InternalMass in Refrigerated Warehouse; Thickness vs. Surface Area
I'm running the RefrigeratedWarehouse idf model from E+ example files. We are performing a parametric study on the thermal mass of the frozen goods, which are modeled using InternalMass objects. I experimented with increasing/decreasing the thermal mass by scaling either the Surface Area of the InternalMass object or the Thickness of the associated Material object; both yield the same amount of thermal mass [kg] and specific heat [J/K] in the zone.
Other than looking at big picture meter timeseries like Electricity:Facility and Refrigeration:Electricity, are there specific Heat Transfer Surface output variables (or other Output:Variables) that would be worth investigating to see whether changing thickness vs. surface area of InternalMass has more impact on passive thermal storage using precooling setpoint schedules?
The first-principles hypothesis is that surface area is the more impactful parameter, but I'm curious how to "prove" this using E+ output.
I'd post-process:
Surface Outside Face Temperature
Output:Variable, *, !- Key Value Surface Outside Face Temperature, !- Variable Name Hourly; !- Reporting Frequency
... to stay well within food safety temperature ranges, e.g. within 3°C. Other than that, refrigeration equipment cooling rate vs facility peak cooling demand, I guess.
I think more of produce exposed area vs thickness as constraints (e.g. pallet/rack size, bulk vs itemized). My 2-cents.
I am requesting Surface Inside Face Temps, b.c. the internal mass objects don't transfer heat w/ outside surfaces (similar to adiabatic boundary condition) according to the E+ IO reference? Frankly docs have conflicting info about the outside surface heat transfer characteristics. Thanks for the advice.
I think you're referring to this: "the zone will only exchange energy with the inside of the Internal Mass construction.". I had added both inside & outside output variables (basic test), and did notice differences between both, even for something thin like 6" of wood. The outside face doesn't interact (directly) with the zone, yet I believe the runtime differences indicate if the mass is acting as a sink or source (and by how much). No harm done by adding it.
No harm done by adding the outside face output variable? Sure. I just expected the heat flux values for that variable to be zero after reading the docs on InternalMass. Is this not the case?
I believe the IO Reference is simply stating that the parent zone (or any other zone, or the outdoors) can't directly interact with the outside of the internal mass construction. But that unseen surface/node does interact with the inside of the internal mass construction, and does have capacitance (same as if it were adiabatic). There should be some difference in reported results if testing 24" of concrete (instead of 6" of wood).