Letters: November/December 2008

November/December 2008
A version of this article appears in the November/December 2008 issue of Home Energy Magazine.
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Not Too Steamed

Regarding the article “Naturally Circulating Hot Water Systems” (Sept/Oct ’08, p. 6), I think Mr. Greenberg’s response is fine as far as it went, but there’s another possibility as to what this system might be. To recap: There is no circulator, and the supply pipes are larger than return pipes.

This might be a Vapor steam system. This type of system was the Cadillac of heating back in the day, and is still one of the best out there. Normally we find Vapor on high-end jobs, but I have seen Vapor systems in two-story row houses in the Baltimore area that were installed when the houses were built.

The typical Vapor system radiator or convector has a 3/4-inch supply connection and a 1/2-inch return. Most often there will be a thermostatic trap, water seal, or other device at the radiator return connection, but Vapor systems exist that did not have anything but a standard return elbow. The latter type is easy to misidentify as hot water.

Vapor system piping generally features a large steam main, at least 2 inches diameter, and two returns for each main that are smaller—one near the floor, called a wet return, and another overhead, called a dry return. The latter carries water and air from the radiators. The air is discharged through a central vent, and the water is returned to the boiler. But there are Vapor systems that omitted the wet return.

Our company specializes in steam, Vapor, and water-heating systems, and would be happy to assist Mr. Ianuzzi and his friend. They should feel free to call us at (410)321-8116.

Frank “Steamhead” Wilsey
All Steamed Up, Incorporated
Towson, Maryland



Earthquake Drill

Out here in California on the Hayward Fault, our block of neighbors have to prepare for a week or so of (1) no electricity, (2) no natural gas, and (3), no water out of the tap. Some thought a portable generator was the way to go, but obviously that can only power one household at a time. I thought a better idea would be to (1) have several inverters that can run off cars, and (2) have at least one inverter power a small 110V chest freezer, which could make a lot of ice, which could then be distributed to the various available refrigerators in the 25-household area.
I see several good $200 freezers, but none shows how many watts are pulled at start-up, so I cannot match an inverter to a freezer. Kilowatt-hours per year do me no good. Please advise.

I also would recommend 50- to 75-ft extension cords, fitted for 12 volts, as people could light the inside of their houses from the street, then recharge the car battery by turning on the engine. LED lights for 12 volts would use less energy than converting to 110 in the inverter and then running lights. Thanks!

Scott Bergquist
Albany, California
Technical Editor



Steve Greenberg replies:
This is more of a disaster preparedness question than a home energy use question. The annual energy use of the freezer is a good indication of how much energy will be required to operate it, and this is certainly relevant when power is in short supply. But as far as sizing an inverter to power it, you need to know the current draw (amps) under normal operation, and the starting inrush current. Most refrigerators and freezers use a capacitor start motor, which reduces the starting inrush, but it’s still there.  Most inverters are able to handle a certain amount of starting inrush beyond their continuous-duty rating. Contact the manufacturer of the freezer to get the running and starting current; then check inverter ratings to get a combination that will work. Be sure to oversize the inverter somewhat to compensate for overoptimistic ratings on the part of the inverter manufacturer, voltage drops in the 12V and 120V connections, and so on.

Regarding use of motor vehicles as a power source, they are very inefficient as generators (since the engines are sized for about 100 kW, but the generator is almost always well under 1 kW), and their batteries aren’t designed for deep discharging, but they are ubiquitous.

Doing power distribution at 12 volts is problematic in that the current required for a given load is 10 times what it would be at 120 volts. This makes voltage drop in the distribution a concern for all but small loads (which I suppose is what you’re proposing anyway).

I live in the Westbrae district of Berkeley, right near you, and our neighborhood has a generator (provided by the city as part of our cache). Since refrigerators draw 100 to 200 watts when running, and the generator is rated at 5 kW, 20 or more could be operated at the same time. Of course, a distribution system of cords needs to be provided, but with a couple of hours of power each day to each refrigerator, the food can be kept from spoiling. By rolling the generator around the neighborhood, such a scheme could work for quite a while, running on gas siphoned from cars. The generator is noisy and polluting, but it uses much less fuel per kWh delivered than using car engines. At least one of the neighbors has a portable generator, which adds to our options.

Another option is to convert a house with a PV system to one that can operate from batteries as well as connected to the grid. This house could serve as a center where folks could come for information and to organize, recharge cell phones, and so on.

Obviously the car scheme, the generator scheme, and the PV scheme are not mutually exclusive. Best of luck with your preparations. 

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