Adding Solar Elements to Your Current Heating System
If your home is like most others in the country, at least in respect to the majority of new constructions, you rely on a furnace for your heat, usually one fed by oil or gas that grumbles to life whenever you turn up the thermostat. Often, that initial grumbling will be followed by a metallic dinging or the whining or whooshing of your floor registers (or vents) coming to life. What's happening is that a fan is pushing your warm air through the registers and the colder air is being sucked through return registers back to the central heating source. This is what's known as a forced-air system. It gets you heat when you want it, fast, and it can send cool air around your home just as quickly.
But it's hard to make a forced-air system super-efficient. That's because you cannot easily heat just the room or rooms you need (say, the bedrooms at night) and leaky ducts are common, leading to wasted energy and money. According to the 2008 guide Energy for Sustainability, energy lost through leaky ducts may increase your home heating and cooling costs by 20% to 30%. Overall, that could add an astounding $10 to $15 billion per year in additional fuel costs to families across the country.
If you're living in an older home, you may well have hot water baseboard heat. In this case, a boiler driven by gas, propane, oil, or electricity heats your water, which is then piped to baseboard units that are attached at floor level to the walls of your rooms. Warm air rises through the vents as the hot water moves through the pipes in a process known as convection.
Both of these systems can be adapted to a solar-powered system, although the methods will differ considerably. In the first case, you are interested in heating the air. In the second, you're heating water, and the principles are nearly identical to the system used for heating your home's running water via solar—the only difference is in the way that heat is distributed.
If you're building a new home, many more options are available for designing a solar heating system that's best suited to your climate and needs. While most existing systems can be adapted to solar, you can gain real advantages by making your distribution system as efficient as your energy collection—by installing, say, radiant floor heating—or by using several renewable energy systems in combination.
Knowing the Hardware
Most often a solar heating system begins on the roof, with the collectors. Black solar flat plate collectors—essentially a metal box insulated in glass—absorb the heat from the sun and transfer that heat to either air, some type of fluid, or water. The collector contains a sensor that lets a controller know when it's hotter in the collector than inside your house. That activates a fan (in the case of air) or a pump (in the case of fluid or water) that will get the heat moving into your home.
One important feature of solar heat to keep in mind is that your solar collectors are not producing heat that's as hot as the heat produced by your traditional furnace or boiler. That means you need a steadier, more regular supply to reach the same warming effect as you achieve now in a shorter period by simply cranking up the thermostat. Your regular forced-air furnace produces what's known as high-grade heat—from 140 to 160 degrees F. Solar collectors operate best with low-grade heat—from 80 to 140 degrees F. If the collector were set to run at a higher temperature, the whole system would be less efficient—you'd have more heat loss through the collector's components and a less steady delivery to your home.
Pipes will deliver the heat from the collectors to your home. These must be well insulated and, if they are traveling any distance, installed below the frost line. For maximum efficiency, you always want your collectors to be located as close to the home as possible. But sometimes the easiest way to incorporate solar heating into an existing home is to build a new, smaller structure on your property—a studio, shed, or children's playhouse—that can double as your home's solar heating center. Mother Earth News released an article on how to go about constructing a separate building with ground-mounted collectors that are easy to install and maintain. Such a building can also provide a ready place to store the associated large thermal storage tank. The heated water or fluid will have to travel a greater distance to reach the home, and, in general, will work best when it can deliver heat at the lowest possible temperature. In the Montana home that the article's authors used as a guide, they coordinated the system with a radiant floor heating system that can utilize heated water that's as low as 85 degrees F.
BRITA BELLI is editor of E and author of The Complete Idiot's Guide to Renewable Energy for Your Home.