Wednesday, October 22, 2008

Storing Heat

A comment on my previous post contained this request: "Would you be interested in recapitulating what you did to maximize your south facing windows to make the most of your solar capture." Interested? Definitely!

There are four aspects to solar heat.
  • Orientation - Windows must face solar south to maximize solar heat gain.
  • Glazing - Based on the size of the building a sufficient amount of glass with a high solar heat gain coefficient (SHGC) must be installed.
  • Insulation - Sufficient insulation must be quality installed to minimize heat loss.
  • Mass - Sufficient quality mass must be present to capture and retain heat.
A book could be written on each of the above items but the request in the comment focuses on the subject of mass.

Heat can be stored in several types of mass -- concrete, stone, steel, adobe, water, etc. I chose to store heat in water which holds about three times more heat by volume than concrete. The installation of water-filled barrels was less expensive and took less labor than any other option I considered.

Water-filled barrels to store heat.
Water-filled barrels to store heat. The barrels are exposed to direct sunlight. (Larger version)

The challenge was to do something functional that would be somewhat attractive. When I decided to build an "attached greenhouse" I conceived of a functional structure with a stone floor and as much salvaged material as possible. I always plan projects with Julie. As the discussion evolved she wanted more living space with a relaxed atmosphere. In the end we decided to lay barrels on their sides to create a lower shelf that would not block as much view out the windows. This reduced the volume of water from 14 vertical barrels containing 770 gallons to 8 horizontal barrels containing 440 gallons. This is a significant reduction but the extra mass is needed only for a short period in the coldest part of the winter.

Picket fence to hide barrels.
Picket fence to hide barrels. (Larger version)

The south sides of the barrels are exposed to direct sunlight. The north sides are hidden by a picket fence (Julie's idea) that allows air circulation. The shelf above the barrels is plywood. We have concrete board on hand and we are searching for tile to finish the shelf. The addition of concrete board, thinset and tile will provide more heat storage.

Sunlight on tile over concrete.
Sunlight on tile over concrete. (Larger version)

We installed a tile floor above concrete mixed on site with cement and crushed glass. This provides additional heat storage but the amount is minimal compared to the water. The sun hits the north part of floor that isn't shaded by the shelf. As winter progresses the sun will move deeper into the room and more floor will receive direct sun but more floor will be shaded. It will be interesting to see the sun and shade patterns as the solar year progresses.

This is a portion of what we've done to store heat. I haven't addressed the solar closet which is an additional heat store that I'll discuss sometime in the future. Also, I found a section of used hot water baseboard heater ($20 from Habitat for Humanity Store) that I'll adapt to collect heat and pipe into additional water store in another room. I plan on a thermosiphon loop rather than using a pump.

Here are three previous posts that deal with passive solar heat:

Free Heat
Construction Update
A Heated Response

These external links have good ideas and background knowledge.

Passive Solar Architecture - Heating
Solar DIY Space Heating Projects

(In my next post I'll respond to questions related to wind and solar electric generation. In a future post I'll address minimizing heat in the sun room in the hottest part of the year.)


Blogger Alex Pendragon said...

Paul, I have to ask; why didn't you paint the barrels flat black? Is that color blue more retentive?

10/22/2008 01:31:00 PM  
Blogger MojoMan said...

This is good and interesting stuff!

Like Michael, I was wondering about the color of the barrels. Also, do you have a way to close things up on a cold night to minimize heat loss back through the glass? Can you monitor the actual temperature of the barrels?

10/22/2008 07:24:00 PM  

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