[BLDG-SIM] RETScreen SWH

[Jeff Haberl]

This is a fundamental issue with solar thermal systems. Getting above 50, 60,70% contribution gets very hard for space heating, and/or systems combined with DHW. This is because the last few % are in the coldest months with little solar. Hence, the decrease in annual contribution as you add panels. The same is not true for DHW because of the flatter monthly load. 

Jeff
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Jeff S. Haberl, Ph.D., P.E.............................jhaberl at esl.tamu.edu

Professor......................................................Office Ph: 979-845-6507

Department of Architecture.......................Lab Ph: 979-845-6065 

Energy Systems Laboratory.......................FAX: 979-862-2457 

Texas A&M University..............................77843-3581

College Station, Texas, USA.......................URL: www-esl.tamu.edu

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----- Original Message -----
From: BLDG-SIM at gard.com <BLDG-SIM at gard.com>
To: BLDG-SIM at gard.com <BLDG-SIM at gard.com>
Sent: Wed Aug 08 15:14:08 2007
Subject: [BLDG-SIM] RETScreen SWH

Hi (again),

I'm sizing some solar hot water panels for a project (solar heat for an indoor pool).  When choosing the number of panels, I discovered something curious:

After I get up to about 65% solar energy for the system, the efficiency of adding new panels drops off.  For example, the first panel provides 2.66 MBtu, but the 33rd only 2.00 MBtu.  Is this because I've reached the point where the panels are too big for the load some of the time??  I assume this could be improved by adding thermal storage.

Thanks,


-- 
Karen Walkerman
Second Law Consulting
802-238-0980
kwalkerman at gmail.com