[BLDG-SIM] Heat gain from light pipes

Ellis, Peter peter_ellis at nrel.gov
Thu Jan 22 10:51:25 PST 2004


 
Hi Vikram, 
 
The latest release of EnergyPlus (v. 1.1.1) added a model for light pipes, i.e. tubular daylighting devices.  The model is fully described in the documentation that comes with the program.  
 
Just to give you an idea in brief, light pipes can add both solar gains and conductive/convective gains to the space below.  The solar gains are calculated by analyzing the multiple internal reflections of the incident beam, sky, and ground radiation entering the pipe.  The amount of radiation transmitted depends on the incident angle, reflectivity, and geometry of the pipe, and on the properties of the glazing at either end of the pipe.  Fortunately, all of this is entirely handled by the program.  
 
The conductive/convective gains, on the other hand, require the user to enter an effective thermal resistance (R-value) between the top and bottom of the light pipe.  The problem is knowing what R-value to use.  Very little research has been done on this area of the problem (as of about 1 year ago--the last time I looked).  I have only found one paper that analyzes the conductive/convective behavior of light pipes:  
 
Harrison, S. J., McCurdy, G. G., Cooke, R.  "Preliminary Evaluation of the Daylighting and Thermal Performance of Cylindrical Skylights", Proceedings of International Daylight Conference, Ottawa, Canada, 1998, pp. 205-212.
 
They report an average thermal resistance of 0.279 m2 K/W for a pipe measuring 1.83 m by 0.33 m.  
 
Hope this helps!
 
Peter Graham Ellis
National Renewable Energy Laboratory
Center for Buildings and Thermal Systems
1617 Cole Boulevard
Golden, Colorado 80401-3393
303-384-7443
peter_ellis at nrel.gov
 
 
 
-----Original Message-----
From: Vikram Sami [mailto:Vikram at ensargroup.com]
Sent: Wednesday, January 21, 2004 4:04 PM
To: BLDG-SIM at gard.com
Subject: [BLDG-SIM] Heat gain from light pipes


Hi,
I have a question about light pipes. We are using then for a project, and I was wondering if there was any way to calculate the heat transmitted to the space below through the pipes.
 
Thanks
 
Vikram Sami

ENSAR Group, Inc.
2305 Broadway
Boulder, C0 80304
(303).449.5226 Tel
(303).449.5276 Fax





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