[Greenbuilding] Solar Water Heater Tilt
Gary
gary at BuildItSolar.com
Mon Feb 9 09:24:21 CST 2009
> From: Lawrence Lile <LLile at projsolco.com>
> Subject: [Greenbuilding] Solar Water Heater Tilt
> To: GB REPP <GREENBUILDING at listserv.repp.org>
> Message-ID:
> <AC254829C2A6324CB4DF94CED1DB37FB46818F16E7 at exchange.ProjSolCo.local>
> Content-Type: text/plain; charset="us-ascii"
>
>
>
> The standard answer for tilting your solar water ehater collector is latitude plus 15 degrees. For my latitude that is about 54 degrees.
>
> This article
> http://www.macslab.com/optsolar.html
>
> seems to indicate that you can do a little better overall if you tilt a little more toward the winter sun. For my latitude (38.9 deg.) the author recommends about 64 degrees.
>
>
> However, others have argued that you don't really get much sun int he winter, more cloudy days, colder ambient, and you don't really gain so much from optimum tilt. it is "good enough" just to surface mount the collectors on a south facing roof and be done with it. It is a lot simpler to mount a collector flat against the roof than tilt it, and they say it makes little difference.
>
> Overall I expect this system to produce all of my hot water in the summer and about half of it in the winter. I have enough metering history on my hot water heater that I'll be able to tell, very closely, if this is the case.
>
> My South roof is 4:12, or about 18 degrees. So the question is, how much difference will it make if I mount solar collectors flat against the 4:12 roof, versus at one of those two angles? I'd like to be able to say "yes, that will make such and such quantifiable production of hot water".
>
> If you need to know, I have two AEC 4X7 ft. collectors and 85 gallons of water storage.
>
> Would RETscreen be able to answer such a question? That alone would be a good reason to get it running, I haven't really tried it out.
>
>
> -Lawrence
>
>
Hi,
You can get a pretty good idea just by running Radiation On Collector
for the two tilt angles and do the "calculate for months". Free
download here:
http://www.builditsolar.com/Tools/RadOnCol/radoncol.htm
Runs for 18 degs and 55 degs are pasted in below.
The last column is the one you want to compare.
You may have to change to a fixed width font to make the output readable.
On total radiation, 18 degrees wins by a bit year round, but 55 degrees
provides much more even year round radiation, and may provide more hot
water if you can't actually use all the hot water that 18 degrees
produces in the summer -- so maybe this does not really answer the
question after all :)
Bear in mind that the outputs are for a fully sunny day.
As yet another approach, I use a large collector area and a very steep
tilt angle (70+ degs) -- this seems to be working well in the
fall/winter (90% fraction so far), and I think will also do fine in the
summer without overheating so much:
http://www.builditsolar.com/Experimental/PEXColDHW/Overview.htm
Radiation On Collector Runs:
18 degrees tilt:
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: 18.0 (deg) measured from horiz
Latitude: 38.9 (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 2238 130 2368 1353 127 1480
2 21 2639 158 2797 1713 154 1867
3 21 2932 208 3140 2015 203 2218
4 21 3095 302 3396 2148 294 2442
5 21 3155 383 3538 2187 373 2561
6 21 3162 423 3585 2173 413 2586
7 21 3054 415 3469 2124 405 2529
8 21 2914 354 3268 2041 345 2386
9 21 2729 254 2982 1893 247 2140
10 21 2467 179 2646 1613 174 1788
11 21 2168 136 2304 1310 133 1443
12 21 2038 117 2155 1179 114 1294
Sum 32591 3059 35649 21749 2984 24733
Radiation in BTU/day
55 degree tilt:
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: 55.0 (deg) measured from horiz
Latitude: 38.9 (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 2238 130 2368 1879 102 1981
2 21 2639 158 2797 2078 124 2203
3 21 2932 208 3140 2072 164 2236
4 21 3095 302 3396 1811 237 2049
5 21 3155 383 3538 1575 301 1877
6 21 3162 423 3585 1465 333 1798
7 21 3054 415 3469 1520 327 1847
8 21 2914 354 3268 1713 279 1992
9 21 2729 254 2982 1934 199 2134
10 21 2467 179 2646 1965 141 2105
11 21 2168 136 2304 1824 107 1931
12 21 2038 117 2155 1735 92 1827
Sum 32591 3059 35649 21573 2406 23979
Radiation in BTU/day
Gary
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