Question about EPmaterials' specificHeat

Hi everyone,

While using “Energyplus Opaque Material” node I need to input the “specificHeat” to make the material work. But the “Energyplus Nomass Opaque Material” node doesn’t have this value. So the simulation can be done either with or without this value? Dose the energy simulation only takes R value as the construction’s all need?
And I also found while read the library’s EPmaterials’ comments from “Decompose EPMaterial”, there is no “thickness”/“density"and"specificHeat” for some materials. Can I ask how to give these materials thickness so their R values can be calculated?
One last question about the specificHeat is that is it a value related to the heat storage coefficient (unit:W/m2·K)? Can it be calculated from the later?

Thank you all for the help.

Specific heat capacity (J/kg K) is a measure of how much energy (i.e. Joules, kWh) is stored per unit mass, per unit temperature (i.e. kg K) of a material. An EnergyPlus NoMass Opaque material by definition contains no mass, so it has no specific heat capacity.

What this means in terms of heat transfer is that no-mass materials don’t have a “thermal mass” where heat conduction is calculated with respect to time and space (transient conduction), instead it’s heat conduction is calculated across the material instantly in time, with respect only to space (steady-state conduction). In the former case, the material’s mass plays a role because it directly corresponds to how much heat can be held, while in the latter mass plays no role, in general only the depth of the material matters.

Since there’s no mass in such materials, you only need to account for the thermal power (or rate of energy with respect to time) that interacts with the surface of the material. So R-value or heat storage coefficient as you call it (m^2K/W) is therefore the only input you need for no-mass materials. Specific heat can’t be calculated from this value because it’s only providing surface data, not mass.

One last clarification. Sometimes you’ll get Resistivity as a value (mK/W) which you can multiply by the depth of your material to turn it into R value (m^2K/W).


Hi Saeran,
Thank you so much for the detailed explain. Can I ask if I can mix the materials with mass and the ones only got R values in one model for simulation? Is it OK if some walls in one zone have the specific heat value but others not?

Yes you can.
You assign a construction for each surface.

Thank you Abraham:grinning: