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.

Gary

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. 

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.

More details and a place to add comments or report your results here...

Gary

January 4, 2013

A Unique and Cost Effective Solar Space Heating System

Taylor's space heating system has a couple of unique features that I like and think are worth taking a look at if you are planning a solar space heating system.

He describes the system on his blog here...

One of the unique features is the use of inexpensive pool heating collectors.  He adds polycarbonate glazing to the collectors to get the performance up in the same area as commercial glazed space heating collectors.  The danger here is that if the collectors are stagnated (no flow), the temperatures inside the collector can get high enough to damage the the polypropylene pool heating collector.  To avoid this he fits the glazing with some air leakage paths to bring the stagnation temperatures down.

The glazed pool heating collector.

This is the same idea that I have been looking into on our new inexpensive, off-the-shelf solar water heating system.   I think this idea has a lot of promise for getting solar water and space heating costs down.  But, bear in mind that its still on the experimental side.

The other feature I like in the system is that Taylor uses a commercial off the shelf water to air heat exchanger to distribute the solar heat to the house.

The water to air heat exchanger -- has to be one of the funkiest looking ones ever!

Even with the relatively low temperature hot water that solar heating systems typically provide, these heat exchangers will deliver quite a bit of heat.  On Taylor's system, the airflow through the heat exchanger is driven by a fan that is PV powered.

One thing to bear in mind about heat distribution for solar heating systems is that unless you have an exceptionally well insulated house, or a very large solar collector array, the solar heat will be a supplement that reduces your heating bill, not your only source of heat.  This being the case, the thing you want the heat distribution system to accomplish is to be able to always deliver the solar heat you collect during a day to the house during that day and through the night.  Its not important that the solar heat distribution system be able to supply the whole heat loss of your house on a cold day -- you have a furnace for that.  What's important is that all of the solar heat that you collect gets delivered to the house overnight.  This can make a world of difference in the size of the distribution system needed.

For a ton of other solar space heating systems and ideas go here...


Gary
December 17, 2012

DIY Heat Recovery Ventilator (HRV)

An HRV pulls fresh air into the house and exhausts stale air to the outside.  In the HRV, the fresh and stale air pass through a heat exchanger that recovers most of the heat remaining in the stale air to heat the incoming fresh outside air -- thus providing a significant saving in energy to heat the incoming air.

While I've been looking for material on building an HRV, I've not had much luck in finding anything that appeared to have a chance of working well over time.  This book from William Shurcliff that has a little on a DIY design, but its pretty minimal.

Paul from BC noted the above page and came through with the article below describing an HRV design that uses sheets of Coroplast material for the heat exchanger.  Paul actually built one of these for his own house some time back and it worked well for the time period he was in that house.  It seems to me that the Coroplast has a descent chance of holding up well in the somewhat hostile (wet and even icy) environment inside an HRV heat exchanger.  Thank you Paul for sending this in!

The Coroplast HRV design

Full details on building the Coroplast sheet HRV...

New section on HRV's ...

A completed HRV

Gary
December 8, 2012

Solar Greenhouse Research -- No Heat Needed

Here are three solar greenhouse projects just added to the site.  One in Missouri, another in Manitoba, and our new solar greenhouse in Bozeman.

Solar Greenhouses are roughly defined as greenhouses that can grow things through the winter without supplementary heat -- that is, they are 100% solar heated.

A University of Missouri Solar Greenhouse with 18 Year Track Record

This is a greenhouse I ran across while looking for a good design for our own solar greenhouse project.  It was designed and built by the Univ of Missouri extension about 18 years ago, and has been used for researching winter greenhouse growing since then.  

Its designed to work well through the winter with the steeply tilted, double wall glazing, the north roof sloped to reflect light on the growing area, all surfaces insulated except the south glazing, and thermal mass in the form of water barrels.

It successfully grows through the winter with no supplemental heating.

We liked it enough to model our solar greenhouse (see below) generally after it.

For all the details...

Solar Greenhouse Research in Manitoba

These are some articles and a paper on a solar greenhouse research project in Manitoba.  Part of the project involved taking a wide greenhouse and subdividing it into 4 separate, side by side spaces.  Each space was used to test a different glazing or insulating scheme through the winter.

Links to two articles and a paper on this project here...

Solar Experimenation "Thing" in Montana

This is our new solar greenhouse project here in Bozeman.  It is actually a scaled down version of the U of M greenhouse above.  

While its intended to be our greenhouse for the long run, we plan to first use it to do some testing of the performance of low thermal mass sunspaces attached to a house and used for space heating of the house, and then for testing the idea that it possible to build a small (tiny) room in one end of the GH that will be able to maintain a comfortable temperature through the winter on just solar.  This is a tall order in our climate, but we will see what can be done later this winter.

The GH with its 60 deg tilt, south facing glazing -- all other surfaces are insulated.

Building the frame

Temperatures in the first three days after being closed in.

30F outside -- 120F inside.

Any ideas or suggestions on this project would be appreciated.

All the details here...

Gary

Large DIY Solar Space and Water Heating System in Maine

Steve has designed and built a very nice solar space and water heating system in Maine.   The system has a number of interesting and unique features including,

• A large "hizer" collector with full width "risers" running horizontally.
•  Integration of the solar heating with the existing boiler.
• A Steve made controller for the system.
• A new technique for making the PEX heat exchangers.
• Drain back of the collector to a tank 70 ft from the collector.

The 28 ft wide Hizer style collector

The collector is 28 ft wide and is built as a single "hizer" style collector rather than 7 or so side by side vertically oriented collectors that would normally be used.

Picture with glazing off showing the Hizer style "risers".

Building a wide collector like this as a single unit and with the horizontal "riser" layout simplifies the plumbing, reduces labor, reduces material needed, and reduces the cost of the collector.

In this system, the solar heat source and boiler heat source are integrated into a single heating system.   And, the system also provides domestic water heating.

System diagram showing integration with existing boiler system.

Steve worked out a way to recoil the PEX heat exchangers to improve heat transfer and make them more efficient.

The tool for recoiling the PEX to make more efficient heat exchangers.

The system uses a Steve designed and built controller.

Circuit diagram for the system controller.

All of the design and build details are provided in a 15 page pdf that can be downloaded here....

Gary

A Unique DIY Solar Pool Heating Collector Using PVC Pipe

This pool collector is a different slant on pool collector design, and may have some unique benefits for some people.

In a nutshell, the collector consists of large diameter supply and return manifolds that are connected by closely space half inch PVC pipe risers.  The manifolds supply water to the risers, which pick up the solar heat and deliver it to the pool.

The half inch PVC risers are attached to the PVC manifolds by drilling and taping a half inch NPT pipe thread in the manifold for each PVC riser pipe.  Then male threaded to PVC adapter fittings are used to attach the half inch PVC to the manifolds.  This is a nice, simple, reliable and inexpensive way to make the collector.  Since the collector is custom made, it can be built to fit the roof space available.  The riser runs can be made quite long, allowing one large collector to be used instead of several smaller one.

The standard mat style pool heating collectors may be a better choice if they are readily available where you are and can be fit into the space you have.  Matt came up with this design because he was in a country where the mat style collectors were not available at a reasonable price, and this design proved to be a good alternative.  The cost may end up being more or less than the mat collectors depending on where you are and how big the collectors are.

The pdf that Matt provides has a great deal of good detail on the design and build for the collector and provides plenty of detailed instruction for people who have not worked with PVC before.

All the detail on this PVC pool heating project here...

Gary

Off-The-Shelf DIY solar water heating -- Version 2

I've had a bit of a reset on the Off-The-Shelf solar domestic water heating system.

The idea of this system is to provide a very easy to build DIY solar domestic water heating system that uses off the shelf collector, tank, controls, etc.  -- a system in which you just install the off the shelf components rather than building your own collector and tank.  The objective is to keep the total cost to about $1000 (compared to about $8000 for commercially installed systems).

The first version of this system used plastic mat style pool heating collectors installed in a horizontal format and at a not very steep tilt angle.  I've decided to change to a vertically oriented mat style pool heating collector installed at a steep tilt angle.   The advantages include an easier and cleaner installation, better cold season performance, less susceptibility to summer overheating, and more flexibility in trying a vented glazing system to increase winter performance without overheating.

The new collector

The new collector is a single 4 by 10 ft pool heating collector mounted off my existing Solar Shed.  The vertical mount appears to be more secure and less subject to sags and folds -- it basically hangs from the upper manifold with straps to secure it from winds.  Its easy to install and appears to be quite secure.
More collector area could be provided by going with a 4 by 12 collector and/or adding a 2nd collector.

The same Softank that was used on version 1 is retained.

The plot below shows one sunny days performance.

Sunny day performance

On this sunny October day, the collector heated the 132 gallons of water from 83F to 110F.  It was mostly sunny with an ambient temperature of about 70F -- so, this is quite nice performance.

For later in the season when ambient temperatures are lower, I intend to try some form of vented glazing to see if the winter performance can be improved over that of an unglazed collector -- stay tuned.

All the details on the build and performance to date...

If you have any ideas for improving this design, please let me know.

Gary

New DIY Solar Water Heating Kit from AmericanSolarTechnics

Tom Gocze from AmericanSolarTechnics has come out with a kit for a solar domestic water heating system that is designed from the ground up for DIYers.  

The 4 collectors.

The kit uses four small collectors, each of which is 4 by 4 ft and weighs only about 20 lbs.  The collectors hook up in series for easier plumbing connections.  The light weight, manageable size, and easier plumbing connections make for an easier DIY installation.

The collector absorbers are copper tubes with aluminium fins, and the collectors are glazed with twinwall polycarbonate.

The storage tank is the SofTank, which AmericanSolarTechnics has been selling for some time.  The tank capacity is about 200 gallons.  I have one of these tanks and I like it.  It is a unique design that uses an outer fabric sleeve to bear the water pressure loads.  Inside the sleeve are several layers of polyiso foam board insulation, and inside the insulation is a high temperature liner that contains the hot water.

The SofTank

Copper pipe coil heat exchangers transfer heat to the tank from the collectors, and heat your domestic water using heat stored in the tank.  Your current hot water heater acts as the backup heater when solar is not available.

Tom has felt for a long time that solar water heating systems are too expensive -- something I strongly agree with.  This kit is his effort to bring the price down to a reasonable level that offers a good payback.  The kit is $2750 -- this compares with typical commercial systems costing around $8000.

While the system is not yet SRCC certified, this is in the plans.

The AmericanSolarTechnics DIY Solar water heating system...

A listing of solar water heating kits at Build-It-Solar...

Gary

DIY Insulating Window or Door Shutters Using Astrofoil Reflective Insulation

Bruce has worked out a DIY thermal shutter design that uses Astrofoil to provide a high R value, easily installed thermal shutter for windows or doors.

Astrofoil is similar to Reflectex, but is stiffer and holds it shape better for thermal shutters.  Both products are basically polyethylene bubble sheet with a reflective layer on each side.  While the bubble sheet is not thick enough to provide a lot of R value, the two reflective layers and the air films on each side of the foil makes for a good R value thermal shade.

Astrofoil thermal shutters in the open position.

Same shutter closed for the night.

The Astrofoil can be used with or without a frame.  The pictures above show the very nice looking DIY wood frames with Astrofoil inserts, and the picture below shows Astrofoil without a frame placed in a window.  The frameless version is made by just cutting the Astrofoil a little larger than the window frame opening and pushing it into place.

The 5 minute Astrofoil shutter -- cut it out and push it into place.

All the details here...

Gary