Sunday, January 29, 2012

Mother Earth News Article on Our Solar Water and Space Heating System

The new (February 2012) issue of Mother Earth News has an article on our DIY solar system that heats water for domestic use AND also provides space heating.

The article provides a good and detailed overview of the system in about 5 pages--

- If you want a good detailed overview of how the system works to see if it might be for you, go to the Mother Earth Article -- its available on the Mother Earth website here...

- If you decide you want a much more detailed version that covers the full design as well as design alternatives, and provides detailed build instructions, then go to the 100 page write up here...

The MEN article.

The emphasis for this system was to provide both solar space heating and solar domestic water heating while still keeping the system simple and easy to build.  All the lessons learned over the past five years by me and others who have built the system are included.


Wednesday, January 18, 2012

An Easy/Good DIY LED Can Light Retrofit

Home Depot is selling a nice and easy to install LED retrofit for can lights.  We decided to try one as we have lots of can lights that would benefit from an efficient retrofit.

It is equivalent to a 65 watt incandescent, and has a 2700K color temperature -- nice and warm.   Output is 575 lumen.  Power consumption 10.5 watts.
Price is $40 -- kind of pricey, but see the payback comments below.  Claimed life is 20 years.

It is said to be dimmable, but apparently not all dimmers are compatible with it.

The 117 reviews on the HD site show a nearly 5 out of 5 stars with very few unhappy people.  Lots of very favorable comments.

The installation was relatively easy.  You take out the old can light bezel and remove the stuff holding the old can socket in place.  You then rotate out the little metal wings on the new fixture and just push it up into the old can housing -- very simple.  They can be removed by rotating the fixture CCW.

The springy metal pieces wedge into the existing can
light housing to hold the new fixture in place.
We also sealed up the openings and cracks in the existing can housing to reduce infiltration.

If you are going from incandescent bulbs to this LED, the saving is 55 watts.  This adds up pretty quickly.  For our usage and power costs, the payback period on saved electricity is only about 3 years. 

The lighting is very nice.

Nice warm lighting.

All the details on the installation and the payback calculations here...

Hundreds more conservation projects...


Saturday, January 14, 2012

Solar Cooking After Dark -- A DIY Stored Heat Solar Cooker

Mik has been working on a way to collect and store solar energy during the daytime so that it can be used after sunset to cook meals.   He is looking for ideas to solve some of the technical issues that still remain, so if you have any ideas.

Reflector from satellite dish heating the bundle of iron rods.

Mik's solar cooker uses a concentrating reflector to heat a bundle of iron rods to very high temperatures.  Once the rods are heated, they are stored away in an insulated container to retain heat.  Later in the day (after the sun has set), the stored heat is used for cooking.

Diagram showing the design of the heat storage unit.

Cooking on stored heat.

While this is not the first solar collector to use stored heat, it is a very simple design that can be built fairly easily and cheaply in a low tech environment.  It could potentially reduce the amount of fossil fuel use by allowing people to cook with solar at normal meal times without regard to whether the sun is present at that time or not.

Mik has run into some material and insulation challenges in this project, and is looking for advice.

All the details on Mik's stored energy solar cooker... 
There is a comment section at this link.


Friday, January 6, 2012

Large Thermosyphon Collector Updates and Developments

I've been using a very simple solar thermosyphon collector to heat my shop for several years.  It is large and puts out a lot of heat -- its also simple, cheap, and low maintenance.  Where we live it has a kind of amazing one year payback on the cost of materials to build it.
The large thermosyphon shop heating collector
The collector has been getting some attention lately and that coupled with some new testing and 9 years of accumulated experience makes me think its time to do an update.  This update covers a lot of territory:
  • A new commercial version of the collector 
  • A video featuring the collector
  • Potential changes and refinements
  • Maintenance and upkeep over 9 years
  • Testing effect of reducing vent size to make construction easier
  • More accurate collector efficiency measurements

A New Commercial Version 
Paul House  of Choice Energy here in Bozeman  is offering a commercial version of the collector.  He will build one on your wall for about $2000.  In our climate, the collector offers about a 5 year payback (rebates could make it even shorter).  This is the best rate of return I know of for commercially installed collectors by a wide margin.  For example, if you compare it to the popular SolarSheat commercial collector, it is about 5 times more cost effective on a dollars per BTU basis.

A New Video on the Collector
There is a new video in works on the collector being done by Peter and Dana.  This is the first in a series of videos they are doing that will feature renewable energy projects in the SW Montana area.  They were out capturing video and audio before Christmas, and the final product should be out in a month or two -- I'll post a notice when its available.   I think this series of videos is going to be very interesting as there is a lot going on the renewable energy front in this area.

Paul and Gary on video day

Potential Changes and Refinements
The collector has performed very well, but, as always, there are a few things I would do differently if starting over.  So, this section lists a few small changes and one large change I would make.

The small changes have to do with details of the absorber installation, flashing, glazing...   just small refinements.

Collector cross section (from Home Power article)
The absorber change has to do with the tilt of the screen layers.

The one big possible change would be to revise the design to allow the collector to pass more daylighting into the shop area.  On my other shop, I use this glazed door arrangement, and I have to say I just love the solar daylighting it provides -- it not only helps when doing work, but it also just gives the place a more pleasant feeling.  I'd like to incorporate some some glazed area in the back wall of the thermosyphon collector that would add this solar daylighting feature.   If you have any ideas on good ways to do this, please let me know.

Testing Smaller Vents
Paul suggested the idea of using a large hole saw to cut the inlet and outlet vents for the collector.  This would save some work and look nicer.  The potential downside is that a 6 inch or even 8 inch hole saw results in a smaller vent size than the design guide lines for these collectors specify.  

The two adjacent bays of the collector used to test
effect of smaller vents.
In order to get an idea what the performance penalty for the smaller vents might be, I masked down the vents on one bay, and then compared the heat output from this bay to the adjacent bay with the full sized vents.  Unfortunately, there is a pretty big penalty for the 6 inch round vents, and even the 8 inch round vents show a drop in heat output.  It looks like a 9 inch circular vent would be about right.

Efficiency and Flow Rate Testing
While doing the small vent testing, I also had another go at testing the efficiency of the collector.  I have somewhat improved instrumentation and accounted for more of the odds and ends that effect efficiency.  Its difficult to get good efficiency measurements on any solar air heating collector because measuring airflow accurately is hard.  Getting good airflow measurements on the thermosyphon collector is even more difficult due to the large vents with low vent velocities.    But, I do think these new measurements are pretty good.  

Bottom line is that for the full sun, moderate winter day I tested on, the efficiency comes out between 62 and 65%  -- this is really very good, especially considering how simple and inexpensive the collector design is.

Logger plot used for vent size and efficiency estimates.
There are also some test results on collector flow rate, dust filter effects on flow rate, and on using the back surface of the collector as a radiant room heater.

Through the first 9 years, the collector maintenance has been very minimal.  

The poly back draft dampers have been replaced once at a cost of 2 cents per damper.

I painted the outside of the collector frame last year.

The fact that the collector does not have a fan or controller eliminates the two most maintenance prone items on solar air heating collectors. 

After 9 years, the polycarbonate glazing still looks very good.

If you have any thoughts or suggestions on the collector, please let me know.

Collector parts diagram (from Home Power article)

January 6, 2012

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