3.1.9 Loads Calculation

The loads calculations described in this section relate to the simulation engine and not to the procedure used the design engineer to size and select equipment.

Internal Loads

The Rating Software shall be capable of calculating the hourly cooling loads due to occupants, lights, receptacles, and process loads.

The calculation of internal loads shall account for the dynamic effects of thermal mass.

The Rating Software shall be capable of simulating schedules for internal loads in the form given in Appendix C.

The simulation of cooling load due to lights shall account for:

• The effect of the proportion radiant and convective heat, which depends on the type of light, on the dynamic response characteristic; and
• A portion of heat from lights going directly to return air, the amount depending on the type and location of fixture.

Building Envelope Loads

The Rating Software shall calculate heat transfer through walls, roofs and floors for each thermal block, accounting for the dynamic response due to thermal characteristics of the particular construction as defined in the Building Descriptors in Chapter 6.

The calculation of heat transfer through walls and roofs shall account for the effect of solar radiation absorbed on the exterior surface, which depends on orientation, reflectance and emittance of the surface.

The Rating Software shall calculate heat transfer through windows and skylights, accounting for both temperature difference and transmission of solar radiation through the glazing.

Calculation of cooling load due to transmission of solar radiation through windows and skylights shall account for:

• The angular incidence of the direct beam sunlight and the angular and spectral dependence of the solar properties.
• Orientation (azimuth and tilt of surface).
• The effect of shading from overhangs side fins, louvers or neighboring buildings or terrain.

Infiltration

The Rating Software shall be capable of simulating infiltration that varies by the time of day and day of the week.