Severe Error: Temperature out of Bounds (Low)

edit

Hi, when I get an error like this in EnergyPlus it usually has very little to do with that surface or that zone. Usually it is a problem elsewhere. I would check the errors you have above and correct as many of those as possible. Also make sure your air flow rates add up and are reasonable. Check your sizing objects, especially zone and system sizing. Finally check the sizes and efficiency you have put on your equipment that sometimes also causes this error.

The last time I got this error (last week) it was because I had incorrectly sized my chilled ceilings water flow rate. The time before (the week before) my air flow rates where not adding up in my AHU objects. I have been modelling with EnergyPlus for ages too!

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.

1. Create the interior walls/ceilings/floors with multi-layer Material objects rather than Material:NoMass objects.
2. Add InternalMas

For 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.