Passive solar heating and cooling may not sound exciting or even effective, but if you’re off-grid, you definitely should learn more. When done right, passive solar can help offset electric costs by a great deal.
How does passive solar design for homes work?
Passive solar heating basically involves trapping solar radiation in the form of heat, and then holding on to it for longer periods. The lightweight materials we use in building construction are poor in absorbing and retaining heat. Instead of them, if denser materials are used to capture the solar heat, it will get released slowly during the night, keeping the house warm. Preventing the trapped heat to escape into the cold night air is also part of the system.
Passive solar cooling of homes is a different story altogether. It hinges on providing proper shading over windows and other external openings. A typical example is the extensively overhanging roofs in traditional buildings of tropical areas. Creating thermal currents that remove warm air from the house and fill it with cool air is also important. Since the same building has to be warmer in winter and cooler in summer, passive solar thermal regulation takes a lot of planning right from selection of the site.
Some of the major techniques employed in this system are:
This is the first step in securing the solar energy for passive heating. Solar radiation can pass through glass and heat up the internal air as well as the interior surfaces. Glazing the wall that faces the sun for most part of the day can bring in maximum heat. So in the northern hemisphere we glaze the south-facing wall. People in the southern hemisphere may do the opposite.
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Since winter is the time we require passive solar heating the most, the positioning of the glass windows is also crucial. It should be planned according to the sun’s position at your place during winter. The use of glass should be optimized, too. You don’t want all that warmth you trapped during the day to quickly escape at night through unnecessarily big glass windows as it happened with earlier designs.
The use of large amounts of glass on the southern wall of the house, to receive as much sunlight as possible in winter, was popularized in the 1970s with the right intentions. But did it achieve the desired outcome? No. The glazed walls and windows did do their job. The rooms facing south remained toasty through the day, too, but by dusk they lost all their warmth. This was mainly because the internal structure of the house failed to absorb the warmth of the sun and keep it in. The large windows played a part, too.
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Now we know how, with a fraction of that glazing, the goal of residual warming can be achieved. Using materials with higher thermal mass for constructing the walls is the key. By thermal mass we mean the capacity of a material to absorb and contain heat. Brick, cement and plaster provide high thermal mass, while dry wall is very poor in comparison. Wall papering further reduces the amount of heat absorbed by the wall. Dense materials take longer to heat up but, once warmed, they lose their warmth just as slowly. Earthen houses of olden days had excellent thermal mass and provided better thermal regulation in the absence of power.
Insulation is as important in retaining the warmth as thermal mass, if not more. If the heat escapes from the house through the walls and the windows, the very purpose of passive solar heating is defeated. Even in the case of normal electrical heating, faulty insulation is one major cause of heat loss.
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For passive solar cooling of the home, shading is essential. While a glazed southern wall is great in winter, it can make the adjacent room a furnace in summer. Shading the windows from the sun during most part of the summer day will prevent overheating. Knowing the changing positions of the sun during summer months is essential to create proper shade.
Hot air rises up. That’s elementary science. When the warm air moves to the upper layers, cool air flows into this void. These convection currents can be utilized to cool the house to some extent by positioning windows correctly. Roof vents, with or without fans, also help.
Why should you invest in passive solar thermal regulation? Here are several reasons:
1. Power savings
Passive heating and cooling of the home can reduce the need for powered air conditioning/heating to a great extent. If the building is designed to receive the warmth of the sun and trap it inside during the winter months, the heating bills can drop considerably. On the other hand, keeping the rooms shaded from the intense rays of the sun during the summer days, and allowing cool air currents to carry away the heat from the indoor air, the need for supplemental cooling is reduced.
In a new building constructed on the principles of passive solar thermal regulation, the consolidated savings can be as high as half the normal expense of powered heating and cooling. Old buildings can be retrofitted to reap some of the power-saver benefits, but the cost of alteration should be taken into account.
2. Cost effectiveness
The idea of using solar power for passive heating and cooling is not new. Traditional architectural styles in areas of extreme weather have always employed some of these elements in their building structures. Unlike active solar power systems, it does not involve any mechanical or chemical devices. All it takes is correct positioning of doors and windows, use of construction materials that offer thermal mass, and insulation.
The structural elements required for maximizing passive solar thermal control are ideally incorporated into the building at the time of design and construction. There is no question of additional costs, then. If changes have to be made in the existing structure, the cost involved should justify the benefits obtained. Sometimes minor changes can make a big difference.
3. Crisis management preparedness
This may not seem like a big advantage when we are safe and comfortable. But if a prolonged power failure were to happen due to some natural calamity, or by the act of man, how prepared are we? Being at least partially self-sufficient in our energy needs will help us hold out for longer and tide over such situations.
Do you have any tips for using passive solar in a home? Leave your tips in the section below:
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