RE: TRNSYS and Infra Red radiators

[Jeff Thornton <thornton@xxxxxxxxxxxx>]

Unfortunately, none of the standard TRNSYS solar collector models separates longwave radiation losses from convective losses.
A first approximation could be to use the global heat loss coefficient (UL) with a fictitious ambient temperature which is a weighted average between air temperature and sky temperature.


FYI:

We have modified one of our TESS collector models for a project with the National Renewable Energy Laboratory to do solar collection and infrared cooling for unglazed solar collectors.  The UL and FRTAN parameters were moved to INPUTs and are now calculated based on equations of the form:

FrTan = a - b * Windspeed Reduction Factor * Current Wind Speed
FrUL = c + d * Windspeed Reduction Factor * Current Wind Speed

where a,b,c, and d are user-defined values.  This formulation corresponds to the current test reporting method for unglazed collectors.  The incident radiation INPUT is also slightly modified for the new collector model to account for radiation exchange:

TAMB_K=Current Ambient Temperature+273.15
TSKY_K=Current Sky Temperature+273.15
SIGMA=3.6*5.67E-08              !KJ/H.M2.K4
LONGWAVE=SIGMA*((TAMB_K**4)-(TSKY_K**4))
NET_IT_COL=Current Total Incident Solar Radiation - LONGWAVE

NET_IT_COL is then passed to the new collector model as an INPUT.

If anyone has any questions about this model or any of the TESS component library models they may reply directly to this e-mail.

Jeff