RE: TRNSYS and Infra Red radiators

[Michaël Kummert <kummert@xxxxxxxxxxxxx>]

Dear Maurice,

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.

Even if you would find suitable weighting factors, you would still have to take into account wind speed since I assume your "collector" is unglazed. Type72 could make a good basis for a first-approach: it allows you to specify a full performance map with 3 independent variables (Solar radiation, DT/G and wind speed). Please note, however, that Type73 is currently NOT able to simulate the behavior of a solar collector with a negative useful gain. So do not use it "as is" for your application.

Some references on radiative losses from solar collectors:

- Summers, D. A. (1995) "Thermal Simulation and Economic Assessment of Unglazed Transpired Collector Systems".
  M.S. Thesis at the SEL. Available on the web: http://sel.me.wisc.edu/Publications/Theses/theses2.html
  (not directly applicable to your case but includes a discussion of IR losses)

- The recent EN standard on solar collectors (EN 12975-2) includes some recommandations on simulation of IR losses (e.g. section 6.2.4.8.1). 
 
Regards,
 
Michaël
 
_________________________________________________

Michaël Kummert

Solar Energy Laboratory - University of Wisconsin-Madison
1303 Engr Res Bldg, 1500 Engineering Drive
Madison, WI 53706

Tel: +1 (608) 263-1589
Fax: +1 (608) 262-8464
E-mail: kummert@engr.wisc.edu

SEL Web Site: http://sel.me.wisc.edu
TRNSYS Web Site: http://sel.me.wisc.edu/trnsys



> -----Original Message-----
> From: owner-trnsys@relay.doit.wisc.edu
> [mailto:owner-trnsys@relay.doit.wisc.edu] On Behalf Of Jong, M.J.M.
> Sent: Friday, January 24, 2003 02:33
> To: TRNSYS E-mail group (E-mail)
> Subject: TRNSYS and Infra Red radiators
>
>
> Dear TRNSYS users,
>
> At this moment I am involved with a project to design a house
> that is provided with an Infra Red radiation cooling system.
> The Infra Red cooling system is a kind of solar collector
> that will be located on a flat roof of a house. During the
> clear summer nights (with a low sky temperature), the
> collector will be switched on. The water that flows trough
> the collector will be cooled during  these nights and the
> water will be stored in a storage tank. During the day in
> summertime, the cold water will be used in the tubes of the
> floorheating system to cool the house.
>
> As far as I know, there is no TRNSYS type to simulate this
> Infra Red radiator. Does anybody has experiences with
> simulating a Infra Red radiator or does anybody know if there
> is a type that I can use ? Please let me know.
>
> With kind regards,
>
> Maurice Jong.
>
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>
> Maurice Jong
> ECN - Energy research Centre of the Netherlands              
> Department: DEGO
> P.O. Box 1    1755 ZG  Petten                         Country:   The
> Netherlands
> Telephone:    +31 (0)224 564938                              
> Fax:       +31
> (0)224 568966
> E-mail: jong@ecn.nl                                   Internet:
> http://www.ecn.nl/dego
>
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>