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ypically, one or a combination of the following passive solar heat techniques: direct gain, indirect gain, and isolated gain will always find use in building design and construction. For example, nearly every building utilizes some form of the direct gain because it is the least complicated. Ordinary clean windows provide a great deal of direct gain heating collection.

Similar to all other heating systems, solar heat can be supportive or the anchor. And if supplies of gas and oil should be in short supply; remember, the sun is always there.

Well-positioned solar collection systems start the heating process by transforming the sun’s energy into usable heat. Domestic and commercial buildings designed for direct gain solar heat collection usually need conventional heating to supplement heating requirements.

Today, designing new energy efficient buildings for the best solar advantage is common practice. This also includes retrofitting older buildings. Both are possible by applying the following design principles:

• Building parts facing north and south should be longer than those facing east or west.
• South facing parts of the building should receive full sunlight from 9:00 am to 3:00 pm (solar heat time) in the solar heating months.
• Interior south facing spaces should be those requiring the most heat and light, and just the opposite on the north facing spaces.
• Open floor plans optimize passive solar systems.
• Overhang porch roofs (shade) prevent entry of summer sunlight into the interior.

This is a good place to introduce the little understood solar heating collection systems. Unless your dwelling is a cave, its original design and construction usually included one or a combination of solar heating collection methods. Though even cave openings provide some semblance of solar heating.

Moreover, retrofitting any of these methods to older structures will provide improvement, that is, unless it’s a cave. In any case, each of the systems listed below deal with converting sunlight into usable energy, specifically for heating.

1. Direct Gain Solar Energy Collection System
2. Indirect Gain Solar Energy collection System
3. Isolated Gain Solar Energy Collection System

I’ve included three additional methods to enhance the three systems further. As an example, the mass wall works with both direct and indirect gain systems.

1. Mass Wall Solar Collection Method
2. Water Wall Solar Collection Method
3. Roof Pond Solar Collection Method

Retrofitting any of these is possible; however, older structures may require remodeling to achieve the benefit. Okay, let’s look at the systems and their pro’s and con’s.

Direct Gain Solar Collection System
Of passive solar heat, this is most commonly used system in architectural design. It’s simply sunlight striking southern exposed windows and heating the interior. Architects and designers have long incorporated this system in buildings. Basically it's SOP, nothing extraordinary, other than basically, buildings need windows.

However, whenever possible, the buildings main windows should face south. This system works very well, with multiple (glazed) pane windows installed, and especially when there’s sufficient structural mass to store the solar heat. The mass should be insulated concrete and or masonry walls. Insulating concrete floors is another issue.

Though not as effective, a possible substitute for the lack of concrete and masonry construction in older buildings is using dark colors when decorating.

When exposed to sunlight, such windows will utilize 60 to 75% of the sun’s energy. The principle is; during the night, when interior spaces tend to cool, heat stored in the walls and floors radiate heat by convection into the living spaces. If the wall/floor mass is sufficient, solar energy storage will provide effective heating during night-time hours.

Advantages

• System simplicity
• Multiple pane glass windows are an inexpensive form of solar collector
• Usually, entire system cost is or can compare to conventional building
• Multiple pane windows provide not only solar collection, but a source of daylight, and a visual connection to the outside

Disadvantages

• Solar ultraviolet radiation causes deterioration of cloths fabrics and some artwork
• Loss of privacy
• Heat loss in floors placed on soil
• Ten-degree temperature swings are common
• Large window blinds or other movable heat-loss insulation systems may be cumbersome, but are generally required

Indirect Gain Solar Collection System
This system works with mass storage. The mass stores direct sunlight and then radiates the heat by convection into the desired spaces.

Sunlight need not travel through such spaces as will benefit from solar heating. Instead, systems such as roof ponds, mass walls and water walls provide thermal heat storage.

During evening hours, when normal interior cooling takes place, thermal radiation from the preheated mass enters into the desired spaces. Such mass utilizes 30 to 45% of the sun’s energy passing through the glass adjacent to the thermal mass.

Advantages

• Living spaces are more comfortable due to controllability of thermal energy delivery
• Less general impact on buildings design
• Complete evening and night time privacy compared to direct systems
• Ultraviolet deterioration and glare into the living space contents is not a problem
• Temperature swings are less than direct systems

Disadvantages

• Heat loss is increased
• Mass walls must be shaded and vented outdoors to prevent overheating during summer months

Isolated Gain
Basically, isolated gain systems use the solar heat collected in one space for use in another. In other words, this system separates solar heat collection from the main living areas. For example, solariums, sun porches, and other solar energy collection sunspaces are used.

Solar energy entering sunspaces heat masonry walls, concrete floors, water containers and the air within the sunspace. Sunspace temperatures usually rise during daylight hours. Properly sized overhangs will shade living spaces from solar heat that enters the sunspaces through vertical glass walls and windows.

Such systems utilize 15 to 30% of the sunlight striking the sunspace’s multiple pane glazed glass. At night, heat distribution into living spaces can use one or a combination of: windows, doors, floor, strategically placed ceiling vents and fans, also conduction through a shared mass wall.

However, closing doors and windows during this time allows the sunspace to retain the heat while maintaining comfortable temperatures in the living space. Thermal energy that builds up is then available for use during evening and nighttime hours.

Greenhouses fit into the category; however, they may or may not be included with isolated gain systems. If heated air is shuttled into a living space, then they are. However, living spaces and plant growing areas may not be compatible because of excessive moisture. Nevertheless, heated air can feasibly flow into living spaces from them.

Advantages

• Small temperature changes in primary living spaces
• Additional living space available most of the year
• Relatively inexpensive
• Acts as buffer between outdoors and principal spaces

Disadvantages

• Complexity of design requires careful planning to achieve optimum solar heating while maintaining aesthetical harmony
• Overheating potential during summer months requires thermal control

Sizing the walls to maintain solar heating for extended periods provide warm comfortable air for interior living spaces. With a well-insulated exterior, the mass will contain solar heat for 2 or 3 days of cloudy weather.

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Water Wall Technique
Water is an excellent, heat storing substance. In fact, it’s nearly twice as effective as either concrete or stone. For every degree of temperature (F) rise, a single cubic foot of water will store 62 Btu’s of energy. The same temperature rise in a comparative volume of stone or concrete will only hold 32 Btu’s.

The atomic (H2O) molecules that make up water are miniscule and therefore tightly laced together. Consequently, surface heat collection; pass every tiny change in temperature through the convection process to each molecule in the water’s volume. Its surface radiates this heat into the surrounding air thus providing heat or cooling for the living areas.

Due to the nature of water, heat looses are insignificant and therefore provide more efficient collection and heat storage than either concrete or stone.

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Roof Pond Technique
A flat roof is the primary requirement for this system, although the exception to this is a pitched roof glazing covered attic. Water is contained as before only in the attic space. This method is actually more effective than the flat roof method.

A second important requirement is that this system is limited to single story or the upper story of buildings. Though the idea of a roof pond system may sound somewhat peculiar, it isn’t. In fact, it is a very effective solar heat and cooling collecting and distribution system.

The third requirement is for outdoor roof top systems only. These require an insulating cover for both heating and cooling.

Approximately 6 to 12 inches of water contained for example, on a flat roof, held in ample sized plastic or fiberglass containers covered by glazing. Installed correctly, concealment of the dark colored containers is simple.

Water, contained in tanks or clear plastic bags collect and store solar thermal energy effectively. During colder months, removing the insulating cover during the day allows the water to absorb solar heat and radiates it into the building below.

During warm months when cooling is desirable, removing the insulated cover in the evening exposes the water to the cooler evening air. Heat is absorbed from below during the day, and then radiates into the cooler air at night.

Advantages

• Highly efficient
• Adaptable to heating and cooling

Disadvantages

• Requires structural integrity to handle up to 65 lbs per square foot dead load
• Requires an elaborate drainage system
• Requires movable insulation covering
• Requires elaborate drainage system

Even though the system is more complicated than other passive systems, it can provide effective heating and cooling for homes and commercial buildings.

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Now you have a good idea what passive solar heat Gain is all about. There’s one last important thing to remember: whatever system you choose, insulation from outside air temperature variations is always required. Remember, heat loss defeats system effectiveness, whether the thermal mass connects to the ground or free air, insulation will resolve this issue.

Glaze or Glazing is simply a transparent or translucent coated glass or plastic used to admit light and to reduce heat loss. The coating material used permits maximum sunlight passage while reducing reflected heat losses. Return back to where you were.

For everything, you ever wanted to know about building, construction, planning, passive solar cooling and heating systems and much much more here’s the place to find it.

How about overhangs, wanna know more?

Use this: a complete glossary on solar energy.

Solar heat is a wonderful thing - Collect some then go home