Solar home – Incorporating passive solar and active solar

Whether your reason is to save money on your utility bills, reduce (or potentially even eliminate) your dependence on fossil fuels, do your part for the environment, or be a leader of your peers; there are many reasons to incorporate passive solar and active solar into your home. A solar home is not a new concept, ancient people didn’t have fossil fuels on which to depend for their heating and cooling, and thus designed their civilizations around the movements of the sun.

As the Greek philosopher Aeschylus wrote more than 2000 years ago:

Only primitives & barbarians lack knowledge of houses turned to face the Winter sun.”

And yet…. virtually every subdivision built in Canada in the past 40 years completely disregards solar exposure as a significant design component. As the price of fossil fuels becomes less stable and climate change becomes more of a threat, it becomes apparent that this needs to change.

What is Passive Solar?

Imagine if you could get 40% or more of your home’s winter heating needs met for free. Imagine if the same technique that heated your home in winter for free also kept it cool in the summer for free. All of this is accomplished simply by placing more windows facing south, shading them appropriately and utilizing thermal mass within the home to capture that heat. This is all that is required when passive solar heating a home. This could be achieved today without any technological breakthrough or added cost by simply planning to make every home a solar home. Now imagine how much less fossil fuel energy North America would use if this type of layout was a standard in new neighborhoods or in new buildings. But what is the best way to achieve this in individual buildings?

The optimal situation is to limit the size and quantity of windows facing north, east and west as they are a source of heat loss in winter and of heat gain in the summer. By ensuring that the south facing windows are adequately shaded, the building will stay cool automatically in the summer and (depending on your climate) may even negate the need for an air conditioner. Passive solar design is a fundamental component of a solar home.

A solar home is passive

When faced south (give or take 30 degrees), a great source of day lighting within a passive solar building is available all year, particularly in the winter time. But don’t over do it with regards to windows. As indicated above windows are the main source of heat gain in hot months and one of the main sources of energy loss in colder months, especially if they are over used within the building.  This is because even the highest quality triple pane Passive House certified windows have a  low thermal resistance of about R9 (U=0.06 W/mhr).[i] This means that if you are spending money to build walls that meet R30 or R50 to reduce your energy usage (which you should… particularly if you want a passive, energy efficient building), it makes sense that you want to reduce the wall space where the best thermal resistance you can achieve is R9.

Not only that, but when you consider that windows are quite costly per unit area compared to walls, it makes sense from a financial point of view to be strategic when sizing and placing windows. A good rule of thumb is to have between 6 percent and 10 percent of glass area on the south wall and no more than 4 percent glass on the north wall, in comparison to the square footage of the house.[iii]  With the proper sized overhang, the correct building orientation (long side running east to west—design it this way if possible) and substantially more windows on the south side, a building will capture a great deal of heat in the winter and keep it out in the summer, while still having a nice source of light year round.

A great and handy resource for understanding and calculating window sizes, shading, building orientation and solar gains can be found in the paid version of my book available here:

 

passive solar, active solar home orientation

An illustration of the sun’s path through the sky in the northern hemisphere. Notice how the hot summer sun is shaded by the roof and the winter sun is allowed to enter the building via windows to provide heat. Receive bonus sustainability points for designing the overhang to incorporate photovoltaic panels or solar thermal panels. Note: If you live in the southern hemisphere, the sun will always be somewhere in the north. [iv]

passive solar

Passive solar heating through south-facing windows, properly sized shading and thermal mass.[v]

What is Active Solar?

Unlike Passive Solar which operates without energy input, Active Solar utilizes mechanical or electrical energy to convert solar energy into another more useful form of energy such as for heating, cooling or for the production of electrical energy. This is accomplished either through solar thermal water systems, solar thermal air systems or photovoltaic (solar) panels. Incorporating Active Solar technologies into a Passive Solar design creates the possibility of building a net zero home. Because a net zero home is one that produces as much or more energy than it uses over the course of a year, the intelligent construction of new neighborhoods could be a potential solution to fight climate change. Such a solution is one that is truly Future Proof™.

Next you will need to understand solar panels for the home.

This post makes more sense when you understand the big picture. Sections from the post are taken from the book “How to Future Proof Your Home: A Guide to Building with Energy Intelligence in Cold Climates” by Shane Wolffe. Buy the book or get a free version here to understand the big picture.

If your job is related to Passive Solar design, Active Solar devices or solar homes, click here to join a community of green building experts that are dedicated to making the world a better place.

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[i]Windows are typically thermally rated using U values where U is the symbol for heat flow. To calculate the R-value of windows you are selecting simply take the inverse of the U value.  R =1/U or U = 1/R. High-efficiency window information from: http://www.efficientwindows.org/ufactor.cfm

[ii] In a super-insulated house with good solar access and high thermal mass, this number is likely to be much higher, though the heat load is dependent on the outdoor air temperature, location and time of year.

[iii] For a free guide to understanding Passive Solar Design for window sizing and to potentially hire Saskatchewan based experts in Passive Solar Design, visit www.howtousesolar.com

http://www.passivehouse.ca/passive-solar-design/

 

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