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SUN:
Learning to live with the sun using Passive Solar design concepts

As the Zen master said to the hot-dog vendor: "Make me one with everything".  Well, part of being one with the environment is utilizing the natural solar cycles, rather than fighting them.  Ignoring earth covered home designs for the moment, much can be done to a conventional home design to cut winter heating costs and summer cooling costs.

The no-brainer in this area is INSULATION.  Insulation inhibits the flow of heat energy between your climate-controlled living space and the environment.  But insulation is never perfect, and the human desire to have natural light in a home makes it important to understand just how to deal with sunlight.

A plain glass window has an R value of 1, which is about as insulating as the hole that the window is in.  Even expensive low-e windows only improve this by a factor of 2 or 3 times.  Hardly anything when compared to the R13 required for most exterior walls.  So in Winter, windows permit a huge outflow of heat.  Likewise in Summer, not only does heat conduct in through the window, but solar radiation (sunlight) is transmitted, raising internal temperatures significantly.

What can be done?

After doing some research, I've determined that the common thinking seems to be summed up as follows:  

Since the earth's axis is tilted, the sun rises higher in the sky in Summer than in the Winter.  In a Northern Hemisphere Winter, the sun rises in the South East, stays low in the South sky, and then sets in the South West.  In Summer, the sun rises more in the North East, quickly gains height to a higher elevation than in Winter, and then sets back in the North West.  So the best things to do in the Northern Hemisphere are:

  • Orient the house such that the major axis runs east-west.  
  • Limit the number and size of windows on the Northern side of the house, to reduce Summer heating of the interior.
  • Place more windows on the Southern side of the house.  Use wide eaves and tall shade trees to limit solar radiation in the Summer, yet provide plenty of solar heating in the Winter.

In colder climates, it's important to store as much of the incoming solar energy during the day as possible, and then allow it to continue heating the house during the night.  The best way to store this heat is in a large thermal mass.  One popular (and patented) way to do this is with a thick slab floor.  This floor could be solid concrete, or a layer of rock.  Since the incoming sunlight will only heat the South side of the slab (via the windows) several ingenious methods have been devised to circulate air through the slab.  This air serves to moderate the temperature of the slab during the day, and help heat the air within the house during the night.  

In his book "The Passive Solar House", author James Kachadorian proposes an innovative way to rearrange the building materials of your house to construct a highly effective passive solar slab.  A taste of his design is shown below.

Note that cinder blocks paced on edge, and covered with a thin concrete slab, form a series of air channels in the floor.  Slots formed at the North and South edge of the slab act as air registers.  

The author suggests that the addition of some supplemental ventilation increases the system's efficiency, and permits the addition of a cooling system for summer.   Kachadorian provides tables of thermal data, and "do it yourself" worksheets to evaluate your own thermal designs.    

Another key element to successfully using passive solar heat in winter is preventing the heat from radiating out of the windows at night.  Solutions to this problem range from basic blinds to internal thermal shutters.

OurCoolHouse

In Our Cool House, the design has a primary South orientation which contains the bulk of the windows. Some smaller windows are located on the West and East walls, but these are designed to capture morning and evening sun. The North, NE, and NW walls are below grade and contain no windows. All windows are protected by 24" eaves which have been sized in conjunction with the windows (using this spreadsheet) for optimal summer shade and winter solar gain. Our 6" slab is a great thermal store, but we use water (rather than air) as the thermal transfer medium.  Water filled tubes embedded in the slab can be used as passive thermal circulators, or if the conditions are extreme, they can be used to provide heated or chilled water.

For more details regarding this design, visit our Final Design page and watch my cool Summer and Winter shade animations.

Design Concepts
Earth - Sun - Water - Hybrid
© 2000-2015, Phil and Lisa's relaxed lifestyle home.
An exercise in Energy Smart, Not So Big living.
www.OurCoolHouse.com - Ideas@OurCoolHouse.com

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This site is all about building a cool, energy efficient house, that makes maximum use of earth sheltered design, passive solar heating and cooling, geothermal exchange energy management, and right sizing of the house for it's designated use. The home's placement is on a south-facing hillside in Deep Creek Lake, Maryland. This site describes the design process, the technologies used and the expected results. We also have a comprehensive Links Page for anyone who is also interested in designing a similar project.