Our Low Thermal Mass Sunspace Project in Home Power Magazine

I did an article for Home Power on the Low Thermal Mass Sunspace concept -- its in the Dec 2013 issue, which is just coming out.

William's Minnesota LTMS 

I'm a big fan of the Low Thermal Mass Sunspace (LTMS).  In a nutshell, this is an attached sunspace in which the design is optimized for providing maximum heat to the attached house.  The main design characteristics are:

• Double glazing with tilt angle optimized for winter collection
• Unglazed surfaces in the sunspace are dark in color to absorb sun well
• Unglazed surfaces are well insulated to reduce heat loss
• Unglazed surfaces are low in mass so that they don't suck up heat you want to go to the house
• A high capacity fan/duct system delivers heated air to the house as fast as the sunspace makes it

Some of this may seem strange at first compared to the usual sunspace design guides, but its all aimed at maximizing heat production and in getting as much of the heat as possible to the house. 

It turns out that if you follow these design guides, the LTMS will produce heat for the house just as efficiently as a good commercial collector with the same glazed area -- AND it will give you all the benefits of a sunspace as well.  Benefits include: great place to have cup of coffee in the sun, great playroom or family hangout, all season clothes line drying, wood drying, ...  

About the only downside of the LTMS is that when the sun goes down it goes cold quickly, so its not a space to hang out in after sunset, or go grow plants in cold climates.

The performance is impressive.  My test LTMS with 200 sf of glazing produced 200K BTU of heat for the house on one sunny winter day -- equivalent to nearly 3 gallons of propane burned in a typical furnace.

The test LTMS under construction.

I also tested the performance of my test sunspace when it was closed in, but not insulated and with a dirt floor -- in this configuration it only delivered 1/3 of the heat to the house than the finished sunspace with insulated low mass surfaces.

The finished test LTMS

I've done a section on LTMS's that goes into quite a bit of detail on on the design, performance testing, and includes some great LTMS examples contributed by Mike, Nick, and William. 

Mike's example LTMS -- heating the house and solar drying clothes!

Nick's 3 story LTMS that provides most of the heat for his
very difficult to heat old home.

The Home Power article covers everything in the LTMS section in one place and the Home Power editors have worked it into something that is clear, easy to read, and still quite detailed.

Gary
November 9, 2013