Reducing your winter heating costs Part 3 — Passive Solar Heating

How thermal mass can help you heat your home for free

Over the last couple of weeks we have looked at a number of ways for you to heat your home while reducing your carbon footprint and lowering your utility bill. But how would you like to heat your house for free? You don’t have to lift a finger; no mechanics, no moving parts and no electronics. If this sounds too good to be true, then keep reading.

Passive solar heating utilizes the floors, walls and other thermal masses to absorb solar energy during the day and distribute this heat back into the home during the colder evening hours. Solar heating can be combined into new building designs or retrofitted to your existing structure to provide heating, cooling and natural light.

Passive solar pizzazz: How it works

Sunlight is streamed in through properly-oriented, south-facing windows. This provides heat and natural light during the daytime. The solar heat is stored in ‘thermal mass’; construction materials that are able to absorb and retain heat such as concrete walls and floors, bricks and tiles. Through a process of natural convection, these thermal masses radiate heat back into the house during the cooler winter evenings. Unlike other heating systems, passive solar systems do not require large capital outlay and do not contribute to the emission of greenhouse gases. Your building will be sunnier with the benefit of natural light while indoor temperatures do not fluctuate dramatically, giving you greater heat stability.

Aperture: Let the sun shine in

Large south-facing windows (within 30 degrees of true south) are necessary to allow the sun’s energy in. These windows should not be shaded by trees, buildings or other obstacles between 9am and 3pm in the cool winter months. When implementing a passive solar design, window choices are integral to its success. Window glazing will regulate the influx of sunshine over the seasons. When selecting windows for passive solar systems in cooler climes, choose glazing that affords a solar heat gain coefficient of 0.6 or more. The windows should have a U-factor of at least 0.35 or less (this reduces conductive heat transfer). During the warmer, summer months, thermal masses are shaded with the use of window awnings or deciduous trees.

Creating an insulated building envelope will help you to maximize the heat gained though passive solar systems. Although passive solar construction is not necessarily more expensive than regular construction techniques, when combined with an insulated building envelope, it will save an astounding amount in heating costs over the life of the building.

Thermal Mass: Heat for your home, by your home

A thermal mass usually has a dark surface to maximize solar absorption. Thermal mass is made from materials that are able to absorb the most sunlight and radiate it back into the room when the temperature drops. The most advanced insulation envelopes also happen to be the best thermal masses. Insulated Concrete Forms (ICFs) combine expanded polystyrene insulation with concrete thermal mass. The concrete in ICF wall systems absorbs and stores heat while the insulation works to retain the heat. The ICF walls alone can save you 30 to 50% on your heating bill and reduce your home’s carbon footprint significantly.

There are other materials that are routinely used as thermal masses including masonry, large decorative stones and water. Water storage units can be placed near south-facing windows to absorb the sun’s rays during the day and radiate heat into the building at night.

Phase change materials are the most modern addition to the thermal mass quiver. These materials use chemical bonds to store and later release solar heat. This is achieved when the materials change from solid to liquid phases and back again.

Although passive solar systems are often used in conjunction with other heating methods, it is possible to heat your home solely through passive solar.

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