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usefulness of software simulation

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Posted by Martin Trautmann on June 18, 2008, 11:20 am
 

Hi all,

the problem we face is a roof and garden which offers worst conditions
for solar energy.

However, since we do want to use wood pellet heating (which becomes more
and more common im Germany due to increasing energy prices), we would
like to support this system within summer. Otherwise the system has to
be heated up completely, just for some minutes a day in order to prepare
warm water for the shower etc.


The parameters are

- roof: 45 degree

- ridge: 13 degrees north-north east
  Thus the roof points more to the east, in order to catch morning sun,
  instead of west, where we might collect and store heat for the next
  morning when we will need most warm water.

- location: 48.0000 / 7.8500


One expert recommended two fields, one to the east, double size to the
west, on the 45 degree roof. Tube collectors should be used in order to
rotate them for optimisation (best angle towards the sun, but I do not
know which one this would be).

Another expert recommended to use an eastern collector only. Same size
(about 6 square meters), preferably on the dormer, at 30 degrees, since
this would collect sun light for a longer period, when the sun moved on
towards south and west.

What we want to achieve is that the wood pellet heating has to run less
(best: almost never) in summer, offering the optimum concerning price,
efficiency, energy saving and life time improvements, with a small
accepted penalty for the more enviroment friendly solution.


Now we wonder what might help best for about 150 litres warm water a day
(5 persons) (maybe more? the standard assumes 50 litres @ 60 degree
celsius). We do not expect to heat in winter by sun - although any
heating support would be welcome.

Oh, btw the recommendation was to store about 800 or 500 litres.

I wonder whether there are useful simulation tools which might consider
different collector types and effects of tube orientation. Any
suggestion?

Thanks,
Martin

Posted by gary on June 18, 2008, 2:13 pm
 

Hi,
If you only need collection in the summer, horizontal collectors work
well through the summer.

You can use this software to evaluate the effects of azimuth and tilt
of collectors:
http://www.builditsolar.com/Tools/RadOnCol/radoncol.htm

There is a run pated in below that shows a horizontal collector at 48
latitude.
The last column is the solar radiation on 1 sqft of collector in BTU/
hr (sorry about US units).
It gets up to 2600 BTU/hr in mid summer -- thats a lot.
This is under full sun conditions -- no clouds.
You can download the software and run it yourself for other collector
orientations.

As a rough rule of thumb, you can assume 50% efficiency, so half of
this heat goes to heating your water.
To heat 30 gallons a day from 60F to 120F takes 15000 BTU -- this
might be typical for 2 people.

Another option would be put a collector mount on the south eave:
http://www.arttec.net/SolarDHW/4_Collectors/index.htm

Gary


Radiation On Collector run for 1 sqft of horizontal collector.
Month by Month Summary of Sun on Collector
(100% sunny weather)

  Collector Area:        1.0 (sqft)
  Collector Azimuth:     0.0 (deg) measured from South
  Collector Tilt:        0.0 (deg) measured from horiz
  Latitude:             48.0 (deg)
  Altitude above SL:     0.0 (ft) Above Sea Level

Date ----  Sun ----------------  Collector -----------------------
Month Day  Direct   Di-   Total    Direct      Difuse     Total
           Normal   fuse
   1   21   1731     101   1832        508        101        609
   2   21   2287     137   2424        907        137       1044
   3   21   2781     197   2979       1381        197       1578
   4   21   3080     300   3381       1816        300       2116
   5   21   3260     396   3655       2095        396       2491
   6   21   3314     443   3758       2183        443       2627
   7   21   3157     429   3586       2044        429       2473
   8   21   2896     352   3248       1728        352       2080
   9   21   2577     239   2817       1300        239       1540
  10   21   2129     154   2283        841        154        995
  11   21   1654     104   1758        484        104        588
  12   21   1441      83   1524        363         83        446
Sum        30308    2936  33244      15651       2936      18587

Radiation in BTU/day






Posted by Martin Trautmann on June 19, 2008, 11:43 am
 On Wed, 18 Jun 2008 07:13:23 -0700 (PDT), gary@builditsolar.com wrote:

Thanks, I'll give it a try. It's the wrong OS for me, so it will take
some time.

- Martin

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