Internal Gains

Anything producing heat as a waste product affects the heating and cooling loads within the house. The waste heat causes an increase in the cooling energy consumption, and a decrease in the heating energy consumption. The Home Energy Saver accounts for internal gains by passing information about internal heat loads to the DOE-2 building simulation engine. Information about the number of occupants and the energy consumption for lighting and gas and electric appliances (including the water heater) for all equipment located within the conditioned space is sent as internal gains to DOE-2.

Energy use fractions (fraction of heat assumed to be an internal gain) for the large appliances are based on values used for the Building America Research Benchmark (Hendron and Engebrecht 2009): 

 Appliance  Fraction  Fraction
(Legacy system)
Dishwasher
 60% 75%
Clothes Washer
 80% 80%
Clothes Dryer
15%
15%
Stove and Oven
      electric
      gas
 
80%
80%

70%
50%
Refrigerator
      first
      second and third
 
100%
100%

100%
0%
Freezer 100%
0%

Other internal gain assumptions are as follows:

  • 100% of small appliance loads are assigned as sources of internal gains except for satellite dishes, sump pumps, well pumps, spas, engine block heaters, doorbells, and grills.
  • Water heater standby loads are included if the water heater is located in the basement or indoors. Water heater standby is assumed to be 1.77% of rated input for electric water heaters and 2.37% of rated input for fuel water heaters.
  • Occupants are assumed to have a sensible load of 230 Btuh and a latent load of 190 Btuh per person.
  • All lighting energy is assumed to be an internal gain.
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