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samschaperow

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Posts: 13
Reply with quote  #21 
Hi Gordy:

I had read that people use thermostats that will activate the fan when the temperature differential is sufficient.  Otherwise, the vent closes to prevent unwanted hot air to enter the home.  Covering numerous panels, or a huge one, sounds daunting (not to mention questions of aesthetics) or expensive to get an automated one. 

Sam of CT

gbwillson

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Reply with quote  #22 
Sam-

Most collectors ARE permanently installed, but they don't have to be. Mine get moved seasonally as I don't have the space on the south side of my home for a permanent mount. So you could consider a seasonal instal as long as you have a place to store the unit. But I would install permanently if I could. 

Excessive heat is not normally a problem in the warm months as the sun is at a high angle, limiting heat collecting. A cover is often used. A cover can be natural plantings, tarps, plywood or the unit could be left exposed. But if left exposed, you should figure a way to vent the excess heat from entering your home. In no case should the unit be uncovered, with no ventilation during the warmer months!

Julian's design is very good, but it is designed for a smaller area, such as a room. It is not designed for large amounts of heat collection. So a different design is needed to heat large areas, such as a house.

With all of the windows windows on the South side of your house, a long, low profile collector might be your best bet. You could install a collector below the windows on the first floor. If the unit was 4' high and 16-24' long you would get a lot of heat. There are several examples of this size and configuration, but I am a strong proponent of a ZeroPass design which works best in a long configuration, and at high volumes of airflow. With a 4'x20' ZP collector you could expect more than 20,000 BTU's output per hour. That's like 4+ electric space heaters running while the sun is shining. That much warm air blowing directly into a single room would soon overheat the area. But if the air can be more evenly distributed, it will do a great job of warming the house overall. My collectors warm my basement, which in turn warms the main floor. The heat is absorbed and slowly given back for several hours after the sun has set. 

Also, I noticed from the photo of the South side of your house that the yard is almost completely shaded. With another 5-6 weeks before the Winter solstice, how much more of the house will be shaded? 

Greg in MN
Rick H Parker

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Reply with quote  #23 
Excessive heat is not normally a problem in the warm months as the sun is at a high angle, limiting heat collecting. A cover is often used.

A well calculated overhang could be the answer to overheating.

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Rick H Parker
Kansas, USA
Electronics Engineering Technologist
samschaperow

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Posts: 13
Reply with quote  #24 
I just spent about 10 minutes on the internet trying to figure out what a ZP is, but I'm still not sure.  What's a ZP?

I'm trying to consider, too, how much sun I get.  I'd have to see how things go on the bottom floor when the sun gets lower as winter comes.  I think the windows stay sunny, with shade occurring on the wall under the windows.  If so, then it wouldn't work well to have 1st floor below-windows panels.  Maybe I should do 1st floor higher up panels like to the left and right of windows.  Though, the top floor would probably work well to have one panel spanning much of the length of the house below the windows.  Of course to the left and right of the windows the spaces would work well in terms of amounts of sun.  

Especially w/2nd floor panels, I'd want them permanently installed and also not needing me to white tarp them.  I don't know how I'd put an overhang that's aesthetically okay, functional, and would have a good payback (but if you all didn't know, there's a calculator that can be used to figure out overhangs: http://www.susdesign.com/overhang/).  Why not, for overheating concerns, just have a lever in the vent that drops off a part of the vent (do this instead of covering the panels)?  E.g., have a hole cut into the bottom of the vent, which is sealed w/weatherstripping during warm weather, but that I can then move the latch so it drops down and allows for air to pass through it, thus allowing the unwanted hot air to be vented out.  If this does work, would I still have concerns about heat build-up in the house from having walls covered in black panels?  I mean, wouldn't it mean the walls would be warmer, in turn causing the heat to transfer into the house (not nearly as much as if the vent were venting into the house, but still of enough significance to offset a significant portion of the benefits during cold times to have the panels)? 

Here are additional pics:
1. 11/17 @ 2:44PM
11-17; 2;44PM.jpg 
2. 11/20 @ 9:37AM
11-20; 9;37AM.jpg 
3. 11/20 @ 10:33AM
11-20; 10;33AM.jpg 

According to the pics, at this time I get good sun in a lot areas as of about 10:30AM (I'd think even if I could get sun at 9:30, that it would be very angled early sun that's not very helpful).  At about 2:45PM the sun is at quite an angle, so I'd think not as good.  I think by about 3:30 it is pretty poor (very angled for this south wall).  So, 5 hours of sun, with about 4 hours that's not very angled.  This would be the usual northern (CT and similar areas) angles of sun.  Do you all get good heating even when the sun is as angled as in the 11/17 @ 2:44PM pic?  Do you find that you still get a good payback if you had the amount of hours of sun I get?




gbwillson

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Reply with quote  #25 
ZP is short for ZeroPass. This collector design is similar to the standard two screen collector, except that the air passes BETWEEN the two screen layers, instead of through the layers of screen. The ZP has a few advantages over the 2-screen collector.

ZeroPass Solar Heater.jpg 

First, it heats the air passing through it the entire length of the collector instead of just when the air passes through the screens. This means the air in a ZP is heated from both the top and bottom screens, like it has dual heating elements. This allow the ZP to produce much higher output temperatures and 2-3 times more BTU's in most cases for same-sized units. The downside is that the ZP requires more fan capacity to keep the output temps low to extract this heat and keep the unit operating efficiently. Most of the ZP's built so far have been in an elongated configuration, rather than square. But that doesn't mean other shapes won't work as long as there is enough fan capacity to keep the unit output temps efficient.

You have to figure that between 10am and 3pm are going to be peak sun times. You will still get heat earlier and later, but at a diminished rate. So figure maybe 6 hours total run-time during the shortest sunny winter days. But this will increase as the sun angles improve. But any and all added heat will keep the furnace off and reduce the amount of money spent for heating for several hours after a collector has shut down for the day.

In your case, the upper back of the house below the windows looks like the best location, unless there are leaves on those trees that haven't fallen. But you are starting pretty late in the season for a major build to be installed above ground level. I know I'd sure hate to climb a ladder to install a heavy collector in the cold and snow. I'm just starting my new ZP unit this week, but it will be mounted on wheels and simply rolled into place, so snow and cold won't be an issue.

Greg in MN

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