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transfer through building envelopes, from the outside, and into spaces. A
brief explanation of this method follows, but the RTS method of calculation
is defined in detail in Chapter 30 of the 2005 ASHRAE Handbook:
Fundamentals , as well as in the Load Calculation Applications Manual ,
also published by ASHRAE (visit www.ashrae.org for details).
The RTS calculation method determines cooling loads based on an
assumption of steady periodic conditions, such as occupancy, design-day
weather, and cyclical 24-hour heat gain conditions. Two time-delay effects
are addressed during cooling load calculations:
• Delay of conductive heat gain through opaque massive exterior surfaces,
such as exterior walls, the building roof, and floor slab on or below
grade
• Delay of radiative heat gain conversion to cooling loads
Figure 8.12 shows a flowchart summarizing the RTS calculation method,
also found in Revit MEP 2015 Help.
Figure 8.12 Radiant Time Series (RTS) calculation flowchart
Exterior building elements conduct heat because of a temperature
differential between indoor and outdoor air; solar energy is absorbed by
exterior surfaces as well. Because each surface has a mass and an associated
thermal capacity of the materials that make up its construction, a time delay
occurs from when the heat input of the outdoor and solar loads becomes
 
 
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