Materials with a low thermal emittance surface have been used for many years to create reflective insulations that reduce the rate of heat flow across building envelopes. Reflective insulation technology is now being ...Materials with a low thermal emittance surface have been used for many years to create reflective insulations that reduce the rate of heat flow across building envelopes. Reflective insulation technology is now being combined with other energy conserving technologies to optimize overall thermal performance. The basis for the performance of reflective insulations and radiant barriers will be discussed along with the combination of these materials with cellular plastic or mineral fiber insulations to form hybrid insulation assemblies. Calculations of thermal resistance for enclosed reflective air spaces and current field data from Southeast Asia will be presented. These data show that reductions in heat transfer across the building enclosure can be effectively reduced by the use of enclosed reflective air spaces and attic radiant barriers. Reflective technology increases the overall thermal resistance of the building enclosure when used to insulate poured concrete structures.展开更多
The R-value is defined as,“a measure of the resistance of an insulating or building material to heat flow,expressed as R-11,R-20,and so on;the higher the number,the greater the resistance to heat flow(Random House,20...The R-value is defined as,“a measure of the resistance of an insulating or building material to heat flow,expressed as R-11,R-20,and so on;the higher the number,the greater the resistance to heat flow(Random House,2016).”The first thermodynamic principle violated by the R-value is the singular use of the word heat flow.Heat flow,or transfer,occurs in three distinct ways;conduction,convection,and radiation.The R-value test will only measure a bulk insulations resistance to conductive heat transfer.This type of heat flow is almost undetectable in the built environment,regardless of climate or season-resulting in the R-value myth.In winter,the stack effect will cause convective flows through the home as warm air under pressure rises and escapes through the top,requiring an equal amount of cold replacement air to infiltrate at the bottom.On hot sunny days,the exterior of the home absorbs long wave ultra violet(UV)rays from the sun and reemits this radiant heat energy into the residence.The thermodynamics of an occupied structure under varying atmospheric conditions is not well understood,leading to major inefficiencies.The goal of this conceptual study is to reveal the shortcomings of current insulation practices at the residential level,conceptualize a series of related issues for future study and develop a preliminary methodological concept for resolutions to the problems identified.Conclusions indicate that further research needs to be dedicated to replacing the R-value rule with a realistic metric that considers the efficiency,health,and safety of the entire building.展开更多
文摘Materials with a low thermal emittance surface have been used for many years to create reflective insulations that reduce the rate of heat flow across building envelopes. Reflective insulation technology is now being combined with other energy conserving technologies to optimize overall thermal performance. The basis for the performance of reflective insulations and radiant barriers will be discussed along with the combination of these materials with cellular plastic or mineral fiber insulations to form hybrid insulation assemblies. Calculations of thermal resistance for enclosed reflective air spaces and current field data from Southeast Asia will be presented. These data show that reductions in heat transfer across the building enclosure can be effectively reduced by the use of enclosed reflective air spaces and attic radiant barriers. Reflective technology increases the overall thermal resistance of the building enclosure when used to insulate poured concrete structures.
文摘The R-value is defined as,“a measure of the resistance of an insulating or building material to heat flow,expressed as R-11,R-20,and so on;the higher the number,the greater the resistance to heat flow(Random House,2016).”The first thermodynamic principle violated by the R-value is the singular use of the word heat flow.Heat flow,or transfer,occurs in three distinct ways;conduction,convection,and radiation.The R-value test will only measure a bulk insulations resistance to conductive heat transfer.This type of heat flow is almost undetectable in the built environment,regardless of climate or season-resulting in the R-value myth.In winter,the stack effect will cause convective flows through the home as warm air under pressure rises and escapes through the top,requiring an equal amount of cold replacement air to infiltrate at the bottom.On hot sunny days,the exterior of the home absorbs long wave ultra violet(UV)rays from the sun and reemits this radiant heat energy into the residence.The thermodynamics of an occupied structure under varying atmospheric conditions is not well understood,leading to major inefficiencies.The goal of this conceptual study is to reveal the shortcomings of current insulation practices at the residential level,conceptualize a series of related issues for future study and develop a preliminary methodological concept for resolutions to the problems identified.Conclusions indicate that further research needs to be dedicated to replacing the R-value rule with a realistic metric that considers the efficiency,health,and safety of the entire building.
