Saturday, June 11, 2011

Solar Heat from the Attic

I think everyone has gone up to the attic and been surprised by how hot it is.  Its just a small step from observing the heat to wondering if you could make use of it somehow. 

I added a new section that gathers together a few schemes for using attic heat for space or water heating, and other things -- here are a few samples -- see the link below for all the details.

Tim just did a project on EcoRenovators that makes use of attic heat in a nice simple way --he  just blows hot attic air down into the house when the attic is hot and house needs heat -- nice and simple, and it works.

Tims heat from the attic systemThis is Tim's setup -- it uses a chimney that is not in use anymore to channel the air down to the kitchen.  A homemade differential controller decides when to turn the blowers on.

The picture to the left is the "Black Roof" solar heating scheme.  This scheme basically harvests attic heat for space heating with just a few simple components and a blower.  It is said to be effective in cold climates that get quite a bit of sun -- eg Colorado.

There have been a number of schemes to use the attic heat to preheat domestic water.  This is a recently announced commercial offering that uses PEX tubes installed in the attic vent system to harvest heat.

Another idea that I like is picking up the inlet air for the clothes dryer from the attic.  Electric clothes dryers are big time energy users -- they not only use about 4 KWH of electricity per load, but they also end up sucking cold outside air into the house as they blow the air they have just heated out into the cold (wasting all the heat they just added to it).  If you could work out a way to pull hot air from the attic for the dryer it would eliminate all this cold air infiltration and the drywer could use less electricity since its inlet air would be hot already.  The nice thing about this is that you can time the drying to coincide with times when the attic is hot.

The ability to pull useful heat out of the attic will depend a lot on the climate you live in.   In our very cold climate, the space heating applications would be limited to the shoulder seasons, but this still could be an important source of heat.  The link below has my logged hourly attic temperatures for about a year.

If the use of attic heat idea could be incorporated in the initial design of the house there are all sorts of interesting and cost effective things that could be done to make the attic an effective heater.  Things like designing the attic to be a more efficient collector through the design of the roof surface, the attic vent system, and selective use of insulation on non-collecting surfaces could make the attic a fairly efficient and very large solar collector for not a lot of extra expenditure.  Introducing glazing could make the attic collector competitive with commercial air heating collectors.   

Got any ideas on any of this?  Have you used attic heat?  How?

All the details on the schemes above as well as several more interesting ideas are detailed here...


Tuesday, June 7, 2011

Efficient Cars Roundup from Solar Today

The current issue of Solar Today has their 4 th annual Efficient Cars Roundup.  I did not see the first three, but the fourth is a dandy -- partly because there is quite an interesting batch of new efficient cars to look at, and partly because of the excellent data table that is included in the article.
The interesting batch of new cars includes several real, honest electric cars (like the Leaf), several real, honest plug in hybrids (like the Volt), and a good selection of regular hybrids, gas engines, diesels, and one Honda CNG powered car.  Its nice that we have gotten to the point where hybrids can be referred to as "regular".

If you are one of the people (like me) who really wonder whether an electric car with its zero tail pipe emissions is really so squeaky clean when you trace the electricity back to the electric power plant (which has a 50 - 50 chance of being coal fired), then this is a good article to read.  The table that comes with the article has columns like: "12K mile E-mode carbon footprint with 100% coal", and "12K mile E-mode carbon footprint with 50% coal".   It also includes emissions data for using biofuels, 10 yr cost for both electric and fossil fuels, and more.   This is the best summary I've seen as far as being able to make quick comparisons on operating costs and green house gas emissions.  Much more helpful than the new EPA new car window stickers.

I think that some of the comparisons will surprise you.

The article is a free download from Solar Today, and there is even a downloadable spreadsheet version of the table.

Good stuff.

For more on efficient transport options, see my "Solar & Efficient Vehicles" page...

/* Start Analytics ---------------- */ /* End Analytics ---------------- */