Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
There are few clues about this severe error on UnmetHours. Although this is a very old question, I add another possible cause for those who have the same problem.
When we get this severe error, we may find the following message at the end of the err file.
************* ===== Final Error Summary =====
************* The following error categories occurred. Consider correcting or noting.
************* Temperature (low) out of bounds
************* ..A temperature out of bounds problem can be caused by several things. The user should check:
************* ..1) the weather environment (including the horizontal IR from sky)
************* ..2) the level of interal gains with respect to the zone
************* ..3) the thermal properties of their materials. And other things.
************* ..A common cause is a building with no or little thermal mass - all materials with Material:NoMass definitions.
In my case, this was exactly the cause. I used Material:NoMass for all walls/roofs/floors/ceilings, and the zones with the severe error had large windows.
EngineeringReference gives us a clue as to why this is the case. "There are potential issues with having a resistance-only layer at either the inner or outer most layers of a construction. A little or no mass layer there could receive intense thermal radiation from internal sources or the sun causing the temperature at the inner or outer surface to achieve very high levels."
However, sometimes we need to use Material:NoMass especially for ASHRAE90.1 Baseline case where the U-value is specified. There are two options to avoid the severe surface temperature error.
Material objects rather than Material:NoMass objects.InternalMasFor the option 2, there is no standard for how much InternalMass should be added. I often refer to DOE's Prototype Building Models. They have InternalMass objects to account for interior furnishings.
Material,
Std Wood 6inch, !- Name
MediumSmooth, !- Roughness
0.15, !- Thickness {m}
0.12, !- Conductivity {W/m-K}
540.0000, !- Density {kg/m3}
1210, !- Specific Heat {J/kg-K}
0.9000000, !- Thermal Absorptance
0.7000000, !- Solar Absorptance
0.7000000; !- Visible Absorptance
Construction,
InteriorFurnishings, !- Name
Std Wood 6inch; !- Outside Layer
InternalMass,
Perimeter_bot_ZN_3_InternalMass_1, !- Name
InteriorFurnishings, !- Construction Name
Perimeter_bot_ZN_3, !- Zone or ZoneList Name
, !- Space or SpaceList Name
626.8258; !- Surface Area {m2}
In the Prototype Building Models, InternalMass objects are added to all conditioned zones, and the each Surface Area on InternalMass is set at twice the floor area of each zone regardless of the building type such as office, retail, residential, etc.
