Editorial: That 3,000-Lb Gorilla in the Garage

September 11, 2006
September/October 2006
A version of this article appears in the September/October 2006 issue of Home Energy Magazine.
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        With high gasoline prices, one’s attention naturally turns to that thirsty, 3,000-lb gorilla in the garage: the car. But how does gasoline consumption compare to the energy used inside an average home? Five years ago, the average home budgeted almost exactly the same amount of money for household energy use (that is, electricity and natural gas) and vehicle fuel. Last year, the average car consumed 590 gallons, which cost the average driver about $1,800. But the typical household has approximately two vehicles, so per-household consumption is roughly $3,600/year. In contrast, the bill for a home consuming 10,000 kWh/year and 1,000 therms/year is much less—about $1,700 annually. Today, rising costs of gasoline continue to outstrip cost rises for electricity and natural gas, so an everincreasing portion of a consumer’s energy budget goes to fueling a car. It’s worth paying attention to the efficiency of that (very) large appliance in your garage. You may be surprised.
        About 80% of each gallon of gas is used to propel the car, while the remaining 20% is used to provide distinctly homelike services such as heating, cooling, ventilation, and light. The air conditioner has a capacity equal to that used in a small house; it’s sized that way because, unlike the one in your house, you expect the air conditioner in your car to bring the temperature from ovenlike to comfortable in two minutes. Inside, you will find appliances—radio,TV,PC,and sometimes even a refrigerator. Cars have an insulated envelope,made up of windows (single glazed, some operable, others not); walls; and a roof. These surfaces—especially the windows—experience solar gain, which needs to be carefully managed. A complicated control system works to keep the occupants comfortable.
        Curiously,auto manufacturers have little incentive to save energy in these aspects of energy use.Why? Because the lights, air conditioner, fans, radio, and twin DVD players in the back seat are switched off during the fuel economy test.Making the lights or air conditioner more efficient won’t improve the official mpg rating. When automakers decide they want to save that 20% of fuel consumption, they might look to the home for conservation ideas, including insulation, high-COP (coefficient of performance) air conditioners, spectrally-selective windows, efficient fans, and low-standby appliances. There’s good reason to believe that efficiency makes sense, especially for these electrical devices. Electricity generated on board costs about $1/kWh. This is equivalent to roughly 10 times what the average consumer pays for electricity from the local utility. Indeed, enginegenerated power is so expensive that it might pay to displace some of it with a PV on the car roof (which puts a new meaning to the term “sun roof”). At least one company already offers a PV system as an aftermarket option for the Toyota Prius. A zero-energy home is nearly commercial, but alas, a zero-energy car is too far away.
        Home Energy generally ignores the gorilla in the garage,though we often call your attention to the water heater,washing machine, and other appliances that may be sharing the room with that behemoth. Vehicles and their energy use have traditionally been outside the scope of this magazine, because we focus on the home. But there are two reasons why this approach may be obsolete. First, perhaps as early as next year, a few cars will plug into the home’s wiring systems in order to recharge. In this sense, the car will soon become just another home appliance, not much different from an oversized Dust Buster. And second, Americans are spending an increasing number of hours inside their cars. Indeed, one could argue that Americans already live in their cars, and that the car is an extension of the home. Certainly the demand for drink holders, DVD players, mobile refrigerators, high-power audio systems, and even PCs suggests that more activities than simply driving are taking placing in America’s cars.
        No, you won’t see a review of the 2007 Toyota Prius or the GMC Envoy in Home Energy, but you can be sure that we are watching that gorilla carefully for further signs of domestic behavior— including a sorely needed diet.
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