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Simulated Internal Gains

Internal gains are incurred from occupants' activities and their usage of lights, appliances, domestic hot water fixtures and miscellaneous loads. Internal gains are composed of sensible and latent heat gains. Convective electric heaters and humidifiers can be used to simulate the internal gains prescribed by the House Simulation Protocols (HSP) [1].

Heaters normally have much larger power than the sensible hourly load profiles prescribed and there is some time delay while the heater ramps up to full power. Therefore, heaters' power consumption needs to be monitored and feedback signals need to be provided to the data acquisition (DAQ) system in order to precisely control the heat output.

Ultrasonic humidifiers are recommended instead of steam humidifiers for hourly latent load generation and simulation [2]. Ultrasonic humidifiers can release moisture instantaneously at room temperature without warm-up period once turned on. This technology decouples the latent load from the sensible load, and allows separate control and generation. On other occasions, when precise hourly load control is not necessary, steam humidifiers can still be used.

Depending on the questions the researcher is trying to answer, internal gains can be generated at a whole-house level or can be distributed to rooms where air distribution may be of interest, for instance [2].

Photo shows a small space heater on the floor of a room.Photo shows a humidifier set up on a countertop in a home. The humidifier is attached to sensory equipment.

Space heater used to simulate sensible

A humidifier used to introduce latent loads


  1. Hendron, R. and Engebrecht, C. Building America House Simulation Protocols. National Renewable Energy Lab, October 2010. NREL/TP-550-49426.
  2. Fang, X.; Christensen, D.; Barker, G.; Hancock, E. (2011). Field Test Protocol: Standard Internal Load Generation in Unoccupied Test Homes. 16 pp.; NREL Report No. TP-5500-51928; DOE/GO-102011-3321.