Sunday, January 20, 2013

Muli-Purpose Low Thermal Mass Sunspaces

I've been working for the past couple months on a new section on Low Thermal Mass Sunspaces.  In the course of doing the testing and putting this material together, I've become a real believer in this kind of sunspace design -- it offers an exceptional combination of space heating performance and multiple use living space that is hard to beat.  I think that if more people came to appreciate how well these low thermal mass sunspaces perform, they would be far more popular.

Low thermal mass sunspaces are very efficient in making a lot of heat that can then be exported to heat the home that the sunspace is attached to.  When designed correctly, they can be just as efficient as high quality active solar collectors for home heating, but in addition to providing space heating, they provide a whole raft of other uses -- including:
  • Space to lounge in the sun (even when it 10F outside).
  • Space to read the paper and have a cup of coffee in the sun.
  • Space for the kids to play.
  • Four season space to dry clothes -- a major energy and carbon saving in itself.
  • Space to dry and store firewood, or have a workshop, or may other uses.
In addition, sunspaces can be very visually appealing and are more likely to pass muster with your HOA or your spouse than are active solar collectors.  I believe that they are also likely to increase the value of your house more than other energy saving investments due to their aesthetic appeal and mulit-purpose nature.

These sunspaces are efficient space heaters because their design is optimized to generate a lot of heat and to get that heat to the house.  They intentionally have very little thermal mass -- this makes them heat up very quickly, and the heat they generate is transferred to the house rather than being used to heat thermal mass in the sunspace. 

I don't know of any other solar investment that is so cost effective as an energy and carbon saver, and at the same time provides so many other family benefits.
Included in the new section:
- A design guide that explains what the low thermal mass sunspace is, how it works, and why its efficient.  The guide also covers a number of design guidelines that you want to follow to make a sunspace that is both an efficient heater and a pleasant place to spend time.   

- Some careful tests done on my sunspace to measure the actual heat output and efficiency for an optimized sunspace and compares it to high quality active solar collectors.  The bottom line is that a well designed low thermal mass sunspace is just as efficient as a space heater as high quality active solar collectors -- and you can enjoy a nice morning cup of coffee in the sun sitting inside your collector!

Another result that emerges from this testing is that there are several design rules that need to be followed if the sunspace is to be an efficient producer of heat.  
- Several good and detailed descriptions of low thermal mass sunspaces that cover the whole wide range of possible designs.   Here are some examples of the examples:

This is Mike's retrofitted low thermal mass sunspace in the Colorado mountains.  It is an efficient space heater for the house, but also provides a wide range of other uses including lounging in the sun, kids play area, and a clothes drying area that saves an additional 1200 KWH a year in itself -- just this side benefit is equivalent to the yearly output of a 1000 watt PV array. And, it looks great.

This is Nick Pine's new cutting edge three story low thermal mass sunspace.  Nick has tried a number of innovations in this sunspace including DIY clear polycarbonate glazing, a unique air distribution system, and a mesh scheme that promises even more efficient operation.

This is Architect William Sikora's modern and elegant low thermal mass sunspace in Minnesota.  The sunspace not only looks great, but it is designed to be very simple in operation and maintainable by the home owner using only ordinary tools.

There are other examples that show how very low budget versions of the sunspaces can be built that are still effective heaters, and an example of a 100% solar heated home that uses a low thermal mass sunspace as the only heat source.

The main index for the new Low Thermal Mass Sunspace section ....

I want to particularly thank Mike P., Nick Pine, and William Sikora for taking the time to document their sunspaces.

For all you low thermal mass sunspace owners out there, I hope you will use the comments section (or email me) to pass on your experiences with your sunspaces.


Friday, January 4, 2013

A DESIGN CHALLENGE for pop can and downspout collector builders

Solar air heating collectors that use columns of aluminum soda pop cans or that use metal gutter downspouts as the absorber are quite popular. 
pop can collector
Greg's pop can collector in work
In this design, the supply air flows into a plenum at one end and is distributed to the pop can columns or downspouts, the air then flows up the pop cans.  The sun striking the outside of the black painted cans heats them up, and this heat is transferred to the air flowing up through the cans. 

One of the challenges for an efficient design is to get the same flow in each of the pop can columns.   Having unequal flows in the columns makes for a less efficient collector with some parts of the collector running hotter than they need to and losing heat out the collector glazing.
When I built a downspout collector for testing against other collector types, I was unable to come up with a plenum design that gave an even flow in the downspouts...  I think that this may have been a significant part of why the collector did not do so well in the testing compared to the screen absorber.

Sooooo, if you are building or have a pop can or downspout collector, how about testing the flow in each column, and see how the flow comes out on yours.  If its not close to the same in each column, maybe you can experiment around with changes to the collector to get the flow to even out? 

Testing for even flow is easy to do, and coming up with a collector/plenum design that provides even flow to all the can columns would be a real benefit to a lot of collector builders. 

On my prototype, I measured the flow by making a small hole in each column, and then read the column air velocity by inserting a wind meter in the hole.

The results looked like this...

Flow in each of the 13 columns.

January 4, 2013

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