Heat Transfer From Ventilation Ducts And Changes In Supply Air Temperature

Energy lose and consumption in buildings has led to a great need for energy saving and energy efficient solutions for buildings.In the future,next generation of buildings should take high energy performance solutions in order to avoid much energy lose and consumption.Because future buildings are considered air tight and highly insulated,the energy performance of ventilation system is so important in the future and,in most cases,this require a mechanical ventilation system to secure air quality and thermal comfort.Depending on building complexity and design,the pathways for the ventilation ductwork can be long,and the heat exchange between the duct walls and the surrounding environment can be high.As a result from that,there are changes in supply air temperature and uncontrolled energy exchange in the building,which in turn can cause unnecessary energy loss for the building operation.It also has much influence on people's thermal comfort in the buildings.Therefore the tremendous efforts and emphasis have been put on knowledge of heat transfer from ventilation ducts.The aim of the project is to gain more knowledge of about heat exchange between ducts and zones in future lowenergy building.The heat transfer phenomena is well understood,but measurements are needed to evaluate the performance of mathematical duct models for use in simulation tools.In order to get more knowledge about the heat exchange between ducts and surrounding environment,laboratory measurements and calculation of mathematical models of a duct system are needed with variable airflow rate in the field.This work presented is conducted in Norwegian University of Science and Technology.A test rig with a ventilation system and a sealed room is designed and built in the thermal engineering lab.Experiments are conducted with different inlet air flow rate and different air temperature.Air and duct temperature of different locations are measured.Simultaneously,calculation with different kinds of mathematical models are conducted,which are verified by the measurement.The mathematical models are built by different approaches.The results of the experimental measurements are presented in this thesis to show the air temperature in the duct,which is divided into three groups of test points.The comparison between measurement results and calculation results is conducted in order to assess and verify the performance mathematical models,especially for the models in energy simulation tools Energy Plus and Trnsys.Besides,the ventilation system with insulated duct is also tested in the measurements.The results of that are compared with uninsulated duct system in order to know the heat exchange difference between insulated ducts and uninsulated ducts.