If you’re a homeowner who’s interested in reducing energy costs, the double envelope house is a model you should consider. This house is a type of passive solar house that uses a solarium to collect solar energy. The house has two sets of walls, hence the double envelope in its name, that allow warm air to circulate around the living quarters. Of course, when you’re considering any type of home, there are pros and cons to consider. To figure out if the double envelope house is right for you, here are some of the most important pros and cons to consider.
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Pros: Reduces Energy Costs
By far, the biggest advantage of the double envelope house is the money saved on energy costs. The greenhouse that’s incorporated into the south side of the house paired with sub-floor cooling tubes create a convective loop that keeps the living quarters at a comfortable temperature. The envelope design of the house acts as a collection and storage space that stores energy collected during the sunny periods of a winter day.
In the summer, this cycle is reversed when the windows at the upper part of the house are opened. Hot air is forced to evacuate, keeping the living quarters cool. The envelope house is about 80% energy-efficient in both summer and winter, which can drastically cut energy costs.
Pros: Doesn’t Require Maintenance
Non-solar heating options include forced air and hot water systems. In a hot water system, small pipes filled with hot water to baseboard convectors, creating a convective loop. In a forced air system, a duct system transports heated and cooled air to different areas of the house. In both of these type of systems, there are parts that can fail or require periodic maintenance. For homeowners, those extra costs can add up, and an out-of-order system can leave you stranded in the cold.
Even if you opt for an active solar heating system, it requires a system of pumps, pipes, and collectors. Just like non-solar heating options, these parts can require repair or replacement. With a double envelope house, you don’t have to worry about maintenance since the system is built into the house’s design.
Pros: More Aesthetically Pleasing Than Active Systems
If you want to use solar energy to help heat and cool your house, you can choose between a passive system like the double envelope house or an active system. No matter what type of active system you choose, you’ll likely need to install a collector (or several) in order to harness solar energy. A collector is usually costly and likely does not suit the design aesthetic of your home as they are large, noticeable structures. The double envelope system allows for more variance in design without the added bulk of solar collectors.
Cons: Stores Heat for Less Time
The passive solar system of the double envelope house can’t store heat as long as an active system. The double envelope house can store energy for about 72 hours, so extended periods without adequate sun exposure could be problematic. Active solar energy systems can store energy for longer periods of time with features like battery banks or grid-inter-tie.
Since traditional methods of heating or cooling your home don’t rely on the sun for energy, these methods of regulating your home’s temperature are more reliable in places where sunlight may be scarce.
Cons: Not Suited for All Climates
The double envelope house isn’t ideal for all climates, especially extreme ones. In a hotter climate, the design would likely need extra attention in order to remain adequately cool. Such provisions might include window shades, a roof overhang, or additional vents to help expel hot air.
If you live in a polar climate, the double envelope house unfortunately isn’t for you. The passive heating system just isn’t quite enough to properly heat living quarters in consistently cold temperatures.
Cons: Temperatures May Be Inconsistent
Due to the nature of the double envelop design, hot and cool are are constantly circulating around the house. This means that there can be variation in temperature from area to area. If you’re someone who wants to be able to maintain complete, consistent control over the temperature of the house, a double envelope design may not be for you.
For homeowners looking for a low-maintenance solar energy option, the double envelope house has some very significant positive aspects. An 80% energy self-sufficiency rate can go a long way towards reducing the costs of maintaining a home. As long as you don’t live in a particularly extreme environment, a double envelope house is an option worth exploring.
Tony Fallaver is a freelance writer and marketing consultant for general contractors and construction companies like Joel & Co. Construction.