Friday, January 28, 2011

Solar Water Heating Using a Unique Master and Slave Collector Design

Gordon has added solar water heating to his very very efficient home.  The system is loosely based on the our $1K solar water heating design, but incorporates some really interesting changes.

The collector uses a large "slave" collector to enclose and improve the efficiency of a smaller "master" collector.  This is design developed by Dinh Khanh some years  back and is explained in detail by William Shurcliff in this chapter of his book on solar innovations...   Basically, the larger slave air heating collector provides a warm environment for the small water heating master collector.  In Gordon's rough test, the slave collector increases the heat output of the master collector by about 50%.  This is the only application of the Khanh design that I know of, and, so far, it looks like it will do well.

The "master" water heating collector is about the top 2/3rds and the "slave" collector
extends over it and all the way to the ground.
The three small panels inside the slave are PV panels to drive the pump.

Gordon's tank and heat exchanger design are also unique.   He used a galvanized metal livestock tank lined with and EPDM liner mounted inside a well insulated wood frame.

The tank with the copper coil heat exchanger about to be installed.

The heat exchanger uses two 75 foot coils of 3/8 inch diameter copper pipe hooked up in parallel.  Using multiple small diameter coils in parallel should increase the heat transfer surface area and efficiency while still keeping the water pressure drop small.

This shows the valving that allows the heat source to be
the electric tank, solar heat, or both.
 The full story on Gordon's solar water heating system with construction details...

Details on the $1K solar water heating system...

If you have not read the story on Gordon's conversion of an old schoolhouse into a VERY low energy consumption and very attractive house, its a good one...

For the full text of the book by Dr. Shurcliff mentioned above, "New Inventions in Low-Cost Solar Heating -- 100 Daring Schemes Tried and Untried" go here...   This book is my all time favorite solar book -- it is a 1979 book and is out of print, but Dr. Shurcliff allowed me to scan it in and make it available as a free download.  The book was written during a period when many creative people were working on solar heating, and the ideas are as fresh, innovative, and interesting now as they were then.


Thursday, January 27, 2011

Volkswagon XL1 Concept Car

The XL1 is the latest in VW's 1-litre car strategy.  The aim for the 1-litre strategy is to develop a practical car that will use only one liter of fuel to travel 100 km  -- equivalent to 240 miles per gallon.

This amazing latest version carries two adults in side by side seating. The latest prototype can go 100 km on 0.9 liter of gas -- 260 mpg!

The car accomplishes amazing fuel efficiency through low weight, very low aerodynamic drag, and a very efficient diesel/hybrid power train. 

The low weight is accomplished in part through the use of a carbon fiber composite body.  Advanced materials are used in other areas to reduce weight, and the seating for only two people no-doubt also helps.  The empty weight of the XL1 is 1750 lbs -- and this includes the battery pack for the hybrid power train.

The low aerodynamic drag is accomplished through a combination of a very low drag coefficient and a low frontal area. The XL1 has a frontal area of 1.5 sm and a drag coefficient of 0.186.   Compare this to a VW Golf with a frontal area 2.22 sm and Cd of 0.312.  The drag force is proportional to the product of frontal area and drag coefficient, so the XL1 drag force at any given speed will be about 40% of a Golf.
Much of the frontal area reduction is achieved by reducing the height, which must make for an interesting seating position.

The car is powered by the combination of a 0.8 liter turbo charged diesel engine and a 20 KW ( 27 hp) electric motor.  The The car is a plug in hybrid, and can run on electricity alone for up to 22 miles.  The engine was derived directly from the current TDI VW engine.

All the information above is derived from the VW press release, which I suppose is fluffed up a bit, but even allowing for  some VW optimism, the car is an amazing accomplishment.  It shows the synergistic effect that applying a whole range of technologies to a new design can bring.  Just think of the impact that widespread use of this kind of design could have.

More information:
A fairly detailed desctription of the the XL1 design...

An overview on AutoBlogGreen...

Some nice pictures on AutoBlog...


Wednesday, January 19, 2011

Ken's DIY Solar Air Heating Collector -- Aluminum Soffit Absorber

Ken sent in the details for his solar air heating collector.  The collector uses an efficient flow through absorber that is made from vented aluminum soffit material.

Flow through absorber designs like Ken's are very effective at picking up the heat from the absorber, and give high collector efficiencies.

This is how the collector works -- cool room air enters at the bottom, flows up and toward the back through the vented soffit absorber, and then out the outlet at the top.  The air flowing through the soffit material efficiently picks up heat from the solar heated soffit material.

This picture of the collector on its side before the glazing is installed shows the vented aluminum soffit material that acts as the absorber.  The air flows through the small vent holes in the soffit material, picking up heat at it goes through.

The picture above shows the collectors metal frame made from stud track material.

See all the construction details on Ken's collector...

Thanks to Ken for sending this in!


Sunday, January 16, 2011

Ken's Large Solar Water Heating System

This is a very nicely done solar water heating system that generally follows the $1K design, but has a lot of excess capacity that can be used for hot tub or space heating purposes.

200 sqft of collector mounted on roof -- a nice look!
 Ken was able to get a set of older, but unused collectors from Craig's list.  The six collectors provide  nearly 200 square feet of collector area, so the system has excess capacity that Ken plans to use for hot tub heating and/or space heating.

 The tank is a very nicely done EPDM rubber lined tank with a capacity of nearly 500 gallons.  The design details on the tank are very nicely done, and it should be a good source of design information if you are building a tank for your system. 

The EPDM lined, non-pressurized nearly 500 gallon tank.

The PEX coil heat exchanger has been recoiled for improved heat transfer.

The 300 ft coil of  PEX heat exchanger recoiled for better efficiency.
All the details on Ken's system...

Thank you Ken for sending this in!


Tuesday, January 4, 2011

Sand Bed Heat Storage for Solar Home Heating Systems

Heat storage for solar home space heating systems is normally done with a large water tank.  The water in the tank is heated by the solar collectors, and the heat is then drawn out from the tank when needed to heat the house.
Schematic of a sand bed heat storage system.

 Another alternative that is gaining some followers is to store the heat in a sand bed located directly under the house.  Most commonly the sand bed extends under a large part of the house and is typically a couple feet thick.  The bottom and edges of the sand bed are insulated from the surrounding dirt using rigid foam board insulation.  The house floor slab is often poured directly over the top of the sand.  PEX pipes are run through the sand and water heated by solar collectors is circulated through the coils in the sand bed to heat the sand.
Pretty simple.

The potential advantages of this approach are that its very simple in that there is really no heat distribution system required -- the sand bed directly heats the floor slab.  It also allows quite a bit of storage at a relatively low price.  It allows enough storage that for a very well insulated home, its possible to store up a bit of the winter heat needs in the sand bed in the fall. 

One unique feature of the sand bed storage scheme is that the living space is directly coupled to the heat storage.  This makes the system simple and basically eliminates the need for a heat distribution system, but it also means that there is less control of heat transfer from the heat storage to the living space.

There is not a lot out there on sand bed storage, but I've collected what I could find on this page....

The recent article in Solar Today on sand bed storage got me to thinking and running a few numeric checks, and I have to say I'm a bit skeptical of some of the claims made for sand bed storage in the article.  I've included these thoughts at the link above, and would appreciate your thoughts on them.  If you have experience with a sand bed storage home, I'd love to hear about it.

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