The Energy-Efficiency Pyramid
Modeled on the ‘food pyramid,’ the conservation pyramid is a guide for energy retrofit work
We’re all familiar with the food pyramid — the triangle with grains and cereals at the bottom and fats and sugars at the top. Inspired by the food pyramid, a Midwestern electric utility, Minnesota Power, has created a useful graphic called the energy conservation pyramid. (According to a Minnesota Power spokesperson, the originator of the conservation pyramid was Bob McLean, the chief operating officer at Hunt Utilities Group.)
The energy conservation pyramid includes ten levels. Like the food pyramid, it’s read from the bottom up. Homeowners who are uncertain of the best way to lower their energy bills should start at the lowest level of the pyramid and work their way up. In general, one shouldn’t proceed to a higher level until the actions below that level have been completed.
Actions near the bottom of the pyramid are much more cost-effective than actions near the top of the pyramid. At current energy prices, in fact, the actions listed on the top two layers are never cost-effective.
The rules displayed in the energy conservation pyramid are not set in stone; every house is different, and different climates dictate different strategies. But it’s hard to quibble with the pyramid’s basic hierarchy.
From the bottom up, here are the pyramid’s ten steps.
1. Home energy auditEnergy audit that also includes inspections and tests to assess moisture flow, combustion safety, thermal comfort, indoor air quality, and durability.
Before beginning any energy retrofit work, a homeowner needs information — information best obtained through a home energy audit.
A good home energy audit always includes a blower-door test; most audits also include a thermographic inspection. To be sure your auditor is well trained, choose one certified by RESNET, BPI, or CBPCA.
A home energy audit can cost as much as $600. Thanks to subsidies from utilities and local governments, however, the cost of a home energy audit is often much less. Yet even if you pay the full cost of an energy audit, the money will be well spent.
Why spend hundreds of dollars on an energy audit? I can think of several reasons:
- When considering energy retrofit work, most homeowners prioritize the wrong steps. An energy audit provides valuable information to counterbalance misleading advertising pitches for worthless products.
- Your audit is likely to reveal unseen defects in your home — for example, thermal bypasses (air leaks) through convoluted, hidden chases, or insulation gaps revealed by an infrared camera.
- At the end of your audit, you’ll receive a customized list of the most important energy retrofit steps for your house — a list that may differ from your assumptions (or even from the recommendations of the energy conservation pyramid).
- By identifying the most important retrofit tasks for your specific house, a good audit can save you hundreds of dollars that might have been wasted on inappropriate work.
2. Low-cost measures to reduce plug loads
The next step, though obvious, is often neglected: turn things off.
Inattention and laziness are responsible for a significant amount of energy waste; this step off can yield significant savings for a very small investment. To lower your electric bill:
- Turn off the lights when you leave a room.
- Turn off appliances that aren’t being used.
- When not in use, unplug chargers for cell phones and similar battery-operated gadgets.
- Put televisions and other “instant on” appliances on a plug strip — and remember to turn off the plug strip when the appliance isn’t in use.
The next step is very cost-effective: make sure your house is incandescent-free. Since most LED lamps are still less efficient than CFLs — and far more expensive — CFLs are still the best lamp for most fixtures.
For kitchens and basements, consider installing fixtures that use efficient linear fluorescent tubes (T5 or T8 tubes).
4. Air sealing
Air-sealing work is best done by an experienced home-performance contractor equipped with a blower door. Although this step usually costs hundreds of dollars, it will usually yield a quick payback in energy savings.
Air sealing work is not the same as caulking. Many homeowners have spent hours wandering around their house with a caulk gun — on the interior, filling cracks between window trim and plaster, or on the exterior, filling cracks between clapboards. Most of this caulking is a total waste of time. In fact, by trapping water, most exterior caulking does more harm than good.
Blower-door directed air sealing work is usually concentrated in a home’s basement (especially at the rim-joist area) and attic (where huge thermal bypasses are often hidden under a layer of fiberglass batts). Most air leaks are best addressed with two-component spray polyurethane foam.
5. Efficient appliances
Once you’ve paid for blower-door-directed air sealing, it’s time to take a close look at your appliances. If some of your major appliances — your refrigerator, clothes washer, or dishwasher — are more than ten years old, you may want to replace them with more efficient models.
Don’t be tempted to buy a bigger refrigerator; small is good. Pay close attention to the yellow EnergyGuide labels — especially the annual kWh number — when you go appliance shopping.
6. Insulation improvements
Ideally, your home has plenty of insulation in the attic, above-grade walls, and basement walls. But if you’re insulation isn’t up to snuff, it’s well worth improving it.
In colder climates, it makes sense to install R-60 insulation in your attic — as long as the attic is accessible and roomy enough to accommodate the insulation depth.
If your stud bays are empty, they can be filled with dense-packed cellulose insulationThermal insulation made from recycled newspaper or other wastepaper; often treated with borates for fire and insect protection. installed through holes drilled from the exterior.
Basement walls can be insulated on the interior with rigid foam insulation or closed-cell spray polyurethane foam.
7. Water heating
If the configuration of your home’s plumbing pipes permits, you should install a drainwater heat-recovery device — especially if members of your family prefer showers to baths.
If you have an old, inefficient water heater, you may wish to replace it. Options include:
- A high-efficiency gas-fired water heater;
- A high-efficiency electric resistance water heater;
- A heat-pump water heater;
- An instantaneous gas-fired water heater;
- An indirect water heaterWater heater that draws heat from a boiler used for space heating; a separate zone from the boiler heats potable water in a separate, insulated tank via a water-to-water heat exchanger. See tankless coil. connected to a boiler;
- Any of the above, supplemented by a solar water heater.
Of all of the options listed in this section, the fastest payback will probably come from the drainwater heat-recovery device. Although a new water heater can lower your energy bills, you shouldn’t expect a fast payback on the investment.
8. Space heating and cooling equipment
When inefficient heating or cooling equipment gets old enough to replace, be sure to invest in the most efficient available equipment. If you’re shopping for a new furnace, look for a high AFUEAnnual Fuel Utilization Efficiency. Widely-used measure of the fuel efficiency of a heating system that accounts for start-up, cool-down, and other operating losses that occur during real-life operation. AFUE is always lower than combustion efficiency. Furnaces sold in the United States must have a minimum AFUE of 78%. High ratings indicate more efficient equipment. (in the 90s). If you are shopping for a new air conditioner, look for high SEER(SEER) The efficiency of central air conditioners is rated by the Seasonal Energy Efficiency Ratio. The higher the SEER rating of a unit, the more energy efficient it is. The SEER rating is Btu of cooling output during a typical hot season divided by the total electric energy in watt-hours to run the unit. For residential air conditioners, the federal minimum is 13 SEER. For an Energy Star unit, 14 SEER. Manufacturers sell 18-20 SEER units, but they are expensive. (14 or higher).
There’s an important reason why energy-efficiency experts recommend holding back on the purchase of new heating and cooling equipment until air sealing and insulation work is complete: envelope improvements may permit heating and cooling equipment to be downsized. If you replace your heating and cooling equipment before finishing necessary air-sealing work or insulation upgrades, you’ll waste money on oversized equipment.
9. Replacement windows
We’ve now reached the top of the pyramid. Further measures will probably reduce your home’s energy consumption, but they are unlikely to be cost-effective. The reason these measures are at the top of the pyramid is that few homeowners want to spend more on retrofit work than they will ever see in savings.
In a heating climate, the installation of low-eLow-emissivity coating. Very thin metallic coating on glass or plastic window glazing that permits most of the sun’s short-wave (light) radiation to enter, while blocking up to 90% of the long-wave (heat) radiation. Low-e coatings boost a window’s R-value and reduce its U-factor. storm windows is more cost-effective than installing new replacement windows.
If, for reasons unrelated to saving money, you insist on new windows, be sure to choose windows with low-e glazing. Glazing with a low U-factorMeasure of the heat conducted through a given product or material—the number of British thermal units (Btus) of heat that move through a square foot of the material in one hour for every 1 degree Fahrenheit difference in temperature across the material (Btu/ft2°F hr). U-factor is the inverse of R-value. is desirable in all climates. In climates with cold winters, south-facing windows should have a high solar heat-gain coefficient (SHGCSolar heat gain coefficient. The fraction of solar gain admitted through a window, expressed as a number between 0 and 1.); in climates where air-conditioning bills are high, windows should have a low SHGC.
10. Renewable energy equipment
At the top of the pyramid is the category of work least likely to provide a payback: the installation of a photovoltaic system or a wind turbine. There are many reasons you may want to have PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow. panels or a wind turbine, but saving money isn’t one of them.
Remember, it makes no sense to invest in an expensive PV system until after you have invested in all of the other measures listed on the pyramid.
No silver bullet
One of the Minnesota Power representatives who makes regular use of the conservation pyramid is Dean Talbott, a program manager for the utility.
“I handle a lot of customer calls, and lately I’ve seen a growing interest in renewable energy,” Talbott told me. “A lot of callers are looking for the silver bullet. I just got a call this week from a residential customer who’s spending $200 a month on electricity, and he told me he wants to install solar and wind. I told him he’d be better off to start with efficiency upgrades first.”
Last week’s blog: “Air Conditioner Basics.”
- Minnesota Power
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