Hybrid Car – More Fun with Less Gas

Is my near horizontal collector that bad?

register ::  Login Password  :: Lost Password?
Posted by gosolar23 on December 1, 2005, 4:55 pm
 
600 sf of trickle collector, around 25 deg sloped south.  Polycarbonate
covering.  Aluminum siding just like Harry Thomasson wanted.

Using day long insolation for January, I get around 1000 BTU/ft2.   I
guess for suny days that is around 600,000 BTU.  Maybe 40% efficiency
ok around 240,000 BTU's. Maybe 12 days of clear days a month?   3
million BTU's.

Looking at horizontal collector, my ASHRAE books states 1400 BTU's for
vertical for the day.   I guess these are clear days and not month long
averages.

but wholly smokes, come May through September, I am putting almost .7
Million btu's a day probably 20 days a month.  My 8,000 gallon tank
will increase about 10 degrees a day excluding losses.   Size does
matter!

Eric


Posted by Gary on December 1, 2005, 7:32 pm
 
gosolar23 wrote:

Hi Eric,

Here is the month by month radiation on a collector facing south at
43 deg lat (Seattle?)  -- First is for 25 deg tilt, 2nd for 43 deg tilt.

25 degree tilt:

Month by Month Summary of Sun on Collector
(100% sunny weather)

   Collector Area:      600.0 (sqft)
   Collector Azimuth:     0.0 (deg) measured from South
   Collector Tilt:       25.0 (deg) measured from horiz
   Latitude:             43.0 (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   2048     119   2167     792721      68000     860721
    2   21   2487     149   2635    1022636      85150    1107786
    3   21   2871     204   3075    1209435     116595    1326030
    4   21   3093     301   3395    1281601     172363    1453964
    5   21   3191     387   3578    1296833     221428    1518261
    6   21   3234     433   3667    1285059     247489    1532547
    7   21   3091     420   3512    1259149     240314    1499463
    8   21   2911     354   3265    1216673     202305    1418978
    9   21   2668     248   2916    1133738     141772    1275510
   10   21   2318     168   2486     959848      96062    1055910
   11   21   1973     124   2097     764550      70913     835464
   12   21   1775     102   1877     672827      58333     731160
Sum        31660    3009  34669   12895069    1720724   14615793

Radiation in BTU/day  <-----Note: BTU input per day for full sunshine

Month by Month Summary of Sun on Collector
(100% sunny weather)

   Collector Area:      600.0 (sqft)
   Collector Azimuth:     0.0 (deg) measured from South
   Collector Tilt:       43.0 (deg) measured from horiz
   Latitude:             43.0 (deg)
   Altitude above SL:     0.0 (ft) Above Sea Level



43 degree tilt:
Date ----  Sun ----------------  Collector -----------------------
Month Day  Direct   Di-   Total    Direct      Difuse     Total
            Normal   fuse
    1   43   2048     119   2167     968418      61759    1030177
    2   43   2487     149   2635    1165508      77335    1242843
    3   43   2871     204   3075    1271627     105894    1377521
    4   43   3093     301   3395    1224367     156544    1380911
    5   43   3191     387   3578    1150553     201107    1351660
    6   43   3234     433   3667    1106826     224775    1331601
    7   43   3091     420   3512    1113883     218259    1332142
    8   43   2911     354   3265    1160048     183739    1343787
    9   43   2668     248   2916    1188420     128761    1317181
   10   43   2318     168   2486    1096083      87246    1183329
   11   43   1973     124   2097     935195      64405     999600
   12   43   1775     102   1877     845042      52979     898022
Sum        31660    3009  34669   13225969    1562803   14788772

Radiation in BTU/day

Not much difference in year round collection.  For 25 degrees the
winter months are down some and summer months up some -- not exactly
what you would like for space heating, but its still a lot of heat for
a pretty inexpensive system.
You can download the program that generated these tables at BuildItSolar:
http://www.builditsolar.com/Tools/RadOnCol/radoncol.htm
if you want to play around with the angles some more.

8000 gallons seems like an awful lot of tank to me.

Be interesting to hear how your PC test comes out.



--


Gary

www.BuildItSolar.com
gary@BuildItSolar.com
"Build It Yourself" Solar Projects










----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.newsfeeds.com  The #1 Newsgroup Service in the World! 120,000+
Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

Posted by Iain McClatchie on December 1, 2005, 8:56 pm
 Gary,

Can you tell us a little more about this "diffuse" component?  Is this
the
light off the blue sky?  Do you have any references for the intensity
of
this source?

I ask because I'm trying to model the amount of light (not heat) coming
through my north-facing clerestory windows, so I can size them
appropriately.  Most rooms in the house have both north and south
windows.  The south windows let in most of the light, and the north
windows are supposed to let in enough light to brighten the walls
around the south windows enough to reduce the contrast between
those walls and the view from outside.  We're probably going to tint
the south windows as well, to help, but this is all subject to some
calculation.


Posted by Gary on December 2, 2005, 1:43 am
 Iain McClatchie wrote:

The algorithm is from Solar Thermal Engineering, Lunde.

It is for clear skys, sunny days.

About the diffuse component he says:
"To obtain global irradiance the additional diffuse irradiance
reflected from clouds and clear sky must be included.  This adds only
5 to 10% when there is clear blue sky, but the diffuse component is a
much higher proportion of the total when there are haze or clouds
present.  "

He gives diffuse as Idn*C, and tabulates C for each month.  C is low
in the winter -- around 0.057 in Dec, Jan, about 0.07 in March, Oct,
up to a max of 0.136 in mid summer.
Where Idn is the direct normal solar radiation level.

I suspect there is better stuff out there for your purposes.

I believe that under clear sky conditions, the diffuse component is
not uniform over the full sky, but is larger near the sun.

One way you could get actual diffuse readings for your area is to
download the TMY2 weather file for your area, and just scroll through
it looking at the direct and diffuse values.  I think that there are
public domain TMY file viewers out there.



Gary



--


Gary

www.BuildItSolar.com
gary@BuildItSolar.com
"Build It Yourself" Solar Projects









----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.newsfeeds.com  The #1 Newsgroup Service in the World! 120,000+
Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

Posted by nicksanspam on December 1, 2005, 9:07 pm
 It's bad enough to convince many people that "solar heating won't work."



GE's lab tests say the polycarbonate may only last 2 years. Why not call
and ask for a graph of their results? One layer will have significant heat
loss via evaporation from the siding and condensation under the glazing.
 

NREL says 680 Btu/ft^2 falls on the ground and 1050 falls on a south
wall on an average 48.7 F January day with a 55.6 daily max in SF, so
the average daytime temp is about 52. The average windspeed is 10.4 mph,
which makes the outer glazing loss about 2+10.4/2 = 7.2 Btu/h-F-ft^2.

A square foot of 25 degree south tilted collector has 0.906 ft^2 of
horizontal surface and 0.423 ft^2 of south wall surface, so it would
collect 0.906x680+0.423x1050 = 1060 Btu/day, of which 954 might pass
through a single polycarb layer. What do you plan for an average day
water temp?

With Tw (R) water in the collector and glazing temp Tg (R), 100(Pw-Pa)
= (Tg-(52+460))7.2 Btu/h-F-ft^2 might flow through the glazing, with
Pw = e^(17.863-9621/Tw) and Pa = e^(17.863-9621/Tg) "Hg, so... with Tw
= 560 R (100 F) and Pw = 1.935 "Hg. Tg = 538.8-13.89e^(17.863-9621/Tg).
Tg = 530 F (70 F) on the right makes Tg = 528 on the left, then 529.0,
528.8, and 528.9 R (68.6 F), so (68.8-55)7.4 = 102 Btu/h would flow out
from the glazing, leaving about 954/6h-102 = 56.6 Btu/h of useful heat,
about 600x56.6 = 34K Btu/day from 600 ft^2 of glazing. There's no useful
heat output at 119 F.


You might do a TMY2 simulation. Or look into cogen. You might run the
exhaust from a grid-tied Honda EU2000 into a natural gas water heater.

Nick


This Thread
Bookmark this thread:
 
 
 
 
 
 
  •  
  • Subject
  • Author
  • Date
please rate this thread