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Passsive Solar Heating

written by: •edited by: Lamar Stonecypher•updated: 3/28/2010

Most of our homes already receive passive solar heating through the windows. This free renewable energy can be further exploited by the use of simple energy saving techniques. These include the addition of thermal mass in a Trombe Wall or building a conservatory on a south facing wall of your house.

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    Introduction to Passive Solar Heating

    New build houses are being designed to face south, being spaced to avoid over-shading each other as much as possible and, have thermal mass built in. Thermal mass is the ability of a material to absorb and store thermal energy, in this case solar energy, releasing it slowly when the ambient temperature drops.

    There are numerous methods of passive solar heating which can be applied to your house, from heat absorbent walls to sunrooms, greenhouses and conservatories being built to the south facing side of the dwelling.

    This is a free supply of thermal renewable energy which will not only lower heating expenditure, but also decrease your carbon dioxide emissions to the atmosphere.

    This is another article on renewable energy in the domestic and commercial sectors. Here we will examine the different techniques employed in the application of passive solar energy.

    We begin by listing of the more popular techniques which are in use today.


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    Passive Solar Heating Techniques

    These include the following,

    • Trombe Wall
    • Conservatory/Glasshouse
    • Thermal Mass Floors

    Trombe Wall

    This wall is named after its designer Francis Trombe who built the first one in the early 1960’s.

    The wall operates on the principle of thermal mass whereby solar thermal heat is absorbed into the wall during the day, then at night the heat is released from the inside of the wall into the main living room.

    There are several variations of the original design, each having their own use for particular applications.

    The one we shall examine can be incorporated in the original construction of the house or retro-fitted to a south facing wall.

    The dimensions of the wall will vary due to the size of the living room and the outside area available, remembering that if you use an existing window you will lose daylight and your view. Ideally the wall should be built facing as near south as possible and be about 500mm thick, running from foundations up to below the eaves.

    It should be constructed from a thermal mass substance such a concrete or rammed earth with a dark absorptive coating on the outside. Vents should be cut out at the bottom and the top of the wall and these should penetrate through into the living room. These have louvers which can be opened or shut manually or temperature controlled adjusting the flow of hot air into the living room.

    A double or triple glazed glass unit is fitted against the outside of the wall, leaving a gap between the wall and the unit. The unit should run from the bottom to the top of the wall along its full length, being held in place by a wooden frame.

    Summertime use of Trombe Wall

    If the wall is constructed as part of a new build, then the roof should be designed with an overhang which will partially shade the wall from the sun during May through August. The sun will start to become lower in the sky during winter and spring, so the overhang will not impede the sunshine during the cold seasons.

    If the wall is to be retro-fitted then some type of shading during the summer months will be required. This can be as simple as planting a row of deciduous trees a couple of meters in front of the wall, their foliage shading the wall in summer. Come autumn the leaves will fall letting the sunshine through to the wall. A more expensive method would be to use an awning or louver blinds as a sunshade.

    During the winter months the wall will emit heat to the house but also loose heat through the glazed unit. To prevent this heat loss a means of external insulation can be applied to the glazed unit. This can be of louver design or a thick insulated roller blind either of which can operate on a timer, dropping down at night and lifting at daybreak.

    It may be an idea to investigate fitting an insulated roller blind in the gap between the wall and the glazed unit as this would not be affected by inclement weather conditions.

    Thermal Mass Floors

    Once again these can be retrofitted to the living room. They consist of a layer of concrete 100-150mm deep laid on top of an insulated 50mm boards of MDF nailed onto the top of floorboards. Any heating pipes or electric cabling currently running under the floorboards should be rerouted as access for maintenance will be restricted once the concrete is down.

    The floor will absorb heat from the hot air and store it, releasing eat again at night time. This will be impeded if carpeting is used on the floor so either the concrete should be sanded and painted or tiled using ceramic or clay tiles.

    Sunhouses and Conservatories

    Either of these can be fitted retrospectively and used as a means of passive solar heating. You will probably get more use out of a conservatory than a sunhouse but conservatories can be expensive, although they add to the value of the property.

    We have a conservatory at the back of our bungalow which faces south/west and we gain solar heat all year, once it warms up. We just use the inside doors to distribute the heat but there are a few methods of hot air circulation such as fitting vents and fans which can be applied.

    Horizontal or vertical blinds can fitted to the conservatory windows, used as sunshades during the summer months, in conjunction with manual or automatic vents and windows. The fitting of a heater or radiator to the conservatory is not recommended as this negates its purpose.

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    Passive Solar Heating Sketches

    Trombe Wall and Thermal MassTrombe Wall Shading Methods