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Internal Gains

Inside a building, people, appliances, office equipment, lighting, and other devices produce heat. The combination of all these items that produce heat within a building are called internal gains and represents a significant contribution, sometimes the largest contribution, to the cooling requirements for a building. In addition, they offset the amount of heat from the HVAC system that is needed at a given time. Typically, the peak value is entered in the input objects for this group such as the maximum number of people, the total power of equipment, or the total lighting power and then a schedule is used to modify that value each hour of the year. It is just as critical that the schedule values are realistic for your building as is the peak value. For almost all buildings, it is rare that the peak occupancy occurs for more than a few hours per year if at all and this is especially the case for retail stores, theaters, and sports complexes. Even office buildings when counting vacations and people out of the building for meetings will rarely have peak occupancy.

The most common internal gain input objects that are shown in almost all the example files are:

  • People -- specifies not only the sensible, latent and radiant heat from people but also includes ways of reporting the comfort of occupants using a variety of thermal comfort models. The DynamicClothing.idf example file shows how to use the thermal comfort models.
  • Lights -- describes the heat related to lighting systems.
  • ElectricEquipment -- describes the heat related to electrical appliances, office equipment, and other heat sources that are powered by electricity.
  • GasEquipment - specifies the heat related to cooking appliances and other equipment that uses natural gas.

Less common internal gains input objects include:

  • OtherEquipment - describes any heat gain or loss (sensible, radiant, and/or latent) that impacts the space but does not consume utility energy in the simulation. Typically used to model a process load which is not to be included in the overall building energy consumption.
  • ElectricEquipment:ITE:AirCooled - see the 1ZoneDataCenterCRAC_wApproachTemp.idf example file.
  • SwimmingPool:Indoor - see the 5ZoneSwimmingPool.idf example file.

Other

  • ComfortViewFactorAngles -- allows the specification of how different surfaces impact the thermal comfort calculations for the occupants. See the PurchAirWithDaylightingAngleFac.idf example file.

The Internal Gains group also contains input objects related to zone contaminant sources and sinks. The input objects include modeling components that impact contaminant concentrations which are scheduled, pressure driven, use a cut off model, assume a decaying source, surface diffusion, or using a deposition velocity model. The input objects described in this section are further explained in the InputOutputReference under the heading "Group-Internal Gains."