of heating is the major difference between intermittently heated buildings and continuously heated buildings.For aboveground and semi-underground intermittently heated rooms,the influence of OVB during off-periods on mean radiant temperature and indoor thermal comfort level are studied in the whole heating season.The results show that the OVB during non-heating periods can significantly decrease the mean radiant temperature and indoor thermal comfort level during heating periods for both aboveground and semi-underground rooms,and the influence on aboveground room is more significant than that on semi-underground room.The effect of the OVB during non-heating periods on the indoor thermal comfort is more significant for larger air change rate during non-heating periods and non-heating durations,lower outdoor air temperature during the non-heating periods and heat capacities of internal building envelope.To improve the poor indoor thermal environment during the heating periods of intermittently heated rooms,two solutions are provided for different requirements in this work.One is decreasing the air change rate during non-heating periods to some extent based on the predictive model of minimum PMV during heating periods proposed by the present study.The sensitivity of the allowed value of air change rate during non-heating periods at the minimum PMV of-0.5 to outdoor air temperature is related to the heat capacity of internal building envelope and non-heating duration.The other solution is to use preheating,which can meet the requirements of occupants for both ventilation and indoor thermal comfort.The solution can be quickly optimized by using the corresponding predictive model of minimum PMV affected by preheating,while the heating energy consumption will also be increased.