Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
The EnergyPlus Material:AirGap object only accepts an input value of thermal resistance. OpenStudio supplies an interface for the EnergyPlus input, and thus typically doesn't allow input in excess of what the underlying EnergyPlus object requires.
The reason that EnergyPlus doesn't accept the thickness of the air gap as an input for this object is that the thermal resistance of an air layer depends on more than just the thickness (e.g. orientation, heat flow direction, cavity enclosing material emissivity, how much the air is allowed to move within the cavity, etc.), so you pretty much need to use an empirical value. Table A9.4A of ASHRAE 90.1-2010 gives some values of cavity space R-values depending on cavity thickness, envelope component type, and effective emissivity. Table 3 in ASHRAE Fundamentals Chapter 26 has even more.
| | 2 | No.2 Revision |
The EnergyPlus Material:AirGap object only accepts an input value of thermal resistance. OpenStudio supplies an interface for the EnergyPlus input, and thus typically doesn't allow input in excess of what the underlying EnergyPlus object requires.
The reason that EnergyPlus doesn't accept the thickness of the air gap as an input for this object is that the thermal resistance of an air layer depends on more than just the thickness (e.g. orientation, heat flow direction, cavity enclosing material emissivity, how much the air is allowed to move within the cavity, etc.), so you pretty much need to use an empirical value. Table A9.4A of ASHRAE 90.1-2010 gives some values of cavity space R-values depending on cavity thickness, envelope component type, and effective emissivity. Table 3 in ASHRAE Fundamentals Chapter 26 has even more.
