Construction tab in model data under Construction header
You can select the inside and outside surface convection algorithms in the Model data on the Construction tab under the Surface Convection header. This provides you with the option of making different selections in different parts of the building.
You can select from a range of EnergyPlus inside convection algorithms for calculating the convection between internal zone surfaces and the rest of the zone air in the simulation calculations:
1-Detailed - correlates the heat transfer coefficient to the temperature difference for various orientations. This model is based on flat plate experiments.
2-Simple - applies constant heat transfer coefficients depending on the surface orientation.
3-CIBSE - applies constant heat transfer coefficient derived from traditional CIBSE values.
4-Ceiling diffuser - a mixed and forced convection model for ceiling diffuser configurations. The model correlates the heat transfer coefficient to the air change rate for ceilings, walls and floors.
5-Cavity - This algorithm correctly calculates the convection coefficients for a narrow sealed vertical cavity based on the ISO 15099 standard. Natural convection model correlated for air in a narrow vertical cavity that is sealed and not ventilated. This applies both to the air gap in between panes of a window or to the air gap between the Trombe wall glazing and the inner surface (often a selective surface). The 5-Cavity Inside convection algorithm is not available at the surface level.
Paraphrased note from EnergyPlus developers: "The Trombe wall convection coefficients only make sense for a zone. They are specific coefficients calculated for a narrow enclosed space. The two major walls of a Trombe wall zone are so close together that the convection patterns for the two walls actually interact. If they are close enough they can fight each other and totally stagnate the convection cell in the space. This is not free-boundary convection such as that found in a typical room. Therefore, it does not make sense to apply these coefficients to a single surface. The algorithm analyzes the zone to figure out which are the two major surfaces and then sets the coefficients on those surfaces. The other minor surfaces receive negligible convection."
To avoid discontinuities in surface heat transfer rate calculations, all correlations are extrapolated beyond the lower limit of the data set (3 ACH) to a natural convection limit which is applied during the hours when the system is off. These models are explained in greater detail in the EnergyPlus Engineering Reference Document.
You can select from a range of EnergyPlus outside convection algorithms:
1-Detailed - all other methods apply heat transfer coefficients depending on the roughness, windspeed, and terrain of the building’s location.
2-Simple - applies heat transfer coefficients depending on the roughness and windspeed. This is a combined heat transfer coefficient that includes radiation to sky, ground, and air. The correlation is based on Figure 1, Page 25.1 (Thermal and Water Vapor Transmission Data), 2001 ASHRAE Handbook of Fundamentals.
3-CIBSE - applies heat transfer coefficients depending on orientation, derived from traditional CIBSE values.
4-BLAST,
5-TARP,
6-DOE-2,
7-MoWiTT
These are convection-only heat transfer coefficients; radiation heat transfer coefficients are calculated automatically by the program. All algorithms are described more fully in the EnergyPlus Engineering Reference.
When the surface is wet (i.e. it is raining and the surface is exposed to wind) then the convection coefficient appears in results as a very large number (1000) and the surface is exposed to the Outdoor Wet Bulb Temperature rather than the Outdoor Dry Bulb Temperature.
Inside and Outside convection algorithm settings can be made in various places.
Model options dialog (Heating design, Cooling design, Simulation tabs)
Calculation options dialog (Heating design, Cooling design, Simulation)
Model data on Construction tab
You cannot make changes to individual surface convection settings where the surface is an internal partition.
Note: the equivalent inside and outside surface convection options in the Calculation and Model options dialogs control building default values (equivalent of making a setting in Model data at building level) and changes at block, zone or surface levels in the Model data will override these settings.