The removal building heat load and electrical power consumption by air conditioning system are proportional to the outside conditions and solar radiation intensity. Building construction materials has substantial effe...The removal building heat load and electrical power consumption by air conditioning system are proportional to the outside conditions and solar radiation intensity. Building construction materials has substantial effects on the transmission heat through outer walls, ceiling and glazing windows. Good thermal isolation for buildings is important to reduce the transmitted heat and consumed power. The buildings models are constructed from common materials with 0 - 16 cm of thermal insulation thickness in the outer walls and ceilings, and double-layers glazing windows. The building heat loads were calculated for two types of walls and ceiling with and without thermal insulation. The cooling load temperature difference method, <em>CLTD</em>, was used to estimate the building heat load during a 24-hour each day throughout spring, summer, autumn and winter seasons. The annual cooling degree-day, <em>CDD</em> was used to estimate the optimal thermal insulation thickness and payback period with including the solar radiation effect on the outer walls surfaces. The average saved energy percentage in summer, spring, autumn and winter are 35.5%, 32.8%, 33.2% and 30.7% respectively, and average yearly saved energy is about of 33.5%. The optimal thermal insulation thickness was obtained between 7 - 12 cm and payback period of 20 - 30 month for some Egyptian Cities according to the Latitude and annual degree-days.展开更多
Analogizing with the heat conduction process,the entransy dissipation extremum principle for thermal insulation process can be described as:for a fixed boundary heat flux(heat loss)with certain constraints,the thermal...Analogizing with the heat conduction process,the entransy dissipation extremum principle for thermal insulation process can be described as:for a fixed boundary heat flux(heat loss)with certain constraints,the thermal insulation process is optimized when the entransy dissipation is maximized(maximum average temperature difference),while for a fixed boundary temperature,the thermal insulation process is optimized when the entransy dissipation is minimized(minimum average heat loss rate).Based on the constructal theory,the constructal optimizations of a single plane and cylindrical insulation layers as well as multi-layer insulation layers of the steel rolling reheating furnace walls are carried out for the fixed boundary temperatures and by taking the minimization of entransy dissipation rate as optimization objective.The optimal constructs of these three kinds of insulation structures with distributed thicknesses are obtained.The results show that compared with the insulation layers with uniform thicknesses and the optimal constructs of the insulation layers obtained by minimum heat loss rate,the optimal constructs of the insulation layers obtained by minimum entransy dissipation rate are obviously different from those of the former two insulation layers;the optimal constructs of the insulation layers obtained by minimum entransy dissipation rate can effectively reduce the average heat loss rates of the insulation layers,and can help to improve their global thermal insulation performances.The entransy dissipation extremum principle is applied to the constructal optimizations of insulation systems,which will help to extend the application range of the entransy dissipation extremum principle.展开更多
文摘The removal building heat load and electrical power consumption by air conditioning system are proportional to the outside conditions and solar radiation intensity. Building construction materials has substantial effects on the transmission heat through outer walls, ceiling and glazing windows. Good thermal isolation for buildings is important to reduce the transmitted heat and consumed power. The buildings models are constructed from common materials with 0 - 16 cm of thermal insulation thickness in the outer walls and ceilings, and double-layers glazing windows. The building heat loads were calculated for two types of walls and ceiling with and without thermal insulation. The cooling load temperature difference method, <em>CLTD</em>, was used to estimate the building heat load during a 24-hour each day throughout spring, summer, autumn and winter seasons. The annual cooling degree-day, <em>CDD</em> was used to estimate the optimal thermal insulation thickness and payback period with including the solar radiation effect on the outer walls surfaces. The average saved energy percentage in summer, spring, autumn and winter are 35.5%, 32.8%, 33.2% and 30.7% respectively, and average yearly saved energy is about of 33.5%. The optimal thermal insulation thickness was obtained between 7 - 12 cm and payback period of 20 - 30 month for some Egyptian Cities according to the Latitude and annual degree-days.
基金supported by the National Key Basic Research and Development Program of China(‘973’Program)(Grant No.2012CB720405)the National Natural Science Foundation of China(Grant No.51176203)the Natural Science Foundation for Youngsters of Naval University of Engineering(Grant No.HGDQNJJ11008)
文摘Analogizing with the heat conduction process,the entransy dissipation extremum principle for thermal insulation process can be described as:for a fixed boundary heat flux(heat loss)with certain constraints,the thermal insulation process is optimized when the entransy dissipation is maximized(maximum average temperature difference),while for a fixed boundary temperature,the thermal insulation process is optimized when the entransy dissipation is minimized(minimum average heat loss rate).Based on the constructal theory,the constructal optimizations of a single plane and cylindrical insulation layers as well as multi-layer insulation layers of the steel rolling reheating furnace walls are carried out for the fixed boundary temperatures and by taking the minimization of entransy dissipation rate as optimization objective.The optimal constructs of these three kinds of insulation structures with distributed thicknesses are obtained.The results show that compared with the insulation layers with uniform thicknesses and the optimal constructs of the insulation layers obtained by minimum heat loss rate,the optimal constructs of the insulation layers obtained by minimum entransy dissipation rate are obviously different from those of the former two insulation layers;the optimal constructs of the insulation layers obtained by minimum entransy dissipation rate can effectively reduce the average heat loss rates of the insulation layers,and can help to improve their global thermal insulation performances.The entransy dissipation extremum principle is applied to the constructal optimizations of insulation systems,which will help to extend the application range of the entransy dissipation extremum principle.
