NOTE: This Article can be read in conjunction with the "Backup Heating Systems Chart" and "When the Sun Hides: Backup Heating Systems for Passive Solar Houses."
CHOOSING A "BACKUP" HEATING SYSTEM
Philip S. Wenz
COPYRIGHT, Philip S Wenz, 2006
Originally Published in Ecological Home Ideas Magazine, Fall 2006 Issue
If you want a clean, alternatively-powered backup heating system for your passive solar home, chances are you'll end up choosing to generate your own electricity with photovoltaic (PV) panels. Although building regulations and initial costs may pose some obstacles (see accompanying article: Backup Heating Systems), the bottom line is that over time you can recoup the entire cost of a photovoltaic system.
The key to making domestic electrical generation pay isn't a technological advance but a policy called net metering. Available by law in 35 states, net metering is an arrangement between you and your power company that in essence allows you to run your electric meter backwards, charging your power company for the electricity that you generate at home. If, in the course of a year, you generate more electricity than you use, you pay nothing. (Unfortunately, the power company doesn't pay you either, but at least you can run your heating system and, if you install a big enough PV array, your water heater, appliances and lights—all for free.)
Of course, PV panels are subject to the same down time as your passive solar house—when the sun's not shining, you're not generating any electricity. But net metering regulations anticipate that problem by requiring power companies to bill you once annually for your year around use. In the summer, when there is plenty of sunlight and little need for heat or electric lighting, you will typically generate far more power than you need. By the time the short, cold days of winter come around, you've built up enough electrical credits to offset your use—especially if you live in a well insulated, passive solar home. (To learn more about net metering and see if it is available in your state, go to the US department of energy's web page at www.eere.energy.gov/greenpower/markets/netmetering.shtml.)
Once you're generating electricity, your heating options open up. Do you want warm floors of tile or, perhaps, bamboo? How about that seldom used guest room? Can you cut construction and operating costs by installing an electric baseboard heater there that would consume too much energy in your living room?
Electric resistant heat coils work the same way whether they're buried in floor tiles or encased in baseboard or wall heaters. When electricity flows through a wire with a high degree of resistance, radiant heat is produced. Persons or objects in the path of that radiant heat are warmed. Although the rate of converting electricity to heat is almost 100%, it takes a great deal of electricity, flowing constantly, to heat a room. While electric resistance systems are the cheapest to install, they are by far the most expensive to operate.
Heat pumps, which move heat rather than burning fuel or using electricity to produce it, are two to three times more efficient (200 to 300%) than electric resistant devices. A typical heat pump, which can fit into a closet, can replace a forced-air furnace or heat water for traditional wall radiators or heated floors. Household refrigerators and air conditioners are heat pumps. If you were to turn a window mounted air conditioner backwards, it would blow heat into the room and cool the great outdoors. In fact, heat pumps can both heat and air condition your house, saving a great deal of equipment cost in hot climates.
Despite their overall efficiency, however, heat pumps aren't always the right choice. The initial cost of the unit and associated ducting or pipes generally make them more appropriate for larger projects—spaces over 1500 square feet—whereas electric resistant heaters, where allowed by code, can be the best choice for additions or single rooms.
Because of the initial cost of a PV array or lack of access to net metering, home electrical generation is not for everyone. Of the many alternatives, pellet stoves probably offer the best combination of environmental friendliness and cost. Initially developed by the EPA to use lumber mill or agricultural waste such as sawdust or corn, these stoves burn so efficiently that they don't even require chimneys—they can be vented right through the wall. And, they don't get hot to the touch. While a pellet stove won't qualify under the codes as your passive solar home's "primary" heat source, it certainly can become the heater you use most of the time, giving your fossil fuel burner a long, long rest.
NOTE: This Article can be read in conjunction with the "Backup Heating Systems Chart" and "When the Sun Hides: Backup Heating Systems for Passive Solar Houses."