Radiant Time Series (RTS) Procedure (spreadsheet method)

ASHRAE Fundamentals 2001 in Chapter 29.27-29.37.

The RTS method is suitable for peak design load calculations, but it should not be used for annual energy simulations due to its simplified assumptions such as steady-periodic conditions.

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Conduction time factor (CTS) and radiant time factor (RTS) takes into account (1) and (2).

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The RTS calculation procedure as presented on the following figure:

1. calculate 24h profile of heat gain for design day; apply CTS

2. split heat gain into radiant and convective part

3. apply RTS

4. calculate cooling load as a sum of convective heat gain and delayed radiant part of heat gain

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The sol-air temperature represents outdoor design air temperature that combines convection to the outdoor air, radiation to the ground and sky, and solar radiation heat transfer effects on the outer surface of a building.

A practical method for cooling load calculations requires computer application. With computer application available simplified methods are not necessary because heat balance equations can be numerically solved in a few seconds on a PC.

The following manual method is suppressed, but not invalidated or suppressed.

Posted in Fundamentals of Heating. Ventilating, and Air-Conditioning